Pressure swing absorption with recycle of void space gas
First Claim
1. A pressure swing adsorption process for separating a feed gas containing at least nitrogen and oxygen into more strongly adsorbed oxygen and less strongly adsorbed nitrogen in at least two parallel zones of adsorbent, each zone proceeding through a series of steps out of phase with the other zone comprising;
- (a) said feed gas at elevated pressure is contacted with a zone of a carbon molecular sieve adsorbent selective for oxygen, the oxygen is adsorbed and the nitrogen passes out of said zone as a product;
(b) said zone is initially depressurized countercurrently to remove void space gas and adsorbed gas as depressurization gas, with said depressurization gas recycled to a reservoir at an intermediate pressure and mixed with feed gas;
(c) said feed gas and depressurization gas are compressed to said elevated pressure of step (a);
(d) said zone is further depressurized to a lowest pressure by venting to regenerate said carbon molecular sieve adsorbent; and
,(e) said zone is repressurized to said elevated pressure of step (a) with feed gas and nitrogen.
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Abstract
The present invention is a pressure swing adsorption process for separating a more strongly adsorbed gas component from a less strongly adsorbed gas component in a feed gas mixture at higher recoveries and productivity and less capital cost by the use of void space gas recycle, membrane based nitrogen enrichment of feed gas and the elimination of pressure equalization steps. The process is particularly amenable to air separation wherein nitrogen product is recovered and an oxygen byproduct is removed.
47 Citations
11 Claims
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1. A pressure swing adsorption process for separating a feed gas containing at least nitrogen and oxygen into more strongly adsorbed oxygen and less strongly adsorbed nitrogen in at least two parallel zones of adsorbent, each zone proceeding through a series of steps out of phase with the other zone comprising;
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(a) said feed gas at elevated pressure is contacted with a zone of a carbon molecular sieve adsorbent selective for oxygen, the oxygen is adsorbed and the nitrogen passes out of said zone as a product; (b) said zone is initially depressurized countercurrently to remove void space gas and adsorbed gas as depressurization gas, with said depressurization gas recycled to a reservoir at an intermediate pressure and mixed with feed gas; (c) said feed gas and depressurization gas are compressed to said elevated pressure of step (a); (d) said zone is further depressurized to a lowest pressure by venting to regenerate said carbon molecular sieve adsorbent; and
,(e) said zone is repressurized to said elevated pressure of step (a) with feed gas and nitrogen. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A pressure swing adsorption process for separating a feed gas containing nitrogen and oxygen into more strongly adsorbed oxygen and less strongly adsorbed nitrogen in at least two parallel zones of adsorbent, each zone proceeding through a series of steps out of phase with the other zone comprising;
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(a) said feed gas initially contacts a membrane selectively permeable to oxygen to increase the nitrogen content of said feed gas as a reject stream; (b) said reject stream at elevated pressure is contacted with a zone of a carbon molecular sieve adsorbent selective for oxygen, the oxygen is adsorbed and the nitrogen passes out of said zone as a product; (b) said zone is initially depressurized countercurrently to remove void space gas and adsorbed gas as depressurization gas, with said depressurization gas recycled to a reservoir at an intermediate pressure and mixed with feed gas; (c) said feed gas and depressurization gas are compressed to said elevated pressure of step (b); (d) said zone is further depressurized to a lowest pressure to regenerate said carbon molecular sieve adsorbent and the resulting gas released during further depressurization is passed over an oxygen permeate side of said membrane as a sweep gas to enhance permeation of oxygen through said membrane; and
,(e) said zone is repressurized to said elevated pressure of step (b) with feed gas and nitrogen.
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Specification