Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran ... the number of heat exchangers required for the same heat duty.
2011 2nd International Conference on Chemistry and Chemical Engineering IPCBEE vol.14 (2011) © (2011) IACSIT Press, Singapore
Energy Optimization of Crude Oil Separation Plant Eid M. Al-Mutairi, Amir Mirgani, Bander F. Daajani and Bilal A. Qureshi Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Abstract. This paper shows how the application of pinch technology can lead towards great energy savings. Pinch analysis has proved to be a simple concept in a field known for complex mathematical methods. Reports of industrial applications claim design improvements in energy saving, due to optimizing the number of heat exchangers required for the same heat duty. The approaches to calculate maximum energy recovery and minimum number of units at different ΔTmin values made it possible for design engineers to distinguish between good and bad network structures prior to design. New graphical methods have been developed for HEN by using the advanced composite curves and grand composite curve to achieve the minimum utilities (hot & cold) requirement. 'Pinch Analysis' is often used to represent the application of the tools and algorithms of Pinch Technology for studying industrial processes. Developments of rigorous software programs such as ‘Heat-Int.’ have proved to be very useful in pinch analysis of complex industrial processes with speed and efficiency. However, the final result is a reduction of energy costs. Keywords: energy, optimization, pinch analysis, oil refining 1. Introduction Process integration can lead to a substantial reduction in the energy requirements of a process. In recent years, much work has been done developing methods for investigating energy integration and the efficient design of heat exchanger networks. One of the most successful and generally useful techniques is that developed by Bodo Linnhoff and other workers: pinch technology. The term derives from the fact that in a plot of the system temperatures versus the heat transferred, a pinch usually occurs between the hot stream and cold stream curves. In this paper, crude separation plant is studied from energy perspectives. The energy is optimized through targeting procedure developed by Linnhoff and others. The main purpose of the Crude Separation Plant is to process the Arabian light crude oil and remove light hydrocarbon vapors from unstabilized crude oil as shown in figure 1. A secondary purpose is to condense and recover these vapors as useful naphtha and LPG products. It also contains the pressurized sewer system equipment. The pressurized sewer system is designed to receive toxic or volatile waste streams from various process plants. These waste streams are collected in a series of receiver drums. Vapors are vented to the process flare and liquids pumped to crude or off-spec product storage tanks for rerun or further processing. Crude oil flows to LP flash spheres to remove the light volatile components. Heat exchangers heat the oil after the flash spheres to vaporize more light components. The oil then passes into the second-stage flash drum. The secondary purpose is achieved in the second-stage flash drum. Some of the gas is condensed and the rest is compressed. The combined stream passes into the light condensate fractionation plant. LPG and naphtha products are recovered in this plant. Then the desalter unit removes residual water, salts, and other impurities from stabilized crude oil planned for sale. The Merox treating process is used to treat light straight-run naphtha to eliminate mercaptan sulfur compounds to less than 5.0 wt ppm. This reduces the total sulfur content in the finished product. Liquidliquid extraction of mercaptan compounds reduces the total sulfur contents of the finished product. The Amine treating substantially removes all the hydrogen sulfide and carbon dioxide from process plant sour gas streams. 156
There are three types of the utilities to provide cooling and heating requirements to support the operation of the plant and produce the final products. These utilities consist of cooling water, low and high pressure steam and hot oil.
Figure 1 Process Flow Diagram
2. Objectives The main objectives of this study are to perform the following tasks: 1- Determine minimum energy requirement (MER) targets, that is, to compute the minimum usage of heating and cooling utilities when exchanging heat between the hot and cold streams in process. 2- Design a network to meet the (MER) target, that is, to position heat exchangers in a network, assuming overall heat- transfer coefficients. To introduced a unit –by- unit method beginning at the closet approach temperature difference (the pinch), 3- Reduce the number of heat exchangers in MER net works, by relaxing the MER target and breaking the heat loops (i.e allowing heat to flow across the pinch), or alternatively, by employing stream splitting. 4- Use the grand composite curve to assist in the selection and positioning of appropriate types of hot and cold utilities in the network. 5- The prime objective of pinch analysis is to achieve financial savings by better process heat integration (maximizing process –to- process heat recovery and reducing the external utility loads).
3. Results and Discussion This study was conducted based on the current operation parameters such as supply and target temperatures and heat capacity flow rate for each hot and cold streams. It has been considered that all flowmeters and temperature devices are calibrated and functioning as well. The preliminary results reveal that the hot utility requirement for this plant is 23.44 MW and the cold utility requirement is 5.9 MW as shown in Figure 2 for composite curves. The pinch temperature is 75 oC therefore, the hot pinch temperature is 80 oC and cold pinch temperature is 70 oC at ∆Tmin = 10 oC. This data was generated by using Heat Int software for data illustrated in table 1. The actual heating utility at this plant is 33.93 MW which is more that the required by 44.75% while the actual cold utility is 13.9 MW which is greater than the requirement by 100%. Hence, the targeting of energy shows that there are huge possibility for energy savings in teh crud 157
stabilization plant. The grand composite curve generated by the Heat-int software as illustrated in figure 3 shows that the utility selection for steam at 170 oC and 200 oC based on the operating parameters should give 23 MW and 23.5MW respectively. In the other hand, the cooling utility at 27oC should give about 6 MW.
Figure 2: Composite curves for hot and cold streams.
Figure 3: Grand Composite Curve
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Figure 4 Grid diagram for the CSP process.
4. Conclusion This study shows that the process optimization and heat integration study for either new or existing plant will help in saving more resources and achieve high profitability. The Heat Int. software is an excellent tool that can be utilized to determine the minimum requirements for hot and cold utilities. So far, the crude separation plant almost meets the hot utility requirements but there is an extra amount of cold utility in use that needs to be minimized in order to meet the minimum cold utility requirements.
5. Acknowledgement The author acknowledges the financial support provided by King Fahd University of Petroleum & Minerals (KFUPM).
6. References [1] Coulson & Richardson’s Chemical Engineering, Vol. 6, 4th edition, Chemical Engineering Design. K. Sinnott, Published by Elsevier Butterworth-Heinemann Linacre House, Jordan Hill, Oxford, 2005. [2] Pinch Analysis for the Efficient Use of Energy, Water and Hydrogen, Canada, 2003. (http://cetc_varennes.hrcan.gc.ca) [3] Pinch Technology: Basics for Beginners (www.cheresources.com/pinchtech1.shtml (8/2008) ) [4] Warren D. Seider, J .D. Seider, Dainel R. Lewin, Product and process design principles synthesis, and evaluation, Published by John Wiley & Sons Inc., USA, 2003. [5] Smith, R., Chemical Process Design and Integration, Center for Process Integration, School of Chemical Engineering and Analytical Science, University of Manchester, Published by John Wiley & Sons Ltd., UK, 2005.
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