Dynamic analysis of a novel standalone liquid air energy storage system for industrial applications

Liquid air energy storage (LAES) is increasingly popular for peak-load shifting of power grids, which includes air liquefaction at off-peak hours and power generation at peak hours. The standalone LAES system does not rely on external cold and heat sources, and hence is more favorable for applications. In the standalone LAES system, heat storage in the air liquefaction process and cold storage in the power generation process play a key role on the system performance. The previous studies often chose propane/methanol as cold storage materials, and thermal oils as heat storage materials, which show a relatively higher system performance. However, propane, methanol and thermal oils are flammable, have a high capital cost and require strict safety measures, which are unfavorable for some industrial applications. To address this issue, we propose a novel standalone LAES system with pebbles/rocks as both cold and heat storage materials in packed beds. Such stores have a low capital cost and a high chemical stability and have not been studied in detail before. The dynamic effect of packed beds on the proposed LAES system is investigated from start-up to stable operation for the first time. Our simulation results show that it takes ~10 days for the system to reach a stable operation from start-up mainly due to the cold accumulation in the packed bed, and the average liquid air yield increases from 0.23 at the start-up to 0.56 in the stable operation. Besides, the proposed LAES system gives a round trip efficiency of ~42.8% and a combined heat and power efficiency of ~82.1%. These findings provide valuable information for industrial applications of the LAES technology.