WO2020010392A1

WO2020010392A1 - Methods, apparatus and systems for concentrating a gas

Info

Publication number: WO2020010392A1
Application number: PCT/AU2019/050719
Authority: WO
Inventors: David Joseph PEAKE; Roger Paul RASSOOL
Original assignee: Freo2 Pty Ltd
Priority date: 2018-07-09
Filing date: 2019-07-09
Publication date: 2020-01-16
Also published as: AU2019300935A1

Abstract

The present invention relates to methods, apparatus and systems for producing a gas derived from the atmosphere which is enriched in oxygen or nitrogen for use in medicine, aquaculture, and various industrial applications. The invention may be embodied in a method for purifying a target gas from a mixture having a first and second gas and a second gas, providing a first vessel having a material selective for the first gas over the second gas, providing a second vessel having a material selective for the first gas, contacting the gas mixture to the gas retaining material of the first vessel under conditions allowing for the first gas to be retained by the gas retaining material of the first vessel, allowing the second gas to separate from the first gas retained on the gas retaining material of the first vessel, and allowing the first gas to release from the gas retaining material of the first vessel under conditions that prevent or inhibit mixing of released first gas with the released second gas. In another form the invention may be embodied in an apparatus providing a combined vacuum source and pressure source, the apparatus comprising first and second chambers, a first piston sliding within the first chamber and a second piston sliding within the second chamber, the first and second pistons being coupled such that the first and second pistons move in concert.

Description

METHODS. APPARATUS AND SYSTEMS FOR CONCENTRATING A GAS

FIELD OF THE INVENTION

The present invention relates to the field of gas concentration. In particular, but not exclusively, the invention relates to methods, apparatus and systems for producing a gas derived from the atmosphere which is enriched in oxygen or nitrogen. The produced gas may be used in medicine, aquaculture, and various industrial applications.

BACKGROUND TO THE INVENTION

A gas stream that is enriched in oxygen is useful in many regards. A gas stream that is enriched in oxygen may be used in a medical setting to provide a patient having a respiratory condition with oxygen at a higher partial pressure than that found in the atmosphere. Administration of medical oxygen is often a life-saving treatment, which has been a standard of care in well- resourced settings for more than fifty years. In particular, the continuous delivery of oxygen to neonates, infants, children and adults in need is important in the treatment of conditions such as acute respiratory infection (principally pneumonia), the leading cause of death in young children worldwide. The effective management of pneumonia is integral to reducing mortality in younger children. Oxygen therapy is used to treat hypoxaemia, which is a life-threatening feature of severe pneumonia resulting from impaired pulmonary function.

Other applications for oxygen enriched gas streams include aquaculture. It is often necessary to oxygenate water to facilitate the growth of an economically important organism such as a fish, a crustacean, a mollusc, a plant or an algae. In many circumstances the organism is grown in a contained or semi- contained body of water, with nutrients provided and water condition carefully controlled to maximise growth. Aquaculture typically operates under high stocking densities, intensive feeding rates, and high levels of waste production and as a result requires higher levels of oxygen as compared with natural waters. With many organisms all requiring oxygen stocked in a relatively small area, available oxygen in the water must be sufficient to sustain the population. In fish farming, for example, suboptimal dissolved oxygen levels dramatically increases the risk of large or total fish losses once the oxygen levels decrease below a threshold. In many instances, simple agitation of the water is inadequate to properly oxygenate aquaculture water, and direct injection using an oxygen enriched gas is required.

Sufficient oxygen levels are required for efficient aerobic digestion processes to take place. For example, aerobic digestion is commonly used in sewage treatment to reduce the volume of sludge product. Aerobic digestion is also used to treat and reduce other organic wastes such as food, paper and plant material. In these uses, it is typical for air, and preferably oxygen enriched air, to be injected about the digestion reactants.

Typically, atmospheric air is used as a starting material to produce an oxygen enriched gas stream. Prior art systems exploit a separation method of some description to preferentially remove the majority of nitrogen gas, thereby leaving a gas stream that is enriched in oxygen.

It is known in the art to use various media to“scrub” nitrogen from the air, and in particular zeolite is well used for that purpose. Zeolite is known to act as a“molecular sieve” selectively adsorbing nitrogen in preference to oxygen. Air is contacted to the zeolite, and once the majority of nitrogen has bound the unbound gases (principally oxygen) are removed to provide an oxygen rich gas stream.

Means for concentrating oxygen typically rely on pressure swing adsorption (PSA). In terms of hardware, a PSA oxygen concentrator comprises an air compressor, first and second cylinders each filled with zeolite pellets, and a pressure equalizing reservoir. The first cylinder receives a stream of air from the compressor for around 3 seconds. During that time the pressure in the first cylinder rises from atmospheric to about twice normal atmospheric pressure and the binding regions on the zeolite becomes saturated with nitrogen. Oxygen gas remains largely free about the zeolite, and is the predominant gas species free in the first cylinder, amongst relatively small amounts of argon, carbon dioxide, and other minor atmospheric components. An exit valve opens, allowing the oxygen-enriched gas to a pressure equalizing reservoir, which connects to an output line. The same process is replicated in the second cylinder, although slightly delayed in time such that the first and second cylinders alternately output an oxygen-enriched gas. Using two adsorbent cylinders allows near-continuous production of the target gas. An alternative to PSA is a vacuum swing adsorption (VS A) system. VS A differs primarily from PSA in that PSA vents to atmospheric pressures (and uses a pressurized gas feed into the separation process) while VS A typically draws the gas through the separation process with a vacuum. The vacuum is typically generated by a blower.

PSA and VSA systems are typically configured to output oxygen enriched gas at pressure such that the gas is forced out of the system and toward its intended destination. For example, a system may have an output line carrying pressurized oxygen enriched gas toward a storage reservoir, an aquaculture aeration device or a patient-worn oxygen mask.

It is a problem in the art that VP A and VSA systems rely on powered machinery such as blowers, air compressors and the like. The need for powered machinery adds to the expense of construction of a system, introduces maintenance requirements and potential points of failure, and also establishes the need for electrical power.

While electrical power adds expense to the operation of a system, there is the further problem that in many locations a dependable power supply is simply not available. For example, Africa has one of the lowest electrification rates of the developing world, and grid power throughout much of that continent is intermittent and unreliable. Power outages occur at alarming rates ranging from 25 days per year in Senegal, 63 days per year in Tanzania and more than 140 days per year in Burundi. Similar situations exist elsewhere in the developing world where the supply of electricity is inherently unreliable.

The usefulness of battery backup systems to power such concentrators in the event of outages is limited, particularly given significant power requirements of the concentrators, potentially exceeding inverter capacity typically aimed at running other utilities/appliances, such as computers, lights, fans and televisions. Furthermore, capital costs for such systems are significant (typically over US$1,000), and batteries have limited lifespans and require expensive replacement. Thus, many medical facilities in the developing world struggle to provide medical grade oxygen to patients in dire need of oxygen therapy.

Aquaculture may be carried out in remote locations, and even in regions having a dependable power supply it is often the case that the cost to extend grid power to the aquaculture site can be technically difficult or economically prohibitive. In any event, minimising the amount of electrical power needed to drive a VS A or a VP A system is desirable given the general aim of reducing greenhouse gas emissions into the environment.

Similar problems arise in the need to remove or enrich gas species from the air other than oxygen or nitrogen. For example, it may be necessary to remove or enrich lower abundance species such carbon dioxide or argon. Such problems are further applicable to gas mixtures other than air, such as industrial process gas mixtures and exhaust gas mixtures.

It is an aspect of the present invention to overcome or ameliorate a problem of the prior art by providing a method, a system, or an apparatus that is capable (either on its own or in combination with another method, system or apparatus) of purifying a gas from a gas mixture. In an alternative aspect, the present invention provides an alternative to prior art means for purifying a gas from a gas mixture.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

SUMMARY OF THE INVENTION

In a first aspect, but not necessarily the broadest aspect, the present invention provides a method for at least partially purifying a target gas from a gas mixture, the method comprising the steps of: providing a gas mixture comprising a first gas species and a second gas species, providing a first vessel having a gas retaining material selective for the first gas species over the second gas species, providing a second vessel having a gas retaining material selective for the first gas species, contacting the gas mixture to the gas retaining material of the first vessel under conditions allowing for the first gas species to be retained by the gas retaining material of the first vessel, causing or allowing the second gas species to separate from the first gas species retained on the gas retaining material of the first vessel, and causing or allowing the first gas species to release from the gas retaining material of the first vessel under conditions that prevent or inhibit mixing of released first gas species with the released second gas species.

In one embodiment of the first aspect, the method does not require supply of the gas mixture at a pressure that is higher than about atmospheric pressure.

In one embodiment of the first aspect, the method is devoid of an apparatus for supplying the gas mixture at a pressure at about atmospheric pressure, or at a pressure above about atmospheric pressure.

In one embodiment of the first aspect, the apparatus for supplying the gas mixture at a pressure at about atmospheric pressure, or at a pressure above about atmospheric pressure is a gas blower or a gas compressor.

In one embodiment of the first aspect, the method is operable without the requirement for the gas mixture, or the first gas species, or the second gas species to have a pressure that is higher than about atmospheric pressure.

In one embodiment of the first aspect, the step of causing or allowing the first gas species to release from the gas retaining material of the first vessel is effected or assisted by the application of a vacuum to the interior of the first and/or second vessel.

In one embodiment of the first aspect, the vacuum is provided by one or more vacuum sources(s).

In one embodiment of the first aspect, the one or more vacuum sources is/are alternately applied to the first and second vessels.

In one embodiment of the first aspect, the one or more vacuum sources is/are alternately applied to the first and second vessels in a cyclical manner, and for a plurality of cycles. In one embodiment of the first aspect, the one or more vacuum sources is/are alternately applied to the first and second vessels so as to provide substantially continual stream(s) of the first and/or second gas species.

In one embodiment of the first aspect, the vacuum is provided by a single vacuum source and the vacuum source is alternately applied to the first and second vessels.

In one embodiment of the first aspect, the vacuum source is a combined vacuum source and pressure source.

In one embodiment of the first aspect, the combined vacuum source and pressure source is configured so as to alternately provide a source of vacuum and a source of pressure.

In one embodiment of the first aspect, the combined vacuum source and pressure source is configured so as to alternately provide a source of vacuum and a source of pressure in a cyclical manner, and for a plurality of cycles.

In one embodiment of the first aspect, the combined vacuum source and pressure source is configured to operate reciprocally such that generation of a vacuum contemporaneously generates a pressure.

In one embodiment of the first aspect, the combined vacuum source and pressure source is an apparatus having a piston sliding within a piston chamber and wherein the reciprocal operation is provided by a piston sliding within the piston chamber.

In one embodiment of the first aspect, the apparatus comprises first and second chambers, a first piston sliding within the first chamber and a second piston sliding within the second chamber, the first and second pistons being coupled such that the first and second pistons move in concert.

In one embodiment of the first aspect, the first and second pistons are coupled by way of a rod.

In one embodiment of the first aspect, the first and second chambers are separated by a gas- tight divider, and the rod traverses the divider via an aperture contained therein. In one embodiment of the first aspect, the apparatus comprises sealing means configured to allow the rod to slide bi-directionally through the aperture while preventing or inhibiting the passage of a gas between the first and second chambers.

In one embodiment of the first aspect, the first chamber of the apparatus has first and second gas ports, and the second chamber of the apparatus has third and fourth gas ports, each of the gas ports configured to allow the passage of a gas between its respective chamber and the exterior of the apparatus.

In one embodiment of the first aspect, the apparatus is configured such that with regard to the first chamber the first piston is slidable between the first and second gas ports, and with regard to the second chamber the second piston is slidable between the third and fourth gas ports.

In one embodiment of the first aspect, where the first and second pistons are coupled by way of a rod, the rod has a length such that with regard to the first chamber the first piston is limited in its travel through the first chamber so as to not be slidable beyond the first and/or second gas port, and with regard to the second chamber the second piston is limited in its travel through the second chamber so as to not be slidable beyond the third and/or fourth gas ports.

In one embodiment of the first aspect, the apparatus is configured such that: the first piston divides the first chamber into first and second sub-chambers, the first sub-chamber being in gaseous communication with the first gas port and the second sub-chamber being in gaseous communication with the second gas port, and the second piston divides the second chamber into third and fourth sub-chambers, the third sub-chamber being in gaseous communication with the third gas port and the fourth sub-chamber being in gaseous communication with the fourth gas port.

In one embodiment of the first aspect, the apparatus is in gaseous communication with the first and second vessels such that when a vacuum is applied alternately to the second and third chambers, the first and second pistons are caused to move resulting in the first and fourth sub- chambers alternately admitting and pressurizing a gas species released from the gas retaining material. In one embodiment of the first aspect, the target gas species is diatomic oxygen.

In a second aspect, the present invention provides an apparatus for providing a combined vacuum source and pressure source, the apparatus comprising first and second chambers, a first piston sliding within the first chamber and a second piston sliding within the second chamber, the first and second pistons being coupled such that the first and second pistons move in concert.

In one embodiment of the second aspect, the first and second pistons are coupled by way of a rod.

In one embodiment of the second aspect, the first and second chambers are separated by a gas- tight divider, and the rod traverses the divider via an aperture contained therein.

In one embodiment of the second aspect, the apparatus comprises sealing means configured to allow the rod to slide bi-directionally through the aperture while preventing or inhibiting the passage of a gas between the first and second chambers.

In one embodiment of the second aspect, the first chamber of the apparatus has first and second gas ports, and the second chamber of the apparatus has third and fourth gas ports, each of the gas ports configured to allow the passage of a gas between its respective chamber and the exterior of the apparatus.

In one embodiment of the second aspect, the apparatus is configured such that with regard to the first chamber the first piston is slidable between the first and second gas ports, and with regard to the second chamber the second piston is slidable between the third and fourth gas ports.

In one embodiment of the second aspect, where the first and second pistons are coupled by way of a rod, the rod has a length such that with regard to the first chamber the first piston is limited in its travel through the first chamber so as to not be slidable beyond the first and/or second gas port, and with regard to the second chamber the second piston is limited in its travel through the second chamber so as to not be slidable beyond the third and/or fourth gas ports. In one embodiment of the second aspect, the apparatus is configured such that: the first piston divides the first chamber into first and second sub-chambers, the first sub-chamber being in gaseous communication with the first gas port and the second sub-chamber being in gaseous communication with the second gas port, and the second piston divides the second chamber into third and fourth sub-chambers, the third sub-chamber being in gaseous communication with the third gas port and the fourth sub-chamber being in gaseous communication with the fourth gas port.

In a third aspect, the present invention provides a system for concentrating a gas in a gas mixture, the system comprising the apparatus of an embodiment of the second aspect (and particularly an embodiment where a first piston divides a first chamber into first and second sub-chambers, the first sub-chamber being in gaseous communication with the first gas port and the second sub-chamber being in gaseous communication with the second gas port, and a second piston divides the second chamber into third and fourth sub-chambers, the third sub- chamber being in gaseous communication with the third gas port and the fourth sub-chamber being in gaseous communication with the fourth gas port), and a first vessel having a gas retaining material selective for a first gas species and a second vessel having a gas retaining material selective for the first gas species, wherein the first vessel is in gaseous communication with the first sub-chamber, and the second vessel is in gaseous communication with the fourth sub-chamber

In one embodiment of the third aspect, the system comprises a vacuum source in gaseous communication with the second sub-chamber and the third sub-chamber, the system configured such that vacuum can be applied alternately to the first and second sub-chambers in a cyclical manner.

In one embodiment of the third aspect, the system is configured such that when the vacuum source is applied alternately to the second and third chambers, the first and second pistons are caused to move resulting in the first and fourth sub-chambers alternately admitting and pressurizing a target gas species released from the gas retaining material. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows highly diagrammatically the method steps and apparatus for a preferred system of the present invention. For clarity of the drawings, the components are numbered for Step 1 only. The components for Steps 2 to 8 are identical to those shown for Step 1.

FIG. 2 is a cross-sectional diagram of a preferred pump of the invention. The diagram is not drawn to any scale, and the scale of each of the components is not necessarily consistent with the scale of other components.

DETAILED ESCRIPTION OF THE INVENTION INCLUDING PREFERRED

EMBODIMENTS

After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects apply to specific exemplary embodiments, and not necessarily to all embodiments covered by the claims.

Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

Reference throughout this specification to“one embodiment” or“an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. It will be appreciated that not all embodiments of the invention described herein have all of the advantages disclosed herein. Some embodiments may have a single advantage, while others may have no advantage at all and are merely a useful alternative to the prior art.

The present invention is predicated at least in part on the discovery that an oxygen enriched gas stream can be produced from atmospheric air with there being no need for a blower, compressor or similar contrivance needed to drive the process. Instead, the present invention is operable with a vacuum, and particularly a vacuum that may be obtained without the need for a vacuum pump. The vacuum may be provided by way of a simple siphon mechanism operable on a head of water which may be naturally provided in the environment. By this arrangement, electrical power is not required (i) to power a blower or a compressor, or (ii) provide a vacuum. The present invention is therefore able to provide a simple and cost- effective means for providing an oxygen enriched gas stream that consumes little or no electrical power. Moreover, the present invention is able to provide the oxygen enriched gas stream at a pressure greater than atmospheric pressure.

Reference is made herein to a“first gas species” and a“second gas species”. Reference is also made a“target gas species” and a“non-target gas species”. Such terms are used to define generically different gas species which may be separated. For example, in the context of an oxygen concentrator used to supply oxygen enriched gas for medical use the target gas may be considered to be oxygen. Alternatively, in the same context the target gas may be considered to be nitrogen as that gas species is targeted for removal by the zeolite. The nitrogen may be considered the first gas species, with oxygen the second gas species, or vice-versa.

Reference is made to FIG. 1 which shows a highly preferred system of the present invention executing highly preferred method steps of the present invention. In the embodiment of FIG. 1, the system and methods are configured to input air and to output a gas stream that is concentrated in respect of oxygen. Turning firstly to the system components there is shown a first vessel (10) and a second vessel (15). The vessels (10) and (15) are essentially identical, being fabricated of metal (other similarly rigid materials being contemplated) and being of substantially gas-tight construction. Each vessel (10) and (15) contains zeolite pellets which present a very large microporous surface area inside the vessels (10) and (15), the zeolite acting to adsorb nitrogen from air and output an enriched oxygen stream (0₂ concentration about 90% vol/vol). The zeolite may be regenerated by decreasing the pressure to release the adsorbed nitrogen. The use of two vessels allow for one vessel to be outputting oxygen (being the target gas species in this exemplary application), while the other vessel is exhausting nitrogen (being a non-target gas species). The roles of the vessels are swapped in a cyclical manner such that a substantially continuous stream of a gas mixture being enriched in oxygen is supplied.

The enriched gas stream may be conveyed to a human patient in need of oxygen supplementation, or to a diffuser so as to oxygenate a body of water. Having the benefit of the present specification, other uses will be apparent to the skilled person all of which fall within the ambit of the present invention. For example, the present invention may be applied to the removal of carbon dioxide in a chemical synthesis step. Another application is in the separation of carbon dioxide from biogas to increase the methane ratio. Hypoxic air fire prevention systems may be used to produce air with a low oxygen content (i.e. enriched in nitrogen).

Moreover, the use of adsorbents other than zeolite are contemplated depending on the application at hand. For example, an adsorbent such as activated carbon, silica gel, alumina, or a resin may be used. In addition to their binding selectivity for different gases, zeolites and carbon molecular sieves may rely at least in part on a size exclusion mechanism to exclude some gas molecules from the structure based on the size of the molecules, thereby restricting the ability of the larger molecules to be adsorbed.

In any event, the vessels (10) and (15) are each have upper connection lines (20) and (25) respectively, and lower connection lines (30) and (35) respectively. The lower connection lines (30) and (35) connect to a valve (40 (which in this embodiment is a 5/3 valve) configured to connect the vessels (10) and (15) alternately to a vacuum source (not shown) or to the atmosphere. Thus, when the vessel (10) is connected to the atmosphere, vessel (15) is connected to a vacuum source, and when the vessel (15) is connected to the atmosphere, vessel (10) is connected to a vacuum source. This switching of the vacuum source from one vessel to the other is accomplished by electrical or electronic means given that the 5/3 valve (40) is solenoid operated. In other embodiments, switching of the vacuum may be effected pneumatically, for example by way of an air-piloted valve.

The connection lines (30) and (35) allow for the free passage of gas in a bi-direction manner based solely on the pressure differential along the line. The upper connection lines (20) and (25) have potential for connection by way of shunting valve (45) (which in this embodiment is a 2/2 valve) allowing for gaseous communication (or no gaseous communication) between the two vessels (10) and (15), as required in purging and depressurization steps as further described infra. The shunting valve (45) is a solenoid valve in this embodiment and therefore electrically or electronically controllable. In other embodiments, switching of the vacuum may be effected pneumatically, for example by way of an air-piloted valve.

The system comprises a gas pump (50) which is shown in greater detail in the drawing of FIG. 2. In the context of the preferred system described herein the pump (50) functions to extract target gas species which is free (i.e. not adsorbed by the zeolite) from the vessels (10) and (15), and output the target gas at super-atmospheric pressure to an end user (such as a patient). The gas pump (50) functions also to convey air into the vessels (10) and (15) because extracting oxygen through lines (20) and (25) reduces the pressure in vessels (10) and (15) respectively, thereby creating a pressure differential across valve (40), which causes air to flow from the atmosphere to vessel (10) or vessel (15).

The non-target gas (nitrogen in this example) is removed by the vacuum applied through valve (40).

Structure and operation of the pump (50) will be more fully appreciated by reference to the diagrammatic representation of FIG. 2. In this preferred embodiment, the pump (50) is comprised of a first cylindrical chamber (55) and a second cylindrical chamber (60). The chambers (55) and (60) may be formed by disposing a gas-tight divider (65) within a single cavity. The chambers (55) and (60) have the same diameter in this embodiment (the diameter being fixed along the chamber length), and are also mutually coaxial. In some embodiments, advantage is gained where the chambers (55) and (60) are of different diameter, or of different volume. For example, by applying the vacuum to a wider diameter chamber the gas pressure attained will be higher for a given vacuum.

The divider (65) is fixed in position, so as to provide a first chamber (55) of the same volume as the second chamber. In some embodiments it may be preferred to provide chambers of unequal volume. The pump (50) comprises first and second pistons (70) and (75), disposed within the first and second chambers (55) and (60) respectively. Each piston (70) and (75) is constructed so as to sealingly and slidingly engage with the wall of its respective chamber (55) and (60). As for a piston in an internal combustion engine, the outer diameter of the pistons (70) and (75) are dimensioned so as to snugly fit within the chamber (55) or (60). Piston rings (not shown) are provided about the external circumference of the pistons (55) and (60), the rings being fabricated from a deformable polymer which compresses against the inner chamber wall, thereby providing the required sealing engagement. As an alternative to piston rings, knife- seal pistons may be used. A lubricant may be required so as to facilitate the required sliding engagement between the pistons (70) and (75) and the inner walls of the chambers (55) and (60).

The piston rod (80) must pass through the divider (65), an aperture (85) being provided in the divider (65) for that purpose. The aperture comprises one or more annular seals to inhibit or prevent leakage of gas between the chamber (55) and (60).

The pistons (70) and (75) are movable laterally (as drawn) and bi-directionally. As will be appreciated from the drawing, the pistons (70) and (75) must move in concert, i.e. in the same direction and for the same distanceAs will be more fully explained infra, gases are able to flow into and out of the first (55) and second (60) chambers and so a chamber that decreases in volume acts to increase the pressure of any gas within, thereby causing expulsion of the gas from the chamber so long as an outlet port is provided. Conversely, a chamber that increases in volume acts to decrease the pressure of any gas within, thereby causing admission of a gas from outside the chamber so long as an inlet port is provided.

It will be appreciated that the piston (70) divides its respective chamber (55) into first and second sub-chambers (90) and (95), and that the piston (75) divides its respective chamber (60) into third and fourth sub-chambers (100) and (105). The pistons (70) and (75) are maintained in mutual fixed spatial relation by a rigid connecting rod which is coaxial with the pistons (70) and (75), and also the cylindrical chambers (55) and (60). Thus, movement of the pistons (70) and (75) acts to continuously alter the volumes of each of the first (90), second (95), third (100), and fourth (105) sub-chambers resulting in complex contemporaneous movements of gas through the present system. Moving the pistons (70) and (75) to the right increases the volumes of the first (90) and third (100) sub-chambers, while at the same time decreasing the volumes of the second (95) and fourth (105) sub-chambers. Conversely, moving the pistons (70) and (75) to the left decreases the volumes of the first (90) and third (100) sub-chambers, while at the same time increasing the volumes of the second (95) and fourth (105) sub-chambers

Each of the first (90) and fourth (105) sub-chambers of the pump (50) has a gas inlet port (110) and (115) respectively and a gas outlet port (120) and (125) respectively. The inlet ports (110) and (115) are in gaseous communication with the upper connection lines (20) and (25) respectively. Upper connection lines (20) and (25) are in turn in gaseous communication with the vessels (10) and (15) respectively. Flow of a gas from the first (90) or fourth (105) sub- chambers into the vessels (10) or (15) respectively is prevented by check valves (130) (135) respectively. The only route by which a gas may exit the first (90) or fourth (105) sub-chambers is by way of gas outlet ports (120) and (125) respectively. Backflow of gas into the first (90) or fourth (105) chamber is prevented by check valves (140), (145) respectively. The function of sub-chambers (90) and (105) is to pump target gas species from the vessels (10) and (15) respectively, with the arrangement of check valves (130), (135), (140) and (145) ensuring only a one-way conveyance of gas.

Turning now to the second (95) and third (100) sub-chambers, these spaces are involved in generating the motive force required to move the pistons (70) and (75) left and right. The motive force is obtained from a vacuum applied alternately to the second (95) and third (100) sub-chamber in a cyclical manner. Where a vacuum is applied, it is by way of port (150) (for sub-chamber 95) or port (155) (for sub-chamber (105)). The ports (150) and (155) are in gaseous communication with a valve (160) (in this embodiment being a 3/2 valve) arranged so as to switch the vacuum provided by a vacuum source (not shown) in gaseous communication with the valve between the second (95) and third (100) sub-chambers.

As an alternative to the above the line (30) may be connected to port (155), with the line (35) connected to port (150). This allows valve (40) to also assume the role of valve (160). Because it takes approximately 4 seconds for vessels (10) and (15) to return to atmospheric pressure they effectively stop the pump (50) from extracting.

Application of vacuum to the second sub-chamber (95) decreases the pressure therein and causes movement of the pistons (70) and (75) to the right (as drawn). As the pistons (70) and (75) move, the valve (160) admits atmospheric air into the third sub-chamber (100) as its volume expands. The air admitted into the third sub-chamber (100) is never used as a starting gas mixture in a process for purifying a target gas, and is admitted into the system only to prevent seizure of the pistons (70) and (75) as would be caused by formation of a vacuum in the third sub-chamber (100).

Once the pistons (70) and (75) have moved a sufficient distance to the right, movement to the left (as drawn) is commenced by application of a vacuum to the third sub-chamber (100). As the pistons (70) and (75) move, the valve (160) admits atmospheric air into the second sub- chamber (95) as its volume expands. The air admitted into the second sub-chamber (100) is never used as a starting gas mixture in a process for purifying a target gas, and is admitted into the system only to prevent seizure of the pistons (70) and (75) as would be caused by formation of a vacuum in the second sub-chamber (95).

Each movement of the pistons to the right or to the left may take several seconds.

In light of the above, it will be apparent that the second (95) and third (100) sub-chambers are involved in driving the pistons (70) and (75) left and right alternately in a cyclic manner so as to drive the pump (50). Conversely, the first (90) and fourth (105) sub-chambers are involved in conveying a process starting gas mixture (such as atmospheric air) into a vessel (10) or (15), and conveying a gas mixture enriched in a target gas (such as oxygen) from the vessel (10) or (15) to an end user of the target gas. As the volume of the first (90) or fourth (105) sub-chamber reduces, the target gas contained therein is compressed to an extent and is therefore pressurized. Usefully, this pressurization propels the target gas toward the end user via a connection line of some description.

It will be appreciated that the present invention is not limited to any arrangement where the second (95) and third (100) sub-chambers are configured as the driving sub-chambers. For example, the pump (50) may be configured such that the third (100) and fourth (105) sub- chambers function to drive the pump, with the first (90) and second (95) sub-chambers act to extract and compress a gas species which remains unbound to the gas retaining material. In this alternative configuration, the cross-sectional areas of the driving sub-chambers (100) and (105) could be made different those of the extractor/compressor sub-chambers (90) and (95). Use of different cross-sectional areas allows for modulation (such as amplification or de- amplification) of the maximum pressurization of the gas species which remains unbound to the gas retaining material with respect to the vacuum applied to the pump (50).

Description of the operation of the entire system (i.e. the pump (50), in combination with zeolite-containing vessels (10) and (15)) is now provided.

Reference is made to FIG. 1. It should be noted that the pistons (70) and (75) are shown in the same fixed position in FIG. 1. In reality, the pistons (70) and (75) move left and right, and the drawn position is for illustrative purposes only and will not necessarily be accurate. However, each piston’s direction of movement are shown at Steps 2 and 6.

The description refers to purification of oxygen from atmospheric air, however it will be understood that the invention is not limited to that application.

Step 1: Repressurisation / Evacuation

At this step, air has been previously contacted with the zeolite to allow binding of nitrogen (the non-target gas species) thereto). Oxygen (the target gas species) not adsorbed to the zeolite has been previously conveyed from the vessel to the end user, leaving the nitrogen bound to the zeolite of the second vessel (15).

At Step 1 as drawn, a vacuum source (not shown) is applied to the second vessel (15) via the lower connection line (35) and valve (40). The downwardly directed dashed arrow line indicates the direction of gas flow effected by the application of vacuum. The vacuum thus acts to desorb nitrogen from the zeolite and to evacuate the desorbed nitrogen from the second vessel (15). In this exemplary application the nitrogen is considered a waste product and is discharged to the atmosphere.

Contemporaneous with application of the vacuum, the valve (40) allows for admission of atmospheric air into the first vessel (10) via the lower connection line (30), the direction of air flow being shown by the upwardly directed solid arrow line. At this time the shunt valve (45) is closed. As an example, where it is desired to establish a vacuum of -65 kPa in vessel (15) a vacuum source capable of establishing a vacuum of about -80 kPa is applied to vessel (15) and a threshold trigger of -65 kPa is set. The air admitted into the first vessel (10) is a starting gas mixture from which oxygen is purified. Step 2: Extraction / Evacuation

The vacuum source is maintained in connection with the second vessel (15) and therefore nitrogen is continued to be desorbed and evacuated from the second vessel (15). The top of the first vessel (10) is connected to the first sub-chamber (90) of pump (50) via upper connection line (20), check valve (130) and port (110). Contemporaneously, the vacuum source is connected to second sub-chamber 95 thereby driving the pistons (70) and (75) to the right (as drawn). This movement of the pistons (70) and (75) increases the volume of the first sub-chamber (90) thereby forming a vacuum therein. The so-formed vacuum draws oxygen (which is unbound to zeolite, and therefore free to move) from the first vessel (10) and into the first sub-chamber (90). The pistons (70) and (75) movement to the right also causes the fourth sub-chamber (105) to pressurise, forcing oxygen stored therein and provided by the previous cycle towards the end user via port (125) and check valve (145).

Step 3: Purge

The vacuum source is disconnected from the second sub-chamber (95) by the action of valve (160). Practically, there may be no requirement to disconnect the vacuum source where the pistons (70) and (75) have travelled as far as possible and therefore cannot move any further in the direction of travel even if a driving vacuum continues to be applied. In any event the vacuum applied to the second vessel (15) is maintained at this time. Vessels (10) and (15) are connected by action of the shunting valve (45) causing flow of all gases in the vessels (10) and (15) through the zeolite beds and towards the vacuum source.

Step 4: Pressure Equalisation

By action of the valve (40), the vacuum source is disconnected from the bottom of the second vessel (15), and also the bottom of the first vessel (10) is isolated from the atmosphere. The shunting valve (45) remains open to allow the pressure in the first (10) and second (15) vessels to equalize. At the start of pressure equalisation one vessel may at about -12 kPa and the other may be at about -45 kPa. During equalisation the vacuums in vessels (10) and (15) alter upwardly or downwardly over a period of time, approaching each other until equalisation is stopped when the higher of the two decreases to about -28 kPa. Step 5: Evacuation / Repressurisation

By action of the valve (40), the vacuum source is connected to the bottom of the first vessel (10) by way of lower connection line (30), the pressure in the first vessel (10) is lowered to cause the preferential removal of nitrogen from the zeolite in the first vessel (10). Contemporaneously, the second vessel is connected to the atmosphere by the action of valve (45) and via the lower connection line (35), in preparation for removal of free oxygen via the top of the second vessel (15) in the next step. Step 6: Extraction / Evacuation

The vacuum source is maintained in connection to the first vessel (10), continuing the removal of nitrogen therefrom. The top of the second vessel (15) is connected to the fourth sub-chamber (105) of the pump (50), and contemporaneously the vacuum source is connected to the third sub-chamber (100) of the pump (50), forcing the pistons (70) and (75) to move to the left. This movement increases the volume of the fourth sub-chamber (105) causing a vacuum to form therein and in turn draw free oxygen from the second vessel (15) into the fourth sub-chamber. The piston movement also causes the first sub-chamber (90) to pressurise, forcing the stored oxygen (produced in the previous cycle) to be expelled towards the end user. Step 7: Purge

The vacuum source is disconnected from the pump (50) by the action of valve (160) thereby ceasing any gas flow into or out of the pump (50). The shunting valve (45) is opened top thereby connecting the top of the first (10) and (15) second vessels. By action of the valve (45) the bottom of the first vessel (10) is connected to the atmosphere via lower connection line (30), and the bottom of the second vessel (15) is connected via lower connection line (35) to the vacuum source. The shunting valve (45) is opened so as to allow both first (10) and (15) second vessels to be purged.

Step 8: Pressure Equalisation

By action of the valve (40), the vacuum source is disconnected from the bottom of the second vessel (15), and also the bottom of the first vessel (10) is isolated from the atmosphere. The shunting valve (45) remains open to allow the pressure in the first (10) and second (15) vessels to equalize. It should be noted that the pistons (70) and (75) are not in continuous movement. The pistons (70) and (75) remain stationary during the purge and pressure equalization steps, moving only during the evacuation/extraction steps.

Steps 1 through 8 as defined supra are repeated cyclically a plurality of times so as to provide a substantially continuous stream of oxygen enriched gas.

It is instructive to note at this point that the entire system is driven by way of a vacuum only that is alternately applied to second (95) and third (100) sub-chambers. This is distinct from prior art systems whereby a blower or compressor is required to force the starting material (i.e. the gas mixture; typically atmospheric air) into each of the vessels alternately so as to provide sufficient force to push the target gas under pressure to the user. For example, a prior art vacuum pressure swing adsorption system uses either two separate drives: one generating a vacuum (to separate target gas species from non-target gas species) and another generating pressure (to force the purified target gas out of the system and toward the end user). The pump (50) of the present system provides a reciprocating pressure arrangement to extract the target gas from the vessels (10) and (15). By this arrangement, there is no requirement for a feed blower which in turn eliminates the need for one drive in the system. Advantage is gained in that the cost of producing and maintaining a target gas purification system is decreased. The reliability of the system is also improved given that there is no blower to malfunction or fail.

As will be noted, a vacuum source is connected to valve (45) and valve (160). The vacuum may be provided by a single source that (via a simple splitter) is applied to both valves (45) and 160. Alternatively, two discrete vacuum sources may be provided.

In some applications, the present invention is implemented in remote locations where a vacuum source (such as a vacuum pump) is not available, or a power source is not available, or where economic factors demand or prefer that a powered vacuum source is not used. In such cases, a source of flowing water (such as a natural stream or a man-made arrangement of flowing water) may be used to provide the vacuum needed for operation of the present system.

In one exemplary arrangement water is diverted from a stream in such a way to provide at least 1.5 metres of available height difference (‘head’) between inflow and outflow. This head may be obtained by running a pipe along an inclined stream. A section of the pipe is raised approximately 7 metres vertically and then directed back into the stream. Towards the top of the pipe (which functions as a siphon), air is entrained into the water flow. In this region, the pressure of the flowing water is significantly below atmospheric pressure. As air is entrained into the stream of water flowing through the siphon, it functions as a pressure interchanger between the two fluids, and a vacuum is produced at the siphon opening. This vacuum provides the pressure differential required to operate the present system. The absence of moving parts in the water minimises capital and maintenance costs and there are reports of a similar pressure interchanger operating continuously and maintenance free for more than fifty years. No water is consumed, as the air-carrying water flows back into the same stream. Further, because airflow is in the direction of the stream and this section has no contact with the patients, medical grade materials are not required and the process is independent of water quality.

It will be appreciated that relatively low levels of vacuum are achievable by siphon-based means as described above. In that regard, representative vacuums of between about -10 kPa to about -90 kPa are applicable. The present apparatus, systems and methods are advantageously operable on the relatively low vacuums available by siphon-based methods.

The present apparatus, systems and methods may be scaled according to a required flow rate of target gas. Skilled artisans have for many years been capable of determining the bed size of a gas adsorbent (such as zeolite) required to provide a given target gas production rate. Such capabilities extend to designing connecting lines, reservoirs, pumps and the like required to process gases entering and exiting the system. Having the benefit of the present specification, a skilled artisan is capable of dimensioning and otherwise configuring any system described herein to achieve a given production rate. Such dimensioning and configuring extends to the dual piston pump (where used) of the present systems given the details of operation provided herein.

The present systems may further comprises a conduit to convey an enriched gas to a storage means (such as an expandable bladder) or directly to an end user. Where the end user is a patient requiring oxygen therapy, the system may comprise medical grade tubing through which oxygen enriched gas passes, the tubing is gaseous communication with an oxygen mask of the type applied to the patient face for the delivery of a medical gas. Where the end user is a body of water used for aquaculture, or a sewage pond, or a water requiring remediation, the conduit of the system may be in gaseous communication with an aeration device such as a perforated bubbling device, an oxygen injector, an oxygen saturator (such as a Speece cone), or a U-tube oxygenator, all of which are contrivances known to the skilled artisan.

It will be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. Functionality may be added or deleted from the diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention. 740 Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAIMS:

1. A method for at least partially purifying a target gas from a gas mixture, the method comprising the steps of:

providing a gas mixture comprising a first gas species and a second gas species, providing a first vessel having a gas retaining material selective for the first gas species over the second gas species,

providing a second vessel having a gas retaining material selective for the first gas species,

contacting the gas mixture to the gas retaining material of the first vessel under conditions allowing for the first gas species to be retained by the gas retaining material of the first vessel,

causing or allowing the second gas species to separate from the first gas species retained on the gas retaining material of the first vessel, and

causing or allowing the first gas species to release from the gas retaining material of the first vessel under conditions that prevent or inhibit mixing of released first gas species with the released second gas species.

2. The method of claim 1, that does not require supply of the gas mixture at a pressure that is higher than about atmospheric pressure.

3. The method of claim 1 or claim 2, that is devoid of an apparatus for supplying the gas mixture at a pressure at about atmospheric pressure, or at a pressure above about atmospheric pressure.

4. The method of claim 3, wherein the apparatus for supplying the gas mixture at a pressure at about atmospheric pressure, or at a pressure above about atmospheric pressure is a gas blower or a gas compressor.

5. The method of any one of claims 1 to 4 that is operable without the requirement for the gas mixture, or the first gas species, or the second gas species to have a pressure that is higher than about atmospheric pressure.

6. The method of any one of claims 1 to 5, wherein the step of causing or allowing the first gas species to release from the gas retaining material of the first vessel is effected or assisted by the application of a vacuum to the interior of the first and/or second vessel.

7. The method of claim 6, wherein the vacuum is provided by one or more vacuum sources(s).

8. The method of claim 7, wherein the one or more vacuum sources is/are alternately applied to the first and second vessels.

9. The method of claim 8, wherein the one or more vacuum sources is/are alternately applied to the first and second vessels in a cyclical manner, and for a plurality of cycles.

10. The method of claim 9, wherein the one or more vacuum sources is/are alternately applied to the first and second vessels so as to provide substantially continual stream(s) of the first and/or second gas species.

11. The method of any one of claims 7 to 10, wherein the vacuum is provided by a single vacuum source and the vacuum source is alternately applied to the first and second vessels.

12. The method of any one of claims 7 to 11, wherein the vacuum source is a combined vacuum source and pressure source.

13. The method of claim 12, wherein the combined vacuum source and pressure source is configured so as to alternately provide a source of vacuum and a source of pressure.

14. The method of claim 13, the combined vacuum source and pressure source is configured so as to alternately provide a source of vacuum and a source of pressure in a cyclical manner, and for a plurality of cycles.

15. The method of any one of claims 12 to 14, wherein the combined vacuum source and pressure source is configured to operate reciprocally such that generation of a vacuum contemporaneously generates a pressure.

16. The method of claim 15, wherein the combined vacuum source and pressure source is an apparatus having a piston sliding within a piston chamber and wherein the reciprocal operation is provided by a piston sliding within the piston chamber.

17. The method of claim 16, wherein the apparatus comprises first and second chambers, a first piston sliding within the first chamber and a second piston sliding within the second chamber, the first and second pistons being coupled such that the first and second pistons move in concert.

18. The method of claim 16, wherein the first and second pistons are coupled by way of a rod.

19. The method of claim 16, wherein the first and second chambers are separated by a gas-tight divider, and the rod traverses the divider via an aperture contained therein.

20. The method of claim 19 wherein the apparatus comprises sealing means configured to allow the rod to slide bi-directionally through the aperture while preventing or inhibiting the passage of a gas between the first and second chambers.

21. The method of any one of claims 17 to 20, wherein the first chamber of the apparatus has first and second gas ports, and the second chamber of the apparatus has third and fourth gas ports, each of the gas ports configured to allow the passage of a gas between its respective chamber and the exterior of the apparatus.

22. The method of claim 21, wherein the apparatus is configured such that with regard to the first chamber the first piston is slidable between the first and second gas ports, and with regard to the second chamber the second piston is slidable between the third and fourth gas ports.

23. The method of claim 22, wherein where the first and second pistons are coupled by way of a rod, the rod has a length such that with regard to the first chamber the first piston is limited in its travel through the first chamber so as to not be slidable beyond the first and/or second gas port, and with regard to the second chamber the second piston is limited in its travel through the second chamber so as to not be slidable beyond the third and/or fourth gas ports.

24. The method of claim 23, wherein the apparatus is configured such that:

the first piston divides the first chamber into first and second sub-chambers, the first sub-chamber being in gaseous communication with the first gas port and the second sub- chamber being in gaseous communication with the second gas port, and

the second piston divides the second chamber into third and fourth sub-chambers, the third sub-chamber being in gaseous communication with the third gas port and the fourth sub- chamber being in gaseous communication with the fourth gas port.

25. The method of claim 24, wherein the apparatus is in gaseous communication with the first and second vessels such that when a vacuum is applied alternately to the second and third chambers, the first and second pistons are caused to move resulting in the first and fourth sub-chambers alternately admitting and pressurizing a gas species released from the gas retaining material.

26. The method of any one of claims 1 to 25, wherein the gas species released from the gas retaining material is diatomic nitrogen.

27. An apparatus providing a combined vacuum source and pressure source, the apparatus comprising first and second chambers, a first piston sliding within the first chamber and a second piston sliding within the second chamber, the first and second pistons being coupled such that the first and second pistons move in concert.

28. The apparatus of claim 27, wherein the first and second pistons are coupled by way of a rod.

29. The apparatus of claim 28, wherein the first and second chambers are separated by a gas-tight divider, and the rod traverses the divider via an aperture contained therein.

30. The apparatus of claim 29 wherein the apparatus comprises sealing means configured to allow the rod to slide bi-directionally through the aperture while preventing or inhibiting the passage of a gas between the first and second chambers.

31. The apparatus of any one of claims 27 to 30, wherein the first chamber of the apparatus has first and second gas ports, and the second chamber of the apparatus has third and fourth gas ports, each of the gas ports configured to allow the passage of a gas between its respective chamber and the exterior of the apparatus.

32. The apparatus of claim 31, wherein the apparatus is configured such that with regard to the first chamber the first piston is slidable between the first and second gas ports, and with regard to the second chamber the second piston is slidable between the third and fourth gas ports.

33. The apparatus of claim 32, wherein where the first and second pistons are coupled by way of a rod, the rod has a length such that with regard to the first chamber the first piston is limited in its travel through the first chamber so as to not be slidable beyond the first and/or second gas port, and with regard to the second chamber the second piston is limited in its travel through the second chamber so as to not be slidable beyond the third and/or fourth gas ports.

34. The apparatus of claim 33 configured such that:

35. A system for concentrating a gas in a gas mixture, the system comprising the apparatus of claim 34, and a first vessel having a gas retaining material selective for a first gas species and a second vessel having a gas retaining material selective for the first gas species, wherein the first vessel is in gaseous communication with the first sub-chamber, and the second vessel is in gaseous communication with the second vessel.

36. The system of claim 35, comprising a vacuum source in gaseous communication with the second sub-chamber and the third sub-chamber, the system configured such that vacuum can be applied alternately to the first and second sub-chambers in a cyclical manner.

37. The system of claim 36 configured such that when the vacuum source is applied alternately to the second and third chambers, the first and second pistons are caused to move resulting in the first and fourth sub-chambers alternately admitting and pressurizing a target gas species released from the gas retaining material.