Pressure swing adsorption with direct and indirect pressure equalizations

Claim 1

In a pressure swing adsorption process for the selective adsorption of at least one component of a feed gas mixture in an adsorption system having at least five adsorbent beds, each of which undergoes, on a cyclic basis, higher pressure adsorption, cocurrent depressurization to upper intermediate pressure with release of void space gas from the product end of the bed for direct passage to another bed initially at lower pressure to equalize the pressure therebetween at said upper intermediate pressure, further cocurrent depressurization to lower intermediate pressure with release of additional void space gas from the product end of the bed for direct passage to a different bed initially at lower pressure to equalize the pressure therebetween at said lower intermediate pressure, countercurrent depressurization to a lower desorption pressure and/or purge with release of gas from the feed end of the bed at said lower desorption pressure, partial repressurization to said lower intermediate pressure by the passage of void space gas from a different bed initially at higher pressure directly to said bed to equalize the pressure therebetween at said lower intermediate pressure, further partial repressurization to said higher intermediate pressure by the passage of void space gas from another bed initially at higher pressure directly to said bed to equalize the pressure therebetween at said upper intermediate pressure, and final repressurization from said upper intermediate pressure to said higher adsorption pressure, the improvement consisting essentially of: (a) upon completion of direct pressure equalization by the passage of void space gas from a bed being cocurrently depressurized directly to another bed in the adsorption system initially at lower pressure for pressure equalization therebetween at said upper intermediate pressure, and prior to the initiation of direct pressure equalization between said bed being cocurrently depressurized and a different bed in said system by the passage of void space gas from said bed being cocurrently depressurized directly to said bed initially at lower pressure for pressure equalization therebetween at said lower intermediate pressure, introducing void space gas released from the product end of said bed being cocurrently depressurized to an external storage tank initially at lower pressure for subsequent pressure equalization usage, said bed and external storage tank being at an intermediate pressure after pressure equalization therebetween, said intermediate pressure being lower than said upper intermediate pressure and higher than said lower intermediate pressure; and (b) passing said void space gas from said external storage tank at said intermediate pressure to an adsorbent bed in the system initially at lower pressure and being repressurized for indirect pressure equalization therebetween, said indirect pressure equalization of the bed being partially repressurized occurring immediately after partial repressurization to lower intermediate pressure by direct pressure equalization with another bed and immediately before partial repressurization to upper intermediate pressure by a second direct pressure equalization with a different bed, said indirect pressure equalization thus being intermediate two direct pressure equalizations in which void space gas is passed directly from said other beds to said bed being partially repressurized to upper intermediate pressure prior to final repressurization to higher adsorption pressure, whereby product recovery and/or purity is enhanced by said inclusion of at least one indirect pressure equalization immediately between two direct equalizations.