FR2557808A1 - Pressure swing adsorption system for gas sepn. - Google Patents

Abstract

In usinq a sinqle bed of selective adsorbent to separate one main component, to be received in a tank, of a gas mixt., with the absorbent reqenerated when completely charged with another main component, the process operates at high, intermediate and low pressure. A prodn. stage during which bed and tank are taken from intermediate to max. high pressure is followed by flushing, accompanied by rapid redn. of bed pressure to min. value (pref. below atmos.), and then build-up back to intermediate value. A system reading high pressures incorporates a compressor, but a low pressure system has a simpler and cheaper fan. Pressure in prod. tank is detected by a sensor which initiates cycle steps, opening and closing valves, only in response to demand for the prod. gas, rather than in timed sequence.

Description

Single bed pressure switching adsorption gas separation system.

The present invention relates to pressure-switched adsorption, used to separate gas mixtures into their constituents.

More specifically, the invention has been developed in conjunction with such a system in which the air is separated into two streams, a first stream containing mainly oxygen and a second stream containing mainly nitrogen. The first stream is usually used and the second stream is discharged into the atmosphere, but other arrangements are also possible.

Such systems and the devices used to implement them have been widely used, in particular in very large units which produce tons of oxygen per day, as is necessary for heavy industrial uses, for example refining processes. petrochemical and wastewater treatment plants r etc. Much smaller units using pressure-switched adsorption cycles (hereinafter abbreviated as PCA) have not been incorporated into much smaller plants producing order of only a few liters of oxygen per minute as is necessary in medical applications, especially for patients suffering from respiratory disorders.

Another general field of application of technology
ACP is found in various medium-sized industries. These use devices with cycles
ACP, which produce high purity oxygen for the on-site production of oxygen in different areas, for example on offshore oil production platforms. Another industrial application is found in the jar workshops automobile exhaust, in which a stream of oxygen is used to supply oxy-acetylene cutting torches.

In other applications of cycles and technologies
ACP, other gas mixtures can be separated into their constituents and any selected gas can be used. For example, the air can be separated so as to obtain a stream of high purity nitrogen, nitrogen being used as a protective gas in certain welding applications or in other industrial applications. In addition, carbon dioxide can be extracted from industrial gas mixtures to conserve carbon dioxide or any other gaseous component. The field of application of the ACP technology, in connection with the present invention, is not limited to the production of oxygen streams of high purity, even if this is the embodiment which will be described here.

In all these numerous embodiments, the present invention is applicable to the entire field of ACP technology.

Some ItCP techniques work on the basis of membranes or other means of selective separation. However, the most common type, the type to which the present invention applies, relates to ACP techniques based on a full bed of adsorbent materials, such as molecular sieves. The particular adsorbent material is chosen to have a preference for a particular gas in the gas mixture which constitutes the feedstock of the device implementing the ACP cycles considered. When it is desired to extract oxygen from the air, the adsorbent material preferably retains nitrogen by allowing oxygen to flow more quickly through the bed and thus to exit in the form of a relatively high purity oxygen stream, which constitutes a very great simplification of an otherwise extremely complex physico-chemical system. When the bed of adsorbent material is saturated with nitrogen, it is then necessary to depressurize and to sweep in reverse the bed with oxygen, which evacuates the nitrogen and prepares the bed to extract the oxygen again of the feed charge.

Within this general category of ACP adsorbent bed devices and systems, the prior art describes devices using multiple beds and devices using a single bed. When production is continuous, it is extremely advantageous to use at least two beds, one bed being in production while the other bed is being scanned in reverse, so that the overall system continuously produces oxygen. A secondary stream of the product leaving the bed in production is used as a reverse sweep current for the bed to be regenerated.

However, in some cases, a single bed is extremely desirable. The single bed system has the great advantage that its cost is lower, its reliability is higher due to a much smaller number of parts in the device implementing the cycle, and its weight is lower. Even if the demand is more or less continuous, the intermittent production of a type of single bed system, which relates to the present invention, can be made more or continuous care by the addition of a buffer tank in the device. This characteristic is used in the present invention, but several variants can be applied to it which constitute a part of the improvement of the present invention compared to the prior art.

Common single-bed ACP systems of the prior art present the problem that the compressor capacity suffers a loss of almost 50%. In other words, when the compressor brings air to the adsorption bed in the production cycle, the capacity of the compressor is used to the full. However, when the bed is in the regeneration part of the cycle, the production of the compressor is often simply vented to the atmosphere or otherwise lost. Alternatively, the compressor could be started and stopped, but this is of course an extremely severe service for the compressor, which therefore shortens its service life. In addition, the repeated starting and stopping of the compressor in an ACP cycle raises many mechanical and technical problems. When using a centralized source of compressed air, such as when there is a significant need for air compressed in a single factory, such as a large exhaust workshop with many service halls, the problem is then simplified because the central compressed air source has its own buffer tank and the air is used in one place if it is not in another. However, even in this case, the present invention in one of its forms provides an advantage in that the single bed system is easily adapted, which allows the user to take advantage of the intrinsic advantages of these single bed systems. .

 In many cases where there is a central air source, the ACP device tends to have multiple beds and, therefore, to be large. Thus, the invention allows a new step forward in that it teaches a method for using a single bed PCA device in a factory with multiple users, having a central compressed air source.

Furthermore, it was common in the prior art to operate in ACP mode between atmospheric pressure and a pressure higher than atmospheric pressure, that is to say the working pressure of the compressor. In one of its aspects, the present invention is based on the discovery that the particular cycle used in a single-bed ACP system according to the invention operates more efficiently between the pressure of the compressor and a pressure below atmospheric pressure . This increase in operating efficiency is another advantage of the present invention over the prior art, which is an unexpected advantage.

The present invention solves many other problems of the prior art by its various combinations of cycles which provide advantages in the art.
ACP and especially in single bed adsorption systems.

A first aspect of the present invention relates to an ACP cycle which is particularly suitable for the single-bed adsorption system: this will be detailed below.

There are basically two realizations in which the cycle is used, and several characteristics and combinations of these characteristics are applicable to the two realizations.

For convenience, the two embodiments are called the high pressure version and the low pressure version.

The high pressure version is based on a conventional compressed air source. It can be either a specialized compressor that is part of the device in which the ACP cycle is established, or it can be a central source of compressed air, as is usually found in installations with several users.

The second embodiment, called the low pressure embodiment, includes a blower as the source of the supply gas.

A particular feature of this application, which is carried out around the relatively low pressure blower, is the use on both sides of the blower, the discharge at a pressure higher than atmospheric pressure and the admission to a sub-atmospheric pressure. risk. These two pressures are very advantageously used at different points in the cycle. One of the advantages is that the blower is used 100t of the time and can operate continuously. This is to be compared with previous single bed systems, in which the compressor or the source of compressed air worked under vacuum for about 50% of the cycle, that is to say during the regeneration of the bed.

In addition to the two main embodiments, the present invention also describes a certain number of characteristics which, in certain cases, are applicable to both embodiments and which, in other cases, are only applicable to the high pressure version.

Among these characteristics, mention may be made of means so that the apparatus in which the system and the cycle of the invention are incorporated operates only on demand, which constitutes a notable step forward in the art.

Until now, PCA devices have often had a timer, which worked regardless of demand.

In other words, once the machine started, it performed the first stage for so many seconds, the second stage for so many seconds, etc., and continued the cycle in this way, whether or not there was a request and what whatever the size of the demand. In the present invention, a piezo-sensitive switch is provided in close association with the holding tank in order to control the cycle according to demand.

Thus, the durations of each stage in the cycle can vary considerably and vary depending on the size of the adsorption bed, the capacity of the supply blower, as well as the importance of the demand. These demand-sensitive means can be applied to the two embodiments of the invention.

An important advantage of the invention in this regard is that one can completely eliminate the cost, assembly time, weight and other characteristics inherent in the use of such a timer, often a cam timer or an electronic timer.

Another advantage of this second embodiment is that the relatively simple low pressure blower is much less expensive and less complex than a conventional air compressor with its numerous moving parts.

Another characteristic of the invention, which can be applied to both high pressure and low pressure production, is an arrangement of two tanks, a first tank being provided for bringing into the system a gas of purge and / or equalization, and a second tank being provided as a supply holding tank in order to ensure the user a constant supply without tip. A check valve is provided to ensure this operating mode.

The following characteristic only applies to the first high pressure embodiment. This characteristic comprises a supply valve arranged essentially at the inlet of the compressed supply air into the system.

This valve is not desirable when the system operates with a specialized compressor, that is to say a compressor which is constructed to supply the apparatus of the invention and has no other function than the latter, and then it is important to unload the compressor when the bed is regenerated in order to avoid the compressor working against a closed valve. Such a configuration, i.e. the compressor working against a closed valve, would quickly damage the compressor. In addition, when the compressor is discharged, it consumes less energy, which is another advantage of the invention. However, this characteristic has the disadvantage, in common with the prior art, of wasting the capacity of the compressor. This supply valve is necessary when the invention is used in a multipurpose installation, that is to say say with a central compressor, because then the compressor never works against a closed valve, but feeds a central tank.

As stated previously, the present invention is based in part on the discovery that the operation of an ACP cycle between sub-atmospheric pressure and pressure greater than atmospheric pressure, as opposed to a cycle operating between atmospheric pressure and a pressure above atmospheric pressure, as is common in the prior art, leads to an operating cycle having better efficiency. In the second embodiment, this object is obtained by the use of the two sides of the fan. Even in the first embodiment, this operating mode is obtained by installing a venturi arranged at the outlet of the waste gases from the single bed and operating with the air at relatively high pressure of the feedstock in order to create at this exit an sub-atmospheric condition, which then literally sucks the spent gas out of the bed without the use of any individual source of vacuum.

Another characteristic of the invention is to be considered with the heat exchanger encountered in prior devices. Indeed, if a volume containing sufficient mass with suitable heat transfer characteristics and thermal capacity is installed so that the hot supply air passes through it and then the nitrogen lost in the reverse direction, it thermal equilibrium is established which eliminates or reduces the need for a heat exchanger in the supply air.

This technique also potentially eliminates the need for an individual water separator.

The invention will be better understood on reading the detailed description, given below by way of example only, of several preferred embodiments, in conjunction with the attached drawing in which - Figure 1 is a diagram of the first embodiment of the present invention; - Figure 2 is a diagram illustrating the cycle and the other characteristics of the first embodiment of Figure 1; the pressures indicated being those corresponding to the end of the stages of the cycle; - Figure 3 is a pressure curve showing the operation of the bed in the first embodiment; - Figure 4 is a view similar to Figure 1, schematically illustrating a second embodiment of the present invention; - Figure 5 is a diagram of the cycle, similar to Figure 2, illustrating the operation of the second embodiment; and - Figure 6 is a p r e s s i o n curve similar to Figure 3, but illustrating the operation of the second embodiment.

Reference is first made to FIGS. 1, 2 and 3, in which we see a first embodiment of the invention, which includes a compressor 12, the discharge of which feeds through the valve 10 the single bed of ACP 14 of the 'invention.

The compressor 12 has a relatively high discharge pressure, of the order of 414 kPa of relative pressure. All the pressures considered below and indicated in the drawing are relative pressures, the atmospheric pressure being considered to be equal to zero. The compressor 12 is a specialized compressor for the system of FIG. I, that is to say that it is a separate compressor which can be autonomous in the apparatus, but which has no other function than d 'feed bed 14. This is to be compared to multi-user installations, in which a single and important source of compressed air serves several "consumers".

In some prior systems, which are intended to be specialized systems, there is a buffer tank at the location of the valve 10 in FIG. 1. This allows samples to be taken from the buffer tank for other uses, but has the same disadvantage of wasted compressor capacity and cost, because the compressor works continuously against the relatively high pressure in such a buffer tank. Consequently, the buffer tank should not be used at the outlet of the compressor unless there is another use for air. However, if we have other uses for air, then it is no longer really a specialized system in the sense that this term is used here.

A variant of this first embodiment is a configuration in which the valve 10, the supply valve, is completely eliminated. In this case, the opening of the valve 20 in the purge phase 2 allows the adsorber to depressurize to atmospheric pressure and at the same time the output of the compressor is discharged or discharged into the atmosphere. Thus, when the valve 10 is deleted in FIG. 1, the compressor never works against a closed valve, because as long as the system performs cycles, the outlet of the compressor, or else is evacuated through the valve 20, or is used to feed the bed 14, because the valve 30 is open.

In other words, considering the column "open valves" in Figure 2, one of the valves 20 or 30 is always open and therefore the compressor never works against a closed valve.

In this case, that is to say when the valve 10 is removed, the invention prevents the compressor from working against a closed valve in all cases. At the same time, by discharging the compressor, less energy is consumed because when the purge valve 20 is open, the compressor simply discharges into the atmosphere instead of discharging against a charge. In high pressure systems without a specialized compressor, valve 10 would be provided to isolate the air supply and save the supply air.

When used, the valve 10 is of the normally closed type; it is not used with a specialized compressor.

If, for some reason, it was used with a dedicated compressor, it would remain energized and fully open during the entire cyclic process.

Thus, the compressor 12 delivers air through the pipe 16, alternately to the bed 14, or to the atmosphere through the pipe 18 and the valve 20. Another pipe 24 goes from the opposite end of the bed 14 through the valve 30, similar to the valve 20, to a supply buffer reservoir 28. A purge limitation orifice 26 is mounted in parallel with the valve 30. The final output of the product is regulated by a valve throttle 34 and a pressure regulator 36.

The valves 10, 20 and 30 are controlled by a sensitive piezo element 22 or by a predetermined timing device, via the control pipes in 40-10, 40-20 and 40-30 respectively.

The use of the pressure switch 22 is a step forward in that this can eliminate the need for the use of expensive timing devices and allows automatic deceleration of the compressor according to demand. In other words, the compressor would only have to supply pressurized air in response to the use of the product.

The following example is intended for a better understanding: the pressure switch 22 is of the differential type with adjustable reset. In service, if its upper set point is 414 kPa of relative pressure, it switches the electrical position at this time. If its preset point is 380 kPa of relative pressure, the pressure in the buffer tank 28 must drop at this point to reset the pressure switch 22. In normal operation, the pressure switch 22 allows the valve 20 to be closed and to the valve 30 to be opened during the pressurization of the bed 14 and the buffer tank 28. When the pressure rises to the set point of 414 kPa relative pressure of the
pressure switch 22, the position of the valve is reversed, the valve 20 opens and the valve 30 closes. The pressure in the bed 14 then drops to atmospheric pressure and a purge in the opposite direction of the gas produced begins with the orifice 26, which slowly depressurizes the buffer tank 28. If no product is removed by the valve throttle 34, it takes about five minutes for example to reach the lower set point of 380 kPa of relative pressure of the pressure switch 22. During this time, the compressor is evacuated in the open air through the valve 20, does not requiring only a minimum of electrical current. If the pressurization time is only 15 seconds and if the purge interval (minimum power) is 5 minutes, a "slowdown of 300/315" is achieved, or 95% when there is no load of product.This does not mean that the current consumed is only 5 of the nominal current, but that, for 95% of the time, the compressor operates without load i.e. it consumes its zero load current ; the latter varies from 15t nominal to a little more depending on the type of compressor chosen.

This "95% slowdown can be achieved for the zero charge condition as a function of an optimization of the diameter of the purge orifice 26. When a gaseous product is removed from the buffer tank 28 in addition to the purge gas, the pressure in the buffer tank drops more quickly. For a nominal product flow, for example, the reset point of 380 kPa of relative pressure can be reached in 15 seconds. In this case, the deceleration ratio for the flow of nominal or maximum product would be 15/50 or 50%.

It should be noted that, in the case of a variable demand for the product, substantial current savings can be made.

As mentioned earlier, a preset timer can be used in place of the pressure switch 22, but it must be set to meet the requirements for the full load time of the product.

As will be described in more detail below, the invention comprises two additional characteristics which can also be used at will in the apparatus of FIG. 1. These two characteristics are the venturi extractor for used gases 42 and the additional tank 56 and the check valve (see Figure 4) to ensure a regular supply.

The optional venturi extractor 42 works to create local aid at low pressure during the purge stage by using the discharge of the compressor which is also evacuated to the atmosphere. In other words, at stage 2, that is to say at the purge stage, the discharge of the compressor is simply evacuated through the venturi 42. Thus, the compressed air exits through the pipe 18 and the valve 20, but, thanks to the venturi device 42 which facilitates and accelerates the purging stage by aspirating the used gases, in particular nitrogen, out of the bed 14. As will be discussed in more detail below with regard to the second embodiment, it has been unexpectedly found that operation between a pressure above atmospheric pressure and a pressure below atmospheric pressure increases the efficiency and the ease of implementation of cycles operating in this way. This is to be compared with the conventional prior art, in which these systems operated between atmospheric pressure and pressures above atmospheric pressure.

We now refer to Figure 2, on which the duration of each stage is approximate. These times are set in response to the actual demand to which the system is subjected, as described above with respect to the pressure switch 22.

The cycle has three stages, stage "4" being in fact the start of another cycle and being identical to stage 1.

As indicated at the bottom of FIG. 2, the pressures indicated are the pressures at the end of each stage and are relative pressures, the atmospheric pressure corresponding to zero. Stage 1 is a production stage, the bed produces oxygen which is sent through the open valve 30 to the reservoir 28. This continues until the pressure in the reservoir 28 reaches the preset switching point, at namely 380 kPa in the example considered. At this time, the cycle advances to stage 2, in which an auxiliary current arriving through the orifice 26 is allowed to pass in the opposite direction through the bed 14, downwards in FIG. 1, to sweep the nitrogen out of the bed, by line 18, extractor 42, iu valve now open 20 to escape to the atmosphere.

This stage continues for a relatively short time, 15 seconds in the example considered. The next stage 3 is an equalization stage, in which the valve 20 is closed, the valve 10 is reopened to bring feed gas to the bed 14, and the system re-pressurizes until equalization. After equalization, the current is automatically reversed through the line 24 and the valve 30 now open to start production stages 1 and 4.

Referring to Figure 3, we see the pressure in the bed 14 throughout the cycle. It is significant that the very brutal fall which occurs at the point 30 seconds, that is to say at the time of the purge, occurs very quickly.

This allows more efficient use of the purge gas.

This sudden drop is obtained by the use of relatively large valves to obtain this rapid flush.

As it appears from FIGS. 1 and 2 and from the preceding description, it can be seen that the valve 20 has two purposes.

During the purge stage 2, in this first embodiment in which the compressed gas is at high pressure, the valve 20 allows both the depressurization of the bed 14 to the lowest pressure (which is the atmospheric pressure in the figure 2 or which may be subatmospheric if the optional venturi extractor for used gases 42 is provided), and also the evacuation to the atmosphere of the discharge from the compressor 12. The two functions of "purging" of the bed and "unloading" of the compressor are carried out simultaneously and through this single valve 20.

This double service of the valve 20 is another important step forward of the invention and increases by comparison with the prior art the advantages of this invention, namely: low cost, fewer parts, greater reliability, reduced weight, lower cost manufacturing, etc.

Referring now to Figure 4, we will describe in detail the second embodiment. The identical, equivalent or similar parts to those described above in relation to FIG. 1 are identified by the same references, increased by 100.

The embodiment of Figure 4 is constructed around a blower 44 which can be any one of various different types.

Figure 3 shows the variations in pressure in bed 14 and relates directly to the cycle diagram of Figure 2. Figure 3 is understood relatively well itself and we can clearly see the sudden drop in total pressure pressure purge at point 32 seconds.

 Referring now to FIG. 4, this low pressure version is built around the blower 44.

Atmospheric air is sucked from the inlet side of the blower through a pipe 46 through which the air flow is regulated by a valve 110, which is controlled by the pressure and control controller 122. Between the suction side of the blower 44 and the valve 110t a pipe 48 enters the pipe 46 as a variant for supplying air to the inlet side of the fan. The flow rate through the pipe 48 is regulated by a valve 70, itself controlled by the switch 122.

The discharge or superatmospheric side of the blower 44 supplies its flow through a pipe 116 which enters a heat exchanger 52. The pipe for venting the system 118 is derived from the pipe 116 between the fan 44 and the heat exchanger 52. The venting is controlled by a valve 120, itself controlled by the switch 122.

After the heat exchanger 52, the flow rate in the pipe 116 is regulated by a valve 60, which feeds the pipe 48, which returns to the inlet side of the blower 44, as shown. In addition, the valve 60 in the pipe 116 regulates the flow arriving at the inlet of the bed 114.

The flow rate in the outlet pipe of the bed 124 is regulated by a valve 130 which, in turn is controlled by the switch 122. The orifice 126 is indicated in dashes, because it is an optional feature in the production of this figure 4.

Since a single bed ACP system has swings and irregularities in the output product flow, the invention has an optional feature to provide constant supply and to regulate the supply of the product. For this purpose, a check valve 54 is provided in the pipe 124 and an equalization tank 56 between the valves 54 and 130. The equalization tank 56 is connected in the pipe 124 between these two valves 130 and 54.

After the buffer tank 128, the components are the same as those described in the embodiment of FIG. 1, the marks having been increased by 100.

Referring now to FIG. 5, we see a cycle diagram for the apparatus of FIG. 4. This cycle diagram generally corresponds to the first embodiment of the system of the invention shown in FIG. 2.

He has in common with him that the times indicated are only approximate, these times being obviously controlled by 1 ecommutate ur depression and control 122, in the same way as has been described above with regard to the component similar 22 in FIG. 1.

In the first stage, the system being in production, the valve 110 is open and the valve 70 is closed, therefore the blower 44 sucks in atmospheric air. The valve 120 is closed and therefore the current flows through the line 116 and the open valve 60 to the bed 114 which produces the desired gas. The valve 130 is open to allow the gaseous product to pass to the equalization tank 56 and to the buffer tank 128. The check valve 54 serves to prevent a return out of the buffer tank when the cycle begins the second stage, namely the purge. The equalization tank 56 then supplies gas for this purpose and the check valve 54 isolates the buffer tank 128 in order to serve the consumer. Because the tanks 56 and 128 are at the same pressure, the outlet of the tank 56 cannot open the non-return valve 54 against the equal pressure in the tank 128 and, therefore, this gas is used to purge the bed 114.

In purge stage 2, the valves 110, 60 and 130 close and the valves 70 and 120 open; therefore, the blower draws air from the equalization tank 56 through the orifice 126, in opposite direction through the bed, then through the valve 70 to the inlet side of the blower 44 and from there through the now open vent valve 120.

we can thus see how the blower 144 works with a 100% efficiency, that is to say that it operates continuously. In the first stage, it supplies air at a pressure higher than atmospheric pressure, which is brought to bed 114. In the next purging stage, the intake side of the blower 44 is used and the used gases are literally sucked out from bed 114 and sent to the atmosphere through the vent valve 120. It should also be noted that, and this appears more clearly in FIG. 6, the purging stage is carried out starting from a super pressure. atmospheric pressure of 103 kPa and the pressure drops to an atmospheric pressure of -55 kPa. It has been found that the operation between a super-atmospheric pressure and a sub-atmospheric pressure increases the operating efficiency, the flow rate in general and improves the ACP cycle operating in this way. This improvement is a significant step forward compared to the prior art, in particular when it is coupled with the low pressure and low cost blower 44 of this embodiment.

Claims (14)

Claims  1. Pressure switching adsorption machine, characterized in that it comprises a single bed (114) and gas supply means, these gas supply means comprising a low pressure blower (44 ). 2. Machine according to claim 1, characterized in that it comprises means for performing a cycle ACP, this cycle comprising at least a first stage in which supply gas is supplied to a single bed and a second stage in which purge gas is circulated outside this single bed, means for using the blower for practically 10-0% of its operating time, this blower having a relatively higher pressure supply side and a relatively lower pressure suction side, this machine comprising means for venting (118, 120) , conduit means (116) connecting the side of the relatively higher pressure blower to the single bed to effect the # first feeding stage, and conduit means for connecting the side of the relatively lower pressure blower to the single bed and to the venting means for carrying out the second stage of purging. 3. Machine according to claim 1, characterized in that means are provided so that the pressure decrease which occurs in the bed during the purge at the second stage takes place quickly. 4. Machine according to claim 1, characterized in that it operates according to an adsorption cycle by pressure switching with multiple stages and in that rhythm means are provided for controlling the duration of each stage in the cycle. 5. Machine according to claim 2, characterized in that the single bed is subjected to a high pressure, a low pressure and an intermediate pressure and that its low pressure is sub-atmospheric. 6. Machine according to claim 3, characterized in that it comprises heat exchanger means (52) and means for positioning this heat exchanger so that a heat exchange takes place between the gas supplied to the single bed and the purge gas coming out of this bed. 7. Machine according to claim 4, characterized in that pressure equalization tank means (56) are associated with the outlet of the gaseous product from the single bed. 8. Machine according to claim 5, characterized in that the air is the gas treated by this ACP cycle and in that the oxygen is the gaseous product. 9. Machine according to one of the preceding claims for separating oxygen from the air, characterized in that it comprises a single bed (114) of adsorbent material, a buffer tank (128), a low pressure blower ( 44) having a supply side and a suction side for supplying ambient air to this single bed from its supply side, the single bed having a first end and a second end, these two ends being able to serve both gas inlet and gas outlet from the single bed, venting means (118, 120), duct means (116) connecting together the blower, the venting means and the first end of the bed ; valve means (60) in the duct means, control means (122) for these valve means, means for removing oxygen from this single bed via the second end, the duct means being arranged and controlled by the valve means so that the suction side of the blower is connected to the single bed during a purge stage to suck the used gases out of the bed and direct these used gases to the setting means open air, which results in the blower being used almost 100% of the time the machine ACP works, acting both to supply air during the production stages and to remove waste gases during the purge stages. 10. Machine according to claim 9, characterized in that it comprises means (128) for the gas product reservoir and in that the control means (122) comprise means for measuring the pressure of the gas product in these means of tank, from which it follows that the machine operates in response to the demand for gaseous product coming from the tank means rather than as a function of predetermined durations for each stage of its operating cycle. 11. Machine according to claim 9, characterized in that it comprises means for operating the cycle between the high pressure, the low pressure and the intermediate pressure, the system comprising reservoir means for receiving the gaseous product leaving the bed single, the cycle comprising a production stage in which the pressure in the bed and in the reservoir means is increased from the intermediate pressure to the high pressure, a purge stage in which the pressure in the bed is reduced by this high pressure up to the low pressure, and a pressure equalization stage, in which the pressures in the bed and in the reservoir means are made equal to the intermediate pressure.  12. Machine according to claim 9, characterized in that it comprises heat exchanger means (44) and means for positioning these heat exchanger means so that a heat exchange takes place between the gas brought to the single bed and the purge gas leaving this single bed. 13. Machine according to claim 9, characterized in that it comprises rhythm means for controlling the duration of each stage in the cycle. 14. Machine according to claim 9, characterized in that pressure equalization tank means (56) are associated with the gaseous product output of the single bed.