Toward more Efficient Large-Scale Green Hydrogen Systems via Waste Heat Recovery and ORC

This research models a 20 MW PEM hydrogen plant. PEM units operate in the range of 60 to 80 ⁰C based on their locations and sizes. This study aims to recover the waste heat from modules to enhance the efficiency of the plant. In order to recover the heat, two systems are implemented: (a) recovering the waste heat from each PEM module and (b) recovering the heat from hot water for producing electricity using an organic refrigerant cycle (ORC). The model is made by ASPEN®, and the ORC is optimized using Python. The ORC module is optimized to maximize the produced electricity and enhance the cycle's efficiency. The system is a closed-loop cycle operating at 25 ⁰C and ambient pressure. The 20 MW PEM electrolyzer model produces 363 kg/hr of hydrogen and 2877 kg/hr of oxygen. Based on the higher heating value (HHV) of hydrogen, the plant produces 14302.2 kWh of hydrogen energy equivalent. The ORC is being maximized by increasing the electricity output from the turbine and reducing pump work while maintaining energy conservation and the mass balance. Solving equation 6 resulted in the electricity power output reaching 555.88 kW and the pump power reaching 23.47 kW.