Exergy and pinch investigation of a novel configuration for the liquid hydrogen production by polymer electrolyte membrane electrolyzer and mixed refrigerant-absorption cooling cycles

The increase in global energy consumption leads to international commitments to replace fossil fuels and reduce environmental consequences. To improve and reduce the imbalance between the production and use of renewable energy, new ways should be considered for the distribution, and transmission, storage of global energy. Liquid hydrogen is a clean fuel that can be used for long-term storage and transportation to distant places. High energy consumption, losses due to boil-off gas, and low exergy efficiency in hydrogen liquefaction units are the main challenges. Waste heat recovery from various industries in the form of refrigeration can be used in hydrogen production and liquefaction. This study proposes an innovative process configuration for the generation of liquid hydrogen. The proposed process consists of a polymer electrolyte membrane electrolyzer, a Kalina power unit, a cascade absorption-compression refrigeration cycle, and three multi-component refrigerant cascade processes. The simulation of the proposed structure is performed in ASPEN HYSYS and m-file MATLAB. The verification is conducted highly accurately based on reference data. The proposed hybrid configuration produces 2066 kmol/h liquid hydrogen, 1033 kmol/h oxygen, and 14,572 kmol/h hot water using a power consumption of 272.2 MW. The proposed system's energy, exergy, pinch, and sensitivity are analyzed to give a better insight into its capabilities. Results show the total specific energy consumption of the present study is lower than similar studies in this field. In addition, the cooling capacity per unit flue gas mass flow rate obtained in the present study is 4.70 % and 7.69 % higher than similar studies, respectively. Also, the exergy efficiency of the proposed structure is 23.58 %, demonstrating an increase compared to the reference data. The exergy analysis indicated the highest exergy destruction was related to the PEM electrolyzer, followed by heat exchangers and reactors. Minimum pinch temperatures of the HX2, HX3, and HX4 exchangers based are achieved at 1.000, 1.006, and 1.020 K, respectively. The performed sensitivity analysis indicates that by increasing the temperature of flue gas from 600 to 1000 K, the specific power consumption of the liquid hydrogen production process decreases from 7.354 to 7.208 kWh/kgLH2.