Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
1998-12-11
2001-09-25
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S099000, C095S106000, C095S115000, C096S130000, C096S143000, C096S146000, C096S154000
Reexamination Certificate
active
06293998
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for use in adsorption processes. More particularly, the present invention relates to the use of a layer of adsorbent paper containing a solid adsorbent and disposed in a spirally wound configuration to perform adsorption and desorption based separation and sorption cooling processes.
BACKGROUND OF THE INVENTION
Pressure and temperature swing adsorption processes and sorption cooling processes typically employ some adsorbent disposed in a metal vessel and on a metal screen or surface which provides support for the adsorbent and permits the adsorbent to be placed in contact with the fluid stream containing the adsorbable component over the range of conditions necessary for the adsorption and desorption. The metal structures and physical arrangement of these devices has placed certain process limitations which restrict the amount of adsorbent which actually comes in contact with the fluid stream, or is accompanied by heat transfer inefficiencies inherent in the disposition of the adsorbent.
Pressure and Temperature Swing Adsorption
Processes based on the selective adsorption of a fluid or a component of a fluid stream generally involve contacting the fluid stream with the selective adsorbent in an adsorption zone and the process is carried out in a series of steps. The adsorption zone is maintained at adsorption conditions favorable to selectively adsorbing a portion of the fluid stream or an adsorbable component of the fluid stream and producing an adsorption effluent which has a reduced concentration of the adsorbed component relative to the fluid stream. The adsorbable component is then desorbed from the adsorption zone by either reducing the pressure of the adsorption zone to a desorption pressure, or by increasing the temperature of the desorption zone to a desorption temperature. At the desorption conditions, the adsorbable component is purged from the adsorption zone. Following the desorption step, the adsorption zone is purged to remove the adsorbed component. The adsorption zone is then returned to the adsorption conditions by either cooling the adsorption zone or by repressurizing the adsorption zone. In addition to the above discrete steps, additional integration which link a first adsorption zone with another adsorption zone which is out of phase with the first adsorption zone are provided to conserve energy such as pressure equalization steps to reduce overall efficiency in pressure swing adsorption processes.
In pressure swing adsorption (PSA), a multi-component gas is typically fed to at least one of a plurality of adsorption zones at an elevated pressure effective to adsorb at least one component, while at least one other component passes through. At a defined time, the feedstream to the adsorber is terminated and the adsorption zone is depressurized by one or more cocurrent depressurization steps wherein pressure is reduced to a defined level which permits the separated, less strongly adsorbed component or components remaining in the adsorption zone to be drawn off without significant concentration of the more strongly adsorbed components. Then, the adsorption zone is depressurized by a countercurrent depressurization step wherein the pressure on the adsorption zone is further reduced by withdrawing desorbed gas countercurrently to the direction of the feedstream. Finally, the adsorption zone is purged and repressurized. The final stage of repressurization is typically with product gas and is often referred to as product repressurization. In multi-zone systems there are typically additional steps, and those noted above may be done in stages. U.S. Pat. No. 3,176,444 issued to Kiyonaga, U.S. Pat. No. 3,986,849 issued to Fuderer et al., and U.S. Pat. No. 3,430,418 and U.S. Pat. No. 3,703,068 both issued to Wagner, among others, describe multi-zone, adiabatic pressure swing adsorption systems employing both cocurrent and countercurrent depressurization, and the disclosures of these patents are incorporated by reference in heir entireties. The above-mentioned patents to Fuderer et al., and Wagner are herein incorporated by reference.
Various classes of adsorbents are known to be suitable for use in PSA systems, the selection of which is dependent upon the feedstream components and other factors generally known to those skilled in the art. In general, suitable adsorbents include molecular sieves, silica gel, activated carbon, and activated alumina. For some separations, specialized adsorbents can be advantageous.
In thermal swing adsorption (TSA) wherein the adsorbent undergoes a regeneration with steam or with a stream of heated fluid such as a slip stream of treated adsorption effluent from another adsorber. The steam or heated fluid is introduced to the adsorption zone in a desorption mode to desorb the adsorbed impurities and purge them from the adsorption zone. The desorbed impurities may be recovered, for example, by condensation of the hot regenerant stream as in the example of using steam as a regenerant, or disposed of by incineration when a heated fuel gas is employed as the regenerant. In a typical TSA installation, two or more adsorption zones are operated in an alternating manner to provide continuous treating wherein at least one adsorption zone is operating in an adsorption mode while another is operating in a desorption mode.
Generally, PSA and TSA processes are carried out with the selective adsorbent disposed in fixed beds and the fluid streams are passed through the fixed bed adsorption zones at varying conditions depending upon the particular cycle taking place. Often PSA cycles are limited by the hydraulics of the fixed bed which relate to the actual height of the bed, the adsorbent particle size, and the density of the adsorbent particle. Some TSA processes are carried out by disposing the adsorbent on a paper in an adsorbent wheel as exemplified in U.S. Pat. No. 4,402,717 to Izumo et al. In Izumo et al., an apparatus for removing moisture and odors from a gas stream comprises a cylindrical honeycomb structure made from corrugated paper, uniformly coated with an adsorbent and formed in the shape of a disk or wheel. The multiplicity of adsorbent-coated parallel flow passages formed by the corrugations in the paper serve as gas passage ways which are separated as a zone for the removal of water and odor causing components in the gas, and as a zone for the regeneration of the adsorbent. The zones for removal and regeneration are continuously shifted as the wheel is rotated circumferentially about its central axis. For example, monolithic or honeycomb structures rotate around either a vertical or a horizontal axis. Solvent-laden air flows through the wheel parallel to the axis of rotation. All but a small portion of the adsorbent is always removing water and odor causing components. The other (small) portion of the wheel is undergoing thermal regeneration—usually in the opposite flow direction. The wheel continuously rotates to provide a continuous treated stream and a constant concentrated stream. The coated wheel units suffer many disadvantages. They require a large physical space to accommodate the enclosure for the wheel having the multiple removal and regeneration zones, and the associated gas transfer equipment (fans and blowers). The adsorbent-coated paper has limited range of humidity and temperature within which it can maintain its structural integrity. This failure also limits the regeneration medium to dry, moderate temperature gases and air. The contact between the adsorbent and the gas stream and hence the adsorbent capacity for volatile organic compounds is limited to the very thin layers of adsorbent on the surface of the paper. U.S. Pat. No. 5,580,369, which is hereby incorporated by reference, discloses an adsorbent wheel which is composed of an organic synthetic paper support and an adsorbent dispersed in the paper support comprised of a Y-type zeolite blended with either silica gel, alumina, or X-type zeolite. U.S. Pat. No. 5,338,450 attempts to overcome problems
Davis Mark M.
Dolan William B.
Tang Man-Wing
Silverman Richard P.
Spitzer Robert H.
Tolomei John G.
UOP LLC
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