DE2631890A1 - METHOD AND DEVICE FOR ENRICHING ONE MAIN COMPONENT OF A GAS MIXTURE CONTAINING AT LEAST TWO MAIN COMPONENTS - Google Patents

Description

PATKNTANWAtT

: «PL. ing. K. BLOLZEK : 'HiIiXFPINB-WBIiSBB-STBASSB 14 8000 ATTGSBUKG

TEtEFOIi 816475 TELEX 533 202 patol d

W. 812

Augsburg, July 13, 1976

BOG Limited, Hammersmith House, London W6 9DX, England

Method and device for the enrichment of a main component of at least two main components containing gas mixture

The invention relates to a method for enriching a main component of at least two main components containing gas mixture, the mixture with a Adsorbent is brought into contact, which adsorbs one of the main components preferentially.

609685/0844

The inventive method is particular, however not exclusively applicable to the production of essentially pure oxygen or pure nitrogen from air.

The term main component is understood to mean a component of a gas mixture which is present in the mixture in a proportion of at least 5 % by volume and preferably at least 10 % by volume.

As is known, a main component of a gas mixture containing at least two main components can thereby be obtained separated from the mixture so that the gas mixture passes through an adsorption bed with an adsorbent it is guided that either the desired component or another main component of the mixture is adsorbed preferentially, so that by regeneration of the bed or by collecting the residual mixture that has passed through the bed, the the desired component is obtained in enriched form.

It has also been suggested for one of these Process in which the desired component is adsorbed to include a process step during which the bed prior to stripping the desired component from the bed using substantially pure Product gas is purged to purge gas that has accumulated in the bed during previous steps in the process and the product gas available from the bed

6 0 9 8 "81 /" θ 8 4 4

₃ 2631830

would contaminate. This will to some extent the Improved the purity of the product gas available from the bed.

However, as in practice those used in such procedures Adsorbents also to some extent the less adsorbable components of the bed adsorb gas mixture passed through and also a certain proportion of the preferably adsorbed main component letting it pass through the bed is through regeneration of the bed or through Collecting the gas which has passed through the bed, with a certain proportion of the available product gas contaminated with other components present in the mixture.

For example, if a zeolite adsorbent is used to extract oxygen from air, which preferentially adsorbs nitrogen, the purity of the oxygen is limited to 95% in economical operation, since a certain amount of nitrogen passes through the zeolite sieve and not together with that in the zeolite sieve separable argon content of the atmospheric air gets into the oxygen forming the product. If, on the other hand, a charcoal sieve is used to extract oxygen from air, this is in contrast to a zeolite sieve

85/0844

not nitrogen, but the oxygen preferentially adsorbed, but also a considerable quantity of nitrogen from atmospheric air is adsorbed, 30 that the purity of by the subsequent desorption of the bed, usually by evacuating ₈ Sauer3toffgasproduktes available from economic deposition cycles carried out at about 80% is limited. The rest of the product gas consists largely of nitrogen. The argon concentration should be limited to 1.25 % of the nitrogen concentration, ie to 0.25 % for a product gas with 80 % oxygen or to O ₉ 5 % for a product gas with 60% oxygen.

Is obtained in processes in which nitrogen from air by a pressure swing process using either a molecular sieve zeolite, or a carbon molecular sieve of _a nitrogen at economical operation contains about 1% to 2% oxygen. When using a zeolite molecular sieve, the nitrogen is contaminated by other small gas components, such as water vapor and carbon dioxide, in addition to the oxygen content just mentioned, so that these small gas components have to be removed by adsorption, for example, either at the beginning or at the end of the process. Is becoming

$ 09885/0644

However, if a carbon molecular sieve is used to extract nitrogen, the product gas is practically moisture-proof. and carbon dioxide free.

According to the invention, a method of the type set out in the introduction is characterized in that the gas mixture is passed through at least two adsorption beds arranged one behind the other, of which one adsorption bed preferably adsorbs one main component Adsorbent and the other adsorption bed one preferably adsorbing the other or another main component Contains adsorbent, and that a gas mixture is obtained from each adsorption bed, which a larger proportion of the contains a main component mentioned as the mixture supplied to this adsorption bed and the following in each case Adsorption bed is fed or withdrawn as a product from the last adsorption bed.

It can be seen that this represents an increased proportion of the a gas mixture comprising a main component from each of the Adsorption beds either by collecting what has passed through Gas or by regeneration of the bed, for example by a pressure swing adsorption system, is available, depending according to the adsorbent contained in the bed concerned.

The inventive method is particularly for economic production of essentially pure oxygen or nitrogen from air using coal and zeolite molecular sieves are applicable as adsorption beds. However, the method according to the invention can also be used for economic separation of other gas mixtures with two or more main components are used for which adsorption means for preferential adsorption of at least two of the main components are available.

When using the method according to the invention for obtaining oxygen from air, the air can be passed through a coal sieve and the product gas obtained from the coal sieve can be fed to a zeolite sieve, whereby an oxygen product with a purity of more than 99 % is obtainable. There is only a small loss of yield if the energy consumption is not increased excessively in comparison with a method in which only a single coal screen is used. Alternatively, the 90 % to 95 % oxygen-containing product of a zeolite sieve can be fed to a carbon sieve, which in turn results in an oxygen product with a purity of more than 99 % .

§09885 / 0844

Another advantage of the method according to the invention is that in a single plant both nitrogen and oxygen are considerably less Costs can be gained out of the air, as it is with the help of two plants, each only delivering a single product is possible, each of which is fed with air «,

In addition, by means of the method according to the invention a high purity nitrogen product using a series connection of a carbon screen and a zeolite screen can be obtained economically.

If the method according to the invention applied for the recovery of oxygen or nitrogen from air, it is usually not necessary to smaller components such as water vapor and carbon dioxide to remove ₈ as these components are deposited in the course de3 method of the invention anyway _s separately from the air supplied for example by adsorption, however, an initial separate separation of these small components can be done in the usual manner, if desired.

The invention also relates to an apparatus for carrying out the method by at least two series-connected adsorption beds, one of which preferentially adsorbs the one main component

Adsorbent and the other an adsorbent which preferably adsorbs one or another main component contains, further through a gas feed line for introducing the gas mixture into the first adsorption bed and through a Gas line for introducing the intermediate product obtained from the first adsorption bed into the second adsorption bed is characterized.

The invention is explained below with the aid of a few exemplary embodiments for the recovery of essentially pure oxygen or nitrogen from air with respect to the adjacent Drawings described in more detail. In the drawings show:

Fig. 1 is a schematic representation of a

Two-bed system for the extraction of oxygen from air,

Fig. 2 is a schematic representation of a

Two-bed system for the extraction of nitrogen from air,

Fig. 3 is a schematic representation of a

system containing three two-bed groups for the production of nitrogen from air,

- 8 -609885 / 08U

Pig. 4 shows the operational sequence of the in Fig.

the system shown,

Fig. 5 is a schematic representation of a

other two-bed systems for the production of nitrogen from air, and

Fig. 6 shows the working cycle of a multiple

Arrangement of the system shown in Fig. 5 illustrative diagram.

The pressure values given in the following exemplary embodiments are in each case absolute pressures.

The arrangement shown in FIG. 1 has an adsorption bed which forms a first stage and which consists of a coal screen unit 10, and an adsorption bed which forms a second stage and which consists of a zeolite screen unit 11. The coal screen unit 10 forming the first stage is supplied with air at a pressure of 1.1 bar by means of a fan via a line 12. At the top of the coal bed 10, residual gas is drawn off through a line 13 under a pressure of 1.05 bar. This residual gas contains 96.2 % nitrogen, 2 % oxygen and 1.7 % argon and is

S0988S / Q844

can be used, for example, as an inert gas. A vacuum pump is connected to the bottom of the coal bed 10 via a line 15, by means of which a product gas with 60 % oxygen, 39.5 % nitrogen and 0.5 % argon is drawn off from the bed 10 under a pressure of 1.1 bar. This product gas is then compressed in a compressor 16 to a pressure of 1.8 bar and fed via a line 17 to the zeolite bed 11 forming the second stage, and an oxygen product is obtained via a line 18 which is connected to the top of the zeolite bed 11 with 99 % oxygen and 1 % argon. After the product gas has been collected, the bed is emptied via a line 19 and the gas flowing out through this line has an oxygen concentration which falls from 60% to 40 %. This gas is recirculated into the coal bed 10, which forms the first stage, in order to flush the air out of this bed at the end of the adsorption taking place in bed 10. Waste gas with 80% nitrogen and 20 % oxygen is drawn off from the bottom of the zeolite bed 11 by means of a vacuum pump 20 via a line 21.

It will be noted that the carbon screen 10 forming the first stage and the zeolite screen forming the second stage 11 in the usual way with pressure swing adsorption cycles work. The coal screen 10 is in the just mentioned Flushed way before the product gas leaves the adsorbent is evacuated. The zeolite sieve 11 is over the

- 10 -

609835/0844

Line 19 emptied before the waste gas is withdrawn from the adsorbent through the line.

It has been shown that of 1000 volume units of the air introduced into the first stage 10, 682 volume units of residual gas from the first stage, which has a quality suitable for many inert gas applications, further 161 volume units of oxygen with a purity of 99 % and 157 volume units of waste gas from the second stage 11 arise.

In Fig. 2, a pressure swing adsorption system for the recovery of nitrogen from air is shown. This system has a first adsorption stage 22, which consists of a coal molecular sieve unit, and a second adsorption stage 23, which consists of a zeolite molecular sieve unit; air is introduced at the bottom of the first stage 22 via a line 24. The carbon sieve preferentially adsorbs the oxygen from the air as well as carbon dioxide and humidity. The gas exiting at the top of the first stage 22 has a high nitrogen content with about 2 % oxygen and is fed via a line 24 to the zeolite molecular sieve unit 23, which preferably adsorbs nitrogen, so that the gas from the second stage 23 by means of a vacuum pump 26 Product gas withdrawn via a line 25 in the

- 11 -

is essentially free of oxygen, carbon dioxide and moisture. At the top of the unit 23 is a waste gas that consists of nitrogen-contaminated oxygen with an oxygen content of less than 21 % and is returned via a line 27 to the first adsorption stage 22 to re-pressurize and flush the coal screen .

The two adsorption stages 22 and 23 again work in the usual manner in pressure swing adsorption cycles. In the case of the coal bed 22, the working cycle initially comprises the free supply of air through the line 24, then the Evacuation of this bed by means of a vacuum pump 28 via a line 29 and finally the refilling of this Bed via line 27 with waste gas from the zeolite bed 23. For zeolite bed 23, the cycle of operation includes supplying gas through line 24 followed by purging the zeolite sieve with nitrogen, which via line 30 and finally evacuating this bed through line 25 to remove the nitrogen product.

The advantages of this method are firstly that the normally used when using a zeolite molecular sieve drying beds used to protect this molecular sieve from moisture can be dispensed with, as a result of which

- 12 609885 / 08U

results in a cost saving and, secondly, that the Waste gas from the second stage used beneficially can be to repressurize the first stage and rinse out. In addition, the air fan, which is normally connected upstream of the first stage, can be omitted, as the air as a result of the vacuum created in the second stage is sucked into the first stage.

In practice, this will be done with reference to FIG. 2 procedures described normally employing at least three sets of carbon and zeolite sieve units run which are operated cyclically in this way, each sieve group ate itself in a different one in each time pum Cycle phase is. This makes it possible to have an almost continuous flow of nitrogen as a process product obtain. Such an arrangement is now based on FIG. described in more detail.

There are three coal beds 31, 32 and 33 and also three Zeolite beds 34, 35 and 36 are provided, one below the other are connected in such a way that the gases flowing off from the upper sides of the coal beds 31, 32 and 33 as feed gas into the Zeolite beds 34, 35 and 36 are introduced. The arrangement air is supplied via a line 37, which is connected by lines each provided with a valve 38 or 39 or 40

- 13 109805/0044

each of the carbon beds 31, 32 and 33 is connected. A line 40 for waste gas from the coal beds is with connected to each of these carbon beds by lines each provided with a valve 41 or 42 or 43. In the In line 40, a vacuum pump 44 is switched on in order to be able to draw off the waste gases from the coal beds. the Upper ends of the carbon beds 31, 32 and 33 are each connected via a line into which a valve 45, 46 and 47, respectively is connected to the respective associated zeolite bed 34 or 35 or 36. One with a vacuum pump 49 The line 48 provided is used to draw off the product gas from the zeolite beds and is each provided with a valve 50 or, 51 or 52 provided connecting lines with these Zeolite beds connected. In addition, the line 48 is downstream of the vacuum pump 49 via a valve 53 in each case or 54 or 55 provided lines with the input rare connected to the zeolite beds, through which nitrogen can be introduced into the zeolite beds in order to reduce the adsorption Rinse medium in these beds prior to regeneration of these beds. A line 56 is used to discharge the Waste gas au3 the zeolite beds and is provided via lines provided with a valve 57, 58 and 59, respectively the other sides of the zeolite beds 34, 35 and 36 connected . In addition, a control unit is in line 56

- 14 -

arranged valve 60, which is actuated by a pressure sensor 61 and the pressure in the line 56 upstream of the Valve 60 holds constant. The line 5.6 is finally Via valves 62, 63 and 64 connected to the outlet sides of the coal beds 31, 32 and 33 to remove the waste gas from the Introduce zeolite beds into the coal beds in order to put them under pressure again.

In each one consisting of a coal bed and a zeolite bed The same process takes place in the adsorption bed set, but the cycles in the three adsorption bed sets take place out of phase with one another. A The full cycle is described below with reference to the das Coal bed 31 and the zeolite bed 34 containing adsorption bed set described. However, the same processes also take place in the other two sets of adsorption beds, and the complete cycle is shown schematically in FIG. 4 for all three sets.

In the first adsorption bed set with the carbon bed 31 and the zeolite bed J> k , the carbon bed 34 is connected to the air supply when the valve is opened and the valve 45 opens in a programmed manner, so that a control flow of about 2% oxygen and 98 % nitrogen

- 15 -

09885/0044

can flow from the coal bed 31 into the zeolite bed 34. When beds 31 and 34 are brought to atmospheric pressure have been, the valves 38 and 45 and close valves 53 and 57 open so that the zeolite bed is purged with pure nitrogen. That through the line effluent waste gas, which has an oxygen content between that of air and zero, flows through the control valve 60 and fills up the coal bed 32, which has previously been evacuated. At the same time it opens the valve 41 and the coal bed 31 are evacuated by the pump. Then the valves 57, 53 and close and valve 50 opens, allowing pure nitrogen from the zeolite bed 34 by means of the vacuum pump 49 is evacuated. At the same time, the valve 62 opens, whereby the coal bed 31 with the help of waste gas from the Zeolite bed 36 is brought to atmospheric pressure. At this Operating mode, the process results in the product as nitrogen, which is essentially free of oxygen, carbon dioxide and Moisture is provided that the vacuum pump 39 does not require water for operation. The carbon dioxide, the moisture and the oxygen from the air supplied is sucked off by means of the exhaust gas vacuum pump 44.

5 and 6 show a further possible embodiment of the method according to the invention for obtaining Nitrogen. In this arrangement, a zeolite molecular

- 16 ßQ988S / Q8U

3 sieve unit 70 is used as the first stage adsorbent and a carbon molecular sieve unit 70 is used as the second stage adsorbent. At the inlet of the zeolite unit 70, air is supplied and oxygen-rich exhaust gas is drawn off from this unit via a line , the zeolite unit 70 is evacuated via a line fk by means of a vacuum pump 75 to remove a gas mixture containing mainly nitrogen but also about 2% oxygen also contaminated with carbon dioxide and moisture i3t. This mixture is compressed in a compressor and fed to the coal filter unit 71 under a suitable feed pressure, for example 3.7 bar. After the gas has passed through the carbon screen unit, the nitrogen, which is essentially free of oxygen, carbon dioxide and moisture, is collected in a line 77; it is used as a purge gas during the initial stage of cleaning the zeolite screen. As the evacuation of the carbon sieve unit 71 progresses, the waste gas is increasingly contaminated with oxygen, carbon dioxide and moisture and is then passed directly into the exhaust pipe 73. The outlet of the vacuum pump 78 is via a first line provided with a valve 80 to the inlet side of the zeolite sieve unit

-17 609885 / 0S44

and a second line provided with a valve 81 connected to the exhaust pipe 73. During the aforementioned initial stage of evacuation of the coal bed 71 the valve 80 remains open, so that the waste gas withdrawn from this coal bed for cleaning the zeolite sieve can get into the zeolite bed. When the exhaust gas evacuated from the coal bed 71 becomes increasingly stronger Oxygen, carbon dioxide and moisture is contaminated, valve 80 closes and valve 81 opens, in order to introduce this gas directly into the exhaust pipe 73. Another line 82 connects the outlet side of the vacuum pump 75 with the inlet of the zeolite sieve unit 70 to the To supply the main part of the cleaning gas for the zeolite sieve unit. This cleaning gas is used during the Cleaning phase initiated in the zeolite unit.

The zeolite sieve unit 70 and the coal sieve unit work in turn in a known manner in pressure swing adsorption cycles. In the case of the zeolite sieve unit, the cycle includes the introduction of air, then the cleaning of the Adsorbent and finally evacuation of the unit. For the coal screen unit, the cycle includes the Gas supply via line 74 and then the evacuation over line 79.

- 18 -

S09885 / 08U

It can turn three sets of zeolite and charcoal sieves in the in Pig. 5 to a system can be combined with each set of adsorbent beds following the same cycle but opposite the other sets works out of phase, so that a substantially continuous stream of nitrogen is available as product is. 6 shows schematically the cycles of the zeolite beds forming the first stage of each set in one such an arrangement and also the phase relationship of the cycles of the individual zeolite beds to one another. The two The dashed lines drawn in cleaning phases of the zeolite beds each show the direction of flow of the Exhaust gas from the coal sieves through lines 79 to the controlled by valves 80 and 81. It can be seen that this exhaust gas is in addition to that supplied through line 82 Gas is used to clean the zeolite sieve 70, when valve 80 is open and valve 81 is closed, while in the following section the cleaning phase of the Coal beds 71 the exhaust gas directly into the exhaust pipe is initiated, so that the remaining cleaning of the zeolite bed 70 'only by the supplied via line 82 Gas takes place. The advantage of this arrangement is that the exhaust gas from the carbon molecular sieve is useful as a purge gas can be used during the initial stage of cleaning the zeolite bed.

- 19 -

Claims (27)

Claims ί 1.) A method for the enrichment of a main component of a gas mixture containing at least two main components, the mixture being brought into contact with an adsorbent which preferably adsorbs one of the main components, characterized in that the gas mixture is passed through at least two adsorption beds connected in series in which one adsorption bed contains adsorbent adsorbent which preferably adsorbs one main component and the other adsorbent bed contains adsorbent adsorbent which preferably adsorbs the other or a different main component, and that a gas mixture is obtained from each adsorption bed which has a larger proportion of said one main component than that supplied to this adsorption bed Contains mixture and is fed to the respective following adsorption bed or withdrawn as a product from the last adsorption bed. 2. The method according to claim 1, characterized in that said one main component is nitrogen. 3. The method according to claim 1, characterized in that that said one main component is oxygen. - 20 - 0344 4. The method according to claim 2 or 3 »characterized in that the gas mixture is air and that one Adsorption bed a preferably oxygen adsorbent adsorbent and the other adsorption bed preferably contains nitrogen adsorbing adsorbent. 5. The method according to claim 4, characterized in that the one adsorption bed and a carbon molecular sieve the other adsorption bed contains a zeolite molecular sieve, 6. The method according to claim 4 or 5 and claim 2, characterized in that said one adsorption bed the said other adsorption bed is connected upstream and that said one bed after the introduction of air regenerated for the purpose of obtaining a gas mixture with enriched oxygen content and this gas mixture obtained introduced into the other bed and that finally the oxygen not adsorbed by this other bed is collected as a product. 7. The method according to claim 6, characterized in that that said other bed is emptied after an adsorption phase and the gas mixture flowing off during emptying for rinsing said one bed after it - 21 - 609885/0844 Adsorption phase and used before its regeneration will. 8. The method according to claim 4 or 5 and claim 3> characterized in that said one adsorption bed is connected upstream of said other adsorption bed and that the gas not adsorbed in one bed during the adsorption phase is introduced into the other bed and this other bed is regenerated after an adsorption phase for the purpose of recovering the product. 9. The method according to claim 8, characterized in that that the gas not adsorbed by said other bed during the adsorption phase into said one bed is admitted after this one bed has been regenerated by reducing the pressure before its next adsorption phase is. 10. The method according to claim 8 or 9 »characterized in that said other bed is flushed with product gas after an adsorption phase before the subsequent regeneration of this bed. - 22 - £ 09885/0344 11. The method according to claim 4 or 5 and claim 3, characterized in that said other bed said one bed is connected upstream and that the other bed after air during an adsorption phase has been initiated, regenerated for the purpose of obtaining a gas mixture with enriched nitrogen content, this Gas mixture introduced into said one bed and from this one bed unadsorbed gas as a product is collected. 12. The method according to claim 11, characterized in that that part of the regeneration of the said other Bed from this withdrawn gas mixture for purging this other bed after an adsorption phase and before the subsequent regeneration is used. 13. The method according to claim 11 or 12, characterized in that that said one bed is regenerated after an adsorption phase and that the initial part of the thereby obtained nitrogen-rich part of the exhaust gas for purging said other bed after a Adsorption phase and before its regeneration is used. 14. The method according to any one of claims 1 to 13, characterized in that a plurality of adsorption bed sets '■ - 23 - §09885 / 0844 is used, each sentence of which is at least two Adsorption beds of the type mentioned, and that this adsorption bed sets according to the same cycle, however operate out of phase, so that a substantially continuous product gas stream is obtained as the product. 15. Device for performing the method according to one of claims 1 to 14, characterized by at least two adsorption beds connected in series (10, 11; 22, 23; 31, 34; 70, 7D, one of which is a main component that preferably adsorbs Adsorbent and the other one the other or another main component preferably adsorbent adsorbent contains, further through a gas feed line (12; 24; 37; 72) for introducing the gas mixture into the first adsorption bed and through a gas line (15, 17; 24, 45; 46; 47, 74) for introducing that obtained from the first adsorption bed Intermediate product in the second adsorption bed. 16. The device according to claim 15, characterized in that one (10; 22; 31; 71) of the two adsorption beds preferably contains oxygen adsorbing adsorbent. - 24 - £ 09885/0844 17. Apparatus according to claim 15 or 16, characterized in that one (11; 23; 24; 70) of the two Adsorption beds contain a preferably nitrogen adsorbent adsorbent. 18. Apparatus according to claim 16 and 17, characterized in that one (e.g. 10) of the two adsorption beds is a carbon molecular sieve and the other bed (e.g. 11) contains a zeolite molecular sieve. 19. Device according to one of claims l6 to 18, characterized in that the first bed (10) of the Series connection of an adsorbent which preferably adsorbs oxygen and the second bed (11) of the series connection a preferably nitrogen adsorbent contains adsorbent and that a suction line (15, 17) for introduction of gas regenerated from the first bed is provided to the second bed. 20. The device according to claim 19, characterized by a vent line (19) through which the second The bed is vented and the gas flowing out is in the first bed can be introduced for the purpose of flushing it after an adsorption phase and before its regeneration can. - - 25 609885/0844 21. Device according to one of claims 16 to 18, characterized in that the first bed (22) of the Series connection of an adsorbent which preferably adsorbs oxygen and the second bed (23) of the series connection a preferably nitrogen adsorbent contains adsorbent and that a gas line (24) for feeding gas not adsorbed in the first bed into the second bed and a suction line (25, 26) to the Regeneration of the second bed after the introduction of this gas are provided. 22. The device according to claim 21, characterized by a gas line (27) through which in the second bed unadsorbed gas can be introduced into said one bed after it has been regenerated by reducing the pressure before its next adsorption phase. 23. The device according to claim 21 or 22, characterized by a gas line (30) » via which the second bed can be flushed with product gas after an adsorption phase and before a subsequent regeneration of this bed. 24. Device according to one of claims 16 to 18, characterized in that the first bed (70) of the - 26 - -609885/0844 In series, one preferentially adsorbs nitrogen Adsorbent and the second bed (71) of the series connection a preferably oxygen adsorbing adsorbent and that a gas line (74) is provided through which gas regenerated from the first bed can be introduced into the second bed. 25. The device according to claim 26, characterized by a gas line (28) through which purge gas after a Adsorption phase and before the subsequent regeneration of the first bed can be introduced into this, a part of which has been obtained by a previous regeneration of this first bed. 26. Apparatus according to claim 24 or 25, characterized through a gas line (79, 80), through which cleaning gas, of which the initial part by regeneration of the second bed (17) has been obtained after an adsorption phase before the subsequent regeneration of the first bed can be introduced into this. 27. Device according to one of claims 15 to 26, characterized by a plurality of sets of adsorption beds (31, 34; 32, 35; 33, 36), each of which set - 27 609885/0 844 has at least two adsorption beds of the type mentioned, and by a controller which cycles these adsorbent bed sets in equal cycles but out of phase operates so that a substantially continuous stream of product gas is obtained. - 28 - 609885/0844 Blank page