[ gas-liquid separation ]
Fig. 1. Simplified flowsheet for typical green hydrogen production with a PEM electrolyser
Design guidelines for gas-electrolyte separation in green hydrogen production
Green hydrogen produced by electrolysis first requires bulk gas-liquid separation to remove the electrolyte from the hydrogen produced in the electrolyser stack. The geometry of the separator vessel enables bulk separation by gravity. Designs can be configured that provide storage volume for the electrolyte and enable recycle back to the stack inlet. Entrained liquid droplets in the gas then require removal using outlet devices such as mesh pads, vanes, and coalescence filters, before subsequent drying and purification. This article discusses the basic considerations regarding the sizing of these separator vessels and the selection of appropriate coalescing media for the hydrogen market. The total energy efficiency of green hydrogen production can be enhanced through a well-designed gas-electrolyte separation stage.
Daniel Telford, Hydrogen R & D Engineer, Parker Hannifin
Separation by gravity- design guidelines
Basic gas-liquid separator design is largely based upon the desired liquid volume and the gas / vapour velocity. Liquid surge time is often expressed in minutes of residence time when the separator is half full. For most applications, such as a distillation column reflux drum,
5 – 10 minutes to reach half full is considered appropriate.¹ The holdup volume is often defined as the time taken to reduce the liquid level from normal to empty with a normal outlet flow and in the absence of feed flow.² Thus, the dimensions of a separator vessel are defined in part by the required liquid holdup volume and the capacity
30 Hydrogen Tech World | Issue 22 | June 2025