Green Hydrogen Purification Using PSA
Specific process configurations, purity levels and performance data to be confirmed by Howe Baker engineering before publication.
Key Takeaway
Hydrogen produced by water electrolysis contains moisture and trace impurities including oxygen that must be removed before the hydrogen can be used for fuel cell applications, grid injection or industrial uses. PSA purification — often referred to as PSA polishing in this context — is one of the processes used to bring electrolyser-derived hydrogen to the required purity level, typically in combination with a drying step and catalytic deoxo unit.
Hydrogen from Water Electrolysis
Water electrolysis splits water molecules into hydrogen and oxygen using an electric current. Electrolysis technologies used for green hydrogen production include Polymer Electrolyte Membrane (PEM) electrolysers and Alkaline electrolysers, with Solid Oxide Electrolysis (SOE) at an earlier stage of commercial deployment.
The hydrogen produced by electrolysis is typically at high purity relative to reformate from an SMR, but it contains moisture that must be removed and may contain trace oxygen from gas crossover across the membrane. For many applications, the electrolyser product requires further purification before it meets the applicable specification.
Green Hydrogen Purity Requirements
The required purity for green hydrogen depends on its end use. ISO 14687 defines hydrogen quality grades for various applications including fuel cell electric vehicles (FCEV), industrial uses and grid injection. The applicable grade determines the impurity limits — for moisture, oxygen, nitrogen, hydrocarbons and other trace components — that must be met by the purification system.
For fuel cell vehicle hydrogen, ISO 14687 Grade D is the relevant standard. Grid injection requirements vary by jurisdiction and gas grid specification.
Purification System Configuration
Purification of electrolyser hydrogen typically involves a combination of steps. Moisture removal is commonly achieved using a TSA molecular sieve drying system. Trace oxygen removal requires a catalytic deoxo unit — a reactor containing a precious metal catalyst that promotes the reaction of residual oxygen with hydrogen to form water, which is then removed in a downstream drying stage.
If further impurity removal is required — for example, residual nitrogen or trace hydrocarbons — a PSA polishing step may be included downstream of the drying and deoxo stages.
Specific configurations used in Howe Baker green hydrogen purification systems to be confirmed by Howe Baker engineering before publication.
Balance-of-Plant Engineering for Green Hydrogen
The electrolyser is the core equipment in a green hydrogen plant, but the balance-of-plant (BOP) engineering — which includes hydrogen drying, purification, compression, storage and dispensing or export systems — is a significant part of overall project scope and cost.
BOP engineering for green hydrogen projects requires integration of the purification system with the electrolyser output conditions, the downstream compression and storage requirements, and the applicable product specification. Howe Baker's engineering scope for green hydrogen projects covers the purification and BOP systems.
Howe Baker Green Hydrogen Purification
Howe Baker provides engineering services for green hydrogen purification systems including PSA polishing, TSA drying and deoxo system integration. Engineering scope covers process design, equipment specification and integration with the broader electrolyser BOP and hydrogen export system.
Common Questions
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