An external-compression air separation unit with energy storage and its thermodynamic and economic analysis

Abstract

Long-term supply demand balance in a power grid may be maintained by electric energy storage. Liquid air energy storage (LAES) can effectively store off-peak electric energy, and it is extremely helpful for electric decarburisation; however, it also has problems of high cost, long investment payback period and low efficiency because of its very low liquefaction temperature. Air liquefaction is the basic process of air separation, and the total electricity consumption of air separation units in China accounts for about 5.24 % of its national electricity consumption. Moreover, there remains a surplus of production capacity in air separation. This paper proposes an external-compression air separation process, with liquid air energy storage function. It can effectively reduce the power consumption cost of air separation unit while realizing peak load shifting. The system consists of three subsystems, namely, air separation; air liquefaction and storage; and power generation and air recovery. Research on equipment power consumption, economic benefits, and power grid peak shaving effect, indicates that the round-trip efficiency is 54.52 %, the electricity cost saving rate is 5.13 % based on Shanghai's peak-valley industrial electricity price, and the minimum dynamic payback period is 5.5 years. The large-scale application of this process can reduce the average peak-to-valley difference rate in China by 4.95 %. The transfer of peak regulating load to the base load of the power grid can save 5.2 × 106 toe, which will result in a 2.1 × 107 ton reduction in carbon dioxide emissions annually.