CFD simulations of electrolyte flow uniformity and recirculation in alkaline water electrolysis cells
(2024) European PhD Hydrogen Conference (EPHyC2024), Symposium on Production — Location: Ghent, Belgium (20.March.2024)
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- In the coming years, considerable efforts will have to be made to reduce greenhouse gas emissions to as close to zero as possible in order to limit the increase in global average temperature to 1.5°C, as stated in the Paris Agreement [1]. One way to decarbonize a wide range of sectors – including transport, iron and steel production and chemicals manufacture – is to use green hydrogen as an energy carrier to store and deliver usable and clean energy. Currently, the most mature technology used to produce hydrogen is Alkaline Water Electrolysis (AWE). It uses an alkaline solution, typically KOH between 1 and 6 M, at a temperature in the range 30-80°C, a diaphragm and Ni-based electrodes. This process can be further enhanced in terms of sustainability through the utilization of renewable electricity for conducting electrolysis. The primary hurdle associated with this technology revolves around improving the efficiency and diminishing capital expenditure (CAPEX) of the electrolyzer [2]. Recent experimental studies in our group have shown that it is possible to significantly improve the performance of such alkaline electrolyzers by shifting from traditional gap cells to zero-gap cells, wherein the anodic and cathodic chambers are filled with 3D porous electrodes such as foams and 3D-printed structures [2,3]. The advantage of using such 3D structures is that the available surface area for hydrogen production is much higher. At the same time, increased hydrogen production may lead to stagnant gases trapped in the complex porous channels of the foam. This is the reason why optimised electrolysis cells with forced electrolyte flow have been developed at the lab scale to favor bubble removal. A double elbow configuration was also used in order to guide the flow and enhance its spread throughout the cell, to take advantage of the whole area provided by the 3D electrodes [2]. Efforts have then been made in order to apply the same methodology – i.e. using 3D porous electrodes and forced electrolyte flow – to an industrial scale electrolyzer. Unfortunately, it was impossible to get such low cell voltages as with the lab-scale setup. This is mainly due to the fact that the pilot cells are not optimized for forced electrolyte flow, leading to a non-optimal distribution of the electrolyte and therefore to a poorer performance of the electrolyzer. The aim of this work is to perform Computational Fluid Dynamics (CFD) simulations to assess the behavior of the electrolyte within a pilot cell in order to find some optimal configuration that homogenizes the flow, reduces recirculation of the electrolyte and favors bubble removal. The main objective of this research is to define parameters – based on a Residence Time Distribution (RTD) analysis – that will allow to compare the performance of different cell configurations. The first parameter will be used to evaluate the level of flow uniformity inside the electrolysis cell while the second one will give an estimation of flow recirculation. Modification of the injection channels as well as the addition of porous media will be considered as options to improve the performance of the electrolyzer.
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Van Droogenbroek, K., Georgiadis, C., & Proost, J. (2024). CFD simulations of electrolyte flow uniformity and recirculation in alkaline water electrolysis cells. European PhD Hydrogen Conference : book of abstracts, p. Abstract 64. https://hdl.handle.net/2078.5/233432