Anatomy of the alkaline electrolyser optimisation The key challenges in monitoring hydrogen and oxygen concentrations in alkaline electrolysers, considering flow and operating conditions
Gregory Yakhnin, Galina Gurina, and Gregory Shahnovsky Modcon Systems Ltd
A lkaline electrolysers (AELs) are widely used for hydrogen production due to their robustness, cost-effectiveness, and industrial scalability. However, accurately measuring gas purity and operational conditions in real time presents challenges, particularly with fluctuating pressure, temperature, humidity, and hydrogen-to-oxygen ratio (US Department of Energy, 2023) . Typical operating conditions in AEL systems include: • Pressure fluctuations: 0.8-40 bara • Temperature: 40-90°C • Relative humidity (RH): 20-100% • Flow velocities: 0.5-10 m/s • KOH traces: 0-1,000 ppm This article examines the typical flow and operating conditions of AELs, highlighting key challenges in online monitoring of hydrogen (H₂) and oxygen (O₂) concentrations (Brauns & Turek, 2020; Kreuter & Hofmann, 1998; Nikolaidis & Poullikkas, 2017). Beyond traditional
measurement issues, it also explores how the Fusion Method and integration with Modcon.AI improve measurement reliability, enable real-time optimisation, and significantly reduce the total cost of ownership for electrolyser systems. Overview of the AEL process stages The AEL process can be broken down into several operational phases: • Start-up • Hydrogen ramp-up Each process phase alters relative humidity (RH), pressure, flow, and gas composition, complicating accurate O₂ and H₂ measurements, which are crucial for safety and optimisation (IEC, 2017; ISO, 2025) . Sampling from high- pressure lines is difficult due to the need to prevent leaks. Traditional analysers need gas extraction and conditioning, whereas in-situ analysers measure O₂ directly in high-pressure pipelines, eliminating the need for separate sampling and conditioning (Modcon, 2025) . Relative humidity profile RH can range from low levels during start- up to nearly 100% during steady hydrogen and oxygen generation (Vaisala, 2025). This variability can distort analyser readings and introduce condensation risks. RH varies with changes in temperature, pressure, and the presence of liquid water across the system. During start-up/shutdown, • Electrolysis (inside the electrolyser) • Gas separation (after the separator) • Gas drying (after the dryer) • Steady production • Shutdown
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Figure 1 Relative humidity across AEL process stages Process stage
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