Title of Invention

"A METHOD AND DEVICE FOR OXYGEN ENRICHMENT OF AIR WITH SIMULTANEOUS DEPLETION OF CARBON DIOXIDE"

Abstract

The invention relates to a method for reducing the carbon dioxide concentration in air of a closed or partially closed unit of space. The inventive method comprises the steps of removing an air flow from the unit of space, guiding the air flow in a membrane systems that contains least one membrane module having a CO2/O2, selectivity of greater 2, removing the carbon dioxide permeated through the membrane, and returning the air flow that has been depleted of carbon dioxide in the membrane system to the unit of space. The inventive method can be optionally combined with an oxygen enrichment method. The invention also relates to corresponding devices for carrying out the inventive method.

Full Text

The present invention relates to a method and an apparatus for reducing the carbon dioxide concentration in air in closed or partly closed units of space, if necessary at the same time as oxygen enrichment. The breathing in of oxygen produces carbon dioxide as a "waste gas" . Carbon dioxide is an odorless gas that occurs naturally in air in a very small proportion of 0.03 vol%. Higher carbon dioxide contents in the surrounding air have an unfavorable physiological effect on humans. As small a concentration as 0.5 vol% C02 in the surrounding air produces typical symptoms such as headache, which is why the maximal workplace concentration of C02 is set at 0.5 vol% (5000 ppm) . In closed air conditioned spaces for example it is therefore desirable to be able to regulate the carbon dioxide content in the air wherein excess C02 is continuously removed from the air. Moreover, lowering of the C02 content can be advantageously combined with additional measures for improving the room climate for example by enrichment of the room air with oxygen as well as air conditioning. Conventional oxygen enrichment methods for improvement of the air quality in closed air circulation systems and rooms or cabins are mostly based on pure oxygen enrichment devices such as for example pressure swing adsorption systems or hollow fiber membrane systems. Corresponding devices are described for example in U.S Patents 4,867,766; 5,890,366; 6,427,484; 5,158,584 and 4,896,514. Some of the prior art devices identified above provide conditioning of the oxygen-enriched air. Systems have also been proposed (e.g. German Patent 195 45 764) which remove carbon dioxide with adsorbers. This technology however has the disadvantage of also simultaneously dehumidifying the air. The consequence is either very costly adsorber regeneration with hot air or vacuum as well as a separate humidif ication of the room air, or disposal of the used adsorber cartridges, which makes the corresponding systems uneconomical for most applications. In order to avoid the disadvantageous physiological effects of carbon dioxide enrichment in room air stated above there is a demand for suitable methods and devices which make possible a depletion of the carbon dioxide content in room air, and can if necessary simultaneously climatize or enrich the air with oxygen. It was therefore the object of the present invention to make available a method and a dedicated apparatus for the regulation of the carbon dioxide content in closed or partially closed air circulation systems and rooms or cabins, especially for the depletion of carbon dioxide content, which overcome the disadvantages of the state of the art. It was a further object of the present invention to make available a method and a dedicated apparatus for the depletion of carbon dioxide from air in closed or at least partly closed units of space, which makes possible a simultaneous enrichment of the air with oxygen. It was especially an object of the present invention to provide a method and an apparatus of the type stated above, which in an inexpensive and if possible low-noise way depletes carbon dioxide in a block of air and if necessary essentially simultaneously permits enrichment of oxygen. The objects stated above are solved by means of the features of the independent method claims and device claims. Preferred embodiments of the method in accordance with the invention or as the case may be of the device in accordance with the invention are defined in the dependent claims. In accordance with the invention a method is made available for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, comprising the following steps: Extraction of an air stream from the unit of space; Feeding of the air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Removal of the carbon dioxide permeated through the membrane; Return of the air stream depleted of carbon dioxide in the membrane system into the unit of space. In accordance with another aspect of the present invention a method for the oxygen enrichment of air with simultaneous depletion of carbon dioxide in a closed or partially closed unit of space is provided, comprising the following steps: Extraction of a first air stream from the unit of space; Feeding of the first air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Removal of the carbon dioxide permeated through the membrane; Return of the first air stream depleted of carbon dioxide in the membrane system into the unit of space; Enrichment of a second air stream with oxygen by means of an oxygen enrichment system, which produces an oxygen enriched and a nitrogen enriched air stream; Feeding of the oxygen enriched air stream into the unit of space; and Separate removal of the nitrogen enriched air stream. In accordance with another aspect of the present invention a device is provided for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, comprising: Arrangements for withdrawal of an air stream from the unit of space; Arrangements to feed the air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Arrangements for the removal of carbon dioxide from the permeate side of at least one membrane module; Arrangements for the return of the air stream depleted of carbon dioxide into the unit of space. In accordance with a further aspect of the present invention a device for the oxygen enrichment of air with simultaneous depletion of carbon dioxide in closed or partially closed circulation loops is provided, comprising: Arrangements for extraction of a first air stream from the unit of space; Arrangements to feed the first air stream into a membrane system containing at least one membrane module having a C02/02 selectivity greater than 1; Arrangements to remove carbon dioxide from the permeate side of at least one membrane module; Arrangements to return the first air stream depleted of carbon dioxide in the membrane system into the unit of space; An oxygen enrichment system which produces an oxygen enriched and a nitrogen enriched air stream from a fed-iri second air stream; Arrangements to feed the oxygen enriched air stream into the unit of space; as well as Arrangements to discharge the nitrogen enriched air stream. Within the framework of the present invention the terms "oxygen enrichment" or "nitrogen enrichment" in each case signify an air composition which has a higher proportional volume percent of oxygen or nitrogen than natural air. Under "carbon dioxide enriched" or "carbon dioxide depleted" an air composition is to be understood with elevated or decreased proportional volume percent of carbon dioxide relative to the starting air composition before treatment in the membrane system. In accordance with the invention, by membrane module is to be understood as a suitable geometric arrangement of membrane surfaces in the form of an assembly whose retentate side or upstream flow regions and permeate side or downstream flow regions are technically separated from each other, so that substantially continuous material crossover can essentially occur only by permeation through the membrane between retentate or upstream sides and permeate or downstream sides. The membrane module usable in accordance with the invention can, based on the possibly high packing densities of more than 1000 m2/m3, preferably more than 1500 nr/m3 and especially more than 2000 m2/m3, be set up advantageously with very small dimensions. A "membrane system" in the sense of the invention is an arrangement of at least one, preferably a plurality of membrane modules fitted with suitable devices for feeding or discharge of air or other gas mixtures to the upstream side of the membranes or membrane modules, as well as devices for removal of permeated gases from the downstream side of the membranes or membrane modules. In accordance with the invention it has been shown that with the use of membrane systems control or adequate depletion of the carbon dioxide content can be achieved in room air in a simple, continuous and economic manner, without relying on adsorption cartridges which must be regularly exchanged and regenerated. In accordance with the invention, it is known moreover that from health and economic aspects meaningful oxygen enrichment depend especially on a functioning interplay between oxygen enrichment on the one hand and the specific depletion of carbon dioxide and if necessary on the other hand on additional odorous substances which up to now has not found any consideration in the state of the art. The present invention makes possible an effective and economic regulation of the C02 content of room air as well as, in a preferred embodiment, an essentially simultaneous enrichment of oxygen and depletion of carbon dioxide, preferably with simultaneous depletion of other odorous substances and possibly control of air moisture and temperature. An advantageous additional effect of the present invention is also that the quota of air can be freed of bacteria or viruses, since these are effectively filtered out in the membrane modules that are utilized. In accordance with a first aspect of the invention it has been surprisingly shown that control or depletion of the C02 content in room air can thereby be advantageously facilitated, that the C02 can be continuously taken by selective permeation from the air of a unit of space in a circulation stream and again fed back by the use of selective membrane systems. This is especially surprising since the low proportional percentage of C02 in room air necessitates a not only selective but also very effective gas separation. The present invention is based hereon that one makes use of the relatively higher permeation of C02 molecules relative to oxygen through certain membranes. This predominantly kinetic effect also facilitates the highly selective and therewith very economical separation of gases with very small proportional volume percentages. According to the present invention, first of all a type of device or method is provided without adsorber which can effectively decrease the C02 content of air. The method in accordance with the invention or the device for depletion of carbon dioxide can moreover be simply and effectively combined with other methods of improvement of air quality. In the following the method and devices in accordance with the invention are described in detail. In connection with the combination of C02 depletion and oxygen enrichment, features described for C02 depletion are evidently also applicable to pure C02 depletion methods and devices, but this must in each case be stated explicitly. In accordance with a preferred aspect of the invention the combination of an efficient method of oxygen enrichment (or nitrogen depletion) by means of an oxygen enrichment system suitable for this, together with the appropriate method for selective depletion of carbon dioxide, in accordance with the invention, is particularly advantageous. It has been surprisingly shown that the combination of a continuously operating membrane system containing membranes which have a high carbon dioxide selectivity, and with which the bulk of the carbon dioxide can be taken from the loop, with for example a conventional pressure swing adsorption system or membrane process, through which the nitrogen can be obtained from an air circulation loop, or the air be enriched with oxygen, is highly effective at simultaneously low operating costs for a continuously operating device. According to the method in accordance with the invention for the depletion of C02 from the air, if necessary with simultaneous enrichment of oxygen, a (first) air stream is taken from a unit of space by means of suitable devices, for example by means of an appropriate exhaust device or a ventilation blower. A unit of space in the sense of the invention can be any desired block of air essentially closed off or at least partially marked off from the surrounding environment, for example the air in a room, a building, a pressurized cabin in a motor vehicle, airplane, ship or streetcar, a tent, under a mosquito net, air-breathing systems, diving suits, respiratory protection equipment, an inhalation loop or suchlike. Since oxygen enriched air also has a higher specific weight, as a matter of principal environments which are open at the upper portion, such as tubs and the like are also conceivable in the sense of the present invention. This first air stream taken from a unit of space is subsequently fed for example via suitably sized and configured tubes, hoses or air channels, into a membrane system, which is fed to at least one membrane, conventionally a complete membrane module consisting of a suitable assembly of membranes preferably with high C02/02 selectivity. Preferably the selectivity of the membrane module or as the case may be of the membranes contained therein is greater than 1, for example 1.1 or 1.5, especially preferred greater than 2. The CO-2/02 selectivity is understood here as the ratio of the relative permeation rates of C02 to 02 through the membrane, so that a C02/02 selectivity of greater than 1 signifies that carbon dioxide permeates through the membrane faster than oxygen. A C02/02 selectivity of greater than 2 signifies that the permeation rate of carbon dioxide through the membrane is more than double the permeation rate of oxygen. It is specially preferred that the C02/02 selectivity for the membrane system employed in accordance with the invention is greater than 3, and especially greater than 5. The person skilled in the art is aware that a higher selectivity is generally associated with a lower throughput through the membrane, while very open-pore systems with large throughput have a lower separation selectivity. In the selection of membranes for use here, appropriate compromise should be made for the actual purpose of the application. In accordance with the invention, suitable membrane systems with C02 selective membrane modules contain membranes consisting of carbon membranes, ceramic membranes, plastic membranes, as well as combinations and/or composites of these membranes. Appropriate selective membranes or membrane modules for a usable membrane system in the present invention are described for example in German Patent 10 013 457, WO 01/68533, German Patent 10 051 910, WO 02/32558 as well as German Patent 19 849 216 and WO 00/24500. The membranes, membrane systems and membrane modules described therein, if necessary after appropriate modification of their physicochemical properties, are suitable in principle as membranes and in membrane modules in the membrane system that is used in the present invention. In the method and devices of the present invention membranes or membrane modules are preferred from pyrolytically prepared carbon-based material, like those described in WO 02/32558 and materials prepared by the methods described therein, including the ceramic materials mentioned there. Other preferred materials for membranes and membrane modules in the method and devices of the present invention are described in German Patent Application 102 33 182. In order to further increase the C02-selectivity of membranes used, the membrane materials mentioned above can additionally be surface modified into especially preferred embodiment forms of the invention, for example through oxidative or reductive surface treatment with suitable oxidizing or reuucmy ctyeiius, j^y means of impregnation with metal salts, especially transition metal salts, by incorporation of metals, especially transition or noble metals, or by coating of the membrane surfaces with membrane active plastic layers. Membranes employed in accordance with the invention can for example have the following active layers: polysulfone, polyoctylmethylsiloxane, polyetherimide, silicone, ethylcellulose, polyphenylene oxide, polycarbonate as well as combinations thereof. The person skilled in the art will thus dimension the membrane system as a function of the total amount of air flow to be treated, so that a sufficient membrane surface is available, so as to remove carbon dioxide in sufficient quantity from the first air stream by permeation through the membrane. For this purpose it is also possible for example to combine a plurality of membrane modules in a membrane system. In that connection the combined membrane modules can have identical or different C02/02 selectivities, for example the combination of one or a plurality of membrane modules with a smaller C02/02 selectivity for the pre-enrichment of C02 in the permeate with one or a plurality of modules with a C02/02 selectivity of greater than 1, which can if necessary also have different membrane areas. In the membrane system carbon dioxide is transferred through (permeates) the membrane predominantly on the basis of its higher permeation rate. The non-permeated, now carbon dioxide enriched remainder of the first air stream, which was withheld from the membrane, is for example discharged again via a retentate-side outlet port of the membrane system and via appropriate devices, for example blowers or pumps, and is returned in a circulation loop into the unit, of space from which the first air stream was taken. The carbon, dioxide is removed through the membrane on the permeate side of the membrane/membrane module. In an embodiment of the invention, the removal can be carried out by suction with, or application of, reduced pressure or vacuum to the permeate side of the membrane system by using suitable apparatus, e.g. pumps. Moreover the permeated carbon dioxide can also be removed by means of absorption in suitable liquid absorbers such as for example organic amines, alcohol amines and the like. Diethanolamine is preferred. The advantage in use of especially selective carbon dioxide absorbing organic liquids for C0:; removal is that here the membranes can be made open-pored, whereby the throughput and therewith the effectiveness of the method in accordance with the invention is further increased. In accordance with another embodiment of the invention the permeated carbon dioxide is removed by means of a purge gas stream. For this purpose the purge gas is fed and discharged by means of suitable devices, for example pumps and/or blowers. As purge gas, generally air, for example fresh air from outside the loop is used. However any other suitable gas or gas mixture can be used, for example nitrogen enriched air from the oxygen enrichment system. The usable oxygen enrichment system can in accordance with the invention be any system known to the art for enrichment of oxygen from air. Examples of usable oxygen enrichment systems in accordance with the invention are pressure swing adsorption systems and hollow fiber membrane modules, which according to construction and the membrane material used can be operated with over pressure or reduced pressure, for example by application of a vacuum. Appropriate pressure swing adsorption apparatus and methods which can be used in the present invention are for example devices based on zeolite adsorption means such as are described in U.S. Patent 4,685,939. Other suitable pressure swing adsorption devices, which can be used as oxygen enrichment systems in the present invention, are described for example in U.S. Patent 5,890,366, in U.S. Patent 4,896,514 as well as U.S. Patent 4,867,766. Insofar as a pressure swing adsorption system is used in the present invention the pressure swing adsorption system preferably comprises a compressor for compression of the second air stream, e.g. to a pressure of 0.12 MPa to 1.0 Mpa, preferably 0.15 MPa to 0.25 MPa; and one to ten, preferably 2 adsorption chambers containing zeolite molecular sieves per unit. For large scale installations a plurality of these units can be employed. Additionally in accordance with the invention, pressure swing adsorption systems operating at reduced pressure are also usable, in which case a vacuum pump is usually employed instead of a compressor. In accordance with the invention hollow fiber membrane-based systems usable as oxygen enrichment systems are for example described in German Patent 19 645 764 as well as U.S. Patent 5,158,584. Also plastic membrane separation systems such as are described in U.S. Patent 6,427,484 are usable in the method and the device of the present invention. Further, membrane-based air separation devices relying on zeolite membranes, zeolite mixed-matrix systems, carbon or polymer membranes, can be used for the oxygen enrichment system employed in accordance with the invention. It is preferred that a second air stream is fed to the oxygen enrichment system in suitable fashion, from where the oxygen enrichment system produces an oxygen-enriched air stream and a nitrogen-enriched air stream. The nitrogen enriched air stream is suitably bled off separately or rejected as the case may be. The oxygen enriched air stream is additionally fed to, or together with, the carbon dioxide depleted first air stream to the unit of space. It is preferred that the carbon dioxide depleted first air stream is united with the oxygen enriched air stream from the oxygen enrichment system before being returned to the unit of space. In an especially preferred embodiment of the invention the device in accordance with the invention comprises 02 sensors C02 sensors or air quality sensors as well as coupled therewith computer-aided control devices for adjustment of the stream volumes of the air streams returned to the; unit of space from the membrane system and the oxygen enrichment system. By means of one of this type of device it is possible for example, to establish and maintain a defined average oxygen content and/or carbon dioxide content of the air in the unit of space. The second air stream can originate from fresh or surrounding air, for example in spaces or buildings, or outside air. In accordance with a preferred embodiment of the method, in accordance with the invention or the device according to the invention, the second air stream is at least also partly removed from the unit of space, from the first air stream before the membrane system or from the carbon dioxide depleted first air stream. The partitioning of the second air stream from the unit of space or from the first air stream can be carried out by means of any devices known to a person skilled in the art of splitting up gas volume streams. In accordance with the invention it is further preferred for economic reasons, that the first air stream has a larger volume than the second air stream. It is preferred that the volume ratio of the first air stream to the second air stream lies in the range from 500:1 to 2:1. In preferred embodiments the first air stream and the second air stream or the oxygen enriched air stream resulting therefrom can be passed across an active carbon filter in order to remove unwanted odorous substances, dust or the like. This serves especially for the pre-purification of the air, so as to maintain constant membrane performance and prevent premature blocking of the pores. It is provided moreover in a preferred embodiment if necessary to temper, moisten or to climatize individual air streams. For dwindling separation effectiveness resulting from impurities, sediment, collections of moisture or blockages of the membrane pores in accordance with the inventive membrane system the membranes can from time to time be cleaned or regenerated. In the case of electrically conductive membrane modules e.g. for carbon-based membranes, electrically inductive resistance heating can for example be carried out whereby the membranes are heated so that impurities are evaporated or oxidatively broken down. However other heat sources are usable in order to clean the membranes thermally, such as hot air blowers, radiators, infra-red radiation, heat pipe radiation, heat-ray tubes, fluorescent lamps, electrical heating lines, induction heating and suchlike. Also the cleaning by means of compressed air or passing solvents through the membrane systems are usable in a few embodiments. Moreover, the membranes can be cleaned and if necessary sterilized by means of suitable oxidation means, for example ozone or gamma rays. A preferred embodiment of a combination method in accordance with the invention is furthermore illustrated in the attached flow diagram in accordance with Figure 1. Figure 1 shows an essentially closed unit of space AB, from which a first air stream la with elevated carbon dioxide proportion is extracted and fed to the purge gas membrane system Ml. In the purge gas membrane system, carbon dioxide permeates preferentially through the membrane module (not shown) due to its higher permeation rate, and carbon dioxide enriched air remains on the retentate side of the membrane module. This held back air stream Ib enriched in C02, is returned again into the unit of space AB. The C02 (or the permeate sided appearing air with a significantly increased proportion of C02) permeated through the membranes of the membrane module is removed from the purge gas membrane system Ml, by means of a purge gas stream Ic, as carbon dioxide loaded purge gas stream Id. Parallel to this a second air stream 2a is fed into an oxygen enrichment system M2, which produces a nitrogen enriched air stream 2c, which is removed, as well as an oxygen enriched air stream 2b, which is fed into the unit of space AB, in order to raise the relative oxygen content of the air there. 1. A method for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, comprising the following steps: Extraction of an air stream from the unit of space; Feeding of the air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Removal of the carbon dioxide permeated through the membrane; Return of the air stream depleted of carbon dioxide in the membrane system into the unit of space. 2. A method for the oxygen enrichment of air with simultaneous depletion of carbon dioxide in a closed or partially closed unit of space, comprising the following steps: Extraction of a first air stream from the unit of space; Feeding of the first air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Removal of the carbon dioxide permeated through the membrane; Return of the first air stream depleted of carbon dioxide in the membrane system into the unit of space; Enrichment of a second air stream with oxygen by means of an oxygen enrichment system, which produces an oxygen enriched and a nitrogen enriched air stream; Feeding of the oxygen enriched air stream into the unit of space; and Separate removal of the nitrogen enriched air stream. 3. The method according to Claim 1 or 2, characterized in that the permeated carbon dioxide is removed by means of reduced pressure, vacuum or by purging the permeate side of at least one membrane module with a purge gas stream of the permeate side of the membrane module. 4. The method according to Claim 1 or 2, characterized in that the permeated carbon dioxide is discharged by absorption in suitable absorber liquids. 5. The method according to any one of Claims 2 through 4, characterized in that the carbon dioxide depleted first air stream is cleaned before return into the unit of space with the oxygen enriched air stream from the oxygen enrichment system. 6. The method according to any one of Claims 2 through 5, characterized in that the second air stream originates at least partially from the unit of space, from the first air stream before the purge gas membrane system or the carbon dioxide depleted first air stream. 7. The method according to any one of the preceding Claims, characterized in that the unit of space is selected from a building, a room, a pressurized cabin in a motor vehicle, airplane, ship or streetcar, a tent, under a mosquito net, from air-breathing systems, diving suits, respiratory protection equipment, or an inhalation loop. 8. The method according to any one of the preceding Claims, characterized in that at the least one membrane module contains carbon membranes, ceramic membranes, plastic membranes, and combinations and/or composites of these membranes. 9. The method according to any one of Claims 2 through 10 character! zed in that the oxygen enr:rhment system used is a pressure swing adsorption system, a hollow fiber membrane module or a membrane-based air separation device on the basis of zeolite membranes, zeolite mixed-matrix systems, carbon or polymer membranes. 10. The method according to any one of Claims 4 through 9, characterized in that the purge gas is air which is, if necessary, tempered and/or climatized. 11. The method according to any one of Claims 2 through 10, characterized in that the volume ratio of the first air stream to the second air stream lies in the range from 500:1 to 2:1. 12. A device for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, comprising: Arrangements for withdrawal of an air stream from the unit of space; Arrangements to feed the air stream into a membrane system containing at least one membrane module having a C02/02 selectivity greater than 1; Arrangements for the removal of carbon dioxide from the permeate side of at least one module; Arrangements for the return of the air stream depleted of carbon dioxide in the membrane system into the unit of space. 13. A device for the enrichment of oxygen from air by simultaneous depletion of carbon dioxide in closed or partially closed loops comprising: Arrangements for extraction of a first air stream from the unit of space; Arrangements to feed the first air stream into a membrane system containing at least one membrane module having a C02/02 selectivity of greater than 1; Arrangements to remove carbon dioxide from the permeate side of at least one membrane module;Arrangements to return the first air stream depleted of carbon dioxide into the unit of space; An oxygen enrichment system, which produces an oxygen enriched and a nitrogen enriched air stream from an introduced second air stream; Devices for feeding the oxygen enriched air stream into the unit of space; as well as Devices for discharge of the nitrogen enriched air stream. 14. The device according to Claim 12 or 13, characterized in that the devices for removal of carbon dioxide comprise devices for provision of reduced pressure or vacuum on the permeate side of the membrane system. 15. The device according to Claim 12 or 13, characterized in that the devices for removal of carbon dioxide comprise devices for feeding and discharge of purge gas in the membrane system. 16. The device according to any one of Claims 12 through 15, characterized in that the oxygen enrichment system is a pressure swing adsorption system, a hollow fiber membrane module or a membrane-based air separation device on the basis of zeolite membranes, zeolite mixed-matrix systems, carbon or polymer membranes. 17. The device according to Claim 16, characterized in that per device the pressure swing adsorption system comprises; A compressor for compression of the second air stream; and One to 10 adsorption chambers containing zeolite molecular sieves. 18. The device according to any one of claims 12 through 17, characterized in that the membrane system comprises at least one membrane selected from carbon membranes, ceramic membranes, plastic membranes, and combinations and/or composites of these membranes. 19. The device according to any one of claims 14 through 18, characterized in that the device comprises CO2 sensors, O, sensors or air quality sensors as well as computer- aided control devices coupled therewith for adjustment of the volume streams of the air streams returning from the membrane system and the oxygen enrichment system into the unit of space. 20. A method for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, substantially as hereinbefore described with reference to the accompanying drawings. 21. A device for the depletion of carbon dioxide in the air from a closed or partially closed unit of space, substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

2808-delnp-2005-abstract-(14-08-2007).pdf

2808-delnp-2005-abstract.pdf

2808-delnp-2005-claims-(14-08-2007).pdf

2808-delnp-2005-claims.pdf

2808-DELNP-2005-Correspondence-Others-(03-03-2008).pdf

2808-delnp-2005-correspondence-others.pdf

2808-delnp-2005-description (complete)-(14-08-2007).pdf

2808-delnp-2005-description (complete).pdf

2808-delnp-2005-drawings-(14-08-2007).pdf

2808-delnp-2005-drawings.pdf

2808-delnp-2005-form-1.pdf

2808-delnp-2005-form-18.pdf

2808-delnp-2005-form-2-(14-08-2007).pdf

2808-delnp-2005-form-2.pdf

2808-DELNP-2005-Form-26-(14-08-2007).pdf

2808-delnp-2005-form-26.pdf

2808-delnp-2005-form-3.pdf

2808-delnp-2005-form-5.pdf

2808-delnp-2005-pct-304.pdf

2808-delnp-2005-pct-306.pdf