耦合LNG冷能的液态空气储能系统和液态CO_(2)储能系统对比分析

Comparative study on liquid air energy storage system and liquid carbon dioxide energy storage system coupled with liquefied natural gas cold energy

为解决压缩气体储能系统中外加冷源的供应问题,同时高效利用液化天然气(LNG)冷能,构建了耦合LNG冷能的液态空气储能系统(LNG-LAES)和耦合LNG冷能的液态CO_(2)储能系统(LNG-LCES),并进行了热力学和经济性对比分析。结果表明:气体压缩、膨胀做功和LNG换热环节在两系统中?损较大,是系统优化关键环节;适当增加储释能压力及LNG压力会提升系统性能,而LNG温度过低会降低系统性能。LNG-LAES的最优[火用]效率、膨胀发电量、储能密度分别为57.53%、13.08 MW、79.61 kW·h/m^(3),均高于LNG-LCES(43.42%,5.44 MW,41.16 kW·h/m^(3));但LNG-LCES的循环效率和冷能利用率更高,对LNG温度波动有更强适应性,并在经济性方面表现较优。耦合LNG冷能的两种液态气体储能相比常规未耦合LNG的储能系统循环效率提高了7%~25%,可为改进储能系统性能提供一定参考。

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(CO_(2))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/m^(3),higher than those of the LNG-LCES,namely 43.42%,5.44 MW and 41.16 kW·h/m^(3),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.