Numerical modeling and analysis of the effect of pressure on the performance of an alkaline water electrolysis system

•A numerical model of an alkaline water electrolysis system is developed.•Pressure effect on the performance of the AWE system is investigated.•High operating pressure decreases the overvoltages due to improved bubble kinetics.•Pressure increase enhances the hydrogen purity without a desiccant device.•Increase in purity is not significant at approximately 20 bar or higher. Hydrogen is considered a promising green energy carrier due to its long storage period and zero harmful emissions. The green hydrogen produced by water electrolysis using renewable energy is indispensable for expanding the renewable energy grid and establishing a clean energy society. As renewable power sources are widely deployed, hydrogen can be utilized to connect the energy demand section with the energy supply section. To transport hydrogen to demand sites, one of the most common commercial methods is hydrogen compression. Notably, high-pressure water electrolysis does not need to additionally compress hydrogen, which can significantly diminish the cost of hydrogen production. In this study, to evaluate the effect of the operating pressure on the performance of an alkaline water electrolysis (AWE) system, a numerical model of the AWE system was developed using Aspen Plus®. The AWE system is comprised of the AWE stack, water pumps, heat exchangers, separator, condenser, and electric heat pump (EHP) system. The AWE stack model is validated by comparing the current–voltage polarization curve with experimental data. Simulation results show that an appropriate pressure makes the system more efficient due to decreasing the power consumption of the balance of plant (BOP). Furthermore, high-pressure water electrolysis has a large advantage for obtaining high-purity hydrogen (over 99.9%) without using a water adsorption device.