Multi-objective optimization of a hydrogen liquefaction process coupled with mixed refrigerant cycle and steam methane reforming

Liquid hydrogen (LH2) storage is a feasible way to store and transport hydrogen with the advantage of high energy density, which is of great significance to the development of hydrogen energy and environmental protection. However, the energy consumption, economic costs and carbon emissions of large-scale hydrogen liquefaction plants tend to be high because of the large cooling capacity needed at liquid hydrogen temperature. To improve thermodynamic efficiencies, reduce economic costs and CO2 emissions, a new hydrogen liquefaction process coupled with mixed refrigerant (MR) precooling cycle and steam methane reforming (SMR) is proposed. Furthermore, liquefied natural gas (LNG) cold energy is used to precool the process and evaporated natural gas is used as raw material for SMR to produce hydrogen. Multi-objective optimization method is introduced to comprehensively optimize the specific energy consumption (SEC), economic costs and CO2 emissions. The thermodynamic model and optimization program are established in Aspen HYSYS and MATLAB. The SEC, economic costs and CO2 emissions of the optimized results that take the balance of economic costs and CO2 emissions are 9.38 kWh/kg, 5.419 × 106 $/year and 1.898 × 107 kg/year, respectively. Besides, it is found that there is no trade-off relationship between SEC and economic costs.