EP0888164A1

EP0888164A1 - Method and device for selectively separating at least one component from a gaseous mixture

Info

Publication number: EP0888164A1
Application number: EP97906050A
Authority: EP
Inventors: Jacques Ribesse
Original assignee: TAMOX SPRL
Current assignee: TAMOX SPRL
Priority date: 1996-03-04
Filing date: 1997-03-04
Publication date: 1999-01-07
Also published as: WO1997032656A1; BE1010028A6; AU2088197A

Abstract

A method and a device for selectively separating at least one component from a gaseous mixture by adsorption using at least one adsorbent material (7) selected according to the gaseous mixture and the components thereof to be selectively separated. The method comprises naturally feeding the gaseous mixture by suction into a container (1-4) in which the adsorbent material (7) has previously been desorbed and the internal pressure is at a predetermined vacuum level, pressure feeding the gaseous mixture into the same container (1-4) to cause complementary adsorption, and simultaneously removing the non-adsorbable component(s) from said container (1-4), and generating a predetermined vacuum inside the container (1-4) while feeding in a counter-flow of a predetermined amount of the previously produced unadsorbed component(s).

Description

"Method and device for the selective separation of at least one component from a gas mixture"

The present invention relates to a process for the selective separation of at least one component from a gas mixture by adsorption using at least one adsorbent material chosen as a function of the gas mixture and of its components to be separated selectively. Prior state of the art

The separation of gases by selective adsorption on adsorbent material, possibly on molecular sieves, and by pressure fluctuations is a well-known technique, which has been widely developed since 1970 and is covered by numerous patents.

An example of a commonly used PSA (Pressure Swing Adsorption) system is shown in FIG. 1 and comprises two or three reservoirs A, B, C, filled with specific adsorbent material (s). A gas blower to be treated D feeds one of the tanks A, B, C, by opening the corresponding valve E. The gas to be treated (for example air) passes through one of the tanks, for example A, in which the gas to be rejected is adsorbed, the non-adsorbed gas (for example oxygen) leaves the tank A via the valve FA open at this time, and the tank G, towards use. During this operation, the reservoir B is evacuated by means of a vacuum pump H via the corresponding valve IB. The adsorbed gas (for example nitrogen) is thus partially removed.

Likewise, the reservoir C, previously evacuated, is filled by introducing pure gas via the valve FC, the corresponding valve IC being closed. With this operation, the adsorbed residual gas is discharged down from the tank C, the upper part of the tank C being completely desorbed. This operation is "repressu¬ risation". After a fixed period of time, the circuits are inverted, i.e. gas to be treated towards the tank B, evacuating the tank

C and repressurization of reservoir A, at a constant rate of approximately

30 seconds for example, by operating the corresponding valves E, I, F, thus obtaining almost continuous operation

The evolution of the pressures in the tanks is shown in Figure 2.

J1 Introduction of raw gas under pressure and production of pure gas, J2 Desorption of adsorbed gas by vacuum, J3. Repressurization using pure gas.

Disadvantages of known systems as described above 1) High consumption of energy absorbed by overpressure machines, and especially by the vacuum pump

It is indeed necessary to carry out a vacuum at very low absolute pressure level to desorb an appreciable quantity of adsorbed gas to be rejected. This appears in FIG. 3 representing the characteristics of gas adsorption for a molecular sieve or adsorbent material. specific for nitrogen adsorption from air The partial pressure P of the gases is plotted on the abscissa and the mass M of gas adsorbed on the ordinate.

The distribution in atmospheric air is of the order of 80% nitrogen (N ₂ ), gas to be adsorbed, for 20% oxygen (O ₂ ). So, for a crude gas (or air) pressure of 1.2 bar, the partial pressure of nitrogen is of the order of 0.95 bar and there corresponds a mass of nitrogen ni and that of oxygen is of the order of 0.25 bar and it there corresponds an oxygen mass o1

If for the desorption, a vacuum of 0.15 bar is carried out, the partial pressure of the nitrogen is then 0.135 bar and this provides a desorption up to level n2 The mass of gas actually desorbed from the adsorbent material is therefore n1-n2 and a significant amount of energy must be spent on the vacuum pump H to create the vacuum of 0.15 bar 2) A high frequency is imposed on the valves E and I which equip the reservoirs, FIG. 1, and which operate approximately every 30 seconds at least, and therefore perform approximately one million operations per year, while the molecular sieve allows a significantly higher frequency of operations. As a result, the quantity of molecular sieve, an expensive material, to be used is very high. In addition, the maintenance cost of these valves E and I, which are highly mechanically stressed when it comes to valves for high flow installations, is very high.

3) The known systems include six valves of large dimensions and operating at high frequency for the dimensions used; this constitutes a limitation of the production capacity of the known units, for example to a limit of ± 100 T / d of pure gas for the case of oxygen, beyond which the unit cost of the equipment becomes prohibitive. 4) The speed of passage of the gases in the molecular sieve or adsorbent mass, at the right of the injection of gas to be treated and at the outlet of the desorbed gases, is very high. This leads to an erosion of the adsorbent mass. Indeed, the mass of desorbed gas can represent approximately ten times the mass of pure gas produced. In addition, these large variations in the flow rate of gases in the molecular sieve do not allow rational use of the adsorption / desorption properties of these materials.

5) Other PSA systems have been patented, for example that of US-A-2,033,777, the system of which is composed of eight containers and two flat rotary valves ensuring the distribution of gases. This long cycle system (45 seconds) requires a high amount of molecular sieve (expensive) and uses a two-stage vacuum system, up to 0.04 bar, therefore results in high energy consumption.

Although rotary valves replace the many necessary slide valves, they include sliding plates which must be provided with special and complex means, not described, to ensure sealing. 6) Another example is the subject of US-A-5,133,784. The system described therein comprises twenty-four containers in the form of rotating segments around a fixed gas distribution device. This fast cycle system provides molecular sieve gain due to speed. It is however very complex and consumes an amount of energy as high as the other known conventional systems. It has a fixed distributor which must supply the twenty-four rotating containers and which each have two openings. The systems ensuring sealing are not described.

The object of the present invention is to remedy the drawbacks of known techniques and methods, and in particular: to significantly reduce energy consumption by more than 20%, to reduce the mass of expensive adsorbent material by more than 40%, to reduce maintenance costs and improve the reliability of the gas separation device, - reduce the investment costs of the units.

The process of the invention has no technical limitation as regards production capacity, it makes it possible to produce units of all sizes, which are largely competitive with giant cryogenic systems.

To this end, the process of the invention comprises the following four phases carried out periodically, successively in the order below, in the same container comprising the adsorbent material, the phases being specific and essential to the whole process:

a natural admission by suction of the gaseous mixture into the container whose adsorbent material has been previously desorbed and whose internal pressure has been brought beforehand to a determined vacuum level, the admission being maintained until the internal pressure arrives at a value close to, but lower than, atmospheric pressure, partial adsorption thus taking place during this admission,

- then admission under pressure of the gas mixture into the same container, giving rise to additional adsorption, and simultaneously to evacuation from the container, of the non-adsorbable component (s), until a determined pressure is obtained, higher than atmospheric pressure, a setting under a determined vacuum of the interior of the container, giving rise to partial desorption and evacuation of the component or components previously adsorbed by the adsorbent material, and

- by continuing said defined vacuum, an introduction, against the current, of a determined quantity of the non-adsorbed component or components produced previously, to give rise to a lowering of the partial pressure of the component or components previously adsorbed and still present , so as to cause additional desorption and evacuation of the adsorbed component (s). For convenience, we call this phase "rinsing", not to be confused with scanning by repressurization, because this phase according to the invention operates under vacuum.

According to one embodiment of the invention, the above four phases are carried out periodically in four containers of the same capacity and, while a first container is subjected to natural admission, a second is subjected to admission under pressure, a third is subjected to determined vacuuming and a fourth is subjected to introduction against the current and under vacuum.

Advantageously according to the invention, a duration of a cycle of the four phases is divided into four quarters of equal duration for each phase and a quarter of duration is chosen so as to be less than a time limit for saturation of the adsorbent material contained in a container and not by the mechanical strength of the devices.

According to a preferred embodiment of the invention, when the gas mixture is atmospheric air, the adsorbable components being nitrogen, carbon dioxide and water, and the non-adsorbable components are oxygen and argon, the determined vacuum is between 0.2 and 0.5 bar absolute and is preferably of the order of 0.3 bar absolute; then the determined pressure higher than atmospheric pressure is advantageously between 1, 1 and 2 bars absolute and is preferably of the order of 1, 2 bars absolute. According to another preferred embodiment of the invention, when the gas mixture is atmospheric air and the adsorbable component is oxygen, the non-adsorbable component being nitrogen, then the determined pressure greater than atmospheric pressure is advantageously between 2 and 7 bars absolute and is preferably of the order of 4 to 6 bars absolute; the determined vacuum is then between 0.3 and 0.7 bar absolute and is preferably of the order of 0.5 bar absolute.

According to another advantageous embodiment of the invention, for the adsorption, a passage of the gas mixture is arranged so that it circulates at practically constant speed through the adsorbent material, compensating for its loss of component ( s) adsorbable (s) by a progressive reduction in the cross-section of passage through the adsorbent mass, and for desorption, a passage in the opposite direction of the gaseous components is arranged through the adsorbent material so that they circulate at a speed that is also practically constant, as a function of the gradual increase in the volume of gas desorbed.

The present invention also relates to a device for implementing the method according to the invention.

The device of the invention comprises: - a blower for producing the determined pressure higher than atmospheric pressure, a vacuum pump for producing the evacuation, an atmospheric air intake and a collector of component (s) not adsorbable (s),

- four identical separate containers, intended to receive the adsorbent material (s),

a rotary distributor of the new type, arranged for a sequential and selective communication of each container and at least the entry of atmospheric air, of the blower and, according to two respective paths according to the phase in progress, of the vacuum pump, and - control and drive means for the periodic rotation of the rotary distributor. According to the invention, in the above-mentioned device:

each container comprises a gas mixture admission chamber on one side of the adsorbent material and a discharge chamber of the non-adsorbable component or components on the other side of the adsorbent material, an intake grid between the material adsorbent and the intake chamber and a discharge grid parallel to the intake grid and arranged opposite the adsorbent material, between the latter and the discharge chamber,

- The intake grid has a passage surface of the gas mixture greater than a passage surface presented by the discharge grid, the adsorbent material having a regular and progressive variation in cross section, from the corresponding dimensions of the grid. intake up to the corresponding dimensions of the discharge grid, - optionally a separation grid is provided each time between two different adsorbent materials and is arranged parallel to the intake and discharge grids,

- Preferably, the passage of the gas and the aforementioned passage surfaces are arranged so that during adsorption, on the one hand, the gas mixture entering through the intake grid and progressing in the adsorbent material and, on the other hand, the non-adsorbable component (s) discharged through the discharge grid have a practically constant speed and so that during desorption, a passage in the opposite direction of the gaseous components also takes place at a practically constant speed,

- a periodic and selective communication of each container and the collector of non-adsorbable component (s) is carried out, either by another rotating distributor or by a pair of valves controlled periodically, in rhythm with the distributor turning point cited first, by the appropriate control means.

According to a preferred embodiment of the invention, the four containers are four independent tanks, cylindrical or frustoconical. According to another preferred embodiment of the invention, the four containers are four separate compartments formed in a common enclosure by partition walls, the enclosure preferably being cylindrical, the compartments then forming truncated sectors around the axis of cylinder

According to an advantageous embodiment of the invention, the dispenser comprises

- five stages arranged one next to the other in the direction of the axis of rotation, - a stator for selective connection

- to the blower on a first stage,

- at the entry of air at atmospheric pressure to a second stage,

- the vacuum pump on a third stage,

- to the vacuum pump, via a buffer tank and a non-return valve, on a fourth stage,

- to each of the receptacles on a fifth so-called connecting stage, the latter preferably being arranged in the middle part of the dispenser,

a rotor with internal channels, parallel to the axis of rotation, for the selective and periodic communication of each container connected to the fifth stage and respectively,

- the entry of atmospheric air through a first channel,

- from the blower by a second channel,

- the vacuum pump via a third channel,

- from the buffer tank by a fourth channel, the stator comprising on each stage, for the selective connection, four orifices opening inwards and arranged at 90 ° from one another and the rotor comprising, at the connecting stage to the four containers, four orifices located at 90 ° from one another and opening towards the outside so as to be able to put in communication a container and a corresponding channel according to the process phase to be carried out in a container and, on each other stage, a single orifice arranged to put a corresponding channel in communication with an orifice of the same stage of the stator according to said process phase According to a particular embodiment of the invention, - an annular seal is arranged between each stage to make a seal between two stages, this seal preferably being carried by the stator, and - between two orifices of the connecting stage in the containers, there are each at least one and preferably two sections of seal extending from one annular seal to the other and each arranged near an orifice of this stage, each joint section preferably carried by the stator. According to an advantageous embodiment of the invention, in order to best avoid unauthorized gas passages between two orifices of the stage of connection to the receptacles, in addition that between each stage there is arranged an annular seal to achieve a sealing between two stages, this seal preferably being carried by the stator, at the place where each conduit connecting to a container opens into the stator of the distributor, a sealing ring is arranged each time

* which is mounted so as to be able to slide in leaktight manner in the duct, along the axis thereof, and so as to be able to be brought into abutment by one of its ends against the rotor, * whose end in abutment against the rotor is shaped to the diameter of the rotor in order to conform to the shape and ensure a tight contact therein and is open to enter into selective communication of gas passage with a respective orifice of the rotor,

* whose other end opens in the conduit and * which is pushed, at least in service, by means against said rotor for sealing.

According to a particularly advantageous embodiment of the invention, the intake and / or evacuation and / or separation grids have passage holes whose circumference is each time a frustoconical surface pierced at the point which it - even is directed towards the adsorbent material, avoiding blockage by the adsorbent material. According to a particularly preferred embodiment of the invention, the seals and the seal sections are grooves longitudinalemeπt either on their face facing the rotor when they are carried by the stator or on their face facing the stator when carried by the rotor, so as to cause a labyrinth effect for any gas between two contiguous stages of the distributor

According to the invention, frustoconical containers are preferred for the production of nitrogen as a non-adsorbable component and they preferably have a ratio of 0.6 to 0.8 between their base diameter and that of the top and a ratio of 0, 8 to 1, 5 between their average diameter and their height, these frustoconical containers being further advantageously arranged so that their axes of revolution are vertical.

According to another feature of the invention, the four orifices of the rotor, on the connecting stage of the containers, are formed by numerous orifices with rounded edges.

According to an additional feature of the invention, a buffer tank and a non-return valve allow the realization of the vacuum rinsing phase against the current via the vacuum pump, without interfering with the evolution of the suction pressure of this same vacuum pump during the previous desorption phase by setting a specific vacuum

Other details and particularities of the invention will emerge from the secondary claims and from the description of the drawings which are annexed to the present specification and which illustrate, by way of nonlimiting examples, embodiments of the method of the invention and embodiments of the device of the invention for implementing the method thereof

Figure 1 shows schematically the known PSA device or system, explained above

FIG. 2 represents the evolution of the pressure (P) in bar, on the ordinate, as a function of time (t) in seconds, on the abscissa, in the reservoirs of FIG. 1, during the steps carried out in the case of the device or system of this figure 1 FIG. 3 represents the paces of the curves giving the adsorbed masses (M) of oxygen and nitrogen as a function of their partial pressures (P) in bar, in the case of an adsorbent material favorable to the adsorption of 'nitrogen. FIG. 4 schematically represents, in an elevation view, a device of the invention for implementing the method of the invention.

FIG. 5 schematically represents, in a plan view, the device of FIG. 4. FIG. 6 represents the evolution of the pressure (P) in bar, on the ordinate, as a function of time (t) in seconds, on the abscissa , in the reci¬ pients of Figures 4 and 5, during the steps carried out in the method of the invention.

FIG. 7a represents, seen from the inside, a development, parallel to the axis of rotation, of an embodiment of a stator used for the implementation of the method of the invention.

FIG. 7b represents, seen from the outside, a development, parallel to the axis of rotation, of an embodiment of a rotor to be used with the stator of FIG. 7a. FIG. 8 schematically represents, in axial section, an embodiment of a container used for the implementation of the invention.

FIG. 9 schematically represents, in axial section, another embodiment of a container used for the implementation of the invention.

FIG. 10 schematically represents in axial section a variant of a dispenser according to the invention.

In the various figures, the same reference notations designate identical or analogous elements. Figures 4 and 5 show a device according to the invention.

This new device comprises four cylindrical containers 1 to 4 equipped with separation grids 5 and 6 between which are the molecular sieves 7 used for the adsorption and desorption of gases under the effect of programmed variations in pressure. These adsorbent materials 7 are composed of specific materials depending on the nature of the gases to be adsorbed, for example H ₂ O, N ₂ or O ₂ , etc.

A gas distributor 8 is composed of a stator 9 and a rotor 10 The latter is driven in a sequential rotary movement by a motor device 11 (by successive quarter turns)

A gas blower to be separated 12 sends the gas to a stage of the distributor 8 Likewise, an incorporation pipe by suction of gas to be treated is connected to another stage of the distributor 8 via the conduit 13

A vacuum pump 14 is connected to the distributor 8, on the fourth floor

A fifth stage of the distributor 8 collects the gases from the high desorption, explained below, via the conduit 15, the reservoir 16, the non-return valve 22 and the vacuum pump 14

The pure gas leaves one of the containers 1 to 4 via valves 17 and is collected in a tank 18 before use. In addition, it is carried out reverse rinsing of the molecular sieves or adsorbent materials 7 by incorporation of pure gas by means of valves 19 Although this does not appear in the diagrams of Figures 4 and 5, valves 19 are part of a flow control system while valves 17 are not part of it The four containers are connected to the part distributor central 8 via pipes 20 and filters 21

The gas distributor 8 is divided into five stages The rotor 10 and the stator 9 are provided with gas passage orifices and circular and vertical seals described below The rotor 10 is internally divided into four longitudinal compartments a, b, c , d

Operation

Part of the gas to be treated is introduced by natural aspiration into a container 4, for example under vacuum via a conduit 13, the distributor 8, the internal conduit d, the conduit 20 and the corresponding filter 21 This container was previously under vacuum (approximately 0.3 bar absolute) The gas to be treated fills container 4, from the periphery towards the center, and its pressure rises gradually to a value close to atmospheric pressure A large quantity of gas is adsorbed in the molecular sieve 7, without removal of the non-adsorbed gas

Simultaneously, another part of the gas to be treated is introduced into the next container 1 via the blower 12, the upper stage of the distributor 8, the internal channel a of the rotor 10, the corresponding conduit 20 and the filter 21 This gas increases the pressure in the container 1 and the adsorption of gas components continues there This gas passes through the container 1 from the peripheral part towards the center The non-adsorbed gas (pure gas) is collected thanks to the grid 6 placed in the center and is directed outwards via valve 17 and tank 18, and towards use

Simultaneously, the adsorbed gases contained in the molecular sieves of the reservoir 2 are desorbed, by suction using the vacuum pump 14 via the conduit 20, the filter 21, the distributor 8 and the internal channel b of the rotor 10 The pressure is therefore gradually lowered in this tank 2

Simultaneously, the final desorption of the gases contained in the molecular sieves 7 of the reservoir 3 already vacuum is carried out, by incorporation of pure gas via the corresponding valve 19 This gas strongly lowers the partial pressure of the gas adsorbed in the molecular sieve 7 and rejects the latter to the vacuum pump 14 via the conduit 20, the filter 21, the distributor 8, the internal channel c, the conduit 15 and the intermediate tank 16 which is maintained under a certain regulation vacuum thanks to the action d 'a non-return valve 22 It can be seen in Figure 6, that the non-return valve 22 opens at point R of phase L4 when the pressure R' of phase L3 has become sufficiently low, about 0.5 bar

After a period of time defined by the adsorption / desorption kinetics of the molecular sieve 7, ie 5 to 15 seconds, the rotor 10 of the distributor 8 is rotated by 1/4 of a turn and the role of the containers is thus changed gas to be treated aspirated to container 1, gas to be treated blown to container 2, partial desorption of container 3, final desorption by rinsing with pure gas under vacuum of container 4 Figure 5 gives a representation of the evolution of pressures in containers 1 to 4

L1 filling of gas to be treated in a container by suction, gas adsorption, L2 injection of the supplement of gas to be treated with overpressure, additional adsorption of gas and emission of pure gas, L3 desorption of gas contained in molecular sieves 7 by suction of the vacuum pump 14, L4 total desorption of the molecular sieve by reverse vacuum sweeping using pure gas

It should be noted that the vacuum necessary to ensure the desorption of the gases contained in the molecular sieve 7 will be less high, according to the invention, than in known systems, sott a vacuum pressure of 0.3 bar absolute instead of 0, 15 bar absolute, see Figure 3 As an example vacuum pressure = 0.3, partial pressure of residual nitrogen N ₂ = 0.27 bar, hence the quantity of residual gas adsorbed = n3

By vacuum sweeping with pure gas, the partial pressure of residual nitrogen N ₂ becomes 0.1 bar, hence the quantity of residual nitrogen becomes equal to n4 The gas actually desorbed by the molecular sieve becomes n1- n4 which is larger than n1-n2 It follows that for an energy expenditure of the vacuum pump operating at 0.3 bar absolute, better performance is obtained than that obtained in conventional systems operating at 0.15 bar absolute. as a consequence, there is a considerable gain in energy In addition, only part of the gas to be treated, ie 50%, must be overpressed. This results in an additional gain in energy consumed The gas distributor

A particular form of the distributor 8 is shown and it constitutes an essential part of the device of the invention since it ensures an operation adapted to the kinetics of adsorption / desorption of the molecular sieve 7 and to the carrying out of the specific cycles of the process invented.

Figures 4 and 5 and Figures 7a and 7b give the representation of a distributor 8 applied to the invention The rotor 10 has longitudinal partitions forming channels a, b, c, and d (Figure 5).

The distributor 8 comprises five stages separated by annular seals 23. Four stages correspond to the four phases of the process and the central stage distributes the phases to the containers. On the central floor, there are 24 "vertical" seals to seal between the containers. Splitting the vertical joints 24 eliminates a short circuit during the rotation of the distributor 8 and, moreover, halves the rate of leaks. As a variant, at least at the point where each conduit 20 connecting to a container 1 to 4 opens into the stator 9 of the distributor 8, a sealing ring 30 can be arranged each time mounted so that it can slide so sealed in the conduit 20, along the axis thereof. The sliding is provided so that the ring 30 can be brought into abutment against the rotor 10 by one of its ends which is shaped to the diameter of the rotor 10, to conform to the shape and to ensure there a sealed contact, and which is open to be able enter into selective gas passage communication with a respective orifice of the rotor 10. The other end of the ring 30 opens in the corresponding conduit 20 (provided for example with a connection flange 31).

The sealing ring 30 is pushed, at least in service, by means 32, such as a helical spring, against said rotor 10 for sealing. A person skilled in the art is able to choose the material or materials best suited for the ring 30 and for the seal which it must provide in order to also eliminate any leakage and / or a gas short-circuit from a orifice thus equipped towards another orifice of the distributor 8 during the rotation of its rotor 10.

The rotor 10 is stopped during the running time of each phase, then performs a rotation of a quarter turn in less than a second. The average speed of rotation of the distributor 8 is of the order of one revolution per minute. This system therefore makes it possible to apply short phase times, linked to the adsorption / desorption performance of the molecular sieve 7. It should be noted that the parts of the rotor 10 in contact with the seals 23, 24, if necessary the sealing rings 30, are filled with a layer of ceramic oxide of very hardness, layer treated by polishing to reduce the forces. friction (shaded in Figure 7b) Constant speed gas transfer container

A particular feature of the invention is the distribution of the gas within the adsorbent masses 7 A particular form of distribution of the gases in the containers 1 to 4, particularly for the production of oxygen from the air, is explicit in view of Figure 8 The gas to be treated is introduced into the container via a pipe 20 through the periphery A special grid 5 of large area allows the gas to be distributed homogeneously, at low speed in a first adsorbent mass 7A, to retain a elements of the gas, H ₂ O for example The grid 5 has special characteristics, and in particular has conical holes whose tip is turned towards the adsorbent material and is pierced, so as to prevent any obstruction of these orifices by the adsorbent mass 7 The gas continues to run horizontally and passes through a grid 25 separating the adsorbent material 7A from another adsorbent material 7B which r is a component of the gas, N ₂ for example After adsorption of this gas, the pure gas (not adsorbed) is collected in the central space produced by a grid 6 having the same characteristics as the grid 5 According to this particular embodiment, the gas passes through the adsorbent mass 7 at constant speed, which prevents the material constituting these masses 7A, 7B from crumbling and improves the kinetics of adsorption / desorption operation The ratio between the quantities of gases entering and leaving the container and the pure gas is 10 to 1 for the production of oxygen and argon from atmospheric air Another particular form (not shown) of containers is produced in a single enclosure, divided into four sealed compartments by vertical walls Other types of receptacles will be produced preferably, in the case of separation of a component with a low concentration of gas, for example for the production of nitrogen as pure gas. In the latter case, the passage of gases can be vertical in a cylindrical container or slightly conical (Figure 9) and of low height.

The arrows in FIGS. 8 and 9 indicate the direction of flow of the gas to be separated, arriving via line 20, and of pure gas, also said to be non-adsorbable, during the adsorption phases. The term “non-adsorbable component (s)” means the component (s) which it is wished to leave through the reservoir 18 and lead to what is called use. It goes without saying that there can always be a relatively weak adsorption of the non-adsorbable component (s).

In the case of nitrogen production (then considered as a non-adsorbable component), oxygen being considered as a component to be adsorbed, it is preferable to make a seven-stage distributor, the two additional stages then serving to replace the valves 17 and 19 and to fulfill their functions in the same way as the other stages already explained.

Those skilled in the art know well in which case of adsorbent material one can call it "molecular sieve" and he will have no difficulty in understanding that the two meanings have been used in parallel to demonstrate that the invention applies in either case.

The orifices provided in the stator 9 and rotor 10 for the selective matching of the receptacles 1 to 4 with specific gas conduits via the channels a, b, c and d need not be better described. It can be specified, however, that to facilitate the passage of the "vertical" seals 24, it is advantageous that the orifices 26 (FIG. 7b) of the central stage of connection to the containers 1 to 4, on the rotor 10, are formed of several circular holes, like a colander. The orifices 27 of the other stages do not pose any problem of passage of seals and can be formed in various ways depending on what the skilled person considers best suited to the case in hand. The seals 23 and 24 are shown fixed on the stator 9 They can however just as easily be mounted on the rotor 10 They preferably have, on the side of the element on which they are not fixed but on which they rub, grooves longitudinal forming labyrinths for gas tending to pass from one floor to another

It should be understood that the invention is in no way limited to the embodiments described and that many modifications can be made to these without departing from the scope of the present invention.

Thus, the containers, tanks, distributors, etc., can occupy, as the case may be, the necessities and the choice of the person skilled in the art, a position different from the vertical position shown in FIGS. 4, 5, 7a, 7b, 8 and 9 quantified advantages of the method and the devices according to the invention

The following table gives a comparison between the performance of known PSA systems and that of the process according to the invention in the case of air separation for the production of oxygen. There is a better use rate of the molecular sieve (55% ), a significant energy saving (from 24 to 26%), a construction cost lowered by 20% and the possibility of building large units

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Comparative performance

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Claims

1. Process for the selective separation of at least one component from a gas mixture by adsorption using at least one adsorbent material (7) chosen as a function of the gas mixture and its components to be separated selectively, the process comprising the four following phases (L1 to L4) carried out periodically, successively in the order below, in the same container (1-4) comprising the adsorbent material (7), the phases (L1 to L4) being specific and essential for whole process: - a natural intake (L1) by suction of the gas mixture into the container (1-4) whose adsorbent material (7) has been previously desorbed and whose internal pressure has previously been brought to a vacuum level determined, the admission (L1) being maintained until the internal pressure reaches a value close to, but lower, at atmospheric pressure, a partial adsorption thus taking place during this admission (L1 ),

- then an admission under pressure (L2) of the gaseous mixture into the same container (1-4), then giving rise to additional adsorption, and simultaneously to an evacuation from the container (1-4), of the non-adsorbable component (s) , until a determined pressure, higher than atmospheric pressure, is obtained,

- placing under a determined vacuum (L3) inside the container (1-4), giving rise to partial desorption and evacuation of the component or components previously adsorbed by the adsorbent material and, - continuing said placing under determined vacuum, an introduction

(L4), against the current, of a determined quantity of the non-adsorbed component (s) produced previously, to give rise to a reduction in the partial pressure of the component (s) previously adsorbed and still present, so as to cause desorption and additional evacuation of the adsorbed component (s).

2. Method according to claim 1, characterized in that one carries out periodically the fourth phases (L1-L4) above in four containers (1-4) of the same capacities and in that, while a first container (4) is subjected to natural admission (L1), a second (1) is subjected to pressure admission (L2), a third (2) is subjected to determined vacuum (L3) and a fourth (3) is subjected to the introduction (L4) against the current and under vacuum.

3. Method according to either of Claims 1 and 2, characterized in that a duration of a cycle of the four phases (L1-L4) is divided into four quarters of equal duration for each phase and in that that a quarter of duration is chosen so as to be slightly less than a time limit for saturation of the adsorbent material (7) contained in a container (1-4) and not by the mechanical strength of the devices.

4. Method according to any one of claims 1 to 3, characterized in that, the gaseous mixture being atmospheric air, the adsorbable components being nitrogen, carbon dioxide and water, the non-adsorbable components being oxygen and argon, the determined vacuum is between 0.2 and 0.5 bar absolute and is preferably of the order of 0.3 bar absolute and in that then the determined pressure greater than the atmospheric pressure is advantageously between 1, 1 and 2 bar absolute and is preferably of the order of 1, 2 bar absolute.

5. Method according to any one of claims 1 to 3, characterized in that, the gaseous mixture being atmospheric air, the adsorbable component being oxygen, the non-adsorbable component being nitrogen, then the determined pressure above atmospheric pressure is advantageously between 2 and 7 bars absolute and is preferably of the order of 4 to 6 bars absolute and in that the determined vacuum is between 0.3 and 0.7 bar absolute and is preferably around 0.5 bar.

6. Method according to any one of claims 1 to 5, characterized in that, for the adsorption, a passage of the gas mixture is arranged so that it circulates at practically constant speed through the material adsorbent, by compensating for its loss of adsorbable component (s) by a gradual reduction in the cross-section of passage through the adsorbent mass, and in that for desoφtion, a passage in the opposite direction of the gaseous components is arranged through the adsorbent material so that they circulate at a speed which is also practically constant, as a function of the progressive increase in the volume of gas desorbed.

7. Device for implementing the method according to any one of claims 1 to 6, characterized in that it comprises:

- a blower (12) to produce the determined pressure higher than atmospheric pressure, a vacuum pump (14) to produce the evacuation, an inlet (13) of atmospheric air and a manifold (18) of non-adsorbable component (s),

- four identical separate containers (1-4), intended to receive the adsorbent material (s),

- A rotary distributor (8) arranged for a sequential and selective communication of each container (1 -4) and at least the inlet (13) of atmospheric air, the blower (12) and, according to two respective paths according to the phase in progress, of the vacuum pump (14), and

- control and drive means (11) for periodic rotation of the rotary distributor (8), further characterized in that

each container (1-4) has a gas mixture admission chamber on one side of the adsorbent material (7) and a discharge chamber of the non-adsorbable component (s) on the other side of the adsorbent material ( 7), an intake grid (5) between the adsorbent material and the intake chamber and an evacuation grid (6) parallel to the intake grid (5) and disposed opposite the adsorbent material (7), between the latter and the evacuation chamber, - The intake grid (5) has a passage surface for the gas mixture greater than a passage surface that has the discharge grid (6), the adsorbent material (7) having a regular and progressive variation in section right, from the corresponding dimensions of the intake grille (5) to the corresponding dimensions of the exhaust grille (6),

- optionally a separation grid (25) is provided each time between two different adsorbent materials (7A, 7B) and is arranged parallel to the intake (5) and discharge (6) grids, - preferably, the passage of the gas and the aforementioned passage surfaces are arranged so that during adsorption, on the one hand, the gas mixture entering through the intake grid (5) and progressing into the adsorbent material (7) and, on the other on the other hand, the non-adsorbable component (s) discharged through the discharge grid (6) have a practically constant speed and so that during desorption, a passage in the opposite direction of the gaseous components also takes place at a practically constant speed,

- a periodic and selective communication of each container (1-4) and of the collector (18) of non-adsorbable component (s) is carried out, either by another rotating distributor or by a pair of controlled valves (es ) periodically, in rhythm with the rotary distributor (7) mentioned first, by the appropriate control means.

8. Device according to claim 7, characterized in that the four containers (1-4) are four independent tanks, cylindrical or frustoconical.

9. Device according to claim 7, characterized in that the four containers (1-4) are four separate compartments formed in a common enclosure by partition walls, the enclosure preferably being cylindrical, the compartments then forming sectors around of the cylinder axis.

10. Device according to any one of claims 7 to 9, characterized in that the distributor (8) comprises

- five stages arranged one beside the other in the direction of the axis of rotation, - a stator (9) for the selective connection

- to the blower (12) on a first stage,

- at the air inlet (13) at atmospheric pressure on a second stage,

- to the vacuum pump (14) on a third stage, - to the vacuum pump (14), via a buffer tank

(16) and a non-return valve (22), on a fourth stage,

- to each of the containers (1-4) on a fifth so-called connecting stage, the latter preferably being arranged in the middle part of the dispenser

(8), - a rotor (10) with internal channels (a, b, c, d), parallel to the axis of rotation, for the selective and periodic communication of each container (1-4) connected to the fifth floor and respectively,

- the inlet (13) of atmospheric air by a first channel (d),

- the blower (12) by a second channel (a), - the vacuum pump (14) by a third channel (b),

- the buffer tank (14) by a fourth channel (c), and further characterized in that the stator (9) has on each stage, for the selective connection, four orifices opening inwards and arranged at 90 ° from one another and in that the rotor (10) comprises, on the stage of connection to the four receptacles (1-4), four orifices located at 90 ° from one another and s' opening outwards so as to be able to put a container (1- 4) into communication with a corresponding channel (ad) according to the process phase to be carried out in a container and, at each other stage, a single orifice arranged for putting a corresponding channel in communication with an orifice on the same stage of the stator (9) as a function of said process phase.

11. Device according to claim 10, characterized in that

between each stage there is an annular seal (23) for sealing between two stages, this seal preferably being carried by the stator (9), and - Between two orifices of the stage of connection to the containers, there is each time at least one and preferably two sections (24) of seal extending from an annular seal (23) to the 'other and each arranged near an orifice of this stage, each joint section (24) being preferably carried by the stator (9).

12. Device according to claim 10, characterized in that

- Between at least two stages, an annular seal (23) is arranged to seal them, this seal preferably being carried by the stator (9), and at the place where each conduit (20) connecting to a container (1-4) opens into the stator (9) of the distributor (8), each time there is a sealing ring (30)

* which is mounted so as to be able to slide in leaktight manner in the duct (20), along the axis thereof, and so as to be able to be supported by one of its ends against the rotor (10),

* the end of which bears against the rotor (10) is shaped to the diameter of the rotor (10) to conform to the shape and ensure there is a tight contact and is open to enter into selective communication of gas passage with a respective orifice of the rotor (10),

* the other end of which opens in the conduit (20) and

* which is pushed, at least in service, by means (32) against said rotor (10) for sealing.

13. Device according to any one of claims 7 to 12, characterized in that the intake grids (5) and / or evacuation (6) and / or separation (25) have through holes the periphery is each time a frustoconical surface pierced at the point which itself is directed towards the adsorbent material (7).

14. Device according to either of claims 11 and 12, characterized in that the seals (23) and, where appropriate, the sections (24) of the seal are grooves longitudinally either on their side facing the rotor (10) when they are carried by the stator (9) or on their side facing the stator (9) when they are carried by the rotor (10), so as to cause an effect of labyrinth for any gas between two contiguous stages of the distributor (8).

15. Device according to claim 8, characterized in that frustoconical containers are preferred for the production of nitrogen as a non-adsorbable component and in that they have a ratio of 0.6 to 0.8 between their base diameter and that of the top and a ratio of 0.8 to 1.5 between their average diameter and their height, these frustoconical containers being further advantageously arranged so that their axes of revolution are vertical.

16. Device according to any one of claims 10 to 14, characterized in that the four orifices of the rotor (10), on the connecting stage of the containers (1-4), are formed by numerous orifices with rounded edges .

17. Device according to any one of claims 7 to 16, characterized by the presence of a buffer tank (16) and a non-return valve (22) allowing the realization of the phase (L4) of rinsing under vacuum against -current, via the vacuum pump (14), without interfering with the evolution of the suction pressure of this vacuum pump (14) during the phase (L3) of desorption by placing under a determined vacuum.