Dynamic mass- and energy-balance simulation model of an industrial-scale atmospheric alkaline water electrolyzer

This study introduces a dynamic simulation model for an industrial-scale atmospheric alkaline water electrolyzer system. The model is parametrized and validated using measurement data from a real 1-MW atmospheric electrolyzer supplying hydrogen to an industrial process. The system behavior and energy losses are studied by simulating steady-state operation at a range of operational loads. As load decreases, energy efficiency improves, in contrast to previously published results concerning a 3-MW 16-bar system. This can be attributed to better stray-current management in the atmospheric system, promoted in part by maintaining high gas-volume fractions in the stack’s outlet manifold channels, which in turn is achieved with a lower lye circulation flow rate. Noteworthily, water vaporization inside the generated gas bubbles cools down the stack and maintains the temperature difference between its inlet and outlet at beneficial levels when less heat is removed from the stack by the reduced lye flow. This can be regarded as a fundamental benefit of the atmospheric stack design compared to its pressurized counterpart, in which less water vaporization occurs. This work benefits future studies comparing atmospheric and pressurized electrolyzer systems and provides a tool for optimizing energy and cost efficiencies in megawatt-scale Power-to-X applications leveraging water electrolysis. • Atmospheric stacks are inherently less prone to stray currents than pressurized ones. • Stack cooling from atmospheric water vaporization allows lower lye flow rates. • Lower lye flow rate increases manifold gas voidage and helps reduce stray currents. • At nominal load, stray currents consume 1% of stack DC power, overpotentials 23%. • From 100% to 20% load, specific energy consumption decreases from 52 to 47 kWh/kg H2 .