The effect of insulation on boil-off gas in liquid air storage tank

Abstract

Increasing renewable energy is posing a challenge to the stability of electricity grid, and the importance of an energy storage system (ESS) is becoming clearer. A Liquid Air Energy Storage System (LAES) is proposed as one of the promising ESS technologies. LAES converts electricity to liquid air efficiently and economically. However, since the storage temperature of liquid air is -196 degrees C, loss of liquid air is inevitable due to evaporation, i.e., boil-off gas (BOG). A loss of liquid air has negative effect on the round-trip efficiency of LAES; therefore, the BOG rate must be minimized. In this research, the insulation performance of liquid air tank is evaluated. To calculate the heat ingress and BOG rate, a partial equilibrium model is developed. The insulation performance is evaluated with varying insulation thickness, emissivity, aspect ratio and materials. The results show that the BOG rate of vacuum insulation can reach 1.8 %/day. For foam glass insulation, the BOG rate can become 2.25 %/day. With optimal geometry, 0.7 %/day for vacuum insulation and 1 %/day for foam glass insulation can be achieved. The vacuum insulation generally shows better insulation performance, however, there is area where the foam glass insulation shows better performance depending on the insulation thickness and emissivity.