| Due to high energy efficiency and low impact on environment of natural gas, it is one of the most important energy in 21st century, and the tendency is growing. The world market of LNG becomes more prosperous due to the uneven geographical distribution of natural gas. A number of LNG receiving stations have been being built along coastal areas in China considering the energy needs and long-term energy security. Gas form is accepted in the LNG project terminal, which means LNG must release losts of cold energy during the gasification process. Constructing a reasonable LNG power plant is one of the most effective method. The paper based on this idea to study how to use Rankine cycle to recycle the cold energy and the following work was finished:Consulted and studied the main public documentations and papers about LNG cold utilization. Analysed LNG cold power system process and working fluid selection. Summarized several main unsolved issues which were the foundation of this paper.Built gasification model based on LNG thermaldynaic properties, which included the acclivitous liquid region, the plane latent heat region, the acclivitous latent heat regionand and the acclivitous vaporization region. Analysis was undertaken based on low-temperature Rankine cycle system. The comparison of several kinds of Rankine cycles show that: sub-critical saturation cycle is the best option of Rankine cycle of LNG cooling energy and the condensing temperature is based on parameters (temperature and pressure) of LNG and each working fluid has the best evaporation temperature.According to the basic selection principle for working fluid,system net generation, safety, GWP value etc. should be considered. Meanwhile, the heat source temperature should be lower than the critical temperature of working fliud, and the condensing pressure of working fliud should be higher than atmospheric pressure to reduce the investment and operating costs of maintenance of vacuum. Working fluid was filtered depending on the operating temperature range. Different working fluids, such as R152a,R407C,R600,R1270,R600a,R290,R134a,R143a,R404A,R410A,R507A,Kr,R50,R1150,R170 etc. are analyzed and evaluated according to net power generated. The results indicate that R1150 and R170 are suitable when the condensing temperature is less than -45℃, R152a and R407C are feasible when the condensing temperature is higher than -25℃, R1270 and R290 are suitable when the condensing temperature is between -45℃and -25℃.Traditional exergy analysis can identify clearly the major equipments of exergy losses and thus improvement target, but it is difficult to put forward an improved scheme for the whole sysytem. Pinch analysis can be represented using simple diagram and point out the correct direction for optimization, which can offset the shortage of exergy analysis. By combining the strengths of both methods, T-?-H analysis method was proposed and introduced to evaluate the system. By analyzing and evaluating three kinds of cascade cycles, the optimization cascade cycle of two-stage with gas elicitation was identified.The temperature of sea water is variational because of geographical and seasonal effect. The higher sea temperature is, the greater the optimal evaporation temperature and the net power generation could be achieved. LNG cold power generation was built by using from solar hot water as heat source and producing chilled water for small LNG gasification station. Considering the comprehensive value of cold source and heat source, the system exergy efficiency had been improved.
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