Utmost substance recovery and utilization for integrated technology of air separation unit and liquid air energy storage and its saving benefits

The integration of air separation units (ASUs) and liquid air energy storage (LAES) (ASU-LAES) can bring very good economic benefits based on their resource complementarity at the same low-temperature energy level. Two types of novel process flows are proposed in this paper for ASU-LAES. These flows can use the ASU to recover the maximum amount of refrigerated air from energy storage process to the front or back of the air compressor (i.e., pre- or post-machine recovery), so as to improve the energy efficiency and economic benefits. The pre-machine recovery process flow can achieve an electrical roundtrip efficiency of up to 76.38%. Although a lower refrigeration expansion ratio is used in the post-machine recovery process flow, it can form an air refrigeration cycle without passing through air compressor. Its exergy loss from expansion and compression is smaller, which maximizes liquid air storage. The electrical round-trip efficiency can reach up to 72.9%, and the larger storage scale increases its economic benefit compared to the pre-machine recovery. Based on the peak-to-valley price ratio of 3.4:1, the post-machine recovery process flow can save up to 13.23% of electricity cost compared to the conventional ASU. The dynamic payback period of the LAES is 2.27 years. Compared to ASU-LAES without recovery of refrigeration air, the electricity cost-saving ratio is improved by 134.9%, and the dynamic payback period of the LAES is shorten by 41.8%.