Process modelling of an alkaline water electrolyzer

• Published in: International journal of hydrogen energy 2017-06, Vol.42 (24), p.15689-15707
• Main Authors: Haug, Philipp, Kreitz, Bjarne, Koj, Matthias, Turek, Thomas
• Format: Article
• Language: English
• Subjects: Alkaline water electrolysis; Gas purity; Hydrogen production; Mathematical modelling; Process management
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2017.05.031

In this paper a model for the prediction of the product gas purity in alkaline water electrolysis is proposed. For the estimation of the exhaust gas compositions the operating conditions, such as current density, electrolyte flow rate, concentration and temperature as well as process management possibilities are considered. The development of the model relies on a classical process engineering approach and depicts the electrolysis cell through coupled continuously stirred-tank reactors. Furthermore, the mass transport phenomena between the phases are considered through the application of Reynolds and Sherwood correlations. Finally, the validation of the model is performed through experiments, which are carried out in a lab-scale electrolyzer with a 150 cm2 zero-gap cell and KOH electrolyte at atmospheric pressure. This investigation reveals that gas purity in alkaline water electrolysis is mainly affected by mixing the anodic and cathodic electrolyte cycles, which transport dissolved electrolysis products into the opposite half cell compartments. However, this transport mechanism can be significantly reduced by adjustment of the operating conditions of the electrolyzer. •Modelling of gas crossover mechanisms in alkaline water electrolysis.•Determination of gas bubble diameter and gas holdup in the electrolysis cell.•Model validation through comparison with GC measurements.•Simulation of product gas purity in dependence on electrolyzer process conditions.