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Analysis and Optimization of the Power Cycle Based on the Cold Energy of Liquefied Natural Gas

Liquid natural gas (LNG) delivered by sea-ships contains considerable cryogenic energy which can be used for power generation before its evaporation and introduction into the system of pipe line. Electric power generation utilizing LNG cold energy is a major research direction. There are two kinds of LNG cold energy utilization in electric power generation, that is, independent thermal cycle with natural gas direct expansion and close-loop Rankin cycle. However, the efficiency of LNG cold energy utilization is low. Recently, many efforts have been dedicated to improve the efficiency of LNG cold energy utilization. Different optimizing process has been proposed to improve the utilization of LNG cold energy. However, the optimizing target and methods needed to be further decided. In this paper a new methodology combining the energy level analysis and the pinch analysis is determined. A so-called T-W-H diagram is introduced, where T is temperature, W states the energy level and H indicates the amount of energy. The proposed method can promise modifications quickly for improving a base cycle design. Utilizing this method to analysis the normal Rankin power cycle with LNG cold energy as heat sink, the results show that the thermodynamic imperfection in heat exchanger is the main position for improvement. Based on which two cascading power cycle with LNG cold energy recovery is proposed and the analytical results show that the longitudinal cascading cycle has the high performance than transverse cascading cycle. The simulating results showed that this new method is effective for improving thermodynamic cycle of power generation.