一种新型的基于二氧化碳混合物的液体储能系统

A novel liquid energy storage system based on a carbon dioxide mixture

液化二氧化碳储能(LCES)是扩大可再生能源利用规模、保证可再生能源稳定利用的有效方法。为解决LCES系统中亚临界CO_(2)的有效冷凝问题,本文提出一种新型的基于二氧化碳混合物的液体储能系统(LMES)。选择了两种有机工质R32和R161与CO_(2)混合,通过建立该系统的热力学模型,研究了有机工质质量分数、压缩机压比、泵压比、冷却温度(T6)和环境温度五个关键参数对系统性能的影响。结果表明:采用有机工质与CO_(2)混合可以显著提高工作介质的临界温度,解决LCES系统中CO_(2)的冷凝问题;工质为CO_(2)/R32混合物的系统中,有机工质质量分数的增加虽然会使系统的循环效率和能量密度小幅度降低,但可以有效降低系统的工作压力;增加压缩机压比、提高冷却温度以及降低环境温度均可以提高系统的能量密度;在两种混合物的系统中,均存在一个最佳的冷却温度使系统的循环效率达到最大值,采用CO_(2)/R32混合物时,最佳的冷却温度为42℃,系统的循环效率为57.65%,采用CO_(2)/R161混合物时,最佳冷却温度为45℃,系统的往返效率为50.54%;研究还发现相比于CO_(2)/R161混合物,采用CO_(2)/R32混合物作为储能系统的工质可以获得更高的循环效率和能量密度。

Liquid carbon dioxide(CO_(2))energy storage(LCES)is an effective method for expanding the scale of renewable energy utilization and ensuring the stable use of renewable energy.To solve the problem related to the effective condensation of subcritical CO_(2) in an LCES system,a novel liquid energy storage system(LMES),based on a CO_(2) mixture,is proposed in this paper.Two organic working mediums,R32 and R161,were selected to mix with CO_(2).By establishing the thermodynamic model of the system,the effects of five key parameters on the system's performance were studied,i.e.,the mass fraction of the organic working medium,compressor pressure ratio,pump pressure ratio,cooling temperature(T6),and ambient temperature.The results showed that the mixing of an organic working medium and CO_(2) could significantly increase the critical temperature of the working medium and solve the problem of CO_(2) condensation in an LCES system.In a system with the CO_(2)/R32 mixture as a working medium,the increase in the organic working medium mass fraction slightly reduced the round-trip efficiency and energy density of the system,but it effectively reduced the working pressure of the system.The energy density of the system could be increased by increasing the compressor pressure ratio,thus increasing the cooling temperature and decreasing the ambient temperature.In the system that employed both mixtures,an optimal cooling temperature existed to maximize the system's round-trip efficiency.When the CO_(2)/R32 mixture was used,the optimal cooling temperature was 42℃,and the round-trip efficiency of the system was 57.65%.When the CO_(2)/R161 mixture was used,the optimal cooling temperature was 45℃,and the round-trip efficiency of the system was 50.54%.The research also found that,compared with the CO_(2)/R161 mixture,the application of the CO_(2)/R32 mixture as the working medium of the energy storage system obtained a higher round-trip efficiency and energy density.