Development and thermodynamic analysis of a dual mixed-refrigerant hydrogen precooling process

Abstract Mechanical closed mixed-refrigerant (MR) precooling cycle is an effective method to reduce the precooling power consumption of hydrogen liquefaction, which could be much energy-saving than current liquid nitrogen precooling. In order to reduce the power consumption of current liquid nitrogen precooled hydrogen liquefiers without replacing the precooling heat exchangers, a dual mixed-refrigerant precooling process is proposed and analyzed in this paper. This process consists of a main MR cycle and a secondary MR cycle to delivery cooling power from the main cycle to hydrogen liquefier. The secondary MR is firstly cooled to 83 K by the main MR cycle and then throttled to about 74 K. The cold secondary MR is sent into hydrogen liquefier instead of liquid nitrogen. This dual MR precooling process is combined with a typical 0.46 t/d small hydrogen liquefier, precooling the cycling helium and feed hydrogen to 79 K. The hydrogen ortho-to-para conversion is conducted in an isothermal converter. The simulated hydrogen precooling specific power consumption ( SPC ) of dual MR process is 3.48 kWh/kg-H 2 , which is 15% lower than liquid nitrogen (4.09 kWh/kg-H 2 ). For a typical green hydrogen factory based on renewable energy in Inner Mongolia of China, the simulated hydrogen precooling operation cost of dual MR process is 1.95 CNY/kg-H 2 with local electricity price of 0.56 CNY/kWh, which is 60% lower than liquid nitrogen (4.91 CNY/kg-H 2 with liquid nitrogen supply price of 600 CNY/t).