Indian Institute of Technology Madras Chennai

E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012) Volume 2: NSPSE 2012

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(His Excellency Dr. K. Rosaiah delivering the inaugural address)

(His Excellency Dr. K. Rosaiah and the conference administrators during the inauguration ceremony)

_______________________________________________________________________ Editors: R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian

Indian Institute of Technology Madras Chennai (TN) – 600 036, India. December 2012. _______________________________________________________________________ Supported by the Petrotech Society, India.

E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012) Volume 2: NSPSE 2012

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Editors R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian Indian Institute of Technology Madras Chennai (TN) – 600 036, India December, 2012.

E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012) Volume 2: NSPSE 2012 Indian Institute of Technology Madras, Chennai (TN) - 600 036, India, December 2012 R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian, eds. Preface We are honored to bring you this edited e-book of the proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012), held at the Indian Institute of Technology Madras, Chennai, India, December 6-8, 2012. This volume 2 deals with NSPSE-2012. The drilling technology is an important part of oil, gas, minerals and ore exploration. The engineering activities that drive oil, gas, minerals and ore exploration require constant update as and when new technologies get matured and are made available to the industry. Furthermore, for our economic expansion, India needs economic and efficient energy and knowledgeable and skilled human resource. It is expected that our reliance on petroleum resources will continue in forseeable future too. The ICDT2012 and NSPSE-2012 reported on the latest technologies related to the important topics that are relevant for the industry, practicing engineers and academicians and brought the latest research results and state-of-art technologies to the focus of the participants. The primary objective of the conference and national symposium was to share and disseminate the information and design base being built by the researchers in the area of drilling technology, and petroleum science and engineering; and make available the desired knowledge and skills to the participants to understand the advanced and emerging technologies in drilling and petroleum science and engineering. We would like to thank the keynote speakers for their excellent contributions in research and leadership in their respective fields. We express our gratitude to the workshop organizers, who have been a very important part of the conference and workshop, and, of course, to all participants and research and technical contributors of the ICDT-2012 and NSPSE-2012.

R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian Indian Institute of Technology Madras, Chennai, Tamil Nadu, India. (i)

ISBN: 978-93-80689-13-5 Publisher Indian Institute of Technology Madras, Chennai (TN) – 600 036, India. Cost For hard copy: 500 USD (International buyers), 25 000 INR (Indian buyers); and for soft copy on CD 100 USD (International buyers), 5000 INR (Indian buyers). Purchasing enquiry Dr. R. Sharma, Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai (TN) – 600 036, India, E-mail: [email protected]

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Acknowledgements We are indebted to many organizations and people who have helped with the conference:

People Distinguished keynote speakers (Arranged as per their scheduled talks) Shri Hirak Dutta OISD, India Dr. Robello Samuel Halliburton-Drilling and Evaluation, USA Prof. M. R. Riazi Kuwait University, State of Kuwait Prof. Faisal Khan Memorial University, Canada Dr. Anuj Gupta Texas A&M University at Qatar, State of Qatar Prof. Tae-Wan Kim SNU, Republic Of Korea Prof. T. R. Sreekrishnan IIT Delhi, India Prof. Suparna Mukherji IIT Bombay, India Prof. R. Madhavan Anna University, India Dr. S. Rajashree GE Oil and Gas, India Dr. Pål Skalle NUST, Norway Distinguished special invited speakers (Arranged as per their scheduled talks) Dr. Archana Chugh IIT Delhi, India Dr. Manaswita Bose IIT Bombay, India Local organizing committee (Arranged in alphabetical order by last name) DR. ANANTHANARAYANAN, P. N., AMET University, India DR. AGHALAYAM, Preeti, IIT Madras, India DR. ASOKAN, T., IIT Madras, India DR. BHATTACHARYA, Avik, IIT Bombay, India DR. CHANDRASEKARAN, S., IIT Madras, India DR. CHAUDHURI, Abhijit, IIT Madras, India DR. DUTTA, Suryendu, IIT Bombay, India DR. KUMAR, G. S., IIT Madras, India DR. KUMAR, D., IIT Madras, India (iii)

DR. MADHAVAN, Nandita, IIT Madras, India DR. MUKHERJEE, Rinku, IIT Madras, India DR. NAIR, R. R. IIT Madras, India DR. NAMBI, Indumathi, IIT Madras, India SHRI PRASAD, Divakarla (Ex IOCL), India SHRI PRASAD, Jitendra, ONGCL, India SHRI RAMADASS, G., NIOT, India DR. RAMANATHAN, M., IIT Madras, India DR. SAHA, B., IOCL, India DR. SHANMUGAM, P., IIT Madras, India DR. SRIVASTAVA, Smita, IIT Madras, India Organizing committee Patrons Prof. Bhaskar Ramamurthi, IIT Madras, India Shri Sudhir Vasudeva, Petrotech India Encouragers The Dean (IC and SR), IIT Madras, India The Head, DOE, IIT Madras, India Dr. Anand Kumar, Petrotech India Technical committee (Arranged in alphabetical order by last name) DR. AHMED, Ramadan University of Oklahoma, USA DR. AL-HADRAMI, Hamoud SQU, Sultanate of Oman DR. ARON, David Petroleum Development Consultants, UK DR. AYALA, Luis F. PSU, USA DR. DALAI, Ajay K. University of Saskatchewan, Canada DR. ELSHAHAWI, Hani Shell Inc., USA PROF. GHARBI, Ridha Kuwait University, State of Kuwait DR. GUPTA, Anuj Texas A&M University at Qatar, Qatar PROF. KHAN, Faisal Memorial University, Canada PROF. KIM, Tae-wan SNU, Republic of Korea PROF. MANSOORI, G. Ali University of Illinois at Chicago, USA PROF. OYEKUNLE, L. O. University of Lagos, Nigeria PROF. PATRIKALAKIS, Nicholas Marinos Massachusetts Institute of Technology, USA (iv)

DR. PIMONOV, Evgeny Schlumberger Moscow Research, Russia DR. RACHMAT, Sudjati Institut Teknologi Bandung (ITB), Indonesia PROF. RAHMAN, Sheik UNSW, Australia PROF. RIAZI, M. R. Kuwait University, State of Kuwait DR. SAMUEL, Robello Halliburton-Drilling and Evaluation, USA PROF. SKALLE, Pål NUST, Kingdom of Norway DR. SPEIGHT, James G. Consultant, USA DR. SUICMEZ, Vural Sander Brunei Shell Petroleum, Nation of Brunei PROF. TOWLER, Brian Francis University of Wyoming, USA PROF. WILLENBACHER, Norbert KIT, Germany Advisory committee (Arranged in alphabetical order by last name) DR. ATMANAND NIOT, India PROF. BANIK, P. K. PDPU, India DR. GARG, M. O. IIP, Dehradun, India DR. GOPALAKRISHNAN, P. CRE, Mangalath Pariyarath, India PROF. GUPTA, J. P. RGIPT, India PROF. KUMAR, T. NIT Durgapur, India DR. MUKUNDAN, H. FloaTEC, LLC, USA SHRI PRABHAKUMAR, S. P. ONGCL, India PROF. RAJAN, E. G. PRC(P)L, India DR. (MS.) RAJASHREE, S. S. GE Infrastructure (Oil & Gas), India SHRI SAHA, A. ONGCL, India PROF. VENKATACHALAM, P. CRSE, IIT Bombay, India

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Organizations - Sponsors *** Platinum sponsor ***

Oil and Natural Gas Corporation Limited (ONGCL) (incorporated on 23 June 1993) is a stateowned oil and gas company in India. It is a Fortune Global 500 company ranked 152nd, and contributes 77% of India's crude oil production and 81% of India's natural gas production. It is the highest profit making corporation in India. ONGC is one of Asia's largest and most active companies involved in exploration and production of oil. It is involved in exploring for and exploiting hydrocarbons in 26 sedimentary basins of India. It produces about 30% of India’s crude oil requirement. It owns and operates more than 11,000 kilometres of pipelines in India. The vision and mission of ONGCL is to be a world class Oil and Gas Company integrated in energy business with dominant Indian leadership and global presence. For more information, visit the ONGCL website at http://www.ongcindia.com.

*** Gold sponsors ***

Oil India Limited (OIL) is an Indian public sector oil and gas company based in Assam, India under the administrative control of the Ministry of Petroleum and Natural Gas of the Government of India. OIL is engaged in the business of exploration, development and production of crude oil and natural gas, transportation of crude oil and production of liquid petroleum gas. Recently, the company has taken a leading initiative in the process of constructing a long product pipeline from Numaligarh to Siliguri, India. OIL also sells its produced gas to different customers in India. And, OIL has diversified now into the production of the ‘Liquefied Petroleum Gas (LPG)’ also. For more information, visit the OIL website at http://www.oil-india.com.

***

ITD Cementation India Limited (ITD Cem) offers new and innovative methods of solving present day construction challenges, and the Company is credited with pioneering the art of integrating engineering and innovation with construction practices to maximize benefits to society at large. Over the years ITD Cem has built many iconic projects; notable amongst these are the Birla Copper & the Gujarat Chemical Jetties at Dahej, Shiplift Facility for Seabird, Karwar, 2nd Container Terminal at Chennai, Elevated viaduct, road projects for NHAI and underground tunnels and stations at Delhi Metro. A sampling of large projects awarded to ITD Cem are: the Dry Dock and Slipway for Garden Reach, Kolkata, Wet Basin

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at Mazgaon Dock, Mumbai, Kolkata Airport modernisation, Sripadsagar Dam in Andhra Pradesh, and Tallah Palta Pipeline and Micro Tunnelling at Kolkata. For more information, visit the ITD Cem website at http://itdcem.co.in/.

*** Silver sponsors ***

Garware-Wall Ropes Limited specialize in providing total, customized solutions to the cordage and infrastructure Industry world-wide, and Garware-Wall Ropes Limited is a market driven organization, with ‘Customer Delight’ at the core of all that it does. The company focuses on thorough understanding of the customer’s needs before determining the product / service specifications that will best cater to them. Complementing it is the company’s work culture that nurtures a spirit of enterprise amongst our members. A culture that consistently focuses on ‘bettering the best’ by keeping pace with the latest developments in the field. A culture that does not smother innovative thought by fear of making mistakes and one that lays a plinth of partnership on which our professional interactions with vendors on one hand and customers on the other are based. For more information, visit the Garware-Wall Ropes Limited website at http://www.garwareropes.com/.

***

Hindustan Petroleum Corporation Limited (HPCL) is an Indian state-owned oil and natural gas company based at Mumbai, Maharashtra, India. HPCL has been ranked 267th in the Fortune Global 500 rankings of the world's biggest corporations for the year 2012. HPCL has been growing steadily over the years. At present, HPCL operates two major refineries that produce a wide variety of petroleum fuels and special petroleum products. HPCL is partner in HMEL, a joint venture with Mittal Energy Investments Private Limited. HPCL also owns and operates the largest lubricant refinery in India and produce lubricant based oils of excellent international standards, with a capacity of 335 TMT. HPCL owns a marvellous supply and distribution infrastructure that comprise of terminals, aviation service facilities, LPG bottling plants, lube filling plants, inland relay depots, retail outlets (petrol pumps) and LPG and lubricant distributorships. For more information, visit the HPCL website at http:// www.hindustanpetroleum.com/.

***

Indian Oil Corporation Limited is an Indian state-owned oil and gas corporation with its headquarters in New Delhi, India. The company is the world’s 83rd largest public corporation, according to the Fortune Global 500 list, and the largest public corporation in India with revenue. IOCL and its subsidiaries account for a 49% share in the petroleum products market, 31% share in refining capacity and 67% downstream sector pipelines capacity in India. IOCL is one of the seven Maharatna status companies of India, apart from

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Coal India Limited, NTPC Limited, Oil and Natural Gas Corporation, Steel Authority of India Limited, Bharat Heavy Electricals Limited and Gas Authority of India Limited. IOCL operates the largest and the widest network of fuel stations in the country. IOCL has distinguished itself by focussing on cutting edge research at the research and development center at Faridabad, and there it supports, develops and provides the necessary technology solutions to the operating divisions of the corporation and its customers across the world. For more information, visit the IOCL website at http://www.iocl.com/.

Trademarks and copyrights © All rights are reserved with IIT Madras, Chennai, India.

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Contents Page number Preface

i

Publication details

ii

Acknowledgements

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1) Initiatives towards emerging landscape in environmental management - A case study of Uran plant 1-8 Rashmi Choudhary1, Dolly Valechha2, Sarvesh Chandra Pandey3, Shiv Charan Singh4 1-4 ONGCL, India 2) Selection of suitable metallurgy for tube/tube sheets of heat exchangers of LPG I & II and 3rd stage IHI compressor of Uran Plant - A case study+ 9-10 S. A. Fazal1, Subrahmanya Bhat2, Bipin Kumar3 1-3 ONGCL, India 3) Microbial degradation of paraffins: A review N. Sakthipriya1, M. Doble2, Jitendra S. Sangwai3 1-3 IIT Madras, Chennai, India

11-16

4) Performance analysis of a centrifugal impeller used for crude oil pumping Sayed Ahmed Imran1, Abdus Samad2 1-2 IIT Madras, Chennai, India

17-28

5) Numerical modeling of flow through progressive cavity pump - A review K. R. Mrinal1, Abdus Samad2 1-2 IIT Madras, Chennai, India

29-38

6) Title: The study of oil spill cleanup methods along with comparison+ Saumya1, Md. Hamid Siddique2 1-2 ISM Dhanbad, India

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7) Numerical modelling on remediation of petroleum hydrocarbons under coupled dissolution, sorption and biodegradation for a subsurface system 41-48 M. Vasudevan1, G. Suresh Kumar2, Indumathi M. Nambi3 1-3 IIT Madras, Chennai, India 8) Treatment mechanisms for tank bottom sludge remediation: Challenges and future scope S. Sivabalan1, R. Gardas2, J. S. Sangwai3 1-3 IIT Madras, Chennai, India

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9) Experimental investigations on the phase equilibrium of semi-clathrate hydrates of quaternary system of CO2+TBAB+SDS+H2O 55 - 62 Abhishek Joshi1, Jitendra S. Sangwai2 1-2 IIT Madras, Chennai, India

_________________________________________________________________________________ Extended abstract only. (ix)

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E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012), December 6-8, 2012. Volume 2: NSPSE 2012 Editors: R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian ISBN: 978-93-80689-13-5, Copyright © 2012 by the Indian Institute of Technology Madras, Chennai (TN) - 600 036, India. ________________________________________________________________________________________________

Initiatives towards emerging landscape in environmental management - A case study of Uran plant Rashmi Choudhary1*, Dolly Valechha2, Sarvesh Chandra Pandey3, Shiv Charan Singh4 Oil and Natural Gas Corporation, Mumbai Region, India. 1* 2 3 E-mails: [email protected]; [email protected]; [email protected]; 4 [email protected] * Author for correspondence.

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Abstract: Environmental Management system (EMS) at Uran Plant comprises Real Time Monitoring Stations for Ambient Air Quality, Stack Monitoring Stations and Effluent Treatment Plant. Apart from complying the stipulations of Environmental parameters, the plant has embarked upon several environmental initiatives as continual drivers for improvements keeping in view the emerging landscape in environmental management. Initiatives have been taken for capturing the fugitive emissions from the tanks, assessment of Green House Gas emissions and reduction measures thereof. These measures are, in addition to, process improvement initiatives viz., a improved diffused aeration system and bioremediation. The above efforts serve as a tool to improve environmental management system further. The paper attempts to emphasize on the additional efforts beyond the stipulatory requirement, and presents the initiatives for capturing the fugitive emissions from the crude oil tanks during stabilization through Tank Vapor Recovery Unit (TVRU) and the Flare Gas Recovery Unit (FGRU) that is a Clean Development Mechanism. These two initiatives are paving the way for reduction of hydrocarbon emissions. Precisely to mention, TVRU itself is capturing hydrocarbons approx. 6000-7000SCMD and thus arresting the fugitive emissions while FGRU is under registration for issuance of carbon credits in lieu of 97400 units of CO2 equivalent per year. Process improvement endeavours are another tool in EMS at Uran plant in the form of introduction of the BERMAD valve for effective separation of oil and water. This functions on the density differential and minimizes the ingress of hydrocarbon in the effluent. This is the maiden effort in ONGC. The road ahead encompasses the introduction of the Plasma Thermal Destruction and Recovery (PTDR) for solid waste management. Prior to detailed description of EMS beyond stipulatory requirement a brief account of the plant activity and related aspects are mentioned below. 1. Introduction Uran Plant: Uran Plant is an important asset of Oil And Natural Gas Corporation Ltd. - a state owned Maharatna Public Sector Undertaking. It stabilizes crude oil, produces power, processes natural gas for extracting value added products - LPG, Low Aromatic Naphtha and Ethane-Propane. An EMS framework for managing environmental responsibilities in efficient manner is integrated into overall operations of the Plant. This plant is certified for ISO 9001:2008, ISO 14001:2004, OHSAS 18001:2007 for over a decade. Major initiatives embarked upon by Uran Plant in consonance with emerging landscape in environment management system cover - Capturing fugitive emissions under Methane to Market study, identification of additional potential Clean Development Mechanism (CDM) projects via Green House Gas Accounting Pilot exercise. The Methane to Market study enabled to identify mostly invisible sources of emissions, quantification, and subsequently containment/mitigates strategies for hydrocarbon emissions. The study of Methane to Market measurement was carried out in the collaboration with team from US EPA and methodology employed, IR Camera for detection of fugitive emissions. Study identified sources of emissions from acid gas vent, flanges, valves, crude oil tanks and quantified the emission contribution from each source.

Road ahead in environmental management system envisages the introduction of Plasma Thermal Destruction & Recovery (PTDR) for solid waste management. 2. Methodology: (i) Emission Reduction by Capturing the Fugitive Emission Hydrocarbon emissions absorb Infrared light and IR camera used this characteristic to detect the presence of gas emissions from the equipment, vents, valves etc. Measurements were carried out using High Flow sampler, Turbine meter, Gas Find IR (Infrared) camera, and calibration bags. On the basis of snapshot study of specific emission sources, estimates were generated. Major sources with percent contribution are presented in Fig 1.

Fig 1: Sources and contribution towards emission. Suggestions emerged from the study include reduction of leakages from process vents (e.g. acid gas vent), flanges, equipments, wet seals of compressors and TVRU. (ii) Green House Gases Accounting: The six Greenhouse gases with respective Global Warming Potential (GWP) over period of 100years are CO2 (1), Methane (21), Nitrous Oxide (310), Halo Carbons (140-11,700) and SF6 (2390). In the present study only CO2 has been covered as GHG.

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Sets of data collected for the said pilot study pertained to gas consumption for Power Generation, and for Flaring, Acid Gas, Steam Generation, Quantum of Electrical Power Generation, Total Electricity produced, consumed, imported, and exported. Significant contribution towards GHG Accounting is observed in following areas: Gas consumption for Power Generation, Flaring of gas, Diesel Consumption for power generation.

Fig 2: GHG Accounting on Uran Plant. Identification of Probable Clean Development Mechanism Projects Based on analysis of data, the study finds the opportunity for potential CDM Projects in the following areas • Retrofitting of Turbine components to allow operation of Gas Turbines (GTs) at higher temperature and therefore higher efficiency. • Use of energy efficient appliances/retrofitting with components such as energy efficient motors and lighting, use of variable speed drivers etc This paper is focused on emissions reduction through TVRU and FGRU, and is broadly discussed below. Capturing Hydrocarbon Through Tank Vapour Recovery Unit: TVRU with a capacity of 15000 SCMD installed at Uran with equivalent capacity of a stand by compressor. Vapor generated due to out-breathing and flashing in Intermediate Crude Surge Tanks is routed to Compressor Suction Knock out Drum to discharge knock out drum. Gas is sent to upstream of 2nd stage suction knock out drums of Crude Stabilization Unit off-gas compressor. The schematic diagram of TVRU is shown in Fig. 3. Flare gas Recovery through FGRU: FGRU enables to reduce the carbon foot print and is a clean development mechanism project. Flare Gas Compressor is provided for total capacity of 1.5 LSCMD The schematic diagram of FGRU is shown in Fig. 4. It recycles all the technical flared gases otherwise being led to the flare system (which was sourced from 25 control valves, 600 pressure safety valves, 13 fuel gas purge points, seal purge gas released from compressors and expanders, tanks and other vessels) to put them back to the system in order to recover the valuable hydrocarbons and therefore reduce flaring to zero level. (iii) Environmental Management through Process improvement: Introduction of BERMAD Valve - It is intended to reduce the organic matter load in the effluent treatment system by introduction of BERMAD valves – an automatic system for separation of fluids based on gravity differential and controlled drainage of effluent. Installation of Bermad valves in intermediate tank and storage tank enables removal of water that 3

has infiltrated the crude oil and that has been allowed to separate through gravity. The heavier liquid is discharged through separation valves.

Fig 3: Schematic Representation of TVRU.

FLARE HEADER GAS COOLER

IHI CSU

COMPRESSOR SECONDARY OIL SEP DISCHARGE KOD

SUCTION KOD

LIQUID TO V-901 OIL TANK CUM SEPERATOR

LIQUID TO OWS

OIL COOLER

L/O FILTER PUMP

FLARE GAS RECOVERY UNIT

Fig 4: Schematic Representation of FGRU. The specific gravity differential separation sensitivity is 0.04. This device replaces the manual draining and stops oil carry over to ETP system.

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Fig 5: Schematic Diagram of BERMAD valve. 3. Results and Discussion Capturing Emission through TVRU: On an average fugitive hydrocarbon reduction is to the tune of 60007000SCMD Since December 2010 onwards. The gases which are captured by TVRU are rich in nature having molecular weight in the range of 34. The gas composition and fugitive hydrocarbon reduction of TVRU from Dec. 2010 to July 2012 are given in Fig 6 (a, b).

Fig 6(a): Composition of Tank Vapor.

Fig 6(b): Fugitive hydrocarbon reduction of TVRU. 5

FGRU: The estimated carbon credits from FGRU amounts to 97400 units of CO2 equivalents per year. It makes Uran Plant a zero gas flaring complex. The compressor is designed in a way that it is capable of handling gases of molecular weight 19.5 to 36.2. The Typical flare gas composition from FGRU from is given in Fig 7.

Fig 7: Composition of Flare gas. Road ahead Environmental Management System also envisages inclusion of the Plasma Thermal Destruction & Recovery (PTDR) for solid waste management. It is ideal for disposing any form of mixed plant wastes including e-wastes (no segregation required) in environmentally benign manner. The syn gas produced in this process will be utilized in power generation. The plant will have the capacity for processing of solid waste 1000kg/day and the volume reduction of the waste is to the tune of 200:1. Schematic process description of PTDR is shown in Fig 8.

Fig 8: Schematic Diagram of PTDR Unit. PTDR Process: Waste + Plasma Æ Vitrified slag + Syn. gas. Input waste: Tank bottom sludge, ETP Sludge, Other Hazardous waste like wool, batteries & plastic. 6

Output: Synthesis gas + Residue. 4. Conclusion TVRU is one of the milestone achievements of at ONGC Uran Plant in terms of further reduction of the carbon foot print. This effort also yields cash flow to the company. FGRU is functioning to achieve zero hydrocarbon emissions, and it is enabling to minimize the wastage of precious natural resources. GHG Pilot exercise has already been carried out and identification of potential CDM projects is in progress. Installation of BERMAD valve is yielding good results in terms of preventing hydrocarbon escape into the effluent and thus reducing the organic matter load into it. These initiatives help to cater the emerging landscape in EMS. The above efforts serve as a tool to improve environmental performance and systematic way of managing an organization’s environmental affairs. Acknowledgements Authors extend sincere thanks to Executive Director Plant Manager, Uran for lending encouragement and guidance in preparation of this paper. Thanks are also due to Mr. D. S. Sastry, DGM(P) and Ms. Varsha Boddu AEE(P) for their valuable suggestions. References [1] Birnur Buzcu-Guven, Gas Flaring and venting: Extent, Impacts and remedies, Sep 2010. [2] Environmental Management Systems: A Step-by-Step Guide to Implementation and Maintenance, Christopher Sheldon, Mark Yoxon, Third addition, 2006. [3] EPA-430-F-09-021R, 40 CFR 98, subpart Y, November 2011. [4] The website of US Environment Protection Agency.

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Selection of suitable metallurgy for tube/tube sheets of heat exchangers of LPG 1st, 2nd and 3rd stage IHI compressor of Uran plant - A case study+ S. A. Fazal1*, Subrahmanya Bhat2, Bipin Kumar3 Oil and Natural Gas Corporation, Uran Plant, Uran, India. 2-3 Institute of Engineering and OceanTechnology, ONGC Complex, Panvel, India. E-mail: 1*[email protected] * Author for correspondence. 1*

Extended abstract: Oil and gas produced from Western Offshore fields is received at Uran terminal through sub sea pipelines. The major facilities at Uran include LPG units (LPG I & II), crude stabilization units (CSU), gas sweetening units (GSU), condensate fractionating Units (CFU I & II) and C2-C3 recovery unit. Cooling water as associated utilities is required for process exchangers. Heat exchangers using cooling water as cooling media are used for cooling hydrocarbons either for condensation or lowering temperature for process requirements The crude oil from offshore is subjected to crude stabilization unit (CSU) at Uran Plant and the stabilized crude oil is sent to storage tanks, while the separated gas i.e. CSU off gas is subjected to compression to 54kg/cm2 in three stages before it is sent to GSU. The compressed gas after each stage passes through intercooler and after cooler heat exchangers. The Heat Exchangers (E-207A, E-206, etc.) engaged for CSU off gas are shell and tube type exchanger with floating tube bundle. The fluid in contact with the shell side as well as external surface of the tubes is CSU off gas which is sour and the fluid in contact with the tube internal surface is cooling water. At LPG-I & LPG-II units, propane vapor from propane compressor discharge is condensed in propane refrigerant condenser i.e. Heat Exchangers E-112 Series, and E-512 Series respectively. These heat exchangers are shell and tube with fixed tube type. Frequent choking and scaling in the tube, tube to tube sheet joint leakages and tube leakage have been observed in the recent past affecting the productivity of LPG Plants. The choking and scaling has to be cleared by hydro jet cleaning and the tube leakage is arrested by plugging. All these resulted in the requirement of complete replacement of tubes and tube sheets of heat exchangers within 2 to 3 years. In view of the above problems experienced in Heat Exchangers it was decided to undertake a systematic study for selection of suitable metallurgy for tubes/tube sheets of Heat Exchangers. This study was carried out to identify suitable material of construction which shall provide long term solution to the problem of corrosion. Laboratory investigations on the currently in use MOC has been carried out to assess its susceptibility to corrosion as well as its material integrity. In this technical paper various issues related to material selection for Heat Exchangers under different hydrocarbon environment has been deliberated. The scaling tendencies of the cooling water samples have been evaluated by running the software – “SCALE CHEM” based on Langelier scaling index. Energy Dispersive X-Ray Spectroscopy (EDS or EDX) - a chemical microanalysis technique, in conjunction with scanning electron microscopy (SEM) is used to quantitatively characterize the elemental composition of the corrosion product/ scale on the tube surface.

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EDS analysis of corrosion product samples collected from internal side shows the predominant presence of iron, oxygen, silicon and chloride. The EDS of the external side shows the significant presence of sulphides along with oxides. The source of sulphide is from the CSU off gas, which has about 500ppm of hydrogen sulphide. EDS study was also carried out on the corrosion products collected from the end cover box. The surface features of the failed tubing sample was observed under the stereomicroscope and has revealed deep pitting corrosion attack mostly on the external side of the tube of E-207A Heat Exchanger. A sample of the corroded tube was studied under scanning electron microscope coupled with EDS for their topographical features. The specimens were scanned at various magnifications. SEM studies for the etched transverse section of the specimen tubing showed shallow round edge pits, along the surface. Gravimetric corrosion studies were also carried out by immersion test on the metal coupons prepared from the heat exchanger tube specimen and the coupons were exposed to cooling water. The susceptibility of Heat Exchanger tube material to corrosion on exposure to cooling water is significant and the corrosion rate calculated. From the composition of CSU off gas, partial pressures of carbon dioxide and hydrogen sulphide are calculated and by using the nomogram NACE MR0175/ISO15156 standard in situ pH is determined. Further from the nomogram, severity grade of the corrosion with respect to sulphide stress cracking corrosion has been evaluated. As per the guidelines of NACE MR0175/ISO15156 standard, suitable material of construction (MOC) for tube and tube sheet is Martenisitic stainless steel conforming toUNS S41000 In the case of heat exchangers at LPG Unit I & II, the fluid in contact with the shell and external surface of the tubes is Propane gas and is non corrosive to carbon steel. The scaling tendencies of the water samples by the software – “SCALE CHEM” have shown positive signs of scale formation predominantly of CaCO3. The tendency to form scales by cooling water is confirmed by SEM-EDS studies of the surface of tube. The cooling water flow velocity in the Heat Exchanger tubes is found to be less than the desired optimum velocity of 2m/sec to 3m/sec range. Lower than the desired velocity leads to accumulation of deposits along the tube and thereby facilitate the under deposit crevice corrosion. The X-RD Diffractometric analysis report of corrosion product/deposit samples( wet and dry ) collected from the tubes/tube sheets of Heat Exchangers of LPG I & II-Uran Plant shows predominant presence of Magnetite (Fe3O4).SEM – EDS study on the fresh unused specimen of heat exchanger tube E-112/E-512 revealed presence of micro voids in the matrix as well as internal surface. These sites are prone to localized pitting under deposits. The currently in use material of construction of Heat Exchanger tubes is found to be carbon steel conforming to specifications SA 179. As per the Indian standard “Treatment of water for cooling towers – code of practice – IS 8188:1999, material of construction for heat exchangers at LPG plant is mainly carbon steel. The process at LPG unit I & II at Uran falls under the category of petroleum and related processing applications and hence TEMA class R category heat exchanger is to be used. The currently in use material of construction viz: SA 179 (cold drawn) is adequate as MOC for the tube, SA 266M grade II for tube sheet, and SA 516 M grade 485 for Shell for the heat exchangers at LPG I & II units. The most suitable and economical selection of metallurgy for non-corrosive process fluid and cooling water media is carbon steel. In special cases, based on process fluid corrosivity similar to the present case of IHI third stage exchanger, higher grade MOC suitable for the process fluid are selected in construction of the exchangers.

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Microbial degradation of paraffins: A review N. Sakthipriya1, M. Doble2, Jitendra S. Sangwai3* 1 and 3 Department of Ocean Engineering, IIT Madras, Chennai, India. 2 Department of Biotechnology, IIT Madras, Chennai, India. E-mails: [email protected]; [email protected]; 3*[email protected] * Author for correspondence. Abstract: This report presents the review of the degradation of paraffins using microbes. In the increasing demand for oil and gas, wax deposition plays the major role in oil reservoirs. Deposition of long chain paraffins on the inner walls of the pipelines tends to decrease the crude flow and increase the power required for pump and consequently plugs the line. Different techniques are employed to overcome the wax deposition. Microbial or biodegradation is eco friendly and economically feasible with respect to other techniques involved. Degradation of paraffin is widespread phenomenon in nature. Bacteria can utilize the paraffin substrate as carbon and energy source and grow under either aerobic or anaerobic conditions. Key words: Microbial degradation; paraffin; wax deposition. I. Introduction In the current scenario, wax deposition plays a major role in the oil reservoirs. Crude oil contains significant amount of wax that can crystallize the pipeline. The solubility of wax is decreasing function of temperature [1]. At high temperature, crude oil is a simple Newtonian fluid but when the temperature is reduced due to crystallization the flow property of the crude oil change from Newtonian to very complex Non-Newtonian behavior [2]. The waxes usually contain paraffin range from C18H38 to C40H82, have the tendency to crystallize as the equilibrium temperature and pressure is reached. The wax crystals have the tendency to increase the viscosity. When the temperature is below cloud point/WAT (Wax Appearance Temperature) i.e. the temperature at which the haziness starts appearing on the pipeline, can lead to gelling, which inhibits the flow by causing Non-Newtonian behavior, and increasing the viscosity as the temperature reaches its pour point [3]. Cloud point temperature is decreased by decreasing the apparent molecular weight and the hence the wax precipitation also delayed [4]. Paraffin is deposited throughout the production stream due on one hand to the lowering of the system temperature below the oil pour point and on the other hand to the broken down of the solution [5]. Several methods have been followed to remove the paraffin deposition, including chemical, mechanical and thermal methods [6]. Some of the Chemical methods are solvents, dispersants, surfactants, and wax crystal modifiers [7]. Solvents have the ability to dissolve only a fixed amount of paraffin. Dispersants will break paraffin deposits into smaller particles instead dissolving them and are generally more cost effective than solvents. Surfactants break up the deposits decreases the capillary force and prevent them from reagglomeration. Thermal methods usually involve hot oiling the well tubulars and flow lines regularly. Mechanical methods commonly employed are scrapers conveyed by wire line, sucker rods, and work strings. Microbial treatment will control the paraffin molecule by generating by-products, which act as surfactants and paraffin solvents. The cracking of long chain paraffin will increase the API gravity and lower the cloud point. The bio-production of surfactants and solvents enables the fluid to solubilize the paraffin fractions and

remove paraffin-based skin damage from the well bore. Bio surfactant molecules decrease surface tension, critical micelle concentration and interfacial tension in both aqueous solution and hydrocarbon mixture [8]. Most hydrocarbon compounds exhibit high homolytic and heterolytic dissociation energies of their C-H and C-C bonds and weak chemical reactivity [9]. This report focuses the review of the degradation of paraffins using microbes 2. Wax deposition mechanism The wax crystals have the tendency to increase the viscosity. Paraffin is deposited throughout the production stream due to the lowering of system temperature below the oil pour point [10]. Mostly wax deposition models consider molecular diffusion as the dominating mechanism, but there is some other studies which showed the impact of shear dispersion mechanism [11]. Molecular diffusion occurs automatically when the temperature of the wall reaches the WAT, where the oil gets saturated with wax in solution and wax precipitates out and leads to a concentration gradient between dissolved wax in the turbulent core and the wax remaining in the solution at the wall. Hence, dissolved wax diffuse towards the wall where it is later precipitated [12].

Figure 1: Wax deposition by molecular diffusion [13]. Shear dispersion deals with already formed particles settling on the cold pipe surface due to roughness of the wall and intermolecular forces [14]. Shear dispersion is the controlling mechanism at low temperature and low heat fluxes [15]. 3. Biodegradation Biodegradation is the process by which organic substances are broken down into smaller compounds by living microbial organisms. The microorganisms are used for the reduction of oil viscosity [16]. The metabolism of microbial degradation is biodegradation and production of chemicals like organic fatty acids biosurfactants, alcohols, acetone, ether and gases [17]. The movement of bacteria in well fluids enhances their effectiveness in the breakup of paraffins. The crystallization temperature of wax plays an important role in wax precipitation. Cloud point temperature is the function of solute and solvent weight fraction. The final product of the degradation is carbon dioxide or methane. Organic material can be degraded aerobically, with oxygen, or anaerobically, without oxygen. Crude oil degradation involves systematic reactions producing intermediate compounds, which can be utilized by different group of organism resulting in further degradation [18]. Microorganism used for the degradation should be hydrocarbon utilizing and non pathogenic. The by- products are alcohols gases, acids, biosurfactant and polymers [19]. The biodegradability of crude oil has been investigated in batch cultures [20]. The chemical inertness of carbon – carbon bonding can reduce the biodegradation of hydrocarbon in the absence of molecular oxygen. The microorganism capable of anaerobic degradation of hydrocarbon must develop biochemical reactions independent of oxygen [21]. 12

5. Microbial metabolism of long-chain alkanes Two pathways have been proposed for the oxidation of long chain n-alkanes. 1) The monoterminal oxidation pathway yielding an alcohol intermediate which is oxidized further to an aldehyde and then to an acid. The monoterminal oxidation yielding a n-alkyl hydroperoxide which is then converted to a peroxy acid, an aldehyde and finaily to an acid.[29]. The n-alkane undergoes an oxygen-dependent oxidation to an alcohol catalyzed by a monooxygenase. The alcohol is then oxidized by an alcohol dehydrogenase to an aldehyde. Then, an aldehyde dehydrogenase transforms the aldehyde to a fatty acid. The fatty acid finally undergoes β oxidation during which two carbons are cleaved from the organic acid to give acetyl-CoA and a fatty acidCoA two carbon units shorter than the initial n-alkane. Three different types of induced aldehyde dehydrogenases (NADP+ and NAD+ dependent and nucleotide independent) and 2 different types of constitutive alcohol dehydrogenases have ken identified (NADP' and NAD' dependent)[22]. The aldehyde dehydrogenases have been found associated with hydrocarbon vesicles and bound to the cytoplasmic membrane with the active center of the enzyme in the direction of the periplasmic space. This suggests that there could be two separate destinations for the products such as p-oxidationand wax ester synthesis by aldehyde reductases [23]. The second pathway not involving alcohols intermediate was proposed by Fimerty in 1962. The n-alkane is first oxidized to an n-alkyl hydroperoxide by a dioxygenase. The n-alkyl hydroperoxide is sequentially converted to a peroxy acid, then to an aldehyde and finally to a fatty acid before undergoing p-oxidation [24]. The dioxygenases isolated thus far were found in the cytoplasm of bacteria and did not need anyenzymes. When grown in the presence of long chain hydrocarbons (hexadecane and up), they were more active toward solid than liquid n-alkane. 6. Types of degradation 6.1 Aerobic degradation Important parameter in the microbial degradation of hydrocarbons is the presence or absence of oxygen. Aerobic degradation is the breakdown of organic contaminants by microorganisms in the presence of oxygen. Aerobes use oxygen to oxidize substrates in order to obtain energy. Before cellular respiration begins, glucose molecules are broken down into two smaller molecules. The aerobic activation involves monooxygenase and dioxygenase enzymes. Aerobic, unlike anaerobic digestion, does not produce the pungent gases. During the aerobic oxidation of hydrocarbon, oxygen acts as a terminal electron acceptor and activates the substrate [25]. During reoxidation the fixed carbon is withdrawn photosynthetically by the bacteria and recycled into the inorganic pool giving rise to the oxic atmosphere. 6.2Anaerobic Biodegradation Anaerobic digestion occurs when the anaerobic microbes are dominant over the aerobic microbes. Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. The digestion process begins with bacterial hydrolysis of the input materials in order to break down insoluble organic polymers such as carbohydrates and make them available for other bacteria. Acetogen then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acid. Acetogenic bacteria then convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Methanogen finally are able to convert these products to methane and carbon dioxide. There are four key biological and chemical stages of anaerobic digestion, which are Hydrolysis, Acidogenesis, Acetogenesis and Methanogenesis. The biological breakdown of hydrocarbons in absence of oxygen involves bacteria conserving energy by various metabolic processes, such as chemotrophy and photo trophy. Until now, the pure bacteria responsible for degradation of aliphatic hydocarbons under methanogenic conditions have not been isolated [12]. There are only few reports in the literature are dealing with pure bacterial strains to degrade hydrocarbons as components in a complex hydrocarbon mixture under anaerobic condition [26]. The biological agent present under anoxic conditions exhibits the properties of oxygen involved during the aerobic activation of hydrocarbon [38]. Anaerobic alkane metabolism is induced only in cells grown on alkane and the enzymes clearly substrate induced [27]. 13

7. Conclusion This paper reviewed the aerobic and anaerobic microbial degradation of alkanes as a solution to prevent wax deposition in bore well and pipelines and increase flow assurance. This process has the ability to change the physical and chemical properties of the crude oil and decrease organic nitrogen and sulfur. The qualitative and quantitative changes in the crude oil depend on microbial species and the chemistry of crude oil. Surface tension, interfacial tension and viscosity are the major factors that are influenced by the microbial degradation of paraffins. The cracking of long chain paraffin by microbes will increase the API gravity and lower the cloud point. Bio-surfactants, produced during this process will solubilize the waxy portion and thereby reduce the interfacial tension and decreases the viscosity. Reference 1 Azevedo L.F.A. & Teixeira A.M., (2003), Acritical review of the modeling of wax deposition mechanisms, Petroleum science and technology, Vol.21 393-408. 2 Farina.A and Fasano.A, (1997), Flow characteristic of waxy crude oils in laboratory experimental loops, Mathematical Computational Modeling, Vol.25 75-86. 3 Aiyejina.A, Chakrabarti.DP, Pilgrim.A, Sastry.M.K.S., (2011), Wax formation in oil pipelines: A Critical review, International Journal of Multiphase Flow, Vol.37 671-694. 4 Sadeghazad.A, Gghaemi.N, (2003), Microbial prevention of wax precipitation in crude oil by biodegradation mechanism, Society of Petroleum Engineers, 80529 1-11. 5 Lazar I, Voicu A, Nicolescu C, Mucenica D, Dobrota S, Petrisor IG, Stefanescu M, Sandulescu L, (1999), The use of naturally occurring selectively isolated bacteria for inhibiting paraffin deposition. J Pet Sci Eng,Vol. 22, 161–169 6 Mehboob, F., Junca, H., Schraa, G., Stams, A., (2009), Growth of Pseudomonas chloritidismutans AW-1T on n-alkanes with chlorate as electron acceptor. Applied Microbiology and Biotechnology, Vol. 83 739-747. 7 Etoumi.A, El Musrati.I, El Gammoundi.B, El Behlil.M, (2008), The reduction of wax precipitation in waxy crude oils by Pseudomonas species, Journal of Petroleum Science and Engineering, Vol. 35 12411245. 8 Barker. K.M., (1989), Formation damage related to hot oiling, Society of Petroleum Engineers 16230 371-375. 9 Banat, M., Samarh, N., Murad, M., Horne, R., Banerjee, S., (1991), Biosurfactants production and use in oil tank clean up.World J.Micro. Biotehnol. Vol. 7 80–88. 10 Etoumi, (2007), Microbial treatment of waxy crude oils for mitigation of wax precipitation, Journal of Petroleum Science and Engineering, Vol.55 111-121. 11 Akbarzadeh K. and Zougari M., (2008), Introduction to a Novel Approach for Modeling Wax Deposition in Fluid Flow. 1. Taylor-Couette System, American Chemical Society 12 Bern, P.A., Withers, V.R. and Cairns, J.R., (1981), Wax deposition in crude oil pipelines, Proc European Offshore Petroleum Conference and Exhibition, London, England, 13 Aske N., (2007), Wax- A Flow Assurance Challenge, powerpoint presentation prepared for presentation at NTNU, Trondheim, 14 Burger E.D., Perkins T.K. and Striegler J.H., , (1981), Studies of wax deposition in the Trans Alaska Pipeline 15 Gjermundsen, I., (2003), A model for wax deposition in offshore pipelines, Porsgrunn, 16 Karrick, N.L., (1977), Alteration in petroleum resulting from physical– chemical and microbiological factors. In: Malins, D.C. (Ed.), Effects of Petroleum on Arctic and Subartic Environments and Organisms. In: Nature and Fate of Petroleum, Academic Press, Inc., New York, Vol. 1225–299. 17 Venosa A.D., Zhu X., (2003), Biodegradation of crude oil contaminating marine sharelines and freshwater wetlands, Spill Science and Technology Bulletin, Vol.8 163-178. 18 Joseph G.Leahy and Rita R.Colwell, (1990), Microbial degradation of hydrocarbons in the environment, Microbiological Reviews, Vol.54 305-315. 14

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Atlas R.M. and Bartha R., (1972), Biodegradation of petroleum in sea water at low temperatures, Canadian journal of microbiology, Vol.18 1851-1855. Sakai Y, Maeng JH, Tani Y, Kato, (1994) N,Use of long-chain nalkanes (C13–C44) by an isolate, Acinetobacter sp. M-1. Biosci Biotechnol Biochem,Vol. 58 2128–2130 Kunihiro N, Haruki M, Takano K, Morikawa M, Kanaya S, (2005) ,Isolation and characterization of Rhodococcus sp. strains TMP2 and T12 that degrade 2,6,10,14-tetramethylpentadecane (pristane) at moderately low temperatures. J Biotechnol, Vol. 115 129–136 Heider J, Spormann AM, Beller HR, Widdel F., (1999), Anaerobic bacterial metabolism of hydrocarbons. FEMS Microbiol Rev, Vol. 22 459–73. Fukui M., Harms G., Rabus R., Schramm A., Widdel F., Zengler K., Boreham C., Wilkes H., (1999), Anaerobic degradation of oil hydrocarbons by sulfate reducing and nitrate reducing bacteria, Proceedings of the international symposium on microbial ecology, Canada, Mimmi Throne-Holst, (2007), Bacterial metabolism of long-chain n-alkanes, Applied Microbiol Biotechnology, Vol.76 1209–1221. Grishchenkov.V.G, Townsend. R.T, McDonald.T.J, Autenrieth.R.L, Bonner.J.S, Boronin. A.M, (2000), Degradation of petroleum hydrocarbons by facultative anaerobic bacteria under aerobic and anaerobic conditions, Process Biochemistry, Vol. 35 889–896. Aeckersberg F, Rainey FA & Widdel F, (1998), Growth, natural relationships, cellular fatty acids and metabolic adaptation of sulfate-reducing bacteria that utilize long-chain alkanes under anoxic conditions, Archives oj Microltiology, Vol. 170 361-369 Callaghan, A.V., Tierney, M., Phelps, C.D., Young, L.Y., (2009), Anaerobic biodegradation of nhexadecane by a nitrate-reducing consortium. Applied and Environmental Microbiology 75 13391344.

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E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012), December 6-8, 2012. Volume 2: NSPSE 2012 Editors: R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian ISBN: 978-93-80689-13-5, Copyright © 2012 by the Indian Institute of Technology Madras, Chennai (TN) 600 036, India. _____________________________________________________________________________________________

Performance analysis of a centrifugal impeller used for crude oil pumping Sayed Ahmed Imran1, Abdus Samad2* 1-2 Department of Ocean Engineering, IIT Madras, Chennai, India. E-mails: [email protected]; 2*[email protected] * Author for correspondence. Abstract: This paper is aimed at performance analysis of centrifugal pump impeller to pump crude oil, water and saline water using numerical technique. A three-dimensional flow simulation using Reynolds Averaged Navier Stokes (RANS) equations for the performance analysis of the impeller is carried out after designing the geometry of the impeller by first principle. Standard k-ε two equation model was used for the turbulent closure of steady incompressible flow. Several simulations were done to validate the result with existing work and to analyze the flow field. Investigations show that, the viscosity and density has a significant influence on pump efficiency and power consumption. 1. Introduction Centrifugal pump is a rotodynamic machine which increases the pressure energy of the fluid by velocity change imparted when the fluid flows through impeller. The centrifugal action of impeller blade converts mechanical energy into hydraulic energy at required height. Impeller is rotated with the aid of a motor, creating a low pressure zone at the impeller eye which results in sucking of fluid into the eye. As the impeller rotates the intake fluid is spilled out through the periphery of the impeller. Being widely used in many applications, the pump system may be required to operate over a wide flow range. In this regard, the knowledge about off-design pump performance becomes necessity. Performance analysis of pump/impeller can be studied with the help of computational fluid dynamics (CFD) simulations [1-4]. Flow characteristics like flow separation, inlet pre-swirl and circulation of fluid at outlet can be visualized clearly. To obtain, thorough performance prediction of a specific design on fluid behavior in the machine, numerical simulations is an alternate choice [2-3]. CFD analysis predicts acceptable solutions within limited time, whereas performances achieved by experiments are time consuming [3, 57]. Recently, CFD has acquired a prominent position as industrial design tool for model testing, by significantly reducing design time in a cost effective manner. The conventional design of centrifugal pump impeller requires a thorough understanding of the mechanism of flow inside the impeller and application of empirical formulae along with the usage of different standard charts. Experimental and numerical work, to study the effect of fluids viscosity on the performance of centrifugal oil pump has been reported by several authors [8-15]. The nature of flow pattern inside the impeller shows large increase in the disc friction losses over impeller, shroud and hub. It affects the slip coefficient, increases the hydraulic loss and reduces the flow through impeller [9]. Also, the existence of wide wake near the blade suction side of centrifugal impeller was explained by Li [11]. From the experimental results [10], it was shown that the flow patterns near impeller inlet were much affected by the viscosity compared to flow patterns near impeller outlet. In similar fashion, density has appreciable influence on power consumption. An increase in the density of the fluid always results in increased consumption of shaft power as these parameters are proportional with each other [9-11]. Viscosity reduces performance of impeller, by decreasing the efficiency and increasing consumption of power [11-12, 16]. Many researchers [13-15,17] conducted the experiments on centrifugal oil pumps, by taking viscosity of oil as a function of design and proposed some corrections and these corrections are used as guidelines today for design purpose [16,18]. The limitations found during pumping viscous oil

and denser fluids include decrease in efficiency and increase in consumption of energy for the same flow rate under same speed. The flow physics noticed were wide wake near blade suction side and formation of separation zone [19]. The properties which distinguish crude oil from water are viscosity and density. Crude oils have less density and more viscosity than water. The hydraulic efficiency of the impeller deteriorates with increase of fluid viscosity [19-20]. An increase in the density of the fluid always resulted in increased consumption of shaft power, as shown by Li and Xue [10] and Fard et al. [16]. In this paper, study performance of impeller at different mass flow rates, viscosity and density with constant speed for clear water, saline water and crude well oil were carried out by numerical simulations. 2. Mathematical description 2.1 Geometrical model The detail geometry of radial flow impeller corresponds to the values obtained from the conventional design procedure of impeller design as given in refs. [21-23]. Table 1 features geometric parameters of impeller. Design procedures [22-23] and the input values such as head (H), discharge (Q), and impeller speed in rpm (N) were considered for the same reference. The rotation speed and other dimensions like outer diameter of impeller (D2), outlet width of blade (b2), outlet and inlet blade angles (β2) and (β1) collectively determine the total head generated. The designed blades are of constant thickness (t) and width with trailing edge chamfered. Backward curved vanes mounted on impeller, impart whirling motion to increase the pressure energy of fluid. The following relations are used to calculate the geometrical parameters. Inlet blade angle can be calculated from the relation, (1) The breadth of impeller at inlet; (2) Peripheral velocity at outlet;

(3)

Outlet diameter; (4) Blade number; (5) Volume flow rate; (6)

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Table 1. Features of impeller Parameter Dimension Shaft diameter, Ds 40 mm Hub diameter, Dh 55 mm 160 mm Inlet diameter, D1 54 mm Inlet blade width, b1 30 mm Outlet blade width, b2 23o Inlet blade angle, β1 Outlet blade angle, β2 27o Blade number, z 7 Blade thickness, t 5 mm Outlet diameter, D2 365 mm Table 2. Viscosity and density of different fluids Fluid Viscosity Density [N-s/m2] [kg/m3] Water 1.002E-3 997 Saline-water 1.080E-3 1031 Crude-oil 5.000E-3 835 2.2 Fluid properties Three different fluids; namely water, saline-water and crude oil with their respective density and viscosity at 20oC were used in numerical computations. These liquids are Newtonian fluids. The dynamic viscosity and density for different fluids at 20oC are shown in Table 2. The density and viscosity is a function of temperature [10, 12]. As density has direct influence on power consumption [9, 11], the power consumed by the pump is determined from the relation given by Gulich [24]. (7) 2.3 Numerical formulations To understand and visualize the complex behavior of fluid inside the impeller, CFD is the alternate option and preferred over the experimental approach as the later one is expensive in terms of time and cost. Within reasonable time, the algorithms of advanced solvers perform robust and reliable solutions of flow field. Today CFD is an important tool in the disciplines of heat transfer, fluid mechanics and turbomachinery due to great advance in the development of numerical methods and computing capacity. In case of experimental investigations, large investments of man- power cost, time and space and are essential either for design of a new machine or up gradation of existing machine, with no guarantee of success. CFD tools enable faster geometry modeling and grid generation to speed up the design procedure. Modeling and meshing of the flow domain were carried out by using ANSYS-BladeGen and Turbogrid module. ANSYS-CFX 13.0 was used for the simulations. The steady, incompressible conditions were applied and RANS equations were solved for the flow analysis. At all working conditions, the fluid considered were three-dimensional, turbulent and steady time-averaged flow. The governing conservation equations involved are; Mass conservation equation, (8) Momentum conservation equation, (9) and 19

(10) The fluid flow behavior through the impeller has been predicted by Navier-Stokes equations and turbulence viscosity is computed using standard two equation (k-ε) turbulence model. Here k represents turbulence kinetic energy and ε rate of kinetic energy dissipation. To account for Reynolds number (Re>105) standard k-ε turbulence model was employed. The k-ε turbulence model is a class of RANS models to which two partial differential equations are solved, one for turbulence kinetic energy, k, and another for turbulence kinetic energy dissipation rate, ε, to get length and time scale information needed to form local eddy viscosities [25]. To design the blade profile and flow passage through impeller, point by point method has been adopted [23]. To achieve linear velocity distribution in the viscous sublayer, high number of cells are employed which is termed as linear wall function. When a logarithmic wall function is employed, a coarse resolution near wall is sufficient. In k-ε model, logarithmic wall function is used, because transport equations do not fetch meaningful values for k and ε near a solid surface. A wall bounded flow is defined by a non-dimensional wall distance y+ and it can be in the range of 30-100 [26]. Periodicity is maintained by two symmetry surfaces positioned in the middle of blade passage as shown in Fig.1. The symmetry of impeller geometry imposed to save computer capacity, and the use of periodic boundary conditions for a section of 1/z has been adopted to reduce computation time [27] where z corresponds to number of blades. Its value is 7 obtained from design [22]. Table 3 corresponds to the information pertaining to impeller simulation. The total number of nodes, elements, convergence value and iteration steps have been presented in Table 3. To capture flow behavior more accurately, meshing has been done with Ansys-Turbogrid which generates structured hexahedral elements to define inlet, outlet and flow passage zones. The mesh in the flow passage is with O-grid block and at the inlet and outlet it is with H-grid block. These grid blocks, help to account the wall shear stress and boundary layer losses accurately [28]. The meshing has been shown in Fig 1. Fine mesh at blade leading edge, trailing edge and near wall was adopted [29] for accuracy in result. For accuracy of results, adopting fine mesh at blade leading edge, trailing edge and near wall achieves considerable savings in computer cost compare to local grid refinement or higher order discretization technique [29-31]. Meridional velocity profile at leading edge and trailing edge is a function of the number of nodes [26, 32] which require fine meshing at leading edge and trailing edge. The simulation has been performed on Intel Core 2 Duo having 2.93 GHz processor and 3 GB RAM. Approximately 15 hours of CPU time was required for each case. At wetted walls the velocity no-slip condition was imposed. As the fluid in the suction tank was undisturbed and prevailing pressure was atmospheric, pressure was used as inlet condition. Mass flow rate was set as boundary condition to consider the fully developed and turbulent flow at outlet. Instead of mass flow rate if the pressure difference between inlet and outlet is prescribed, convergence problems can be encountered. It is because the mass flow can oscillate when trying to establish itself as imposed by the pressure difference. This is the reason why pressure at inlet and mass flow rate at outlet were specified [26]. At wetted walls differential of static pressure with respect to its normal is zero due to symmetry in geometry, hence Neumann type of boundary condition has been employed. As the mass flow rate is constant throughout the simulation Dirichlet type of boundary condition [16, 20] has been imposed at the outlet. Turbulence intensity for pumps was chosen to be 5% at inlet [26, 31]. Residual convergence value was set to 1x10-5 as the same criterion was imposed by other authors [26, 31]. Residuals of mass and momentum, in various control surfaces are required for checking convergence and evaluating the quality of numerical solution.

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The simulations were carried out for water, saline-water and crude well oil at different mass flow rate and constant speed. These conditions were employed to calculate the head developed, power consumed and efficiency of the impeller. In this way we could be able to determine the velocity distribution and pressure distribution through the passage between blades.

Table 3. Meshing and boundary conditions. Parameter Description Single impeller Flow domain Periodic Interface Structural/Hexahedral Mesh/Nature 634,161 Nodes 568,620 Elements Water/Saline-water Fluid nature k-ε Turbulence model Pressure Inlet Mass flow rate Outlet Residual convergence 1x10-5 value Time taken for 15 hrs simulation Iteration steps 2000 Mass imbalance 0.0003 m3/s

3 Results and discussions The flow rate, head and rotation of impeller comply with the corresponding specifications given in [22]. Simulated values for water, as fluid, found to be in good agreement with that of the analytical solutions in [22]. Also the computations were carried out at four different flow rates: 91, 100, 105 and 112 kg/s at offdesign conditions. Fig. 2 represents the performance of impeller calculated by analytical and CFD simulations. The validation for water at design point shows a discrepancy of about 9% between the analytical and predicted numerical impeller power. This result is similar to that of the others [31, 33]. 21

Accounting the dominance of body forces, blade kinematics, level of hydraulic impeller efficiencies, considering the statistical distribution of different numerical and modeling error it is accepted that a difference of about 10% result between CFD and analytical is allowed [26]. Power predicted by CFD is greater than the analytical results and this is due to the head predicted by the CFD simulations, which is greater than analytical results [33]. The increase in flow rate results in greater consumption of power by the impeller. The density of crude oil is lesser than water and saline water which causes the least consumption of impeller power [26]. To find the effect of density and viscosity [26, 34-35] on the performance of pump, properties of water with 3.5% salinity and crude well oil was used. Characteristic curves for clear water, saline water and crude well oil have been shown in Fig 3 (a, b and c) at design and off-design conditions. The power-input for pump handling saline-water and crude oil are higher than those for normal water, but the hydraulic efficiency for handling crude-oil and saline-water is lower than that for handling water. The decrease in efficiency, while pumping the crude oil and saline-water is due to the disc friction losses over the outsides of the impeller shroud and hub. These results show a good agreement with the results of Li [20] and Gulich [26]. Pressure and velocity distribution at between impeller vanes at 100 kg/s for normal water, saline-water and crude oil are shown in Fig. 4. The pressure contours represents a smooth flow between the blades and its value increases continuously towards the exit of the computational domain. The fig depicts that the lowest static pressure observed at the impeller inlet on suction side. At this location in centrifugal impeller cavitation usually appears. Here it is above saturation pressure of liquid; hence occurrence of cavitation is ruled out [27]. The highest static pressure occurs at the impeller outlet and the kinetic energy of flow reaches to maximum extent. This is due to the pressure which increases continuously as the mechanical energy given in the form of impeller rotation is converted into the pressure energy. Minimum pressure exists at the suction side and near the leading edge of the blade.

Fig. 2: Result validation for normal water.

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a)

H vs Q

b)

P vs Q

c) η vs Q Fig. 3: Characteristic curves for normal water, saline water and crude oil at 1470 rpm.

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Fig. 4: Pressure and velocity contours at 50% span for 100 kg/s. Fig. 4 shows the relative velocity of fluid between blade passages. The relative velocity in blade channel has a smooth distribution and declines from inlet to outlet. This agrees the analytical results; as fluid flows from inlet to outlet of the impeller, the relative velocity decreases [22]. As the viscosity of the fluid increases the hydraulic efficiency decreases. This is due to decelerated flow in the impeller and increase in friction loss through flow passage over impeller surfaces. Viscous fluids have high internal resistance for flow which results in increase in frictional losses and the disk friction is larger [26]. Denser fluids consume more energy than normal water. This is evident from Fig 3 (b and c).

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Fig. 5: Meridional velocity contours at different mass flow rate for water. Power supplied by the motor at impeller shaft, is the input power obtained by the product of torque acting on impeller and rotation of impeller. Torque comes into picture due to the resultant of pressure and viscous moments acting on impeller. It is obvious that increase in mass flow rate increases the torque acting on impeller and hence power consumption increases. From Fig. 3 it is evident that, increase in flow rate leads to decrease in head and hydraulic efficiency with increase in consumption of power [6]. Velocity of fluid in the impeller has significant effect on pressure variation. By varying mass flow rate, at off-design points a variation in the velocity has been observed shown in Fig. 5. Increase in mass flow rate causes an increase in meridional velocity from inlet to outlet and efficiency decreases consequently. This is obvious from relation (6) [22]. Blade loading at 20 percent span location for different fluids has been shown in Fig. 6. Blade loading chart exhibits the pressure difference between the pressure and suction side. This is due to, increase in static pressure of the incoming flow by diffusion of relative velocity and centrifugal action by impeller. From Fig. 6 it can be observed that, the pressures on both sides of the blade are crossing each other at 97 percent streamwise location near trailing edge. This crossing of pressure is unfavorable to the blades [28]. The pressure on suction side of blade leading edge is more for denser fluid as it is reflected from Fig. 6 (a and b). It is because of density which has direct impact on pressure and as the viscosity increases in Fig. 6 (c) the load on pressure side near leading edge decreases. 4 Conclusions Centrifugal pump impeller performance has been evaluated by numerical simulations for three different fluids. Minimum static pressure has been observed at the suction side near the blade leading edge; whereas the highest static pressure has been observed at the impeller outlet. Relative velocity of the fluid was found to be decreasing from inlet to exit of impeller. An increase in the density of fluid results into increased consumption of power. 25

(a) 20% span

(b) 50% span

(c) 80% span Fig. 6: Blade loading curves at different spans. The increase of viscosity of the fluid causes greater disc friction losses over the outside of the impeller shroud and hub. This results in decreased hydraulic efficiency of the impeller. An increase in the discharge value leads to formation of decreased low velocity zone on the impeller. Increase in the viscosity leads to decrease in the load on pressure side near leading edge. In case of crude oils having high viscosity and density, the consumption of power is more and hydraulic efficiency is low. Nomenclature Symbols Description A Area B Width of blade b Blade width 26

Cp cm D fi g H N Pu Q t U Uj z β δij ε η k µ ρ τij

Pfleiderer’s correction factor Meridional velocity Diameter Body force Acceleration due to gravity Head generated Speed of impeller in rpm Power consumed by the pump Volume flow rate Blade thickness Peripheral velocity Three dimensional velocity vector Blade number Blade angle Kronecker delta Rate of kinetic energy dissipation Hydraulic efficiency Turbulence kinetic energy Dynamic viscosity Density of fluid Viscous stress tensor

Subscripts 1 2 b h im s th

Inlet Outlet Bulk Hub Impeller Shaft Theoretical

5 Acknowledgement Abdus Samad acknowledges Indian Institute of Technology Madras for the new faculty SEED grant to conduct this research. References [1] W. Zhou, Z. Zhao, T. S. Lee and S. H. Winoto (2003), “Investigation of Flow Through Centrifugal Pump Impellers Using Computational Fluid Dynamics”, International Journal of Rotating Machinery, Vol. 9, no. 1, pp. 49-61. [2] Y. Zhang, X. Zhou, Z. Ji and C. Jiang (2011), “Numerical Design and Performance Prediction of Low Specific Speed Centrifugal Pump Impeller”, International Journal of Fluid Machinery and Systems, Vol. 4, no. 1, pp. 133-139. [3] B. Jafarzadeh, A. Hajari, M. M. Alishahi and M. H. Akbari (2011), “The Flow Simulation of a LowSpecific-Speed High-speed Centrifugal Pump”, Applied Mathematical Modelling, Vol. 35, no. 1, pp. 242-249. [4] M. Asuaje, F. Bakir, S. Kouidri and R. Rey (2004), “Inverse Design Method for Centrifugal Impellers and Comparison With Numerical Simulation Tools”, International Journal of Computational Fluid Dynamics, Vol. 18, no. 2, pp. 101-110. [5] J. S. Anagnostopoulos (2006), “Numerical Calculation of the Flow in a Centrifugal Pump Impeller Using Cartesian Grid”, Proc. 2nd WSEAS International Conference on Applied and Theoretical Mechanics, 20-22 Nov., Venice, Italy, pp. 124-129. [6] S. R. Shah, S. V. Jain and V. J. Lakhera (2010), “CFD Based Flow Analysis of Centrifugal Pump”, Proc. 37th National & 4th International Conference on Fluid Mechanics and fluid Power, 16-18 Dec., IIT Madras, Chennai, pp. 1-10. [7] B. Lakshminarayana (1991), “An Assessment of Computational Fluid Dynamic Techniques in the Analysis and Design of Turbomachinery”, The 1990 Freeman Scholar Lecture, ASME Journal of Fluids Engineering, Vol. 113, no. 1, pp. 315-352. [8] W. G. Li (1996), “LDV Measurements and Calculations of Internal Flows in the Volute and Impellers of a Centrifugal Oil Pump”, Fluids Machinery, Vol. 22, no. 2, pp. 18-29.

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[9] W. G. Li and Z. M. Hu (1997), “An Experimental Study on the Performance of Centrifugal Oil Pump”, Fluids Machinery, Vol. 25, no. 2, pp. 3-7. [10] W. G. Li and D. S. Xue (1998), “LDV Measurement of Viscous Flow in a Centrifugal Pump Impeller”, Chinese Journal of Mechanical Engineering, Vol. 34, no. 6, pp. 97-101. [11] W. G. Li (2000), “Effects of Viscosity on the Performance of a Centrifugal Oil Pump and the Flow Pattern in the Impeller”, International Journal of Heat and Fluid Flow, Vol. 21, no. 2, pp. 271-275. [12] W. G. Li and D. S. Xue (2000), “Measurement of Viscous Oils Flow in a Centrifugal Pump Impeller”, Chinese Journal of Mechanical Engineering, Vol. 36, no. 3, pp. 33-36. [13] A. J. Stepanoff (1940), “Pumping Viscous Oils with Centrifugal Pumps”, Oil and Gas Journal, no. 4. [14] N. Telow (1942), “A Survey of Modern Centrifugal Pump Practice for oilfield and Oil Refinery Services”, The Institution of Mechanical Engineering, Vol. 3, no.121. [15] A. T. Ippen (1946), “The Influence of Viscosity on Centrifugal Performance”, Trans ASME, Vol. 68, no. 8, pp. 823-830. [16] M. H. S. Fard, F. A. Boyaghchi and M. B. Ehghaghi (2006), “Experimental Study and ThreeDimensional Numerical Flow Simulation in a Centrifugal Pump when Handling Viscous Fluids”, IUST International Journal of Engineering Science, Vol. 17, no. 3-4, pp. 53-60. [17] S. Itaya and T. Nishikawa (1960), “Studies on the Volute Pumps Handling Viscous Fluids”, Bulletin of JSME, Vol. 26, no. 162, pp.202-212. [18] A. H. Hammoud, K. C. Yassine and M. F. Khalil (2010), “Effect of Oil-in-Water Concentration on the Performance of Centrifugal Pump”, Proc. ICFD 10:, Tenth International Congress of Fluid Dynamics, 16-19 Dec., Ain Soukhna, Red Sea, Egypt, pp. 1-9. [19] W. G. Li (2000), “Effects of Viscosity of Fluids on Centrifugal Pump Performance and Flow Pattern in the Impeller”, International Journal of Heat and Fluid Flow, Vol. 21, no. 1, pp. 207-212. [20] W. G. Li (2008), “Numerical Study on Behavior of a Centrifugal Pump When Delivering Viscous OilsPart1: Performance”, International Journal of Turbo and Jet Engines, Vol. 25, pp. 61-79. [21] A. J. Stepanoff (1964), “Centrifugal and Axial Flow Pumps”, John Wiley and Sons inc., 2nd Edition, New York. [22] S. Lazarkiewicz and A. T. Troskolanski (1965), “Impeller Pumps”, Pergamon Press Ltd., 1st Edition, Oxford, London. [23] A. H. Church (1972), “Centrifugal Pump and Blowers”, John Wiley and sons, Inc., 1st Edition, New York. [24] J. F. Gulich (1999), “Pumping Highly Viscous Fluids with Centrifugal Pumps-Part 1”, World pumps 395, pp. 30-34. [25] D. C. Wilcox (1994), “Turbulence Modeling for CFD”, DCW Industries, Inc., 2nd Edition, La Canada, California. [26] J. F. Gulich (2010), “Centrifugal Pumps”, Springer Publications, 2nd Edition, Berlin. [27] M. Gupta, S. Kumar and A. Kumar (2011), “Numerical study of pressure and velocity distribution analysis of centrifugal pump”, International Journal of Thermal Technologies, Vol.1, no.1, pp. 117-121. [28] J. Desai, V. Chauhan, S. Charnia and K. Patel (2011), “Validation of Hydraulic Design of a Metallic Volute Centrifugal Pump using CFD”, The 11th Asian International Conference on Fluid Machinery and 3rd Fluid Power Technology Exhibition, 21-23 Nov., IIT Madras, Chennai, pp. 1-8. [29] K. H. Wu, B. J. Lin and C. I. Hung (2008), “Novel Design of Centrifugal Pump Impellers Using Generated Machining Method and CFD”, Engineering Applications of Computational Fluid Mechanics, Vol. 2, no. 2, pp. 195-207. [30] J. S. Anagnostopoulos (2009), “A Fast Numerical Method for Flow Analysis and Blade Design in Centrifugal Pump Impellers”, Computers and Fluids, Vol. 38, pp. 284-289. [31] S. P. Usha and C. Syamsundar (2010), “Computational Analysis on Performance of a Centrifugal Pump Impeller”, Proc. 37th National and International Conference on Fluid Mechanics and Fluid Power, 16-18 Dec., IIT Madras, Chennai, India, pp. 1-10. [32] M. Asuaje, F. Bakir, S. Kouidri, F. Kenyery and R. Rey (2005), “Numerical Modelization of the Flow in Centrifugal Pump: Volute Influence in Velocity and Pressure Fields”, International Journal of Rotating Machinery, Vol. 3, pp. 244-255. [33] K. Patel and N. Ramakrishnan (2006), “CFD Analysis of Mixed Flow Pump”, International ANSYS Conference Proceedings. [34] C. H. Liu, C. Vafidis and J. H. Whitelaw (1994), “Flow Characteristics of Centrifugal Pump”, ASME J. of Fluids Eng. Vol. 116, pp. 303-309. [35] A. J. C. Paterson (2004), “High Density Slurry and Paste Tailings Transport System”, International Platinum Conference ‘Platinum Adding Value’, The South African Institute of Mining and Metallurgy, pp. 159-165.

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E-proceedings of the second International Conference on Drilling Technology 2012 (ICDT-2012) and the first National Symposium on Petroleum Science and Engineering 2012 (NSPSE-2012), December 6-8, 2012. Volume 2: NSPSE 2012 Editors: R. Sharma, R. Sundaravadivelu, S. K. Bhattacharyya and SP. Subramanian ISBN: 978-93-80689-13-5, Copyright © 2012 by the Indian Institute of Technology Madras, Chennai (TN) 600 036, India. _____________________________________________________________________________________________

Numerical modeling of flow through progressive cavity pump - A review K. R. Mrinal1, Abdus Samad2* 1-2 Department of Ocean Engineering, IIT Madras, Chennai, India. E-mails: [email protected]; 2*[email protected] * Author for correspondence. Abstract: Progressive cavity pump is designed for pumping fluids containing abrasive solids and high viscosity. The pump consists of a helical rotor which eccentrically rotates within helical stator and forms cavities. The cavities progresses and delivers fluid as the rotor rotates. The pump performance depends on the leakage in the sealing area where the rotor meets the stator. The main difficulty of flow modeling using numerical technique comes from the leakage zone modeling as this zone is very thin and has rotary as well as translator motion of fluid domain. The finite element modeling of stator also faces same issue of having complexity in meshing. In the present article, a detailed study of previous literatures has been reported and conclusion has been made on the issue of numerical modeling. Key words: Artificial lift, progressive cavity pump, slippage loss, numerical modeling. 1. Introduction Artificial lifting is a process used in oil and gas wells to increase pressure within the reservoir and pumps fluid to the surface. When natural drive energy of the reservoir is not strong enough to push the fluid to the surface, an artificial lift is used. Generally, the artificial lifting of fluid is achieved by the use of a mechanical device inside the well. Major types of artificial lift are gas lift, electrical submersible pump, progressive cavity pump (PCP), sucker rod pump and, hydraulic jet pump [1]. Out of these, PCP is widely used in the oil & gas industry for handling viscous crude oils, emulsions, produced water and multiphase fluids etc. The advantages of using PCP as an artificial lift are lower investment and higher efficiency comparing to other artificial lift method to pump heavy and viscous fluids [2]. Rotary pumps are particular type of positive displacement pump that displaces known quantity of liquid with each revolution of pumping element. This is done by trapping liquid between the pumping element and a stationery casing. PCP is a rotary positive displacement pump defined as a machine in which liquid is trapped in confined volumes and transported from inlet port to outlet port by a rotational movement of the pumping element or elements [3]. The PCP consists of metallic single start helical screw rotor which eccentrically rotates within a static two start helical sleeve or stator. It is mainly designed for pumping viscous fluids or fluids contains abrasive solid. It can handle the fluid viscosity ranging from water of viscosity 1cSt to clay, cement and sludge of viscosities up to 1,000,000 cSt. The pump pressure depends on number of stages which is in the range of 80-100psi [4]. There are two types of PCP based on the material used for stator. If the stator is made up of elastomers then it is called elastomeric PCP while if the stator is made up of metal, it is called metallic PCP. In the early 1950's because of the emergence of elastomers an improvement in the design of the PCP introduced by replacing the natural rubber stator by elastomers which have better mechanical properties and allows pumping the fluid which have abrasive and corrosive. But the elastomers cannot resist high temperature, fails during dry running and also are not suitable for fluids having high abrasive particles. Considering these limitations, another type of PCP called metallic PCP was developed. The stator is made up of metal instead of elastomers. The metallic PCP eliminates wear in stator, resists high temperature and thus increases the pump life. The commonly used material for rotor is alloy steel, tungsten carbide or ceramic, while for the stator alloy steels, bronze alloys and elastomers [6].

The PCP has helical rotor which rotates inside a helical stator. The rotor has eccentric movement inside the stator and forms a cavity. During rotor rotation, the cavity progresses and hence the name progressive cavity pump. The eccentric motion of the rotor displaces the fluid within the cavity which moves along the axis from the inlet to exist against the discharge pressure. There is a possibility of leakage or slip back to suction and this is considered as a main problem in PCP which reduces the efficiency of the pump. The leakage problem is mainly seen in metallic PCP due to the presence of clearance between metallic stator and rotor. In case of elastomeric PCP, the clearance is zero or negative; therefore the leakage is negligible until the elastomeric stator wears out or a very high pressure is applied at its discharge end. Internal slip is the phenomenon that defines PCP performance because it is a function of fluid characteristic, the differential pressure and rotor’s kinematics. Internal slip is transitory and not fully developed flow through pump clearances, and it changes instantaneously depending on the rotor position [8, 11]. The first and simplest numerical model to describe the flow inside a PCP was presented by Moineau [7] and it is based on calculating the back flow across the pump considering Hagen-Poiseuille flow. Gamboa et al. [8] presented a new model for calculating slippage by making modification in the previous model. This similar approach of modeling was again used by Pessoa et al. [9] but with some modification. Gamboa et al. [10] modeled three simplified fluid flow model with assumptions. Karthikeshwaran and Samad [11] presented the prediction of leakage for different fluid viscosities and diametric clearances using a CFD model of PCP and the procedure was followed from the concept of Gamboa et al. [10]. Recently, Paladino et al. [12] presented a three-dimensional transient model of PCP using commercially available CFD package ANSYS-CFX. A numerical model from Andrade et al. [13] presents an asymptotic model to describe the single phase flow inside progressive cavities pumps using lubrication theory. The results are close to the experimental results. Alemaskin et al. [14] modeled a three dimensional model of PCP of transient flow. Later Berton et al. [15] presented for the first time a full transient 3D model considering both Newtonian and non Newtonian fluids even with low viscosity. All the results of the above articles show the complexity in meshing and results were approximated. There were some finite element method (FEM) analysis and experiments of PCP also done for improving its design and performance [16-19]. He et al. [16] constructed a three dimensional finite model of PCP. They assumed that the stator is a rigid body. Zhang et al. [17] presented another FEM model for analyzing deformation characteristics of the elastomers in an even thickness PCP under several simulated working conditions. Aurelio et al. [18] studied the performance of metal to metallic PCP by conducting experiments. They obtained characteristics curves and instantaneous pressure profile along the pump with single phase and two phase flow. Noble and Dunn [19] conducted a series of laboratory test programs investigated the buildup of pressure and temperature along the length of a PCP using pressure and temperature sensors embedded in to the pump cavities and elastomers. The testing revealed that the assumption of a linear pressure distribution along the length of PCP is incorrect in many situations and a highly distorted pressure distribution can exist inside the pump. In this paper, a review of fluid flow modeling in PCP and the meshing difficulties has been described. A FEM modeling approaches has also been studied and for both the cases, suggestions have been presented. 2. PCP geometry and operating principle A PCP consists of two helical elements; one inside the other .The inside element is called rotor contains lobe one number less than that of the outer element called stator. The simple PCP consists of single lobe rotor and a double lobe stator which is represented by 1:2. Other complex geometry having larger number of lobes also available in the market but 1:2 configurations is commonly used. Any combination is possible but one condition to be satisfied that stator contain one more lobe than the rotor. The 1:2 PCP also mean that single helix rotor inside a double start helical stator [24].

30

Fig. 1: PCP operating principle. The single start helical rotor (Fig. 1a) has a constant circular section, which is right angle to its axis, at any point along the length .The centre of each successive circular section lies along the helix, the axis of which constitutes the axis of the rotor. The radius of helix is the distance by which the centre of the rotor section is offset from the axis of rotor, is known as eccentricity. The double helix stator (Fig. 1b) has a 31

constant cross-section along its length of a slot configuration of two semicircles, equal to the diameter of the rotor joined by two tangential lines of lengths equal to four times the rotor eccentricity [4]. The operating principle of PCP is first described by Moineau. His work is based on the geometric fact that hypocycloid created when a rolling circle rotates with in a fixed circle twice its size, is a straight line and not a curved one (Fig. 1c). By using this concept he designed a pump without valves. Hypocycloid is a curve formed by fixed point on the circumference of a small circle radius r around the inside of a large circle of radius R (R>r) [22]. Let O and C be the centers of the fixed and rolling circles respectively and P a point the moving circle. When the rolling circle turns an angle in a clockwise direction relative to O. C traces an arc of angular width (θ) in a clockwise direction relative to O. Assuming that the motion starts when P is in contact with the fixed circle at the point Q and also the origin of the coordinate system at O. The coordinates of P relative to O are ( ,) (φ is measured clockwise and it lies in second quadrant) while the coordinates of C relative to O are ( , ). Thus the coordinates of P relative to O are: (1) (2) But the angle θ and Φ are not independent as the arc of the fixed and moving circle that comes in contact (arc QQ1 and Q1P are equal) i.e.

and

substitute in (1) we get:

(3) (4) Equations (3) and (4) are the parametric equations of the hypocycloid. The general shape of the curve depends on the ratio R/r. If this ratio is a fraction m/n in lowest terms, the curve will have m cusps (corners), and it will be completely traced after moving the wheel n times around the inner rim. For the value of R/r =2 in (3) and (4) becomes (5) (6) The fact that y=0 at all times means that P moves along the x axis only, tracing the inner diameter in a to and fro motion. The straight line motion can be utilize to by mounting a rotor at a point A on the rolling circle and enclose the extremes of the rotor motion in the casing (stator) (Fig. 1d) . If the rolling circle rolls around the fixed circle, the rotor follows a straight line motion and up and down in the slot of the casing. The rolling circle becomes a journal which rolls inside a bearing [5]. 3. PCP fluid flow models The role of PCP fluid flow modeling in PCP is very important because it can be used for optimization of the efficiency of the pumps, reduce cavitations and noise. In some cases the experiment on PCP is not possible under extreme conditions and also it is very costly when compared to simulation. Once the model is validated by experimental results, then that model can be used or predicting different operating conditions easily. The usual fluid flow modeling in PCP is modeled with Hagen-Poiseuille and Couette flow along the seal lines between cavities. Poiseuille flow is the flow between two fixed parallel plates separated by distance or through cylindrical pipe and a pressure gradient in the flowing direction. The diving force is the pressure differential in the direction of flow. Couette flow is the flow of fluid in the space between two parallel plates in which one is stationery and other is moving. The driving force is due to the movement of the top plate [25]. The simplest numerical model to describe the flow inside a PCP by Moineau [7] and it is based on calculating the slippage across the pump considering Hagen-Poiseuille flow through the seal line. The slippage is calculated by considering the flow through rectangular channel with uniform clearance in the pump. He derived the slippage formula for the flow in the rectangular channel (Fig.2) between cavities of PCP across the sealing line. The slippage is given by

32

(7) (8)

From the equation (7) it is clear that slippage is a function of pump geometry, fluid property and differential pressure. To reduce slippage differential pressure and clearance have to be reduced and use high viscous fluids (increasing viscosity) and increase number of stages of pump (increasing length). The actual flow (Qa) is obtained by subtracting slippage (Qs) from the theoretical flow (Qth) rate (8). Thus a relation can be calculated between differential pressure and actual flow rate. This model can be used for a qualitative analysis of pump performance but for not quantitative analysis [9]. Later this simple modeling was modified by Gamboa et al. [8]. In this model they consider Couette flow along with Poiseuille flow. Hence the slip between cavities has two components one is the axial flow due to pressure difference (Poiseuille flow) and other transverse flow due to movement of rotor (Couette flow). The curvature of the pump is neglected during the calculation of slippage area. This model shows good performance with high fluid viscosity and also a moderate performance in low viscosity fluids. This similar approach of modeling was again used by Pessoa et al. [9]. But they neglect the effect of Couette flow component because considering the value of slippage due to Couette flow component is small when compared to Poiseuille flow component and also there were some improvement in the calculation of friction factor which allows the flow calculation of low viscosity fluid which was not well succeeded in the previous work. In this model also there were two components of slippage; longitudinal and transversal slippage but the component of slippage is divided by considering components of Poiseuille flow. Here the slippage is calculated from the (4). The variables in the (5) are the length and breadth of the rectangular channel. The longitudinal and transverse slippages are in (5). The calibration parameters LL and LT in (5) can be obtained from a detailed CFD model and which solves the transient Navier Stokes equations within the PCP considering the real geometry and rotor motion [9]. where,

(9)

where,

(10)

Moineau defined the basics of PCP by considering the contact between rotor and stator. But later found that it is not necessary and found that PCP with clearance between stator and rotor will work. After this the metallic PCP come into existence. Gamboa et al. [10] studied the performance of metallic stator by conducting experiments and simulation. They developed simplified model of PCP by using FIDAP, a finite element based fluid dynamics package and compared with the experimental results. They developed three simple CFD models such as: a) Model 1 is infinite parallel model (shown in Fig. 4a) simulate the slippage effect as that of convergent-divergent bearing proposed by Belcher [5]. The slippage in the pump can be approximated as flow between two parallel plates of infinite length separated by a distance equal to the diameter of 33

stator and in between a cylinder is rotating in which the radius of cylinder is equal to the radius of rotor. b) Model 2 is 2D developed or untwisted model (Fig. 4b) consists of untwisted (cylinder) stator and the shape of rotor forms the cavities. The cavity length must be equal to stator pitch and the rotor move axially for the displacement of the fluid. c) Model 3 is full model of one stage of PCP also a simplified model of PCP. They tried to generate 3D modeling, but failed because of distortion of meshing in the internal elements of PCP. Then they modeled slit of pump (shown in Fig. 4c) thereby avoiding mesh distortion. In this model the rotor having rotational motion as well as translational motion. In all the models they assumed that the flow as incompressible Newtonian flow under isothermal. Karthikeshwaran and Samad [11] studied the prediction of leakage for different fluid viscosities and diametric clearances using the CFD model of PCP infinite model developed by Gamboa et al. [10]. The transient three dimensional modeling in PCP is limited because of complex geometry and difficulty in meshing. A detailed three dimensional model of flow within the PCP was successfully implemented by Paladino et al. [12]. The most difficult part in this modeling is the meshing the region between rotor and stator and also the mesh movement in rotor. The results are validated with experimental results from the literature. The model solves mass and momentum conservation equation. The model implemented the full solution of Navier Stokes equation within the PCP. So the simulation can be extended to non isothermal and multiphase flow for future work. The meshing technique used in this work is explained in the next section.

Axial Slip

Transverse Slip

Slip scheme within PCP Fig. 3 Slippage in PCP between cavities [9]

34

Fig. 4 Simplified CFD models [10] Table 1. Important numerical models of PCP Modeling in PCP

Modeling description

Moineau [7] Gamboa et al. [8]

Slippage between cavities is based on based on Hagen-Poiseuille flow. Slippage between cavities was analyzed using Poiseuille and Couette flow components. Two components of Poiseuille flow is considered but neglected Couette flow.

Pessoa et al. [9] Gamboa et al. [10]

Andrade et al. [13] He et al. [16]

They construct three models: a) Flow is between two parallel plates and in between a cylinder is rotating of radius of rotor. b) Untwisted cylinder stator and rotor moves axially. c) Geometry is simplified into a slit. A transient 3D CFD model of metallic PCP for Newtonian and non Newtonian fluids. PCP fluid flow was solved by using lubrication theory. A 3D FEM model in which stator is assumed a rigid body and rotor is deforming.

Zhang et al. [17]

In this FEM model deformation of stator is considered and rotor is a rigid body.

Paladino et al. [12]

Andrade et al. [13] presents an asymptotic model to describe the single phase flow inside progressive cavities pumps using lubrication theory. They consider the flow was Newtonian and the three dimensional cylindrical form of Navier-stocks equation is simplified using lubrication theory. The simplified Navier Stock equation is in the form of two dimensional Poisson’s equation of pressure field and it is solved numerically by central finite difference scheme. The results were close to the 35

experimental and the results obtained by solving the complete three-dimensional transient Navier-Stokes equations with moving boundaries. The computing time required for this model is very less compared to other transient three dimensional models. The model can be used to obtain pump performance predictions and also it can be extended to deformable stator and multiphase. Alemaskin et al. [14] modeled a three dimensional model of PCP of transient Newtonian flow at isothermal condition for a viscosity of 20,000cP. They used ANSYS POLYFLOW (finite element based CFD code mainly used for polymers) which reduces the difficulty in meshing. POLYFLOW is commonly used for simulation of high viscous materials like polymers and also applicable for solving heavy oils. Later Berton et al. [15] presented a full transient 3D model able to predict the flow rate in a metal to metallic PCP, considering both Newtonian and non Newtonian fluids even with low viscosity. In this model the Navier-Stocks equation are solved using commercial solver LEMMA. In this solver, 3D structured volume meshes are automatically generated during the initial step and new nodes positions are then calculated at each subsequent step. The working temperature of PCP is generally 50 to 80° C. In this condition deformation of stator may occur. Also the stator gets depressed because of the rotor motion. The interaction with stator, working temperature and rotor motion cause deformation in rotor. Due to these deformations, the leakage in the PCP increases. FEM modeling can be used for optimizing the deformation in rotor and stator and thereby reducing the leakage. Hence FEM modeling plays a vital role in the design and optimization of the PCP. He et al. [16] constructed a three dimensional finite elemental model of PCP. They assumed that the stator is a rigid body for simplicity and rotor is deforming. The effect of parameters on laden torque was studied by using the simulation software ABAQUS (a finite element analysis software) and the parameters includes interference between stator and rotor, eccentricity, rotor geometry, rotor speed and stator material. The results are agrees with the experimental results. The results show that the amount of interference between stator and rotor is the main factor influencing the laden torque. Zhang et al. [17] presented FEM model for analyzing deformation characteristics of the elastomers in an even thickness PCP under several simulated working conditions. In this model the deformation of stator is consider with cavity pressure coupled with Poisson’s ratio of elastomers. For simplicity the rotor is considered as rigid body and they created hexahedral mesh for the geometry. They found that the even thickness PCP has a better performance and a longer operational life in the deforming conditions. 4. Meshing difficulties in PCP The main difficult in meshing in PCP as stated previously is due to the transient flow character, complex geometry and the moving boundaries. The complexity of geometry is explained in the section 2. The gap between stator and rotor is very less near the sealing region; hence mesh generation for fluid domain is difficult. In the extreme case of a small clearance between the rotor and stator a poor quality mesh causes the solver to fail. For the movement of rotor, moving as well as deformable meshing is required. Tetrahedral and unstructured hexahedral meshes are easier to create in any meshing software without taking much time. But angular distortion during mesh motion is difficult in tetrahedral and unstructured hexahedral meshes which are required for PCP meshing. Hence it cannot be used in mesh generation in PCP. The structured hexahedral meshing is capable of angular distortion. But it will highly distort in the small clearance between stator and rotor. Hence the general meshing technique is very difficult in PCP [12]. Paladino et al. [12, 21] studied different possibility of meshing in PCP and the draw backs of these methods. They also introduce a new technique of meshing in PCP which results the first transient three dimensional modeling of PCP. The main challenging part of this work is meshing. In the initial method they generated mesh for PCP geometry by using ICEM, ANSYS mesh generation software and the rotor motion is implemented by CEL language in the solver (CFX Expression Language). This method requires a stiffness parameter which helps to perform the mesh movement. They find that this method is inadequate; since it produces mesh residual deformation in the successive time steps (Fig. 5).This leads to failure of the solver. In another method the initial mesh generated in PCP by using ICEM as done in the previous method. But here mesh for several positions of the rotor has been generated in the mesh generator. Then the mesh connectivity is implemented by a FORTRAN language. The element distortion which occurs in the previous method can be eliminated because for each position of rotor a mesh is generated. The main 36

disadvantages of this method meshing is small clearance (between stator and rotor) cannot be created in ICEM. Then they found that meshing the rotor with respect to movement with time without using any meshing software and by using FORTAN is the best method of meshing PCP geometry. In this method mesh movement is fully control by FORTAN language. Therefore three dimensional modeling and meshing is not required by using modeling and meshing software respectively because the geometry itself is represented by mesh using FORTAN [20].

Mesh for initial time

Mesh for 8th time step Fig. 5 Element distortion due to numerical diffusivity on the mesh motion calculation [21] 5. Conclusions In this paper the geometry details, numerical flow modeling and related meshing difficulties of PCP are discussed. From the discussion in this paper, it was found that the complex geometry, moving boundaries and meshing are the main issue in the PCP flow domain modeling. The meshing complexity arises at the leakage area where the flow area is too thin and the location of the leakage area changes as the rotor rotates and translates. Still a big effort is required to model properly the flow domain so that complex meshing near at leakage area with moving or deforming meshing issues will be solved. Similarly FEM modeling for structural analysis faces difficulty because of complexity in design. A further research is required to handle the deforming stator material due to fluid pressure, temperature and moving fluid domain. Nomenclature Symbols b Breadth of the rectangular channel C Generic constant L Slippage length of rectangular block P Pressure Q Flow rate r Radius of rolling circle R Radius of fixed circle Ra Flow resistances of seal region u Velocity V Rotor velocity in axial direction w Height of the rectangular channel or clearance ∆P Pressure drop θ Angular width in clockwise direction relative to O due revolution of rolling circle µ Viscosity of the flowing fluid φ Angular displacement due to rotation of rolling circle ω Angular velocity of rotor Subscripts a Actual 37

L s T th x, y, z

Longitudinal slippage component Slippage Transverse slippage component Theoretical Coordinates axis

6. Acknowledgement Abdus Samad acknowledges the assistance received from the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India for the FAST Track Scheme for Young Scientists research project (SR/FTP/ETA-0070/2011). References [1] M. Alemi, H. Jalalifar, G. Kamali and M. Kalbasi (2010), “A Prediction to the Best Artificial Lift Method Selection on the basis of TOPSIS model”, Journal of Petroleum and Gas Engineering Vol. 1, no. 1, pp. 009-015. [2] D. Zhou and H. Yuan (2008), “Slip Calculation of Rotational Speed of Electric Submersible Progressive Cavity Pump”, SPE 112881. [3] L.V. Whittaker (2003), “Evaluation and Analysis of Wear in Progressive Cavity Pumps”, Doctoral thesis, University of Hull, United Kingdom. [4] L. Nelik and J. Brennan (2005), “Progressive Cavity Pumps, Downhole Pumps and Mudmotors”, Gulf Publishing Company, Houston, Texas. [5] I.R. Belcher, (1991), “An Investigation into the Operation Characteristic of Progressive Cavity Pump”, Doctoral Thesis, Cranfield Institute of Technology, United Kingdom. [6] J. Gamboa, (2000), “Computational Simulation of a PCP without Interference” (Simulación Computacional de una BCP sin Interferencia), M.Sc. Thesis (in Spanish), Universidad Simón Bolívar, Sartenejas, Venezuela. [7] R. Moineau, (1930), “A New Capsulism”, Doctoral Thesis, The University of Paris, France. [8] J. Gamboa, A. Olivet and S. Espin (2003), “New Approach for Modeling Progressive Cavity Pumps Performance” SPE84137. [9] P.A.S, Pessoa, E.E. Paladino and J.A. Lima (2009), “A Simplified Model for the Flow in a Progressive Cavity Pump”, 20th International Congress of Mechanical Engineering, Gramado, Brazil. [10] J. Gamboa, A. Olivet, J. Iglesias and P. Gonzalez (2002), “Understanding the Performance of a Progressive Cavity Pump with a Metallic Stator”, Proceedings of the 20th International Pump Users Symposium,USA. [11] R. Karthikeshwaran and A. Samad (2011), “Leakage Analysis of Progressive Cavity Pump”, The 11th Asian International Conference on Fluid Machinery and the 3rd Fluid Power Technology Exhibition, Chennai, India. [12] E.E. Paladino, J.A. Lima, P.A.S. Pessoa and R.F.C. Almeida (2011), “A Computational Model for the Flow within Rigid Stator Progressing Cavity Pumps”, Journal of Petroleum Science and Engineering, pp. 178–192. [13] S. F. Andrade, Juliana V. Valério and M. S. Carvalho (2011), “Asymptotic Approach for Modeling Progressive Cavity Pumps Performance”, Mecánica Computational Vol XXIX, pp. 8429-8445. [14] K. Alemaskin, K. Nandakumar, and U. Sundararaj (2006), “Progressive Thinking for Pumps an Article in Fluent News, Applied Computational Fluid Dynamics”, VOL V, pp.22. [15] M. Berton, O. Allain, C.Gaualy and P. Lemetayer (2011), “Complex Fluid Flow and Mechanical Modeling of Metal Progressive Cavity Pumps”, SPE 150419. [16] L. He, X.D. He, H.A. Wu, and X.X. Wang (2010), “Three Dimensional FEM Simulation and Parameter Study on Laden Torque of Interference Friction of PCP”, SPE 135808. [17] J. Zhang, W. Li, S. Zhang, T. Wu, E. Zhou and B. Bai (2010),“A Numerical Study on the Deformation of Even Thickness PCP’s Stator”, SPE 137251. [18] A. Olivet. J. Gamboa and F. Kenyery (2002), “Experimental Study of Two-Phase Pumping in a Progressive Cavity Pump Metal to Metal”, SPE 77730. [19] E. Noble and L. Dunn (2011), “Pressure Distribution in Progressing Cavity Pumps: Test Results and Implications for Performance and Run Life”, SPE 153944. [20] J.A. Lima., E.E. Paladino, R.F.C. Almeida and F.P.M Assman (2011),“Meshing Generation for Numerical Simulation of Fluid–Structured Interaction within Progressive Cavity Pumps”, 20th International Congress of Mechanical Engineering, Gramado, Brazil. [21] E.E. Paladino, J.A. Lima, P.A.S. Pessoa and R.F.C. Almeida (2008), “Computational Modeling of the ThreeDimensional Flow in a Metallic Stator Progressing Cavity Pump”, SPE 114110. [22] E. Maor (1998), “Trigonometric Delights” Princeton University Press, Princeton, New Jersey. [23] K.J. Saveth and S.T. Klein (1989), “The Progressing Cavity Pump: Principle and Capabilities”, SPE 18873. [24] H. Cholet (1997), “Progressing Cavity Pumps”, Editions Technip, Paris. [25] E. Haisler (2001), “Conservation of linear momentum” website address: http://aeweb.tamu.edu/haisler/engr214/Word_Lecture_Notes_by_Chapter/chapter3-part3.doc, accessed on October 10, 2012.

38


The study of oil spill cleanup methods along with comparison+ Saumya1, Md. Hamid Siddique2* 1-2 ISM Dhanbad, India. E-mail: 2* [email protected] * Author for correspondence. Abstract- The complex tanker route and abnormal weather condition cause sea accidents. Spilled oil from such stranded ship pollutes the ocean environment. It also damages the regional economics. This paper considers some various methods that have, or might be expected to have, important effects on oil-spill cleanup. The purpose is to develop background information that will assist in the evaluation of oil-spillcontrol and that should be of value when planning an oil-spill removal and response system. BACKGROUND All marinas are expected to practice smart pollution prevention measures while handling and storing petroleum products. Wherever oil is produced, transported, refined, or released from natural seeps, there will be oil slicks. While most of these spills [1] will be small, a few will be large enough to cause serious impact to the environment unless there is a swift and effective response. Any general knows that, in combat, it is vitally important to 'know your enemy. When combating an oil spill, it is vital for the cleanup team to know the expected fate and behaviour of its enemy, the oil slick. The oil penetrates up the structure of the plumage of birds, reducing its insulating ability, and so making the birds more vulnerable to temperature fluctuations and much less buoyant in the water. Hormonal balance alteration including changes in luteinizing protein can also result in some birds exposed to petroleum. Most birds affected by an oil spill die unless there is human intervention. CURRENT RESULTS Various methods for Cleaning Oil Spills on which we are working are: • Absorbents: We performed our experiment with three different polymers [2] on three different crude oil samples including waxy crude. We used absorbents such as hydrogel, Enviro-Bond 403 and Sodium Polyacrylate [3] powder to conduct our experiment. Hydrogels are super absorbent polymers. Polymers are long chains of molecules that are linked together.We fill a beaker with 500 ml water and poured thin layer of crude sample in it. It was noticed that oil and water layers separated with oil floating on top. Now using the plastic spoon, we sprinkled first polymer sample on the "oil spill" in the beaker and allowed polymer particles to absorb all the oil. When all the oil has been absorbed (3-5 minutes), the polymer-oil cake was lifted from the surface of the water using the fork and placed on the paper plate. The same procedure is repeated with different polymer and crude oil samples in turn. The absorbing power of polymers can be determined by weighing the polymer before and after it absorbs the oil. In our experiment it was observed that hydrogel and Sodium Polyacrylate Powder were capable of absorbing 25 times their weight in liquid. So, they are also called super-absorbents while Enviro-Bond 403 is not considered a super-absorbing material as it has an absorbing power of less than 25.

_______________________________________________________________________________________ + Extended abstract only.

• Solidifying: Every crude oil has a particular pour point [4] at which it ceases to flow and its movement in water is restricted which results in formation of solid cakes. These cakes can be easily flushed or lifted. In our experiment some PPD were added to increase the pour point of our crude oil samples and solid cakes resulted which was easily removed. • Controlled burning can effectively reduce the amount of oil in water, if done properly. In our experiment a controlled burning is done in vacuum chamber with limited supply of air and water quenching facilities is provided. • Dispersants act as detergents, clustering around oil globules and allowing them to be carried away in the water. In our experiment it was observed that smaller oil droplets, may cause less harm and may degrade more easily. But the dispersed oil droplets infiltrate into deeper water and can lethally contaminate coral. • Watch and wait: In some cases, we find that natural attenuation of oil is most appropriate, due to the invasive nature of facilitated methods of remediation, particularly in ecologically sensitive areas. REFERENCES [1] David Dickins, DF Dickins Assocites LLC “Behavior of Oil Spills in ice and implications for Arctic Spill response” OTC conference paper, 2011 [2] Chung, Ting-Horng, NIPER" Thermodynamic Modelling for Organic Solid Precipitation” SPE conference paper, 1992. [3] Williams, S.A., Socony Mobil Oil Co., “The Effect of Temperature on Polyacrylate and CMC Treated Muds”, year 1961 [4] M. M Kulkarni, Louisiana state U and K. Iyer, Thermax India "Effects of pour point depressants on Indian Crude oils" SPE conference paper 2005.

40


Numerical modelling on remediation of petroleum hydrocarbons under coupled dissolution, sorption and biodegradation for a subsurface system M. Vasudevan1*, G. Suresh Kumar2, Indumathi M. Nambi3 1-3 Department of Civil Engineering, IIT Madras, Chennai, India. 2 Department of Ocean Engineering, IIT Madras, Chennai, India. E-mails: 1*[email protected]; [email protected]; [email protected] * Author for correspondence. Abstract: The fate and transport of hydrocarbons in the petroleum fuels present in the natural heterogeneous subsurface is extremely complex due to the interaction of various physical, chemical and biological factors characterizing different phases of the system. Here a numerical model has been developed to understand the effect of mass transfer limited sorption and biodegradation of petroleum hydrocarbon on dissolution mass transfer under various saturation conditions. The concentration of toluene under aerobic biodegradation condition shows gradual removal by flushing with reduction in residual NAPL saturation. It has been found that there is gradual recovery of the electron acceptor if the system is prolonged to higher volumes of flushing. The condition of rate-limited dissolution is highly mass transfer limited such that the bioavailability of the contaminant depends on the dissolution mass flux. Key words: Numerical modelling, petroleum hydrocarbon, dissolution, sorption, biodegradation. 1. Introduction The occurrence of organic immiscible liquid in the subsurface environment has been reported at numerous contaminated sites and the presence of toxic hydrocarbon compounds were found to be persisting in many places. Considering the large scale distribution of petroleum fuels in the emerging economic scenario, the risk associated with leaking and spill of underground storage tanks is of particular concern. In order to estimate the extent of subsurface contamination and to take necessary remediation actions, the physicochemical properties of the system must be understood. Among the various techniques to estimate the risk of contamination, mathematical models have been widely used as effective tool for simulating the contaminant fate and transport under the prescribed conditions. Therefore modelling the contaminant degradation in the subsurface requires an understanding of the relationships between the physical and biological effects on the contaminant fate and transport. The fate and transport of hydrocarbons in the petroleum fuels present in the natural heterogeneous subsurface is extremely complex due to the interaction of various physical, chemical and biological factors characterizing different phases of the system (Chiang et al., 1989; Clement et al., 2004; Yadav and Hassanizadeh, 2011). Moreover, as soon as the contaminants in the non-aqueous phase get into contact with any other phase, it will be partitioned among the phases depending on the partition coefficients of individual components. But even after migration and transport of the free phase compounds, some of the components reside in the soil pores and wedges which is difficult to remove by draining. Because of its persistent nature, the residual non-aqueous phase contaminant can serve as a long-term source of contamination and must be properly included while preparing the site characterization strategies and remediation plans (Nambi and Powers, 2000; Lenhard et al., 2002; Chu et al., 2007).

The dissolution mass transfer from the non-aqueous phase to the aqueous phase is limited by a range of parameters which include properties of the porous media, flow conditions and type of organic compound (Seagren et al., 1999; Mayer and Miller, 1996). Many studies were conducted to assess whether the mass transfer phenomena are rate-limited or equilibrium under similar laboratory conditions (Borden and Piwoni, 1992; Johnson et al., 2003). It is important to estimate the rate-limiting mass transfer process in order to design suitable remediation plan for the contaminated aquifer. Much research has substantiated the important role of adsorptive partitioning of organic compounds onto the aquifer material which is characterized generally by linear sorption isotherms (Allen-King et al., 2002; Kim et al., 2003). The effect of equilibrium sorption has been explained by the retardation of the contaminant movement compared with the fluid flow velocity which causes one of the reasons for mass transfer rate limitation. However, mass-transfer limitations can be important in cases of high pore-water velocity, large ganglia size, and NAPL saturation reducing the effective aqueous permeability (Powers et al., 1994; Seagren et al., 1999; Nambi and Powers, 2000). With increasing aqueous phase concentration, the petroleum hydrocarbons are susceptible for biodegradation either by natural attenuation or by enhanced bioremediation. It has been reported in literature that the presence of electron acceptor is important to consider in the biochemical kinetics to ensure sufficient redox condition in the subsurface. It is important to note that contaminant mass transfer from the organic phase to the aqueous phase by dissolution is the driving path for the biodegradation by micro-organisms. The coupled effect of dissolution and degradation under the influence of sorptive retardation is, therefore, makes the problem very crucial to address (Mihelcic et al., 1993; Molson, 2000; Chu et al., 2004). In the present study, a numerical study has been carried out to understand the effect of mass transfer limited sorption and biodegradation of petroleum hydrocarbon on dissolution mass transfer under various saturation conditions. 2. Model Formulation Numerical modelling has been widely used to simulate contamination scenarios, especially in the subsurface system by solving the governing partial differential equation by either fully coupled or by operator-split approaches (Yang et al., 1995; Molson, 2000; Clement et al., 2004; Couto and Malta, 2008). In order to understand the behavior of the system, a homogeneous saturated aquifer has been considered with a uniform one dimensional Darcy flux over the entire domain. The aquifer is assumed to be contaminated by a single pure hydrocarbon compound. For the purpose of understanding the influence of dissolution on the bioavailability, the inhibitory effects of the toxic compounds at higher concentrations as substrate are neglected. The governing equation for the electron donor (contaminant) contains sink terms such as advection, dispersion, sorption and biodegradation, along with rate-limited dissolution as the sole source term. Aerobic biodegradation conditions are assumed in the saturated aquifer, and the interaction between contaminant and electron acceptor has been studied with respect to the evolution of the residual NAPL saturation. The transport of the electron acceptor is assumed to be non-retarded, but also involves bio-degradation term. The biomass is assumed to be immobile in the system. These three species are connected by the biodegradation term which is explained by the multiplicative Monod kinetics (Couto and Malta, 2008). Developed model equations were solved by finite difference method using Thomas algorithm for the developed tri-diagonal matrix. The governing equation for the electron donor (contaminant) is adopted from Couto and Malta (2008) for the present scenario and is rewritten as; ∂Ca D ∂ 2 Ca v ∂Ca ε 1 ⎡ µ X C ⎤ ⎡ Cea ⎤ = − − (λ Ca − S ) − ⎢ max a a ⎥ ⎢ (1) ⎥ 2 ∂t

R ∂x

R ∂x

R

R ⎣ K s1 + Ca ⎦ ⎣ K s 2 + Cea ⎦

42

The governing equation for the transport of the electron acceptor (oxygen) is given by; ⎡ Ya ⎤ µmax X a Ca ⎥ ⎢ ⎡ Cea ⎤ ∂Cea ∂ Cea ∂C Y ⎥⎢ =D − v ea − ⎢ ea ⎥ ∂t ∂x ⎢ K s1 + Ca ⎥ ⎣ K s 2 + Cea ⎦ ∂x 2 ⎢ ⎥ ⎣ ⎦ 2

The rate of change of concentration of immobile biomass is given by; ∂X a ⎡ Ya µmax X a Ca ⎤ ⎡ Cea ⎤ 0 ∂t

=⎢ ⎣ K s1 + Ca

⎥⎢ ⎥ − K decay ( X a − X a ) ⎦ ⎣ K s 2 + Cea ⎦

(2)

(3)

The mass balance in the sorbed phase concentration is given by; ρ ∂S n ∂t

= ε (C a − S )

λ

(4)

Where Ca and Cea are the concentrations (mg/L) of contaminant and electron acceptor respectively, S=sorbed phase concentration (g/g), µmax= maximum specific substrate utilization rate (g/g/day), Ks1, Ks2= half saturation concentrations (mg/L) for Ca and Cea respectively, Y1, Y2= yield coefficients (-) for Ca and Cea respectively, Kdecay= endogenous decay rate of biomass (day-1), Xa0= initial biomass concentration (mg/L). The above sets of equations (Eq. (1) to (4)) were employed to validate the numerical scheme with the results from Couto and Malta (2008). Considering the rate-limited dissolution in this regard, the governing equation for electron donor is modify as follows; ⎡ µ X C ⎤ ⎡ Cea ⎤ ∂Ca ∂ 2C ∂C K = D 2a − v a + na (Csat − Ca ) − ε (Ca − S ) − ⎢ max a a ⎥ ⎢ (5) ⎥ λ ∂t ∂x nS a ∂x ⎣ K s1 + Ca ⎦ ⎣ K s 2 + Cea ⎦ Where Kna is the dissolution mass transfer coefficient (day-1); Csat is the saturation concentration (mg/L); Sa is the water saturation content. K na =

Sh' Dm d p2

(6)

Dissolution mass transfer term is expressed as Sh' = 12 Re0.75 θ n 0.60 (7) Where Re is the Reynolds number, Dm is the molecular diffusion coefficient of the compound, dp is the mean particle size of the porous media and θn is the non-aqueous phase volumetric content 3. Numerical Solution The finite difference model for the above set of partial differential equations consists of implicit method for advection and Crank-Nickolson method for dispersion. Since different modules are included in the governing equations, a fully-coupled numerical scheme is employed, in which the one of the dependent variable is assumed according to the initial conditions, which is actually predicted later while terminating the iterative loop at the selected tolerance limit of error. Mixed type boundary has been assumed at the inlet and no flux type boundary conditions are assumed at the outlet for the flushing water. Using Thomas algorithm, the tridiagonal matrix system has been solved for the coupled equations under iterative conditions until convergence.

43

Table 1: Initial and boundary conditions for the model (from Couto and Malta, 2008). Initial Conditions Ca(x,t=0)

5.0 (mg/L)

Cea(x, t=0)

0

S(x,t=0)

0

Xa(x,t=0)

0.427 (mg/L)

Boundary Conditions Cea(x=0,t)

10 (mg/L)

Xa(x, t=0)

0.427 (mg/L)

vCai − D

(C

∂Ca ∂x

ai +1

− C ai

∆x

)=0

=0 ( x = L ,t )

4. Results and Discussions Numerical modeling results with our present model (Eq. (1) to (4)) have been validated with the results from Couto and Malta (2008) based on the values given in Table 2. The contamination scenario is represented by a constant initial concentration of electron donor in the system and the electron acceptor is injected continuously. The combined effect of rate-limited sorption and multiplicative Monod biodegradation kinetics were modeled by Couto and Malta (2008) using operator-split approach. However, in our study, the fully coupled model equations were solved under the initial and boundary conditions represented in Table 1. The snapshots of the concentration variation of electron donor and electron acceptor are shown in Fig 1(a) and 1(b). The removal of the electron donor (contaminant) from the domain and the replenishing of the electron acceptor (dissolved oxygen) are found to be matching with the author’s model within the simulation period. Importance of dissolution mass transfer under rate-limited condition is of particular importance for the petroleum hydrocarbons which are present at residual non-aqueous phase saturation functioning as a continuous source of contamination. Results of the dissolution model (Eq. (5)) for a typical petroleum component (toluene) have been simulated under the influence of rate-limited sorption and biodegradation (Fig 2(a) and 2(b)). Variation of the toluene concentration is following the typical dissolution flushing profile within the domain. It is important to consider the degeneration of dissolved oxygen in a typical bioremediation plan because of the chance of contaminant degradation by the inherent micro-organisms even though sufficient supply is maintained for the system. The effect of rate-limited sorption is significantly affecting the concentration profile by retarding the soluble fraction to move further. The soil-water partitioning of toluene is important for the natural organic matter in 44

the soil, based on the availability of organic carbon to adsorb to the soil micro-pores (Clement et al., 2004; Kacur et al., 2005). Table 2: Selected model parameters from literature.

Fig 1: Comparison of present model for (a) electron donor and (b) electron acceptor with that of Couto and Malta (2008).

45

Fig 2: Concentration variation of (a) electron donor and (b) electron acceptor, with time for dissolution model coupled with sorption and degradation. It is observed that the toluene is transported throughout the domain based on the advective-dispersive fluxes. At the end of 60 days, it is completely removed from the system, since the initial residual saturation was only 5% by volume. It is also observed that the electron acceptor, also gets depleted very fast due to the active biodegradation potential of the compound, but it is increasing later as the contaminant is removed. It is expected to have a highly reduced condition in the contaminant source zone as reported by various studies. Effect of dissolution mass flux for the overall removal of toluene from the system is more clearly observed in the concentration snapshots as shown in Fig 3(a) and 3(b). Within 40days, all toluene mass is removed through effluent. Fig 4(b) suggests the need for continuous supply of oxygen even after removal of nonaqueous phase saturation, in order to replenish the dissolved concentration. It is because of the soluble fraction of toluene still present in the aqueous phase which is to be removed by continuous flushing.

Fig 3: Concentration variation of (a) electron donor and (b) electron acceptor, with distance. It has been shown that non-aqueous saturation is decreasing as the source is removed from the system due to the continuous flushing (Fig 4(a) and 4(b)). Since the initial volumetric fraction is very less, the dissolution flux could easily exchange the mass through the phases without mass transfer limitations. We have observed that toluene concentration is still present in the aqueous phase even after removal of the source term because of the retardation effect on the transport under advective-dispersive fluxes.

Fig 4: Evolution of non-aqueous phase volumetric saturation (a) with time and (b) with distance. 46

Sensitivity analysis has been carried out for the most important model parameters such as fluid flow velocity, sorptive mass transfer coefficient and maximum substrate utilization rate. It has been observed that variation of fluid velocity is significantly affecting the toluene concentration profile (Fig 5(a) and 5(b)), because the dissolution mass transfer coefficient is directly proportional to the mean velocity of fluid. Hence at low velocity (0.1m/day), the dissolution has not yet reached the breakthrough, as observed with higher velocity values of 0.5m/day and 1.0m/day. Since the contaminant is in the active degradation stage, the electron acceptor concentration is invariant towards velocity variation.

Fig 5: Concentration variation of (a) electron donor and (b) electron acceptor with change in velocity. The estimation of bio-kinetic parameters is very crucial for the proper representation of the biodegradation scenario. Based on the literature values, the model is found to be invariable towards the variation of µmax (maximum specific substrate utilization rate) as given in Fig 6(a) and 6(b). Since the bioavailability of the contaminant is proportional to the rate of dissolution mass transfer, there is no significant increase in the biodegradation rate for higher values of µmax due to the mass transfer limitation and retardation effects. Similarly the electron acceptor concentration also follows the same trend for variation in µmax.

Fig 6: Concentration variation of (a) electron donor and (b) electron acceptor with change in µmax. It is also observed that increase in the sorptive mass transfer coefficient, the retardation effect is higher for the contaminant (Fig 7(a) and 7(b)). Even though electron acceptor is not retarded by sorption, the effect of sorption on the contaminant has an indirect effect on the electron acceptor, which is also found to be varying with respect to the sorptive mass transfer coefficient. When the retardation effect is more, the electron acceptor takes more time to get replenished to the saturation value. 5. Conclusions The present numerical model is able to represent the combined effects of rate limited sorption and dissolution on the bioavailability of toluene under aerobic biodegradation condition. The results of the study indicate that mass transfer limited dissolution and sorption are the rate-limiting steps for the organic mass removal from the residually trapped aquifer. Treatment systems employing air-sparging and bioremediation are effective for these conditions, provided identification of contaminated source is economic and reliable. Bio-stimulated treatment systems are more promising towards the renovation of petroleum contaminated fields. 47

Fig 7: Concentration variation of (a) electron donor and (b) electron acceptor with change in sorptive mass transfer coefficient. References [1] R. M. Allen-King, P. Grathwohl and P. O. Ball (2002), “New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks”, Advances in Water Resources, Vol. 25, pp. 985–1016. [2] P. J. J. Alvarez and W. A. Illman (2006), “Bioremediation and natural attenuation: Process Fundamentals and Mathematical Models”, John Wiley & Sons, Inc., Hoboken, New Jersey. [3] A. R. Bieledeldt and H. D. Stensel (1999), “Evaluation of biodegradation kinetic testing methods and long term variability in bio-kinetics for BTEX metabolism”, Water Research, Vol. 33, No. 3, pp. 733-740. [4] R. C. Borden and M. D. Piwoni (1992), “Hydrocarbon dissolution and transport: a comparison of equilibrium and kinetic models”, Journal of Contaminant Hydrology, Vol. 10, pp. 309-323. [5] C. Y. Chiang, J. P. Salanitro, E. Y. Chai, J. D. Colthart and C. L. Klein (1989), “Aerobic biodegradation of benzene, toluene, and xylene in a sandy aquifer-data analysis and computer modeling”, Ground Water, Vol. 27, No. 6, pp. 823-834. [6] M. Chu, P. K. Kitanidis and P. L. McCarty (2004), “Possible factors controlling the effectiveness of bioenhanced dissolution of non-aqueous phase tetrachloroethene”, Advances in Water Resources, Vol. 25, pp. 601–615. [7] T. P. Clement, T. R. Guatam, K. K. Lee, M. J. Truex and G. B. Davis (2004), “Modeling of DNAPLdissolution, rate-limited sorption and biodegradation reactions in groundwater systems”, Bioremediation, Vo. 0, No. 12, pp. 47-64. [8] P. R. L. Couto and S. M. C. Malta (2008), “Interaction between sorption and biodegradation processes in contaminant transport”, Ecological Modeling, Vol. 214, pp. 65-73. [9] G. R. Johnson, Z. Zhang and M. L. Brusseau (2003), “Characterizing and quantifying the impact of immiscible-liquid dissolution and nonlinear, rate-limited sorption/desorption on low-concentration elution tailing”, Water Resources Research, Vol. 39, No. 5, pp. SBH 6 (1)-6(8). [10] J. Kacur, B. Malengier and M. Remesikova (2005), “Solution of contaminant transport with equilibrium and non-equilibrium adsorption”, Computational Methods in Applied Mechanical Engineering, Vol. 194, pp. 479–489. [11] S. Kim, I. Hwang, D. Kim, S. Lee and W. A. Jury (2003), “Effect of sorption on benzene biodegradation in sandy soil”, Environmental Toxicology and Chemistry, Vol. 22, No. 10, pp. 2306–2311. [12] R. J. Lenhard, A. R. Kacimov, A. M. Tartakovsky and H. AbdelRahman (2002), “Modeling Residual NAPL in Water-Wet Porous Media”, Journal of Agricultural Science, Vol. 7, No. 2, pp. 1-7. [13] S. M. Maliyekkal, E. R. Rene, L. Philip and T. Swaminathan (2004), “Performance of BTX degraders under substrate versatility conditions”, Journal of Hazardous Materials, B109, pp. 201–211. [14] A. S. Mayer and C. T. Miller (1996), “The influence of mass transfer characteristics and porous media heterogeneity on non-aqueous phase dissolution”, Water Resources Research, Vol. 32, No. 6, pp. 1551– 1568. [15] J. R. Mihelcic, D. R. Lueking, R. J. Mitzell and J. M. Stapleton (1993), “Bioavailability of sorbed- and separate-phase chemicals”, Biodegradation, Vol. 4, pp. 141-153. [16] J. W. Molson (2000), “Numerical simulation of hydrocarbon fuel dissolution and biodegradation in groundwater,. PhD Dissertation, University of Waterloo, Ontario, Canada. [17] S. E. Powers, L. M. Abriola and W. J. Weber Jr. (1994), “An experimental investigation of non-aqueous phase liquid dissolution in saturated subsurface systems: Transient mass transfer rates”, Water Resources Research, Vol. 30, No. 2, pp. 321-332. [18] E. A. Seagren, B. E. Rittmann and A. J. Valocchi (1999), “A critical evaluation of the local-equilibrium assumption in modeling NAPL-pool dissolution”, Journal of Contaminant Hydrology, Vol. 39, pp. 109–135. [19] B. K. Yadav and S. M. Hassanizadeh (2011), “An overview of biodegradation of LNAPLs in coastal (semi)arid environment”, Water Air Soil Pollution, DOI 10.1007/s11270-011-0749-1. [20] X. Yang L. E. Erickson and L. T. Fan (1995), “A study of the dissolution rate-limited biodegradation of soils contaminated by residual hydrocarbons”, Journal Hazardous Materials, Vol. 41, pp. 299-313.

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Treatment mechanisms for tank bottom sludge remediation: Challenges and future scope S. Sivabalan1, R Gardas2, J. S. Sangwai3* 1 and 3 Department of Ocean Engineering, IIT Madras, Chennai, India. 2 Department of Chemistry, IIT Madras, Chennai, India. E-mails: [email protected]; [email protected]; 3*[email protected] * Author for correspondence. Abstract: This report presents the review of degradation of Asphaltenes using ionic liquids. Different kinds of ionic liquids are studied to overcome the scale formation in the tank bottom and to extract the hydrocarbon from this sludge. The influences of contents of sulfur and water, reaction temperature, and transition metal salts on upgrading the viscosity reduction were reviewed. An ionic liquid works effectively which has less alkyl chain length on cation and more charge density on anionic parts of ionic liquids. The transition metal based ionic liquids [(Et)3NH][AlCl4] -Mn+ can further reduce viscosity, average molecular weight and asphaltenes content by the reaction with asphaltenes sulphur, but increasing the water content depressing the recovery of hydrocarbon process by increasing energy of separation. Key words: Asphaltenes degradation; Different kinds of Ionic liquids; Recovery of oil from tar sand; interaction forces 1. Introduction The recent trends of producing waxy and asphaltic crude oil from the reservoir are very common. These types of crude oil typically contents higher hydrocarbon, particularly waxes and asphaltenes, which are mainly in dissolved state at the reservoir conditions. When the crude oil flows from the reservoir to the surface condition, the reduction in the system pressure and temperature makes these components separate from the bulk stream and accumulates [1]. The gradual accumulation of these heavier hydrocarbons is very common in the lower portion of the petroleum storage tanks. This sludge is referred as 'tank bottom sludge' (or tank bottoms).The composition of oily sludge varies due to the large diversity in the quality of crude oils, differences in the processes used for oil-water separation, leakages during industrial processes, and also mixing with the existing oily sludge. Usually, the oily sludge contains water, sand, oils, grease, organic compounds, etc. [2]. The accumulation of oily residues in petroleum industry poses a serious environmental problem. On many occasions, such accumulation renders the tank unusable due to inability to take suction and dispatch crude oil for delivery through pipeline. It is customary to use heated oil and water, dispersant formulations and elaborate oil circulation arrangement to make the sludge soluble and pumpable [3]. The use of expensive bio-surfactants, chemicals and emulsion techniques are not found to be good solutions to treat tank bottom sludge in several occasions. In absence of such arrangement, expensive and time consuming manual cleaning (workers enter the tank and dig out the sludge) becomes necessary [1]. Iconic liquids are one of the promising environments friendly solutions to dissolve the heavier hydrocarbons accumulated as tank bottom sludge. Ionic liquids (ILs) have outstanding chemical and thermal stability(~ -50°C to +250°C), are largely nonflammable, almost negligible vapor pressure(~ 10-11 to 10-10 bar at room temperature), water is easily distilled from the ILs, and both can be reused numerous times and have highly solvating capacity for organic, inorganic and organometallic compounds [4] [5]. Accordingly, they are now being considered as an attractive solvents (green solvents) for many chemical processes and getting increasing attention in research from both academia and industry sector [6]. Ionic

liquid also helps in decreasing crude oil viscosity through catalytic cracking of heavy components as its gets in contact with the heavy oil. Therefore, ionic liquid has a great potential as a good solvent for tank bottom sludge and can be used to increase the efficiency of the surface facilities. Small amount of water was used to recycle IL, and organic solvent could be readily regenerated by distillation [7]. In this review we discuss about the different types of ionic liquids have been used in oil and gas industry for removal of oily sludge and for dissolution of heavy oil through the use of ionic liquids to reduce the viscosity and increase solubility of heavier hydrocarbon in the bulk stream. 2. Dissolution of Asphaltenes Asphaltenes are the low molecular weight n-paraffin insoluble and nonpolar aromatic (benzene/toluene) soluble fraction of the crude oil and it could be identified as poly aromatic condensed rings with short aliphatic chains and polar heteroatoms N, O and S in functional groups such as ketones, thiophenes，pyridines and porphyrins [6]. The solubility of Asphaltenes with ionic liquids is studied for the first time by LIU Yanshen and HU Yufeng et al, Ionic liquids shows very good performance of dissolution with asphaltenes as novel solvents. Ionic liquids are the combination of both cation containing a conjugated aromatic core and anion which are strong hydrogen bond acceptors are most effective. Asphaltenes association could be easily broken by increasing the charge density on the anionic part and decreasing alkyl chain length the cationic head ring of ionic liquids [6]. Chemical treatments of asphaltenes typically done by using the cyclic nonpolar solvents such as xylene, benzene, and toluene (aromatic) which has potentiality to dissolve asphaltenes [4] [8]. They have the similar solubility character for bitumen oil, thereby bitumen oil can be removed effectively [9]. The main characteristic feature of non polar aromatic solvent is its ability to reduce the viscosity of heavy oil and to sharpen the boundaries between the phases [4]. But these aromatic based solvents are volatile and hazardous, so it should be replaced by new solvents, which does not affect the environment [8]. Ionic liquids which has the same cation with different anions, shows the solubility order in the series of [PF6] < [BF4] - < [C1] -, These results says the anion which has more charge density and less size will leads to give more hydrogen bonding interaction with asphaltenes unit followed by better solubility [6]. Similarly the ionic liquids which has the same anion with different cations, shows the solubility order of [C4isoq]+ > [N alkyl PY]+ > [BMIM]+. This may be due to the cation which having more conjucated core will show better interaction with asphaltenes aromatic unit [10]. Solubility of asphaltenes decreases apparently with an increase in the substituted alkyl chain length of ionic liquids [NbuPY] [C1] < [NprPY] [C1] < [NetPY] [Cl] [6]. -

3. Effects of Transition metal ionic liquids Reducing the viscosity of heavy oil can be achieved by aquathermolysis through the reactions of denitrogenation and desulfurization [11]. Aquathermolysis method is the most effective method to reduce the viscosity of heavy oils, but this method some time will induce the polymerization and also it operates relatively at high temperatures only. Recently room temperature ionic liquids work with more effectively on asphaltic sand degradation reaction [12]. Zou. Et.al found that chloroaluminate(III) ionic liquids/H3PO4 systems were effective reaction medium for asphaltic sands degradation [13]. FAN Hong-fu et.al discussed the effects of different kinds of ionic liquids on the viscosity, hydrocarbon composition and average molecular weights of the heavy oil are investigated before and after the reaction with ionic liquids. Results show that ionic liquids have the ability to reduce the viscosity, average molecular weights, and asphaltenes of the heavy oil. The SARA (saturates, aromatics, resins, asphaltenes) analysis also performed to know the composition changes before and after the reaction with ionic liquids. The result gives the asphaltenes contents get decreased while all other contents such as saturates, aromatics, resins get increased after the reaction with ionic liquids [12].

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Table: 1 Effect of ionic liquids [12] System Untreated oil [(Et)3NH][Al Cl4] [(Et)3NH][Al Cl4]-Ni2+ [(Et)3NH][Al Cl4]-Fe2+ [(Et)3NH][Al Cl4]-Cu+

Hydrocarbon composition w / % saturates 28.4

aromatics 27.6

resins 32.4

asphaltenes 11.6

Viscosity reduction (%) -

Avg. Molecular weight 584

Content of Sulphur

29.4

28.3

32.8

9.5

44.05

453

0.86

30.6

29.2

33.6

6.6

64.76

369

0.26

29.8

28.5

32.5

9.2

61.43

412

0.52

30.2

28.7

33.8

7.3

62.62

385

0.34

1.68

There are three different metal modified ionic liquids have been chosen along with non metal ionic liquid to do the reaction with pre analyzed heavy oil. Among those three metal ion, Ni2+ based [(Et)3NH][AlCl4]-Ni2+ has the best performance on viscosity reduction, asphaltenes content reduction, as well as to reduce the average molecular weights of the heavy oil. The contents of the sulphur also decreased in the case of [(Et)3NH][AlCl4]-Ni2+ after treated with ionic liquids [12]. 4. Reaction mechanism between Ionic liquids and heavy oils Nowadays, ionic liquids are widely used in extraction, desulfurization, and scale removal because of their excellent solubility and catalytic properties in a wide temperature range [14]. In the reaction mechanism between ionic liquids and heavy oil, first step is the reaction of organic sulphur from heavy oil with transition metal modified ionic liquids to form the intermediate complex (S―›M+), which will helps to weaken the C-S bonds followed by breakage of the heavy oil molecules, The result of this reaction, H2S released and the content of the sulphur get reduced in the heavy oil [15]. Thus, the decrease of the viscosity, average molecular weight and asphaltenes reduction of the heavy oil treated by ionic liquids may be caused by the breakup of C−S bonds [12]. The combination of little amount transition metal salt with the ionic liquids can also enhance viscosity reduction [15].

Figure: 1 Reaction mechanism between ionic liquids and the heavy oil [12].

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FAN Ze-xia et.al discussed the effect of water content in the heavy oil has the negative effect on the viscosity reduction of heavy oil, The result of their study shows the contents of sulphur and asphaltene in the oil samples increase and viscosity reduction ratio decreases with the increase of water content. If the water content in the heavy oil sample is more than 20%, it is very difficult to enhance the viscosity reduction of the heavy oil. Less than 10% of water content is better. The reason for this, imidazolium based ionic liquid will have the more acidic proton on the ring, this proton can easily form a strong hydrogen bond when it is contacted with water and it reducing the activity of ionic liquids [15]. 5. Recovery of oil from tar sand

Figure 2.General diagram for solvent extraction processes by using ionic liquids [7]. Typically in oil sand industry the recovery of oil from tar sand could be achieved by Water based extraction process (Hot water extraction process), but this method requires higher temperatures and mechanical work [4] [7]. Alternatively, the ionic liquids (green solvents) having the unique behavior to enhance the recovery of bitumen from oil sand [7]. This reaction was performed in room temperature (~25°C), tar sand (oil sand) is simply mixed with an ionic liquid and a non polar solvents it gives a multiphase system consist of mixture of sand, clay, an ionic liquid layer and an organic layer containing bitumen oil with non polar solvents. In the mixture there are three different phases, the top one consist of bitumen/toluene solution, the middle phase is IL with some amount of bitumen and the bottom layer is sand/IL slurry. All these phases have separated by using pipette and its solvents are evaporated. Finally this extraction process was confirmed by recording Infrared spectroscopy experiment for both original tar sand and the residual sand. Methylene and methyl CH stretching modes between 2800 and 3000 cm-1 can be clearly seen in the spectrum of the original tar sand and it gets disappear in the residual sand [4]. This extraction is much favors in basic medium i.e. pH values more than 7, since these bitumen have more attraction with sand in acidic medium [16].If extraction conducted over a long period of days, the bitumen can be contaminated with carbonates [17]. The ionic liquids which have low surface tension showed a high efficiency of bitumen recovery [7].

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Figure: 3 Comparison of the infrared spectra of the original tar sand and the residual sand [4].

Figure: 4 Phases formed by mixing an oil/sand mixture with ionic liquid [18]. 6. Interaction between Ionic liquids and bitumen oil The separation of oil from sand is mainly depending on the interaction between sand and bitumen oil [4]. Masliya et.al discussed the effect of interaction between oil and sand components in the separation process by measuring repulsive force between bitumen and silica particles [19]. Atomic Force Microscopy (AFM) has been used to study interaction forces and adhesion forces between bitumen surfaces and silica in the presence of liquid medium [18]. Adhesion force between bitumen and silica are significantly smaller in the presence of ILs than in aqueous solution. Similarly the contact angle between the bitumen oil and water droplets are ‫׽‬90, but in the case of bitumen oil and ionic liquid are ~73 [18]. These results show the separation is easier by using ionic liquids rather than water. The interface tension and surface tension between bitumen and silica decreased in the presence of ionic liquids, to facilitate their separation [7]. Schramm and Smith et.al discussed the thermodynamic forces which play major role in the separation process [20]. Thermodynamic researches indicate that the energy of separation of silica from oil is smaller in an ionic liquid medium than in aqueous solution [18]. 7. Conclusion This paper reviewed the degradation of tank bottom sludge as a solution for the scale formation in tank bottom of petroleum industry. Surface tension, interfacial tension and viscosity are the major factors that are reduced by the addition of ionic liquids on oily sludges. Experimental results show that ionic liquids have the ability to reduce the viscosity, average molecular weights, and asphaltenes of the heavy oil. Ni2+ based transition metal [(Et)3NH][AlCl4]-Ni2+ ionic liquids has the best performance on the reduction of viscosity, asphaltenes content as well as to reduce the average molecular weights of the heavy oil. Also it reduces the 53

content of sulphur. Thus, the decrease of the viscosity, average molecular weight and asphaltenes of the heavy oil treated by ionic liquids may be caused by the breakup of C−S bonds. The presence of water content in the heave oil has the negative effect on the viscosity reduction of heavy oil, less than 10% of water content is better for good recovery. Asphaltenes unit get broken easily, when increasing the charge density on the on the anionic part and decreasing alkyl chain length on the cationic head ring of ionic liquids. The completion of the extraction process was confirmed by using infrared spectroscopy, this extraction is much favors in basic medium i.e. pH values more than 7. Ionic liquids enhanced the separation by diminishing the adhesive force and contact angle between bitumen and silica. Thermodynamic calculation also support for the ionic liquids, because it decreasing the energy of separation of silica from oil is smaller in an ionic liquid medium than in aqueous solution. Therefore, ionic liquid has a great potential as a good solvent in tank bottom sludge for scale removal and can be used to increase the efficiency of hydrocarbons recover process from that oily sludges. This processes would minimizes the waste. References 1. United States Patent number, 4364776. 2. United States Patent number, US 2011/0042318A1. 3. United States Patent number, US005085710A. 4. Painter PP, Williams P, Lupinsky A (2010b) Recovery of bitumen from Utah sands using ionic liquids. Journal of Energy & Fuels, 24, 5081-5088. 5. Welton, T, (1999), Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis, Chem. Rev., 99, 2071–2083. 6. Liu Y, Hu Y, Wang H (2005) Ionic liquids: Novel solvents for petroleum asphaltenes. Chinese Journal Chemical Engineering, 13, 564-567. 7. Xingang Li, Wenjun Sun, Guozhong Wu (2011), Ionic Liquid Enhanced Solvent Extraction for Bitumen Recovery from Oil Sands, 25, 5224–5231. 8. De Boer,R.B，Leerlooyer，K., Eiger，M.R.P，van Berg en，A.R.D，“Screening of crude oils for asphalt precipitation: theory practice and the selection of inhibitors”，SPEPF,5, 55-6l (1995). 9. Wang, S.; Liu, J.; Zhang, L.; Masliyah, J.; Xu, Z, (2010), Interaction Forces between Asphaltene Surfaces in Organic Solvents, Langmuir, 26, 183–190. 10. Visser ，A.E．，Holbrey，J. D ，Rogers ，R.D ，(2011)“ Hydrophobic ionic liquids incorporating N-alkyl isoquinolinium cations and their utilization in liquid-liquid separation” , Chem. Comm., 2484-2485. 11. Zhao X F, Liu Y J, Fan H F, Zhong L G, (2002), Study on feasibility of heavy oil aquathermolysis. Journal of Fuel Chemistry and Technology, 30(4): 381–384. 12. Fan H, Li ZB, Liang T (2007) Experimental study on using ionic liquids to upgrade heavy oil. Journal of Fuel Chemistry and Technology, 35, 32-35. 13. Zou C J, Liu C, Luo P Y, (2004) Catalytic degradation of macromolecule constituents of asphaltic sand in ionic liquids. Journal of Chemical Industrial and Engineering (China), 55(12): 2095−2098. 14. Wang L S, You Q, Zhao F L, (2005), Research on ionic liquid as scale removal of barium sulphate. Chinese Journal of Applied Chemistry, 5, 603–604. 15. Fan ZX, Wang TF, He YH (2009) Upgrading and viscosity reducing of heavy oils by [BMIM][AlCl4] ionic liquid. Journal of Fuel Chemistry and Technology, 37, 690-693. 16. Dai, Q.; Chung, K. H, (1995), Bitumen-sand interaction in oil sand processing, Fuel, 74, 1858–1864. 17. Garcia, J.; Torrecilla, J. S.; Fernadez, A.; Oliet, M.; Rodriguez, (2010), (Liquid + liquid) equilibria in the binary systems (aliphatic, or aromatic hydrocarbons + 1-ethyl-3 methyl imidazolium ethylsulfate, or 1-butyl-3methylimidazolium methylsulfate ionic liquids), J. Chem. Thermodyn., 42, 144–150. 18. Hogshead CG, Mannebach E, Williams P, Lupinsky A, Painter PP (2011) Studies of bitumen-silica and oil-silica interactions in ionic liquids. Journal of Energy & Fuels, 25, 293-299. 19. Liu, J.; Xu, Z.; Masliya, J, (2003), Studies on Bitumen-Silica Interaction in Aqueous Solutions by Atomic Force Microscopy, Langmuir, 19, 3911–3920. 20. Schramm, L. L; Smith, R. G, (1985), The influence of natural surfactants on interfacial charges in the hot water process for recovering bitumen from the Athabasca oil sands , Colloids Surf., 14,67–85.

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Experimental investigations on the phase equilibrium of semiclathrate hydrates of quaternary system of CO2+TBAB+SDS+H2O Abhishek Joshi1, Jitendra S. Sangwai2* 1 Schlumberger, India 2 Department of Ocean Engineering, IIT Madras, Chennai, India. E-mails: [email protected]; 2*[email protected] * Author for correspondence. Abstract: Semiclathrate hydrates of tetra-n-butyl ammonium bromide (TBAB) offers potential solution for gas storage, transportation, separation of flue gases and CO2 sequestration. Experimental set up, namely, high pressure reactor, is developed as a part of this work. Experimental studies are carried out to test the efficacy of the newly developed experimental set-up for understating the phase stability of semiclathrate hydrates. Experiments are carried out on a semiclathrate hydrate system of CO2+TBAB+SDS+H2O for 5, 10 and 20 weight percent (wt %) of TBAB to determine the phase equilibrium temperature and pressure conditions. The data on phase equilibria of semiclathrate hydrates for 5 wt % and 10 wt % TBAB shows good agreement with the published data from the open literature. It is also observed that the presence of Sodium Dodecyl Sulphate (SDS) does not influence the equilibrium conditions for semiclathrate hydrate system. The model predictions of the phase equilibria model for semiclathrate hydrates developed in earlier work (Joshi et al., J Nat Gas Chem, 2012) are found to be in good agreement with the data generated in this work. Re-nucleation (memory) effect of semiclathrate hydrates of CO2 is studied for few cases of TBAB concentration in an aqueous solution. The equilibrium point obtained for memory effect and the regular experimental run are observed to be quite close. It is observed that, for the case of no memory effect, with the increase in the TBAB percentage in the system, the time required for nucleation reduces. In case of memory effect, for the same TBAB concentration, the incipient pressure and temperature required for re-nucleation increases while the time required for re-nucleation of semiclathrate hydrate decreases. This study, in general, indicates that with increase in the concentration of TBAB in the system does help to form semiclathrate hydrates at early stage. Keywords: Carbon dioxide; Clathrate Hydrate, Phase Equilibria; Semiclathrate Hydrate. Introduction Natural gas hydrates, also referred to as clathrate hydrates, are formed under the extreme conditions of low temperature and high pressure, when gases like carbon dioxide, methane, nitrogen, etc., comes in contact with water. Gas hydrates are compounds in which guest molecules are enclosed by three-dimensional cage like lattice structure made by host water molecules [1]. The cages are destroyed by destabilizing the phase equilibrium condition, typically, by raising the temperature or decreasing the pressure or by employing chemical inhibitors. Semiclathrate hydrates are similar to the gas hydrates, but have a different lattice structure as compared to the gas hydrates. This structural difference arises because semiclathrate hydrates are formed when the gas hydrate system contains some thermodynamic promoter, like, Tetra-n-ButylAmmonium Bromide (TBAB); Tetra-n-Butyl- Ammonium Chloride (TBAC); Tetra-n-Butyl-Ammonium Fluoride (TBAF); etc. TBAB in water forms a semiclathrate hydrate which shares similar physical and structural properties as true clathrate hydrates. The principal difference is that, unlike true clathrates, where the guest molecules are not physically bonded within the water structure, in semiclathrate hydrates, the guest molecules of TBAB may, both form the part of the water lattice and occupy cages, in addition to gas molecules which occupy the remaining cages [2 – 5].

Typically, semiclathrate hydrates are formed at lower conditions of pressure and temperature as compared to gas hydrate system for same gas as a guest molecule. Semiclathrate hydrates have wide range of engineering applications such as carbon dioxide sequestration, transportation and storage of natural gas and flue gas separation, etc [6 – 10]. Arjmandi et al. [2] conducted experiments to determine the equilibrium temperature and pressure of semiclathrate hydrates of methane, carbon dioxide and nitrogen with varying percentages of TBAB in the aqueous system. The TBAB weight percentage (wt %) was varied from 5 wt % to 42.7 wt % and data sets on equilibrium temperature and pressure was recorded. The equilibrium data published by Arjmandi et al. [2] clearly shows a parallel shift to the right in the equilibrium curve of semiclathrate hydrates as compared to that for the pure clathrate hydrate systems. This shift implies that semiclathrate hydrates are formed at much milder conditions of temperature and pressure as compared to pure natural gas hydrates. Several researchers [11 – 15] conducted experiments to determine equilibrium temperature and pressures of semiclathrate hydrate systems. Duc et al. [11] conducted phase stability experiments on carbon dioxide semiclathrate hydrates for varying TBAB wt % from 4.95 wt % to 65 wt %. Lin et al. [12] studied the phase equilibrium and the dissociation enthalpy of carbon dioxide semiclathrate hydrates formed in the presence of TBAB. Sakamoto et al. [13] studied the thermodynamic behavior of hydrogen semiclathrate hydrates formed in an aqueous solution of TBAB. Li et al. [14] conducted experiments for semiclathrate hydrates of carbon dioxide for 5 and 10 wt % of TBAB. Sun et al. [15] determined equilibrium temperature and pressure of methane hydrates for 5 wt % to 45 wt % percentages of TBAB in the system. Li et al. [16] and Ding et al. [17] performed experiments to study the formation and dissociative behavior of methane semiclathrate hydrates in an aqueous system containing TBAB. Mohammadi et al. [18] conducted experiments to determine the phase behavior of an aqueous system of methane and hydrogen sulfide in the presence of TBAB. Acosta et al. [19] performed experiments on the semiclathrate hydrates formed by mixture of methane and carbon dioxide. The authors varied the wt % of TBAB in the system from 5 wt % to 20 wt %. Meysel et al. [20] conducted experiments for a quaternary mixture of (CO2 + N2 + TBAB + H2O) and determined the equilibrium temperature and pressure of semiclathrate hydrates formed by the mixture of gases. Zhong et al. [21] determined the formation temperature and pressure conditions for semiclathrate hydrates formed using a mixture of gases in an aqueous solution of TBAB. In this work, an experimental study is performed on the phase behavior of semiclathrate hydrates of quaternary mixture of CO2+TBAB+SDS+H2O system for varying wt % of TBAB in an aqueous solution. An experimental procedure is verified for couple of sets of data on aqueous TBAB system from an open literature. A developed model for phase behavior of semiclathrate hydrates system [22] is applied for the experimental data generated in this work. Re-nucleation (memory) effect is examined for semiclathrate hydrates of carbon dioxide and the effect of TBAB concentration on the incipient conditions (pressure, temperature and time) required for re-nucleation is discussed. Experimental details The heart of the experimental set-up is a high pressure reactor (hydrate view cell) as shown in Figure 1. The volume of the high pressure reactor is about 1 liter. The maximum operating pressure of the reactor is 10 MPa while the design pressure is 15 MPa. The reactor has a magnetic stirrer which has a maximum rotation speed of 1000 rotations per minute (rpm). The high pressure reactor is installed with pressure transducers and temperature sensor, Pt-100. The reactor also has a jacket within which ethylene glycol+water solution is circulated from the Julabo® water bath at desired temperature. The reactor and the Julabo® water bath is connected to the computer (PC; Intel® core i-5, 2 GB RAM) and operated on-line. The data on pressure and temperature as a function of time is acquired at an interval 30 seconds and stored in the PC.

56

Figure 1: Details of the experimental setup used in this work. 1: CO2 Gas Cylinder; 2: High Pressure Reactor; 3: Julabo® Water Bath; 4: Temperature Control Panel; 5: Temperature and Pressure Data Acquisition Unit; 6: Computer; 7: Vacuum Pump. TBAB (in the powder form) and SDS used in this work are of ultrapure quality and is supplied by Sisco Research Laboratory Private Limited, Mumbai. De-ionized water obtained from Millipure® deionized set-up is used to make TBAB solution of varying wt % as per the requirement. Carbon dioxide gas used in this work is 99.5 % pure and is supplied by Bhuruka Gas Agency, Banglore, India. The weighing balance is provided by RADWAGTM, model number ASX/220. It gives weight up to four decimal places of accuracy. The carbon dioxide cylinder is equipped with a heater at the outlet which helps a smooth flow of gas to the reactor at desired pressure. Typically two methods, the isochoric and the isobaric methods, are used for the determination of phase equilibrium of semiclathrate hydrates. In this work an isochoric method is used. In this method (which is most widely used for determination of equilibrium point of hydrates systems) the volume of the system is kept constant. The temperature of the system is reduced, which results in the reduction of system pressure. An abrupt fall in pressure of the system is observed at the onset of hydrate nucleation. After attaining sufficient pressure drop, the system is heated slowly till it comes to its initial pressure condition. This is evident from retracing of the heating profile with the initial cooling profile. The point of equilibrium is decided as the intersection of tangents drawn on heating and cooling line. Results and Discussion Firstly, we presents the results on experimental study on the phase behavior of semiclathrate hydrate system of quaternary mixture of CO2+TBAB+SDS+H2O for 5, 10 and 20 wt % of TBAB along with the model predictions of Joshi et al. [22]. Several experiments are performed to accumulate the data sets on equilibrium pressure and temperature conditions of semiclathrate hydrate of CO2. Table 1 gives the details of experiments performed in this study. The weight percentage mentioned in Table 1 is on the basis of volume of the water. This is followed by the discussion on the re-nucleation effect of semiclathrate hydrates of carbon dioxide and the effect of TBAB concentrations on the same.

57

Table 1: Details of the experiments performed in this studya System TBAB wt % No. of data points on Equilibrium P and T CO2+TBAB+H2O 5 6 CO2+TBAB+H2O 10 5 CO2+TBAB+H2O 20 7 a SDS wt % used in all above experimental runs is 0.025 wt %. Experimental Results Figures 2 - 4 show the experimental data on phase equilibrium for carbon dioxide semiclathrate hydrate system with 5 wt%, 10 wt% and 20 wt% TBAB, respectively. The equilibrium data obtained in this work is compared with the equilibrium data available in an open literature [2, 11, 16, etc.]. It is found that the data obtained in this work is in well agreement with the equilibrium data from the literature for 5 and 10 wt % of TBAB in the system. As mentioned, we have performed experiments with an addition of 0.025 wt % of SDS in TBAB aqueous solution. The obtained results from this work show that the presence of SDS in the system does not influence the phase equilibrium of semiclathrate hydrates of carbon dioxide. It is to be noted here that no separate study is performed to see the increase in rate of reaction of semiclathrate hydrate formation, but we expect the formation to be fast in presence of SDS as experienced by other researcher for clathrate system. Model predictions The Chen and Guo model [23, 24] for clathrate hydrates of natural gases in extended by Joshi et al. [22] for semiclathrate hydrate system of CH4, CO2 and N2 and found satisfactory in predicting the phase equilibrium conditions. The model is applied for the data sets generated in this work. The model predictions for the 5 and 10 and 20 wt % TBAB+CO2 system are observed to be in well agreement with the data from the open literature and the data developed in this work (Figures 2 - 4). 7 6

Pressure, MPa

5 4 3 2

Memory Effect

1 0 275

280

285

290

295

300

Temperature, K

Figure 3: Experimental results for carbon dioxide semiclathrate hydrates with 5 wt % TBAB. Experimental values are shown by symbols and model predictions by lines. ∆: Duc et al. [11]; ◊: Li et al. [14]; ●: this work; ○: 5 Memory effect, this work; x: Pure Carbon Dioxide [1]; ——: Model Predictions [22]; - - - : Model Predictions for pure CO2 hydrates [23]. Re-nucleation Effect in Semiclathrate Hydrate The purpose of this study is not to analyze the re-nucleation (memory) effect in detail, but to get an inference on the effect of TBAB concentration on this process. To understand the memory effect in detail one may require more sophisticated analytical/visual techniques. For this, out of several experimental runs (as in Table 1), three cases, one each from 5, 10 and 20 wt % TBAB cases is considered for which the initial conditions of system pressure is nearly same. This is around 2.25 MPa of initial system pressure and initial temperature of nearly in the range 298.15 - 300.15 K. It is to be noted here that in order to draw realistic and practical conclusions and inferences, same initial conditions of system pressure and temperature are considered for the three cases of wt % of TBAB as 58

mentioned. 7

Pressure, MPa

6 5 4 3

Memory Effect

2 1 0 275

280

285

290

295

300

Temperature, K

Figure 4: Experimental results for carbon dioxide semiclathrate hydrates with 10 wt % TBAB. Experimental values are shown by symbols and model predictions by lines. ○: Arjmandi et al. [2]; : this work; □ Memory effect, this work; ∆: Pure Carbon Dioxide [1]; —— Model Predictions [22]; - - - : Model Predictions for pure CO2 hydrates [23]. 5 4.5 4

Pressure, MPa

3.5 3

Memory effect

2.5 2 1.5 1 0.5 0 275

280

285

290

295

Temperature, K

Figure 5: Experimental results for carbon dioxide semiclathrate hydrates with 20 (this work) and 42.5 {Arjmandi et al. [2]} wt % TBAB: Experimental values are shown by symbols and model predictions by lines. : 20 wt %, this work; □: 20 wt %, memory effect, this work; ○: 42.7 wt % {Arjmandi et al. [2]}; x: Pure carbon dioxide [1]; —— Model predictions of Joshi et al. [22] (this work, for 20 wt % TBAB); : Model predictions of [22] (this work, for 42.7 wt % TBAB);- - - : Model predictions for pure CO2 hydrates [23] The Table 2 gives a comparative study between the difference in insipient temperature and pressure conditions at which nucleation starts in case of first run and a run with memory effect (second experimental run for re-nucleation effect) along with the corresponding time of nucleation to re-form the semiclathrate hydrates in the system for 5, 10 and 20 wt % of TBAB. The equilibrium point obtained for memory effect and the regular experimental run are observed to be quite close (also shown in Figures 2 – 4). It is observed from Table 2 that, for the case of no memory effect, with the increase in the TBAB percentage in the system, the time required for nucleation reduces. In case of memory effect, for the same TBAB concentration, the incipient pressure and temperature required for re-nucleation increases while the time required for re59

nucleation of semiclathrate hydrate decreases. This study, in general, indicates that with increase in TBAB wt % in the system does help to form semiclathrate hydrates at early stage. Table 2: Temperature and pressure variation with time during the memory effect phenomenon P and T Condition at first run Sr. No.

a

TBAB Wt %

P and T Condition at re-nucleation (memory effect)

T1 a (K)

P1a (MPa)

t1a (sec)

T2b (K)

P2b (MPa)

t2b (sec)

1

5

275.5

1.97

510

277.05

2.06

450

2

10

276.65

1.88

420

278.57

1.97

300

3

20

277.15

1.87

330

275.85

1.89

240

T1, P1, t1 = Incipient temperature, pressure and time at nucleation of semiclathrate hydrates (at T2, P2, t2 = Incipient temperature, pressure and time at re-nucleation of semiclathrate hydrates

b

Conclusion Experiments are carried out on a semiclathrate hydrate system of CO2+TBAB+SDS+H2O for 5, 10 and 20 weight percent (wt %) of TBAB to determine the phase equilibrium temperature and pressure conditions. The data on phase equilibria of semiclathrate hydrates for 5 wt % and 10 wt % TBAB shows good agreement with the published data from the open literature. It is also observed that the presence of Sodium Dodecyl Sulphate (SDS) does not influence the equilibrium conditions for semiclathrate hydrate system. The predictions of the model for phase behavior of semiclathrate hydrates developed in earlier work (Joshi et al., J Nat Gas Chem, 2012) was found to be in well agreement with the experimental results generated in this work. The memory effect phenomenon is studied for few cases of TBAB concentration. The increases in concentration of TBAB in the system helps to reduce the time required for re-nucleation of semiclathrate hydrates. In case of memory effect, for the same TBAB concentration, the incipient pressure and temperature required for re-nucleation increases while the time required for re-nucleation of semiclathrate hydrate decreases. This study, in general, indicates that with increase in TBAB wt % in the system does help to form semiclathrate hydrates at early stage. Acknowledgment Authors would like to thank Director, National Institute of Ocean Technology (NIOT) and NIOT – IITM cell for the encouragement towards setting up the laboratory facilities. Thanks are due to Dr. S. Ramesh, Dr. Ramadass from NIOT and Professor S. K. Bhattacharyya of IIT Madras for their valuable comments and cooperation extended during the work. A financial support from NIOT, Chennai, India, through grant; OEC/10-11/105/NIOT/JITE is also gratefully acknowledged. References [1] E. D. Sloan, C. A. Koh. Clathrate Hydrates of Natural Gases, 3rd Edition, New York: CRC Press, 2008. [2] M. Arjmandi, A. Chapoy, B. Tohidi. J. Chem. Eng. Data, 2007, 52, 2153-2158. 60

[3] W. Shimada, T. Ebinuma, H. Oyama, Y. Kamata, S. Takeya, T. Uchida, J. Nagao, H. Narita. Jap. J. Appl. Phys. Part 2 Letters, 2003, 42, L129-L131. [4] W. Shimada, T. Ebinuma, H. Oyama, Y. Kamata, H. Narita. J. Cryst. Growth, 2005, 274, 246-250. [5] W. Shimada, M. Shiro, H. Kondo, S. Takeya, H. Oyama, T. Ebinuma, H. Narita. Acta Cryst. Sect. C, 2005, 61, 65-66. [6] S. Li, S. Fan, J. Wang, X. Lang, D. Liang. J. Nat. Gas Chem., 2009, 18, 15-20. [7] T. J. Hughes, K. N. Marsh. J. Chem. Eng. Data, 2001, 56, 4597-4603. [8] V. Belandria, A. H. Mohmmadi, A. Eslamimanesh, D. Richon, M. F. Sanchez-Mora, L. A. GaliciaLuna. Fluid Phase Equilibr., 2012, 322-323, 105-112. [9] H. Ida, M. Ono, N. Takasu. Carb. Techn. Conf. Proc., Florida, USA, 2012. [10] S. Fan, S. Li, J. Wang, X. Lang, Y. Wang. Energ. Fuel, 2009, 23, 4202-4208. [11] N. G. Duc, F. Chauvy, J. M. Herri. Energ. Conv. Manag., 2007, 48, 1313–1322. [12] W. Lin, A. Delahaye, L. Fournaison. Fluid Phase Equilibr., 2008, 264, 220-227. [13] J. Sakamoto, S. Hashimoto, T. Tsuda, T. Sugahara, Y. Inoue, K. Ohgaki. Chem. Eng. Sci., 2008, 63, 5789-5794. [14] S. Li, S. Fan, J. Wang, X. Lang, Y. Wang. J. Chem. Eng. Data, 2010, 55, 3212-3215. [15] Z. G. Sun, L. Sun. J. Chem. Eng. Data, 2010, 55, 3538-3541. [16] D. L. Li, J. W. Du, S. S. Fan, D. Q. Liang, X. S. Li, N. S. Huang. J. Chem. Eng. Data, 2007, 52, 1916–1918. [17] Y. Ding, J. Gong, Y. Peng. J. China Univ. Petro. (Ed. Nat. Sci.), 2011, 35, 150-153. [18] A. H. Mohammadi, D. Richon. J. Chem. Eng. Data, 2010, 55, 982-984. [19] H. Y. Acosta, P. R. Bishnoi, M. A. Clarke. J. Chem. Eng. Data, 2011, 56, 69-73. [20] P. Meysel, L. Oellrich, P. R. Bishnoi, M. A. Clarke. J. Chem. Therm., 2011, 43, 1475-1479. [21] D. L. Zhong, Y. Ye, C. Yang. J. Chem. Eng. Data, 2011, 56, 2899-2903. [22] A. Joshi, P. Mekala, J. Sangwai. J. Nat. Gas Chem., 2012, in press. [23] G. J. Chen, T. M. Guo. Fluid Phase Equilibr., 1996, 122, 43-65. [24] G. J. Chen, T. M. Guo. Chem. Eng. J., 1998, 71, 145-151.

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About the editors

R. Sharma is associated with IIT Madras, Chennai, India. His research interests are computer aided geometric design, computational geometry, visualization, and their applications in design, manufacturing and robotics; dynamic data driven forecasting systems; and participatory/democratic economy. He can be contacted at: [email protected].

R. Sundaravadivelu is associated with IIT Madras, Chennai, India. His research interests are computer-aided structural analysis; design; and experimental studies of coastal and offshore structures. He can be contacted at: [email protected].

S. K. Bhattacharyya is associated with IIT Madras, Chennai, India. His research interests are computer aided analysis of ship and offshore structures; and dynamics of floating bodies. He can be contacted at: [email protected].

SP. Subramanian is associated with IIT Madras, Chennai, India. His research interests are petroleum geology; marine geology; and marine survey. He can be contacted at: [email protected].

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Indian Institute of Technology Madras Chennai (TN) – 600 036, India December 2012.

ISBN: 978-93-80689-13-5

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