Study On Power Storage Using Thermodynamic Cycles Of Cold Energy Storage And Recovery Of Liquefied Natural Gas

As a clean, efficient energy, Natural gas is applied to more and more fields, and has been playing an increasingly important role in China's national economy. Liquefied natural gas could be perfectly reduced about 600 times than that of natural gas at atmospheric pressure and at a low temperature. Energy consumed during natural gas liquefaction process is transformed into cold energy stored in liquefied natural gas. The recovery and utilization of liquefied natural gas cold energy during liquefied natural gas gasification process, indicates the transformation of cold energy in liquefied natural gas into other form of energy. In the thesis, the research on simulation and optimization of the coupling process of cold energy storage and recovery of liquefied natural gas are based on the thermodynamics theory, the aim of which is to reduce the sum of power consumption and improve the economic benefits each year of the coupling process.The utilization of cold energy storage and recovery of liquefied natural gas can achieve the intermittent operation of natural gas liquefaction at night and liquefied natural gas gasification during the day, which is of great significance to improving the stability of the electricity system, city's economic benefits, energy conservation and emission reduction. However, so far the research on the coupling process of cold energy storage and recovery of liquefied natural gas has not been reported. In the thesis, a coupling process of cold energy storage and recovery of liquefied natural gas is simulated using the software Aspen Plus. The calculation data of each node of the coupling process are obtained, which include state parameters of each node such as pressure, temperature, enthalpy, entropy, vapor fraction, mass flow, etc., and power consumption and generation, as well as heat duty of heat streams. The simulation results indicate that the coupling process meets the requirements of thermodynamic theory, and factually reflects Operating conditions of the coupling process.Based on the process simulation, a optimization model of the coupling process of cold energy storage and recovery of liquefied natural gas is established and a sensitivity analysis is made for the operating variables, which takes compression ratio of pumps and turbines, phase state of natural gas and refrigerant in pumps and turbines, pressure drop of throttle valves as constraint conditions, and compression ratio of compressor in the mixed refrigerant refrigeration cycle, inlet temperature of throttle in open natural gas liquefaction cycle, mass flow of mixed refrigerant, condensation temperature of Rankine cycle, inlet and outlet pressure of turbines in open liquefied natural gas cycle and Rankine cycle as optimization decision variables, and maximum annual net profit as objective function. On the platform of software Aspen Plus, the optimization model of the coupling process is solved by FORTRAN program. Ultimately, expected optimization results is achieved.In this paper, the research on the coupling process of cold energy storage and recovery of liquefied natural gas, is of great social and economic benefits, and affects theoretical guidance and practical value on social production.