Decarbonisation Technology August 2025 Issue

Why nitrogen is present: • Ambient air ingress: The most common source of nitrogen is air ingress into the electrolyser. Since air is ~78% nitrogen, any ingress into the system – via seals, flanges, valves, or fittings – will introduce nitrogen contamination. This is common during start-up, vacuum conditions, or unsealed maintenance events. Furthermore, nitrogen is frequently used as an inert purge gas during start-up, shutdown, or maintenance. Any remaining traces of nitrogen can mix with H₂ or O₂ streams after purging. In cases where storage tanks or compressors use nitrogen buffers or interfaces, the nitrogen can diffuse backwards into the product gas lines, especially during pressure fluctuations or valve leakage. In some industrial setups, nitrogen may be introduced via closed-loop water systems, shared utilities, or poorly degassed feedwater. Why it matters: • Nitrogen is inert but dilutes hydrogen or oxygen, affecting product purity specifications. • Nitrogen influences thermal conductivity, which can affect the performance of gas analysers. • It can skew online measurements, particularly if not properly accounted for in the analyser calibration. Compensation for nitrogen content in online oxygen or hydrogen analysis is essential for accurate, reliable reading. Calibration relevance: Nitrogen gas is commonly used as the zero-calibration gas for MOD 1040 and 1060 analysers. This means that the presence of nitrogen in the process can be treated as a background offset. If known, it can be compensated for in the analyser’s signal processing to improve accuracy. Fusion Method for hydrogen electrolysers with complex gas mixtures Overview In hydrogen electrolyser applications, gas compositions often include H₂, O₂, N₂, and water vapour (H₂O). Accurate measurement of O2 and H 2 in this mixture is critical for optimising efficiency, safety, and product quality. While optical technology used for O 2 measurement is very specific and free of significant cross- interferences, the thermal-conductivity method used for H 2 analysis is not specific

and, therefore, gas composition can affect this measurement. Fusion Method for hydrogen analysis The Fusion Method is a powerful measurement strategy that combines data from multiple sensor technologies to compensate for interfering components and deliver a precise analysis of hydrogen concentration. The method involves multi-sensor integration, where data from various analysers (such as thermal conductivity, optical, and electrochemical) are combined at multiple levels (Duro, 2024) : • Data-level fusion: Raw sensor signals (for example, from thermal conductivity and optical sensors) are merged to generate more accurate gas composition results. • Feature-level fusion: Key attributes like water vapour, oxygen, and nitrogen content are extracted to correct hydrogen readings. • Decision-level fusion: AI-driven logic interprets fused sensor data to make real-time adjustments or diagnostics (Dutta & Upreti, 2021) . Application in electrolyser gas streams In the presence of H₂, O₂, N₂, and H₂O vapour, traditional thermal conductivity analysers may suffer from cross-interference and environmental variability. The Fusion Method corrects for this by: u Using multi-gas models: Applying mathematical models that account for thermal conductivity contributions from each gas. v Measuring oxygen directly: Knowing O₂ concentration allows H 2 to be inferred in binary or ternary mixtures. w Monitoring water vapour impact: Since water vapour has a similar thermal conductivity to O₂, moisture correction is crucial at the high- water vapour concentration (evaluated at more than 15% by volume). x Considering nitrogen dilution: N₂ may be present due to air ingress or as a purge gas. Its influence is factored into the fusion model. Hydrogen calculation example (ternary gas system) For a mixture containing H₂, O₂, and H₂O: k_mix = (X_H₂ × k_H₂) + (X_O₂ × k_O₂) + (X_ H₂O × k_H₂O) Where: