Control Valve Selection for PEM Electrolyzers

Renewable or `green’ hydrogen, produced by the electrolysis of water, using renewable electricity, has been described as the `fuel of the future’. However, companies such as Plug Power are building cost-effective green hydrogen ecosystems that are already rapidly advancing its role in decarbonizing industry and transport. Plug Power is the world’s largest user of liquid hydrogen, and has also developed its own proton exchange membrane (PEM) electrolyzer ELX stack technology to produce hydrogen in both its own facilities and those of third-party clients. ​The company currently has electrolyzer projects under way on six continents, including the world’s first offshore floating electrolyzer.

During their presentation at the Emerson Exchange EMEA 2024, Vince van Goozen and Atri Biswal from Plug Power outlined some of these projects, but also explained that the company has extensive in-house experience right across the hydrogen ecosystem. This makes them ideally placed to offer advice on meeting the challenges within the industry.

In the presentation, Van Goozen focused on the challenge of selecting the right control valves for PEM electrolyzers. Plug Power offers several different sized electrolyzers, including 1 MW, 5 MW and 10 MW solutions. Van Goozen showed a typical layout of the company’s standardized 5 MW system. A utility enclosure incorporates water purification and control panels, with a `process enclosure’ containing anode separator, anode pump, heat exchanger, stacks, cathode separator and hydrogen deoxidizer/dryer. Connecting air cooler and chiller complete the system.

5 MW PEM electrolyzer process flow.

To ensure safe and efficient operation, different types of valves are required. The valves are categorized based on the challenges presented by the fluid or application. The valve groups are ultra pure water valves, hydrogen valves, oxygen valves and utilities valves. In the case of ultra pure water valves, preventing contamination of the fluid is critical. To avoid this, the control valve material and finishing is key, in addition to the good controllability during the start-up, normal operations and turndown phases. The FisherTm EZ valve from Emerson, which has a compact design, a wide Cv range and electropolishing on wetted surfaces, has been deployed and the result has been minimal contamination.

In the hydrogen section, downstream of the hydrogen deoxidizer/dryer, valves must be able to withstand the full pressure drop during start-up as well as keep differential pressure at a minimum during normal operation. With hydrogen being flammable, it is essential to avoid excessive leakage. Emerson’s Fisher EZ valves with a BSPP flange connection and ISO 15484 certified packing have been deployed. These have helped to reduce time to start-up and enable a flexible production rate. Emissions have also been minimized.

Biswal explained that ultra pure water in the cathode separator is recycled back into the system and the flow is controlled by the cathode separator level control valve. The high pressure drop occurring across the valve leads to a sudden release of hydrogen dissolved in the water (a phenomenon called “outgassing”). This creates a risk of erosion, which can lead to contamination of the ultrapure water. The solution for this application is the Fisher easy-e ES control valve with micro-flat cavitation trim, flash basket, erosion-resistant Alloy6 overlay and electropolishing on cast wetted surfaces. Offering the necessary protection from outgassing and cavitation, the valve solution has proven to be very reliable, with minimal water contamination. Another benefit is that installation costs are lower as fewer bends and smaller actuators are needed than for comparable valves.

Pure oxygen can ignite and oxidize metallic and organic compounds. To control oxygen venting from the anode separator, a Fisher GX valve with a large size CF3M body to reduce velocity, is appropriate. It has a European Industrial Gases Association (EIGA) compliant design, and is a compact valve with a high control range, making it ideal for this type of application.

Cooling water moving between air cooler and heat exchanger has a high flow rate but low differential pressure. This application requires a compact valve with high turndown rates that can control a high flowrate. Another challenge is that the ambient temperature is not constant and production rates vary. Fisher V-notch ball valves are ideal for this application, with an optimized valve design that provides a high flow capacity for the size of the valve. High controllability is possible, with the Fisher V-notch allowing equal percentage characterization but with ball valve capacity.

Van Goozen concluded that optimal selection of components requires a deep understanding of the process.​​ Traditional sizing and selection based on datasheets can lead to non-reliable design, mistakes and lack of optimization of production and the supply chain​. The early involvement of a vendor such as Emerson is key to ensure piping design and process conditions can accommodate an optimized solution.



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