Alkaline Electrolyzer KOH Circulation System P&ID Standard

Alkaline electrolyzers rely on a concentrated aqueous KOH solution (typically 25–30 wt%) as the electrolyte to facilitate OH⁻ ion transport between nickel-based electrodes. The KOH circulation system maintains uniform concentration, removes ohmic heat from the stack, prevents gas bubble accumulation at electrodes, and mitigates carbonate precipitation (from CO₂ ingress). The P&ID standard codifies engineering best practices—including dual-pump redundancy, inline conductivity/temperature/level transmitters, corrosion-resistant materials (e.g., 316L SS, Hastelloy C-276, or fluoropolymer-lined components), and pressure-relief paths—to ensure continuous, safe operation under dynamic load-following conditions typical of renewable-powered hydrogen plants. Critically, the standard defines functional safety requirements: e.g., automatic shutdown triggers upon low electrolyte level (<70% tank capacity), high stack temperature (>90°C), or loss of circulation flow (<1.2 m/s velocity in main loop), all aligned with SIL-2 integrity targets per IEC 61511. Furthermore, it mandates traceability of instrumentation tags (e.g., FT-101 for flow transmitter, LIC-201 for level indicator controller), valve failure modes (FO/FC), and grounding/isolation protocols for electrochemical grounding loops to prevent stray current corrosion.