WO1986005119A1

WO1986005119A1 - Pressure swing cycles for gas separations

Info

Publication number: WO1986005119A1
Application number: PCT/US1985/001474
Authority: WO
Inventors: John Schlaechter; Roy Steven Brown
Original assignee: Guild Associates, Inc.
Priority date: 1985-02-28
Filing date: 1985-08-01
Publication date: 1986-09-12
Also published as: EP0215000A1

Abstract

A gas separation apparatus and cycle in which a compressor (4) is the source of a pressure differential (5 and 6) and flow regulator means (V1-V6) cyclicly direct the flow of source gas (9) to and purge gas (11) from an adsorbent bed (1). A separated gas component is directed from the bed (1) to a product vessel (7) for pressure regulated (V7) dispensation (10). The compressor (4) and product vessel (7) together provide purge gas flow through the adsorbent. The apparatus and cycles can be ganged to provide multi-component gas separations.

Description

- t-

PRESSURE SWING CYCLES FOR GAS SEPARATIONS

RELATED APPLICATION

This application is a continuation-in-part of co-pending applications, Serial No. 475,543, filed March 15, 1983; now allowed, Serial No. 706,402, filed February 28, 1985; and Serial No. 707,057, filed March 1, 1985.

FIELD OF THE INVENTION

This invention relates to an improved pressure swing adsorption cycle which is preferably useful for continuous gas separations.

BACKGROUND OF THE PRIOR ART

Sorptior cycles involve the process of physical adsorption and the manipulation of a fluid through a medium .ch las a selective affinity for a component specie,, or specie of the fluid. As a multi-component fluid passes through he medium, the species or specie is "adsorbed", and the fluid exiting the medium contains a predetermined species in a quantity less than that in the fluid originally entering, or conversely, the fluid exiting is relatively enriched in proportion to the components of the fluids which are not adsorbed. Certain media are capable of "desorbing" the specie after adsorption (such as when they are heated or subjected to a

BAD ORIGINAL "purge"); and an adsorption/desorption "cycle" is well known.

Sorption technology is of practical use in many applications of gas separation or purification. In these instances, given a particular commercial application, a cycle and corresponding apparatus is devised to accomplish a given task. The apparatus generally consists of one or more "beds" containing the sorbent medium, which is selected because of its affinity for a particular specie. A multiplicity of valves, pumps, connectors, regulators and other mechancial devices are interconnected to each other and to the bed(s) to permit repeated adsorption/desporption in a cycle to achieve an operating ^* result consistent with the intended application.

Pressure swing adsorption cycles have been found generally to be useful in oxygen concentration systems which provide a source of a relatively small volume of -nirified oxygen from an ambient air supply and in other separations of multi-component gases.

A continuous process gas separation unit using an adsorption cycle provides advantages in portability and continuous operation.. Several small scale oxygen concentration units are now commercially available and are typically used for ^' hospital or home health care therapeutic applications. Using air as an ambient source, these units generally provide flow rates of oxygen of from about 2 to 5 liters per minute at purity levels, depending on the rate of demand of from 95% at low demand to 80% at high demand. Disadvantages in such presently available units are that in general a high, consistent purity of oxygen cannot be delivered at a high output rate, even despite the generally "low" volume oxygen production requirements imposed on the system. Thus, the currently available "small volume" oxygen concentration air separation units are generally unable to meet a reasonably anticipated 5 liter per minute flow rate of delivery of pure 95% oxygen gas. In addition, even though such presently available units are advantageous over supplies of liquid or bottled gas, the bulk and weight of the adsorption unit is considerable.

Thus there exists a need for an improved gas separation system, and a cycle useful in the system, for supplying a continuous volume of a single purified gas, or useful as a source of mutliple purified gases, for an industrial, research, university or laboratory application which meets stringent demands of reliability, compactness and consistent supply required.by a high purity gas source.

OBJECTS OF THE INVENTION

It is an object of this invention to provide an improved gas concentration cycle by which a relatively low volume of high purity oxygen (if an ambient source is air) is continuously provided in a cycle which requires an apparatus of smaller volume and lower weight than that conventionally in use. It is a further object to provide a pressure swing adsorption cycle which provides an efficient use of the pressure source and the adsorption bed and thereby reduces the number of separate elements required in such an apparatus.

In particular, it is an object in one embodiment to provide a pressure swing adsorption cycle suitable for continuous use in a low volume unit which, in a compact volume of less than three cubic feet and a weight of less than 50 pounds, can reliably deliver oxygen of a purity of 95% at a flow rate of 5 liters per minute using air as the ambient source.

In such an embodiment, it is a further object to adapt such apparatus for the therapeutic treatment of pulmonary disorders and to otherwise provide a source for the continuous delivery of purified oxygen consistent with a human physiological demand.

Another object is to apply the simplicity and/or small size inherent in this cycle to the production of oxygen or to the separation of multi-component gases for industrial, laboratory or research use, or other applications, where a continuous gas supply is required.

And it is yet a further object to adopt such a pressure swing cycle to a "ganged" apparatus in which the separation of purified components of a multi-component feed gas can be achieved through the interconnection of preselected absorbent beds operating cyclically in accordance with the principal cycle of the invention. Thereby, there will be provided a continuous source of multiple purified gases derived from a single multi-component feed mixture.

These and other objects of the invention will be apparent from the following description of the preferred embodiment, taken in conjunction with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an apparatus which is capable of using the cycle.

Figures 2A and 2B show a cycle of the invention with respect to fluid flow in the apparatus of Figure 1.

Figure 3 illustrates a co-product gas separation using a ganged system of the invention in a co-ordinated cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A pressure-swing adsorption device in accord with the invention uses an adsorption vessel to purify a gaseous feed stream. An efficient implementation of a single bed system is illustrated in Figure 1; although this description represents the preferred embodiment, additional variations and improvements are possible with respect to apparatus and configurations using this system.

In Figure 1, adsorbent bed, 1 consisting of a volume of adsorbent medium such as a molecular sieve adsorbent is connected at the opposite ends thereof 2 and 3 by a valve system including valves VI, V2, V3, and V4 - - which operationally connect, according to a predetermined cycle, bed end 2 to source 4 which is capable of providing a higher pressure at 6 and a lower pressure at 5 with respect to a given "ambient" pressure level. The valve system VI, V2, V3 and V4 may be a single co-ordinated

"4-way" valve. The opposite end of bed 3 is connected by a check valve V5 and restriction valve V6 to a product tank/surge vessel 7. "Valves" V5 or V6 may similarly comprise a single flow regulator means. A supply of product gas at a regulated pressure is obtained from the vessel through valve V7. The source of the gas or fluid to be purified is introduced to the system at inlet 9. A product gas outlet is provided at 10 and a waste gas outlet is shown at 11.

In prior art single bed cycles, the compressor is not used effectively, while the adsorption vessel is undergoing the regeneration step. However, in the use of an apparatus 'in accord with the cycle of the invention, the compressor is used to lower the vessel pressure during regeneration, thereby improving regeneration efficiency.

In the preferred embodiment, purification of air to produce oxygen or oxygen-enriched air is one useful example of the cycle. During the adsorption phase of a cycle shown in Figure 2A, a compressor, or other source of a pressure differential, pumps air from the atmosphere to an adsorption vessel, through valves V3 and V2, while valves VI and V4 (not shown) are closed. The adsorption vessel is filled with a suitable adsorbent such as molecular sieve. In an oxygen concentration system the adsorbent will have a preferential affinity for nitrogen, and will remove nitrogen from the passing stream. The nitrogen depleted gas passes through a flow regulator comprising check valve, V5, and the parallel, partially restricted line, V6, and enters the product tank, 7. A flow of gas is drawn from this tank at outlet 10 as the product supply of "purified" oxygen.

When the adsorbent's capacity for nitrogen is sufficiently exhausted, the position of the valves is reversed and the system will be purged as the cycle is shown in Figure 2B. Nitrogen-enriched gas is drawn from the adsorption vessel 1 through valves VI and V4 while valves V3 and V2 (not shown) are closed. Since the compressor discharge is at atmospheric pressure, this creates a vacuum in the adsorption vessel. Product enhanced fluid from the product tank 7 is also drawn through the restricted line including the flow regulator,

V6, to purge the adsorbent. As the adsorption vessel pressure drops, the effect of this purge becomes more efficient. In this regard, proper design with respect to overall system pressure insures that the pressure in the product tank is sufficient to supply both product and purge flows. After sufficient purge has been provided to exhaust all nitrogen retained by the bed during the previous adsorption step, the cycle sequence is repeated.

Flow patterns of the repetitive operating cycle of the invention are shown in Figures 2A and 2B which respectively depict the process and purge states of a single bed system. EXAMPLE I

In a demonstration of the cycle of the apparatus, a compressor adsorbing system configured in accordance with Figure 1 was interconnected with a 10 pound enclosed bed of a densely packed molecular sieve adsorbent (Grade 13X) . At a pressure level of 2.8 p.s.i.g. provided by the compressor and a suction of -2.4 p.s.i.g. during the purge stage, and using a product vessel enclosing a volume of approximately 6 liters, with ambient temperature air (25°C) as the fluid source, the enhanced efficiency of the cycle of the invention was able to produce a consistently high purity (90%) supply of oxygen at a rate in the range of approximately four to five liters per minute (or, alternatively stated 95% oxygen at the rate of 4.5 liters per minute) .

The relative .direction of gas flow during the first (adsorption) and second (purge) cycle stages is respectively set forth in Figures 2A and 2B. In these respective cycle stages, the flow control valves or regulators, which may be combined in a single co-ordinated flow control means are in the status set forth in Table I:

Table I

Relative Position of Flow Regulator Means

Cycle Stage 1 Cycle Stage 2

Valve/Flow Cont :rol Means (Absorption) (Purge) in Figure I (Figure 2A Figure 2B

VI Closed Open

V2 Open Closed

V3 Open Closed

V4 Closed Open V5 Open Closed

V6 Open to provide restricted flow V7 Open to provide pressure regulated product

The enhanced cycle of the invention provides an essentially continuous delivery of a high purity oxygen in a level consistent with anticipated demands of a low volume need in an apparatus having a simplified mechanical configuration.

EXAMPLE II

The method and apparatus is useful to provide a continuous therapeutic supply of oxygen at a level required by an individial patient for the treatment of chronic obstructive pulmonary diseases and other health conditions. Thus the oxygen concentration system will provide a source of purified oxygen from an ambient air supply to a single, individual patient. Such oxygen concentration systems are used in the treatment of chronic obstructive pulmonary diseases (COPD) as a result of advances in the medical field which suggest that 24-hour continuous oxygen therapy is a preferred treatment of diseases which include chronic bronchitis, emphysema and asthma. A unit in the configuration of Example I may be adapted to provide flow rates of oxygen of from about 2 to 5 liters per minute at purity levels, depending on the -,o- rate of demand, of from 95% at low demand to 80% at high demand to satisfy an individual patient's therapeutic need.

The improved oxygen concentration system of the invention is adaptable for medical treatment applications and meets the stringent demands of reliability, compactness and consistent supply of high purity oxygen in a level which is consistent with the anticipated physiological need of an individual patient. The utilization of such an enhanced cycle in treatment apparatus for chronic obstructive pulmonary disease or for other therapeutic purposes to an individual patient provides the therapeutic benefit of the essentially continuous delivery of a high purity oxygen in a level ' consistent with anticipated physiological demands of an individual patient in an apparatus having a simplified mechanical configuration.

EXAMPLE III

The cycle in a further modification can be adapted to an adsorption process for a bulk separation and high purity recovery of multiple components in a gas system, such as the co-production of continuous sources of oxygen and nitrogen from an ambient air supply. In general, the separation of two components, for example, "gas A" and "gas B", from a single source feed gas in which these gas A and gas B components are present may be achieved using a cycle adopted from Example I. In a two gas unit, two different adsorbents are required. The -it- first has a preferential adsorption characteristic, either kinetic or equilibrium, for component gas A. The second adsorbent, in an alternate vessel must preferentially adsorb component gas B. For purposes of illustration, a separation of nitrogen and oxygen from air, with high purity recovery of both products is described below.

Figure 3 presents an apparatus configuration useful in an oxygen/nitrogen separation, co-production cycle. The air separation process incorporates two adsorption vessels or beds. A first bed 21, contains a zeolite molecular sieve (MS) and the other bed, 22, contains a molecular sieve carbon (MSC) . A four-way valve, 23, operatively interconnects the two systems. Two surge, storage vessels respectively for oxygen, 24, and nitrogen, 25, are provided respectively having pressure regulated outlets corresponding to V7 described in Example I. In this representation, the co-ordinated single 4-way valve, 23, combines the functions of separate valves, VI, V2, V3 and V4 previously described in Example I. In Figure 3, the four connections to valve 23 are identified respectively as A, B, C and D. Feed gas valve 26 and waste gas valve 27 are also included and a compressor 28 having a suction inlet 29 and elevated pressure outlet 30 are also included.

As in the purification cycle of Example I, a first separation is accomplished by passing feed gas, such as air, by reason of the pressure difference produced by the compressor, into the first bed where predetermined component A of the mixed gases in the feed is adsorbed. The gas continues to flow into a first storage vessel which receives the gas described as "feed less A". After a sufficient time period, a valve is activated to provide suction from the compressor to lower the pressure of the first bed and desorb the component A from the bed. This gas stream, now enriched in component A, is fed into the second bed where adsorption of the component B occurs and the product gas A flows into the second product storage vessel. The cycle is repeated several times to separate the respective gas A (feed gas less gas B component) and gas B (feed gas less gas A component) components in the feed gas stream. Some gas may be vented after each cycle to purge contaminants which may have been adsorbed on -the ^■ feed end of the beds.

As in the apparatus of Example I, between the adsorbent beds and storage vessels, a check-valve or other flow regulator such as that comprising V5 and V6 allows the respective product gas A and- gas B to pass unrestricted into the storage vessel during the adsorption state of the cycle sequence for each of the respective beds. During a desorption step when the pressure in the adsorbent vessel drops below the pressure in the storage vessel the check-valve restricts the flow of the product gas back into the adsorbent vessel (V5) . However, a small flow of product gas is preferably allowed to bypass the check valve through a purge valve or orifice (V6) . This supplies product quality gas as a purge to the adsorbent bed during the low pressure desorption step. With reference to the apparatus of Figure 3, an air separation is described^* beginning with the entry of an ambient source of feed air in which air valve 26 is open.

Four-way valve 23 has two different orientation states with respect to the respective low pressure, suction or inlet side 29 of compressor 28 and the high pressure, discharge or outlet side 30 of the compressor. In the first cycle stage feed air valve 26, is open, and the feed air passes directly in an isolated path to the inlet side 29 of the compressor, where the pressure is raised and air flow continues through compressor outlet 30, then through the valve to vessel 21. The flow path through valve 23 is from A to B to the compressor and from the compressor to C to D to the bed.

Vessel 21 is an encloseable volume comprising an absorbent bed within a container having an inlet, 31, and an outlet, 32. Absorbent beds are known devices. In an air separation, the first bed, 21 contains a Zeolite Molecular Sieve Adsorbent having an preferential affinity for nitrogen such as a 5A or 13X type of molecular sieve.

The gas at this time in vessel 21 is at an elevated pressure and a predetermined component thereof is adsorbed onto the molecular sieve.

In an air separation, nitrogen is adsorbed and the oxygen component product gas leaves the vessel through the valve system 37 comprising regulators V5 and V6, to surge tank 24, which is also at an elevated pressure. An outlet 33 for the surge tank through a flow regulator or valve, 39, equivalent to V7 in Example I provides a delivery means for the product gas. This first cycle stage gas flow corresponds to the first cycle stage described in Example I.

Assuming an optimum air separation, 100% of the nitrogen component of the feed air will be stored in the vessel, 21. The term "storage" with reference to the adsorbent beds includes nitrogen adsorbed in the molecular sieve and nitrogen present as a gas in the space surrounding the molecular sieve. In the gas in the vessel, oxygen may also be stored in the vessel both loaded on the adsorbent and present in the void volume. In a reverse flow through the vessel, 21, this stored gas mixture of oxygen depleted air, (which includes a higher ^* proportion of nitrogen relative to oxygen, when compared to the feed air) is drawn from the bed 21 to inlet 29 of the compressor and through the compressor. In this stage, some product gas from surge storage tank 24 flows through the vessel as a purge flow.

After a first flow from the feed source, 26, through inlet 29 and outlet 30 of the compressor, to bed 21 and surge storage tank 24, the position of the four-way valve is reset for the next,cycle stage. The position of valve 23 is changed to direct flow from the bed 31 to D to B, through the compressor and from C to A in an isolated flow path. At this point the adsorbent in the vessel 21 contains an adsorbed gas. In the case of an air separation, the adsorbent contains oxygen depleted air, i.e. having a higher concentration of nitrogen. When the 4-way valve is reset, the gas flow through the vessel is also reversed and the oxygen depleted air of the vessel is drawn to the low pressure side of the compressor, then out of the compressor at an elevated pressure, and is directed to the alternate vessel 22 to its inlet 34.. In this manner, the feed gas for the second bed is an enriched purge gas from the first bed. This second cycle stage corresponds in part to the second cycle stage of Example I, except that instead of exhausting the purge flow of gas into the atmosphere, the "purge" flow from the first bed becomes the "source" flow for the second bed.

Vessel 22 contains an adsorbent different from that of vessel 21. The adsorbent of vessel 22 is complementary to the adsorbent of vessel 21. In the case of an air separation, this adsorbent is a molecular sieve carbon in which the bulk of the micropores have a diameter of approximately 5 Angstroms having a preferential rate of oxygen adsorption.

Thus in vessel 22, the remaining oxygen component of the gas is adsorbed and purified nitrogen flows from the outlet of this adsorbent bed 35 to the surge storage tank 25 where it may be dispensed through valve 40 to an outlet, 36.

After this flow occurs in vessel 22, oxygen is stored on the molecular sieve carbon and in the spaces surrounding the sieve. As in the case of vessel 21, there is also some nitrogen present on the sieve and in the spaces. The four-way valve is now switched drawing gas - ι<_- from vessel 22 through the valve to the compressor suction 29 out through the compressor exhaust 30 and back into bed vessel 21 where the adsorption cycle with respect to that bed is repeated. This position permits flow from A to B through the compressor to C to D.

The alternate switching between beds is repeated a predetermined number of times, based on design considerations, until after a predetermined number of repetitions the waste valve 27 is opened on the back flow step and a "new" volume of feed air is introduced through valve 26. Opening of the waste valve is the concluding step of a repeating cycle; and the opening of the feed valve is the first .step of the next subsequent cycle.

In general, selection of appropriate adsorbents suited to a particular need or product is within the skill of the art. In air separations of oxygen and nitrogen utilizing a zeolite molecular sieve and a molecular sieve carbon, adsorption occurs at different rates. In a molecular sieve carbon the rate of adsorption is a more important factor in separation efficiency than the equilibrium capacity of the absorbent in the separation-. An alternate direct connecting flow valve between vessel 21 and vessel 22 such as indicated at 41 by the dotted lines in Figure 3 may be provided to regulate gas flow to an appropriate rate to adapt to the different adsorption characteristics of the adsorbent in each vessel .

*_*_*

Claims

- n- WHAT IS CLAIMED IS:

1. A gas concentration apparatus which delivers a continuous quantity of a purified gas from a multi component supply gas source consisting of:

A. a serially interconnected

(1) source inlet communicating with the supply source;

(2) a purge outlet;

(3) a compressor having an inlet and an outlet for providing a pressure difference with respect to an ambient pressure level;

(4) a bed containing a purgeable adsorbent having a selective affinity for gas other than the gas to be purified; and

(5) a product vessel having an outlet and pressure regulated means in said outlet for the delivery of the purified gas; the serial interconnection between said source inlet, purge outlet, compressor, bed and vessel comprising gas flow path means connected between: (a) the vessel and the bed, (b) the bed and the compressor inlet and outlet, (c) the compressor inlet and the source inlet; and (d) the compressor outlet and the purge outlet;

B. gas flow control means in said gas flow path means being operated in a repeating cycle in which:

(1) in a first cycle stage the gas flow control means are operated to provide supply gas from the source inlet through the inlet of the compressor to introduce said supply gas to the bed at an elevated pressure, whereby gas other than the gas to be purified is adsorbed by the absorbent, and to deliver a purified gas from the bed to the vessel; and

(2) in the second cycle stage the gas flow control means are operated to flow purified gas from the vessel to the bed whereby the absorbent in the bed is purged of adsorbed gas by a suction gas flow from the vessel in a reverse direction through the bed and from the bed to the inlet of the compressor and through the outlet of the compressor to said purge outlet.

2. The apparatus of Claim 1 in which the supply gas source is ambient air at atmospheric pressure; the adsorbent bed is an enclosed volume of a molecular sieve adsorbent having an affinity for nitrogen; the purified gas is oxygen; and the second cycle stage purge of the bed occurs at a pressure which is less than atmospheric pressure.

3. The apparatus of claim 1 interconnected to a second bed containing a purgeable absorbent having a selective affinity for a second gas and a second product vessel having an outlet and pressure regulated means in said outlet for the delivery of the second gas; the interconnection between said first apparatus and said second bed and second vessel comprising gas flow path means connected between: (a) the second vessel and the second bed, (b) the second bed and the compressor inlet and outlet, and (c) the compressor inlet and the first bed; and including gas flow control means in -»<^**._ said gas flow path means in the second cycle stage, the gas flow control means are operated to provide a supply gas for the second bed from the purge gas of the first bed through the compressor to introduce said supply gas to the second bed at an elevated pressure, whereby a gas component is adsorbed by the adsorbent of the second bed and the second product gas is delivered to the second product vessel; and in which in a third cycle stage the gas flow control means are operated to flow purified gas from the second product vessel to the second bed whereby the adsorbent in the second bed is purged of adsorbed gas component by a suction gas flow from second vessel in a reverse direction through the second bed to the inlet of the compressor and through the outlet of the compressor, whereupon the cycle is repeated.

4. The apparatus of claim 3 including a flow regulator means directly interconnecting the first and second beds, said flow regulator comprising means to regulate gas flow between the beds at a rate appropriate to the adsorption characteristics of the adsorbent in each bed.

5. The apparatus of .claim 3 including a waste outlet interconnected to the compressor outlet through which purge gas flow from the beds is exhausted from the apparatus.

6. The apparatus of Claim 1 in which the supply gas source is ambient air at atmospheric pressure;; the first adsorbent bed is an enclosed volume of an adsorbent having an affinity for nitrogen; the second adsorbent bed -ao- is an enclosed volume of an adsorbent having an affinity for oxygen; the product gas of the first product vessel is oxygen and the product gas of the second product result is nitrogen.

7. A method for the essentially continuous delivery of a source of purified gas consisting of deriving an enriched supply of the purified gas from an interconnected:

(1) source inlet communicating with a supply source;

(2) a purge outlet communicating with an exhaust;

(3) compressor having an inlet and an outlet for providing a pressure difference with respect to an ambient pressure level;

(5) a product vessel having an outlet and pressure regulating means in said outlet for the delivery of the purified gas; the interconnection between said compressor, source inlet_* purge outlet, bed .and vessel being effected by operable flow control means interconnecting respectively: (a) the vessel and the bed, (b) the bed and the compressor; (c) the compressor inlet and the source inlet; and (d) the compressor outlet and the purge outlet; and in which the flow control means are operated in a repeating cycle in which: - 2.1 —

(A) in a first cycle stage the flow control means are operated to ^* provide a supply gas from the source inlet through the inlet of the compressor to introduce said supply gas to the bed at an elevated pressure, whereby gas other than the gas to be purified is adsorbed by the adsorbent, and to deliver a purified gas from the bed to the vessel; and

(B) in the second cycle stage the flow control means are operated to flow the purified gas from the vessel to the bed whereby the absorbent in the bed is purged of adsorbed gas by a suction gas flow from the vessel in a reverse direction through the bed and from the bed to the inlet of the compressor and through the outlet of the Compressor to the purge outlet; and

(C) delivering said purified gas from said product vessel outlet.

8. A method for the essentially continuous co-production of purified gases consisting of deriving the purified gas from an interconnected:

(1) source inlet communicating with a supply source;

(2) a purge outlet communicating with an exhaust;

(3) compressor having . an inlet and an outlet for providing a pressure difference with respect to an ambient pressure level;

(4) a first bed containing a purgeable adsorbent having a selective affinity for a first gas; and ■4.2- - a second bed containing a purgeable adsorbent having a selective affinity for a second gas; and

(5) a first and second product vessels, each having an outlet and pressure regulating means in said outlet for the delivery of purified gas; the interconnection between said compressor, source inlet, purge outlet, bed and vessel being effected by operable flow control means interconnecting respectively: (a) the first vessel and the first bed, (b) the first bed and the compressor; (c) the compressor inlet and the source inlet; and (d) the compressor outlet and the second bed; (e) the second bed and the second vessel; and (f) the compressor outlet and a waste outlet; and in which the flow control means are operated in a repeating cycle in which:

(A) in a first cycle stage the flow control means are operated to provide a supply gas from the source inlet through the inlet of the compressor to introduce said supply gas to the first bed at an elevated pressure, whereby a first gas is adsorbed by the adsorbent, and a second gas is delivered from the bed first to the first vessel; and

(B) in the second cycle stage the flow control means are operated to flow the second gas from the vessel to the first bed whereby the adsorbent in the bed is purged of the adsorbed first gas by a suction gas flow from the vessel in a reverse direction through the bed and from the bed to the inlet of the compressor and through the outlet of the compressor to introduce said first gas to the second bed at an elevated pressure, whereby the second gas is adsorbed by the adsorbent, and the first gas is delivered from the second bed to the second vessel; and

(C) in a third cycle stage the flow control means are operated to flow the first gas from the second vessel to the second bed whereby the adsorbent in the second bed is purged of adsorbed second gas by a suction gas flow from the vessel in a reverse direction through the bed and from the bed to the inlet of the compressor and through the outlet of the compressor, whereupon the cycle is repeated; and

(D) delivering said purified first and second gases from the respective product vessel outlets of the first and second vessels.

9. The method of claim 8 including the elimination of a waste gas from the cycle during a purge stage of the first or second bed.

10. A method for the continuous delivery of- a therapeutic amount of oxygen to a human patient comprising the administration of the product gas of the apparatus of claim 2 to the patient.