Simulation And Optimization Of The Liquefied Natural Gas Cold Energy Stored And Recovery Process

The compressor shaft work, that is mechanical energy, is transformed to the internal energy of liquefied natural gas (LNG) in the natural gas liquefaction. The volume of LNG, of which temperature is-162℃, is about 600 times smaller than that of natural gas itself, and is a convenient form to transport. It’s necessary to transform the LNG to gas on the terminal to provide users. The LNG energy during gasification is about 830-890kJ/kg and required to recover.The paper based on the study of LNG technology and cold energy recovery in the domestic and overseas introduces three typical LNG processes and three ways to recovery LNG cold energy. The relationship of physical property of LNG varying with the atmosphere pressure and temperature is studied. And the calculation equations of physical property and the process calculation method are determined, such that the physical equations of LNG and ammonia water are SRK and NRTL-RK respectively, while both the mixed refrigerant and smoking equation are Peng-Rob, and Wegstein for process convergence calculation and SQP for optimization are chosen. The simple LNG process of the single-stage propane pro-cooled mixed refrigerant cycle with the relatively smaller power consumption and exergy loss is the part of the coupled process by comparing the work, exergy loss and economy of three different mixed refrigerant cycles. State parameter of each point (temperature, pressure, enthalpy and entropy, e.g.) and process parameters (power consumption, heat, e.g.) are obtained by simulating the coupled process of LNG cold energy stored and recovery in Aspen Plus with Sequential modular method. The effects of the provided pressure natural gas, the pressure at the outlet of compressors and throttle valves on the COP and exergy efficiency in LNG process, and the effects of the pressure at inlet and outlet of turbines, the maximum temperature of the furnace and condensing temperature on the thermal and exergy efficiency of the cold energy recovery process are made sensitivity analysis. The results of optimization are got and then compared with the simulated results, the economic benefit of the coupled process and the segmented exergy efficiency as the objective function by combining Aspen plus with FORTRAN. Optimized feasibility is assured to provide efficiency enhancement of the coupled process of the LNG cold energy stored and recovery with the theoretical foundation.