Design and analysis of steam methane reforming hydrogen liquefaction and waste heat recovery system based on liquefied natural gas cold energy

To improve the utilization rate of liquefied natural gas (LNG) cold energy, reduce hydrogen (H2) liquefaction cost, recover waste heat and reduce carbon dioxide (CO2) emission, this study designs a steam methane reforming (SMR) H2 liquefaction and waste heat recovery system based on LNG cold energy for the production of 10 tons of liquid hydrogen (LH2) per day. Parameters analyses and optimization, exergy analyses and economic analyses of the system are carried out and compared with other H2 liquefaction systems. The results show that: under the optimal conditions, the values of specific energy consumption (SEC), coefficient of performance (COP) and exergy efficiency (ƞex) were 5.93 kWh/kg LH2, 0.2225 and 53.24%, respectively. Exergy losses of system is mainly distributed in heat exchange equipment and compressors. Decreasing the heat exchange equipment cold and heat sources inlet temperature difference and reducing the compressors compression ratio were beneficial to reduce equipment exergy losses. The pre-cooling performance of LNG is better than that of liquid nitrogen (LN2) and mixed refrigerant (MR). Compared with the pre-cooling H2 liquefaction system without waste heat recovery, the SEC decreased by 0.26 kWh/kg LH2 and ƞex increased by 2.28%. Research results are conducive to resource conservation and environmental protection.