Gas separation: apparatus – Solid sorbent apparatus – Plural solid sorbent beds
Reexamination Certificate
2000-06-09
2002-06-18
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Plural solid sorbent beds
C096S130000, C096S150000, C096S154000
Reexamination Certificate
active
06406523
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to gas separations conducted by pressure swing adsorption, and in particular applications to oxygen or nitrogen separation from air and to hydrogen purification. A particular application is for oxygen enrichment to mobile fuel cell power plants, for which efficient and compact machinery will be required.
BACKGROUND OF THE INVENTION
Gas separation by pressure swing adsorption (PSA) is achieved by coordinated pressure cycling and flow reversals over an adsorbent bed which 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 adsorbent bed from a first end to a second end of the bed, 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 bed. A “heavy” product enriched in the more strongly adsorbed component is exhausted from the first end of the bed. The light product is usually the desired product to be purified by PSA, 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 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 a bed and the second product delivered from the second end of the bed when the pressure in that bed is elevated to a higher working pressure, while the second product is exhausted from the first end of the bed at a lower working pressure which is the low pressure of the cycle.
The conventional process for gas separation by pressure swing adsorption uses two or more adsorbent beds in parallel, with directional valving at each end of each adsorbent bed to connect the beds in alternating sequence to pressure sources and sinks, thus establishing the changes of working pressure and flow direction. This conventional pressure swing adsorption process makes inefficient use of applied energy, because of irreversible expansion over the valves over large pressure differences while switching the adsorbent beds between higher and lower pressures.
DISCLOSURE OF 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 centrifugal compression machinery cooperating with one or multiple PSA modules in parallel. Each PSA module comprises a plurality of adsorbers, with each adsorber having a flow path contacting adsorbent material between first and second ends of the flow path.
Each PSA module further has a first valve means cooperating with the adsorbers to admit feed gas to the first ends of the adsorbers, and to exhaust heavy product gas from the first ends of the adsorbers. Each PSA module also has a second valve means cooperating with the adsorbers to deliver light product gas from the second ends of the adsorbers, to withdraw light reflux gas from the second ends of the adsorbers, and to return light reflux gas to the second ends of the adsorbers. The term “light reflux” refers to withdrawal of light gas (enriched in the less readily adsorbed component) from the second ends of adsorbers via the second valve means, followed by pressure let-down and return of that light gas to other adsorbers at a lower pressure via the second valve means. The first and second valve means are operated so as to define the steps of a PSA cycle performed sequentially in each of the adsorbers, while controlling the timings of flow at specified total pressure levels between the adsorbers and the compression machinery.
The PSA process of the invention establishes the PSA cycle in each adsorber, within which the total working pressure in each adsorber is cycled between a higher pressure and a lower pressure of the PSA cycle. The PSA process also provides a plurality of intermediate pressures between the higher and lower pressure. The compression machinery of the apparatus in general includes a feed gas centrifugal compressor and a second product gas exhauster. The exhauster would be an expander (e.g. radial inflow turbine) when the lower pressure is at least atmospheric pressure. The exhauster would be a vacuum pump when the lower pressure is subatmospheric. A light reflux gas expander may also be provided for energy recovery from light reflux pressure let-down, and may for example be used to drive a light product compressor.
In the present invention, the feed compressor will typically supply feed gas, in several stages at discrete intermediate pressures for feed pressurization of the adsorbers as well as the higher pressure for light product production, to the first valve means. The exhauster will typically receive second product gas, in several stages at discrete intermediate pressures for countercurrent blowdown of the adsorbers as well as the lower pressure, from the first valve means. The light reflux expander may also perform pressure let-down on several separate light reflux stages, sequentially drawn from the second valve means at a set of discrete intermediate pressure levels, and after expansion returned to the second valve means at a lower set of discrete intermediate pressure levels. Heat exchangers may be provided to heat gas streams about to be expanded, for thermally boosted energy recovery.
In order for the flowing gas streams entering or exiting the compression machinery at each pressure level to be substantially uniform in pressure and velocity, each PSA module will preferably have a sufficiently large number of adsorbers for several adsorbers to be undergoing each step of the PSA cycle at any moment. During pressurization and blowdown steps, the several adsorbers passing through the step would be in sequentially phased converging approach to the nominal pressure level of each step by a throttling pressure equalization from the pressure level of the previous step experienced by the adsorbers. Flow is being provided to the adsorbers in a pressurization step or withdrawn in a blowdown step by the compression machinery at the nominal pressure level of that step. Hence flow and pressure pulsations seen by the compression machinery at each intermediate pressure level are minimal by averaging from the several adsorbers passing through the step, although each adsorber undergoes large cyclic changes of pressure and flow.
A preferred way to provide a large number of adsorbers in a mechanically simple PSA module is to install those adsorbers as angularly spaced elements in a rotor, whose opposed faces engaging across sealing faces with a ported stator sealing faces will provide the first and second valve means. By providing a sufficient number of ports with suitable angular spacing to accommodate each of the desired pressure levels (higher, lower and intermediate) in each of the first and second valve faces, a desired PSA cycle can be achieved. The present invention provides high surface area parallel passage adsorbers suitable for high frequency operati
Connor Denis J.
Doman David G.
Jeziorowski Les
Keefer Bowie G.
Larisch Belinda
Klarquist & Sparkman, LLP
QuestAir Technologies Inc.
Spitzer Robert H.
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