Thermodynamic and economic analysis of a novel hydrogen liquefaction process with LNG precooling and dual-pressure Brayton cycle

Liquid hydrogen with high energy density and cleanliness is a superior alternative to current energy carriers. However, high costs and low efficiency are barriers to liquefy hydrogen. To reduce the energy consumption and investment costs of hydrogen liquefaction, a hydrogen liquefaction process that utilizes a direct expansion cycle of liquefied natural gas for hydrogen precooling and a dual-pressure Brayton cascaded cycle for hydrogen cryocooling is proposed. The hydrogen liquefaction performance and economic benefits of the proposed process are assessed by comparing it with two reference processes with different cryo-cooling cycles. The results reveal the advantageous operating costs and capital costs of the proposed process, especially in terms of the costs of helium and heat exchangers. Moreover, the specific energy consumption of the proposed process is 6.60 kWh/kgH2, which is 4.0% and 4.5% lower than those of the reference processes. The exergy losses and exergy efficiency of the proposed process are 12.36 MW and 47.0%, respectively, and the exergy losses are mainly caused by the compressors and expanders. The energy consumption of the proposed process decreases at first and subsequently increases with the increasing pre-compression pressure of helium.