Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2000-12-08
2003-02-04
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S102000, C095S103000, C095S105000, C095S113000, C095S130000, C096S125000, C096S130000, C096S143000, C096S150000
Reexamination Certificate
active
06514319
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to gas separations conducted by pressure swing adsorption (PSA), and particularly to air separation to generate concentrated oxygen or to air purification to remove carbon dioxide or vapour contaminants. In particular, the present invention relates to a rotary valve gas separation system having a plurality of rotating adsorbers disposed therein for implementing a pressure swing adsorption process for separating out the gas fractions.
Four possible applications of the present invention are:
(a) Home use medical oxygen concentrators;
(b) Portable oxygen concentrators;
(c) Ultra low power oxygen concentrators, e.g. for third world medical clinics; and
(d) Manually operated oxygen concentrator or air purifier for survival life support.
BACKGROUND OF THE INVENTION
Gas separation by pressure swing adsorption is achieved by coordinated pressure cycling and flow reversals over an adsorber that preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. The total pressure is elevated during intervals of flow in a first direction through the adsorber from a first end to a second end of the adsorber, and is reduced during intervals of flow in the reverse direction. As the cycle is repeated, the less readily adsorbed component is concentrated in the first direction, while the more readily adsorbed component is concentrated in the reverse direction.
A “light” product, depleted in the more readily adsorbed component and enriched in the less readily adsorbed component, is then delivered from the second end of the adsorber. A “heavy” product enriched in the more strongly adsorbed component is exhausted from the first end of the adsorber. The light product is usually the desired product to be purified, and the heavy product often a waste product, as in the important examples of oxygen separation over nitrogen-selective zeolite adsorbents and hydrogen purification. The heavy product (enriched in nitrogen as the more readily adsorbed component) is a desired product in the example of nitrogen separation over nitrogen-selective zeolite adsorbents. Typically, the feed is admitted to the first end of an adsorber and the light product is delivered from the second end of the adsorber when the pressure in that adsorber is elevated to a higher working pressure. The heavy product is exhausted from the first end of the adsorber at a lower working pressure. In order to achieve high purity of the light product, a fraction of the light product or gas enriched in the less readily adsorbed component is recycled back to the adsorbers as “light reflux” gas after pressure letdown, e.g. to perform purge, pressure equalization or repressurization steps.
The conventional process for gas separation by pressure swing adsorption uses two or more adsorbers in parallel, with directional valving at each end of each adsorber to connect the adsorbers in alternating sequence to pressure sources and sinks, thus establishing the changes of working pressure and flow direction. The basic pressure swing adsorption process makes inefficient use of applied energy, because of irreversible expansion over the valves while switching the adsorbers between higher and lower pressures. More complex conventional pressure swing adsorption devices achieve some improvement in efficiency by use of multiple “light reflux” steps, both to achieve some energy recovery by pressure equalization, and also desirably to sequence the light reflux steps so that lower purity light reflux gas reenters the second end of the adsorbers first, and higher purity light reflux gas reenters the second end of the adsorbers last, so as to maintain the correct ordering of the concentration profile in the adsorbers.
The conventional method of supporting the adsorbent is also problematic. There is a need for rigid high surface area adsorbent supports that can overcome the limitations of granular adsorbent and enable much higher cycle frequencies. High surface area laminated adsorbers, with the adsorbent supported in thin sheets separated by spacers to define flow channels between adjacent sheets, formed either as stacked assemblies or as spiral rolls, have been disclosed by Keefer (U.S. Pat. Nos. 4,968,329 and 5,082,473).
U.S. Pat. No. 4,968,329 discloses related gas separation devices with valve logic means to provide large exchanges of fresh feed gas for depleted feed gas. Such large feed exchanges may be required when concentrating one component as a desired product without excessively concentrating or accumulating other components, as in concentrating oxygen from feed air containing water vapour whose excessive concentration and accumulation would deactivate the adsorbent.
Siggelin (U.S. Pat. No. 3,176,446), Mattia (U.S. Pat. No. 4,452,612), Davidson and Lywood (U.S. Pat. No. 4,758,253), Boudet et al (U.S. Pat. No. 5,133,784), and Petit et al (U.S. Pat. No. 5,441,559) disclose PSA devices using rotary adsorber configurations. Ports for multiple angularly separated adsorbers mounted on a rotor assembly sweep past fixed ports for feed admission, product delivery and pressure equalization. In this apparatus, the relative rotation of the ports provides the function of a rotary distributor valve. All of these prior art devices use multiple adsorbers operating sequentially on the same cycle, with multiport distributor rotary valves for controlling gas flows to, from and between the adsorbers.
The prior art includes numerous examples of pressure swing adsorption and vacuum swing adsorption devices with three adsorbers operating in parallel. Thus, Hay (U.S. Pat. No. 4,969,935) and Kumar et al. (U.S. Pat. No. 5,328,503) disclose vacuum adsorption systems which do not achieve continuous operation of compressors and vacuum pumps connected at all times to one of the three adsorbers. Such operation is achieved in other three adsorber examples provided by Tagawa et al. (U.S. Pat. No. 4,781,735), Hay (U.S. Pat. No. 5,246,676), and Watson et al. (U.S. Pat. No. 5,411,578), but in each of these latter examples there is some undesirable inversion of the ordering of light product withdrawal and light reflux steps so that process efficiency is compromised.
SUMMARY OF THE INVENTION
The present invention is intended to enable high frequency operation of pressure swing and vacuum swing adsorption processes, with high energy efficiency and with compact machinery of low capital cost. The invention applies in particular to air separation.
The invention provides an apparatus for PSA separation of a gas mixture containing a more readily adsorbed component and a less readily adsorbed component, with the more readily adsorbed component being preferentially adsorbed from the feed gas mixture by an adsorbent material under increase of pressure, so as to separate from the gas mixture a heavy product gas enriched in the more readily adsorbed component, and a light product gas enriched in the less readily adsorbed component and depleted in the more readily adsorbed component. The apparatus includes compression machinery cooperating with three adsorbers mounted in a rotary PSA module.
Each adsorber has a flow path contacting adsorbent material between first and second ends of the flow path. The adsorbers are mounted at equal angular spacings in an adsorber housing, which is engaged in relative rotation with first and second valve bodies to define rotary sealing faces of first and second valves adjacent respectively the first and second ends of the adsorber flow paths. In some preferred embodiments, the adsorber housing is a rotor (the “adsorber rotor”) which rotates while the first and second valve bodies together form the stator. In other preferred embodiments, the adsorber housing is stationary, while the first and second valve bodies achieve the valving function. Fluid transfer means are provided to provide feed gas to the first valve body, to remove exhaust gas from the first valve body, and to deliver product gas from the second valve body.
The first valve admits feed gas to the first end of th
Keefer Bowie G.
McLean Christopher
Klarquist & Sparkman, LLP
QuestAir Technologies Inc.
Spitzer Robert H.
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