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 conversion gases, or to separate oxygen (O₂) and nitrogen (N₂) from air.

The adsorption process is based on gas molecules binding to an adsorbent material. The adsorbent bed is specially selected depending on the gas to be adsorbed. Ideally, only the gas to be separated is adsorbed, while all other gases in the mixture pass through the adsorbent bed. Frequently, adsorbents containing carbon (e.g. activated carbon or carbon molecular sieves) and oxide adsorbents (e.g. zeolite) are used. The purity of the adsorbed 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 adsorbent binds the easily adsorbable gas molecules, while gas molecules that are not readily adsorbable or not adsorbable at all pass through the bed. The adsorbent bed continues to adsorb gas molecules until it reaches its full capacity.

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

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

Repressurization: the adsorber is pressurized using a feed gas mixture or the target gas until the process conditions for adsorption have been restored.