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Tail gas

Tail gas is the low-pressure stream released from a pressure swing adsorption unit as its beds are depressurised and purged. It holds the removed impurities with the hydrogen that was not recovered, and is usually used as fuel.

Also written as: PSA off-gas

Tail gas explained

Tail gas flow and composition fluctuate through the cycle, so a surge drum smooths them before the burners. Tail gas pressure is a design choice: lower pressure improves recovery but may require a compressor to reach the fuel system.

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Hydrogen recovery
Hydrogen recovery is the fraction of the hydrogen entering a purification unit that leaves as product, stated as a percentage. In a pressure swing adsorption unit the remainder leaves in the tail gas. Recovery trades against product purity.
Pressure swing adsorption (PSA)
Pressure swing adsorption (PSA) separates gases using beds of solid adsorbent that hold impurities at high pressure and release them when pressure is lowered. Several beds cycle in sequence, so purified gas, typically hydrogen, is produced continuously.

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