CH620594A5 - Process and apparatus for separating the components of a gas mixture - Google Patents

Description

The present invention relates to a method 35 and an apparatus for separating a gas mixture, in particular for increasing the proportion of one of the gas components in the gaseous mixture.

In conventional gas separation using adsorption methods, it is customary to pass the gas mixture under 40 pressure into an adsorbent bed and to obtain from the bed an enriched gas mixture which is the desired product and is still under a small positive pressure. If the product is to be obtained at a higher pressure, it must be compressed 45 separately. The adsorbent bed is normally regenerated prior to its full saturation by applying a vacuum to the bed which has the effect of withdrawing the adsorbed components of the gas mixture, so that the bed is ready for further supply of the starting gas mixture 50 to be separated. It will be appreciated that such plants may require three separate pumps to produce product gas under higher positive pressures and, consequently, may be rather complex plants with relatively high capital requirements and energy consumption, particularly since the pressure required to compress the starting gas mixture is significant Can consume a lot of energy.

The object of the invention is therefore to eliminate these disadvantages. For this purpose, it proposes a method, the features of which are characterized by patent claim 1. A device for performing this method is defined by claim 23.

It has been found that the method according to the invention, for example for the production of oxygen-rich gas 65 from air, can have the advantage over the prior art that larger ones with an equally high vacuum for regeneration and at the same pressure of the product gas

Oxygen yields are available and better oxygen purity can be achieved more easily. In addition, the need for electrical energy to generate a given amount of oxygen can be reduced.

The method according to the invention is particularly suitable for the generation of oxygen-rich or nitrogen-rich gases from air, but also for the separation of many other gas mixtures. When an oxygen-rich gas is needed, the bed is usually filled with a zeolite molecular sieve, and when a nitrogen-rich gas is needed, the bed is usually filled with a carbon molecular sieve.

In the method according to the invention and the device according to the invention, a plurality of adsorbent beds, e.g. B. two or three adsorbent beds, each bed going through a similar cycle, but not in phase with the other bed or beds, so that a practically continuous supply of product gas is caused.

Preferably, the adsorbent bed or each of the adsorbent beds is regenerated after the adsorption by evacuating the bed. It is also preferred that after this evacuation and before the next entry of gaseous mixture into the bed, a gaseous mixture enriched in the product gas is admitted into the bed, the pressure in the bed after this inlet of gaseous mixture being below atmospheric pressure. Such reduced pressure in the bed helps to draw the gaseous mixture into the bed the next time gaseous mixture is admitted into the bed. Furthermore, the enriched gaseous mixture can be admitted before the bed is evacuated, possibly even during the entire evacuation, so that it acts as a cleaning gas that contributes to the regeneration of the adsorbent. In this way

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a lower vacuum can be used to regenerate the adsorbent. In a device according to the invention, in which several beds are provided, the enriched gaseous mixture let into the bed in the manner described above is preferably removed from the product outlet of the other or another bed.

The yield of product, usually in a three bed device, can be improved by collecting only a first part of the gas withdrawn from each bed (commonly referred to as the "first fraction") and the rest of this gas "( second fraction ») used as part of the feed for another bed. The second fraction is usually not as rich in the desired gas as the first fraction, but is richer in this gas than the gaseous mixture that is the rest of the bed feed.

With many gaseous mixtures, it may be necessary to provide a pre-cleaning stage to remove contaminants such as water vapor. The flow rate of the starting gas mixture that is drawn into the adsorbent bed is preferably not constant. This speed is relatively high at the beginning of the gas inlet period and drops to a minimum value precisely when refilling gas is to be passed to the next bed in a two-bed system or gas from a second fraction is to be passed to the next bed in a three-bed system. The maximum speed can be several times the minimum speed. This feature leads to advantages over processes in which the source gas is forced into the plant and a variable feed rate cannot be easily achieved. For source gas at atmospheric pressure, i.e. not under pressure, the source gas is drawn into the plant at the speeds required by the cycle, while if the source gas is compressed in the cycle, the device must be arranged to either gas stores in the system in a memory or controls the working pressures in the system, whereby these pressures can vary as required. A process with supply under atmospheric pressure thus has the advantages that no gas storage vessels are required and that the process cycles can be selected in such a way that they result in the greatest efficiency, without the pressure that one has to vary pressures or gas must be stored in order to To balance gas flows.

According to one embodiment of the invention, in the case of gaseous mixtures which contain a certain gas component and at least two other constituents, the mixture can be passed in succession through a first adsorbent bed, which preferably adsorbs one of the other constituents, and through a second adsorbent bed, which the other or the other components are preferably adsorbed, sucked, at least partially under the effect of a reduced pressure, the z. B. is generated by a pump that can create a low vacuum and at the same time compress the gas to an excess pressure, which is connected to an outlet of the second adsorbent bed, whereupon the beds are regenerated, preferably at least partially by evacuation before any further gaseous mixture into the beds.

If this embodiment is chosen, the adsorbent beds can have separate layers of adsorbent materials contained in a single vessel. At least three similar pairs of the adsorbent beds are preferably provided, the pairs of beds being operated with similar cycles but not in phase with one another, so that a practically continuous stream of the desired gas is generated.

An inventive method and an inventive device, which have the first and second adsorbent beds, are suitable for the separation of argon from a gaseous mixture which also contains oxygen and nitrogen, for. B. air or oxygen-rich feed that can be withdrawn from the rectification column of a cryogenic air separation plant.

In the first example, namely air as the feed material, the aforementioned first adsorbent bed preferably contains an adsorbent which selectively adsorbs nitrogen, e.g. B. a zeolite molecular sieve. An oxygen-rich gaseous mixture, typically containing 95% oxygen and 5% argon, is generated and passed through the other bed of adsorbent which selectively adsorbs oxygen, e.g. B. a carbon molecular sieve.

The yield, usually in a system comprising three pairs of beds, can be improved by collecting as product only a first part of the gas withdrawn from each pair of beds (commonly referred to as the "first fraction") and the rest this gas «(second fraction») used as part of the feed for another bed. In the example given above, in which the first bed contains zeolites, this bed also removes moisture in the feed air. The second fraction, which comprises a gas in which the product gas is only partially enriched, is therefore a dry gas and should be in the first zeolite adsorbent bed at a location downstream of the first part that removes moisture from the supplied air , are introduced. This first part serves as a drying bed integrally connected to the first adsorbent bed, but in other embodiments a separate drying bed can be provided. So far, the percentage of argon extracted from a side-by-side air separation plant has been limited by practical considerations governed by nitrogen pollution of the argon produced.

Using such a method and apparatus, the argon can be extracted from such a facility without the normally inevitable nitrogen contamination.

A cold gas stream, e.g. B. 12 '/ <argon, 87% oxygen and 1% nitrogen, can be withdrawn from the system and heated to atmospheric temperature in a heat exchanger. The first bed of adsorbent into which such a heated gas mixture enters preferably contains a material that selectively adsorbs nitrogen, such as a zeolite molecular sieve.

In this way an argon product is obtained which is practically free from contamination with nitrogen and oxygen. A stream of exhaust gas from the aforementioned evacuation stage can be returned to a rectification column of the air separation system after cooling in a heat exchanger. Such an exhaust gas is preferably used to heat the above-mentioned gas mixture obtained from the air separation system, in which argon is then enriched by a process according to the invention.

An advantage of using a method according to the invention and a device according to the invention for cleaning an argon flow obtained from an air separation plant is that they allow a potentially larger percentage of argon extraction from the plant than the conventional process because the argon-rich feed flow is not chosen on the basis of considerations controlled by the need to keep the contamination of the argon-rich stream taken from the rectification column of the plant with nitrogen at the minimum value. Moreover, the one contained in this stream of argon

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Cold is recovered by heat exchange with the recycle stream of exhaust gas mentioned above, whereas in a conventional process a portion of this cold is usually lost in the liquid argon product stream from the air separation unit. Another advantage is that the liquid and vapor flows in the rectification column are not significantly affected by the extraction of the argon-rich stream compared to the same extraction in a conventional process in which the argon sub-column receives gaseous feed from the low pressure column of a cryogenic air separation plant and returns a stream of liquid to the same column. These advantages make it possible to extract argon from the plant with a minimum degree of influence on the distillation behavior of the plant for the separation of air. In this example, the feed material is already dry.

Although the inventive method and the inventive device, which have first and second adsorbent beds, are particularly suitable for the production of argon from gaseous mixtures of argon, oxygen and nitrogen, they could also be used as a product for the production of other gases, e.g. B. for the production of hydrogen from a mixture with methane, carbon dioxide, carbon monoxide and moisture, which was obtained by steam reforming a hydrocarbon and subsequent rearrangement reaction to increase the proportion of hydrogen. In this last example, the first adsorbent bed is expediently a carbon molecular sieve which selectively adsorbs the moisture, the carbon dioxide and part of the methane. The other bed suitably consists of zeolite, which adsorbs carbon monoxide and a larger part of the rest of the methane.

Some embodiments of the method and the device according to the invention for separating the components of a gaseous mixture are now described for example with reference to the accompanying drawings; in the drawing represent:

1 is a schematic representation of a two-bed device according to the invention,

2 is a diagram explaining the operation of the device of FIG. 1;

3 shows a schematic illustration of a modified embodiment of the device from FIG. 1,

4 is a diagram explaining the operation of the device of FIG. 3,

5 shows a schematic illustration of a three-bed device according to the invention,

6 is a diagram explaining the operation of the device of FIG. 5;

7 shows a schematic illustration of a modified embodiment of the device from FIG. 5,

8 is a diagram explaining the operation of the device of FIG. 7;

9 shows a schematic illustration of a pressure swing adsorption device according to the invention,

10 is a diagram explaining the duty cycle of the device of FIG. 9, and

11 shows a schematic illustration of a part of a cryogenic air separation system which comprises a device according to the invention.

1 and 2 of the drawing, an apparatus for producing oxygen-rich gas comprises two beds 10 and 11, which are filled with zeolite molecular sieve, preferably of the 5A type, with drying sections 12 and 13 at the inlet ends of the beds, the silica gel , activated aluminum oxide, silicon oxide-aluminum oxide or zeolite molecular sieve 5A or another zeolite molecular sieve.

Air is supplied to the beds 10 and 11 through the line 15 and the valve lines 16 and 17. The gas generated is withdrawn from the beds by the compressor 18 via line 19 and the valve lines 20 and 21. The compressor 18 is a pump that can create a low vacuum and at the same time can compress the gas to an overpressure. The beds are regenerated by a vacuum pump 22 which is connected to the beds by line 23 and valve lines 24 and 25. The beds can be refilled with product gas through the valve lines 26, 27 and 28.

The beds perform similar cycles, but not in phase, as shown in Fig. 2. When air is to be admitted into bed 10, the bed is under negative pressure and valve lines 16 and 20 are open.

Air is drawn into the bed and generated oxygen is drawn out of the bed by the compressor 18, which applies a slight negative pressure to the outlet end of the bed while compressing the gas thus drawn off to a positive pressure. Towards the end of this part of the cycle, the valved line 28 opens and product quality gas is introduced into the bed 11 by the action of the vacuum in bed 11 at a rate controlled by the valved line 26 sucked to refill bed 11 so that at the end of this sub-cycle it reaches a pressure below atmospheric pressure, preferably of about 500 torr. At this point, valve lines 16, 20 and 28 close, line 17 opens to admit air into bed 11, and valve line 21 opens to withdraw generated oxygen from the Allow bed 11. The valve 24 provided with a valve also opens so that the bed 10 can be regenerated by evacuation.

Towards the end of this part of the cycle, the valved line 24 closes and the valved line 27 opens, so that the bed 10 increases to about 450 to 550 torr, e.g. . B. 500 Torr, backfill. In this way, the two beds work to form a continuous stream of oxygen products. It should be noted

that at the beginning of each part of the cycle, the pressure at the inlet to the product compressor 18 momentarily drops to about 500 torr in the bed that is turned on before rapidly rising to a level just below atmospheric pressure. Also in this cycle, the vacuum pump 22 is not used during the refilling period. If half a cycle lasts 60 seconds, the evacuation typically takes 40 seconds and the refill takes 20 seconds.

The applied pressure swings cycle and the execution of the oxygen enrichment in the molecular sieve sections of the beds are also suitable for the effective operation of the drying sections of the beds in order to protect the molecular sieve sections against moisture in the let-in air.

3 and 4 illustrate a modification of the system shown in Figs. 1 and 2, in which a purge of product quality gas is introduced into the bed being evacuated, i. H. the bed is regenerated by the combined effect of flushing and evacuation. This has the advantage that the value of the vacuum is reduced in comparison with that which is required for the vacuum regeneration alone. Thus, the requirements of the method for the vacuum pump are reduced by this modification, so that the total energy consumption is reduced.

Figure 3 illustrates a system similar to Figure 1, with similar 5

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parts are identified by the same reference numerals. In addition, a vacuum flushing line 30 with a control valve and further lines 31 and 32 provided with valves are present. There are three possible sequences of operations to effect the purging given below, the first two of which use the vacuum purging lines, while the third does not, so that it can be applied directly to the embodiment of FIG. 1.

a) Using the vacuum purge line, the valved line 31 or 32 is opened when an appropriate vacuum has been achieved in the bed in question that is being evacuated and the purge rate is adjusted to match the value of the vacuum during the Remaining the evacuation period almost constant. The bed is then refilled through the refill line 27 or 28.

b) Using the vacuum purge line, the valve line 31 or 32 is opened as soon as the bed is evacuated and is kept open throughout the evacuation period. The refilling then takes place through line 27 or 28.

c) No vacuum purge line is used, but the valved backfill line 27 or 28 is opened before the evacuation is complete to provide the purge stream which becomes the backfill stream when the evacuation stops.

If the zeolite molecular sieves are replaced by carbon molecular sieves, the methods and devices described above with reference to FIGS. 1 to 4 produce nitrogen. The main sections of the beds are filled with the carbon molecular sieve, which is suitable for adsorbing oxygen quickly and nitrogen slowly. The drying section of the bed can consist of the same carbon molecular sieve or a drying agent such as silica gel, activated aluminum oxide or silicon oxide-aluminum oxide. The pressure in the bed at the end of backfilling is believed to be above 400 torr.

Using the basic atmospheric pressure cycle or vacuum purging modification, the process produces a nitrogen enriched product while an oxygen rich exhaust gas is drawn off by the vacuum pump. The nitrogen product obtained in this way normally contains approx. 1% oxygen and is practically free from contamination by moisture and carbon dioxide.

5 and 6, a three-bed device is shown. Compared to the two-bed system, the three-bed system has the advantages that the vacuum pump is fully utilized and that a "second fraction" of oxygen-rich gas can be introduced after a bed has been refilled, which improves the process's fatigue efficiency.

Fig. 5 shows the arrangement of the valve lines and Fig. 6 shows the working cycle of the valves. Turning to bed 110, the vented air supply lines 116 and 120 are initially open. Towards the end of the sub-cycle, when the oxygen concentration at the outlet begins to drop, the valve line 120 closes and the valve line 150 opens to introduce a second fraction of product into bed 210 that is currently is completely refilled. At the end of the sub-cycle, the valve lines 150 and 116 close and the valve line 124 opens, so that the bed is evacuated to e.g. B. 150 Torr is regenerated. After the evacuation is complete, the valve line 124 closes and the valve line 127 opens to raise the bed to about 500 to

600 torr, e.g. B. 550 torr to refill; at this point valve line 127 closes and valve line 151 opens to admit a second fraction of gas from bed 111 while valve line 120 opens and oxygen produced is pulled out of bed by the product compressor 118.

If the sub-cycle lasts one minute, the refill time is approx. 40 seconds and the "second fraction" time is 20 seconds.

Studies have shown that to perform the cycle in the range of high ambient temperature, about 35 to 40 ° C, advantageously a stronger vacuum, e.g. B. of 50 Torr is applied. This stronger vacuum is also advantageous when it is necessary to carry out the process near the upper limit of the purity of the oxygen product of 95%.

A modification of this system is shown in FIGS. 7 and 8, in which the vacuum regeneration of the beds is supported by purging with gas of product quality. The vacuum purge is carried out during the evacuation period and a line 160 is provided for this purpose. As with the two-bed system described above with reference to FIGS. 1 to 4, the flushing can be carried out in at least three ways:

a) Through a vacuum purge line 161 or 162 or 163, starting when the vacuum reaches a selected value, and at a rate set by the valve in line 160.

b) Through a vacuum flush line 161 or 162 or 163 during the entire evacuation period.

c) By starting to refill a bed before the evacuation is over.

As with the two-bed process, the same process becomes useful for producing a nitrogen-rich product in the range of 99% nitrogen, balance oxygen, which is virtually free of moisture and carbon dioxide when beds 110, 111 and 210 are used with a carbon molecular sieve with or without drying sections 112, 113 and 212 fills. Again, the pressure in the bed after filling is believed to be over 400 torr.

9 and 10 of the drawing, an apparatus for recovering argon from an oxygen-rich feed comprises three adsorption columns 310, 311 and 312. Each column contains a layer of carbon molecular sieve in the vicinity of its inlet and a layer B of zeolite as an overlying layer Adsorbent.

The device has an inlet conduit 313 through which feed material, which is practically at atmospheric pressure, is drawn in as described below. The argon generated is withdrawn through outlet line 316 by a compressor 314 in that line; this compressor gives the argon at a required pressure, e.g. B. from 0.7 kg / cm2. Line 316 is provided with a branch circuit line 317 for a purpose described below. The columns 310, 311 and 312 can be evacuated through the line 319 by means of a vacuum pump 320. The second gas fraction from each column can be recirculated through lines 321, 322 and 323, respectively.

Looking at a duty cycle in column 310, valve 324 opens and at the same time valve 325 opens, so that the feed material is drawn through adsorbent layers A and B and argon is drawn off through line 316. As the feed material passes through carbon layer A of column 310, oxygen is removed from the feed material so that a practically oxygen-free mixture of argon and nitrogen enters the zeolite section, where the nitrogen is removed and a prak5

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table pure argon product is withdrawn from the outlet end of the column. When the level of impurities in the argon product begins to increase, valve 325 closes and valve 326 opens, with a "second fraction" passing into column 312 at a location above first drying section 5 of carbon layer A of column 312 becomes. At the end of the second fraction, valves 324 and 326 close and valve 328 opens to regenerate the adsorbents by evacuation. After the evacuation is complete, valve 329 opens to refill bed 310 with product quality gas, and after valve 329 closes, valve 326 'opens so that the second gas fraction from column 311 flows into column 310, and at the same time valve 325 opens, so that the generated argon is withdrawn. When the second fraction is finished, valve 326 'closes and valve 324 opens to admit feed gas. If three carbon-zeolite elements work in this cycle, but are shifted 120 ° relative to each other, a continuous argon product stream is withdrawn. This cycle is shown schematically in FIG. 10. The column is evacuated to approximately 70 torr by pump 320 during the regeneration of adsorbent layers A and B.

If each column has a selected vacuum, such as 500 to 600 torr, e.g. B. about 550 Torr reached (but lower 25

Pressures can be advantageous), line 317 is automatically closed during backfilling by a pressure sensitive control device 332 so that the column is under vacuum when valve 326 'opens for the second fraction.

It will be appreciated that the feed material is drawn into line through line 313 by the action of pump 314 and indirectly by the action of vacuum pump 320 which regenerates the adsorbent materials.

The position of the inlet for the second fraction in the columns depends on the composition of the feed material and any impurities such as moisture and carbon dioxide present therein. The inlet can be in any position from the column inlet to the connection of the zeolite and carbon layers A and B.

Fig. 11 schematically illustrates part of a cryogenic air separation plant comprising a pressure swing adsorption device as described above with reference to Figs. 9 and 10; it is represented schematically by block 350. A cold gas stream, e.g. B. 12% argon, 87% oxygen and 1% nitrogen is withdrawn from a rectification column 351 of the air separation unit. This stream is heated to atmospheric temperature in a heat exchanger 351 and cooled by the cold gas stream withdrawn from column 352 before it is returned to the column, so that the coldness of the gas stream withdrawn from column 351 is recovered.

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Claims (35)

620 594 2nd PATENT CLAIMS 1. A method for separating the components of a gas mixture, in particular for increasing the proportion of one of the gas components in the gaseous mixture, characterized in that the gas mixture is in a practically non-pressurized state through a bed (10, 11; 110, 111, 210 ; 310, 311, 312) of an adsorbent, which preferably adsorbs one or more components of the gas mixture, under the action of a reduced pressure applied to an outlet (19; 119; 316) of the bed, and then forwards the bed the further inlet of the gaseous mixture into the bed (10, 11; 110, 111, 210; 310, 311, 312). 2. The method according to claim 1, characterized in that the gaseous mixture is air. 3. The method according to claim 1, characterized in that one of the gas components is oxygen. 4. The method according to claim 3, characterized in that a Zeloith molecular sieve is used as the adsorbent. 5. The method according to claim 1, characterized in that one of the gas components is nitrogen. 6. The method according to claim 5, characterized in that a carbon molecular sieve is used as the adsorbent. 7. The method according to any one of claims 1 to 6, characterized in that one uses several adsorbent beds (10,11; 110,111, 210; 310, 311, 312), each of which goes through an at least approximately the same cycle, but compared to the cycle of other bed or beds so that a practically continuous supply of product gas is generated. 8. The method according to any one of claims 1 to 7, characterized in that the adsorbent bed or each adsorbent bed is regenerated by evacuating the bed. 9. The method according to claim 8, characterized in that after the evacuation of the bed (10, 11; 110, 111, 210; 310, 311, 312) and before the next admission of gaseous mixture into the bed, a gaseous mixture enriched in the gas into the bed, the pressure in the bed after this introduction of the gaseous mixture being below atmospheric pressure. 10. The method according to claim 9, characterized in that the enriched gaseous mixture is let in before the evacuation of the bed (10, 11; 110, 111, 210; 310, 311, 312) has ended. 11. The method according to claim 10, characterized in that one lets in the enriched gaseous mixture during the entire evacuation of the bed, so that it acts as a purge gas and contributes to the regeneration of the adsorbent. 12. The method according to any one of claims 9 to 11, characterized in that several beds are used, which as indicated in the bed (10,11; 110,111, 210; 310, 311, 312) is taken in, enriched gaseous mixture from the product outlet (19; 119; 316) of the other or another bed. 13. The method according to any one of claims 1 to 12, characterized in that several adsorbent beds (110, 111, 210; 310, 311, 312) are used and only a first part of the gas withdrawn from each bed is collected as a product and the rest of this Gases used as part of the feed for another bed. 14. The method according to any one of claims 1 to 13, characterized in that in the adsorbent beds (10, 11; 110, 111, 210; 311, 312) gaseous impurities, such as. B. steam removed from the mixture. 15. The method according to claim 14, characterized in that the gaseous impurities in one of the main adsorbent layer of each bed (10, 11; 110, 111, 210; 310, 311, 312) upstream pre-cleaning stage (12, 13; 112, 113, 213) removed. 16. The method according to any one of claims 1 to 15, characterized in that the gaseous mixture contains the desired gas component and at least two other constituents, the mixture being successively passed through a first adsorbent bed (310A, 311A, 312A), which is one of the other constituents preferably adsorbed, and sucked through a second adsorbent bed (310B, 311B, 312B) that preferentially adsorbs the other or another of the other components, at least in part under the effect of a reduced pressure applied to an outlet of the second adsorbent bed , and then regenerated the beds before further admission of the gaseous mixture into the beds. 17. The method according to claim 16, characterized in that one uses adsorbent beds with separate layers (A, B) of adsorbent materials, which are contained in a single vessel. 18. The method according to claim 17, characterized in that one uses at least three at least approximately the same pairs of adsorbent beds (310A / B, 311A / B, 312A / B), the pairs of beds being operated with at least approximately the same cycles, the Cycles are shifted against each other, so that a practically continuous flow of the desired gas is generated. 19. The method according to any one of claims 16 to 18, characterized in that the gas is argon and the other components of the gaseous mixture contain oxygen and nitrogen. 20. The method according to claim 19, characterized in that the gaseous mixture is an oxygen-rich feed material which is withdrawn from the rectification column (35) of a cryogenic air separation plant. 21. The method according to claim 19, characterized in that an adsorbent which selectively adsorbs nitrogen is used as the first adsorbent bed, and an adsorbent which selectively adsorbs oxygen is used as the other adsorbent bed. 22. The method according to any one of claims 1 to 21, characterized in that the reduced pressure is applied to the bed or beds using a compressor (18; 118; 314) which releases product gas under an excess pressure. 23. The device for carrying out the method according to claim 1, characterized by a bed (10, 11; 110, III, 210; 310, 311, 312) for receiving an adsorbent which preferably adsorbs one or more components of the gas mixture, means (15 ; 115; 313) for directing the gas mixture to an inlet (16, 17; 116, 117, 216) of the bed, means (18; 118; 314) for applying a reduced pressure to a product outlet (19; 119; 316 ) of the bed, means (22; 122; 320) for regenerating the bed (10, 11; 110, 111, 210; 310, 311, 312) and means for controlling all the above-mentioned means so that the device operates one cycle with the gaseous mixture by means (18; 118; 314) for applying a reduced pressure to a product outlet (19; 119; 316) of the bed in a practically non-pressurized state by means (15; 115; 313) for guiding the gas mixture to an inlet of the bed (10, 11; 110, 111, 210; 310, 311, 312) and then through it s bed are sucked while the means (22; 122; 320) are not in operation for regenerating the bed, whereupon the means (22; 122; 320) for regenerating the bed are activated in order to regenerate the adsorbent in use in the bed while the means (15; 115; 313) for guiding the gas mixture to an inlet of the bed and the means (18; 118; 314) for applying the reduced pressure are isolated from the bed. 24. The device according to claim 23, characterized in 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd 620 594 net that the means for applying a reduced pressure comprise a pump (18; 118; 314), which apply a reduced pressure to the product outlet (19; 119; 316) and to compress product gas withdrawn from the bed through this outlet to an overpressure can 5 25. The device according to claim 23 or 24, characterized in that the means for regenerating the bed comprise means (22; 122; 320) for applying a vacuum to the bed. 26. Device according to one of claims 23 to 25, 10 characterized in that the adsorbent is a zeolite molecular sieve. 27. The device according to one of claims 23 to 25, characterized in that the adsorbent is a carbon molecular sieve. 15 28. Device according to one of claims 23 to 27, characterized by a plurality of at least approximately identical adsorbent beds and means for operating these beds according to the cycle described above, but the cycles of the individual beds (10, 11; 110, 111, 210; 310, 311, 312) are mutually displaced. 29. The apparatus of claim 28, characterized by means (150, 151, 152) for directing gaseous mixture from the outlet end (120, 121, 220) of any bed to the inlet end (116, 117, 216) of another of the beds, 25 wherein the the control means mentioned above are suitable for decommissioning the means (115) for directing the gas mixture to an inlet (116, 117, 216) of a bed, until a first part of the gas has been withdrawn as a product from the outlet of the bed. 30th 30. Device according to one of claims 23 to 29, characterized in that the main adsorbent layer of each bed (10, 11; 110, 111, 210; 310, 311, 312) has a separate pre-cleaner stage (12, 13; 112, 113, 213) for removing contaminants from the gaseous mixture. 31. The device according to any one of claims 23 to 30, characterized by two adsorbent beds (A, B) connected in series, which, from a gaseous mixture which contains the desired component and at least two other components, the relevant components different from the desired component preferably adsorb, the means (314) for applying a reduced pressure being connected to a product outlet of the second bed (310, 311, 312) connected in series. 32. Device according to claim 31, characterized in that the adsorbent beds (310, 311, 312) have separate layers (A, B) of adsorbent material which are contained in a single vessel. 33. Apparatus according to claim 31 or 32, characterized by at least three identical pairs of adsorbent beds (310A, 310B, 211A, 311B, 312A, 312B) of the type defined above, the control means operating these pairs of beds with at least approximately the same cycles that are out of phase with each other. 34. Device according to one of claims 31 to 33, characterized in that the first adsorbent bed in the row is a zeolite molecular sieve and the second adsorbent bed in the row is a carbon molecular sieve. 35. Device according to one of claims 31 to 34, characterized by a cryogenic air separation system upstream of the adsorbent beds with a rectification column (351), from which the oxygen-rich feed material is withdrawn.