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Abstract The dual mixed refrigerant (DMR) cycle, which pre-cools natural gas with the mixed refrigerants and then liquefies the natural gas with another set of mixed refrigerants, is well known for having the highest efficiency among the liquefaction cycles. Its possible application to LNG FPSO is also extensively investigated. In this study, the optimal operating conditions, such as the equipment's flow rate, pressure, temperature, and refrigerant composition per flow of the DMR cycle, were determined in consideration of power efficiency. To determine the optimal operating conditions, a mathematical model was formulated based on the mathematical model of the single mixed refrigerant (SMR) cycle with additional consideration of tees, phase separators, and common headers. In the mathematical model, the 227 operating conditions were defined as unknowns and 196 equality constraints related to the thermodynamics for the equipment were formulated. Further, the 15 given variables related to the natural gas, compressor efficiency and seawater coolers were used. This mathematical model can be regarded as the optimization problem, in which the number of unknowns is larger than the total number of equality constraints and given variables. To obtain the optimal operating conditions, the minimization of the required power for the compressors at the cycle was defined as an objective function. Moreover, set as design variables were the 16 operating conditions, such as flow rate, pressure, temperature and composition of the main and precooling refrigerant, natural gas temperature after precooling, and flow rate ratio for the tee. In addition, the temperature conditions for the equipment’s operation were used as inequality constraints. The optimal operating conditions were then obtained by using a hybrid optimization method that consists of the genetic algorithm (GA) and sequential quadratic programming (SQP). The calculation results show that the required power at the obtained conditions was decreased by 34.5% compared with that of the relevant patent obtained in 2001, and 1.2% compared with the corresponding value from the past relevant study carried out in 2008.
Publication Date 2011-06-19

Kyu-Yeul Lee, Ju-Hwan Cha, Joon-Chae Lee, Myung-Il Roh, Ji-Hyun Hwang, "Determination of the Optimal Operating Condition of Dual Mixed Refrigerant Cycle at the Pre-FEED Stage of LNG FPSO Topside Liquefaction Process", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2011, Maui, USA, pp. 151-158, 2011.06.19-24


List of Articles
번호 분류 제목 Publication Date
130 International Conference Ji-Hyun Hwang, Joon-Ho Min, Young-Joo Ahn, Hee-Chang Kim, Myung-Il Roh, Kyu-Yeul Lee, "Optimized Methodology to Build an Integrated Solution to Offshore Topside Process Engineering", Proceedings of ISOPE 2008, Vancouver, Canada, 2008.07.06-11 file 2008-07-06
129 International Conference Ju-Hwan Cha, Seung-Ho Ham, Kyu-Yeul Lee, Myung-Il Roh, Kwang-Pil Park, Heung-Won Suh, "Discrete Event/Discrete Time Simulation of Block Erection by a Floating Crane based on Multibody System Dynamics", Proceedings of ISOPE 2009, Osaka, Japan file 2009-06-21
128 International Conference Ji-Hyun Hwang, Ju-Hwan Cha, Seung-Ho Ham, Bo-Ram Kim, Myung-Il Roh, Kyu-Yeul Lee, "Establishment of Offshore Process FEED Method for Oil-Based FPSO Topsides Systems", Proceedings of ISOPE 2009, Osaka, Japan, pp. 144-150, 2009.06.21-26 file 2009-06-21
127 International Conference Ji-Hyun Hwang, Young-Joo Ahn, Joon-Ho Min, Gwang-No Lee, Ho-Jin Jeong, Mung-Yu Kim, Hee-Chang Kim, Myung-Il Roh, Kyu-Yeul Lee, "Application of an Integrated Basic Process Engineering Solution to Generic LNG FPSO Topsides", Proceedings of ISOPE 2009 file 2009-06-21
126 International Conference John-Kyu Hwang, Geun-Jae Bang, Myung-Il Roh, Kyu-Yeul Lee, "Detailed Design and Construction of the Hull of an FPSO(Floating, Production, Storage, and Off-loading unit)", Proceedings of ISOPE 2009, Osaka, Japan, pp. 151-158, 2009.06.21-26 file 2009-06-21
125 International Conference Bo-Hyun Lee, Kyoung-Sik Chang, Bum-Sang Yoon, Joo-Sung Lee, Myung-Il Roh, "Large Eddy Simulation of Fully Turbulent Channel Flow Using Variational Multiscale Method", Proceedings of the 23rd Asian-Pacific TEAM(Technical Exchange and Advisory Meeting on Marine Structures) 2009, Kaohsiung, Taiwan, pp. 93-97, 2009.11.30-12.03 file 2009-11-30
124 International Conference Yoon-Nam An, Joo-Sung Lee, Myung-Il Roh, Bum-Sang Yoon, Kyoung-Sik Chang, "Parametric Study of Isogeometric Analysis Using NURBS", Proceedings of the 23rd Asian-Pacific TEAM(Technical Exchange and Advisory Meeting on Marine Structures) 2009, Kaohsiung, Taiwan, pp. 169-173, 2009.11.30-12.03 file 2009-11-30
123 International Conference Yoon-Nam An, Joo-Sung Lee, Myung-Il Roh, Bum-Sang Yoon, Kyoung-Sik Chang, "Parametric Study of Mesh Refinement in Isogeometric Analysis", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2010, Beijing, China, pp. 809-812, 2010.06.20-26 file 2010-06-20
122 International Conference Yoon-Nam An, Joo-Sung Lee, Myung-Il Roh, Bum-Sang Yoon, Kyoung-Sik Chang, "Shape Optimization of Structural Member Based on Isogeometry Concept", Proceedings of the 24th Asian-Pacific TEAM(Technical Exchange and Advisory Meeting on Marine Structures) 2010, Vladivostok, Russia, pp. 343-348, 2010.08.23-26 file 2010-08-23
» International Conference Kyu-Yeul Lee, Ju-Hwan Cha, Joon-Chae Lee, Myung-Il Roh, Ji-Hyun Hwang, "Determination of the Optimal Operating Condition of Dual Mixed Refrigerant Cycle at the Pre-FEED Stage of LNG FPSO Topside Liquefaction Process", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2011, Maui, USA, pp. 151-158, 2011.06.19-24 file 2011-06-19
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