Pressure Swing Adsorption

Reliable control at all stages in the process

Pressure swing adsorption is a process that separates single gases from a gas mixture. It is mainly used in chemical and petrochemical processes as well as the steel industry, for example to recover hydrogen (H₂) from coking or conver-sion gases, or to separate oxygen (O₂) and nitrogen (N₂) f ro m air.

The adsorption process is based on gas molecules binding to an absorbent material. The adsorbent bed is specially se-lected depending on the gas to be absorbed. Ideally, only the gas to be separated is adsorbed, while all other gases in the mixture pass through the adsorbent bed. Frequently, absorbents containing carbon (e.g. activated carbon or car-bon molecular sieves) and oxide absorbents (e.g. zeolite) are used. The purity of the absorbed gas not only depends on the adsorbent used. The temperature and pressure during the process are important as well. As a result, the control valves used also contribute considerably to the quality of the end product.

The pressure swing adsorption process is divided into four stages that occur in cycles:

Adsorption: adsorption takes place at high pressure (up to 40 bar). The feed gas is fed through an adsorbent bed. The absorbent binds the easily absorbable gas mol-ecules, while gas molecules that are not readily absorbable or not absorbable at all pass through the bed. The absorbent bed continues to absorb gas molecules until it reaches its full capacity.

Depressurization: depressurization is the first regen-eration (desorption) step of the full absorbent bed. As the pressure drops, the gas molecules in the adsorbent bed are released and the target gas is discharged from the absorber vessel.

Purging: the adsorbent bed is purged with the target gas to fully regenerate it.

Repressurization: the absorber is pressurized using a feed gas mixture or the target gas until the process condi-tions for adsorption have been restored.