Integration of liquid air energy storage with ammonia synthesis process for resource efficiency and cost-effectiveness

Liquid air energy storage (LAES) uses air or nitrogen as both energy storage medium and working fluid. Such a working fluid is directly exhausted during power recovery stage, leading to resource waste. The synthesis of ammonia, a promising hydrogen carrier, on the other hand, requires nitrogen as feed, which is produced by an air separation unit (ASU). The ASU is an energy intensive process, which often works continuously, consuming both peak and off-peak electricity and hence has a high operating cost. This work aims to address the issues by integrating the LAES with the ammonia synthesis process, denoted as LAES-NH3 thereafter. Such an integrated system works in the following manner: at off-peak hours, the ASU operates to provide nitrogen for both the ammonia synthesis and the charging cycle of the LAES; at peak hours, the exhausted nitrogen from the LAES power recovery process is fed to the ammonia synthesis process. In this way, the ASU only operates at off-peak times with low-cost electricity, thus reducing the operating costs of the ASU; the LAES will benefit from reduced capital costs by sharing some key components with the ASU, and the LAES is operated independently from the ammonia synthesis. Thermodynamic and economic analyses are conducted on the proposed LAES-NH3 system. Our analyses show ∼38 % reduction in the ASU operating cost during ammonia synthesis, and a reduced initial investment cost of the LAES by 11.3 %.