Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
1999-03-16
2001-04-17
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S098000, C095S105000, C095S130000, C096S130000, C096S144000
Reexamination Certificate
active
06217635
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus using a single adsorption zone for producing an enriched stream of a first gas from a stream containing the first gas and at least one second gas. In one embodiment, the method and apparatus may be used to obtain a concentrated stream of oxygen from air.
BACKGROUND OF THE INVENTION
Various different methods have been developed for separating gases and producing a concentrated stream of a selected gas. One particular method which has been used in industry is the pressure swing adsorption process. Generally, these processes use an adsorbent which, under elevated pressure conditions, preferentially adsorbs a targeted gas over other gases present in a gas stream. Accordingly, the adsorbent could be selected to preferentially adsorb an undesirable gas from a gas stream thereby leaving a gas stream having an increased concentration of the gases remaining in the gas stream. An example of such a process would be the use of a pressure swing adsorption process to produce an oxygen enriched air stream. The adsorbent would be selected to preferentially adsorb nitrogen over oxygen. Thus, after the adsorption process is conducted, the pressurized air in contact with the adsorbent contains a higher percentage by volume of oxygen. This oxygen enriched air may then be vented from the adsorption chamber and the adsorbent purged (at reduced pressure conditions) to remove the adsorbed nitrogen. Alternately, such a process may be used to preferentially adsorb a targeted gas (e.g. oxygen) thereby also producing an enriched stream of oxygen.
Various different processes have been designed to utilize the selective adsorption ability of zeolite. Examples of these include, Bansal (U.S. Pat. No. 4,973,339), Stanford (U.S. Pat. No. 4,869,733) and Haruna et al (U.S. Pat. No. 4,661,125).
The process and apparatus of Bansal, Stanford and Haruna et al each utilize two adsorption chambers. The use of two adsorption chambers is undesirable as it unnecessarily complicates the apparatus since it requires additional valving and control means to cycle each adsorption bed through a pressurization cycle and a purging cycle. Further, this adds to the cost of the apparatus and decreases the reliability of the apparatus.
Other disadvantages of existing designs is the requirement to use expensive valve control means. In particular, solenoids are frequently required to switch the adsorption chamber from a pressurization mode to a purging mode. These controls are expensive and also prone to failure after extensive use.
Further, existing designs utilize electronics (e.g. micro-processors) to control the cycling of the adsorption chamber. This adds to the cost of the equipment and also requires an electrical power source to operate the process. Further, the electronic components may be damaged in harsh environments and this limits the applications of some existing designs.
SUMMARY OF THE INVENTION
In accordance with the instant invention, a portion of the enriched fluid produced in an adsorption chamber is used to purge the adsorbed fluid from the adsorption chamber. Thus only a single source of motive force (i.e. the source for pressurizing the adsorption chamber for operating the adsorption cycle) is required. According, the construction of the contactor is simplified and the reliability of the unit may be increased.
To this end, in accordance with the instant invention there is provided a fluid concentrator for obtaining an enriched stream of a first fluid from a fluid stream containing the first fluid and at least one second fluid, the concentrator comprising:
(a) an adsorption chamber having an inlet for introducing the fluid stream to the adsorption chamber, the adsorption chamber operable to produce the enriched stream during a first cycle and the adsorption chamber having an outlet for venting the enriched stream from the adsorption chamber;
(b) a pressurizable storage chamber positioned downstream from the adsorption chamber and in flow communication with the adsorption chamber for receiving at least a portion of the enriched fluid stream;
(c) at least one passageway connecting the adsorption chamber and the storage chamber in flow communication through at least one valve to provide a first flow rate of the enriched fluid in the downstream direction and a second flow rate of the enriched fluid upstream to the adsorption chamber;
(d) an enriched fluid outlet in flow communication with at least one passageway for delivering a portion of the enriched fluid stream downstream of the concentrator; and,
(e) a purge valve in flow communication with the inlet of the adsorption chamber and moveable between a closed position and an open position in which the adsorption chamber is purged during a purging cycle
whereby during the first cycle the enriched fluid stream travels in the downstream direction and during the purging cycle a portion of the enriched fluid stream travels in the upstream direction into the adsorption chamber.
The first flow rate may be greater than the second flow rate or, alternately, the second flow rate may be greater than the first flow rate.
In one embodiment, the fluid stream is at an elevated pressure when introduced to the adsorption chamber and the elevated pressure of the fluid stream provides essentially the only motive force to operate the concentrator.
In one embodiment, wherein the concentrator operates on a pressure differential in the adsorption chamber of 5 to 15 psig.
In another embodiment, the at least one valve comprises a venting valve moveable automatically from a first position in which the venting valve restricts the venting of the enriched fluid from the adsorption chamber into the passageway to a second position in which the venting valve vents the enriched fluid from the adsorption chamber into the passageway at an increased rate when the pressure in the adsorption chamber reaches a preset level.
In another embodiment, the at least one valve seals the adsorption chamber from the at least one passageway when the differential pressure between the adsorption chamber and the passageway is less than a preset level.
In another embodiment, the venting valve moves automatically from a first position in which the venting valve restricts the venting of the enriched fluid from the adsorption chamber into the passageway to a second position in which the venting valve vents the enriched fluid from the adsorption chamber into the passageway at an increased rate when the pressure in the adsorption chamber reaches a first preset level. Preferably, the venting valve seals the adsorption chamber from the passageway when the differential pressure between the adsorption chamber and the passageway is less than the first preset level. Further, the venting valve is preferably automatically moveable to a third position in which the venting valve vents enriched fluid from the passageway to the adsorption chamber when the pressure differential between the adsorption chamber and the passageway is less than a second preset level.
The storage chamber may be part of the passage way. Alternately, the storage chamber and the outlet may be separately in flow communication with the venting valve. The storage chamber is preferably drivingly connected to the purge valve (eg. by a mechanical linkage) whereby the storage chamber automatically causes the purge valve to be moved to the open position when the pressure within the storage container reaches a preset pressure. The storage chamber may be expandable due to the pressure of the enriched fluid provided thereto to automatically commence the purge cycle when the storage container reaches a preset pressure.
The enriched fluid outlet may have a flow restrictor associated therewith (eg an aperture or it may be a narrower diameter passage) whereby the pressure within the storage chamber is pressurized when the adsorption chamber vents enriched fluid into the passageway.
In accordance with the instant invention there is also provided a pressure swing adsorption apparatus for producing an enriched f
Conrad Helmut Gerhard
Conrad Wayne Ernest
Szylowiec Ted
Bereskin & Parr
Fantom Technologies Inc.
Mendes da Costa Philip C.
Spitzer Robert H.
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