Pressure swing adsorption depressurization

Processes involving total-pressure reduction to remove the adsorbed species, called pressure-swing adsorption (PSA) or heatless adsorption, are mechanically complex, since they must include separate adsorption, depressurization, desorption, and repressurization steps. To accommodate a steady flow of feed and products, several beds - usually three or more in parallel -are used. A typical four-bed process flowsheet is shown in... 

The third process used in the production of carbon dioxide is pressure swing adsorption. The feed gas usually contains approximately 20 percent carbon dioxide, 70 percent hydrogen, and the remainder methane, carbon monoxide, nitrogen, and water. The feed gas is typically under a pressure of 125 100 psig at temperatures of 80-120°F. The carbon dioxide and water are strongly adsorbed in the adsorb beds and the residual gas stream is depressurized for further recovery. The adsorber vessel is then evacuated through vacuum blowers where the carbon dioxide, which has been adsorbed by the bed, is released at purities of essentially 99+ percent pure. 

After further heat recovery, final cooling and condensate separation (6), the gas is sent to the pressure swing adsorption (PSA) unit (7). Loaded adsorbers are regenerated isothermally using a controlled sequence of depressurization and purging steps. 

Kg. 9.2-2 Pressure swing adsorption unit with four fixed beds, (a) pressure rise, (b) depressurization, (c) depressurization - purging... 

Ammonia synthesis process selective hydrogen adsorption process by pressure swing adsorption with both co-current and countercurrent depressurization steps. A. Fuderer (Union Carbide Corp.). US 4475929 (1984). 

Steps. A pressure-swing cycle has at least three steps adsorption, blowdown, and repressurization. Although not always necessary, a purge step is normally used. In finely tuned processes, cocurrent depressurization and pressure-equalization steps are frequendy added. 

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