Modeling and analysis of industrial-scale alkaline water electrolyzer systems

Abstract

Hydrogen is viewed as a promising energy carrier for a sustainable future, particularly when generated from renewable energy sources. It is often labeled as the fuel of the future due to its cleanliness, ability to be stored, and portability. In water electrolysis, electric current is used to split water molecules into oxygen and hydrogen gas. Alkaline water electrolyzer plants have the capability to produce hydrogen on a large industrial scale. When these plants are connected to renewable energy sources, the resulting hydrogen is referred to as green hydrogen.

The research carried out in this doctoral dissertation focuses on enhancing the understanding of the water electrolysis process from a system perspective and identifying key parameters that influence the energy efficiency of the plant. To achieve the research goals, a dynamic mass and energy balance process model of an industrial-scale alkaline water electrolyzer plant is developed and verified with process data acquired from an analogous operating plant situated in Finland.

The results indicate that pressurized, industrial-scale alkaline water electrolyzer plants with stacks manufactured in a bipolar configuration experience significant shunt current losses. These shunt currents notably reduce the Faraday efficiency and hydrogen production of the stack, highlighting the importance of addressing them early in the design process. Additionally, the study provides an in-depth analysis of five key thermodynamic and electrical plant process conditions: temperature, mass flow rate, current supply, pressure, and potassium hydroxide concentration. The investigation aims to identify which conditions could be controlled or optimized to enhance plant efficiency. The findings demonstrate that all the analyzed conditions impact plant performance, with pressure having the most significant effect. Furthermore, the study reveals that plant efficiency significantly diminishes during partial and low-load operations, a critical issue when these plants are connected to renewable energy sources where fluctuating operation is expected.