Industrial & Engineering Chemistry Research, Vol.52, No.15, 5341-5356, 2013
Optimal Design of Liquefaction Cycles of Liquefied Natural Gas Floating, Production, Storage, and Offloading Unit Considering Optimal Synthesis
The liquefaction process is regarded as primary among all topside systems in liquefied natural gas floating, production, storage, and offloading (LNG FPSO) applications. The liquefaction process, which typically accounts for 70% of the capital cost of topside process systems and 30 to 40% of the overall cost of LNG FPSO plants, condenses separated and pretreated natural gas into LNG. The volume of liquid occupies about 1/600 the volume of the natural gas. The cycles in the liquefaction process use seven main types of equipment: compressor, seawater cooler, expansion valve, heat exchanger, phase separator, tee, and common header. Different types of liquefaction cycles are determined according to their respective synthesis and optimized operating conditions. This study proposes a generic liquefaction model to represent various types of liquefaction cycles. Twenty-seven feasible liquefaction configurations derived from the generic model are selected to perform the most effective synthesis for the optimization of the liquefaction cycle. With a minimum amount of power required for the compressors, an optimized liquefaction cycle is proposed by obtaining optimal operating conditions in 27 cases. The optimized liquefaction cycle is compared with the dual mixed refrigerant (DMR) cycle for the application of LNG FPSO. Finally, the results show that the amount of power required for the operating conditions was decreased by 7.45% compared with that of the DMR cycle.