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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
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» 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
110 International Conference Nam-kug Ku, Sol Ha, Myung-Il Roh, Kyu-Yeul Lee, "Dynamic Response Analysis of Multibody System in Discrete Event Simulation", Proceedings of ICORES(International Conference on Operations Research and Enterprise Systems) 2012, Algarve, Portugal, pp. 447-453, 2012.02.04-06 file 2012-02-04
109 International Conference Ji-Hyun Hwang, Nam-Kug Ku, Joon-Chae Lee, Myung-Il Roh, Kyu-Yeul Lee, "Optimal Synthesis of LNG FPSO Liquefaction Cycles", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2012, Rhodes, Greece, pp. 927-935, 2012.06.17-22 file 2012-06-17
108 International Conference Tae-Sub Um, Jeong-Hoon Park, Myung-Il Roh, "Determination of Optimal Principal Dimensions of the Hatch Cover for Lightening of a Bulk Carrier", Proceedings of ISGMA(International Symposium on Green Manufacturing and Applications) 2012, Jeju, Korea, pp. 1-7, 2012.08.27-29 file 2012-08-27
107 International Conference Se-Yong Jeong, Seong-Ho Seo, Myung-Il Roh, "A Method for Determining a Ship Economic Route for Fuel Saving", Proceedings of ISGMA(International Symposium on Green Manufacturing and Applications) 2012, Jeju, Korea, pp. 1-5, 2012.08.27-29 file 2012-08-27
106 International Conference Seong-Ho Seo, Myung-Il Roh, Nam-Kug Ku, Kyu-Yeul Lee, "Dynamic Response Simulation of an Offshore Wind Turbine Suspended by a Floating Crane", Proceedings of ISGMA(International Symposium on Green Manufacturing and Applications) 2012, Jeju, Korea, pp. 1-7, 2012.08.27-29 file 2012-08-27
105 International Conference Sang-Rai Cho, Jong-Min Kim, Young-Hun Kim, Joo-Sung Lee, Myung-Il Roh, "Towards More Rational Design of Ship Structures against Collisions", Proceedings of ICCGS(International Conference on Collision and Grounding of Ships) 2013, Trondheim, Norway, pp. 187-195, 2013.06.17-19 file 2013-06-17
104 International Conference Sol Ha, Nam-Kug Ku, Myung-Il Roh, "Ontological Modeling and Process Simulation of LNG FPSO Liquefaction Cycle based on DEVS Formalism", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2013, Alaska, USA, pp. 950-958, 2013.06.30-07.05 file 2013-06-30
103 International Conference Nam-Kug Ku, Sol Ha, Myung-Il Roh, Kyu-Yeul Lee, "Development of a Kernel for Dynamic Analysis of Various Types of Multi-Crane in Shipyard", Proceedings of ISOPE(International Society of Offshore and Polar Engineers) 2013, Alaska, USA, pp. 693-701, 2013.06.30-07.05 file 2013-06-30
102 International Conference Nam-Kug Ku, Sol Ha, Myung-Il Roh, "Crane Modeling and Simulation in Offshore Structure Building Industry", Proceedings of ICCMS(International Conference on Computer Modeling and Simulation) 2014, Barcelona, Spain, pp. 1-7, 2014.02.20-21 file 2014-02-20
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