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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
61 International Conference Kyu-Yeul Lee, Sang-Uk Lee, Doo-Yeoun Cho, Myung-Il Roh, Seong-Chan Kang, Jung-Woo Seo, "An Innovative Compartment Modeling and Ship Calculation System", Proceedings of IMDC(International Marine Design Conference) 2003, Athens, Greece, 2003.05.05-08 file 2003-05-07
60 International Conference Kyu-Yeul Lee, Myung-Il Roh, Sang-Uk Lee, Joong-Hyun Rhim, Seong-Chan Kang, Jong-Hyun Kim, Jeong-Youl Lee, "Development of a Hull Structural CAD System for an Initial Design Stage", Proceedings of International Symposium on PRADS(Practical Design of Ships and Other Floating Structures) 2004, Lubeck Travemunde, Germany, pp. 98-105, 2004.09.12-17 file 2004-09-12
59 International Conference Kyu-Yeul Lee, Myung-Il Roh, Ju-Hwan Cha, "Development of a Non-linear Optimization Program and Its Applications to Shipbuilding", Proceedings of the 1st Mongolia-Korea Joint Workshop on CAD/CAM, Ulaanbaatar, Mongolia, pp. 1-5, 2007.07.08-10 file 2007-07-08
58 International Conference Kyu-Yeul Lee, Myung-Il Roh, Hang-Soon Choi, Woo-Jae Seong, "Development of Hybrid Optimization Method and Its Application to Ship Design Optimization", Proceedings of Pacific 2002 International Maritime Conference, Sydney, Australia, 2002.01.29-31 file 2002-01-29
» 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
56 International Conference Ki-Su Kim, Myung-Il Roh, Sung-Min Lee, Jihye Cha, Jongjin Park, DongYeon Lee, Booki Kim, "An Efficient Method for Cost and Risk Saving in Ship Route Planning", Proceedings of the 31st Asian-Pacific TEAM 2017, Osaka, Japan, 2017.09.25-28 file 2017-09-25
55 International Conference Ki-Su Kim, Myung-Il Roh, Sung-Min Lee, "Toward a Robust Optimization Method for Ship Route Planning Considering Cost and Safety Aspect", Proceedings of ACDDE 2017, Zhangjiajie, China file 2017-08-26
54 International Conference Ki-Su Kim, Myung-Il Roh, Sung-Min Lee, "A Simultaneous Optimization Method of the Direction and Speed for Ship Route Planning", Proceedings of Smart Ship Technology 2017, London, England, 2017.01.24-25 file 2017-01-25
53 International Conference Ki-Su Kim, Myung-Il Roh, Sung-Kyoon Kim, "An Arrangement Design Framework for Ships and Offshore Plants Based on Expert System and Optimization Technique", Proceedings of OMAE 2016, Busan, Korea, pp. 1-5, 2016.06.19-24 file 2016-06-20
52 International Conference Ki-Su Kim, Myung-Il Roh, Seung-Min Lee, "Flooding Analysis Based on PBD (Position Based Dynamics) for Ships and Offshore Structures", Proceedings of ISOPE 2018, Sapporo, Japan, pp. 955-957, 2018.06.10-15 file 2018-06-14
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