Comparative study on liquid air energy storage system and liquid carbon dioxide energy storage system coupled with liquefied natural gas cold energy
In order to solve the main problems of the external cold source for compressed gas energy storage systems,and to effectively utilize the liquefied natural gas(LNG)cold energy,two systems of liquid air energy storage and liquid carbon dioxide(CO2)energy storage systems coupled with LNG respectively(LNG-LAES and LNG-LCES)are established.A comparative study is carried out between the two systems to evaluate their thermodynamic and economic performance.The results show that the exergy loss of the gas compression and expansion processes is larger as well as the process of LNG heat exchange,which provides the direction for system optimization.The rise of energy storage pressure,energy release pressure and LNG pressure can enhance performance of both systems,while the low LNG temperature can reduce the system performance.The exergy efficiency,expansion work and energy-storage density of the LNG-LAES system under optimal conditions are 57.53％,13.08 MW and 79.61 kW·h/m3,higher than those of the LNG-LCES,namely 43.42％,5.44 MW and 41.16 kW·h/m3,respectively.However,the cycle efficiency and cold energy utilization rate of LNG-LCES are higher,it has stronger adaptability to LNG temperature fluctuations,and performs better in terms of economy.These proposed two systems coupled with LNG cold energy perform better in round trip efficiency,7％—25％higher than that of energy storage systems uncoupled with LNG.These results highlight further possibilities for performance enhancement of energy storage systems by integrating LNG.
LNG cold energyliquid air energy storage systemliquid carbon dioxide energy storage systemprocess systemsthermodynamicseconomy
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