Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2002-04-08
2004-03-23
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S098000, C095S100000, C095S103000, C095S138000
Reexamination Certificate
active
06709486
ABSTRACT:
BACKGROUND OF THE INVENTION
Pressure swing adsorption is an important gas separation process which is widely used in the process and manufacturing industries. Pressure swing adsorption (PSA) is used for recovering high-purity gas products from crude process gas streams, for example in hydrogen production, or as an alternative to hauled-in atmospheric gas products or onsite cryogenic air separation processes. The PSA process has been highly developed for the separation of a wide variety of gas mixtures including, for example, the separation of air to provide oxygen and nitrogen products. For smaller product volumes in air separation applications, PSA processes may use a single adsorbent bed and one or more gas storage tanks to provide a constant product flow as well as gas for repressurization and purge. At higher product volumes, multiple adsorbent beds operating in parallel with overlapping cycles are used to generate a constant product gas flow as well as provide gas for repressurization and purge.
Each adsorbent bed in a pressure swing adsorption (PSA) cycle proceeds through a sequence of steps beginning with a feed or adsorption step in which a pressurized feed gas mixture is passed through a bed of adsorbent which selectively adsorbs one or more of the components in the mixed feed gas. A product gas containing the desired component at acceptable purity is withdrawn from the bed until the adsorption step is terminated at a predetermined time.
After termination of the adsorption step, the pressure in the bed is reduced in one or more steps in which gas is transferred at decreasing pressure to one or more other beds to provide pressurization gas to those beds. Final depressurization typically is completed by withdrawing a waste gas in a final waste depressurization or blowdown step. The depressurized bed then is purged with product gas or transfer gas provided from other beds, thereby removing additional adsorbed components and void space gas from the bed.
Upon completion of the purge step, the bed is repressurized to an intermediate pressure by one or more pressurization steps in which gas is transferred from other beds, and the bed then is pressurized further to the feed pressure with feed and/or product gas. The steps are repeated in a cyclic manner.
The transfer of gas from a bed at decreasing pressure to another bed at increasing pressure is an important and highly-developed feature of many PSA cycles. In this bed-to-bed gas transfer process, gas which is below product quality, but which still contains a significant concentration of the final product component, is transferred from the product end of a bed to the product end of another bed. This important step significantly increases product recovery, but must be carefully controlled to meet the required product purity. Optionally, gas of lower quality can be transferred from the feed end of the bed to the feed end of another bed.
Further refinement in the bed-to-bed gas transfer process holds promise for needed improvements in product recovery and product purity, and also for increased productivity, in the PSA process. In particular, there is a need for improved control of gas flow within a bed undergoing gas withdrawal during the gas transfer process. This need is addressed by the present invention as described below and defined by the claims which follow.
BRIEF SUMMARY OF THE INVENTION
An embodiment of the invention includes a pressure swing adsorption process for recovering a less readily adsorbable component from a feed gas mixture comprising at least one less readily adsorbable component and at least one more readily adsorbable component, which process comprises performing cyclic process steps in a plurality of adsorbent beds, each bed having a feed end and a product end and containing adsorbent material which selectively adsorbs the more readily adsorbable component, each bed proceeding in turn through cyclic process segments which include an adsorption-make product segment, a first gas transfer segment in which gas flows from a bed initially at a higher pressure into one or more other beds initially at a lower pressure or lower pressures, a regeneration segment, a second gas transfer segment in which gas flows into a bed initially at a lower pressure from one or more other beds initially at a higher pressure or higher pressures, and a final repressurization segment. The gas transfer segments include
(1) transferring gas from the product end of the bed to the product end of another bed; followed by
(2) withdrawing waste depressurization gas from the feed end of the bed while continuing to transfer gas from the product end of the bed to the product end of another bed;
(3) during either or both of (1) and (2), transferring gas from the feed end of the bed to the feed end or ends of the one or more other beds; and
(4) prior to (1), transferring gas from the product end of the bed at a higher pressure to the product end of another bed at a lower pressure.
The ratio of the volume of gas transferred from the product end of the bed during (1) to the volume of gas transferred from the product end of the bed during (2) may be between about 3 and about 20.
During (2), the ratio of the volume of waste depressurization gas withdrawn from the feed end of the bed to the volume of gas transferred from the product end of the bed may be between about 0.1 and about 0.6.
Another embodiment of the invention relates to a pressure swing adsorption process for recovering a less readily adsorbable component from a feed gas mixture comprising at least one less readily adsorbable component and at least one more readily adsorbable component, which process comprises performing cyclic process steps in a plurality of adsorbent beds, each bed having a feed end and a product end and containing adsorbent material which selectively adsorbs the more readily adsorbable component, each bed proceeding in turn through cyclic process segments which include an adsorption-make product segment, a first gas transfer segment in which gas flows from a bed initially at a higher pressure into one or more other beds initially at a lower pressure or lower pressures, a regeneration segment, a second gas transfer segment in which gas flows into a bed initially at a lower pressure from one or more other beds initially at a higher pressure or higher pressures, and a final repressurization segment. The gas transfer segments include
(1) transferring gas from the product end of the bed to the product end of another bed; followed by
(2) withdrawing waste depressurization gas from the feed end of the bed while continuing to transfer gas from the product end of the bed to the product end of another bed;
(3) during either or both of (1) and (2), transferring gas from a point intermediate the feed end and the product end of the bed to the feed end or ends of the one or more other beds; and
(4) prior to (1), an additional step of transferring gas from the product end of the bed at a higher pressure to the product end of another bed at a lower pressure.
The ratio of the volume of gas transferred from the product end of the bed during (1) to the volume of gas transferred from the product end of the bed during (2) may be between about 3 and about 20.
During (2), the ratio of the volume of waste depressurization gas withdrawn from the feed end of the bed to the volume of gas transferred from the product end of the bed may be between about 0.1 and about 0.6.
The invention also relates to a pressure swing adsorption process for recovering a less readily adsorbable component from a pressurized feed gas comprising at least one less readily adsorbable component and at least one more readily adsorbable component, which process comprises performing cyclic process steps in two parallel adsorbers, each adsorber having a feed end and a product end and containing adsorbent material which selectively adsorbs the more readily adsorbable component. The cyclic process steps include:
(a) providing a pressurized feed gas at superatmospheric pressure and introducing the pressurized feed gas into
Bukowski Justin David
Lee Sang Kook
Air Products and Chemicals Inc.
Fernbacher John M.
Spitzer Robert H.
LandOfFree
Pressure swing adsorption process with controlled internal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure swing adsorption process with controlled internal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure swing adsorption process with controlled internal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3251042