Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
2000-06-26
2002-02-05
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S105000, C095S138000, C095S139000, C096S130000, C096S144000, C426S419000
Reexamination Certificate
active
06344070
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of removing individual ones of a mixture of gases within a controlled environment container and to apparatus for selectively adsorbing components of a gas mixture.
PRESENT STATE OF THE ART
Adsorbent materials can be used to change the composition of a mixture of gases by selective adsorption, using a material which has different tendencies to adsorb different components of the mixture. For example, nitrogen can be generated by selective adsorption of oxygen from air, -or by adsorbing nitrogen and then desorbing the adsorbed gas for collection.
It can be desirable to adjust the content in a mixture of gases of two or more of the components. For example, the storage life of perishable goods within a transportation container can be affected by the amounts of oxygen and of carbon dioxide in the environment within the container.
It is known to use twin adsorbent chambers to separate components of a gas mixture. The adsorbent in the chambers adsorbs one of the components of the mixture preferentially relative to another of the components. Apparatus which comprises two adsorbent chambers allows the adsorbent in one of the chambers to be used for separation while the adsorbent in the other of the chambers is regenerated by passage through it of a purge stream of gas supplied from the outlet of the chamber that is in use for separation.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a technique for separating components of a mixture of gases in which the purge gas is supplied from the chamber that is in use for separation to the chamber that is to be regenerated in a pulse.
Accordingly, in one aspect, the invention provides a method of removing individual gas components of a mixture of gases within a controlled environment container using apparatus which comprises first and second chambers which are arranged in parallel for the gas mixture to flow through them from their inlet ends to their outlet ends and which contain adsorbent material with different affinities for the gas components of the mixture, the method comprising:
(a) supplying the gas mixture to the first chamber so as to pressurise it, while allowing a purge stream to flow from the outlet end of the first chamber to the second chamber to purge adsorbed gas from the adsorbent material in the second chamber, and
(b) supplying a purge pulse of gas from the outlet end of the first chamber to the second chamber to purge adsorbed gas from the adsorbent material in the second chamber, the rate of flow of the purge stream being less than that of the purge pulse.
The method of the invention has the advantage that, by use of a purge pulse of gas from the first container to the second container, the efficiency which the components of the gas mixture can be separated can be increased. This can arise because of the use of the pulse of gas mixture which contains a relatively high proportion of the gas components for which the affinity of the adsorbent is least strong from the first chamber to purge adsorbed gas from the second chamber.
The purge stream and purge pulse will generally flow between the chambers through purge stream and purge pulse conduits, which may be separate or may be provided by a common conduit. Generally, at least one of the purge stream and the purge pulse, and preferably both, will be supplied to the second chamber at the outlet end thereof so that the flows of gas for adsorption and purge gas are countercurrent. When a common conduit is used, its capacity can be controlled by means of a valve which can be removed between first and second positions in which it accommodates the purge stream and the purge pulse respectively. Preferably, the ratio of the rate of flow of gas (measured in terms of weight of gas) in the purge pulse to that in the pulse stream is at least about 1.5, more preferably at least about 1.8, especially at least about 2.0. When the relative flow rates are achieved by different flow capacities in the purge stream and purge pulse conduits, it can be appropriate for the ratio of the capacity (volumetric) of the purge pulse conduit to that of the purge stream conduit to be at least about 1.5, preferably at least about 1.8, especially at least about 2.0. The ratio will generally be less than about 4.0, for example less than about 3.0.
The purge stream can flow from the outlet end of the first chamber to the second chamber substantially continuously while the pressure in the first chamber is greater than that in the second chamber. For example, when the purge stream flows through a purge stream conduit which connects the first and second chambers, it can contain an orifice valve. When a common conduit is used for the purge stream and the purge pulse, it might contain an orifice valve to control the rate of flow of the purge stream; that orifice valve might be capable of being opened to accommodate the flow of the purge pulse, or a by-pass section might be opened for the purge pulse.
Purged gas is discharged from the second chamber while one or both of the purge pulse and the purge stream is supplied to the second chamber. When the purge pulse or the purge stream are supplied at the outlet end of the second chamber, the purged gas will be discharged from the inlet end. The purged gas that is discharged from the second chamber can be vented to the controlled environment container from which the gas mixture is supplied to the apparatus. The invention can thus be used to increase the amount of the component of the gas mixture in the controlled environment container that is the dominant component in the purged gas. The component might be vented to another vessel when the method of the invention is used to purify that component. Alternatively or in addition, the purged gas that is discharged from the second chamber can be vented to atmosphere. A combination of venting to atmosphere and venting to the controlled atmosphere container can be appropriate when the identify of the dominant component of the purged gas changes as it flows.
Preferably, the method of the invention includes the step of venting the first chamber to discharge preferentially the component of the gas mixture for which the affinity of the adsorbent is least strong. The venting step will generally take place after the step of supplying a purge pulse of gas to the second chamber. The vented gas can be discharged to atmosphere when the method is used to reduce the amount of that component of the gas mixture in the controlled atmosphere container. The vented gas can be discharged to the container when the method is used to increase the amount of that component of the gas mixture in the controlled atmosphere container. The vented gas might be discharged to a vessel for storage when the method of the invention is used to purify that gas for collection. The technique provided by the present invention involving use of a pulse or purge gas has the advantage that it enhances the purity with which the least strongly adsorbed component or components of the gas mixture can be separated from the mixture. The invention thus provides an effective technique for purifying that component of the mixture.
The use of first and second chambers containing adsorbent allows the two quantities of adsorbent in the two chambers to be used for adsorption alternately, with one of the quantities being purged for reuse while the other is being used for adsorption. Preferably, the nature and configuration of the first chamber are substantially the same as those of the second chamber. Preferably, the adsorbent material contained within the first chamber is substantially the same as that within the second chamber. The method of the invention preferably includes the steps of equalising the pressures in the chambers and repeating the steps (a) to (d) referred to above with the respective functions of the first and second chambers reversed.
The duration of the steps of the method will be controlled according to factors including the relative proportions of the components in the gas mixture, the capac
Domnick Hunter Ltd
Spitzer Robert H.
Workman & Nydegger & Seeley
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