Patent Application
20050274142
1. Technical Field
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.
2. Related Art
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.
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.
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.
There are also many standard air separation plants in existence, the basic principles of cryogenic air separation having been established in the early 20th 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 (H2O) and carbon dioxide (CO2) 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.
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.
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.
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.
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.
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.
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.
The foregoing and other features of the invention will be apparent from the following more particular description of embodiments of the invention.
The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:
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).
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.
When purified gas stream 46 encounters cooling element 52, oxygen (O2) preferentially condenses (at approximately 84K.) in condensing separator 40 from purified gas stream 46 into oxygen-enriched liquid 10, leaving cold exhaust stream 24. A receiver 60, preferably in the form of an insulated dewar, may be provided to store oxygen-enriched liquid 10 collected from condensing separator 40. A second, portable dewar (not shown) may also be provided with system 8, rather than just an oxygen-enriched liquid tap 84 from receiver 60.
As also shown in
A system controller 90 may also be provided for controlling air mover 12, heat exchanger 20, cryocooler 50 and a reversing valve 92 (discussed below). In one embodiment, system controller 90 adjusts output based on a status of receiver 60. For example, system controller 90 may reduce or stop output if receiver 60 is substantially full. System controller 90 may also control air stream 14 flow rate relative to the available cooling capacity and operating temperatures, to minimize the mass of air that is cooled and re-heated.
System 8 may also include a reversing valve 92 for reversing a flow direction. That is, periodically switching the flow direction such that local atmospheric air 14 passes through first path 22 and exhaust stream 24 passes through second path 26, which may be advantageous periodically to remove build up within system 8 when connected as shown. In particular, because of the freezing of moisture and some trace compounds like carbon dioxide (CO2), the pressure drop or flow rate may be monitored by system controller 90. When the frozen accumulation has diminished the flow to some predetermined level, reversing valve 92 is switched to the alternate position, reversing the flow of air stream 14 and exhaust 30. Exhaust 30 then becomes a re-vaporizing stream that carries away the frozen materials. In this way, the frozen accumulation is never excessive and is managed without costly air separators or concentrators that pre-purify the gas stream before cooling.
In an alternative embodiment, materials captured from the clean out process can be captured as liquids and combined with the dry purified gaseous oxygen 70 to humidify that stream for more comfortable breathing support, e.g., via humidifier 82. Although shown separately, reversing valve 92 may be integrated with heat exchanger 20, for example, by making a rotary heat exchanger 20 that slowly turns against an inlet manifold (partly connected to inlet and partly to exhaust on one end) to bring each of many paths sequentially into contact with the inlet and exhaust on one end, and always in connection with condensing separator 40 on the other end. An auxiliary defroster 94 may also be provided, if desired, to assist in cleaning. The position of auxiliary defroster 94 may vary from that shown.
Turning to further alternative embodiments of the invention, condensing separator 40 can include various elements of known separation means, including but not limited to, distillation columns, rectifiers, vapor-liquid contact surfaces, and other like means of enhancing the preferential condensation-based separation of a component fluid, like oxygen from an air-based mixture. Further, it is within the scope of the invention to conjoin the functions of heat exchanger 20 and condensing separator 40 such that an un-separated liquid exits heat exchanger 20 into condensing separator 40, which may cooperate with receiver 60, cryocooler 50 and such known elements, to provide a distillation column for the un-separated liquid. In addition, as known by those with skill in the art of cryocooler-liquefiers, the pre-cooling heat exchanger 20 may be positioned in parallel with and in thermal contact with the cryocooler cold element 52, thereby sharing thermal gradients with common structure and insulation and thereby achieving correspondingly higher efficiency.
Turning more specifically to the operation of system 8, air mover 10 provides a continuous fresh local atmospheric air stream 14. Local atmospheric air may include, for example, nitrogen (N2), oxygen (O2), and traces of argon (Ar), water vapor (H2O), carbon dioxide (CO2) and other minor elements. Local atmospheric air stream 14 is directed into second path 26 of heat exchanger 20, where it gives up heat to first path 22 (and possibly third path 28), which contains cold exhaust stream 24 (third path 28 would include cool gaseous oxygen 70 forming from oxygen-enriched liquid 10). As air stream 14 loses heat in second path 26, its temperature drops. Some of the air stream's components (particularly water (H2O) and carbon dioxide (CO2)) are condensed or frozen out of the stream early during the cooling process because their temperatures of phase-change are significantly higher than those of the main components, i.e., nitrogen (N2), oxygen (O2) and argon (Ar). Typical trace pollutants like carbon monoxide (CO), hydrocarbons (e.g., CH4), and other more complex compounds also are readily condensible. Normal condensation temperatures for the major constituents of air and their fraction in a standard atmosphere are: water (H2O) at 273K.: 0.1 to 2.8%; carbon dioxide (CO2) at 195K.: 0.035% (CO2 directly freezes and sublimes, no liquid phase at atmospheric pressure); oxygen (O2) at 90.2K.: 20.95%; argon (Ar) at 87.3K.: 0.93%; and nitrogen (N2) at 77.4K.: 78.1%. The remaining cooled gases (i.e., nitrogen (N2), oxygen (O2) and argon (Ar) and traces) form purified gas stream 46, which passes into condensing separator 40 (and receiver 60), where they are exposed to cooling element 52 maintained in the range of approximately 80-90 K. by cryocooler 50. The heat extracted from purified gas stream 46 by heat transfer to cooling element 52 preferentially condenses oxygen (O2) and argon (Ar) (and a fraction of nitrogen (N2) in solution), forming oxygen-enriched liquid 10. Uncondensed nitrogen (N2) (with traces of oxygen (O2), argon (Ar) and other minor constituents) exits condensing separator 40 and reenters first path 22 of heat exchanger 20 as cool exhaust stream 24, where it absorbs heat from air stream 14 in second path 26, then passes through selector valve 92 and exits as exhaust 30. The liquid, oxygen-enriched condensate 10 is partially accumulated in receiver 60 and partially directed through third path 28 of heat exchanger 20 (when provided), exiting, as needed, as purified gaseous oxygen 70 for consumption. Oxygen-enriched liquid 10 is stored until needed (as for mobile patient support), when it can be drawn off as a liquid for use in that form.
As the warmer condensates in heat exchanger 20 accumulate from continuing flow of incoming air, the pressure required to maintain flow will rise. This, or the reduction of flow at fixed pressure, or even passage of a preset interval of time, can be used by system controller 90 to switch reversing valve 92 to its alternate position, reversing connections of first path 22 and second path 26, respectively, between inlet air 14 and exhaust 30. That reversal enables the re-entrainment of warmer condensates, maintaining open paths and free air flow through heat exchanger 20, as described above.
The invention also includes a method for producing oxygen-enriched liquid 10 from local atmospheric air. The method includes forming an input stream 14 of local atmospheric air; using cold exhaust 24 from a closed-cycle cryogenic cooler 50 to remove readily-condensible contaminants from input stream 14 to form a purified gas stream 46; and cryogenically cooling purified gas stream 46 with a closed-cycle refrigerator to condense oxygen to form oxygen-enriched liquid 10. A purified gaseous oxygen 70 may be formed from oxygen-enriched liquid 10 by using heat from input stream 14 to warm a portion of oxygen-enriched liquid 10, e.g., via third path 28.
System 8 provides a number of advantages compared to the prior art. For example, system 8 can be implemented on a much smaller scale. For example, depending on size, an output of system 8 may be less than approximately 10 liquid liters per day. System 8 preferably operates using approximately 110 V electricity, i.e., US household electricity, or 220 V, i.e., European and Japanese household electricity, and is portable by an individual person. System 8 also removes the need for pre-separation of readily-condensible contaminants, including water vapor (H2O) and carbon dioxide (CO2), before cooling by using heat exchanger 20 as a purifier. That is, pre-separation by non-cooling means is not required. Also, no concentrator or other source of previously-separated gas feed stream is required. In addition, oxygen-enriched liquid 10 capacity of receiver 60 can be sized to assure continuous oxygen support through a power outage of any duration. System 8 is particularly useful for cost-effective on-site treatment of emphysema and other disorders requiring continual administration of oxygen, and especially for mobile patients who can receive the gaseous product directly when resting, and use oxygen-enriched liquid 10 as a portable source of gaseous oxygen when mobile. As a result, system 8 provides lower cost oxygen-enriched liquid therapy that can benefit a large number of users that now must use less satisfactory, but cheaper treatments. In particular, insurance-dependent users (notably Medicare subscribers in the US) can receive the preferred treatment while reducing health care cost to insurers. System 8 makes no attempt to separate the argon (Ar) from the oxygen (O2) because the argon is too little to resell and does no harm as a small impurity in the oxygen for most applications.
While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims. For example, system 8 may be used to purify other species from other mixtures than air such as isolating butane from a mixture of hydrocarbons in natural gas. In this case, a similar sequential condensation with reversing flow-re-entrainment for warmer condensates, and an isolated collection chamber and outlet stream for the desired pure condensate would be used.
This application claims the benefit of U.S. Provisional Application No. 60/579,276, filed Jun. 14, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60579276 | Jun 2004 | US |
