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 60 to 80 °C range based on their location and size. This study aims to recover the waste heat from PEM 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; (b) recovering the heat from hot water to produce electricity utilizing an organic refrigerant cycle (ORC). The model is made by ASPEN® V14. After modeling the plant and utilizing the ORC, the module is optimized using Python to maximize the electricity produced by the turbine, therefore enhancing the efficiency. The system is a closed-loop cycle operating at 25 °C and ambient pressure. The 20 MW PEM electrolyzer plant produces 363 kg/hr of hydrogen and 2877 kg/hr of oxygen. Based on the higher heating value of hydrogen, the plant produces 14,302.2 kWh of hydrogen energy equivalents. The ORC is maximized by increasing the electricity output from the turbine and reducing the pump work while maintaining energy conservation and mass balance. The results show that the electricity power output reaches 555.88 kW, and the pump power reaches 23.47 kW.