blue HYSYS v7.3 Manual - Electronic Version

This electronic HYSYS v7.3 manual is a condensed version of your purchased HYSYS v7.3 manual. It contains mostly those pages that have web links. Use the bookmarks to the left to go to a specific page.

Chemical Process Simulation and the Aspen HYSYS Software

Michael E. Hanyak, Jr.

Department of Chemical Engineering Bucknell University Lewisburg, PA 17837

This electronic HYSYS v7.3 manual is a condensed version of your purchased HYSYS v7.3 manual. It contains mostly those pages that have web links. Use the bookmarks to the left to go to a specific page.

Copyright © 1998 to 2012 by Michael E. Hanyak, Jr. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means—electronic, mechanical, photocopying, recording, scanning or otherwise—without the prior written permission of the Publisher, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act. Request to the Publisher for permission should be sent to the address below.

Dr. Michael E. Hanyak, Jr., Publisher Chemical Engineering Department Bucknell University Lewisburg, PA 17837 Email:

[email protected]

I dedicated this book to my wife—Martha Jane—for her love, understanding, and English prowess.

About the Author Michael E. Hanyak, Jr. is Professor Emeritus of Chemical Engineering at Bucknell University in Lewisburg, PA. He received his B.S. from The Pennsylvania State University in 1966, M.S. from Carnegie Mellon in 1968, and his Ph.D. in Chemical Engineering from the University of Pennsylvania in 1976. From 1967-1970, he worked as a senior chemical engineer at Air Products, Inc. in Allentown, PA, where he developed process simulation software for cryogenic systems. He served as Professor of Chemical Engineering at Bucknell University from 1974 to 2010. His teaching and research interests included computer-aided engineering and design, instructional design, pedagogical software tools, and the electronic classroom. With undergraduate and M.S. graduate students, he has developed a thermodynamic software system (BUTS), a linear equation system solver (BLESS), a formative assessment system for teamwork (TEAM 360), and an electronic learning system for engineering problem solving (eLEAPS), of which the last three are an integral part of the freshman introductory course and senior design course in Bucknell’s curriculum for chemical engineering majors. His two manuscripts— Companion in Chemical Engineering (CinChE): An Instructional Supplement and Chemical Process Simulation and the Aspen HYSYS Software— support a team-oriented and problembased-learning environment for the introductory course in chemical engineering. The CinChE manual presents a novel application of a problem solving strategy that enhances students’ higherorder thinking skills of analysis, synthesis, and evaluation. The HYSYS manual is a self-paced instructional document that teaches students how to use effectively a process simulator. With grants from the Air Products Foundation, the General Electric Fund, and the National Science Foundation, Professor Hanyak provided leadership with groups of engineering faculty in pioneering the electronic classroom and active learning in the chemical engineering department and the engineering college at Bucknell University. As an outreach since 2003, he and his colleagues have annually presented summer workshops at Bucknell Univeristy on active learning, cooperative learning, and problem-based learning to nearly 300 engineering faculty from the U.S. and abroad. In 1983, Professor Hanyak served on the original committee that formulated the Writing Program at Bucknell University. He has integrated teamwork, writing, oral communication, and professionalism in the freshman course on stoichiometry, the junior unit operations laboratory, and the two senior design courses, using a fictitious consultant company, the Bison Engineering and Evaluation Firm (BEEF, Inc.). He has authored two BEEF company handbooks to support this integration. As department chairman from 1998-2002, Professor Hanyak supervised the migration to the first outcome-based format for the successful ABET accreditation in 2002, automated the course scheduling process, and spearheaded the electronic assessment of courses in the Chemical Engineering Department. For his love of teaching and non-traditional research in support of that teaching, he received the Lindback Award for Distinguished Teaching from Bucknell University in 2002. He has been a member of the American Institute of Chemical Engineers and the American Society for Engineering Education (ASEE). He is the recipient of the 2011 CACHE Award given by the Chemical Engineering Division of ASEE for significant contributions in the development of computer aids for chemical engineering education. iv

Preface This document entitled Chemical Process Simulation and the Aspen HYSYS Software is a selfpaced instructional manual that aids students in learning how to use a chemical process simulator and how a process simulator models material balances, phase equilibria, and energy balances for chemical process units. A student’s learning is driven by the development of the material and energy requirements for a specific chemical process flowsheet; that is, the toluene alkylation with methanol to produce styrene monomer. This semester-long, problem-based learning activity is intended to be a student-based independent study, with about two-hour support provided once a week by a student teaching assistant to answer any questions. Your feedback is welcomed in order to improve the next version of this instructional manual. Please direct your feedback to the email address [email protected]. This HYSYS manual can be used with most textbooks for the introductory course on chemical engineering, like Elementary Principles of Chemical Processes [Felder and Rousseau, 2005], Basic Principles and Calculations in Chemical Engineering [Himmelblau and Riggs, 2004], or Introduction to Chemical Processes: Principles, Analysis, Synthesis [Murphy, 2007]. It can also be used as a refresher for chemical engineering seniors in their process engineering design course. Because the HYSYS manuscript was compiled using the Adobe Acrobat® system for document processing, it contains many web links. In the Acrobat Reader® version of this instructional manual (the .pdf file), you can access the web links that appear in many of the tutorials and simulation problems of the paper copy. You are encouraged to view electronically the “.pdf” version while you read the paper copy of this instructional manual. Type the following web link to access it: http://www.departments.bucknell.edu/chem_eng/cheg200/HYSYS_Manual/a_blueHYSYS.pdf

The web links access HYSYS “.hsc” files, “.pdf” documents, “.docx” files, and “.xlsx” files that appear in many of the chapters. You can view but not copy or print content within the “.pdf” version of this HYSYS manual. Errata for this version of the HYSYS manual are available at the following web link: http://www.departments.bucknell.edu/chem_eng/cheg200/HYSYS_Manual/a_errataHYSYS.pdf

Downloading the “.hsc”, “.pdf”, “.docx”, and “.xlsx” files from within the electronic version of the HYSYS manual using Internet Explorer®, Firefox® or Safari® should work smoothly. The HYSYS manual contains four chapters. Chapter 1 provides an overview of the problem assignment to make styrene monomer from methanol and toluene. Chapter 2 presents ten tutorials to introduce the student to the HYSYS simulation software—tutorial conventions, HYSYS interface, simulation file creation, heater operation, conversion reactor, process flow diagram (PDF) manipulation tools, Gibbs equilibrium reactor, plug flow reactor, printing capabilities, and spreadsheet programming. The first six of these tutorials can be completed in a two-week period for the introductory chemical engineering course. The other four are intended for the senior-level design course. Chapter 3 provides five single-unit assignments—process stream, pump, cooler, mixer/tee, and reactor—to develop the student’s abilities and confidence to simulate individual process units using HYSYS. These five assignments can be completed over a three-week period. Chapter 4 contains seven assignments—reactor section, cooling/decanting section, methanol recycle purification section, toluene recycle purification section, feed preparation section, recycle mixing/preheating section, and product purification section—to develop the process material and energy requirements for the styrene monomer flowsheet. These seven assignments can be completed over a seven-week period. The HYSYS manual also contains fourteen appendices in support of the four chapters for the steadystate simulation of a continuous process represented by a process flow diagram (PFD). Appendix A describes how to solve a batch example process within the Aspen HYSYS software using a spreadsheet v

operator. Appendix B provides an overview of the steady-state simulation modules for the material and energy balances of some standard unit operations that are detailed in the next ten appendices. Appendix B also provides the conceptual and mathematical models for a process stream divider, often called a TEE. Appendices C to L present the mathematical models and some of their mathematical algorithms for ten standard steady-state process units—process stream, stream mixer, pump, valve, heater/cooler, chemical reactor, two-phase separator, three-phase separator, component splitter, and simple distillation. Appendix N contains the economic model and its HYSYS spreadsheet to determine the net profit for the styrene monomer flowsheet. Finally, Appendix N contains the bibliography for the preface, four chapters, and thirteen appendices. Some of the important web links that appeared in the chapters are also provided in the bibliography. During the 1980’s, a paradigm shift started to take place from the traditional lecture-based deductive approach in the classroom (i.e., sage on the stage) to the student-centered inductive approach (i.e., coach on the side) that incorporates one or more of the following learning techniques—active learning, collaborative learning, cooperative learning, and problem-based learning [Prince, 2004 and Prince and Felder, 2006]. Although the HYSYS manual has been designed for a problem-based learning environment, it can easily be used in other active learning scenarios. Hanyak and Raymond [2009] present the design and application of a team-based cooperative learning environment for the introductory course in chemical engineering, where student learning is driven by solving process unit problems and is supported by the CinChE manual [Hanyak, 2011]. As a self-study activity, how would students determine the material and energy requirements to make styrene monomer from toluene and methanol using Aspen HYSYS? Students work individually to complete the tutorials and exercises in this HYSYS manual according to the schedule given next: Topics

½-Week Project P0

HY.3

F&R: Ch. 4

HY.4, HY.5

F&R: Ch. 6

SM.1, SM.2

{ done as a team }

F&R: Chs. 4, 6

SM.3

F&R: Chs. 7-8

SM.4, SM.5

F&R: Ch. 9

SM.6, SM.7

{ done as a team }

Energy and Energy Balances (no reactions)

2-Week Project P5

HY.1, HY.2

{ done as a team }

Exam II Review, Exam II on Friday

2-Week Project P4

F&R: Ch. 4

{ done as a team }

Chemical Phase Equilibrium

1-Week Project Ex3

2.4, 2.5, 2.6

F&R: Chs. 5, 4

Material Balances, Recycle Processes

2-Week Project P3

F&R: Chs. 2, 3 CinChE: Ch. 3

{ done as a team }

Equations of State, Exam I on Friday

2-Week Project P2

2.1, 2.2, 2.3

{ done as a team }

Material Balances (with and without rxn’s)

1-Week Project Ex2

CinChE: Ch. 1 HYSYS: Ap. C

{ done as a team }

Process Variables; Exp. Data Curve Fitting Project Problems; Thermophysical Properties

2-Week Project P1

HYSYS Section

{ done independently }

Problem-Solving Methodology HYSYS Simulation and Process Streams

1-Week Project Ex1

Source

{ done as a team }

Material/Energy Balances (with reactions) Final Exam, Week of Finals

F&R - the Felder and Rousseau textbook; CinChE – Companion in Chem. Eng. by Hanyak

vi

where in the “Source” column, “CinChE” is Companion in Chemical Engineering: A Instructional Supplement [Hanyak, 2011], “HYSYS” is this Aspen HYSYS manual, and “F&R” is the Felder and Rousseau textbook [2005]. The “HYSYS Section” column identifies the tutorials and exercises in this HYSYS manual. Obviously, the above schedule table is for the introductory chemical engineering course on material balances, phase equilibra, and energy balances. In this course, students must develop their lowerorder thinking skills—knowledge, comprehension, and application—and their higher-order thinking skills—analysis, synthesis, and evaluation—in Bloom’s cognitive taxonomy [1956], in order to become effective problem solvers and to guard against blindly using the Aspen HYSYS software as a black box. The traditional lecture-based format tends to focus on the lower-order thinking skills and usually does not provide a formal emphasis on the higher-order thinking skills. In a problem-based learning environment, student teams that are required to follow the tenets of cooperative learning [Johnson, et al., 1998] can develop both their lower-order and higher-order thinking skills, as demonstrated by Hanyak and Raymond [2009] using team-based projects. In a team-based learning environment, the creative problem-solving methodology emphasized in CinChE [Hanyak, 2011] provides a general framework in which to solve any type of well-defined engineering problem involving material balances, phase equilibria, and energy balances. It is a systems strategy that heavily uses the mental processes of decomposition, chunking, and pattern matching, and it is specifically designed to enhance students’ higher-order thinking skills of analysis, synthesis, and evaluation. In applying this methodology, team members learn how to develop a conceptual model (a diagram), formulate a mathematical model with its assumptions, create a mathematical algorithm, do the numerical solution, conduct heuristic observations, and develop the formal documentation for a problem. In conjunction with the CinChE problem-solving methodology, Projects P0 and Ex1 in the above table are designed as one-week projects that essentially introduce the students to the Aspen HYSYS interface using tutorials from Chapter 2 of this instructional manual. Projects Ex2 and Ex3 occur during an exam week and provide the students with further challenges on using the HYSYS simulator. Projects P1 to P5 are each two weeks in duration. A two-week project of assigned analysis problems on material balances, phase equilibria, or energy balances can drive the learning on how individual process units are modeled and solved. The number of manually-solved analysis problems in a project is equal to the number of members in a team (e.g., four problems for a four-member team). The CinChE problem-solving methodology not only guides the students in solving the analysis problems, it also serves as the critical framework in which to foster communication and teamwork skills using the five tenets of cooperative learning [Johnson, et al., 1998]. As team members are working to solve the analysis problems, they are also independently completing the assigned HYSYS problems (identified in the “HYSYS Section” column of the above table) and documenting their solutions in their technical journals. Once all team members have completed the HYSYS tutorials or problems, they gather as a team to answer the questions posed at the end of each HYSYS problem. While the self-study HYSYS problems serve to help students learn how to use a process simulator, the manuallysolved analysis problems provide the knowledge base of what happens within the black box. In Chapter 4 of this HYSYS manual, Problems SM.1 to SM.7 require the students to develop the process flow diagram to make styrene monomer from toluene and methanol. Each member of a team begins with the process reactor unit for a specifically-assigned temperature, molar conversion, and yield. Subsequent assignments increase the complexity of the flowsheet by adding process units, one by one, until the complete flowsheet is simulated in Aspen HYSYS. The team’s objective is to determine the operating temperature for the reactor, so that the net profit is maximized without considering federal taxes. vii

I would like to thank the General Electric Fund for sponsoring during the summers of 1998 and 1999, under its Faculty for the Future program in the area of undergraduate research, the development of this problem-based learning material on computer-aided chemical process simulation. Jessica Keith (Class of 1998) and Cynthia Caputo (Class of 1999), undergraduate research students in chemical engineering at Bucknell University, deserve special thanks for their contributions to this courseware development project during the summers of 1998 and 1999. Jessica provided initial drafts of Chapters 2, 3, and 4. She also wrote the first draft of the appendices on process simulation modules. Cynthia worked on enhancing the process simulation modules using the MathType software, a mathematical equation editor. Dr. William J. Snyder’s encouragement throughout this project and his idea for the batch problem in Appendix A are very much appreciated. Finally, I thank the Bucknell chemical engineer majors (nearly 400 of them) for their patience, understanding, and feedback while developing this manuscript. Their feedback has been invaluable and has helped to enhance the final document. Michael E. Hanyak, Jr.

viii

Table of Contents About the Author ........................................................................................................................... iv Preface ............................................................................................................................................. v 1. Styrene Monomer Production ................................................................................................ 1-1 Introduction ...................................................................................................................... 1-1 Chemical Flowsheet Description ........................................................................................ 1-2 Flowsheet General Assumptions ........................................................................................ 1-4 Flowsheet Thermodynamic Data ....................................................................................... 1-4 Flowsheet Design Variables ............................................................................................... 1-5 Flowsheet Design Specifications ......................................................................................... 1-6 Flowsheet Economic Analysis ............................................................................................ 1-6 Flowsheet Development Strategy ....................................................................................... 1-7 Your Professional Challenge.............................................................................................. 1-8

2. HYSYS Simulation Tutorials 2.1

2.2

2.3

Process Flowsheet Overview.......................................................................................... 2-1 Tutorial Conventions ...................................................................................................... 2-2 A. Keywords for Mouse Actions ......................................................................................... 2-2 B. Text Formatting ........................................................................................................... 2-2 C. Interactive Process Modeling ......................................................................................... 2-3 D. HYSYS at Your University ............................................................................................ 2-4 E. Your Default HYSYS Preferences .................................................................................. 2-7 Introduction to the HYSYS Interface ........................................................................... 2-8 A. Retrieve a pre-defined simulation file.............................................................................. 2-8 B. Open a pre-defined simulation file in HYSYS .................................................................. 2-9 C. Manipulate stream specifications ..................................................................................2-10 D. Change global preferences ............................................................................................2-12 E. Add variables to the workbook......................................................................................2-13 F. Add a second the fluid package .....................................................................................2-15 G. Program a spreadsheet operation ..................................................................................2-16 H. Document your simulation session .................................................................................2-19 I. Close the simulation case ..............................................................................................2-20 Simulation File Creation................................................................................................2-21 A. Start the HYSYS program ............................................................................................2-21 B. Create a simulation basis ..............................................................................................2-22 C. Find component physical properties ..............................................................................2-23 D. Create a process stream ...............................................................................................2-24 E. Copy and delete a process stream ..................................................................................2-26 ix

F. Specify alternative stream conditions ............................................................................2-28 G. Document your simulation session .................................................................................2-32 H. Close the simulation case ..............................................................................................2-33

2.4

2.5

2.6

2.7

Heater and Case Study ..................................................................................................2-34 A. Retrieve a pre-defined simulation file.............................................................................2-34 B. Open a pre-defined simulation file in HYSYS .................................................................2-35 C. Add a heater operation ................................................................................................2-36 D. Specify the heater outlet condition .................................................................................2-38 E. Perform a case study ....................................................................................................2-39 F. Document your simulation session .................................................................................2-42 G. Close the simulation case ..............................................................................................2-43 Conversion Reactor and Reactions ...............................................................................2-44 A. Retrieve a pre-defined simulation file.............................................................................2-44 B. Open a pre-defined simulation file in HYSYS .................................................................2-45 C. Add a reaction to the fluid package ...............................................................................2-46 D. Add a reactor to the flowsheet .......................................................................................2-49 E. Specify the reactor outlet conditions ..............................................................................2-51 F. Document your simulation session .................................................................................2-53 G. Close the simulation case ..............................................................................................2-54 PFD Manipulation Tools ...............................................................................................2-55 A. Retrieve a pre-defined simulation file.............................................................................2-55 B. Open a pre-defined simulation file in HYSYS .................................................................2-56 C. Zoom flowsheet in and out ............................................................................................2-57 D. Orient some PFD icons .................................................................................................2-58 E. Move some icon labels ..................................................................................................2-59 F. View some operating conditions.....................................................................................2-60 G. Add some documentation text .......................................................................................2-61 H. Connect and disconnect PFD objects .............................................................................2-63 I. Copy a PFD to a Word document ..................................................................................2-68 J. Document your simulation session .................................................................................2-70 K. Close the simulation case ..............................................................................................2-71 Gibbs Equilibrium Reactor ...........................................................................................2-72 A. Retrieve a pre-defined simulation file.............................................................................2-72 B. Open a pre-defined simulation file in HYSYS .................................................................2-73 C. Copy a reactor feed stream ...........................................................................................2-74 D. Add a Gibbs reactor to the flowsheet .............................................................................2-75 E. Specify the reactor outlet conditions ..............................................................................2-77 F. Analyze results for the Gibbs equilibrium reactor............................................................2-79 G. Document your simulation session .................................................................................2-82 H. Close the simulation case ..............................................................................................2-83 x

2.8

Kinetic Model and a Plug Flow Reactor ......................................................................2-84 A. Retrieve a pre-defined simulation file.............................................................................2-84 B. Open a pre-defined simulation file in HYSYS .................................................................2-85 C. Copy a reactor feed stream ...........................................................................................2-86 D. Add a plug flow reactor to the flowsheet.........................................................................2-87 E. Add a kinetic reaction set to the fluid package ................................................................2-89 F. Specify reactor parameters and outlet conditions.............................................................2-92 G. Analyze results for the plug flow reactor ........................................................................2-95 H. Document your simulation session .................................................................................2-96 I. Close the simulation case ...............................................................................................2-98 2.9 HYSYS Printing Capabilities ........................................................................................2-99 A. Retrieve a pre-defined simulation file.............................................................................2-99 B. Open a pre-defined simulation file in HYSYS ............................................................... 2-100 C. Print the PFD and a process unit window ..................................................................... 2-100 D. Print the reactor datasheets ........................................................................................ 2-102 E. Print the case study plot ............................................................................................. 2-103 F. Create a case report ................................................................................................... 2-103 G. Document your simulation session ............................................................................... 2-105 H. Close the simulation case ............................................................................................ 2-106 2.10 HYSYS Spreadsheet Programming ............................................................................ 2-107 A. Retrieve a pre-defined simulation file........................................................................... 2-111 B. Open a pre-defined simulation file in HYSYS ............................................................... 2-112 C. Examine the process flow diagram .............................................................................. 2-113 D. Complete the spreadsheet operator.............................................................................. 2-113 E. Compare the simulation results ................................................................................... 2-116 F. Document your simulation session ............................................................................... 2-117 G. Close the simulation case ............................................................................................ 2-118 3. Process Unit Exercises HY.1 HY.2 HY.3 HY.4 HY.5

Overview ....................................................................................................................... 3-1 Process Stream Simulation .......................................................................................... 3-2 Pump Simulation .......................................................................................................... 3-4 Heater/Cooler Simulation ............................................................................................ 3-6 Mixer/Tee Simulation .................................................................................................. 3-9 Reactor Simulation......................................................................................................3-12

4. Flowsheet Development Exercises Overview ....................................................................................................................... 4-1 SM.1 Styrene Monomer Reaction Section ........................................................................... 4-3 SM.2 Reactor Effluent Cooling/Decanting Section ............................................................. 4-5 xi

SM.3 SM.4 SM.5 SM.6 SM.7

Methanol Recycle Purification Section ...................................................................... 4-8 Toluene Recycle Purification Section ........................................................................4-13 Toluene/Methanol Feed Preparation Section ...........................................................4-17 Recycle Mixing and Preheating Section ....................................................................4-19 Styrene Monomer Purification Section .....................................................................4-23

Appendix A. Example Batch Simulation in HYSYS .............................................................. A-1 Appendix B. HYSYS Steady-State Simulation Modules ......................................................... B-1 Process Module Format ............................................................................................... B-1 Stream Tee Module ......................................................................................................B-3 Appendix C. Process Stream Module ....................................................................................... C-1 Appendix D. Stream Mixer Module ......................................................................................... D-1 Appendix E. Pump Module........................................................................................................ E-1 Appendix F. Valve Module ........................................................................................................ F-1 Appendix G. Heater/Cooler Module ........................................................................................ G-1 Appendix H. Chemical Reactor Module .................................................................................. H-1 Appendix I. Two-Phase Separator Module .............................................................................. I-1 Appendix J. Three-Phase Separator Module ...........................................................................J-1 Appendix K. Component Splitter Module ............................................................................... K-1 Appendix L. Simple Distillation Module .................................................................................. L-1 Appendix M. Styrene Net Profit Analysis ................................................................................ M-1 Appendix N. Bibliography ........................................................................................................ N-1

xii

Chapter 1 Styrene Monomer Production

Chapter 1 Styrene Monomer Production

Chapter 1

Page 1-1

Styrene Monomer Production

Introduction Welcome to the Internship Program in the Process Engineering Department of BEEF, Inc., the Bison Engineering and Evaluation Firm. As a new provisional engineer in this program, you will learn how to develop a chemical process and determine its process requirements for material and energy using the process simulator called Aspen HYSYS®. BEEF is a consultant company that solves chemical processing problems for governmental institutions and industrial companies. Since our clients lack the technical expertise, they hire us to recommend and implement solutions to their chemical processing problems. Solving a client’s problem is a complex activity involving many departments in our company. Our department’s focus is to develop, on paper, a large-scale solution, called a process design, for a chemical processing problem. We accomplish this design by synthesizing a process flowsheet, solving its material and energy balances, sizing and costing its equipment, and determining its profitability. Basically, we determine the feasibility of the process design, that is, is it feasible to build and run this process design. Finally, BEEF communicates a process design to our client in the form of a technical report. Hawbawg Chemical Company has hired us to investigate the feasibility of manufacturing styrene monomer from the raw materials of toluene and methanol. They have completed a royalty deal with Exelus, Inc. to use their proprietary one-step process with a newly-developed catalyst. Styrene monomer is an intermediate material used to make such consumer plastic products as polystyrene packaging and film, cushioning materials, radio and television sets, and toys. About 90% of the styrene monomer marketed in the United States currently uses a two-step process beginning with benzene and ethylene. First, benzene is alkylated with ethylene to form ethylbenzene. After purification, the ethylbenzene is catalytically dehydrogenated to produce styrene. The dehydrogenation step is endothermic and requires a large quantity of steam mixed with the ethylbenzene to maintain the desired reaction temperature, to depress coking of the catalyst, and to dilute the reaction concentration to enhance the reaction equilibrium. However, the Exelus process will produce styrene monomer from toluene and methanol in one step, and steam addition is not required. Some byproduct ethylbenzene is also produced which can be sold to conventional styrene producers. The new catalyst discovered by Exelus might give Hawbawg the opportunity to develop a new, low-cost route to styrene monomer. As a first step in our feasibility study for Hawbawg, your team is assigned the tasks to develop the flowsheet and determine its process requirements for material and energy that maximizes the net profit. The chemical process for converting toluene and methanol to styrene monomer is globally depicted in the diagram below. byproduct

toluene

flowsheet methanol

?

styrene monomer wastes

You must synthesize the process flowsheet, where the chemical reactor is the heart of that flowsheet. This flowsheet will be composed of process units (such as reactors, heaters, coolers, pumps, and distillation columns) that are connected by process streams, and it will conceptually shows the flow of material and energy from the raw materials to the products. Before you look at this flowsheet in detail, you should click here to complete

Chapter 1

Page 1-2


an interactive demonstration on the construction of a simple flowsheet to produce styrene monomer from toluene and methanol. This interactive demo takes about two and half hours to complete. You can stop the demo at any time. When you restart it, you can begin where you had left off. The interactive demo illustrates the basic concepts that you will be learning about in this HYSYS manual on chemical process simulation.

Chemical Flowsheet Description The senior chemical engineers in our Process Engineering Department have formulated several possible process flowsheet designs that could produce styrene monomer. They applied design rules of thumb (a.k.a. heuristic rules) to determine those formulations. In Chapter 4 of this HYSYS manual, you will be introduced to some of those heuristic rules as you build the process flow diagram (PFD) one process unit at a time starting with the chemical reactor and using the Aspen HYSYS® software. Our senior chemical engineers have recommended an initial chemical process design without energy integration to convert toluene and methanol to styrene monomer, as depicted in the following block flowsheet: Q

WS

heater toluene

toluene recycle H2 fuel

pump

Q

Q

decanter

column

organic furnace

reactor

Q

WS

cooler

methanol aqueous

column

methanol recycle heater

ethylbenzene

column

pump

styrene monomer waste water

This flowsheet is an adaption of the one presented in the 1985 American Institute of Chemical Engineers Student Contest Problem [AIChE, 1984]. A flowsheet is a collection of blocks, circles, and arrowed lines. The blocks and circles represent process units, such as reactors, heaters, coolers, pumps, and distillation columns. The solid arrowed lines are process streams (i.e., chemical material flowing in pipes) that are assumed to have uniform temperature, pressure, flow rate, and composition (as a first approximation, these four variables do not vary along the length of a pipe). These four quantities are referred to as the process state of a stream. The dashed arrowed lines represent energy streams of heat ( Q ) and work ( WS ). Usually, they are draw as solid lines but were drawn as dashed ones above, in order to distinguish them from material streams. Basically, the block flowsheet conceptually shows the flow of material and energy from the raw materials (toluene and methanol) to the product (styrene monomer), by-product (ethylbenzene), and wastes (H2 and water).

Chapter 1

Page 1-3


Although it is not shown in the above flowsheet, toluene and methanol at 25°C and 1 atm are first compressed and heated to saturated vapors at 460 kPa. The toluene and methanol recycles are also compressed and heated to saturated vapors at 460 kPa. Then, the two vapor feeds of pure toluene and methanol entering the above flowsheet are mixed with the toluene and methanol recycles to form the process stream to the furnace. The process stream leaving the mixer operation is superheated in a fired furnace to around 465 to 540°C and then fed to the catalytic reactor where the following vapor-phase reactions take place: C7H8

+

toluene

C7H8 toluene

CH3OH

→

methanol

+

CH3OH methanol

C8H8

+

styrene

→

C8H10 ethylbenzene

H2O water

+

+

H2 hydrogen

H2O water

As a first approximation, you can assume that other byproduct formation and polymerization of styrene monomer are negligible and that the catalyst does not coke or deactivate with time. The reactor is assumed to operate adiabatically; that is, it is well insulated and no heat is transferred to the surroundings. In the above block flowsheet, the process stream leaving the reactor is condensed with cooling tower water and cooled to 38°C, forming three phases—vapor, organic, and aqueous—in a decanter. The vapor stream from the decanter contains mostly hydrogen, and it could be used as a fuel. The aqueous stream contains primarily methanol and water, and it is sent to a methanol distillation column. This column’s product stream is the recycled methanol, while its bottoms stream is wastewater, which is eventually discharged at 25°C and 1 atm. The organic stream from the decanter contains mostly toluene, ethylbenzene, and styrene monomer. It is sent to a toluene distillation column. This column’s product stream is the recycled toluene stream containing some methanol, while its bottoms stream contains mostly ethylbenzene and styrene monomer, which are sent to the styrene distillation column. In the styrene column, the product stream is mostly ethylbenzene, and the bottoms stream is mostly crude styrene monomer. Although not shown in the above flowsheet, both of these streams must be cooled to 25°C and 1 atm before each enters a separate storage tank. In the above styrene monomer flowsheet, the process operates on a continuous basis; that is, material is continually flowing into and out of each process unit. The Aspen HYSYS® simulator is designed specifically for a continuous process of multiple process units. It is not designed to handle batch, semi-batch, or semi-continuous process units. In a batch operation, no material is flowing into or out of the process unit like a batch chemical reactor. The batch reactor is charged with materials, the reaction takes place in the reactor container, and at the end of the reaction the material is removed. In a semi-batch process, at least one chemical compound either enters or leaves the process unit, while all other chemical compounds remain within the process unit. In a semi-continuous process, at least one chemical compound enters and leaves the process unit, while all other chemical compounds are processed as batch or semibatch operations. Using the spreadsheet module in Aspen HYSYS®, you can program the solution to the material and energy balances for a batch, semi-batch, or semi-continuous process unit. Appendix A presents an example batch problem for expanding a gas mixture in a cylindrical tank system, a typical problem that you will encounter in the junior-level chemical engineering thermodynamics course. It also describes how to use the HYSYS spreadsheet module to complete the numerical solution to this batch example problem. Before examining Appendix A, you should complete Tutorials 2.1, 2.2, and 2.3 in Chapter 2 of this HYSYS manual.

Chapter 1

Page 1-4


Flowsheet General Assumptions Our client, Hawbawg Chemical Company, expects the plant capacity to be 250,000 metric tons per year of crude styrene monomer with an onstream time of 8,320 hours per year. For a preliminary design study, our senior chemical engineers have provided a list of process simulation assumptions to determine the material and energy requirements for the above process flowsheet as follows: • • • •

Impurities in purchased methanol and toluene are negligible. Yield losses in the chemical reactor due to trace byproducts can be ignored. The catalyst in the chemical reactor does not coke or deactivate with time The chemical reactor is well insulated, and thus no heat is transferred to the surroundings.

• • • •

Mostly methanol partitions into both the organic and aqueous phases of the decanter. Except for methanol, negligible organics will partition into the decanter aqueous phase. Negligible water will partition into the decanter organic phase. The off-gas from the decanter will be given a credit as fuel at its lower heating value.

• • •

The methanol is to be recycled as a saturated vapor at 460 kPa. The toluene/methanol mixture is to be recycled as a saturated vapor at 460 kPa. Water, ethylbenzene and styrene monomer recycled to the reactor feed are at small enough concentrations to pass through as inert compounds.

Flowsheet Thermodynamic Data In your process simulations of the above flowsheet, all necessary thermodynamic calculations for thermophysical properties (such as density and molar enthalpy) and for phase equilibria (such as vapor-liquid or vapor® liquid-liquid) can be done using an equation of state. In the Aspen HYSYS simulator, the Peng-Robinson Stryjek-Vera (PRSV) equation of state is recommended by our senior chemical engineers for the analysis of the manufacture of styrene monomer from toluene and methanol. The PRSV equation is an improvement on the Peng-Robinson (PR) equation of state, and it extends the application of the PR method to moderately non-ideal systems. The physical properties of the six chemical compounds associated with the above flowsheet are summarized below. Their values were extracted from the Aspen HYSYS® databank. Property CAS Registry Number Molecular Weight Normal Boiling Point at 1 atm, °C Critical Temperature, °C Critical Absolute Pressure, kPa Critical Volume, m3/kgmol Acentric Factor ΔHf at 25°C and 1 atm, kJ/kgmol

Hydrogen

Methanol

Water

Toluene

Ethylbenzene

Styrene Monomer

1333-74-0 2.0160 -252.60 -230.86 1925.55 0.0515 -0.1201 0

67-56-1 32.0419 64.65 239.45 7376.45 0.1270 0.5570 -201,290

7732-18-5 18.0151 100.00 374.15 22,120.00 0.0571 0.3440 -241,000

108-88-3 92.1408 110.65 318.65 4100.04 0.3160 0.2596 50,029

100-41-4 106.17 136.20 343.95 3607.12 0.3740 0.3010 29,809

100-42-5 104.152 145.16 362.85 3840.00 0.3520 0.2971 147,400

These thermodynamic data are used in the PRSV equation of state to calculate such thermophysical properties as mass density and molar enthalpy of a mixture of chemical compounds.

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Flowsheet Design Variables In a chemical process simulation, design variables are those variables that you have the freedom to set their values. Our Research and Development Department has conducted some pilot-plant studies on the adiabatic reactor performance of making styrene monomer from methanol and toluene using the newlydeveloped catalyst from Exelus, Inc. In this study, stoichiometric feed (i.e., equal moles of toluene and methanol) to the reactor resulted in the following performance data for the formation of styrene monomer (the product) and ethylbenzene (the byproduct) at a reactor inlet pressure of 400 kPa: X - molar conversion

Y - molar yield

X*Y

X*(1 – Y)

Member Symbol

Inlet T, °C

TL reacted TL fed

SM formed TL reacted

SM formed TL fed

EB formed TL fed

α ♠ ♥ ♣ ♦ ω

465 480 495 510 525 540

0.649 0.679 0.709 0.759 0.819 0.879

0.909 0.869 0.829 0.779 0.719 0.659

0.5899 0.5901 0.5878 0.5913 0.5889 0.5793

0.0591 0.0889 0.1212 0.1677 0.2301 0.2997

TL is toluene, SM is styrene monomer, and EB is ethylbenzene

An Excel version of this table is available by clicking here. In Chapter 4 of this HYSYS manual, you will complete the process simulation of the above flowsheet for an assigned inlet temperature to the chemical reactor. The first column in the above table identifies a team member symbol that will be assigned to you by your project supervisor. That assigned symbol indicates the inlet temperature that you will use in your HYSYS process simulations of Chapter 4. For a HYSYS distillation column simulation, the feed, distillate, and bottoms streams are to be saturated liquids. Nominal atmospheric distillations will operate at 135 kPa top tray pressure and 125 kPa condenser outlet pressure. Avoid column operating pressures above nominal atmospheric. Allow 5 kPa pressure drop between the top of the column and the condenser outlet for a vacuum distillation column. Based on some heuristic rules in engineering practice [Woods, 2007, Ch. 2], the following pressure drops thru process units caused by frictional losses may be assumed: Fired heater Reactor Heat exchangers* (shell and tube sides) Condensers under vacuum Other major equipment Distillation Trays: 1.0 kPa per theoretical stage for pressure columns 0.5 kPa per theoretical stage for vacuum columns

60 kPa 70 kPa 10 kPa 5 kPa 10 kPa

*Includes condensers, vaporizers, interchangers and all other exchangers except condensers operated under vacuum.

For pumps and compressors, the adiabatic efficiency can be assumed to be 75%. The combined mechanical and electrical efficiency for this type of equipment is approximately 90%.

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Flowsheet Design Specifications Design specifications set limits on the values of important calculated variables in a chemical process flowsheet simulation for the stated simulation assumptions and design variables. As recommended by Hawbawg, some design specifications for toluene, methanol, ethylbenzene (EB), styrene monomer (SM), and water in the aromatic and wastewater streams are as follows: Recycle Methanol Recycle Toluene EB Byproduct Crude SM Product Wastewater

No specified limit on toluene. No specified limit on methanol. 4 wt % ethylbenzene maximum. 5 wt % maximum for sum of EB and SM. 0.8 wt % toluene maximum. 3 wt % SM maximum. 300 ppm EB maximum. (ppm is parts per million by weight) Governmental standards on all pollutants

The Environmental Protection Agency (EPA) standards for water pollution are given as the maximum parts per million (ppm on mass basis). These standards are: 80 ppm for toluene, 60 ppm for methanol, 108 ppm for ethylbenzene, and 108 ppm for styrene monomer. With respect to any distillation column that contains styrene monomer, do not exceed 145°C in that column with more than 50 mass% styrene monomer in the bottoms stream, in order to minimize polymerization of the styrene monomer (i.e., solid formation of a polymer).

Flowsheet Economic Analysis For a preliminary design study, the economic viability of manufacturing styrene monomer from toluene and methanol can be determined by maximizing the net profit. The net yearly profit for the styrene flowsheet can be approximated as follows: net profit

=

product sales

+

byproduct sales

+

fuel credit

−

cost of raw materials

−

annualized capital cost

−

utility costs

where each term is $ per year. The annualized capital cost for purchasing the equipment is estimated to be (product sales + byproduct sales)/6 in $/yr. The other terms in this net profit equation can be determined once the material and energy requirements for the above flowsheet are calculated for a specific reactor inlet temperature using Aspen HYSYS®. Appendix M provides details on how to determine these other terms. In Chapter 4 of this HYSYS manual, your team members will determine their net profit for their assigned reactor inlet temperature. Your team will then plot sales (which include the fuel credit), costs, and net profit versus the reactor inlet temperatures to determine that operating temperature that maximizes the net profit. In this plot, you can expect to see the net profit curve exhibit a maximum value either within the range of reactor temperatures or at an end point of the range. That point at which the maximum profit occurs is the “best” temperature at which to operate the adiabatic reactor. Although economics are important in determining the viability of a process flowsheet, other factors such as efficiency, health, safety, reliability, aesthetics, ethics, and social impact are also important. You will study these other factors in the senior-level process engineering course of the chemical engineering curriculum. For this introductory course on chemical engineering, our focus for flowsheet viability will just be the net profit. For the economic analysis of other engineering problems, minimizing the costs can be the objective. Click here to review a simple tank problem that is based on minimizing costs.

Chapter 1

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For the preliminary economic analysis of the above process flowsheet to make styrene monomer from toluene and methanol, the economic data in the table below are to be used to determine the net profit. These economic data are tentative and appropriate only for a preliminary economic evaluation. Raw Materials: Methanol $ 350/metric ton = Toluene $ 650/metric ton = Product Values: Crude Styrene Product $1,540/metric ton = Ethylbenzene Byproduct $ 970/metric ton = Credits: Off-gas from three-phase separator $ 8.53/M kilojoules Utilities: Natural Gas* $12.10/M kilojoules Steam from HP Steam: 6 bar, 158.8°C, saturated vapor $30.29/K kilograms 11 bar, 184.1°C, saturated vapor $30.59/K kilograms 42 bar, 253.2°C, saturated vapor $30.97/K kilograms Cooling Water $ 0.03/K liters Average inlet temperature 31°C Average outlet temperature 41°C maximum Electricity $0.06/kW·h *Assume 90% efficiency for the fired heater fuel usage. The symbols K and M mean a thousand and million, respectively.

$0.35/kg $0.65/kg $1.54/kg $0.97/kg

All of these data are for 2009 and apply to the Houston Gulf Coast area, where the plant will be located.

Flowsheet Development Strategy Using the above assumptions and data, you and your teammates will be analyzing the above styrene monomer flowsheet extensively in this introductory course as a semester-long project using the Aspen HYSYS® process simulator. The goal of the project is for your team to determine the “best” process requirements for material, equilibrium, and energy based on economics. This project is designed as an independent study to sharpen your life-long learning skills. The chapters in this HYSYS manual will guide you as you do this independent study. The development of any process flowsheet is a very complex activity. Engineers handle complexity by a divide and conquer strategy. In this HYSYS manual, Chapters 2, 3, and 4 are the sub-parts of a strategy to develop the flowsheet for the production of styrene monomer from toluene and methanol. These chapters accomplish the following: •

Chapter 2 introduces you to the Aspen HYSYS® process simulation software. Tutorials 2.1 to 2.6 in this chapter provide you with detailed instructions on how to use HYSYS in the Windows environment, in order to do some standard process simulation calculations in the introductory chemical engineering course. Tutorials 2.7 to 2.10 are intended for the senior-level design course in the chemical engineering curriculum.

•

Chapter 3 provides five assignments in which you can develop your abilities and confidence to simulate individual process units using Aspen HYSYS®. These assignments focus on a process stream, pump, heater, mixer/tee, and reactor. Once

Chapter 1


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you’ve completed the assignments, you will have a mathematical understanding of how HYSYS does its calculations for each process unit. •

Chapter 4 contains seven assignments to develop the styrene monomer flowsheet. Each member of your team will begin with the reactor section at an assigned operating temperature and increase the complexity of the flowsheet by adding sections, one by one, until the complete flowsheet is simulated in Aspen HYSYS®. While doing these assignments, you will learn about some heuristic rules that provide guidance on selecting process unit operations in the flowsheet and determining their operating conditions.

You will complete the tutorials of Chapter 2 and the assignments of Chapters 3 and 4 over a 14-week period. Once these tasks are completed, you will have finished the first step in a feasibility study on the production of styrene monomer from toluene and methanol; that is, the development of its flowsheet and processing requirements for material and energy. While completing the tasks of Chapters 2, 3, and 4, you will need to access additional information, which you can find in the appendices. Appendices B to L contain simulation modules for various continuous process unit operations. Each appendix or module provides a mathematical explanation of how Aspen HYSYS does its calculations for that continuous process unit. A module includes a module description, a conceptual model, model assumptions, a mathematical model, example mathematical algorithms, and several HYSYS simulation algorithms. You will need to consult these appendices while doing your assigned tasks in Chapters 3 and 4.

Your Professional Challenge As a new provisional engineer in BEEF, Inc., your professional challenge of developing the styrene monomer flowsheet using Aspen HYSYS® is formable. To complete this challenge, you must develop your critical thinking skills as a problem solver and document your progress in your technical journal. As reported by Halpern [1989, pp. 29-30], critical thinking has two essential components—the mental skills as well as a healthy attitude. As a provisional engineer, you must develop your critical thinking skills by learning the strategies to apply the CinChE problem-solving methodology [Hanyak, 2011] and to simulate the process requirements for a chemical process flowsheet using Aspen HYSYS®. Also, you must develop a critical thinking attitude; that is, you must be willing to plan, be flexible in your thinking, be persistent and not lazy, and be willing to self-correct. You cannot become a critical problem solver without this sort of attitude. As reported further by Halpern [1989, p. xvii], developing your critical thinking skills requires you to be an active learner that completes reading assignments on time, drafts segments of a problem solution in a timely manner, raises questions when needed, documents the solution in a professional manner, and enjoys what you are doing. You begin your journey in applying the self-paced materials in this HYSYS manual. So, please get comfortable, prepare for some hard work, and enjoy this instructional manual on the Aspen HYSYS® simulator. It should be a cinch! BEEF, Inc. hired you as a new employee, because you possess the talent to become a critical problem solver and professional documenter. Welcome to our company, and good luck in your team's development of the styrene monomer flowsheet. Remember our company’s two mottos, “Engineering is 10 % Inspiration and 90 % Perspiration” and “Results not Excuses.”

Chapter 2 HYSYS Simulation Tutorials

Chapter 2 HYSYS Simulation Tutorials

Chapter 2

Page 2-1

HYSYS Simulation Tutorials

Process Flowsheet Overview As stated in Chapter 1, a fundamental aspect of chemical engineering is the design of chemical processes. A chemical process transforms raw materials into products through a series of process units connected by process streams. A process unit or unit operation is equipment that physically and/or chemically changes the chemical compounds passing through it. Increasing temperature, decreasing pressure, and mixing are some examples of physical changes, while chemical reactions cause changes in chemical compounds. Process units are connected by material process streams that carry the chemical compounds at a certain process state—temperature, pressure, flow rate, and composition. Energy streams connected to process units supply the needed energy for an operation or remove energy released in an operation. A schematic diagram called a process flow diagram (PFD) and often referred to as a flowsheet represents a chemical process. A flowsheet shows all process units and streams and how they are connected, as illustrated in Figure 2.1 below. 25°C 3095 kPa 330 kgmol/h 64.8 mol% benzene 33.5 mol% propylene 1.7 mol% propane 0.0 mol% cumene

Q=?

S1

E1 heater

Q=?

S2 350°C 3075 kPa

R1 reactor

S3 350°C 3025 kPa

Figure 2.1. A Simple Process Flowsheet

The arrow lines labeled S1, S2, and S3 are material streams, while the other two arrow lines are energy streams. The two circles labeled E1 and R1 are process units. For the flowsheet in Figure 2.1, the simulation problem is “what heat duty in kJ/h is required to raise the temperature of Stream S1 from 25 to 350°C” and “how much energy in kJ/h is required to operate the reactor at an isothermal condition (i.e., at constant temperature)”? A simulation of a chemical process does the material and energy balances on all of the process units. This information can then be used to see how to manipulate the process to maximize net profit, maximize product rate, minimize energy use, etc. Aspen HYSYS® is a computer program that simulates chemical processes. Using a computer for a process simulation takes a fraction of the time it takes to do it by hand. The speed of a computer simulation allows the user to observe quickly the effect of changes in a simulation. For example, using HYSYS, you can easily compare the amount of product produced using different ratios of starting materials. Doing this comparison with hand calculations would be a long and tedious task and subject to human calculation errors. In this chapter, you will learn how to use HYSYS within the Windows 7 operating system to do some process simulation calculations. You will also gain a better understanding of some chemical process units and how their material and energy balances are solved. This chapter presents ten tutorials to introduce you to steady-state process simulation. They are: (1) tutorial conventions, (2) introduction to the HYSYS interface, (3) simulation file creation, (4) heater and case study, (5) conversion reactor and reactions, (6) process flow diagram (PFD) fundamentals, (7) Gibbs equilibrium reactor, (8) kinetic model in a plug flow reactor, (9) HYSYS printing capabilities, and (10) HYSYS spreadsheet programming. Tutorials 1 to 6 are designed to be used in the introductory course on chemical engineering, often called the stoichiometry or material and energy balance course. Tutorials 7 to 10 are intended for the senior-level process engineering or design course.

Chapter 2

HYSYS Simulation Tutorial 2.1

Page 2-2

Tutorial Conventions Since HYSYS is totally interactive, it provides virtually unlimited flexibility in solving any simulation problem. Please keep in mind that the approaches used in solving each example problem presented in this tutorial chapter may only be one of many approaches. You should feel free to explore other alternatives by consulting the “Help” facility in the Aspen HYSYS® software. This tutorial presents general convention adopted for this chapter. It focuses on terminology used to describe mouse actions and on formatting conventions for text in this chapter. The tutorial also presents general comments on interactive process modeling, the HYSYS way. Finally, you initialize HYSYS for your use at your university.

A. Keywords for Mouse Actions As you read through various procedures in this HYSYS manual, you will be given instructions on performing specific functions or commands. Instead of repeating certain phrases for mouse instructions, we will use a keyword to imply a longer instructional phrase: •

The keywords select, choose, pick, press, or click mean to position the cursor on the object or button of interest, and press the primary mouse button once.

•

The keyword double-click means to position the cursor on the object of interest, and press the primary mouse button twice quickly in succession.

•

The phrase click and drag means to position the cursor on the object of interest, press and hold the primary mouse button, move the cursor to a new location, and release the primary mouse button.

•

The keyword object inspect means to position the cursor on the object of interest, and press the secondary mouse button once.

•

The keyword enter means to position the cursor in an input cell, press the primary mouse button once, type the required information, and then press the key on the keyboard.

For a standard two-button mouse, the primary mouse button is on the left, while the secondary one is on the right, provided you have not changed the mouse settings within the Windows 7 operating system.

B. Text Formatting A number of text formatting conventions are also used throughout this chapter. They help to quickly identify menu commands, buttons, keys on the keyboard, windows or views, areas within windows, radio buttons and check boxes in window areas, material and energy stream names, unit operation names, and HYSYS unit operation types. These conventions are as follows: •

When you are asked to invoke a HYSYS menu command, the command is identified by bold lettering. For example, File indicates the File menu item, while Tools/Preferences… means the Preferences option within the Tools menu.

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•

When you are asked to press a HYSYS button, the button is identified by bold, italicized lettering. For example, Close identifies the Close button within a particular window (i.e., a viewing area on the screen).

•

When you are asked to press a key or keys to perform a certain function, keyboard commands are identified by bold lettering, enclosed by angle brackets. For example, identifies the F1 key on the keyboard. A combination of keys like is to be pressed simultaneously.

•

The name of a HYSYS view (or window) is indicated by bold lettering; e.g., Session Preferences.

•

The name of a Group or Area within a view is identified by bold lettering; e.g., Initial Build Home View.

•

The name of Radio Buttons and Check Boxes are identified by bold lettering; e.g. Default or User Supplied.

•

Material and energy stream names are identified by bold lettering; e.g., S1, Column Feed, and Condenser Duty.

•

Unit operation names are identified by bold lettering; e.g., Flash Separator or Atmospheric Tower. Note that blank spaces are acceptable in the names of streams and unit operations.

•

HYSYS unit operation types are identified by bold, uppercase lettering; e.g., HEAT EXCHANGER, SEPARATOR, and DISTILLATION COLUMN.

•

When you are asked to provide keyboard input, it will be indicated by bold lettering; e.g., “Enter 100 for the stream temperature”.

C. Interactive Process Modeling The role of process simulation in this instructional manual is to improve your chemical process understanding so that you can make the best process decision. A flowsheet solution in the Aspen HYSYS system is an interactive simulation, unlike the Aspen PLUS system which is a batch simulation. The HYSYS solution not only makes the most efficient use of your simulation time, but by building the process model interactively—with immediate access to results—you gain the most complete understanding of your process simulation. The HYSYS software uses the power of Object-Oriented Design, together with an Event-Driven Graphical Environment, to deliver a completely interactive simulation environment where: •

calculations begin automatically whenever you supply new information, and

•

access to the information you need is in no way restricted.

At any time, even as calculations are proceeding, you can access information from any location in HYSYS. Each location is always instantly updated with the most current information, whether specified by you or

Chapter 2


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calculated by HYSYS. This interactive calculation environment is similar to what occurs in a spreadsheet program like Microsoft Excel. In an Aspen PLUS batch simulation, the process information is placed in an input file, that file is then submitted for processing to the process simulator, the results from the simulation are set to a file, and then the results file is viewed to observe any errors or the calculated results. If errors have occurred or the calculated results are not reasonable, then the batch simulation must be restarted by updating the input file. Given the power and flexibility designed into HYSYS, many ways exists to accomplish the same task. The tutorials of this chapter have been designed to show you one way to do each HYSYS task, primarily for simplicity and speed. Other ways do exist, and you can consult the Help facility in the Aspen HYSYS® software to investigate those ways.

D. HYSYS at Your University Before you proceed to learn how to do process simulations, you want to configure some HYSYS preferences and save them as a file for later use. To configure the HYSYS software, proceed as follows: 1. Press keys and then login using your account name and password.

To access the Windows 7 desktop on a computer that is connected to the network at your university.

Click the yellow Windows Explorer icon in the bottom taskbar of the Windows 7 desktop.

To display the Favorites, Libraries, and Computer resources available on your logged-into computer.

Under Computer resources, double click your account name and then double click on your private area.

To open your private folder on the network file server at your university. At Bucknell University, your private area is in partition (\\netspace)(U:).

Object inspect your private folder [i.e., position the cursor on the object and press the secondary (usually right) mouse button once]. Select New/Folder and

To create a new folder in your private area on the network file server at your university. You will use your private aspen_hysys folder to store your HYSYS preferences for later use in this manual.

name your new folder aspen_hysys.

2. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you must type into the web browser.

Note that 

Since you will access this web address often, you should bookmark it in the web browser.

Click here to download the logo image file beef_logo_256.bmp and select the Save button in the File Download window. Then, navigate to your private aspen_hysys folder and click the Save button in the Save As window. If necessary, click the Close button to exit the Download Complete window. If the Paint program opens instead of the File Download window, select the File/Save As... option, navigate to your private aspen_hysys folder and click the Save button in the Save As

To store a copy of our company’s logo image (which has been pre-made for you) into your private area on the network file server at your university.

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Introduction to the HYSYS Interface You will download the existing file t2.02_intro.hsc and then conduct a process simulation in HYSYS using that file. This HYSYS file simulates a material stream containing benzene, propylene, propane, and cumene. It also uses the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package to calculate the thermophysical properties of the stream, such as mass density, molar volume, and molar enthalpy. The conceptual diagram for this stream is: TS1 = 25 C PS1 = 175 kPa nS1 = 200 kgmol / h zS1, BZ = 0.500

S1

zS1, PY = 0.015 zS1, PR = 0.015 zS1,CU = 0.470

The process state of Stream S1 is its temperature, pressure, flow rate, and composition (in this case mole fractions). The material state of Stream S1 is just its temperature, pressure, and composition. Knowing the material state, many properties of the stream can be determined by HYSYS, such as mass density, molar volume, molar enthalpy, surface tension, and viscosity. Process stream states are used to determine the material and energy requirements for process unit operations found in a process flow diagram (or flowsheet). Note that the process state is the material state plus the flow rate. You will practice HYSYS navigation fundamentals and some basic HYSYS capabilities in nine sections— retrieve a pre-defined simulation file, open a pre-defined simulation file in HYSYS, manipulate stream specifications, change global preferences, add variables to the workbook, add a second fluid package, program a spreadsheet operation, document your simulation session, and close the simulation case. To proceed, you must have completed the tasks in Tutorial 2.1.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.02_intro.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual. Click here to download the simulation file t2.02_intro.hsc and then select the Save button in the File Download window. 2. Navigate to a folder in your private area on the network file server at your university. or

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you would type into the web browser or which you would select from your bookmark list. To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation. To store the simulation in one of your private folders as a file on the network file server. or

Chapter 2


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Simulation File Creation In Tutorial 2.2 for the “Introduction to the HYSYS Interface,” you practiced basic HYSYS skills using an existing simulation file t2.02_intro.hsc. Now you will learn how to create and save a simulation file similar to t2.02_intro.hsc. The creation of this file is divided into eight sectionsstart the HYSYS program, create a simulation basis, find component physical properties, create a process stream, copy and delete a process stream, specify alternative stream conditions, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorial 2.2.

A. Start the HYSYS program. After you start the HYSYS program, you need to complete a task before you begin your simulation work. That is, you must load your default HYSYS preferences to overwrite the global preference settings last stored in the computer user area for your login account. Proceed as follows: 1. Choose Aspen HYSYS thru the Start menu on the Windows desktop. Click the middle Maximize Window icon  in the upper-right part of the HYSYS desktop. 2. Choose Tools/Preferences… from the menu bar.

To access the Aspen HYSYS process simulation program. To expand the HYSYS desktop window to fit the full area of the monitor screen. To display the Session Preferences window with tabbed preference views.

Click the Load Preference Set … button in the lower right of the Session Preferences window.

To begin the process of loading your default preferences to overwrite the global preferences in the HYSYS program.

Navigate to your private aspen_hysys folder on the network file server at your university.

To locate the folder containing your default preferences stored in file Aspen HYSYS V7.prf.

Double-click on the file Aspen HYSYS V7, or Select this file and click the Open button.

To load your default preferences into the HYSYS program on the computer you are sitting at.

3. Choose Tools/Preferences… from the menu bar.

To display again the Session Preferences window with tabbed preference views.

Select the Variables/Units page.

To display the Units preference page.

Select my-fps in the Available Unit Sets area.

To make it the chosen unit set, if available.

Click Delete in the Available Unit Sets area.

To delete this cloned set of units, if it is available.

Select SI in the Available Unit Sets area.

To make it the chosen unit set for this session.

Click the Close or X button.

To return to the HYSYS desktop window.

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Page 2-29

satisfied using temperature and pressure (the +2) and mole fractions (the nc). However, other combinations exist, two examples of which are as follows:

TS 1 = tmixH  Hˆ S 1 , PS 1 , Z S 1  TS 1 = tmixS  SˆS 1 , PS 1 , Z S 1  where temperature is calculated knowing either molar enthalpy or molar entropy plus pressure and composition. How does HYSYS solve for temperature in the tmixH equation? The mathematical algorithm to solve for the temperature of the mixture is as follows:

TS 1 = tmixH  Hˆ S 1 , PS 1 , Z S 1  1. ITERATE TS 1 in Hˆ S′1 = hmix [TS 1 , PS 1 , Z S 1 ] UNTIL

calculated Hˆ S′ 1 = specified Hˆ S 1

Thus, HYSYS iterates on the temperature (i.e., guesses values for it) until the calculated molar enthalpy is close in value to the specified molar enthalpy. A similar mathematical algorithm in HYSYS exists for the tmixS equation, as follows:

TS 1 = tmixS  SˆS 1 , PS 1 , Z S 1  1. ITERATE TS 1 in

SˆS′1 = hmix [TS 1 , PS 1 , Z S 1 ] UNTIL

calculated SˆS′ 1 = specified SˆS 1

This section simulates the tmixH and tmixS functions in HYSYS by replicating an existing process stream using the pre-defined file t2.03_replica.hsc. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you would type into the web browser or which you would select from your bookmark list.

Click here to download the simulation file t2.03_replica.hsc and then select the Save button in the File Download window.

To begin the process of retrieving the pre-defined HYSYS file for simulating the tmix function.

Navigate to a folder in your private area on the network file server at your university. or select the computer’s Desktop.

To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer.

Click the Save button, and then click the Close

To save your t2.03_replica.hsc simulation file and

Chapter 2

Page 2-34


Heater and Case Study

Please consult the errata file for changes to Pages 2-41 to 2-43. To access this file, change "a_blue" to "a_errata" in the current web link.

In Tutorials 2.2 and 2.3, you conducted a HYSYS simulation on a single process stream that contained benzene, propylene, propane, and cumene. In this tutorial, you will add a heater unit operation to the simulation and then conduct a case study analysis on that heater. You will begin with the existing file named t2.04_heat.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with four chemical components and a liquid process stream, named S1. The process state of Stream S1 is given below in the conceptual diagram for the heater. Using HYSYS, you will determine what duty ( Q E1 in kJ/h) is required to heat Stream S1 to a saturated vapor at 162 kPa. V f , S1 = ?

Vf ,S 2 = 1.0 

TS1 = 25 C PS1 = 175 kPa nS1 = 200 kgmol / h

TS 2 = ?

Q E1 = ? S1

zS1, BZ = 0.500 zS1, PY = 0.015

E1 heater

S2

PS 2 = 162 kPa nS 2 = ? zS 2, BZ = ? zS 2, PY = ?

zS1, PR = 0.015

zS 2, PR = ?

zS1,CU = 0.470

zS 2,CU = ?

Then you will perform a case study to observe the heat duty-temperature profile for this heater operation. This tutorial is divided into seven sections—retrieve a pre-defined simulation file, open a pre-defined simulation file in HYSYS, add a heater unit operation, specify the heater outlet condition, perform a case study, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorials 2.2 and 2.3.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.04_heat.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual. Click here to download the simulation file t2.04_heat.hsc and then select the Save button in the File Download window. 2. Navigate to a folder in your private area on the network file server at your university. or select the computer’s Desktop.

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you would type into the web browser or which you would select from your bookmark list. To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation. To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer.

Chapter 2

Page 2-44


Conversion Reactor and Reactions In Tutorial 2.4, you conducted a HYSYS simulation on heating a process stream that contained benzene, propylene, propane, and cumene. In this tutorial, you will add a reactor unit operation to the simulation. You will begin with the existing file named t2.05_conv.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with four chemical components and a heater process unit, named E1. Reaction information (i.e., stoichiometric equations with their models) can be attached to certain HYSYS process unit operations to simulate the reaction of chemical compounds. Reactions can be specified in HYSYS by various models—such as conversion, equilibrium, or kinetic models. This tutorial shows you how to add a conversion reactor and the needed reaction information for the isothermal, vapor-phase reaction of propene and benzene to form cumene, as expressed by the following stoichiometric equation: C3H6

propene

+

C6H6

→

benzene

C9H12

cumene

In the conceptual model below, you will determine what duty ( Q R1 in kJ/h) is required to operate the isothermal reactor R1; that is, how much heat is withdrawn from the exothermic reaction, so that the inlet (S2) and outlet (S3) streams are at the same temperature. TS1 =

25  C

PS1 = 3095 kPa

Q E1 = ?

TS 3 = 350  C

Q R1 = ?

PS 3 = 3025 kPa n S 3 = ?

n S1 = 329.6 kgmol / h z S1, BZ = 0.648 z S1, PY = 0.335

S1

E1 heater

z S1, PR = 0.017 z S1,CU = 0.0

S2

TS 2 = 350  C PS 2 = 3075 kPa

R1 reactor

S3

z S 3, BZ = ? z S 3, PY = ? z S 3, PR = ? z S 3,CU = ?

The molar conversion of propene for reactor R1 (i.e., amount reacted divided by the amount fed) is eighty-three percent for a specific catalyst. This tutorial is divided into seven sections—retrieve a pre-defined simulation file, open a pre-defined simulation file in HYSYS, add a reaction to the fluid package, add a reactor to the flowsheet, specify the reactor outlet conditions, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorial 2.4.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.05_conv.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.


Chapter 2

HYSYS Simulation Tutorial 2.5 Click here to download the simulation file t2.05_conv.hsc and then select the Save button in the File Download window.

2. Navigate to a folder in your private area on the network file server at your university. or select the computer’s Desktop.

Note that 

Click the Save button, and then click the Close button, if necessary.

Page 2-45

To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation. To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer. Saving a file to the computer will result in faster simulations, since HYSYS will not have to transfer data over the network. Simulation speed becomes important as your file becomes larger. After you have finished your simulation work, you can drag the file from the Windows desktop to your private folder on the network file server for permanent storage. To save your t2.05_conv.hsc simulation file and exit the Download complete window.

B. Open a pre-defined simulation file in HYSYS. After you start the HYSYS program, you need to complete two tasks before you begin your simulation work. First, you must load your default HYSYS preferences to overwrite the global preference settings last stored in the computer user area for your login account. Second, you must open the pre-defined simulation file. Proceed as follows: 1. Choose Aspen HYSYS thru the Start menu on the Windows desktop. Click the middle Maximize Window icon  in the upper-right part of the HYSYS desktop. 2. Choose Tools/Preferences… from the menu bar.

To access the Aspen HYSYS process simulation program. To expand the HYSYS desktop window to fit the full area of the monitor screen. To display the Session Preferences window with tabbed preference views.

Click the Load Preference Set … button in the lower right of the Session Preferences window.

To begin the process of loading your default preferences to overwrite the global preferences in the HYSYS program.

Navigate to your private aspen_hysys folder on the network file server at your university.

To locate the folder containing your default preferences stored in file Aspen HYSYS V7.prf.

Double-click on the file Aspen HYSYS V7, or Select this file and click the Open button.

To load your default preferences into the HYSYS program on the computer you are sitting at.

3. Choose File/Open/Case… from the menu bar, or

To display the Open Simulation Case window.

Chapter 2


Page 2-55

PFD Manipulation Tools The focus of this tutorial is the HYSYS Process Flow Diagram (PFD). You can use the PFD to satisfy a number of functions while doing a process simulation. In addition to a graphical representation, you can build a flowsheet within the PFD using the mouse to install and connect objects. A full set of manipulation tools is associated with the PFD to allow you to reposition process streams and operations, resize icons, reroute streams, and create documentation text. All of these tools are designed to simplify your development of a clear and concise graphical process representation. You can use these tools to prepare your documentation for your solutions to the assignments in Chapters 3 and 4. In this tutorial, you will learn how to use effectively some of the PFD manipulation tools. You will begin with the existing file named t2.06_pfdtools.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with four chemical components (benzene, propylene, propane, and cumene), a heater process unit, named E1, and a conversion reactor unit, named R1. The reactor converts propylene and benzene to cumene with propane acting as an inert compound. This tutorial is divided into eleven sections—retrieve a pre-defined simulation file, open a predefined simulation file in HYSYS, zoom flowsheet in and out, orient some PFD icons, move some icon labels, view some operating conditions, add some documentation text, connect and disconnect PFD objects, copy a PFD to a Word document, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorials 2.4 and 2.5.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.06_pfdtools.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual. Click here to download the simulation file t2.06_pfdtools.hsc and then select the Save button in the File Download window. 2. Navigate to a folder in your private area on the network file server at your university. or select the computer’s Desktop.

Note that 

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you would type into the web browser or which you would select from your bookmark list. To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation. To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer. Saving a file to the computer will result in faster simulations, since HYSYS will not have to transfer data over the network. Simulation speed becomes important as your file becomes larger. After you have finished your simulation work, you can drag the file from the Windows desktop to your private folder on the network file server for

Chapter 2


Gibbs Equilibrium Reactor

Page 2-72

Please consult the errata file for changes to Page 2-74. To access this file, change "a_blue" to "a_errata" in the current web link.

In Tutorial 2.6, you conducted a HYSYS simulation on a flowsheet that contained a heater and an isothermal reactor that had benzene, propylene, propane, and cumene flowing through them. In Tutorial 2.5, you learned how to define a conversion reaction set for the following stoichiometric equation: C3H6

+

propene

C6H6 benzene

→

C9H12 cumene

You also associated this reaction set with a fluid package and attached it to a conversion reactor unit. Your HYSYS simulation of this reactor determined the heat duty needed to maintain the exothermic reaction at isothermal conditions. In this tutorial, you will add a Gibbs reactor unit to this flowsheet and compare its simulation results to those from the conversion reactor. You will begin with the existing file named t2.07_gibbs.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with four chemical components and a heater process unit, named E1, and a conversion reactor unit, named R1. In most reactor units, catalysts are used to increase the rate of reaction; that is, the speed of converting the reactants into products. Different catalysts when placed in a fixed reactor volume will produce a range of conversions for the reactants; that is, some catalysts will do better than others with respect to conversion. In Tutorials 2.5 and 2.6, you used an experimentally-determined molar conversion for a specific catalyst at a given temperature and pressure of operation. Thermodynamic equilibrium sets a theoretical limit on the extent to which reactants can be converted into products, and this limit cannot be changed by catalysts. This limit is the best you could expect, provided you could find the right catalyst to achieve it. The HYSYS Gibbs reaction model predicts thermodynamic reaction equilibrium by minimizing the total Gibbs free energy of the reacting system, and it does so without having to know the reaction stoichiometry, because it uses atom balances instead of mole balances. When you add a Gibbs reactor to a HYSYS simulation, you can determine the theoretical conversion limit for any reaction. This tutorial is divided into eight sections—retrieve a pre-defined simulation file, open a pre-defined simulation file in HYSYS, copy a reactor feed stream, add a Gibbs reactor to the flowsheet, specify the reactor outlet conditions, analyze results for the Gibbs equilibrium reactor, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorials 2.5 and 2.6.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.07_gibbs.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.


Click here to download the simulation file

To begin the process of retrieving the pre-defined

Chapter 2


Page 2-84

Kinetic Model and a Plug Flow Reactor In Tutorial 2.6, you conducted a HYSYS simulation on an isothermal reactor using a conversion reaction model for the following stoichiometric equation: C3H6

+

propene

C6H6 benzene

→

C9H12 cumene

You specified a molar propene conversion of 83%, and propane was present in the reactor feed as an inert compound. In Tutorial 2.7, you did another simulation on the same isothermal reactor, but you used the Gibbs reaction model to predict an equilibrium propene conversion of 99.1% for the above reaction. This conversion represents the best you could expect; it is the theoretical limit on the propene conversion. In this tutorial, you will again study the isothermal reaction, but you will simulate it using a plug flow reactor with a kinetic model and then compare your results to those from Tutorials 2.6 and 2.7. An experimentally-determined kinetic model for a particular catalyst is used to predict the behavior of a specific reaction to changes in temperature, pressure, and concentration. You will begin with the existing file named t2.08_kinetic.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-StryjeckVera (PRSV) fluid package with four chemical components and a heater process unit, named E1, and a conversion reactor unit, named R1. This tutorial is divided into nine sections—retrieve a pre-defined simulation file, open a predefined simulation file in HYSYS, copy a reactor feed stream, add a plug flow reactor to the flowsheet, add a kinetic reaction set to the fluid package, specify the reactor parameters and outlet conditions, analyze results for the kinetic reactor, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorials 2.6 and 2.7.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.08_kinetic.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.


Click here to download the simulation file t2.08_kinetic.hsc and then select the Save button in the File Download window.

To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation.


To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer. Saving a file to the computer will result in faster simulations, since HYSYS will not have to transfer

Chapter 2


Page 2-99

HYSYS Printing Capabilities This tutorial shows you how to document HYSYS results by printing the process flow diagram (PFD), specification sheets (datasheets), and case reports. A report puts multiple datasheets into one package, and that package can then be printed. Case study tables and plots and flowsheet imbalances on material and energy can also be printed by HYSYS. In this tutorial, you will document the HYSYS simulation from the “PFD Manipulation Tools” of Tutorial 2.6. You will begin with the existing file named t2.09_reports.hsc. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with four chemical components (benzene, propylene, propane, and cumene) and a heater process unit, named E1, and a conversion reactor unit, named R1. The reactor converts propylene and benzene to cumene with propane acting as an inert compound. This tutorial is divided into eight sections—retrieve a pre-defined simulation file, open a predefined simulation file in HYSYS, print the PFD and a process unit window, print the reactor datasheets, print the case study plot, create a case report, document your simulation session, and close the simulation case. To proceed, you should be familiar with the material in Tutorial 2.6.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.09_report.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual.


Click here to download the simulation file t2.09_report.hsc and then select the Save button in the File Download window.

To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation.


Note that 

Click the Save button, and then click the Close

To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer. Saving a file to the computer will result in faster simulations, since HYSYS will not have to transfer data over the network. Simulation speed becomes important as your file becomes larger. After you have finished your simulation work, you can drag the file from the Windows desktop to your private folder on the network file server for permanent storage. To save your t2.09_report.hsc simulation file and

Chapter 2

Page 2-107


Please consult the errata file for changes to Pages 2-116 to 2-117. To HYSYS Spreadsheet Programmingaccess this file, change "a_blue" to "a_errata" in the current web link.

With almost complete access to all process variables in the process flow diagram (PFD), the spreadsheet operator is extremely powerful and has three major applications in HYSYS, as follows: 1. You can program the application of a single equation like the continuity equation, as was the case in Tutorial 2.2 to calculate the pipe diameter for a process stream. 2. You can consolidate process information from various parts of the process flow diagram into a spreadsheet operator. This consolidation conveniently allows you to monitor and change process variables, as will be the case in the problems of Chapter 4 of this HYSYS manual. 3. You can provide your own mathematical model for the material and energy balances of a process unit, because no current HYSYS process unit operator meets your modeling needs. The third application is the focus of this tutorial. You will learn how to program the material and energy balances to replace the HYSYS conversion reactor operator, because its current provision for temperature dependency on molar conversions cannot represent the chemical reaction for styrene monomer from methanol and toluene with a side reaction that forms ethylbenzene. Before we look at the HYSYS spreadsheet implementation for this example, we need to examine its experimental reaction data and its modeling equations for material and energy. Based on the information in Chapter 1 of this HYSYS manual, the vapor-phase reactions to form styrene monomer and ethylbenzene in a catalytic reactor are as follows: Rxn 1:

C7H8

+

toluene

Rxn 2:

C7H8 toluene

CH3OH

C8H8

→

methanol

+

CH3OH methanol

+

styrene

+

water

C8H10

→

H2O

+

ethylbenzene

H2 hydrogen

H2O water

As a first approximation, other byproduct formation and polymerization of styrene monomer are negligible and the catalyst does not coke or deactivate with time. The reactor is also assumed to operate adiabatically. In a pilot-plant study, stoichiometric feed of toluene and methanol to an adiabatic reactor unit resulted in the following experimental data for the formation of styrene monomer (the product) and ethylbenzene (the byproduct) at a reactor inlet pressure of 400 kPa: X - molar conversion

Y - molar yield

X*Y

X - X*Y

Inlet T, °C

TL reacted TL fed

SM formed TL reacted

SM formed TL fed

EB formed TL fed

465 480 495 510 525 540

0.649 0.679 0.709 0.759 0.819 0.879

0.909 0.869 0.829 0.779 0.719 0.659

0.5899 0.5901 0.5878 0.5913 0.5889 0.5793

0.0591 0.0889 0.1212 0.1677 0.2301 0.2997

TL is toluene, SM is styrene monomer, and EB is ethylbenzene

Chapter 2

Page 2-108


An Excel version of this table is available by clicking here. Curve fitting the experimental data for the molar conversion of toluene (X) and the molar yield of styrene monomer (Y) produces the following: X = 0.000021429*T2 - 0.018450*T + 4.5952

(1)

Y = -0.000014286*T2 + 0.011024*T - 1.1289

(2)

where T is the reactor inlet temperature in °C. These two equations will be programmed into a spreadsheet operator to solve the material and energy balances for the adiabatic reactor, because they cannot be implemented in the current HYSYS unit operator for a conversion reactor. Why? The HYSYS conversion reactor only accepts quadratic equations based on the last two columns in the above table, and these last two columns when curve fitted against inlet temperature produce a fourth-order and second-order polynomial, respectively. The mathematical model, variable descriptions, and mathematical algorithm that incorporate Equations 1 and 2 are presented next, where a feed stream (F) enters the adiabatic reactor, and an effluent stream (E) leaves that reactor.

Mathematical Model for an Adiabatic Reactor (1)

n F − n E + 1R1 = 0

total matrial balance

(2)

n F ,TL − n E ,TL − 1R1 − 1R 2 = 0

nc -component matrial balances:

(3)

n F , ME − n E , ME

− 1R1 − 1R 2 = 0

(4)

n F , SM − n E , SM + 1R1

(5)

n F , EB − n E , EB +

(6)

n F ,WA − n E ,WA + 1R1 + 1R 2 = 0

(7)

n F , H 2 − n E , H 2 + 1R1

Eqs. ( 2 ) to ( 7 )

= 0 1R 2 = 0 = 0

(8)

n F = n F ⋅ z F , j ,j

for j = 1, 2,  , nc

(9)

n E = n E ⋅ z E , j ,j

for j = 1, 2,  , nc

(

X TL = n F ,TL − n E ,TL

( 10 ) ( 11 )

YSM =

)

( nE ,SM − nF ,SM ) ( n

n F ,TL F ,TL

toluene conversion

− n E ,TL )

styrene yield

2

( 12 )

X TL =0.000021429 ⋅ TF − 0.018450 ⋅ TF + 4.5952

( 13 )

YSM = − 0.000014286 ⋅ TF + 0.011024 ⋅ TF − 1.1289

2

( 14 )

n F ⋅ Hˆ F − n E ⋅ Hˆ E = 0

( 15 )

Hˆ F = hmix [TF , PF , Z F ]

( 16 )

Hˆ E = hmix [TE , PE , Z E ]

( 17 )

∆P = PF − PE

energy balance

# vars

=

4 ⋅ nc

+

13

# eqns

=

3 ⋅ nc

+

9

DOF

=

1 ⋅ nc

+

4

Chapter 2


Page 2-109

Variable Descriptions for the Mathematical Model Ti

is

the temperature of process Stream i, K.

Pi

is

the pressure of process Stream i, kPa.

ni

is

the bulk (or total) molar flow rate of process Stream i, kgmol/h.

ni , j

is

the bulk molar flow rate of component j in process Stream i, kgmol/h.

nc

is

the number of chemical components or compounds in the mixture.

Zi

is

the bulk mole fractions of all nc-components in Stream i.

zi , j

is

the bulk mole fraction of component j in process Stream i; vector Z i means all elements zi ,1 , zi ,2 ,  , zi , nc .

R1

is

the rate (or extent) of the styrene monomer reaction (i.e., first reaction), kg-rxn/h.

R 2

is

the rate (or extent) of the ethylbenzene reaction (i.e., second reaction), kg-rxn/h.

X TL

is

the molar conversion of toluene (moles of toluene reacted per moles of toluene fed).

YSM

is

the molar yield of styrene (moles of styrene formed per moles of toluene reacted).

Hˆ i ∆P

is

the bulk molar enthalpy of process Stream i, kJ/kgmol.

is

the pressure drop between the inlet and exit streams, kPa.

Ψi

is

a short notation for Ti , Pi , ni , and Z i ; that is, the process state of Stream i.

Mathematical Algorithm for an Adiabatic Reactor  Ψ = E 

reactor  Ψ F , ∆P 

(8)

1.

nF , j ⇐

nF ⋅ z F , j

(12 ) (13 ) (10 )

2.

X TL ⇐

0.000021429 ⋅ TF2 − 0.018450 ⋅ TF + 4.5952

3.

− 0.000014286 ⋅ TF2 + 0.011024 ⋅ TF − 1.1289

4.

YSM ⇐ nE ,TL ⇐

(11)

5.

nE , SM ⇐

nF , SM + YSM ( nF ,TL − nE ,TL )

( 4)

6.

⇐

nE , SM − nF , SM

( 2)

7.

R1 R

2

⇐

nF ,TL − nE ,TL − R1

(1) ( 3)

8.

nE

⇐

nF + R1

9.

nE , ME ⇐

(5)

10.

nE , EB ⇐

(6)

11.

nE ,WA ⇐

( 7 ) 12. nE , H 2 ⇐ ( 9 ) 13. zE , j ⇐ (17 ) 14. PE ⇐

for j = 1, 2,  , nc

nF ,TL − X TL nF ,TL

nF , ME − R1 − R 2 + R n F , EB

2

nF ,WA + R1 + R 2 + R n F ,H 2

1

nE , j / nE PF − ∆P

(15 ) 15.

Hˆ F

⇐

hmix TF , PF , Z F 

(14 ) 16.

Hˆ E

⇐

nF ⋅ Hˆ F / nE

⇐

tmix  PE , Hˆ E , Z E 

(16 ) 17. TE

for j = 1, 2,  , nc

Chapter 2

Page 2-110


In the above mathematical model, the degrees of freedom are (1·nc+4), based on (4·nc+13) variables and (3·nc+9) equations, where nc equals six for the number of chemical components in the system. The 4·nc variables are the twelve component flow rates ( n F , j and n E , j ) and the twelve component mole fractions ( z F , j and

z E , j ) for the feed and effluent streams. The 3·nc equations are Eqs. (2) to (7), (8), and (9) in the above

mathematical model. In the above the mathematical algorithm, the (nc+4) degrees of freedom are satisfied by the temperature, pressure, flow rate, and nc-composition for the feed stream and the pressure drop across the adiabatic reactor. In Step 17 of the mathematical algorithm, the tmix equation is a concise notation that represents the following iteration on the effluent or exit temperature: 17.

ITERATE TE in f ( TE )

(16 )

UNTIL

Hˆ E − hmix [TE , PE , Z E ]

⇐

f ( TE ) = 0

The mathematical algorithm for the adiabatic reactor described above is programmed into a HYSYS spreadsheet operator named “CRs” with inlet Stream 10s and outlet Stream 11s, as outlined below.

HYSYS Spreadsheet for the Mathematical Algorithm of an Adiabatic Reactor A 1 2 3 4 5 6 7 8 9 10 11 12 13

B

STREAM 10s Vapor Fraction: 1 Temperature: 540.00 C Pressure: 400 kPA TL Flow Rate: ME Flow Rate: SM Flow Rate:

500 kgmol/h 500 kgmol/h 0 kgmol/h

EB Flow Rate: WA Flow Rate: H2 Flow Rate:

0 kgmol/h 0 kgmol/h 0 kgmol/h

C

D

E

CURVE-FITTED REACTOR Pressure Drop:

70

Conversion of TL: 0.8809 mol TL reacted per mol TL feed Yield of SM: 0.6583 mol SM per mol TL reacted

F

G

Vapor Fraction: Temperature: Pressure:

STREAM 11s 1 409.32 C 330 kPA

TL Flow Rate: ME Flow Rate: SM Flow Rate:

59.6 kgmol/h 59.6 kgmol/h 289.9 kgmol/h

0.0462 0.0462 0.2248

EB Flow Rate: WA Flow Rate: H2 Flow Rate:

150.5 kgmol/h 440.4 kgmol/h 289.9 kgmol/h

0. 1167 0.3415 0.2248

Total Flow Rate: Specific Enthalpy:

1000 kgmol/h -1.343e4 kJ/kgmol

mol TL reacted = kg-rxn/h for SM =

440.4 kgmol/h 289.9

Total Flow Rate: Specific Enthalpy:

1290.0 kgmol/h -10,410 kJ/kgmol

Total Energy Flow:

-1.343e7 kJ/h

kg-rxn/h for EB =

150.5

Total Energy Flow:

-1.343e7 kJ/h

Mole Fractions:

adiabatic process

Cells B2 to B13 are imported from the process flow diagram (PFD), with Cells B3-B11 being specified and Cells B2 and B12-B13 being calculated in the PFD. Cell D3 is the pressure drop across the adiabatic reactor. It is specified by the user in this spreadsheet named CRs. Cell D5 = 0.000021429*b3^2 - 0.018450*b3 + 4.5952, a curve fit of the toluene fractional conversion (D5) versus inlet temperature (B3). Cell D8 = -0.000014286*b3^2 + 0.011024*b3 - 1.1289, a curve fit of the styrene fractional yield (D8) versus inlet temperature (B3). Cell D11 = d5*b5, is the amount of total toluene that reacts in kg-mol/h. Cell D12 = f7-b7, is the rate (or extent) of reaction for the styrene monomer reaction in kg-rxn/h. Cell D13 = d11-d12, is the rate (or extent) of reaction for the ethylbenzene reaction in kg-rxn/h. Cells F2 to F3 are imported from the PFD. HYSYS calculates them once the pressure, molar enthalpy, total flow, and mole fractions of Stream 11s are set. Cell F4 = b4-d3, is the calculated pressure for outlet Stream 11s, based on the specified pressure drop through the adiabatic reactor unit. Cell F5 Cell F6 Cell F7 Cell F8 Cell F9 Cell F10 Cell F11

= = = = = = =

b5-d5*b5, is the amount of toluene entering minus the amount consumed by the styrene and ethylbenzene chemical reactions in kg-mol/h. b6-d12-d13, is the amount of methanol entering minus the amount consumed by the styrene and ethylbenzene chemical reactions in kg-mol/h. b7+d8*d11, is the amount of styrene entering plus the amount produced by the styrene chemical reaction in kg-mol/h. b8+d13, is the amount of ethylbenzene entering plus the amount produced by the ethylbenzene chemical reaction in kg-mol/h. b9+d12+d13, is the amount of water entering plus the amount produced by the styrene and ethylbenzene chemical reactions in kg-mol/h. b10+d12, is the amount of hydrogen entering plus the amount produced by the styrene chemical reaction in kg-mol/h. b11+d12, is the total flow rate of Stream 11s in kg-mol/h.

Cell F12 = f13/f11, is the specific enthalpy for Stream 11s in kJ/kg-mol. Cell F13 = b13, is the energy balance for an adiabatic reactor. Cells G5 to G10 are the calculated mole fractions for Stream 11s. For example, TL mole fraction = f5/f11, and styrene mole fraction = f7/f11. Once Cells F4, F11, F12, and G5 to G10 are calculated in this spreadsheet named CRs, then HYSYS exports them to the PFD and then automatically calculates the vapor fraction and temperature of Stream 11s. These two are displayed for convenience as the imported values in Cells F2 and F3 of this spreadsheet.

Chapter 2


Page 2-111

This spreadsheet implements the inlet temperature dependence on the toluene molar conversion and styrene molar yield in Cells D5 and D8, respectively. Columns A, C, and E contain textual information solely for documentation purposes. Column B and Cells F2 and F3 contain imported variables from the HYSYS process flow diagram. The red values represent formula expressions from the right side of the various steps in the mathematical algorithm. Calculated Cells F4, F11, F12, and G5 to G10 define the process state of Stream 11s and are exported to the HYSYS process flow diagram. In summary, this HYSYS spreadsheet completes the material and energy balances for the adiabatic reactor unit. In the remainder of this tutorial, you will load an existing file named t2.10_spreadsheet.hsc, examine its process flow diagram, and complete its spreadsheet operator. The pre-defined simulation in this file is set for the Peng-Robinson-Stryjeck-Vera (PRSV) fluid package with six chemical components (toluene, methanol, styrene monomer, ethylbenzene, water, and hydrogen), a partially-completed spreadsheet operator, named CRs, and a conversion reactor unit, named CRc. Two chemical reactions occur simultaneously— one converting toluene and methanol to styrene monomer and another converting toluene and methanol to ethylbenzene. You will compare the simulation results from the spreadsheet operator to those from the conversion reactor operator, in order to validate the material and energy balance calculations within the spreadsheet operator. The remainder of this tutorial is divided into seven sections—retrieve a pre-defined simulation file, open a pre-defined simulation file in HYSYS, examine the process flow diagram, complete the spreadsheet operator, compare the simulation results, document your simulation session, and close the simulation case. To proceed, you must be familiar with the material in Tutorials 2.2, 2.3, and 2.5.

A. Retrieve a pre-defined simulation file. A HYSYS file has been created for you to start the simulation. It is called t2.10_spreadsheet.hsc. This section explains how to download this pre-defined simulation file, and then save it to either the Windows desktop on your logged-in computer or your private area on the network file server at your university. Proceed as follows: 1. Access the electronic version of this HYSYS manual using a web browser like Internet Explorer, Firefox, or Safari. Then, go to this page in that electronic manual. Click here to download the simulation file t2.10_spreadsheet.hsc and then select the Save button in the File Download window. 2. Navigate to a folder in your private area on the network file server at your university. or select the computer’s Desktop.

Note that 

See the Preface section in this HYSYS manual to obtain the web address for the electronic version, which you would type into the web browser or which you would select from your bookmark list. To begin the process of retrieving the pre-defined HYSYS file for this tutorial simulation. To store the simulation in one of your private folders as a file on the network file server. or To save the file on the Windows computer. Saving a file to the computer will result in faster simulations, since HYSYS will not have to transfer data over the network. Simulation speed becomes important as your file becomes larger. After you have finished your simulation work, you

Chapter 3 Process Unit Exercises

Chapter 3 Process Unit Exercises

Process Unit Exercises – Overview

Chapter 3

Page 3-1

This chapter provides five problem assignments to help you develop your abilities and confidence to simulate individual process units using the Aspen HYSYS® process simulation software. Over a fiveweek period, you will have assignments that focus on finding the material and energy balance requirements for the following individual process units: Problem HY.1 HY.2 HY.3 HY.4 HY.5

Description Process Stream Simulation Pump Simulation Cooler Simulation Mixer/Tee Simulation Reactor Simulation

Each of these problems will be assigned to you by your instructor in a memorandum. A “HY” problem contains two parts: A. a guided HYSYS session that helps build your confidence in using the HYSYS software and B. a simulation exercise that tests your knowledge and understanding of a HYSYS simulation. Once you’ve completed these five assignments, you will have a mathematical understanding of how HYSYS does its calculations for each process unit. This chapter assumes you have completed certain tutorials found in Chapter 2. They are Tutorials 2.1 to 2.6. Each assignment in this chapter identifies those tutorials that you should complete before you try to solve the problem. While solving a problem, you will need to consult Appendices B, C, D, etc. in this instructional manual for information on certain HYSYS simulation modules. Each appendix or module provides a mathematical explanation of how HYSYS does its calculations for that process unit. A module includes the following: 1. 2. 3. 4. 5. 6. 7.

a module description, a conceptual model, model assumptions, a mathematical model, process variable descriptions, example mathematical algorithms, and several HYSYS simulation algorithms.

Each assignment identifies which appendix you must consult.

Process Unit Exercises – Problem HY.1

Chapter 3

Page 3-2

HY.1 - Process Stream Simulation The HYSYS simulation module for a process stream is fully defined in Appendix C of this instructional manual. This process stream module contains a module description, a conceptual model, model assumptions, a mathematical model, variable descriptions, mathematical algorithms, and some HYSYS simulation algorithms in functional form. After you read this information about a process stream, you are to practice the HYSYS session below and then complete the simulation exercise. You are to provide for the simulation exercise only a printed copy of the Workbook datasheet in your technical journal. Separately, your team is to document the answers to all questions in the simulation exercise.

A. HYSYS Session This session will show you, in general terms, how to do a HYSYS simulation for a process stream. It assumes you are familiar with the material in Tutorials 2.2 to 2.3 of this instructional manual. You are to find the vapor fraction and heat flow in BTU/hr of a binary mixture of toluene and hexane at 1 atm and 100°C. This mixture is flowing at 100 kgmol/h. The stream is labeled feed and its conceptual diagram is: TF = 100 ° C

TF = 100 ° C

PF = 1 atm n F = 100 kgmol / h

PF = 1 atm n F = 100 kgmol / h

feed

z F ,TL = 0.7

z F ,TL = 0.7

z F , HX = 0.3

z F , HX = 0.3

Using the information above, you are to practice a HYSYS simulation by doing the following: • • • • • • • • • •

Click here to download file HY1.A and save it as HY1.A_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY1.A_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment, open the process stream, and rename it feed. Specify its process state; that is, its temperature, pressure, flow rate, and composition. Change the HYSYS preferences to display the “Field” unit set. Open the Workbook window using its icon in the HYSYS button bar. View the values in the Material Streams page of the Workbook window. Note that specified values appear in blue, while calculated values appear in black. View the Compositions and Component Flows pages in the Workbook window.

After you specify the state of the process stream, HYSYS immediately calculates all of the other properties of that streams (such as mass flow rate, volumetric flow rate, vapor fraction, etc.) using the Soave-Redlich-Kwong (SRK) equation of state. The answers for two of the stream properties are: Vapor Fraction = 0.7807 Heat Flow = -1.237e+6 BTU/h A value for the vapor fraction between zero and one indicates that the process stream exists as a two-phase system (vapor and liquid in equilibrium) at the specified temperature, pressure, and composition.


Chapter 3

Page 3-3

B. Simulation Exercise What are the temperature in °F and the heat flow in BTU/hr of a process stream containing a tertiary mixture of benzene, hexane, and toluene? The stream is at 2 atm and has a vapor fraction equal to zero. The chemical component flows are as shown below. Vf = 0.0

Vf = 0.0

TF =

?

TF =

?

PF = n F =

2 atm

PF = n F =

2 atm

?

n F , BZ = 40 kgmol / h

feed

?

n F , BZ = 40 kgmol / h

n F , HX = 70 kgmol / h

n F , HX = 70 kgmol / h

n F ,TL = 120 kgmol / h

n F ,TL = 120 kgmol / h

Using the information above, you are to complete a HYSYS simulation by doing the following: • • • • •

Click here to download file HY1.B and save it as HY1.B_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY1.B_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment and finish the simulation for the process stream. Print the Workbook datasheet in “Field” units for the Material Streams, Compositions, and Component Flows pages, and then place it into your technical journal.

After all team members have independently documented this simulation exercise in their technical journal, your team is to meet and answer all of the questions in this exercise. Click here to download a Word file, add your team name (e.g., T2 – IGAS), and complete those questions contained within. 1. Which HYSYS simulation algorithm in Appendix C (p. C-5 or C-7) would you use to solve the above problem? What temperature does this algorithm calculate? 2. Which assumption(s) listed in Appendix C support the fact that a process stream has uniform properties throughout its length? 3. What steps in Mathematical Algorithm A would you use to calculate the mass fractions from the mole fractions? Verify that HYSYS has done this calculation correctly. 4. What is the specific enthalpy of the stream in BTU/lb based on the heat flow in BTU/h and the molar flow rate in kgmol/h? 5. What are the definitions of the dew-point temperature and bubble-point temperature? 6. How might you find the dew-point temperature of this stream? What is its value? 7. How does HYSYS calculate the bulk molar enthalpy for Vf =0.40 (see p. C-8)? Verify it. For the team solution to the simulation exercise, your team is to document the answers to all of the questions in the Word file that your team downloaded.


Chapter 3

Page 3-4

HY.2 - Pump Simulation The HYSYS simulation module for a pump operation is fully defined in Appendix E of this instructional manual. This pump module contains a module description, a conceptual model, model assumptions, a mathematical model, variable descriptions, mathematical algorithms, and some HYSYS simulation algorithms in functional form. After you read this information about a pump operation, you are to practice the HYSYS session below and then complete the simulation exercise. You are to provide for the simulation exercise only a printed copy of the HYSYS flowsheet (with a problem number, your name, and date) and the Workbook datasheet in your technical journal. Separately, your team is to document the answers to all questions in the simulation exercise.

A. HYSYS Session This session will show you, in general terms, how to do a HYSYS simulation for the pump operation. It assumes you are familiar with the material in Tutorials 2.3 to 2.4 of this instructional manual. You are to find the power in watts to compress an equimolar mixture of n-hexane and n-octane at 25°C from 1 atm to 4 atm. This liquid mixture is flowing at 100 lb-moles per hour. The pump is labeled P-200, and its adiabatic efficiency is 70 percent. The conceptual diagram is: TE = ? TI = 25 ° C PI = 1 atm n I = 100 lbmol / h z I , HX = 0.5 z I ,OC = 0.5

Wa = ?

Exit

Inlet P2

ε = 70%

PE = 4 atm n E = ? z E , HX = ? z E ,OC = ?

Using the information above, you are to practice a HYSYS simulation by doing the following: • • • • •

Click here to download file HY2.A and save it as HY2.A_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY2.A_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment, open the process stream, and rename it Inlet. Specify its process state; that is, its temperature, pressure, flow rate, and composition.

• • •

Add a pump to the process flow diagram (PFD) and name it P2. Connect its Inlet stream, name its Exit material stream, and name its Wa energy stream. Specify its adiabatic efficiency to be 70% and its exit pressure to be 4 atm.

• • • •

Open the Workbook window using its icon in the HYSYS button bar. View the values in the Material Streams page of the Workbook window. Note that specified values appear in blue, while calculated values appear in black. View the Compositions, Component Flows, and Energy Streams pages in the Workbook.

After you specify the state of the inlet stream, the pump efficiency, and the exit pressure, HYSYS immediately calculates all of the other properties of the material streams (such as mass flow rate, volumetric flow rate, vapor fraction, heat flow, etc.) using the Peng-Robinson Stryjek-Vera (PRSV) equation of state. Also, HYSYS calculates the pump power to be: Power = 804.4 watts


Chapter 3

Page 3-5

Place the cursor over the Wa in the PFD to view the pump power. A positive value for the pump power indicates that energy must be added to the process stream to increase its pressure.

B. Simulation Exercise What adiabatic efficiency and power in kilowatts are required to compress an equimolar mixture of n-hexane and n-octane from 25°C and 1 atm to 40°C and 400 atm? This liquid mixture is flowing at 100 lb-moles per hour. TE = 40 ° C TI = 25 ° C PI = 1 atm n I = 100 lbmol / h z I , HX = 0.5 z I ,OC = 0.5

Wa = ?

Exit

Inlet P3

ε=?

PE = 400 atm n E = ? z E , HX =

?

z E ,OC =

?


Click here to download file HY2.B and save it as HY2.B_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY2.B_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment and finish the simulation for the pump operation. Print the process flow diagram (PFD with a problem number, your name, and date) and the datasheet for all pages in the Workbook, and then place them into your technical journal.

If a consistency error occurs, you forgot to delete the efficiency value. After all team members have independently documented this simulation exercise in their technical journal, your team is to meet and answer all of the questions in this exercise. Click here to download a Word file, add your team name (e.g., T1 – RGAS), and complete those questions contained within. 1. Which HYSYS pump simulation algorithm (pumpa, pumpb, etc. in Appendix E) would you use to solve this problem? What are the given variables and their values? What are the calculated variables and their values? 2. After you examine the process states (i.e., the temperature, pressure, flow rate, and composition) of the inlet and exit streams, please answer the following questions. Why does the exit temperature increase slightly? What is unique about the total molar flow rate and composition? What equations in the math model and steps in the algorithm reflect it? What assumptions support this uniqueness? What are the operating conditions that would invalidate each assumption? 3. What is the ideal work expressed in units of horsepower? 4. In the math algorithm, what variables are only functions of the material state (i.e., the temperature, pressure, and composition) of the liquid? 5. What does the assumption of “adiabatic process” imply? Is this a valid assumption? 6. What is the energy relative imbalance (%RIB)? Show your calculations. The energy %RIB equals 100*(energy flow in - energy flow out) / (energy flow in). For the team solution to the simulation exercise, your team is to document the answers to all of the questions in the Word file that your team downloaded.


Chapter 3

Page 3-6

HY.3 - Heater/Cooler Simulation The HYSYS simulation module for a heater/cooler operation is fully defined in Appendix G of this instructional manual. This heater/cooler module contains a module description, a conceptual model, model assumptions, a mathematical model, variable descriptions, mathematical algorithms, and HYSYS simulation algorithms in functional form. After you read this information about a heater or cooler operation, you are to practice the HYSYS session below for a heater and then complete the simulation exercise for a cooler. You are to provide for the simulation exercise only a printed copy of the performance plot for heat flow versus temperature (with a problem number, your name, and date as its title) and the Workbook datasheet in your technical journal. Separately, your team is to document the answers to all questions in the simulation exercise.

A. HYSYS Session This session will show you, in general terms, how to do a HYSYS simulation for a heater and generate a performance plot for that heater. This session assumes you are familiar with the material in Tutorial 2.4 of this instructional manual. You are to find the duty in BTU/h needed to heat an equimolar mixture of n-hexane and n-octane from 20°C to 200°C at a constant 2 bar. This stream is flowing at 100 lbmoles per hour. The heater is labeled H2. The conceptual diagram is: = TI

20 °C

PI = 2 bar nI = 100 lbmol/h

 =? Q

= TE 200 °C

Inlet

Exit H2

PE = nE =

2 bar ?

z I , HX = 0.5

z E , HX =

?

z I ,OC = 0.5

z E ,OC =

?

Using the information above, you are to practice a HYSYS simulation by doing the following: • • • • •

Click here to download file HY3.A and save it as HY3.A_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY3.A_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment, open the process stream, and rename it as Inlet. Specify its process state; that is, its temperature, pressure, flow rate, and composition.

• • •

Add a heater to the process flow diagram (PFD) and name it H2. Connect its inlet Stream Inlet, name its energy stream as Q, and name its exit stream as Exit. Specify its pressure drop to be 0.0 bar and its exit temperature to be 200°C.

• • • •

Open the Workbook window using its icon in the HYSYS button bar. View the values in the Material Streams page of the Workbook window. Note that specified values appear in blue, while calculated values appear in black. View the Compositions, Component Flows, and Energy Streams pages in the Workbook.

After you specify the state of the inlet stream, the pressure drop, and the exit temperature, HYSYS immediately calculates all of the other properties of the two streams (such as mass flow rate, volumetric flow rate, vapor fraction, heat flow, etc.) using the Peng-Robinson Stryjek-Vera (PRSV) equation of state. Also, HYSYS calculates the heater duty to be:


Chapter 3

 = 3.167×106 BTU/h or 3.341×106 kJ/h Q

Page 3-7

(place cursor over a value displayed for the Q-stream)

Since the Q-term in the energy balance for the heater operation has a positive sign in front of it, HYSYS will always display the heat duty of a heater unit as a positive quantity. In this session, you are to generate a plot of heat duty over the temperature range of 20°C to 200°C at intervals of 5°C. Complete the following general tasks to generate a performance plot: • • • • •

Open the property window of Heater H2 and select its Performance page. Select the Setup option, set Intervals to 36, and check the Dew/Bubble Pts option. Set Temperature, Pressure, Heat Flow, and Vapor Frac. as the only Selected Viewing Variables. Select the Performance/Plots option and set the Y Variable to be the Heat Flow option. Maximize the window and observe the plot of heat flow versus temperature.

You can select the Performance/Tables option to observe the bubble point of 112.8717°C (Vf =0) and the dew point of 132.2303°C (Vf =1) for an equimolar mixture of n-hexane and n-octane at 2 bars.

Simulation Exercise What heat duty in kJ/h is removed from an equimolar mixture of n-hexane and n-octane to cool it at a constant 2 bars from 200°C to a saturated vapor? a saturated liquid? a sub-cooled liquid at 20°C? What are the temperatures of the exit stream in the first two cases? This liquid mixture is flowing at 100 lb-moles per hour. Also, generate a performance plot of the cooler duty over the temperature range of 200°C to 20°C at intervals of 5°C. You are to observe how the cooler duty versus temperature changes within the singlephase regions (vapor and liquid) and the two-phase region (vapor-liquid equilibrium). = TI 200 °C PI = 2 bar nI = 100 lbmol/h

 =? Q

= TE

Inlet

Exit C2

PE = nE =

20 °C 2 bar ?

z I , HX = 0.5

z E , HX =

?

z I ,OC = 0.5

z E ,OC =

?


Click here to download file HY3.B and save it as HY3.B_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY3.B_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment and finish the simulation for the cooler operation. Print the performance plot (with a problem number, your name, and date as its title) and the datasheet for all pages in the Workbook, and then place them in your technical journal.

Since the Q-term in the energy balance for the cooler operation has a negative sign in front of it, HYSYS will always display the heat duty of a cooler unit as a positive quantity.

Chapter 3


Page 3-8

After all team members have independently documented this simulation exercise in their technical journal, your team is to meet and answer all of the questions in this exercise. Click here to download a Word file, add your team name (e.g., T4 – NoGAS), and complete those questions contained within. 1. What is the heat of condensation in kJ/kgmol to cool the equimolar mixture of n-hexane and noctane at 2 bars from the sat’d vapor to the sat’d liquid state? What is the heat of vaporization in kJ/kgmol to heat the same mixture from the sat’d liquid to the sat’d vapor state? What can you conclude about these two latent heat changes? 2. Which HYSYS cooler simulation algorithms in Appendix G would you use to solve for the exit dew-point and bubble-point temperatures? To solve for the exit sub-cooled temperature of 20°C? Which HYSYS cooler simulation algorithm would you use to solve for each point in the performance plot? 3. How do the mathematical models for the cooler and heater units in this problem differ? How are they the same? For the two conceptual diagrams above, what are their heat duties in kJ/h? 4. The total specific energy of a process stream is composed of its internal energy, flow energy, kinetic energy, and potential energy. Note that enthalpy is defined to be internal energy plus flow energy ( Hˆ= Uˆ + PVˆ ). For the sub-cooled exit stream at 20°C, what additional information would you need to know in order to calculate its kinetic energy and potential energy? For a velocity of 1.6 m/s and a height of 10 m, what percentage of the total specific energy of the exit stream is internal energy, flow ( PVˆ ) energy, kinetic energy, and potential energy? What would be the pipe diameter of the exit stream for a velocity of 1.6 m/s? 5. Which equations in the mathematical model would you use to calculate the molar enthalpy of the exit stream given the conditions of the inlet stream and the duty of the cooler? What is the exit stream molar enthalpy for a cooling operation using the inlet stream in this problem and a duty of 1000 kilo-watts? Check that HYSYS calculates the same result. 6. In your printed performance plot, label the dew-point temperature and bubble-point temperature on the temperature axis. After doing this task, you should notice three distinct areas on the plotted curve. Place a label on the liquid portion, vapor-liquid portion, and vapor portion of this plot. This plot of heat flow versus temperature is for a multicomponent mixture. What would the vapor-liquid portion of this plot look like, if the mixture contained only one chemical component (e.g., pure n-hexane)? What does the Gibbs Phase Rule state for the vapor-liquid portion? 7. What is the energy relative imbalance (%RIB) for an exit temperature of 20°C? Show your calculations. The energy %RIB equals 100*(energy flow in – energy flow out) / (energy flow in). For the team solution to the simulation exercise, your team is to document the answers to all of the questions in the Word file that your team downloaded.


Chapter 3

Page 3-9

HY.4 - Mixer/Tee Simulation The HYSYS process simulator can solve the material and energy balances of many unit operations that are interconnected by process streams. For example, two or more process streams can be fed to the HYSYS mixer operation to form one exit stream. This exit stream can then be fed to a HYSYS tee operation to divide it into several streams. Problem HY.4 uses this example to illustrate how to complete a process simulation that has several unit operations in a process flow diagram (PFD). The HYSYS simulation modules for the stream mixer and tee divider operations are fully defined in Appendices D and B of this instructional manual. These two modules contain a module description, a conceptual model, model assumptions, a mathematical model, variable descriptions, mathematical algorithm, and HYSYS simulation algorithms in functional form. After you read the information about the stream mixer and tee divider, you are to practice the HYSYS session below and then complete the simulation exercise. You are to provide for the simulation exercise only a printed copy of the HYSYS flowsheet (with a problem number, your name, and date) and the Workbook datasheets for the mixer and tee operations in your technical journal. Separately, your team is to document the answers to all questions in the simulation exercise.

A. HYSYS Session This session will show you how to do a HYSYS simulation for a stream mixer and a tee, and how to connect two process units. It assumes you are familiar with the material in Tutorials 2.2, 2.3, and 2.6 of this instructional manual. First, a pure heptane stream is mixed with a pure octane stream. The resulting binary mixture is then divided into two streams with different flow rates. You are to find the molar flow rate in kgmol/h and the mole fractions of the tee’s two exit streams. The pure heptane stream is flowing at 100 kg-moles per hour, and the pure octane stream is flowing at 200 kg-moles per hour. Both pure streams are at ambient conditions (25°C and 1 atm). The tee exit streams are also at ambient conditions. Thus, no pressure drop exists across the mixer or the tee. Exit Stream E1 is to contain 40% of the molar flow rate of the inlet Stream Mix to the tee operation. The conceptual diagram is: TE1 = ? PE1 = ? n E1 = ?

TH = 25 ° C PH = 1 atm n H = 100 kgmol / h z H , HP = 1.0

E1

Heptane M-100 mixer

TO = 25 ° C PO = 1 atm nO = 200 kgmol / h zO,OC = 1.0

Mix

Octane

z E1,OC = ?

T-100 tee

E2

n E1 = 0.4 n M

z E1, HP = ?

TE 2 = ? PE 2 = ? n E 2 = ? z E 2, HP = ? z E 2,OC = ?

Using the information above, you are to practice a HYSYS simulation by doing the following: • •

Click here to download file HY4.A and save it as HY4.A_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY4.A_xxx file.


Chapter 3

Page 3-10

• • •

Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment and open process Streams Heptane and Octane. Specify their process states; that is, their temperature, pressure, flow rate, and composition.

• • •

Add a mixer to the process flow diagram (PFD) and name it M-100. Connect its inlet Streams Heptane and Octane, and then name its exit stream as Mix. Specify the exit pressure using Set Outlet to Lowest Inlet on the Design/Parameters page.

• • •

Add a tee to PFD, name it T-100, and then name its exit streams as E1 and E2. Specify flow ratio E1under the Splits section on the Design/Parameters page of T-100. Check that all flow ratios (0.4 for Stream E1 and 0.6 for Stream E2) sum to one.

• • • •

Open the Workbook window using its icon in the HYSYS button bar. View the values in the Material Streams page of the Workbook window. Note that specified values appear in blue, while calculated values appear in black. View the Compositions and Component Flows pages in the Workbook.

In a tee divider, a flow ratio for an exit stream is what fraction of the total flow rate of the inlet stream is to appear in the exit stream. Since the total molecular weight of each exit stream is the same as that of the inlet stream, a flow ratio has the same value whether it is expressed on a mole or mass basis. After you specify the inlet streams to the mixer and the tee flow ratios, HYSYS immediately calculates all of the other properties of the streams using the Peng-Robinson Stryjek-Vera (PRSV) equation of state. For the above simulation, HYSYS calculates the tee exit flow rates and compositions to be: Property

E1

E2

Molar flow rate: Mole fraction heptane: Mole fraction octane:

120 kgmol/h 0.3333 0.6667

180 kgmol/h 0.3333 0.6667

B. Simulation Exercise What are the molar flow rates (lbmol/h) and mass fractions of the exit streams leaving the tee divider in the below chemical process? A binary mixture of methanol and ethanol at 45°C and 300 kPa is mixed with a pure water stream at ambient conditions. The methanol and ethanol component flow rates are 50 kgmol/h and 75 kgmol/h, respectively. The water flow rate is 100 kgmol/h. The resulting 3-component stream is then split into two exit streams. The total molar flow rates for these two exit streams are in a 3:1 ratio, as shown in the diagram below. For the mixer, the exit pressure is equal to the lowest inlet pressure. Using the information in the below diagram, you are to complete a HYSYS simulation by doing the following: • • • • •

Click here to download file HY4.B and save it as HY4.B_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY4.B_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package. Return to the Simulation Environment and finish the simulation for the mixer/tee process. Print the process flow diagram (PFD with a problem number, your name, and date) and the datasheet for all pages in the Workbook, and then place them into your technical journal.


Chapter 3

Page 3-11

TE1 = ? PE1 = ? n E1 = ?

TA = 45 ° C

z E1, ME = ?

PA = 300 kPa

z E1, ET = ?

n A, ME = 50 kgmol / h

E1

n A, ET = 75 kgmol / h Alcohol M-200

TW = 25 ° C PW = 1 atm nW = 100 kgmol / h zW ,WA = 1.0

Mix

z E1,WA = ?

T-200

TE 2 = ?

Water

E2

n E1 3 = n E 2 1

PE 2 = ? n E 2 = ? z E 2, ME = ? z E 2, ET = ? z E 2,WA = ?

After all team members have independently documented this simulation exercise in their technical journal, your team is to meet and answer all of the questions in this exercise. Click here to download a Word file, add your team name (e.g., T3 – MBal), and complete those questions contained within. 1. Which HYSYS stream mixer simulation algorithm in Appendix D would you use to solve the mixer section of this problem? What other unit parameter, which is not referred to in the algorithm, must you specify in HYSYS? 2. Which HYSYS stream tee simulation algorithm in Appendix B would you use to solve the tee section of this problem? Note that the tee divider operation is analogous to a batch process of taking a liquid mixture in a large beaker and pouring it into two smaller beakers. What is true about the state of the material in all three beakers? About the amounts? 3. What are the temperature in °F, molar enthalpy in kcal/kgmole, mass density in kg/m3, molar volume in m3/kgmole, and mole fractions of the tee’s inlet and exit streams? What is unique about these values? What are the temperature, molar enthalpy, mass density, molar volume and mole fractions, in the same units, of the mixer’s inlet and exit streams? How do these values for the mixer streams differ from those for the tee? Why? 4. What is the material relative imbalance (%RIB) for the process flowsheet? Show your calculations. The material %RIB equals 100*(mass flow in – mass flow out) / (mass flow in). You are to draw an overall system boundary around the flowsheet, which contains the mixer and tee operations. The only material and energy streams you are to consider in your imbalance calculation are those that cut your overall system boundary. Therefore, you would not consider Stream Mix in your calculations. 5. What is the energy relative imbalance (%RIB) for the process flowsheet? Show your calculations. The energy %RIB equals 100*(energy flow in – energy flow out) / (energy flow in). For the team solution to the simulation exercise, your team is to document the answers to all of the questions in the Word file that your team downloaded.


Chapter 3

Page 3-12

HY.5 - Reactor Simulation The HYSYS simulation module for a chemical reactor operation is fully defined in Appendix H of this instructional manual. The chemical reactor module contains a module description, a conceptual model, model assumptions, a mathematical model, variable descriptions, mathematical algorithm, and HYSYS simulation algorithms in functional form. After you read this information about the reactor, you are to practice the HYSYS session below and then complete the simulation exercise. You are to provide for the simulation exercise only a printed copy of the HYSYS flowsheet (with a problem number, your name, and date on it) and the Workbook datasheet for the chemical reactor in your technical journal. Separately, your team is to document the answers to all questions in the simulation exercise.

A. HYSYS Session This session will show you, in general terms, how to do a HYSYS simulation for a chemical reactor. It assumes you are familiar with the material in Tutorial 2.5 of this instructional manual. Acrylonitrile is produced by the reaction of propylene, ammonia, and oxygen:

2 C3 H6

+

2NH3

+ 3O2

→

2 C3 H3 N

+ 6 H2 O

where 30 molar percent of the propylene is converted. A 45 mole % propylene and 55 mole % ammonia stream at 25 °C and 1 atm is fed to the reactor. The oxygen is fed to the reactor through an air stream also at 25°C and 1 atm. The feed stream is flowing at 22 kgmol/h, and the air stream is flowing at 78 kgmol/h. Assume an adiabatic reactor with no pressure drop. You are to find the temperature of the reactor product stream in °C. Also, you are to find the dewpoint temperature (Vf = 1) of the reactor product stream. The conceptual diagram is: TF = 25 ° C PF = 1 atm n F = 22 kgmol / h

TP = ? PP = 1 atm n P = ?

z F , PY = 0.45 z F , AM = 0.55

z P, PY = ?

Feed R-200 R-100

TA = 25 ° C PA = 1 atm n A = 78 kgmol / h z A,O 2 = 0.21 z A, N 2 = 0.79

Product

z P, AM = ? z P ,O 2 = ?

Air

ε = 30% of PY

z P, N 2 = ? z P, AN = ? z P,WA = ?

Using the information above, you are to practice a HYSYS simulation by doing the following: • • •

Click here to download file HY5.A and save it as HY4.5_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY5.A_xxx file. Enter the Basis Environment, complete the component list, and note the fluid package.

•

Select the Reactions tab and click the Add Rxn… button in Simulation Basis Manager.


Chapter 3

Page 3-13

• •

Add the conversion reaction, specify its stoichiometry, and set a propene conversion of 30%. Select Reaction Set, click the Add to FP button, and associate PRSV with Global Rxn Set.

• •

Return to the Simulation Environment and open process Streams Feed and Air. Specify their process states; that is, their temperature, pressure, flow rate, and composition.

• • •

Add a conversion reactor to the process flow diagram (PFD) and name it R-100. Connect its inlet Streams Feed and Air, and then name its exit streams as Vapor and noLiq. Select the Global Rxn Set as the reaction set on the Reactions/Details page.

• • • •

Open the Workbook window using its icon in the HYSYS button bar. View the values in the Material Streams page of the Workbook window. Note that specified values appear in blue, while calculated values appear in black. View the Compositions and Component Flows pages in the Workbook.

After you specify the feed and air streams and the chemical reaction, HYSYS immediately calculates all of the other properties of the two exit streams (such as mass flow rate, volumetric flow rate, vapor fraction, heat flow, etc.) using the Peng-Robinson Stryjek-Vera (PRSV) equation of state. For the vapor stream, its temperature is: T = 424.2°C Note that the flow rate of Stream noLiq is zero, because the reaction takes place solely in the vapor phase. Once the property variables of the vapor stream are calculated by HYSYS, they cannot be changed by you, because they appear as black values. To find the dew-point temperature of the vapor stream, you must place a new stream on the process flow diagram (PFD), name it Dew, set its process state by copying information from Stream Vapor using the Define from Other Stream… button, delete the temperature of Dew, and set its vapor fraction to 1.0. HYSYS calculates a dew-point temperature of 43.73°C.

B. Simulation Exercise For the simulation exercise, consider the same reaction and reactor inlet streams that were used in the HYSYS session. Now the reactor is no longer adiabatic. Instead, it is an isothermal process, meaning the product stream is at the same temperature as the two inlet streams, 25°C. What is the reactor duty in kJ/h for this isothermal process? Is the chemical reaction endothermic or exothermic? Must heat be added to or removed from the reactor? TF = 25 ° C PF = 1 atm n F = 22 kgmol / h

TP = 25 ° C

 =? Q

PP = 1 atm n P = ?

z F , PY = 0.45 z F , AM = 0.55

z P, PY = ?

Feed R-200 R-200

TA = 25 ° C PA = 1 atm n A = 78 kgmol / h z A,O 2 = 0.21 z A, N 2 = 0.79

Product

z P, AM = ? z P ,O 2 = ?

Air

ε = 30% of PY

z P, N 2 = ? z P, AN = ? z P,WA = ?

Chapter 3


Page 3-14


Click here to download file HY5.B and save it as HY5.B_xxx, where xxx are your initials. Start the HYSYS software, load your preferences, and open your HY5.B_xxx file. Name the two exit streams as Vapor and Liquid and name the energy stream as Q. Set the exit temperature of the vapor (or liquid) stream to complete the simulation. Print the process flow diagram (PFD with a problem number, your name, and date) and the datasheet for the Workbook minus the Unit Ops datablock, and then place them into your technical journal.

At an exit temperature of 25°C, the product stream will contain two phases—vapor and liquid. In the HYSYS conversion reactor, Streams Vapor and Liquid account for these two exiting phases. After all team members have independently documented this simulation exercise in their technical journal, your team is to meet and answer all of the questions in this exercise. Click here to download a Word file, add your team name (e.g., T6 – EBal), and complete those questions contained within. 1. For the adiabatic reactor in the HYSYS session, only a vapor product stream was needed since the flow rate of the liquid was zero. For the isothermal case, both a vapor and a liquid product stream are required. Why? Above what reactor exit temperature will only a vapor product stream be required? 2. What is the acrylonitrile composition in the liquid product stream in mole fraction? In mass fraction? In parts per million (ppm)? In kg/m3? In kgmol/m3? In molarity (M)? 3. What assumptions were used to solve the isothermal reactor simulation problem? Compare these assumptions to those of the chemical reactor module in Appendix H of this instructional manual. Are the assumptions the same? If not, how do they differ? 4. Write the total mole balance equation for the isothermal reactor problem. What are the value and units for the extent of reaction? What does the extent-of-reaction or R term in the total mole balance signify? 5. What is the energy relative imbalance (%RIB)? Show your calculations. The energy %RIB equals 100*(energy flow in – energy flow out) / (energy flow in). 6. What is the material relative imbalance (%RIB) on a total molar basis? Show your calculations. The total molar %RIB equals 100*(total molar flow in – total molar flow out) / (total molar flow in). 7. What is the material relative imbalance (%RIB) on a total mass basis? Show your calculations. The material %RIB equals 100*(mass flow in – mass flow out) / (mass flow in). How does this value compare with the %RIB on a molar basis? Explain. For the team solution to the simulation exercise, your team is to document the answers to all of the questions in the Word file that your team downloaded.

Chapter 4 Flowsheet Development Exercises

Chapter 4 Flowsheet Development Exercises

Flowsheet Development Exercises – Overview

Chapter 4

Page 4-1

This chapter provides seven problem assignments to help you develop a process flowsheet to make styrene monomer from toluene and methanol by analyzing individual process units and then connecting these individual units to form the complete flowsheet. Before you proceed with these assignments, you must be familiar with the material in Chapter 1 and Tutorials 2.1 to 2.6 of Chapter 2. Also, the problem assignments in Chapter 3 on process units should be completed before you begin your flowsheet analysis in this chapter. Over a seven-week period, you will have assignments that focus on particular sections of the flowsheet, beginning with the reaction section. In these assignments, you will conduct a process simulation on each of the following flowsheet sections using the Aspen HYSYS® process simulation software: Problem SM.1 SM.2 SM.3 SM.4 SM.5 SM.6 SM.7

Description Styrene Monomer Reaction Section Reactor Effluent Cooling/Decanting Section Methanol Recycle Purification Section Toluene Recycle Purification Section Toluene/Methanol Feed Preparation Section Recycle Mixing and Preheating Section Styrene Monomer Purification Section

These seven sections are identified in the following block flowsheet from Chapter 1: Q

WS toluene recycle

heater toluene

H2 fuel

pump SM.2

SM.6

Q

SM.5

SM.1

Q

SM.4

decanter

column

organic furnace

reactor

Q

WS

cooler

methanol

ethylbenzene aqueous

SM.7

column

methanol recycle SM.3

heater

column

pump


Each sectional problem will be assigned under a separate memorandum. Once you’ve completed these assignments, you will have synthesized the process flowsheet for continuous operation and determined its processing requirements for material and energy for a specific reactor inlet temperature. Why a continuous and not a batch operation? Based on a heuristic rule reported by Woods [2007. p. 11], a continuous operation is more economical for product rates greater than 0.1 kg/s. The styrene monomer production rate is 8.35 kg/s (250,000 metric ton per year) for the above process flowsheet.

Flowsheet Development Exercises – Overview

Chapter 4

Page 4-2

Information and data needed to solve the sectional flowsheet problems in this chapter are contained in Chapter 1 and Appendices B to M of this HYSYS manual. Chapter 1 provides detailed technical and economic data for the production of styrene monomer from toluene and methanol. Appendices B to L contain simulation modules for various process unit operations. Each appendix or module provides a mathematical explanation of how HYSYS does its calculations for that process unit. A module includes its description, a conceptual model, model assumptions, a mathematical model, variable descriptions, example mathematical algorithms, and several HYSYS simulation algorithms. Appendix M provides details on how to calculate the net profit of the above process flowsheet for a specific reactor inlet temperature using a HYSYS spreadsheet operator. Please consult the first chapter and the appropriate appendices to complete each sectional problem in this chapter. As indicated in Chapter 1, you are part of a team in the Process Engineering Department of BEEF, Inc. Our client, Hawbawg Chemical Company, needs to know the process flowsheet requirements that maximize the net profit to manufacture styrene monomer from toluene and methanol. The net yearly profit for the styrene flowsheet can be approximated as follows: net profit

=

product sales

+

byproduct sales

+

fuel credit

−


−


−

utility costs

where each term is $ per year. The annualized capital cost for purchasing the equipment is estimated to be (product sales + byproduct sales)/6 in $/yr. The other terms in this net profit equation can be determined once the material and energy requirements of the above flowsheet are calculated for a specific reactor inlet temperature using the Aspen HYSYS® software. Under the directions of your project supervisor, your team members will determine their net profit for their assigned reactor inlet temperature. The table below identifies a team member symbol that has been assigned to you by your instructor. α - 465ºC

♠ - 480ºC

♥ - 495ºC

♣ - 510ºC

♦ - 525ºC

ω - 540ºC

That assigned symbol indicates the reactor inlet temperature that you will use in your HYSYS process simulations of this chapter. If your instructor has not assigned you a symbol, then you are to pick one of the six reactor inlet temperatures to complete the problem assignments in this chapter. After completing all seven problem assignments in this chapter, your team will then plot sales (which include the fuel credit), costs, and net profit versus the reactor inlet temperatures to determine the operating temperature that maximizes the net profit. In this plot, you can expect to see the net profit curve exhibit a maximum value either within the range of reactor temperatures or at an end point of the range. The point at which the maximum profit occurs is the “best” temperature at which to operate the adiabatic reactor, based solely on economics. Beginning with the second problem in this chapter, you will have access to the HYSYS solution for the previous problem thru a web link provided in each problem of this chapter. You are to begin the next problem by starting with the provided solution to the previous problem. Obviously, you are expected to practice professional ethics; that is, not solving your currently-assigned problem by starting with the available solution to the next problem. Failing to practice ethics here will results in plagiarism, which are grounds for termination of your employment at BEEF, Inc.

Chapter 4

Flowsheet Development Exercises – Problem SM.1

Page 4-3

SM.1 - Styrene Monomer Reaction Section The heart of a chemical process flowsheet is the reactor. The first step in synthesizing a flowsheet is to define the reactor operating conditions. These conditions are usually determined experimentally by the Research and Development (R&D) Department in a company, and these experimental data are used to simulate the performance of the reactor. Once the reactor has been simulated, other parts of the flowsheet can be developed. In the “Flowsheet Design Variables” section of Chapter 1, an experimentally-determined performance table is provided for an adiabatic reactor operating at 400 kPa with an equimolar feed of toluene and methanol. For your assigned reactor inlet temperature (as presented in the Overview section of this chapter), you are to use the molar conversion and yield from the performance table to complete an HYSYS reactor simulation that forms styrene monomer and ethylbenzene from toluene and methanol. As stated in Chapter 1, the proposed production rate is 250,000 metric tons per year of styrene monomer. What is the production rate in kgmol/h for a 95% onstream time (8,320 hours per year)? Based on the mathematical algorithm and HYSYS simulation algorithm for a reactor in Appendix H, what variables must be specified in order to simulate your reactor? Your examination of the algorithms in Appendix H should reveal that the feed flow rate and composition to the reactor must be specified instead of the total and component flow rates leaving the reactor. What estimated value do you get for the feed flow rate in kgmol/hr based on 100 percent conversion, no side reaction for ethylbenzene, and the proposed styrene production rate? Please document your calculations. Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. Using your estimated feed flow rate, you are to simulate in HYSYS the conversion reactor for the production of styrene monomer and ethylbenzene from toluene and methanol. What chemical components are in the reactor effluent stream and why? The conceptual model for this adiabatic reactor is as follows:

TS 11

TS 10 PS 10 nS 10 Z S 10

S10 feed

R1 reactor

S11 effluent

PS 11 nS 11 Z S 11

Using the above stream and equipment labels, you are to complete your HYSYS simulation as follows: •

Click one of the following web links to download the starter HYSYS file for your assigned reactor inlet temperature and then save it with your initials in its name to a team folder: SM1_465, SM1_480, SM1_495, SM1_510, SM1_525, or SM1_540.

• • • •

Start the HYSYS software, load your preferences, and open your retrieved starter file. Enter the Basis Environment, complete the component list, and define the chemical reactions. Return to the Simulation Environment and add a conversion reactor to the process flowsheet. Finish the simulation for this flowsheet section as directed in the remaining paragraphs.

Since the chemical reactions take place in the gas phase, label the reactor’s liquid stream as noLiq. For the conversion reactor, two chemical reactions will occur—one producing styrene monomer and the other ethylbenzene, as shown in Chapter 1. The HYSYS percent molar conversion of toluene to form styrene


Chapter 4

Page 4-4

monomer is equal to [overall conversion*yield*100] and that to form ethylbenzene is equal to [overall conversion*(1.00-yield)*100]. After completing this simulation with your estimated feed flow rate, use the HYSYS Adjust operation to iterate on the total molar flow of the reactor feed in order to obtain the desired production rate of styrene monomer in kgmol/hr. To learn how to apply the Adjust operation, access the Help facility in the Aspen HYSYS software. Mathematically, the Adjust operator simulates the following: ITERATE nS 10 in

[T

S 11

UNTIL where

, PS 11 , nS 11 , Z S 11 ] ⇐

reactorA [TS 10 , PS 10 , nS 10 , Z S 10 , CTSM , CTEB , ∆P ]

calculated (nS 11 × zS 11, SM ) = desired nS 11, SM

Z i means mole fractions zi ,1 , zi , 2 ,  zi , nc for nc components in mixture i.

Note that SM is styrene monomer, EB is ethylbenzene, CTj is the percent molar conversion of toluene to form Compound j, and ∆P is the pressure drop across the reactor. These data are provided in Chapter 1. The product (nS 11 × zS 11, SM ) represents the calculated molar flow rate of the styrene monomer in the reactor effluent Stream S11. After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table and graph for this team portion of the assignment. Your team is to plot the inlet toluene, outlet styrene monomer, and outlet ethylbenzene flow rates versus the reactor inlet temperatures. What inlet temperature should the adiabatic reactor operate at, so that the production rate of styrene monomer is maximized and that of ethylbenzene is minimized?

Chapter 4


Page 4-5

SM.2 - Reactor Effluent Cooling/Decanting Section In Problem SM.1, you simulated the reactor in the styrene monomer project using chemical reaction data provided by the Research and Development Department of BEEF, Inc. The Reactor R1 has only one effluent stream, the vapor Stream S11, because the flow rate of Stream noLiq equals zero. Based on physical properties such as critical temperature, critical pressure, and normal boiling temperature for each reaction component, why should the effluent leaving the reactor be only in the vapor or gas phase? To verify the stream phase, it may help to think of a phase (PT) diagram for each pure component. Physical properties of various chemical components are given in Chapter 1. Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. A global flowsheet for a chemical process depicts basically the raw materials entering the flowsheet and the product, byproducts and wastes leaving the flowsheet. Chapter 1 gives a block flowsheet for the chemical process of converting toluene and methanol to styrene monomer. A global flowsheet for the styrene monomer chemical process is shown below. Recycle Reactants Off Gas Byproduct Raw Materials

Reactor

Effluent

Separation Sequence

Pure Product

Wastewater

This global flowsheet shows the reactor producing an effluent stream (containing toluene, methanol, styrene monomer, ethylbenzene, water, and hydrogen), which must be separated to purify the product. The reactor effluent goes through a separation sequence in which the off gas (hydrogen), byproduct (ethylbenzene), pure product (styrene monomer) and waste water are isolated. Unreacted raw materials are also separated in the sequence. The reactants are then recycled back to the reactor. The number of process exit streams—off gas, byproduct, etc.—determines the number of separation units required in the sequence. As a rule of thumb (i.e., a heuristic rule), the number of required separation units is one less than the number of chemical components in the effluent stream, if each chemical component in that stream is to be separated into a pure stream for that component.. The first step in the design of a separation sequence is to decide what the first separation unit is. Some different types of separation are phase splitting, distillation, and extraction. Phase splits are usually the cheapest method of separation, because they only involve the cooling of the material process stream. Think of your separator funnel in organic chemistry labs to visualize a phase split. Therefore, if possible, a phase splitter is the first separation unit in the separation sequence. If the reactor effluent is in the vapor state, it must be cooled to allow a phase separation to take place. In the styrene monomer project, the reactor effluent is cooled to allow the formation of three distinct phases, the vapor phase and two immiscible liquid phases. The two liquids are an organic phase and an aqueous phase. To predict which components each phase contains, remember that “like dissolves like.” The organic phase contains the organics of toluene, ethylbenzene, and styrene monomer. The methanol partitions between both the organic phase and the aqueous phase. A three-phase separator is also known as

Chapter 4


Page 4-6

a decanter. Appendix J provides a mathematical description of how a decanter is modeled. Also, Appendix G describes how a cooling operation functions. You now know that the reactor effluent must be cooled from a vapor phase to a temperature at which three phases exist. You must determine to what temperature the stream is cooled to produce the phase separation. The cooling is typically carried out by a heat exchanger in which the effluent is cooled by a water stream. The cooling water is not directly mixed with the effluent. Rather, the two streams exchange heat thru a metal barrier so that the hot effluent is cooled while the cold water is heated. To design a heat exchanger that cools the hot stream the entire way to the temperature of the cold stream is unfeasible, because such a heat exchanger would be infinitely large in area. Applying a heuristic rule, the hot stream is cooled to within 5 to 10°C of the initial cold stream temperature. As given in the “Flowsheet Economic Analysis” section of Chapter 1, the cooling water is supplied at 31°C. Thus, the reactor effluent is cooled to about 38°C. At 38°C three phases may exist, and they could be separated in a decanter. The next step in the styrene monomer project is to simulate the first separation unit. Within Aspen HYSYS, you are to simulate the effluent cooling and three-phase separator. The conceptual model for the reactor, cooler, and decanter is as follows: S13 QE3 S10

R1

S11

S12 E3

F3

S14

S15



• •

Start the HYSYS software, load your preferences, and open your retrieved starter file. Finish the simulation for this flowsheet section as directed in the remaining paragraphs.

Account for the pressure drops through the cooler (E3) and decanter (F3) using the data in the “Flowsheet Design Variables” section of Chapter 1. The decanter is to operate adiabatically. After simulating Process Unit E3, create a Performance Table and Plot, where the independent variable is temperature and the dependent variables are pressure, heat flow, vapor fraction, vapor mass flow, light-liquid mass flow, and heavy-liquid mass flow. Include the dew-point and bubble-point temperatures in the table and plot. Under the HYSYS Flowsheet/Flowsheet Summary menu, use the Mass/Energy Balance page to view the relative imbalances for material and energy. After completing this simulation with the initial feed flow rate, use the HYSYS Adjust operation to iterate on the total molar flow of the reactor feed in order to obtain the desired production rate of styrene monomer in Stream S14 at 288.5022 kgmol/hr. To learn how to apply the Adjust operation, access the Help facility in the Aspen HYSYS software. Mathematically, the Adjust operator simulates the iteration construct shown below. In this iteration construct, SM means styrene monomer, EB means ethylbenzene, CTj is the


Chapter 4

Page 4-7

percent molar conversion of toluene to form Compound j, and ∆Pm is the pressure drop across process unit m. These data are provided in Chapter 1. ITERATE nS 10 in

TS 11 , PS 11 , nS 11 , Z S 11  ⇐ reactorA TS 10 , PS 10 , nS 10 , Z S 10 , CTSM , CTEB , ∆PR1   PS 12 , nS 12 , Z S 12 , Q E 3  ⇐ coolerC TS 11 , PS 11 , nS 11 , Z S 11 , ∆PE 3 , TS 12  0  ⇐ decanterC TS 12 , PS 12 , nS 12 , Z S 12 , ∆PF 3 , Q F 3 =  Ψ S 13 , Ψ S 14 , Ψ S 15  UNTIL

calculated (nS 14 × zS 14, SM ) = desired nS 14, SM

where Z i means mole fractions zi,1, zi,1, …, zi,nc for nc chemical components in mixture i. The symbol Ψ i means the process state—temperature, pressure, molar flow rate, and mole fractions— of Stream i. The product (nS 11 × zS 11, SM ) represents the calculated molar flow rate of the styrene monomer in the reactor effluent Stream S14. At what temperature in °C do two phases (vapor-liquid) start to occur on cooling? Do three phases (vapor-liquid-liquid) start to occur on cooling? On a molar basis, what fraction of Stream S12 after cooling to 38°C goes to the vapor phase of the decanter? To the organic phase? To the aqueous phase? On a mass basis, what fraction of Stream S12 after cooling to 38°C goes to the vapor phase of the decanter? To the organic phase? To the aqueous phase? After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. The Workbook is to contain only Streams S10, S12, S13, S14, and S15. Thus, Streams S11 and noLiq are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table and graph for this team portion of the assignment. Your team is to plot the inlet toluene ( S10), outlet styrene monomer ( S14), and outlet ethlybenzene (S14) flow rates versus the reactor inlet temperatures. What inlet temperature should the adiabatic reactor operate at, so that the production rate of styrene monomer is maximized and that of ethylbenzene is minimized? The reactor effluent contains the unreacted raw materials of toluene and methanol, the product of styrene monomer, and the byproduct of ethylbenzene. Since perfect separation into a pure chemical component is not possible (i.e., trace amounts of the other chemical components will always exist), you want to minimize the flow rates of these four chemical components in the off-gas stream (S13) and the wastewater stream (S15), because you must pay for the raw materials and you want to sell as much product as possible. Based on the various reactor inlet temperatures, what are the mean averages for the molar percent losses of toluene, methanol, styrene monomer, and ethylbenzene? The molar loss of a specific component equals the sum of the molar flow rates of that component in the off-gas and wastewater streams divided by the molar flow rate of that component in the reactor effluent (either Stream S11 or S12). What conclusions can your team draw about the molar losses for these four chemical components?

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SM.3 - Methanol Recycle Purification Section In Problem SM.2, you simulated the first separation operation, a cooler with a three-phase decanter, in the separation sequence of the styrene monomer project. In Problem SM.3, you will simulate the next operation in the separation sequence, a distillation column. A distillation column uses the difference in boiling-point temperatures to separate the chemical components of a stream. Think of a liquid mixture of two components with each component having different boiling points. If the mixture is heated to a temperature between the boiling points of the two components, the more volatile component (lower boiling-point temperature) vaporizes while the less volatile component (higher boiling-point temperature) remains in the liquid phase. By collecting the vapor, you have effectively separated the binary mixture into two single phases, the vapor phase containing the more volatile component and the liquid phase containing the less volatile. The same principle can be used to separate material process streams with more than two components into two mixtures with fewer components. All of the more volatile components will vaporize, and all of the less volatile components will remain in the liquid. Exactly where the separation occurs, i.e. which components vaporize and which do not, depends on the temperature that the original mixture is heated to. A distillation column is a series of equilibrium stages or trays where each act as a separator according to the boiling points as described above. A column separates a liquid feed stream into two liquid streams—the distillate and bottoms. The temperature of each tray gradually decreases moving from the bottom to top of the column. A reboiler at the bottom of the column heats the liquid in the column to a saturated vapor. This vapor then rises through the trays of the column. As the temperature decreases going up the column, the less volatile components begin to condense and fall back down through the column. By the time the vapor reaches the top of the column at the lowest temperature, only the most volatile components are vapors and exit the column. This vapor stream is condensed to usually a saturated liquid and then split into a reflux stream and distillate stream. The liquid reflux stream is sent back to the column. The more volatile components exit as a saturated liquid in the product stream. The less volatile components exit as a saturated liquid from the reboiler in the bottoms stream. To consider distillation as a possible separation operation, you must compare the normal boiling points and composition of all chemical components leaving the decanter in the aqueous stream. What are the normal boiling points (nbp) for all of those chemical components? What are their mole fractions? List the components and their nbp in order of increasing boiling point in the first two columns of the table below, using the data found in the “Flowsheet Thermodynamic Data” section of Chapter 1 in this HYSYS manual. Then, list the mole fractions of the same chemical components in the third column of the table. Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. Chemical Component

Normal Boiling Point, °C at 1 atm

Mole Fraction in Stream S15

Feed Type

Distribution

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To design a distillation column, you pick two components with adjacent boiling points and largest mole fractions from the above table. The more volatile component is called the light key (LK) and the less volatile component is called the heavy key (HK). The split in the column is between these two key components. A perfect separation means that all of the LK would be in the distillate, and all of the HK would be in the bottoms. However, like in the case of the three-phase separator, a perfect separation is unfeasible. An infinite number of trays in the distillation column would be required to perform a perfect separation. Therefore, a separation level is chosen for the column. Most of the LK exits the column through the distillate, with a little in the bottoms, and most of the HK exits the column through the bottoms, with a little in the distillate. The distillate contains all components more volatile than the LK (non-LK's), and the bottoms contains all components less volatile than the HK (non-HK's). A simple diagram to show the component flows is given next. non-LK' s mos t LK little HK non-LK' s LK

Column

HK non-HK' s little LK mos t HK non-HK' s

In the table above, where you entered in the first three columns the chemical components, their normal boiling points, and their mole fractions leaving in the decanter aqueous stream, you are to complete the fourth and fifth columns. What is the feed type of each chemical component, i.e. state whether each component is a LK, HK, non-LK, or non-HK? What is the qualitative distribution of each component by stating which stream(s) (i.e., distillate and/or bottoms) the chemical component appears in, and in what relative amount, such as all, most or little? Remember that the column is being designed to separate methanol from water. A detailed description of a simple distillation column is given in Appendix L of this HYSYS manual. What are the three main parts of a distillation column? The overall mathematical model for a column consists of a series of smaller math models, one for each of these column parts. In what order are the overall mathematical model equations solved in the column algorithm? How does the column mathematical algorithm in Appendix L differ from the HYSYS simulation algorithm? Why? A generic diagram for the distillation column to separate methanol from water is given below. It contains a partial condenser and several stages above and below the feed stage. However, the simple distillation column in Appendix L has a total condenser, meaning the entire vapor coming off the top of the column is converted to a saturated liquid. To achieve this liquid state, all of the components are assumed to be condensable. However, the aqueous stream from the decanter contains hydrogen, which is noncondensable. Note hydrogen's extremely low boiling point in your table above. Because the column will contain hydrogen, a partial condenser is used in order to allow the hydrogen to be vented out of the column as a vapor in Stream V. The use of a partial condenser instead of a total condenser means that one more variable must be specified for HYSYS to simulate the column. The functional equation for the HYSYS simulation algorithm of this column is as follows:


Chapter 4

 ΨV , Ψ D , Ψ B ,= Q C , Q R 

Page 4-10

rcolumnLK  Ψ F , PC , ∆PC , PR , ∆PR , N S , N FS , R, z B , LK , VRC 

where Q C is the condenser energy rate or heat duty, Q R is the reboiler energy rate or heat duty, Pu is the pressure of the partial condenser or reboiler unit, ∆Pu is the pressure drop across the partial condenser or reboiler unit, N S is the number of column stages, N FS is the feed stage number, R is the reflux ratio,

z B , LK is the total mole fraction of the light key (LK) in the bottoms, and VRC is the vent ratio for the partial condenser. The reflux ratio of R is the reflux total molar flow rate in Stream RF over the distillate total molar flow rate in Stream D. The vent ratio of VR is the distillate vent molar flow rate in Stream V over the feed molar flow rate in Stream F. The vector Ψi is a short notation to represent the temperature, pressure, flow rate, and molar composition (i.e., total mole fractions) of Stream i. Q C

Partial Condenser

Stages

F Feed

RF Reflux

V Vent

D Distillate

Feed Stage Stages

B

Q R

Bottoms Reboiler

Shortcut methods—Fenske-Underwood-Gilliland-Kirkbride—exist to estimate the distillation column design variables for the number of trays (NS), the tray at which the feed enters (NFS), and the molar reflux ratio (R). A shortcut analysis has already been performed for the methanol/water separation to determine these three design variables. To solve the rigorous HYSYS distillation column, more design variables must be specified in addition to NS, NFS, and R. For this problem, all of the design variables are: Number of Stages Feed Stage (from the top of column) Molar Reflux Ratio

= = =

35 10 15 5

permanent number of trays for 465, 480, 495°C reactor inlet for 510, 525, 540°C reactor inlet start with and change to meet desired specs

LK in Bottoms HK in Distillate Molar Vent Ratio

= = =

60 ppm 0.001 1.0e-6

EPA mass fraction limit on methanol in wastewater desired mole fraction of water in recycled methanol vapor vent total flow rate over feed total flow rate

Condenser Pressure Condenser ∆P Tray Column ∆P Reboiler ∆P Reboiler Pressure

= = = = =


distillate pressure leaving the condenser pressure drop across the condenser pressure drop of 1 kPa per tray pressure drop across the reboiler bottoms pressure leaving the reboiler

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The first three items in the above list were determine using the shortcut methods, based on the desired mass fraction for the light key in the bottoms stream, and a reasonable value for the mole fraction of the heavy key in the distillate stream. The remaining items are specifications from Chapter 1 of this HYSYS manual, except for the molar vent ratio. A stricter vent ratio like 1×10-7 will lead to an iteration error of “two liquid phases were found on the condenser stage.” Using 1×10-6 eliminates this error. Using these design specifications, the next step in the styrene monomer project is to simulate the methanol-water separation in HYSYS with the rigorous distillation column operator. The conceptual model for this distillation column is as follows: S17v

QcC3

S17

S16

C3

S18

QrC3



• •


Each starter file includes a valve and heater to prepare the aqueous stream from the decanter, so that it is fed to the distillation column as a saturated liquid at the appropriate pressure (i.e., 135 kPa plus 10, or 15 times 1 kPa per tray for the feed location). This starter file also has an attached rigorous distillation column (C3) in the process flow diagram (PFD). Double click the rigorous distillation column in the PFD, to open its property window. On the Design/Connections page, check the column name, the material and energy stream names, and the entered values for the number of stages and feed stage, which were approximated using the shortcut methods. Make sure the partial condenser is chosen so that the vent Stream S17v does exist. Check that the pressures were entered correctly for the condenser and reboiler, and that their pressure drops are also correct. The pressures of every stage between the condenser and reboiler will be calculated by HYSYS. Go to the Parameters/Profiles page, type 72°C as an estimate for the temperature of the chemical mixture in the condenser at 125 kPa, and type 117°C as an estimate for the temperature of the chemical mixture in the reboiler at 180 kPa. These two estimates were predicated by the shortcut methods. Go to the Design/Monitor page and enter the four values in the “Specified Values” column for the reflux ratio, mass fraction of the LK in the bottoms, mole fraction of the HK in the distillate, and the vent

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ratio. On the Design/Monitor page, the degrees of freedom box in the lower right corner currently show three. It must be zero in order for the column operator to begin the iterative process to converge the material and energy balances for the distillation column. To make this zero, you must tell HYSYS which specifications to use. Click the boxes to the right of the values you specified to make the reflux ratio, mass fraction of the LK in the bottoms, and the vent ratio active specifications. Note that the third specification for the mole fraction of the heavy key in the distillate must be inactive. Once enough variables are specified to satisfy the degrees of freedom, the column operator will try to find a solution using an iteration process, which will be visible in the page. If the iteration process does not automatically start, you can reset the iterative calculations and then start them by using the Reset and Run buttons, respectively. The green converged message will show up in the C3 column window to indicate the rigorous distillation simulation is solved. In the Design/Monitor page, the “Specified Value” and “Current Value” columns display the supplied and calculated values for the four specifications, respectively. When the green converged message appears, the current values for the three checked specifications have converged to within set tolerances for the iterative calculations. Note that the current value for the unchecked heavy-key specification may be far from its specified value. By changing the specified value for the reflux ratio, you can manually iterate (i.e., do trial and error) on the reflux ratio until the desired value for the unchecked specification is matched by rounding its “Current Value” expressed in scientific notation to a value of 10.00e-4. For example, a value of 9.83e-4 rounds to 10.0e-4 or 1.00e-3, and it would be an acceptable match to a “Specified Value” of 1.00e-3. When you supply a change in value for the reflux ratio, sometimes the iteration appears not to converge after 10 to 20 iterations. When this situation occurs, you should click the Stop button, select the Reset button to re-initialize the iteration process, and then click the Run button to restart the iteration. If convergence still does not occur after 10 to 20 iterations, you should stop the iteration process, increase or decrease the value for the reflux ratio, reset the iteration process, and then run the iteration process again. How might the value for the vent ratio be estimated? What are the feed, vent, distillate, and bottoms flow rates in kg/h? What are the mole fractions of the LK in the distillate and the HK in the bottoms? What are the composition profiles of just the LK and HK in the distillation column? Use the Performance/Plots page to print these profiles. Note that methanol is the light key and water is the heavy key in this problem. After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Performance Plot for the composition profile (with your initials in its title, square symbols for methanol, and triangle symbols for water), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. The Workbook is to contain only Streams S10, S16, S17v, S17, and S18. Thus, all other streams are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table and graphs for this team portion of the assignment. How does the reflux ratio vary with the reactor inlet temperature, and the condenser and reboiler heat duties vary with the reflux ratio? As a team, present a table with two plots. What inlet temperature should the adiabatic reactor operate at, so that the reflux ratio, condenser heat duty, and reboiler heat duty are minimized? What conclusion can you draw about the reflux ratio and the two heat duties? The condenser duty versus the reboiler duty?

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SM.4 - Toluene Recycle Purification Section In Problem SM.3, you simulated the distillation column that recovered methanol in the aqueous stream from the three-phase decanter. This recovered methanol will eventually be recycled in a later problem. The next operation in the separation sequence of the styrene monomer project is another distillation column. In Problem SM.4, you will simulate a distillation column to separate reactants from products in the organic stream leaving the three-phase decanter. The organic stream contains both methanol and toluene that are to be recycled back to the reactor. It also contains the styrene monomer product and the byproduct ethylbenzene. As with column C3 in Problem SM.3, you must first compare the normal boiling points and composition of all chemical components leaving the decanter in the organic stream. What are the normal boiling points (nbp) for all of those chemical components? What are their mole fractions? List the components and their nbp in order of increasing boiling point in the first two columns of the table below, using the data found in the “Flowsheet Thermodynamic Data” section of Chapter 1 in this HYSYS manual. Then, list the mole fractions of the same chemical components in the third column of the table. Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. Chemical Component

Normal Boiling Point, °C at 1 atm

Mole Fraction in Stream S14

Feed Type

Distribution

Furthermore, you are to complete the fourth and fifth columns in the above table. What is the feed type of each chemical component, i.e. state whether each component is a LK, HK, non-LK, or non-HK? What is the qualitative distribution of each component? State which stream or streams (i.e., distillate and/or bottoms) the chemical component appears in, and in what relative amount, such as all, most or little. If necessary, refer to the Problem SM.3 handout to refresh your memory about the concept of key and nonkey components. Remember that the column is being designed to separate the reactants from the products. As in the case of methanol column C3, the feed to this distillation column, called C1, contains the non-condensable hydrogen, which means a partial condenser must be used. Column C1 is depicted on the next page. What is the functional form for the HYSYS simulation algorithm for this column, based on knowing the mole fraction of the heavy-key component in the distillate stream? Define each of the variables in this functional form (HINT: Refer to the Problem SM.3 assignment). Shortcut methods—Fenske-Underwood-Gilliland-Kirkbride—exist to estimate the distillation column design variables for the number of trays (NS), the tray at which the feed enters (NFS), and the molar reflux ratio (R). A shortcut analysis has already been performed for the toluene/ethylbenzene separation to determine these three design variables. To solve the rigorous HYSYS distillation column, more design variables must be specified in addition to NS, NFS, and R. For this problem, all of the design variables are:

Chapter 4

Flowsheet Development Exercises – Problem SM.4 Number of Stages Feed Stage Location Molar Reflux Ratio

= = =

30 5th 4

LK in Bottoms HK in Distillate non-HK in Distillate Molar Vent Ratio Reboiler Temperature

= = = ≤

0.0001 3.5 wt% empty 1.0e-2 145°C

desired mole fraction of toluene in bottoms stream start with and change to meet ≤ 4 wt% ethylbenzene combined ethylbenzene-styrene to meet ≤ 5 wt% vapor vent total flow rate over feed total flow rate maximum temperature of the bottoms stream


= = = = =


distillate pressure leaving the condenser pressure drop across the condenser pressure drop of 0.5 kPa per tray pressure drop across the reboiler bottoms pressure leaving the reboiler

Page 4-14

permanent number of trays from the top of the column start with and change to meet desired specs

The first three items in the above list were determined using the shortcut methods, based on the desired mass fraction for the heavy key in the distillate stream and a reasonable value for the mole fraction of the light key in the bottoms stream. The remaining items are specifications from Chapter 1 of this HYSYS manual, except for the molar vent ratio. A stricter vent ratio like 1×10-3 will lead to an iteration error of “two liquid phases were found on the condenser stage.” Using 1×10-2 eliminates this error. Using these design specifications, the next step in the styrene monomer project is to simulate the toluene-ethylbenzene separation in HYSYS with the rigorous distillation column operator. The conceptual model for this distillation column is as follows: S23v

QcC1

S23

S22

C1

S24

QrC1 Using the above stream and equipment labels, you are to complete your HYSYS simulation as follows: •


•

Start the HYSYS software, load your preferences, and open your retrieved starter file.

Chapter 4

•


Page 4-15

Finish the simulation for this flowsheet section as directed in the remaining paragraphs.

Each starter file includes a valve and heater to prepare the organic stream from the decanter, so that it is fed to the distillation column as a partially-vaporized liquid at the appropriate pressure (i.e., 75 kPa plus 2.5, or 80 kPa when rounded up). This starter file also has an attached rigorous distillation column (C1) in the process flow diagram (PFD). Double click the rigorous distillation column in the PFD, to open its property window. On the Design/Connections page, check the column name, the material and energy stream names, and the entered values for the number of stages and feed stage, which were approximated using the shortcut methods. Make sure the partial condenser is chosen so that the vent Stream S23v exists. Check that the pressures were entered correctly for the condenser and reboiler, and that their pressure drops are also correct. The pressures of every stage between the condenser and reboiler will be calculated by HYSYS. Go to the Parameters/Profiles page, type 74°C as an estimate for the temperature of the chemical mixture in the condenser at 70 kPa, and type 143°C as an estimate for the temperature of the chemical mixture in the reboiler at 100 kPa. These two estimates were predicated by the shortcut methods. Go to the Design/Monitor page and enter the four values in the “Specified Values” column for the reflux ratio, mole fraction of the LK in the bottoms, mass fraction of the HK in the distillate, and the vent ratio. On the Design/Monitor page, the degrees of freedom (DOF) box in the lower right corner currently shows zero, because the cells in the “Active” column have been checked for the reflux ratio, the HK in the distillate, and the vent ratio. When the DOF box is zero, the column operator will begin the iterative process to converge the material and energy balances for the distillation column. Note that the second specification for the mole fraction of the light key in the bottoms must be inactive. The fourth and sixth specifications for the styrene mass fraction and reboiler temperature are also inactive. Note that the combined composition of ethylbenzene and styrene monomer in the distillate stream must be ≤ 5 wt%. Also, when the bottoms stream contains more than 50 mass% styrene monomer, its temperature must not exceed 145°C because the styrene monomer polymerizes and forms a solid above that temperature. Once three variables are specified to satisfy the degrees of freedom, the column operator will try to find a solution using an iteration process, which will be visible in the page. If the iteration process does not automatically start, you can reset the iterative calculations and then start them by using the Reset and Run buttons, respectively. The green converged message will show up in the C1 column window to indicate that the rigorous distillation simulation is solved. In the Design/Monitor page, the “Specified Value” and “Current Value” columns display the supplied and calculated values for the desired specifications, respectively. When the green converged message appears, the current values for the three checked specifications have converged to within set tolerances for the iterative calculations. If the combined composition of ethylbenzene and styrene monomer in the distillate stream is not ≤ 5 wt%, then lower the mass fraction specification for the ethylbenzene in increments of 0.005 until the combined specification of ≤ 5 wt% is met. After convergence has occurred, the current value for the unchecked light-key specification may be far from its specified value. By changing the specified value for the reflux ratio, you can manually iterate (i.e., trial and error) on the reflux ratio until the desired value for the unchecked light-key specification is matched by rounding its “Current Value” expressed in scientific notation to a value of 10.00e-5. For example, a value of 9.83e-5 rounds to 10.0e-5 or 1.00e-4, and it would be an acceptable match to a “Specified Value” of 1.00e-4. When you supply a change in value for the reflux ratio, sometimes the iteration appears not to converge after 10 to 20 iterations. When this situation occurs, you should click the Stop button, select the Reset button to re-initialize the iteration process, and then click the Run button to restart the iteration. If

Chapter 4


Page 4-16

convergence still does not occur after 10 to 20 iterations, you should stop the iteration process, increase or decrease the value for the reflux ratio, reset the iteration process, and then run the iteration process again. Finally, redo the HYSYS Adjust operation to iterate on the total molar flow of the reactor feed (S10), in order to obtain the desired production rate of styrene monomer in Stream S24 at 288.5022 kgmol/hr. How might the value for the vent ratio be estimated? What are the composition profiles of just the LK and HK in the distillation column? Use the Performance/Plots page to print these profiles. Note that toluene is the light key and ethylbenzene is the heavy key in this problem. Column C1 is designed to separate the reactants from the products in order to recycle the reactants. The C1 distillate stream (S23) contains the recycled reactants. The recycle stream must be prepared, in order to be mixed with fresh raw materials before entering the reactor. The fresh and recycled reactant streams are mixed as saturated vapors at 460 kPa. Add a pump and heater to distillate Stream S23 to reach the saturated-vapor point at 460 kPa in Stream S26, as show below. You must decide whether to heat the stream first, or to pump it first. Compressing a gas takes much more energy than pumping a liquid. Therefore, if you heat the stream to a saturated vapor first, extra energy will be needed to compress the vapor to the desired pressure. As a heuristic rule, pump the liquid first and then heat it to a saturated vapor. Don't forget to account for the pressure drop across the heater using the data in the “Flowsheet Design Variables” section of Chapter 1. Use the following labels in your simulation: QE5 WP4 S25

S26

S23 E5 P4 C1

After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Performance Plot for the composition profile in Column C1 (with your initials in its title, square symbols for toluene, and triangle symbols for ethylbenzene), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. The Workbook is to contain only Streams S10, S22, S23v, S23, and S24. Thus, all other streams are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table and graphs for this team portion of the assignment. How does the reflux ratio vary with the reactor inlet temperature, and the condenser and reboiler heat duties vary with the reflux ratio? As a team, present a table with two plots. What inlet temperature should the adiabatic reactor operate at, so that the reflux ratio, condenser heat duty, and reboiler heat duty are minimized? What conclusion can you draw about the reflux ratio and the two heat duties? The condenser duty versus the reboiler duty?

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SM.5 - Toluene/Methanol Feed Preparation Section In Problem SM.1, you simulated the reactor to produce styrene monomer from toluene and methanol. You assumed a single reactor feed stream in SM.1 that contained the two reactants in equimolar amounts at 400 kPa. Most likely, the raw materials (i.e., the two reactants) will actually be available individually at some other conditions. In this case, pure toluene and pure methanol are both available at ambient conditions, 25°C and 1 atm. In Problem SM.5, you are to simulate the preparation of toluene and methanol. The pure toluene and pure methanol streams are to be mixed as saturated vapors at 460 kPa. This means that each raw material must be compressed and heated separately before being mixed. Compression of a gas requires considerably more energy than compression of a liquid. As a general heuristic rule, you should first pump the liquid to the desired pressure and then heat the high-pressure liquid to a saturated vapor. You are to simulate the preparation of the two pure raw material streams, one for toluene and one for methanol, from ambient conditions to saturated vapors at 460 kPa. The conceptual model to pump, heat, and then mix the two raw materials is as follows:

QE1

WP1

S3

S2 S1 toluene

P1

E1 M1 QE2

WP2

S6

S5 S4 methanol

S7

P2

E2



• •


The molar flow rates of the two raw materials have been pre-set for you in each starter file; however, you need to supply their ambient condition at 25°C and 1 atm. The phase state of the exit stream from each heater is to be a saturated vapor (Vf = 1.0). The adiabatic efficiency for each pump and the pressure drop across each heater are provided in the “Flowsheet Design Variables” section of this HYSYS manual. After

Chapter 4


Page 4-18

completing your simulation, check the relative imbalances for mass and energy using the Mass/Energy Balance page under the HYSYS Flowsheet/Flowsheet Summary menu. What are the dew-point and bubble-point temperatures of Stream S3 and also Stream S6? What is unique about the dew point and bubble point for each pure chemical compound? Explain this uniqueness using the Gibbs phase rule. Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. What are the heating curves for Heaters E1 and E2; that is, a graph of temperature versus heat duty for each heat exchanger? Click here to view these two heating curves from 25 to 325°C at 460 kPa. On each heating curve, label the two sensible heat regions and the latent heat region. What is the slope of the heating curve in the transition region from the saturated-liquid state to the saturated-vapor state? After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. The Workbook is to contain only Streams S1, S3, S4, S6, and S7. Thus, all other streams are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table for this team portion of the assignment. The ratio of the toluene molar flow to the methanol molar flow is one for each reactor inlet temperature. On average, what are the ratios of the toluene mass flow to the methanol mass flow, the P1 pump work to the P2 pump work, and the E1 heat duty to the E2 heat duty? What conclusion can be drawn about the mass ratio and the pump ratio and why? What conclusion can be drawn about the molar ratio and the heat duty ratio and why?


Chapter 4

Page 4-19

SM.6 - Recycle Mixing and Preheating Section In Problem SM.5, you simulated the compression and vaporization of the two fresh reactant streams (pure toluene S1 and pure methanol S4) from ambient conditions of 25°C and 1 atm to a saturatedvapor state at 460 kPa. The feed to the reactor also contains recycled material from the toluene column C1 and the methanol column C3, as depicted in the following block flowsheet: Q

WS toluene recycle

heater

S26

toluene

SM.2

SM.6

SM.1

Q

SM.5 S7

H2 fuel

pump

SM.4

Q

decanter organic

S9 S10

S8

furnace

reactor

Q

WS

column C1

cooler

methanol S21

ethylbenzene aqueous

SM.7

column

methanol recycle SM.3

heater

column

pump C3


where the red-dashed ovals SM.1, SM.2, etc. in the above flowsheet represent the focus of each styrene monomer problem in this chapter. The two recycle streams (S26 and S21) must be mixed with the fresh reactant stream (S7) and then heated before entering the reactor, creating a recycle loop in the process. In Problem SM.6 you are to simulate the recycle loop. Click here to view a mathematical model and mathematical algorithm for this flowsheet simulation. The conceptual model for mixing and heating the reactor feed is as follows:

QFH1 S26 S7

M2

S8

S9 FH1

S21 Using the above stream and equipment labels, you are to complete your HYSYS simulation as follows: •


Chapter 4

• •


Page 4-20


Your HSYSY process flow diagram (PFD) contains the compression, vaporization, and mixing of the two fresh reactants, as well as the rest of the process unit operations from Reactor R1 to distillation Columns C1 and C3. A set operator labeled MeOH has been added to the PFD to set automatically the total molar flow of the pure methanol stream (S4) using the specified total molar flow of the pure toluene stream (S1). The liquid distillate streams (S17 and S23) from the two distillation columns have been compressed and heated to saturated vapors at 460 kPa, in preparation for their recycle back to the reactor. The hydrogen fuel stream (S13), the two vent streams (S17v and S23v), and the wastewater stream (S18) have been further processed to exit the flowsheet at 1 atm. The recycle loop is currently missing in your HYSYS PFD; that is, mixing the fresh reactants (S7) with the recycled reactants (S21 and S26) to produce the mixed reactants (S8) and then heating those mixed reactants to form the reactor feed (S9). The process state of Stream S9 is calculated based on assuming the process state of Stream S10, which you did in Problem SM.1 for the reactor inlet stream. For valid closure of the material and energy balances, the process state of Stream S9 exiting the fired heater FH1 must be identical to that of Stream S10 entering the adiabatic reactor R1; that is, their pressure, molar flow rate, molar enthalpy, and component mole fractions must agree within set tolerances. To close the recycle loop, you will manually execute the iterative method of successive substitutions for two iterations and then use the HYSYS Recycle operator to finish the iteration process. Proceed as follows to close the recycle loop: 1. Use the HYSYS “Drag Zoom” button to expand the PFD view from Mixer M2 to Reactor R1 and from recycle Streams S26 and S21. 2. Add a mixer operator labeled M2 into the flowsheet to combine the fresh reactant stream with the two recycle streams. The inlet streams to the mixer are S26, S7, and S21, in that order. The outlet stream is labeled S8. 3. Add a heater operator labeled FH1 to increase the temperature of Stream S8 to the reactor inlet temperature that was assigned to you. The heater used to reach such a high temperature in Stream S9 is called a fired heater, basically a furnace that burns natural gas. Use the HYSYS heater with a pressure drop as indicated in the “Flowsheet Design Variables” section of Chapter 1. The resulting outlet pressure must be 400 kPa. You must specify the temperature of Stream S9 using the reactor inlet temperature that was assigned to you. 4. Open the Workbook window. Hide Stream S8 and place Stream S9 before Stream S10 in the Material Streams, Compositions, and Component Flows pages. 5. Compare the temperature, pressure, molar flow rate, and molar enthalpy of Streams S9 and S10 using the Material Streams page in the Workbook window. Compare the component mole fractions of these two streams using the Compositions page. The temperature and pressure of these two streams are exactly the same, because you specified them to be those values. However, the molar flow rate, molar enthalpy, and component mole fractions of these two streams do not match. 6. Assume a new process state for Stream S10 by copying the conditions of S9 into S10 using the Define from Other Stream… button in the property window of Stream S10. Resetting the process state of Stream S10 causes HYSYS to recalculate all of the process units and produce a different calculated S9. The process states of S9 and S10 should now be closer.

Chapter 4


Page 4-21

This iterative technique of successive substitutions is used to find that process state of the reactor feed stream that closes the material and energy balances for the flowsheet recycle. 7. Copy the conditions of S9 into S10 again to assume a new process state for the reactor feed stream. The molar flow rate, molar enthalpy, and component mole fractions should be even closer for these two material streams. You could continue this process, manually performing the iterations of successive substitutions until the process state of S9 is identical to that of S10. However, HYSYS provides the Recycle operator to automate the iteration process. 8. Open the pre-placed recycle operator RCY and connect Stream S9 as the input and Stream S10 as the output to this operator, in order to automate the iteration process. The HYSYS recycle operator continually iterates on the process state of these two streams to close the recycle loop within set tolerances for the pressure, molar flow rate, molar enthalpy, and component mole fractions. It uses an enhanced version of successive substitutions called the Wegstein method. When the recycle operator has converged, you will get a green converged message at the bottom of the recycle property window. 9. Compare the temperature, pressure, molar flow rate, and molar enthalpy of Streams S9 and S10 using the Worksheet/Condition page in the Recycle: RCY window. Compare the component mole fractions of these two streams using the Worksheet/Composition page. The process states of Streams S9 and S10 should now be within set tolerances. Thus, the material and energy balances for the recycle portion of the chemical process flowsheet have been closed. 10. Select the Parameters/Numerical page in the Recycle: RCY window and examine the iteration count; that is, the number of iterations that were required to close the material and energy balances for the flowsheet. Since you did two iterations manually, note that you need to add two to the RCY iteration count. What is the number of total iterations required to close the material and energy balances for the recycle loop in the styrene monomer flowsheet? Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. The Parameters/Variables page within a Recycle operator (like RCY) controls the tolerance tightness of certain process variables for a material stream involved in the iteration process to close the material and energy balances of a recycle loop. Based on information provided through the HYSYS Help menu, the following table presents some of those variables and their tolerances used in Recycle Operator RCY: Stream Variable P - pressure n - molar flow rate

Hˆ - molar enthalpy x j - each mole fraction

Recycle RCY Sensitivity 10 1×10-4

Internal Tolerance 0.01 kPa 0.001 kgmol/s

Tolerance Type absolute relative

Actual Tolerance 0.1 kPa 1×10-7

1

1.00 kJ/s

absolute

1.00 kJ/s

1

0.0001

absolute

0.0001

Subscript “j” is for each chemical component in a mixture of nc chemical compounds. The actual tolerance equals the recycle sensitivity times the internal tolerance.

When a recycle operator is iterating on a material stream, the process variables that uniquely defined the state of that material stream are the pressure, molar flow rate, molar enthalpy, and nc-component mole


Chapter 4

Page 4-22

fractions, whether that stream is a mixture of two or more chemical components or just a mixture of one component (a.k.a. pure compound). The tolerance checks for these variables are given as follows: Stream Variable

P - pressure

Tolerance Check

abs ( Pin − Pout )

≤

0.1 kPa

must match to within 0.1 kPa

≤

1×10-7

must match to within 7 digits

)

≤

1.00 kJ/s

must match to within 1 kJ/s

)

≤

0.0001

n - molar flow rate

abs 

Hˆ - molar enthalpy

 nin − nout    nin  abs Hˆ − Hˆ

(

x j - each mole fraction

abs x j , in − x j , out

(

in

out

Explanation

must match to within

1

for

10, 000

each j-th component in mixture Subscript “in” means Stream S9 and subscript “out” means Stream S10 for recycle operator RCY.

When these (3+nc) process variables have converged, all other variables associated with the material stream will have converged too, like vapor fraction, temperature, and molar entropy. Click here to learn more about the general iteration process on a recycle loop in a chemical process flowsheet (i.e., a PFD). Once HYSYS has closed the material and energy balances, the styrene monomer production rate in Stream S24 must be checked to see if it meets the desired rate given in the “Flowsheet General Assumptions” section of Chapter 1 (i.e., 288.5022 kgmol/h or 250,000 mt/yr). Open the Workbook window, select the Component Flows page, and check the styrene monomer flow rate in Stream S24. Since it is not met, you are to conduct a trial-and-error iteration. Manually change the pure toluene flow rate in Stream S1, hit the key twice, allow HYSYS to complete the re-calculations, observe the styrene monomer flow rate in Stream S24, and stop your manual iteration when the desired styrene flow is met. After completing the iteration on the toluene flow rate in Stream S1, you must check the design constraints given in the “Flowsheet Design Specifications” section of Chapter 1 to see if they have been satisfied. Open the property windows of Columns C1 and C3 and inspect the “Specifications” area in the Design/Monitor page. All design specifications should have been met. What is the equimolar flow rate of pure toluene (S1) and pure methanol (S4) into the flowsheet for a production rate of 250,000 mt/yr of styrene monomer? What are the molar flow rates for toluene and methanol in S10, the stream entering Reactor R1? What are the reflux ratios for Columns C3 and C1? After you have solved the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Workbook datasheet minus the Unit Ops datablock, and the answers to all of the above questions. The Workbook is to contain only Streams S1, S4, S9, S10, and S24. Thus, all other streams are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains a table and graph for this team portion of the assignment. Your team is to plot the pure toluene (S1), reactor inlet (S10), styrene monomer (S24), and ethylbenzene (S24) flow rates versus the reactor inlet temperatures. What inlet temperature should the adiabatic reactor operate at, so that the production rate of styrene monomer is maximized and that of ethylbenzene is minimized? Although equimolar flow rates of pure toluene and pure methanol enter the flowsheet, the molar ratio of toluene to methanol in Stream S10 that enters Reactor R1 is not equimolar. What material stream quantity that enters the flowsheet would you vary to get the toluene-to-methanol ratio in Stream S10 to be equimolar?


Chapter 4

Page 4-23

SM.7 - Styrene Monomer Purification Section In Problems SM.1 through SM.6, you simulated the production of styrene monomer from toluene and methanol, including the separation and recycle of unused reactants. In the resulting flowsheet produced by solving these problems, the bottoms stream (S24) from distillation Column C1 contains both the product styrene monomer and the by-product ethylbenzene. A final distillation column (C2) is needed to purify the two product streams that meet the desired design specifications. In Problem SM.7, you are to simulate the purification of the styrene monomer and ethylbenzene, where ethylbenzene is the light key and styrene monomer is the heavy key. The feed to the ethylbenzene/styrene column (C2) contains non-condensable hydrogen, but since its composition is less than 1 ppm, a total condenser can be used in Column C2, as shown below. QcC2

QE6

WP5 S30 S28

S31 E6

P5

QEC2 V2 S24

S24B

S27

C2

EC2

QE7 WP6 S32 S29

P6

S33 E7

QrC2

What is the functional form of the HYSYS simulation algorithm for Column C2, based on knowing the mole fraction of the light-key component in the bottoms stream? Click here to download a Word file, add your initials to its name, and complete all of the questions contained within. Shortcut methods—Fenske-Underwood-Gilliland-Kirkbride—exist to estimate the distillation column design variables for the number of trays (NS), the tray at which the feed enters (NFS), and the molar reflux ratio (R). A shortcut analysis has already been performed for the ethylbenzene/styrene separation to determine these three design variables. To solve the rigorous HYSYS distillation column, more design variables must be specified in addition to NS, NFS, and R. For this problem, all of the design variables are: Number of Stages Feed Stage Location Molar Reflux Ratio

= = =

100 20th value

permanent number of trays from the top of the column a pre-determined number for each reactor inlet temperature

LK in Bottoms HK in Distillate non-LK in Distillate Reboiler Temperature

= = ≤ ≤

300 ppm 3.0 wt% 0.8 wt% 145°C

desired mass fraction of ethylbenzene in the bottoms stream desired mass fraction of styrene in the distillate stream desired mass fraction of toluene in the distillate stream maximum degradation temperature of the bottoms stream


= = = = =


distillate pressure leaving the condenser pressure drop across the condenser pressure drop of 0.5 kPa per tray pressure drop across the reboiler bottoms pressure leaving the reboiler

Chapter 4


Page 4-24

The first three items in the above list were determined using the shortcut methods and then later refined in a rigorous distillation column, based on the desired mass fraction for the light key in the bottoms stream and the desired mass fraction for the heavy key in the distillate stream. The remaining items are specifications from Chapter 1 of this HYSYS manual. The distillation operation occurs in a vacuum column, because the temperature of the bottoms stream must be less than or equal to 145°C when that stream contains more than 50 mass% styrene monomer. Above 145°C, polymerization of the styrene monomer would occur (i.e., solid formation of a polymer). Using these design specifications, the next step in the styrene monomer project is to simulate the ethylbenzene/styrene separation in HYSYS with the rigorous distillation column operator. You are to complete your HYSYS simulation as follows: •


• •


Beginning with Stream S24, the HYSYS flowsheet in each starter file contains a valve and heater to prepare this stream, so that it is fed to the distillation column (C2) as a partially-vaporized liquid (Vf = 0) at the appropriate pressure (i.e., 45 kPa). Distillation Column C2 produces the distillate and bottoms streams at pressures below ambient. These two streams are compressed and cooled to produce the by-product (S31) and product (S33), which must be stored at ambient conditions until they are sold. The flowsheet also contains two adjust operators—ADJ-TL and ADJ-ME—to meet the two design specifications of 250,000 metric tons per year of product and equimolar toluene and methanol fed to Reactor R1. Operator ADJ-TL iterates on the toluene flow to the flowsheet (S1) until the flow rate of Stream S33 equals 288.5022 kgmol/h, while Operator ADJ-ME iterates on the methanol flow to the flowsheet (S4) until the ratio of the molar flow of toluene to the molar flow of methanol in Stream S10 is 0.9999. The iteration procedures in these two operators are conducted simultaneously. In the HYSYS process flow diagram (PFD), the specifications for all process units between Stream 24 and Streams S31 and S33 have been pre-set for you, except for the light-key mass fraction in Column C2. Double click on the rigorous distillation operator for Column C2 in the PFD, to open its property window. On the Design/Monitor page, enter “3e-4” for the mass fraction of the ethylbenzene in the bottoms stream (i.e., 300 ppm in S33). HYSYS will now continue the iteration process to close the material and energy balances for the recycle loop in the flowsheet. While the iteration process is occurring, close the C2 property window and double click on the ADJ-TL operator to open its property window. In the Adjust/Monitor page, observe the “total iterations” count, which should stop somewhere within the range of 40 to 80 iterations. After the iteration process converges (i.e., stops), close the ADJ-TL property window. Since all HYSYS iteration processes on the flowsheet have been completed successfully, what are the percent relative imbalances on its mass and energy balances? Select the Flowsheet/Flowsheet Summary option and chose the Mass/Energy Balances page, to observe the percent relative imbalances. Right click in the blue header of the Flowsheet Summary window, select the Print Datasheet … option, deselect all data blocks except for the Mass and Energy Balance datablock, preview the datasheet, and then print it. Close the datasheet, the Select Datablock(s) window, and the Flowsheet Summary window, in order to return to the process flow diagram (i.e., the flowsheet).


Chapter 4

Page 4-25

With the HYSYS simulation calculations completed, does the flowsheet meet all of the design specifications that are outlined in Chapter 1 of this HYSYS manual? Double click on the spreadsheet operator labeled design spec to observe if certain calculated values are within their specification ranges. For example, the product stream (S33) is to contain a maximum of 300 ppm by weight of ethylbenzene. Thus, the range on this specification is 0 to 300 ppm. In the design spec spreadsheet, the mass fractions of the organic compounds in the wastewater stream (S18) are not clear. Copy those cells from the spreadsheet and paste them into a newly-opened Notepad document (use Start/All Programs/Accessories/Notepad), in order to clearly observe their values. Right click in the blue header of the Spreadsheet: design specs window, select the Print Datasheet … option, deselect all data blocks except for the Spreadsheet datablock, preview the datasheet, and then print it. Close the datasheet, the Select Datablock(s) window, and the Spreadsheet window, in order to return to the process flow diagram (i.e., the flowsheet). Finally, what are the flowsheet material requirements, sales, costs, net profit, and percent annual return to manufacture styrene monomer from toluene and methanol for your assigned reactor inlet temperature? The material requirements are the total molar flow rates for Stream S1, S4, S10, S31, and S34. The net profit for the styrene monomer flowsheet can be approximated as follows: net profit

=

product byproduct fuel + + sales sales credit ╚════════════╤═══════════╝ sales

−

cost of annualized utility − − raw materials capital cost costs ╚══════════════╤═════════════╝ costs

where each term is $ per year. The annual return is the ratio of the sales over the total capital cost to initially build the chemical plant, which is approximated to be equivalent to the annual product plus byproduct sales. Appendix M provides the economic model for determining the net profit. Furthermore, this appendix describes the HYSYS spreadsheet operator that implements this net profit model. Double click on the spreadsheet operator labeled net profit in the HYSYS flowsheet and follow the instructions presented in Appendix M to finish importing six quantities from the flowsheet into the spreadsheet. Once you have completed the importing process, you can observe the sales, costs, net profit, and percent annual return at the bottom right of the HYSYS net profit spreadsheet. After solving the above problem for your assigned reactor inlet temperature, you must provide documentation in your technical journal for the PFD (with a problem number, reactor inlet temperature, your name, and date), the Workbook datasheet minus the Unit Ops datablock, the Mass and Energy Balance datasheet, the design specs spreadsheet datasheet, and the answers to all of the above questions. The Workbook is to contain only Streams S1, S4, S10, S31, and S33. All other streams are to be hidden. After all team members have independently answered all questions in their technical journal, your team is to meet and compare the HYSYS simulation results for the different reactor inlet temperatures. Click here to complete an Excel template file that contains tables and graphs for this team portion of the assignment. First, your team is to plot the pure toluene (S1), pure methanol (S4), reactor inlet (S10), ethylbenzene (S31), and styrene monomer (S33) flow rates versus the reactor inlet temperatures. What inlet temperature should the adiabatic reactor operate at, so that the production rate of styrene monomer is maximized and that of ethylbenzene is minimized? Second, your team is to plot the sales, costs, and net profits versus the reactor inlet temperatures. At what reactor inlet temperature do you make the most net profit? What is its percent annual return? Third, when examining the economic feasibility of a chemical flowsheet, the annual return on investment for building the chemical plant is the simplest measure used to screen alternative flowsheet simulation solutions. Based on an economic heuristic, a percent annual return greater than or equal to 30% (before considering federal taxes) classifies a flowsheet simulation as being economically feasible. Using the percent annual return, what is the best reactor inlet temperature to make styrene monomer from toluene and methanol? What is its percent annual return?

Appendices

Appendices

Appendix A

Example Batch Simulation in HYSYS

Page A-1

Batch Module Description The Aspen HYSYS® simulator is not designed to handle batch process units, where no material is flowing into or out of the system boundary. Using the spreadsheet module in Aspen HYSYS® and the relationship between specific enthalpy, specific internal energy, and specific volume ( Hˆ= Uˆ + PVˆ ), you can program the solution to the material and energy balances for a batch process. This appendix presents an example problem for expanding steam in a cylindrical tank system, a typical problem that you will encounter in the junior-level chemical engineering thermodynamics course. It also describes how to use the HYSYS spreadsheet module to complete the numerical solution to this batch example for a gas mixture. As shown below, the problem solution consists of a problem statement, a conceptual model, model assumptions, a mathematical model, a mathematical algorithm, the numerical solution, and the heuristic observations. Within the dashed boundary, the system is examined at its initial and final states, ti and tf.

Problem Statement A tank contains 1.00 lbm of steam at 700ºF and 300 psia. It is connected through a valve to a vertical cylinder which contains a frictionless piston. The piston is loaded with a weight so that a pressure of 100 psia is necessary to support it. Initially, the piston is at the bottom of the cylinder. The valve is opened slightly so that steam flows into the cylinder until the pressure is uniform throughout the tank and cylinder. The final temperature of the steam in the tank is found to be 440ºF. Calculate the temperature in ºF of the steam in the cylinder, if no heat is transferred from the steam to the surroundings. Assume three-digits of precision. After solving this problem, what percentage error in the cylinder temperature would you get assuming the ideal gas law? How would you solve this problem if the tank initially did not contain steam but a gas mixture of 50% methane, 30% ethane, and 20% propane on a mass basis?

Conceptual Model initial time, ti

final time, ti

Model Assumptions 1. batch process 2. no chemical reactions 3. neglect KE and PE changes 4. no shaft work 5. adiabatic 6. water in the form of steam is the only compound in the gas mixture 7. if the gas mixture in the tank or cylinder contains two or more compounds, then it is well mixed.

Appendix A

Page A-2


Mathematical Model (1) ( 2)

m C f + mT f − mTi = 0

total mass balance

m C f Uˆ C f + mT f Uˆ T f − mTi Uˆ Ti = 0

energy balance

( 3)

Uˆ C f = umix TC f , PC f , WC f 

specific internal energy

( 4)

Uˆ T f = umix TT f , PT f , WT f 


(5)

Uˆ Ti = umix TTi , PTi , WTi 


(6)

VˆT f = VT f / mT f

a definition

(7)

VˆT f = vmix TT f , PT f , WT f 

specific volume

(8)

VˆTi = VTi / mTi

a definition

(9)

VˆTi = vmix TTi , PTi , WTi 

specific volume

(10 )

VT f = VTi

tank volume

(11)

wC= w= wTi , j f,j Tf,j

for each j

# vars

=

3 ⋅ nc

+

16

# eqns

= 2 ⋅ nc

+

10

1 ⋅ nc

+

6

DOF

=

Variable Descriptions Tkl Pkl

is

the temperature of gas mixture kl in the tank or cylinder, °F.

is

the pressure of gas mixture kl in the tank or cylinder, psia.

mkl Wkl

is is is

the total mass amount of gas mixture kl in the tank or cylinder, lbm. the number of chemical components or compounds in the gas mixture. the mass fractions of all nc-components in gas mixture kl.

wkl , j

is

the mass fraction of component kl in the gas mixture; vector Wkl

nc

means all elements wkl ,1 , wkl ,2 ,  , wkl ,nc in gas mixture kl.

Vkl Vˆ

is

the volume of gas mixture kl in the tank or cylinder, ft3.

kl

is

the specific volume of gas mixture kl in the tank or cylinder, ft3/lbm.

Uˆ kl

is

the specific internal energy of gas mixture kl in the tank or cylinder, Btu/lbm.

Appendix A


Page A-3

Mathematical Algorithm TC f  = batch TTi , PTi , WTi , mTi , TT f , PT f , PC f 

(5)

1.

Uˆ Ti

⇐

umix TTi , PTi , WTi 

(9)

2.

VˆTi

⇐

vmix TTi , PTi , WTi 

(8) (10 )

3.

VTi

⇐

mTi ⋅ VˆTi

4.

VT f

⇐

VTi

(11)

5.

wC f , j ⇐

wT f , j ⇐ wTi , j

( 4)

6.

Uˆ T f

⇐

umix TT f , PT f , WT f 

(7)

7.

VˆT f

⇐

vmix TT f , PT f , WT f 

(6) (1)

8.

mT f ⇐

VT f / VˆT f

9.

mC f ⇐

mTi − mT f

(2)

10.

Uˆ C f

(mTi Uˆ Ti − mT f Uˆ T f ) / m C f

11.

ITERATE on TC f in

( 3)

⇐ f (TC f

)

for j = 1, 2,  , nc

⇐ Uˆ C f − umix TC f , PC f , WC f 

UNTIL f (TC f

)

= 0

As shown in the mathematical model above, the number of degrees of freedom (DOF) is nc+6. For a gas mixture that contains only one pure component like steam, the DOF equals seven. The first line in the mathematical algorithm, called the functional form for batch, identifies seven variables that are to be known in the mathematical model; that is, the initial temperature, pressure, and amount in the tank, the final temperature and pressure in the tank, the final pressure in the cylinder, and the mass fraction of one for pure steam. The primary purpose of Algorithm batch is to solve for the final temperature in the cylinder, as indicated by the quantity on the left-hand side of its equals sign in the functional form. The steps in the mathematical algorithm indicate the order in which the equations of the mathematical model are to be solved for those known variables indicated on the right-hand side of the equals sign in the functional form for Algorithm batch. Steps 1 to 8 in the mathematical algorithm directly determine the indicated quantities on the left-hand side of each arrow ( ⇐ ). Step 9 is the application of the total mass balance. Step 10 calculates the final specific internal energy of the cylinder using the energy balance. Step 11 indicates that the final temperature (TCf) in the cylinder is determined by a trial-and-error or iterative procedure. After assuming a value for TCf, the specific internal energy of the cylinder is determine thru function umix using the assumed temperature, known pressure, and known composition of the final state of the gas mixture in the cylinder. This calculated specific internal energy from function umix is then compared to that value of specific internal energy determined from the energy balance in Step 10. When their difference is close to zero, the correct TCf has been found. When this difference is not close to zero, a new value is assumed for the final temperature in the cylinder, and the iterative procedure is repeated.

Appendix A

E-Z Solve Numerical Solution

// // // //

{ based on steam tables }

Batch Example, Applied Thermodynamics Problem Index T is the tank, while C is the cylinder Index f is final state, while i is initial state Specific Internal Energies and Volumes from the Steam Tables

// Total Mass Balance, kg of steam: m_Cf + m_Tf - m_Ti = 0 //

Energy Balance, kJ: m_Cf * u_Cf + m_Tf * u_Tf - m_Ti * u_Ti = 0

//

Specific Internal Energies, kJ/kg: u_Cf = u_pT("steam", P_Cf, T_Cf) u_Tf = u_pT("steam", P_Tf, T_Tf) u_Ti = u_pT("steam", P_Ti, T_Ti)

// P in kPa; T in °C // P in kPa; T in °C // P in kPa; T in °C

Specific Volumes, m^3/kg: sv_Tf = v_pT("steam", P_Tf, T_Tf) sv_Ti = v_pT("steam", P_Ti, T_Ti)

// P in kPa; T in °C // P in kPa; T in °C

//

//

Tank Volume Constraint: v_Tf = v_Ti sv_Tf = v_Tf / m_Tf sv_Ti = v_Ti / m_Ti

//

Page A-4


// m^3 // m^3 / kg // m^3 / kg

Given: T_Ti

=

371.111

ºC

P_Ti

=

2068.42

kPa

m_Ti

=

0.453592

kg

T_Tf

=

226.667

ºC

P_Tf

=

689.473

kPa

P_Cf

=

689.473

kPa

Calculated: u_Tf

=

2679.69

kJ / kg

u_Ti

=

2894.56

kJ / kg

sv_Tf

=

0.324583

m3 / kg

sv_Ti

=

0.139023

m3 / kg

v_Ti

=

0.0630597

m3

v_Tf

=

0.0630597

m3

Specified Variables: T_Ti = ( 700 - 32 ) / 1.8 P_Ti = 300 * 101.325 / 14.696

// °F to °C // psia to kPa

m_Tf

=

0.194279

kg

m_Cf

=

0.259313

kg

T_Tf = ( 440 - 32 ) / 1.8 P_Tf = 100 * 101.325 / 14.696


m_Tlb

=

0.428313

lbm

T_Cf = ( T_CF - 32 ) / 1.8 P_Cf = 100 * 101.325 / 14.696

// °C to °F // psia to kPa

m_Clb

=

0.571687

lbm

m_Ti =

//

lbm to kg

u_Cf

=

3055.55

kJ / kg

m_Tf = m_Tlb * 0.453592

//

kg

to lbm

T_Cf

=

457.687

ºC

m_Cf = m_Clb * 0.453592

//

kg

to lbm

T_CF

=

855.836

ºF

1.0 * 0.453592

The above numerical solution was generated by using the E-Z Solve software that is provided with the third edition of the Felder and Rousseau textbook [2005]. After the mathematical model in the first column is typed into the E-Z solve program, that program would produce the results show in the second column. Click here to download this mathematical model, save it as a “.msp” file, open it from within the E-Z Solve program, and examine Case A. In the above E-Z Solve mathematical model, built-in functions “u_pT” and “v_pT” were used to determine the specific internal energy and specific volume for pure steam, respectively.

Appendix A


Page A-5

Heuristic Observations A. Numerical Solution The final temperature of the steam in the cylinder is determined to be 856°F, after accounting for precision. Note that it is greater than 700°F, the initial temperature in the tank. Since the internal energy initially and finally must be equal as indicated by the energy balance, the final temperature of the steam in the cylinder must increase to maintain this equality, because the final temperature of the steam in the tank is 440°F.

B. Mathematical Algorithm For the above steam problem, the mathematical algorithm is as follows:

TC f  = batch TTi , PTi , WTi , mTi , TT f , PT f , PC f  How would you solve this steam problem if you knew that TCf = 845°F, and you were asked to solve for TTi instead? The mathematical algorithm would change, since the know variables would be different compared to those in Algorithm batch. By slightly modifying the E-Z Solve mathematical model for this new problem, E-Z Solve would calculate a TTi = 695°F.

C. Mathematical Model Assuming that the pure steam within the system boundary behaves like an ideal gas, the final temperature of the steam in the cylinder is 886°F. See the E-Z Solve solution on Page A-6.

856  F − 886  F % error = ⋅100 = − 3.50 % 856  F D. Conceptual Model If the tank initially contained a gas mixture of 50% methane, 30% ethane, and 20% propane on a mass basis, the mathematical model would be the same, but the specific internal energy and specific volume could be determined using an equation of state in the Aspen HYSYS program. Since Aspen HYSYS is not designed for a batch operation, a HYSYS spreadsheet operator would be used to implement the mathematical algorithm batch. See the HYSYS solution on Page A-7. The final temperature of the gas mixture in the cylinder is 463°C or 865°F.

Appendix A

Page A-6


E-Z Solve Numerical Solution

{ based on ideal gas law } Given:

// // // //

Batch Example, Applied Thermodynamics Problem Index T is the tank, while C is the cylinder Index f is final state, while i is initial state Specific Internal Energies and Volumes based on ideal Gas

// Total Mass Balance, kg of steam: m_Cf + m_Tf - m_Ti = 0 //

Energy Balance, kJ: m_Cf * u_Cf + m_Tf * u_Tf - m_Ti * u_Ti = 0

// //

Specific Internal Energies, kJ/kg:

//

//

dHhat in kJ/mol and dU = dH - d(PV) = dH - R(dT) u_Cf = dHhat("Water_g", Tref, T_Cf)*1000/18.016 - Rkg * (T_Cf - Tref) u_Tf = dHhat("Water_g", Tref, T_Tf)*1000/18.016 - Rkg * (T_Tf - Tref) u_Ti = dHhat("Water_g", Tref, T_Ti)*1000/18.016 - Rkg * (T_Ti - Tref) Specific Volumes, m^3/kg: using the Ideal Gas Law sv_Tf = Rkg * (T_Tf + 273.15) / P_Tf // P in kPa; T in °C sv_Ti = Rkg * (T_Ti + 273.15) / P_Ti // P in kPa; T in °C Tank Volume Constraint: v_Tf = v_Ti sv_Tf = v_Tf / m_Tf sv_Ti = v_Ti / m_Ti

//

Specified Variables: T_Ti = ( 700 - 32 ) / 1.8 P_Ti = 300 * 101.325 / 14.696

// m^3 // m^3 / kg // m^3 / kg


T_Tf = ( 440 - 32 ) / 1.8 P_Tf = 100 * 101.325 / 14.696


T_Cf = ( T_CF - 32 ) / 1.8 P_Cf = 100 * 101.325 / 14.696

// °C to °F // psia to kPa

m_Ti =

//

lbm to kg

m_Tf = m_Tlb * 0.453592

//

kg

to lbm

m_Cf = m_Clb * 0.453592

//

kg

to lbm

Tref Rkg

1.0 * 0.453592

= 200 = 8.314472 / 18.016

// // //

T_Ti

=

371.111

ºC

P_Ti

=

2068.42

kPa

m_Ti

=

0.453592

kg

T_Tf

=

226.667

ºC

P_Tf

=

689.473

kPa

P_Cf

=

689.473

kPa

Tref

=

200

Rkg

=

0.461505

kPa m3 K kg

ºC

Calculated: u_Tf

=

39.8524

kJ / kg

u_Ti

=

262.672

kJ / kg

sv_Tf

=

0.334557

m3 / kg

sv_Ti

=

0.143747

m3 / kg

v_Ti

=

0.0652026

m3

v_Tf

=

0.0652026

m3

m_Tf

=

0.194893

kg

m_Cf

=

0.258699

kg

m_Tlb

=

0.429665

lbm

m_Clb

=

0.570335

lbm

u_Cf

=

430.535

kJ / kg

T_Cf

=

474.681

ºC

T_CF

=

886.426

ºF

°C 3 kPa m / K kg kJ / K kg

In the above E-Z Solve mathematical model, the built-in function “dHhat” determines the molar enthalpy of steam by integrating its temperature-dependent heat capacity from a lower temperature to a higher temperature. Click here to download this mathematical model, save it as a “.msp” file, open it from within the E-Z Solve program, and examine Case B.

Appendix A


Page A-7

{ for three-component mixture }

HYSYS Numerical Solution Process Flow Diagram (PFD)

The process flow diagram (PFD) contains three streams and a spreadsheet operator. The total mass of Stream “Tk i” is set to 1.00 lbm/h, since HYSYS uses flow rates. The fluid package is the Peng-Robinson-Stryjeck-Vera (PRSV) equation of state. Click here to download this HYSYS solution, save it as a “.hsc” file, and open it from within the Aspen HYSYS program.

Workbook Table

Spreadsheet Operator

Columns A, C, and E contain only textual documentation.

Cells B2, D2, F2 - blue specified temperatures imported from the process streams in the PFD. Cells B3, D3, F3 - blue specified pressures imported from the process streams in the PFD. Cells B4, D4, F4 - black calculated molar volumes imported from the process streams in the PFD. Cells B5, D5, F5 - black calculated molecular weights imported from the process streams in the PFD. Cells B6, D6, F6 - red formula (e.g., =b4/b5) for the specific volumes of the three process streams. Cells B7, D7, F7 - black calculated specific enthalpies imported from the process streams in the PFD. Cells B9, D9, F9 - red formula (e.g., =b7-b3*b6) for the specific internal from the specific enthalpy definition. Cell B12 - blue specified total mass flow imported from the process stream in the PFD. Cell B13 - red formula (=b12*b6) for tank volume; Cell D12 - red formula (=b13/d6) for final tank amount. Cell F12 - red formula (=b12-d12) for final cylinder amount, Step 9 in mathematical Algorithm batch. Cell F13 - red formula (=(b12*b9-d12*d9)/f12) for final cylinder specific internal energy, Step 10 in Alg. batch. Iterate on temperature in Cell F2 until Cell F9 is close in value to Cell F13, Step 11 in math Algorithm batch.

Appendix B

HYSYS Steady-State Simulation Modules

Page B-1

HYSYS Simulation Modules The Aspen HYSYS® software system is an integrated engineering environment for the development and analysis of chemical process flowsheets. It provides you with: • steady-state modeling and optimization for process design, and • dynamic modeling for process controllability and control strategy development. Aspen HYSYS® is licensed for educational use only at your university by Aspen Technology, Inc. of Cambridge, MA. As an academic user, you have agreed to use HYSYS only for educational and not commercial purposes. The focus of this Aspen HYSYS handbook is on steady-state modeling, often called chemical process simulation. Appendix B begins with a description of the general format for the process simulation modules presented in various appendices. It concludes with the process simulation module for the stream tee, in order to illustrate that general format.

Process Module Format A chemical process flowsheet is a conceptual representation of the transformation of raw materials into products through a series of process unit operations connected by process streams. Appendices B, C, D, etc. present simulation modules for the material and energy balances of some standard process unit operations. In general, a process unit transforms the material passing through it, and this transformation is represented by a set of algebraic equations, called a mathematical model. This model presents the material balances, energy balance, and thermodynamic relationships for the process unit. Since the mathematical model has more variables than equations, its degrees-of-freedom (DOF) tells you the number of variables that must be specified to solve the equations. The order in which the model equations are solved depends on which variables are specified. This ordering is called a mathematical algorithm. In HYSYS more than one combination of specifications can be used to solve the mathematical model of a process unit. For example, in a pump simulation you can specify the inlet stream and the pressure drop in order to calculate the outlet stream conditions. This type of specification is known in HYSYS as forward propagation; that is, knowing the inlet conditions you can find the outlet conditions. You could also specify outlet information instead of inlet. This type of specification is known in HYSYS as backward propagation. HYSYS can back-calculate for the inlet conditions of a process unit given the outlet conditions and appropriate information to fulfill the degrees of freedom. This flexibility comes from the underlying mathematical equations that exist for each process unit and the different ways these equations can be solved. HYSYS incorporates the mathematical models for many process unit operations and knows which mathematical algorithm of a process unit to use according to which variables you have specified. Some of the process unit operations supported by HYSYS are as follows: • • • • • • • • •

material stream energy stream component splitter compressor / expander cooler / heater heat exchanger LNG exchanger mixer plug flow reactor

• • • • • • • • •

pipe segment pump reactor operations separator / 3-phase separator / tank separation column shortcut column solid separator operations tee valve

Appendix B

HYSYS Steady-State Simulation Modules

Page B-2

You can consult the Visual Encyclopedia of Chemical Engineering Equipment [Montgomery, 2001] for general information on various process units and analytical instruments. If you are logged into Bucknell’s computer network, click here to access this electronic encyclopedia; otherwise, consult with your instructor about its availability at your university. Also, the Help menu command in the HYSYS software describes its supported process units in detail, but it does not provide an analysis of their mathematical models. Appendices B, C, D, etc. of this handbook present the mathematical models and some of their mathematical algorithms for eleven standard process units, in order to help you understand how HYSYS (or any simulation package, as well as hand calculations) solves the material and energy balances of these process units. The process unit modules in these appendices are for the following flowsheet operations: Appendix C D B E F G H I J K L

Module Process Stream Stream Mixer Stream Tee Pump Valve Heater/Cooler Chemical Reactor Two-Phase Separator Three-Phase Separator Component Splitter Distillation Column

Description Contains chemical components flowing at a certain state. Mixes two or more process streams to make one stream. Divides one process stream into two or more process streams. Increases the pressure of a liquid process stream. Decreases the pressure of a process stream. Heats or cools a process stream. Reacts the chemical compounds to form desired products. Separates a process stream into vapor and liquid streams. Separates a process stream into vapor, organic, and aqueous streams. Splits a process stream into two streams at different temperatures. Separate a process stream through a series of equilibrium stages.

The format for each module has been standardized, in order to aid your learning process. This format is as follows: 1. Module Description 2. Conceptual Model 3. Model Assumptions 4. Mathematical Model 5. Variable Descriptions 6. Mathematical Algorithms 7. HYSYS Simulation Algorithms The module description explains the purpose of the process unit operation. The conceptual model depicts the flow of material and energy. The assumptions list the conditions under which the mathematical model is applicable. The mathematical model presents the material balances, energy balance, and thermodynamic relationships for a process unit; that is, the algebraic equations that model a process unit simulation. The mathematical algorithms are representative examples of how the mathematical model could be solved for a specified set of variables that satisfies the degrees of freedom. The HYSYS simulation algorithms are representative examples of what you can specify to do a process unit simulation. These examples include calculations for both forward and backward propagation of information flow. You may want to consult the Help menu command in the Aspen HYSYS software to discover all of the simulation algorithms supported by HYSYS for any process unit operation. This information is also available in the Adobe Reader “.pdf” version of the Aspen HYSYS Unit Operations guide. If you are logged into Bucknell’s computer network, click here to access that guide; otherwise, consult with your instructor about its availability at your university.

Appendix M

Page M-1

Styrene Net Profit Analysis

Net Profit For a preliminary design study, the economic viability of manufacturing styrene monomer from toluene and methanol can be studied by examining the net profit of the chemical process flowsheet. This net profit can be approximated as follows: net profit

=

product sales

byproduct sales

+

fuel credit

+

−


−


−

utility costs

where each term is $ per year, and federal income taxes are not considered. In the net profit analysis, the onstream time is 8320 hours per year, which allows for a 2.5-week shutdown of the chemical plant for annual maintenance. Once the material and energy requirements for a chemical process flowsheet have been calculated using Aspen HYSYS®, the six terms on the right-hand side of the above net profit equation can be modeled by the algebraic equations presented below. All economic data used in these equations can be found in the “Flowsheet Economic Analysis” section of Chapter 1 of this HYSYS manual. This appendix ends with the description of a HYSYS spreadsheet operator that simulates the economic model to determine the net profit for the styrene monomer flowsheet.

Product Styrene Monomer Sales product sales

=

$

Stream S33 flow rate

kg

=

yr

*

*

h

sales price

*

$1.54

*

kg

onstream time

8320 h yr

Byproduct Ethylbenzene Sales byproduct sales

$

=


kg

=

yr

*

*

h

sales price

*

$0.97 kg

*

onstream time

8320 h yr

Hydrogen Fuel-Value Credit fuel credit

$ yr

=

=


kgmol h

*

*

Stream S13 LHV

kJ kgmol

*

*

fuel-value credit

$8.53

M kJ M kJ 106 kJ

*

*

onstream time

8320 h yr

Appendix M

Page M-2


where the lower heating value (LHV) is the energy realized by combusting the fuel minus the latent heat of vaporization for water, since water appears as a vapor in the combustion process. The lower-heating value is automatically calculated by Aspen HYSYS® as one of many properties for a process stream. Streams S13, S17g, and S23g contain off-gases that can potentially be used as fuel. Streams S17g and S23g are ignored in the fuel-value credit, since they only represent 2% of the total molar flow of off-gas in the flowsheet. Stream S13 contains mostly hydrogen and accounts for the other 98% of the off-gas.

Raw Material Methanol Cost methanol cost

$ yr

=

=

Stream S4 flow rate

kg

*

*

h

cost price

$0.35 kg

*

*

onstream time

8320 h yr

Raw Material Toluene Cost toluene cost

$ yr

=

=

Stream S1 flow rate

kg h

*

*

cost price

$0.65 kg

*

*

onstream time

8320 h yr

Annualized Capital Cost Capital cost is the amount of money that you must spend to build the physical plant for a chemical process flowsheet. That money usually must be borrowed from a bank, in order to complete the construction of the physical plant, which can take two to three years to finish. Considering the time value of money, how is the capital cost in dollars accounted for as an annual cost in $/yr over the lifetime of the physical plant, assuming no salvage value for that plant at the end of its lifetime. Money has a time value, known as annual interest. At 6% annual interest, $1000 today is not $1000 in one year, but it is worth $1060 (i.e., $1000 + 0.06*$1000). After two years, it is worth $1123.60 (i.e., $1060 + 0.06*$1060). After three years, it is worth $1191.02 (i.e., $1123.60 + 0.06*$1123.60). In general, the future worth of the present value of money can be calculated as follows: F = P*(1+i)n where F is the future worth, P is the present value, i is the interest rate as a fraction, and n is the number of years. At 6% annual interest rate, $1000 dollars today would be worth $2396.56 after 15 years. If a bank were to lend you $1000 today at 6% annual interest for 15 years, then the bank would charge you $159.77 per year (i.e., $2396.56/15) to recoup the $1000 plus the compounded interest. For a capital investment or cost of $1000 at 6% annual interest for 15 years, an annualizing factor can be determined by taking $159.77 and divided it by $1000 to get 0.15977, which is roughly 1/6 per year. As

Appendix M

Page M-3


an economic heuristic rule, one sixth of the capital cost is the yearly amount to be charged for borrowing the capital cost from a bank at 6% annual interest for 15 years. What is the capital cost for a chemical process flowsheet? As an economic heuristic, the capital cost is roughly equivalent to the sales of the product and byproducts for just one year. For the styrene flowsheet, capital cost

=

(

S33 product styrene sales

$

=

(

$

+

S31 byproduct ethylbenzene sales

)

*

one year

$

)

*

1 yr

+

yr

yr

annualized capital cost = capital cost / 6 in $/yr In summary, the yearly cost to borrow the capital from a bank to build the plant for the styrene monomer flowsheet is one-sixth of its capital investment, where the bank charges 6% annual interest for 15 years.

Electric Utility The utility cost to run a pump or compressor is based on its power in kW, its mechanical and electrical efficiency of 90%, and the cost of electricity, as follows: electric cost

=

$

=

yr

W 0.90

*

kW

*

unitless

electricity price

$0.06 kW ⋅ h

*

*

onstream time

8320 h yr

where W is the shaft work for the process unit, as calculated from the HYSYS flowsheet simulation. This cost equation is applied to each pump (P1, P2, P3, P4, P5, and P6) and to the compressor (K1). The sum of their electric cost is the total electric utility for the styrene monomer flowsheet.

Natural Gas Utility The utility cost to run the fired heater FH1 is based on its heat duty in kJ/h, the 90% thermal efficiency of a furnace to burn the natural gas, and the cost of the natural gas, as follows: natural gas cost

$ yr

=

=

Q 0.90 kJ / h unitless

*

*

natural gas price

$12.10 M kJ

M kJ 106 kJ

*

*

onstream time

8320 h yr

Appendix M

Page M-4


where Q is the heat duty to increase the temperature of the feed stream to the reactor, as calculated from the HYSYS flowsheet simulation.

Heater Utility The utility cost to run a heater is based on the amount of high-pressure steam required to exchange energy with the process stream that is being heated. The heating process takes place in a countercurrent heat exchanger, depicted as follows:

Conceptual Model Steam System Assumptions F feed

E exit

process stream Q H

metal

SO sat’d liq

1. 2. 3. 4. 5.

barrier

42-bar steam

SI sat’d vap

continuous process no chemical reactions neglect KE and PE changes no shaft work steam gives up only its latent heat

steam system

The steam is available as a saturated vapor at 42 bar and 253.2°C, with a latent heat of condensation ( ∆Hˆ cond ) equal to 1697.8 kJ/kg. The mass flow rate of steam required to heat the process stream can be determined from an energy balance around the steam system, as follows:

Q H

=

m steam

*

kJ

=

kg

*

h

h

∆Hˆ cond

kJ kg

The steam cost can be calculated from the following equation: steam cost

$ yr

=

=

Q H ∆Hˆ cond kJ / h kJ / kg

steam price

*

*

$30.97 K kg

K kg 103 kg

*

*

onstream time

8320 h yr

where Q H is the heat duty needed to increase the temperature of the process stream, as calculated from the HYSYS flowsheet simulation. This cost equation is applied to each heater unit (E1, E2, E4, E5, EC1, and EC3), and the sum of their steam cost is the total heater utilities for the styrene monomer flowsheet.

Appendix M

Page M-5


Cooler Utility The utility cost to run a cooler is based on the amount of cooling water required to exchange energy with the process stream that is being cooled. The cooling process takes place in a countercurrent heat exchanger, depicted as follows:

Conceptual Model Water System Assumptions F feed

E exit

process stream Q C

metal

CO water out

1. 2. 3. 4. 5. 6. 7. 8.

barrier

CI water in

cooling water water system

continuous process no chemical reactions neglect KE and PE changes no shaft work cooling water is available at 1 atm. constant pressure process. constant heat capacity for water constant 1.0 kg/liter for water.

The cooling water is available at 31°C (TCI) and can be heated to only 41°C (TCO), with a constant heat

capacity ( Cˆ P , CW ) equal to 4.1852 kJ/(kg·∆°C). The mass flow rate of cooling water required to cool the process stream can be determined from an energy balance around the water system, as follows:

Q C

=

m CW

*

kJ

=

kg

*

h

h

Cˆ P , CW kJ kg ⋅ ∆ C

*

(TCO − TCI )

*

∆ C

The cooling water cost can be calculated from the following equation: cooling cost

$ yr

=

=

m CW

ρ water kg / h kg / L

*

*

cooling water price

$0.03

KL K L 103 L

*

*

onstream time

8320 h yr

where Q C is the cooling duty needed to decrease the temperature of the process stream, as calculated from the HYSYS flowsheet simulation. This cost equation is applied to each cooler unit (E3, E6, E7, E8, and EC2), and the sum of their cooling cost is the total cooler utilities for the styrene monomer flowsheet.

Appendix M

Page M-6


Condenser Utility The utility cost to run a condenser is based on the amount of cooling water required to exchange energy with the overhead vapor in a distillation column. The cooling process takes place in a countercurrent heat exchanger, similar to that used in the above Cooler Utility, where Q C is the cooling duty needed to condense the overhead vapor, as calculated from the HYSYS flowsheet simulation. The cost equation from the Cooler Utility is applied to each condenser unit in Columns C1, C2, and C3, and the sum of their cooling cost is the total condenser utilities for the styrene monomer flowsheet.

Reboiler Utility The utility cost to run a reboiler is based on the amount of high-pressure steam required to exchange energy with the liquid in the reboiler of a distillation column. The heating process takes place in a countercurrent heat exchanger, similar to that used in the above Heater Utility, where Q H is the heat duty needed to vaporize the liquid in the reboiler, as calculated from the HYSYS flowsheet simulation. The cost equation from the Heater Utility is applied to each reboiler unit in Columns C1, C2, and C3, and the sum of their heating cost is the total reboiler utilities for the styrene monomer flowsheet.

HYSYS Spreadsheet Operator The complete economic model to determine the net profit of the styrene monomer flowsheet for a specific reactor inlet temperature is provided as the HYSYS spreadsheet operator named “net profit”. The general content of this spreadsheet is presented in the last two pages of this appendix. In Spreadsheet “net profit”, Columns A and C provide textual documentation. Column B contains economic data, thermodynamic data, and imported quantities from the styrene monomer flowsheet. Columns D, E, and F have formula cells that calculate the economics of the flowsheet. All formulae are used to find the total sales, total costs, net profit, and annual % return, which are displayed in the bottom right portion of the spreadsheet. The annual percent return on the investment to build the chemical plant for making styrene monomer is the net profit divided by the capital cost. For the Problem SM.7 simulation in Chapter 4 of this HYSYS manual, all of the flowsheet quantities in Column B of Spreadsheet “net profit” have been imported for you, except for six of them. In order to complete the net profit calculations, you need to import quantities in Cells B3, B30, B52, B72, B90, and B102. Right click in one of these cells, chose the Import Variable option, and select the HYSYS object and variable associated with that cell, as described in the two tables below. Cell B3 B30 B52

Object Stream S33 Energy WP1 Unit E1

Variable Mass Flow Power Duty

Cell B72 B90 B102

Object Unit E3 Energy QcC1 Energy QrC1

Variable Duty Heat Flow Heat Flow

After you complete the six imports, what are the two largest costs on a percent basis? See Column F.

Appendix M

Page M-7


HYSYS Spreadsheet “net profit” (Part 1 of 2) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

A Product Sales:

B

C Economics:

D

E Net Profit Terms:

F Total Sales is =e7+e13

S33 styrene, kg/h: SM Price, $/kg: S31 E-benz, kg/h: EB Price, $/kg:

1.54 0.97

% thereof: SM Sales, $/h: EB Sales, $/h:

=b3*b4 =b5*b6

Product Sales, $/yr: Fuel-Value Credit: S13 off-gas, kgmol/h: S13 LHV, kJ/kgmol: Credit, $/M kJ:

Onstream, h/yr: 8.53

=(d4+d6)*d9

=e7/f2*100

8320

S17g and S23g off-gas ignored, only Fuel Credit, $/yr:

2% of total off-gas =((b11*b12*b13)/1e6)*d9

=e13/f2*100

Total Mat'ls, $/yr:

=(d18+d20)*d9

=e21/f2*100

Capital Cost, $/yr:

=b25/6

=e26/f2*100

=d38*d9

=e39/f2*100

=d45*d9

=e46/f2*100

Raw Mat'l Costs: S4 methanol, kg/h: MeOH Price, $/kg: S1 toluene, kg/h: TL Price, $/kg:

0.35 0.65

MeOH Cost, $/h: Toluene Cost, $/h:

=b17*b18 =b19*b20

Capital Investment: Capital Cost, $: Annualize, 1/yr: Electric Utility: WP1 Power, kW: WP2 Power, kW: WP3 Power, kW: WP4 Power, kW: WP5 Power, kW: WP6 Power, kW: WK1 Power, kW: Total Power, kW: Electricity, $/kW*h:

=(d4+d6)*d9

1/6

Annualized

0.9