Six bed pressure swing adsorption process with four steps of...

Details Six bed pressure swing adsorption process with four steps of... Six bed pressure swing adsorption process with four steps of...

2000-06-21

2002-09-24

Spitzer, Robert H. (Department: 1724)

Gas separation: processes

Solid sorption

Including reduction of pressure

C095S100000, C095S105000, C095S121000, C095S130000, C095S139000, C095S140000, C095S143000

Reexamination Certificate

active

06454838

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
This invention relates to pressure swing adsorption (PSA) processes, and more particularly to such processes employing multiple adsorbent beds and multiple pressure equalization steps.
PSA processes are well-known for the separation of gas mixtures that contain components with different adsorbing characteristics. For example, hydrogen production via pressure swing adsorption (H
2
PSA) is a multi-million dollar industry supplying high purity hydrogen for chemical producing industries, metals refining and other related industries.
In a typical PSA system, a multicomponent gas is passed to at least one of multiple adsorption beds at an elevated pressure to adsorb at least one strongly sorbed component while at least one component passes through. In the case of H
2
PSA, H
2
is the most weakly adsorbed component which passes through the bed. At a defined time, the feed step is discontinued and the adsorption bed is depressurized with flow co-current to the direction of the feed in one or more steps which permits essentially pure H
2
product to exit the bed with a high recovery of the most weakly adsorbed component, H
2
. Then a countercurrent desorption step is carried out, followed by countercurrent purge and repressurization.
U.S. Pat. No. 3,986,849 to Fuderer et al. discloses PSA processes employing at least seven adsorbent beds, and at least three steps of pressure equalization per bed. This patent teaches that an undesirable reversion of the desorbate profile from the inlet to the discharge end of the bed is substantially reduced when at least three pressure equalization stages are employed. Fuderer et al. does not disclose any embodiments comprising performing four pressure equalization steps in a six-bed apparatus.
U.S. Pat. No. 4,834,780 to Benkmann discloses six-bed cycles with “four- or five-stage cocurrent expansions” (i.e., four or five co-current depressurization steps), and only one adsorber on feed at any time. Two types of six-bed cycles are disclosed—one having three steps of pressure equalization and the other having four steps of pressure equalization. In the cycle with four steps of pressure equalization, the supply of offgas (gas from the feed ends of the beds during the counter-current blowdown and purge steps) is discontinuous, i.e., there are times when no offgas is supplied from the PSA system during the cycle. Discontinuous offgas flow is not desirable in processes in which the offgas is used continuously, such as in hydrogen PSA processes in which the offgas is used as fuel to the steam reformer.
Table 1 shows a six-bed cycle with three steps of pressure equalization, which follows Benkmann's teaching while offgas is supplied continuously:
TABLE 1
A
A
A
A
1
2
3
I
P
P
B
B
G
G
3′
I
I
2′
I
I
1′
R
R
R
1′
R
R
R
A
A
A
A
1
2
3
I
P
P
B
B
G
G
3′
I
I
2′
I
I
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
3
I
P
P
B
B
G
G
3′
I
G
G
3′
I
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
3
I
P
P
B
B
P
P
B
B
G
G
3′
I
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
3
I
1
2
3
I
P
P
B
B
G
G
3′
I
I
2′
I
I
1′
R
R
R
A
A
A
A
Despite the foregoing developments, it would be desirable to provide an improved PSA process which increases production and/or recovery per bed in a multiple bed system.
All references cited herein are incorporated herein by reference in their entireties.
BRIEF SUMMARY OF THE INVENTION
The invention provides a pressure swing adsorption process comprising providing a pressure swing adsorption apparatus having six beds, and equalizing a pressure of each of said six beds in four steps. At all times during the process, at least one of the six beds is providing offgas.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
In embodiments of the invention, the bed that co-currently provides purge gas to another bed also undergoes counter-current depressurization. Table 2 shows a cycle chart in accordance with such embodiments of the invention:
TABLE 2
A
A
A
A
1
2
I
3
P
P
B′
B
G
G
4′
3′
I
2′
I
I
1′
R
R
R
1′
R
R
R
A
A
A
A
1
2
I
3
P
P
B′
B
G
G
4′
3′
I
2′
I
I
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
I
3
P
P
B′
B
G
G
4′
3′
G
G
4′
3′
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
I
3
P
P
B′
B
P
P
B′
B
G
G
4′
3′
I
2′
I
I
1′
R
R
R
A
A
A
A
1
2
I
3
1
2
I
3
P
P
B′
B
G
G
4′
3′
I
2′
I
I
1′
R
R
R
A
A
A
A
In the first step of this cycle, a feed mixture is first sent to the feed end of the bed. The more adsorbable component(s) is (are) adsorbed by the adsorbent, while the less adsorbable component(s) pass(es) through the bed and exit(s) the bed from the product end. This step takes ⅙ of the cycle time and is indicated by “A” on the cycle chart.
The bed then undergoes the first providing pressure equalization step, indicated by “1” on the cycle chart. During this step, the bed provides gas from the product end to a bed that receives pressure equalization (indicated by “1” on the cycle chart) until the pressures in the providing and receiving pressure equalization beds are essentially equal. Then the bed undergoes the second providing pressure equalization step, indicated by “2” on the cycle chart. During this step, the bed provides gas from the product end to a bed that receives pressure equalization (indicated by “2′” on the cycle chart) until the pressures in the providing and receiving pressure equalization beds are essentially equal. Each of the above two providing pressure equalization steps takes approximately {fraction (1/24)} of the cycle time.
Then the bed is idle for approximately {fraction (1/24)} of the cycle time, indicated by “I” in the cycle chart.
Then the bed undergoes the third providing pressure equalization step, indicated by “3” on the cycle chart. During this step, the bed provides gas from the product end to a bed that receives pressure equalization (indicated by “3′” on the cycle chart) until the pressures in the providing and receiving pressure equalization beds are essentially equal.
Then the bed provides purge gas, indicated by “P” on the cycle chart. During this time, the gas exiting the product end of the bed is used to purge the bed receiving purge, indicated by “G” in the cycle chart. This takes approximately {fraction (1/12)} of the cycle time.
Then the bed is depressurized from both the feed and product ends. This step takes approximately {fraction (1/24)} of the cycle time and is indicated by “B′” on the cycle chart. The gas from the feed end is rich in the more adsorbable component. It may be recovered as a product or disposed as waste gas, and in the case of hydrogen purification of a steam reformate of hydrocarbons, it is usually used as fuel for the reformer. The gas from the product end is used for the bed receiving pressure equalization (indicated by step “4′”).
Then the product end is closed while the counter-current depressurization on the feed end continues. This step takes about {fraction (1/24)} of the cycle time and is indicated by “B” on the cycle chart.
Then the bed receives counter-current purge gas from the product end, and allows the gas rich in the more adsorbable component(s) to elute from the feed end of the bed. This step takes approximately {fraction (1/12)} of the cycle time and is indicated by “G” on the cycle chart.
The bed then receives pressure equalization gas from the product end. This step takes approximately {fraction (1/24)} of the cycle time and is indicated by “4′” on the cycle chart.
Then the bed undergoes the third receiving pressure equalization gas step by receiving gas from the product end. This step takes approximately {fraction (1/24)} of the cycle time and is indicated by “3′” on the cycle chart.
Then the bed is idle for approximately {fractio

Affiliated with

Also associated with

Rating

Six bed pressure swing adsorption process with four steps of... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Six bed pressure swing adsorption process with four steps of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Six bed pressure swing adsorption process with four steps of... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2851659