Exergy analysis and optimization of a hydrogen production process by a solar-liquefied natural gas hybrid driven transcritical CO₂ power cycle

A solar transcritical CO₂ power cycle for hydrogen production is studied in this paper. Liquefied Natural Gas (LNG) is utilized to condense the CO₂. An exergy analysis of the whole process is performed to evaluate the effects of the key parameters, including the boiler inlet temperature, the turbine inlet temperature, the turbine inlet pressure and the condensation temperature, on the system power outputs and to guide the exergy efficiency improvement. In addition, parameter optimization is conducted via Particle Swarm Optimization to maximize the exergy efficiency of hydrogen production. The exergy analysis indicates that both the solar and LNG equally provide exergy to the CO₂ power system. The largest amount of exergy losses occurs in the solar collector and the condenser due to the great temperature differences during the heat transfer process. The exergy loss in condenser could be greatly reduced by increasing the LNG temperature at the inlet of the condenser. There exists an optimum turbine inlet pressure for achieving the maximum exergy efficiency. With the optimized turbine inlet pressure and other parameters, the system is able to provide 11.52 kW of cold exergy and 2.1 L/s of hydrogen. And the exergy efficiency of hydrogen production could reach 12.38%.