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  Cryogenically producing oxygen-enriched liquid and/or gaseous oxygen from atmospheric airRelated Patent Categories: Refrigeration, Cryogenic Treatment Of Gas Or Gas Mixture, Separation Of Gas Mixture, Air, DistillationThe Patent Description & Claims data below is from USPTO Patent Application 20050274142. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims the benefit of U.S. Provisional Application No. 60/579,276, filed Jun. 14, 2004. BACKGROUND OF THE INVENTION [0002] 1. Technical Field [0003] The invention relates to cryogenic gas separation, and more particularly, to a system and method for cryogenically producing oxygen-enriched liquid and/or purified gaseous oxygen from atmospheric air, on demand, at or near the point of use. [0004] 2. Related Art [0005] A growing number of aging persons require oxygen therapy, typically in the range of 1-5 liters per minute of purified oxygen introduced to their breathing air to compensate for reduced lung capacity. Many of these people remain mobile and moderately active for many months or years while requiring such therapy. Presently, most of these people are served in their homes by use of an oxygen concentrator, which pressurizes the air and preferentially passes oxygen through a separator (e.g., membrane or pressure-swing absorber), delivering purities in the 90-98% range. In case of power loss, such patients also keep a large pressurized oxygen cylinder on hand. For mobile patients, smaller pressure cylinders are typically used to supply oxygen gas. These bulky, heavy tanks must be pulled by the individual on wheeled carts, which is a difficult and awkward process, especially for elderly people with breathing difficulties. [0006] An alternate approach for supporting mobile oxygen users exists, using unpressurized liquid oxygen (LOX) in small (sub-liter) lightweight portable dewars that are easily carried in belt or backpack. Liquid oxygen is almost 1000 times the density of its atmospheric gaseous equivalent, so the required volume is 5 times smaller than even high-pressure gas (typically at 3000 psi). In addition, LOX eliminates the need for heavy pressurized containment. Present LOX therapy is achieved only at much higher cost than typical gaseous oxygen therapies. LOX therapy is also unavailable to many people, insured or not, because such treatment requires the regular, periodic delivery of large, insulated dewar tanks of LOX to the patients home, solely to allow refilling of the lightweight mobile supply. Accordingly, a concentrator is still used for stationary support because the cost of delivered LOX is too high for stationary use. In this case, only the very inexpensive larger pressure cylinder for back-up supply is avoided. There is also a safety concern with storage of large amounts of LOX, a powerful oxidizer (fire accelerant). Consequently, LOX therapy today is restricted to a minority of relatively wealthy individuals even though many more would benefit by its advantages in comfort and effectiveness if a cost-effective means to provide it can be developed. [0007] In one approach, LOX generation is provided in homes by combining a cryocooler (a closed-cycle cryogenic refrigeration device) with a standard concentrator. One example of this approach is disclosed in U.S. Pat. Nos. 5,803,275 and 6,212,904. A disadvantage of this approach, however, is that a standard concentrator is still required, which adds complexity and cost. [0008] There are also many standard air separation plants in existence, the basic principles of cryogenic air separation having been established in the early 20.sup.th century. See for example, Universal Industrial Gases, Inc., "General Process Description-Cryogenic Air Separation," from their website, June 2004. However, these plants are vastly too large because they necessarily employ industrial-scale structure that is impractical for home production of oxygen-enriched liquid in individual-use quantities. For example, standard plant-size systems use cracking towers that are many feet tall and process many tons of product per day or hour. In addition, older large mass production plants use reversing heat exchangers, but always require pre-separation of water vapor (H.sub.2O) and carbon dioxide (CO.sub.2) to delay the requirement for reversing with the required high internal volume and consequent reversing losses. Furthermore, efficiency is considered tantamount to these systems, which necessitates many features that add costs to the systems, making them impractical for a mass market. [0009] In view of the foregoing, there is a need in the art for an improved solution for efficiently producing oxygen-enriched liquid and/or purified gaseous oxygen from local atmospheric air. SUMMARY OF THE INVENTION [0010] A system and method are disclosed for the production of oxygen-enriched liquid and purified gaseous oxygen from local atmospheric air. In one embodiment, the system includes an air mover for generating a local atmospheric air stream; a cryocooler including a cooling element thermally coupled to a condensing separator; a heat exchanger having a first path for receiving a cold gaseous exhaust stream from the condensing separator and a second path for chilling and removing readily-condensible contaminants from the local atmospheric air stream to form a purified gas mixture stream via heat transfer to the cold gaseous exhaust stream; and a receiver for the oxygen-enriched liquid that condenses from the purified gas mixture stream in the condensing separator, leaving the gaseous exhaust stream. [0011] A first aspect of the invention is directed to a system for producing an oxygen-enriched liquid from local atmospheric air, the system comprising: an air mover for generating a local atmospheric air stream; a cryocooler including a cooling element thermally coupled to a condensing separator; a heat exchanger having a first path for receiving a cold gaseous exhaust stream from the condensing separator and a second path for chilling and removing readily-condensible contaminants from the local atmospheric air stream to form a purified gas mixture stream via heat transfer to the cold gaseous exhaust stream; and a receiver for the oxygen-enriched liquid that condenses from the purified gas mixture stream in the condensing separator, leaving the gaseous exhaust stream. [0012] A second aspect of the invention includes a system for selectively isolating a liquid purified component of a gaseous mixture, the system comprising: a flow generator for generating a gas mixture stream; a cryocooler including a cooling element extending into a condensing separator; a heat exchanger having a first path for receiving a cold exhaust stream from the condensing separator and a second path for chilling and removing contaminants from the gas mixture stream to form a purified cold gas mixture stream via heat transfer to the cold exhaust stream; and wherein the cooling element condenses the liquid purified component from the purified cold gas mixture stream, leaving the cold gaseous exhaust stream, which exits through the first path of the heat exchanger. [0013] A third aspect of the invention relates to a method for producing oxygen-enriched liquid from local atmospheric air, the method comprising the steps of: forming an input stream of the local atmospheric air; using cold exhaust from a closed-cycle cryogenic cooler to remove readily-condensible contaminants from the input stream to form a purified gas stream; and cryogenically cooling the purified gas stream with a closed-cycle refrigerator to condense oxygen to form the oxygen-enriched liquid. [0014] A fourth aspect of the invention is directed to a system for producing purified gaseous oxygen from local atmospheric air, the system comprising: an air mover for generating a local atmospheric air stream; a cryocooler including a cooling element thermally coupled to a condensing separator; a heat exchanger having a first path for receiving a cold gaseous exhaust stream from the condensing separator, a second path for chilling and removing readily-condensible contaminants from the local atmospheric air stream to form a purified gas mixture stream via heat transfer to the cold gaseous exhaust stream, and a third path for transferring heat to an oxygen-enriched liquid that condenses from the purified gas mixture stream in the condensing separator to transform the oxygen-enriched liquid into the purified gaseous oxygen. [0015] The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: [0017] FIG. 1 shows one embodiment of a system for producing oxygen-enriched liquid and/or purified gaseous oxygen from local atmospheric air according to the invention. DETAILED DESCRIPTION [0018] With reference to the accompanying drawings, the present invention includes a miniature oxygen separation and liquefaction system and method, intended for providing oxygen-enriched liquid and/or purified gaseous oxygen for both stationary and mobile patients (or for any other purpose requiring small amounts of oxygen-enriched liquid or purified gaseous oxygen on demand and on-site). [0019] FIG. 1 shows one embodiment of a system 8 for selectively isolating a liquid purified component of a gaseous mixture according to the invention. In accordance with the invention, in one preferred embodiment, system 8 is especially advantageous for producing an oxygen-enriched liquid 10 from local atmospheric air. System 8 includes an air mover 12 (or flow generator) for generating a local atmospheric air stream 14. It should be recognized that the position of air mover 12 may be changed, e.g., to the exhaust side to draw rather than push the flow. Air stream 14 enters a heat exchanger 20 having a first path 22 for receiving a cold exhaust stream 24 from a condensing separator 40 and a second path 26 for receiving air stream 14 and for removing readily-condensible contaminants by condensation, freezing, and (de)sublimation to form a purified gas (mixture) stream 46 from air stream 14. Condensation, etc., occurs in second path 26 via heat transfer to cold exhaust stream 24 in first path 22. As will be described below, readily-condensible contaminants may include, for example, carbon dioxide (CO.sub.2) and water (H.sub.2O). Heat exchanger 20 may be oriented to enable gravity assist, if desired (e.g., slanted or vertical). Once cold exhaust stream 24 passes through heat exchanger 20, it may be released to the atmosphere as exhaust 30. Alternatively, exhaust 30 may be re-routed to a cryocooler 50, described below, for its heat rejection purposes (not shown). Conversely, air stream 14 may be drawn over the cooler rejection surfaces of cryocooler 50 prior to entering heat exchanger 20, thereby increasing the temperature difference between exchanger 20 paths to allow a smaller exchanger and lower cost. [0020] Purified gas stream 46 enters condensing separator 40. System 8 also includes a cryocooler 50 that includes a cooling element 52 that extends into condensing separator 40. Cryocooler 50 can be, for example, of the Stirling type or an orifice pulse tube type. However, cryocooler 50 preferably includes a sealed, closed-cycle and maintenance-free cryogenic cooler so that it is practical for the preferred application, i.e., on-site oxygen generation without skilled operators. "Closed-cycle" means that the cryocooler contains a separate working fluid and does not use expansion of the process fluid itself (here, air or its purified derivatives) as a cooling medium to enable cryogenic separation of that process fluid, which would necessitate provisions for power-consuming compression before condensation, distillation and rectification. In addition, the lack of a high pressure requirement on the process fluid makes use of a reversing valve 92 possible, as will be described in more detail below. This situation is in contrast to conventional larger scale devices that use large-scale motors, e.g., using a 1000 HP or more, to spin compound turbo-compressors and expanders that are entirely inappropriate and impossible to scale down to the sizes of interest of the preferred application. Even known larger, on-site liquefier products use mechanical (kinematic) Stirling machines or Gifford-McMahon refrigerators that are incompatible with the low-maintenance and small-scale requirements of home use liquid oxygen production. To this end, cryocooler 50 may be, for example, of the type available from Clever Fellows Innovation Consortium, Inc. (CFIC) of Troy, N.Y., which are smaller, sealed, closed-cycle cryocoolers that have no regular maintenance requirement over a multi-year service life. Continue reading... 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