Importance of High efficiency Liquid Gas Coalescers in Green Hydrogen Production

Hydrogen produced from an electrolyzer is relatively clean compared to hydrogen produced from traditional Natural Gas reforming. However, it isn’t completely pure and may include the following impurities:

• Very fine electrolyte / water aerosols entrained from the electrolyzer.
• Oxygen gas, typically 1% concentration.
• Water vapour (Hydrogen leaving the electrolyzer is completely saturated).

The industry widely follows the stringent ISO 14687 Hydrogen fuel cell standard for Hydrogen purity. Green Hydrogen producers need to carry-out considerable processing to remove the above-mentioned impurities and meet the purity requirements. (See figure below).

Typically, the industry uses the following for Hydrogen purification:

• Liquid-Gas separation equipment to remove aerosols.
• Deoxo catalyst to remove oxygen.
• Dryer bed to remove water vapor.

Green Hydrogen producers need effective and efficient removal of liquids from Hydrogen gas for the following reasons:

• Protecting the Deoxo Catalyst

Hydrogen leaving the electrolyzer is quite hot and, depending upon the electrolyzer technology being used, may also be at low pressure. As Hydrogen is cooled and compressed, the water vapor condenses out as fine droplets. These droplets can affect the performance and lifetime of the Deoxo catalyst. Having a high performing liquid-gas separator before the Deoxo reactor can reduce the frequency of catalyst replacement for a more cost-effective operation.

• Optimizing the size of the Dryer bed

Hydrogen leaves the Deoxo reactor at a high temperature with a lot of water vapour. The gas needs to be cooled before it can be sent to the dryer bed. The free water generated from condensation, if not removed, can affect the dryer bed performance (by causing channelling, for instance). Ensuring all the free water is removed upfront also helps optimise the design capacity of the dryer bed, thereby reducing capex.

For all the above reasons, it is important that Green Hydrogen producers move away from low efficiency Liquid-Gas (LG) separation equipment like knock-out drums and demisters. In Green Hydrogen, the main mechanism of droplet generation is condensation which results in very fine droplets. Knock-out drums and demisters rely upon gravity and inertial impaction for separation of liquid droplets. However, the very fine droplets tend to get entrained with the gas and are not separated. Alternatively, the vessels containing the demister needs to be designed very large to reduce the gas velocity and prevent entrainment – resulting in high capex costs.

Pall’s Seprasol^® LG Coalescers can provide a separation performance with outlet liquid concentration of less than 0.01 ppm (as per LASE methodology), offering the best protection for Deoxo Catalyst and Dryer beds. Pall coalescers do not rely solely upon gravity or inertial impaction. Pall’s proprietary surface-treated media captures fine droplets and coalesces them to form larger droplets which are then separated from the gas. Here is a video that explains how it works:

Pall’s LG coalescers also have significant advantages over other Liquid- Gas separation equipment (see figure below).

Coalescer turn-down performance is especially important for Green Hydrogen production as the intermittency of renewables can cause fluctuations in Hydrogen production. Finally, Pall’s high efficiency coalescers require a much smaller vessel compared to a knock-out drum or a demister, thereby helping to bring down the cost of a Green Hydrogen project.

Learn more at Pall’s Hydrogen webpage or reach out us to find out how Pall can help you improve the performance of your Green Hydrogen project.