(633b) Investigation of Gas-Liquid Separation in Large-Scale PEM Electrolysis

In light of the urgent need to combat climate change and transition towards climate-neutral energy systems, there is a growing demand for innovative technologies that facilitate efficient and sustainable production of green hydrogen. Electrolyzers have emerged as a promising avenue for hydrogen production, offering scalability and compatibility with renewable energy sources.

Electrolyzer systems using a liquid electrolyte, such as alkaline water electrolysis (AWE) or proton exchange membrane electrolysis, require a separation of the produced hydrogen and oxygen from the electrolyte solution downstream of the stacks. This can be a challenging separation process due to the broad operation range of the electrolyzers and the various phase ratios involved. A further difficulty in the separation is the high amount of recycled electrolyte in the process. Total separation in technical separators is nearly impossible, so the recycling flow leads to time-driven enrichment of bubbles that are smaller than the cut-off bubble size of the separator.

Insufficient separation can lead to reduced product yield and stack lifetime and might negatively impact plant safety. The separation vessels that are used at the industrial scale are mostly designed by volume to provide sufficient residence time for the separation and degassing of smaller bubbles. For plant sizes > 10 MW and at higher pressures, e.g., 30 bar hydrogen pressure for PEM electrolysis, these vessels can contribute considerably to the plant cost.

One work package within the publicly funded project H2Giga-SineWave aims to systematically investigate the phenomena around phase separation for electrolysis plants, focusing on PEMEL. Project partner Linde and the Technical University of Munich pursue the target of improving phase separation and consequently building more compact separators that can cover a wide operating range.

For the separators in PEMEL systems, the task is to separate the highly purified water from the gases hydrogen and oxygen. A test rig was built to investigate this separation. The separation efficiency is measured with a larger separator downstream of the measuring separator. To understand the separation in the measuring separator, optical measurement methods like high-speed cameras and flow microscopes are used to observe the behavior of bubbles in the water.

This submission will give an introduction to the H2-Giga-SineWave project in the context of research activities at Linde and the Technical University of Munich. Further, the test rig for phase separation in PEMEL systems will be presented. Lastly, measurement results regarding separator design criteria will be discussed, and an outlook of the next research activities will be given.