FR2497120A1 - METHOD AND APPARATUS FOR SEPARATING A MIXED GAS SUCH AS AIR - Google Patents

Abstract

PROCESS FOR SEPARATING A MIXED GAS BY ADSORPTION CHARACTERIZED IN THAT TO BEGIN A DESORPTION OPERATION, THE MIXED GAS SUPPLIED BY AN ADSORPTION TOWER 19-21 WHICH COMPLETED ADSORPTION DURING A PRESSURE REDUCTION PERIOD PRIMARY UNLOADED IN THE ADSORPTION TOWER IS SENT TO ANOTHER ADSORPTION TOWER WHOSE PRESSURE HAS BEEN RAISED TO AN INTERMEDIATE PRESSURE SITUATED BETWEEN THE ADSORPTION PRESSURE AND THE DESORPTION PRESSURE, AFTER THE END OF THE DESORPTION OPERATION, BY A GAS NOT PRESENT IN THE ADSORBATE AND CONSTITUTING THE RESULT OF LOW PRESSURE ADSORPTION OR A MIXED GAS SUPPLIED DURING THE PRIMARY PRESSURE REDUCTION PERIOD, TO PERFORM A LOW PRESSURE ADSORPTION OPERATION DURING WHICH THE GAS CONSTITUTING OF ADSORBATE AND CONTAINED IN THE GAS MIXTURE IS ADSORBED.

Description

1. The present invention relates to improvements made to a

  process and an apparatus for the separation by adsorption of a gas mixture, hereinafter called mixed gas,

like air.

  It is well known that the ratio between the N2 gas and the O2 gas entering into the composition of the air is 4: 1, and that the ratio between the partial pressure of the N2 gas and the

  gas 02 is also about 4: 1. The amount of gas ad-

  sorbed by an adsorbent varies in proportion to these partial pressures of the gases. For example, when gas 02 contained in the air is adsorbed with an adsorbent under an air pressure of 5.10 Fa, the partial pressure of gas 2 is approximately 105 Pa. If the pressure is reduced the air from 5.105 Pa to 105 Pa, the partial pressure of the gas O falls

2

  then at 0.2.10 Pa and most of the O2 gas ad-

  absorbed by the adsorbent is desorbed. But in an adsorption separation device of practical dimensions, the O2 gas adsorbed by the adsorbent does not get desorbed when it is sufficient to reduce the air pressure to 10F5Pa. The reason is that when the air pressure in the adsorption tower is lowered to 105 Pa the gas O is desorbed from the adsorbent, so that the partial pressure of the gas O 2 around the adsorbent s' increases but that this partial pressure of the gas 02 around the adsorbent does not decrease due to the too low flow rate of the air passing through the adsorption tower, the result being that the gas 2 is maintained around the adsorbent, that the desorption of gas 02 is not

  not continue and that gas 2 is kept adsorbed by the ad-

  sorbent. We will now describe with reference to FIG. 1 is a known form of an air adsorption separation device which makes it possible to solve the problem which has just been mentioned. Raw air is sent through a main supply pipe a-to an air compressor

  b can be fitted with a post-cooler, a separa-

  drainer, etc., intended to cool and dehumidify the compressed air which should normally be at a high temperature, and if necessary also provided with a refrigerator 2,

  cu analog. Downstream of the compressor, the supply hose

  main tion a is subdivided into two branches c 1, c2. The pipes dl, e1 and a2, e2 for discharging the gas retained in the cavities of the adsorption material, and hereinafter called cavity gas, are mounted in bypass on the supply pipes.

  respective c1 and 2 ', and the valves f to f6 are pre-

  views on the respective pipes. above clt di, a! -2 d2 and e2. A main discharge pipe section g communicates with the discharge pipes d and d2, and it

  is connected to a poop I empty h de-laanelle share a sec-

  main discharge pipe io A section of pipe

  of discharge pri.ncipal i comuniaue also with the tu-

  discharge lines e and -2 A UR pipe common k is

tyauxodccallectu comu .... es ...

  = 2- provided for the respective pipes ci, d and e, while a

  common manifold 1 is pre,; read pcr: - the pipes respec-

  tifs co, d2 and 2. The collecting pipes are connected = desm adsorption towers mi and n filled with adsorbents designated respectively by m, and n. Collector pipes

  o and ú of N2 gas on which are mounted alves

  d0 pectiv-es and r and which start from the adsorption towers T and n reach a common outlet pipe section leading into a tank t to which is connected a main outlet pipe uo The adsorption towers m and n arei arranged to perform an operation alternately

  adsorption and a desorption operation. Assuming hand-

  holding that the adsorption tower m has started an adsorption operation, the valves f1, g are then open and the valves f2 f are closed. As a result, raw air -2 'enc, e' ar ru compressed from the air compressor b is sent through the main supply pipe a, the supply pipe cit

  the valve f1 and the manifold k to the ad tower

  sorption m, and when the raw air passes through the adsorption tower m, the gas 02 (which is a gas constituting the adsorbate) which is contained in the raw air is adsorbed by the adsorbent m1,

  while N2 gas (which is a gas not present in the ad-

  sorbat) is condensed and sent through the outlet pipe o. the valve g and the pipe outlet section s to the tank t and it is then collected outside the system in the form of a product usable via the pipe

  main output u. Furthermore, when the adsorption tower

  tion m begins an adsorption operation as described

  above, the other adsorption tower n begins an operation

  desorption, the valve f opening while the -6

  valves f, f5 and r close. As a result, the air resi-

  duel lying around the adsorbent nor is discharged outside the system by the collecting pipe 1, the valve

  f6, the discharge pipe e2 and the discharge pipe section

  charge j. Then valve f6 is closed and valve f5

  is open. The residual air around the adsorber

  bant n1 is therefore sucked in and discharged outside the system by the manifold 1, the valve f5, the discharge pipe d2, the discharge pipe section y, the vacuum pump h and the pipe section discharge i, which lowers the pressure in the adsorption tower n to the partial pressure of the gas 2 during adsorption, the gas 2 which is adsorbed by the adsorbent n_ being therefore desorbed, this

  to reactivate the adsorbent n.

  Although the adsorption separation apparatus

  crit above, intended for air, can solve the pro-

  problem mentioned above, however, it has a

  comes from the fact that the pressurized air containing a

  high concentration of 2 is discharged outside the system

  t by the main discharge pipe sections j, i

without being used.

  Various methods have been proposed for effective use of

  this pressurized gas, and an example of these processes is

  illustrated in fig. 2. In the separation apparatus by ad-

  sorption shown in fig. 2, part of the N2 gas which has been separated and condensed during an adsorption operation is sent via a regulating valve of

  flow w in an adsorption tower having completed an operation

  reduction pressure, and thus, by lowering the partial pressure of the residual air around the adsorbent, the gas 2 adsorbed by the adsorbent is desorbed, and the desorbed gas 02 is swept and sent into the discharge pipe i and moreover, while having the possibility of not mounting 4. a vacuum pump, part of the N2 gas which has been separated and

  condensed thanks to an important work representing a great

  of expenditure would be consumed in the adsorption tower during a desorption operation. In addition, since the gas discharged through the discharge pipe% is not used, the problem arises of the increased cost in the case where

  the N2 gas is extracted in the form of a product to be used.

  The present invention addresses the aforementioned problem and relates to a method and an apparatus for separating a mixed gas by adsorption, of the type in which an adsorption operation is repeatedly carried out by sending raw gas into a filled adsorption tower of an adsorbent with a view to causing the adsorbent to adsorb a constituent gas

  adsorbate, and extracting a gas not present in the adsorb

  sorbate from said adsorption tower, and an operation

  desorption by reducing the pressure in the tower

  adsorption so that the adsorbent desorbs the gas

  titrating adsorbate that has been adsorbed, and recovering the

  gas constituting the adsorbate, this operation being carried out

  sequenced in several adsorption towers

working alternately.

  According to the invention, this method and this apparatus present

  have the characteristics which are indicated in the

  annexed vendications. To better understand the present invention and its characteristics, a number of embodiments will now be described with reference to the appended drawings in which:

  Fig. l and 2 are diagrams of two forms of an apparatus

  classic adsorption separation board allowing

  implement the air separation process by ad-

  sorption, and Fig. 3 to 7 are diagrams representing various modes

  for the production of separation adsorption apparatus

  lon the invention and intended to separate the air by the process

adsorption.

  If we refer to fig. 3 which relates to a first embodiment of an adsorption separation apparatus

  intended to implement the method, the reference 1 desi-

5.

  a main raw air supply pipe, the part number

  rence 2 an air compressor intended to compress and supply

  ter raw air, this air compressor being provided with a

  post-cooling sitive, a drain separator, etc., to cool and dehumidify the compressed air at high

  temperature, and if necessary, it can also be equi-

  pe of a refrigerator or the like. In addition, the references 3a, 3b, 3c denote raw air supply pipes mounted as a branch on the main supply pipe 1 mentioned above. Cavity gas pipes 4a, 4b and 4c are in parallel on the supply pipes 3a, 3b and 3c. Gas discharge pipes, cavity 5a, 5b and c are also mounted in parallel on the discharge pipes.

  charge of cavity gas 4a, 4b and 4c and of the discharge pipes

  cavity gas charge 6a, 6b and 6c are mounted in parallel

  lele on the cavity gas discharge pipes 5a, 5b and 5c. A common cavity gas discharge pipe 7

  communicates with the discharge pipes 4a, 4b and 4c above

  mentioned while a main cavity gas discharge pipe 8 communicates with the above-mentioned discharge pipes 5a, 5b and 5c. On the discharge pipe 8 is mounted in series a flow regulating valve 9, a balance tank 10 and a valve 11, the outlet of which is connected

  to a main cavity gas discharge pipe 12 comprising

  providing with the discharge pipes 6a, 6b and 6c above-

  mentioned. In addition, the references 13a and 13b designate valves mounted in a pipe which is connected in bypass to the valve 11 and in which a compressor 14 is provided. Valves 15a - 15u are mounted in the respective pipes 3a, 4a, 5a, 6a, 3b, 4b, 5b, 6b, 3c, 4c, c and 6c mentioned above. A common manifold

  16 is associated with the respective pipes 3a, 4a, 5a and 6a above-

  mentioned, while a common collecting pipe 17 is as-

  associated with the respective pipes 3b, 4b, 5b and 6b mentioned above and that a common collecting pipe 18 is associated with the pipes

  respectively 3c, 4c, 5c and 6c above. The system

  takes three adsorption towers 19, 20 and 21, each being

  filled with an adsorbent designated respectively by the

  6.ferences 19a, 20a and 21a. N2 gas outlet pipes referenced 25a, 25b and 25c are mounted in parallel on other respective N2 gas outlet pipes 26a, 26b

  and 26c. In addition, internal gas discharge pipes

  respective vi-t 28a, 28b and 28c are mounted in parallel on the outlet pipes 26a, 26b and 26c, these discharge pipes comunicvant with the main cait gas discharge pipe 12 described above. In addition, a pipe

  manifold 22 is associated with pipes 25a, 26a and 28a above

  above while a collecting pipe 23 is associated with the tubes

  pipes 25b, 26b and 28b and a collecting pipe 24 to pipes c, 26c and 28c. Valves 29a - 29Q are mounted in the respective pipes 25a, 26a, 28a, 25b, 26b, 28b, 25c, 26c and 28e shown above. A common outlet pipe 30 of the N2 gas joint with the outlet pipes 25a, 25b and 25c

  mentioned above and it is connected to a tank which

  free 31 to which is connected a main outlet pipe 32

  N2 gas. A common outlet pipe 33 fie gas N2 cotmmuni-

  only with the pipes. above mentioned output 2ae, 26b and 26c, and it is also connected to a dJ-balance tank 34

  to which is connected a comamun 35 N2 gas outlet pipe.

  The common cavity gas discharge pipe 7 is connected to

  a vacuum pump 36 to which a discharge pipe is connected

  common charge 37 of cavity gas, It will be noted that, for reasons of flexibility, the automatic control device necessary for the operation of the respective valves is not shown, In addition, four towers could be provided

or more adsorption.

  When the adsorption separation apparatus described above operates, the three adsorption towers 19, 20 and 2l are effective: I - a high pressure adsorption operation,

  II primary and secondary pressure reduction operations

  condaire and a desorption operation, and III- an operation of raising pressure to low pressure,

  a low pressure adsorption ventilation and an operation

  pressure rise ration to reach a high pressure, 7. these three operations being repeated sequentially. Yes

  it is now assumed that the adsorption tower 19 has

  mmenté operation I above, only the valves 15a, 29a are open. As a result, raw air compressed by the air compressor 2 is sent to the main supply pipe 1, the supply pipe 3a, the valve

  a and the collecting pipe 16 to reach the ad tower

  sorption 19, and when it passes through the adsorption tower 19, the gas 2 (which is a gas constituting the adsorbate)

  which is contained in the raw air is adsorbed by the adsorber-

  bant 19a, while the gas N2 (which is a gas which is not present in the adsorbate) is condensed and sent by the collecting pipe 22, the outlet pipe 25a, the valve 29a and the common outlet pipe 30 to the equilibrium tank 31, and it is also extracted towards the outside of the system by the

  common outlet pipe 32 in the form of a product used

  corn. When the adsorption tower 19 begins to perform operation I, the adsorption tower 21 begins to perform operation II, so that the valves 15e, 292 and the valve 11 are open and that the valves 15i, 15j , 15k, 29i, 29j and the valves 13a, 13b are closed, so that the primary pressure reduction operation begins in

  the adsorption tower 21 which completed operation I. Pen-

  during this operation, the relative pressure cavity gas

  The high temperature around the adsorbent 21a is sent into the collecting pipe 18, the valve 152 and the discharge pipe 6c to reach the discharge pipe.

  main 12, and it also passes through the collecting pipe

  valve 24, the discharge pipe 28c and the valve 292 for

  come to the discharge pipe 12, and it is also sent

  from the main discharge pipe 12 to the tank 10 through the

  valve 11. When the internal pressures prevailing in the adsorption tower 21 and the tank 10 have reached almost the same level, the valve 11 closes and the valves 13a, 13b open to start the operation of

  secondary pressure reduction. During this operation-

  tion, the pressure of the cavity gas which is sent from the adsorption tower 21 to the main discharge pipe 12, is 8. raised by the compressor 14 to the level of the internal pressure of the tank 10, and it is then sent in the tank 10. When the internal pressure prevailing in the adsorption tower 21 has reached almost the same level as that of the partial pressure of the gas 02 in the raw air which is sent to the adsorption tower 19, the valves 15th, 292, 11, 13a and 13b are closed and a series of pressure reduction operations is then completed. Then, the adsorption tower 21 begins the desorption operation by opening the valve 15j. Of course, we could

  change the switching pressure which has just been

  depending on the concentration of O2 gas supplied

  during the desorption step. When the valve 15j is open or

  green in desorption tower 21, the cavity gas is

  found in the adsorption tower 21 is sucked up and

  loaded in the collecting pipe 18, the valve 15j, the discharge pipe 4c, the common discharge pipe 7, the vacuum pump 36 and the pipe 37, which lowers the partial pressure of the gas 2 of the cavity gas around the adsorbent 21a, resulting in the desorption of the gas 2 which is adsorbed by the adsorbent 21a, the sweeping of the desorbed gas towards the main discharge pipe and its recovery. When the internal pressure prevailing in the adsorption tower 21 has been lowered to a predetermined pressure, the valve 15j is closed and the desorption operation is completed. When the tower

  adsorption 19 begins operation I, the adsorption tower

  tion 21 begins operation III and only valve 29f is

  opened. The low pressure N2 gas found in the

  servoir 34 is therefore sent to the adsorption tower 20 via the main pipe 33, the valve 29f, the supply pipe 26b and the collecting pipe 23, the tower having completed the desorption operation, and c It is then that an operation of raising pressure at low pressure begins. When the internal pressures prevailing in the

  tank 34 and the adsorption tower 20 have become

  tically equal, the 15g valve is open so that

  start the adsorption operation at low pressure.

  During this operation, the cavity gas, which is stored 9. in the tank 10 during the reduction operations of

  pressure, is sent to the adsorption tower 20 via the

  middle of the flow control valve 9, the main discharge pipe 8, the discharge pipe 5b, the valve 15g and the manifold pipe 17, and as a result that the gas 2 contained in this gas is adsorbed by the adsorbent 20a, that the gas N, which is condensed and separated is sent to the reservoir 34 via the collecting pipe 23, the outlet pipe 26b, the valve 29f and the main outlet pipe 33, and that the valves 15g and 29f are closed to end the low pressure adsorption operation

  by monitoring and determining when the concentration

  tion of the O2 gas in this gas begins to rise. Note that we could combine the operation in a single operation

  pressure rise to low pressure and the operation of

  sorption at low pressure by simultaneously opening the valves

  ves 15g and 29f. Depending on the concentration of O2 gas in the low pressure N2 gas sent from the tank 34, a modification could be carried out consisting in opening the valve 15g

  instead of the valve 29f for carrying out the lifting operation

  pressure to reach the low pressure

  by sending the cavity gas into the adsorption tower 20.

  When the adsorption operation is completed in the adsorption tower 20, the valve 29e is open, so that the high pressure N2 gas located in the tank 31 is sent to the adsorption tower 20 by through the common supply pipe 30, the valve 29e, the supply pipe 25b and the collecting pipe 23 so as to

  carry out the high pressure increase operation

  when the internal pressures prevailing in the

  servoir 31 and the adsorption tower 20 have reached an almost equal level, the valve 29e is closed to put

  end of the high pressure raising operation.

  It should be noted that the valve 29e could be kept at the

  open state to prepare the following high pressure adsorption operation. Because the cavity gas which is

  stored in tank 10 is consumed during the operation

  adsorption at low pressure and that the cavity gas 10. consumed is replaced during the secondary pressure reduction operation, it is necessary that the reservoir 10

  has sufficient volume for the conduct of these operations

  tions. In addition, depending on the concentration of the gas 02 contained in the high-pressure N2 gas sent from the reservoir 31, a modification could be made consisting in opening the valve 15e in place of the valve 29e during the pressure raising operation at high pressure so as to send the raw air into the adsorption otion tower 20 and thus perform the pressure raising operation at high pressure. In

  in addition, other modifications could be made to my-

  deny that at the end of the pressure raising operation

  low pressure the adsorption tower 20 starts an operation

  high pressure adsorption and 1Se valves

  i5 29e are simultaneously open for operation

  high pressure pressure expansion and if multaned

  ment the high pressure adsorption operation (which has just been described constituting a first preferred embodiment). In this first preferred embodiment which has just been described, the internal pressure prevailing in the diadsorption tower 21 is lowered by the vacuum pump 36 court than the gas 02 which is. adsorbed by the adsorbent 21a can be

  desorbed. However, according to a second embodiment pre-

  féré which is represented in figt 4, during the operation-

  absorption, valves 15j and 29k are open for

  send the NM gas at low pressure to the adsorption tower 21

  sion contained in the reservoir 34 via a flow regulating valve 39, the main outlet pipe 38, the valve 29k, the outlet pipe 27c and the neck-1 reader pipe 24, so as to lower the partial pressure of

  gas 02 in the adsorption tower 21 and cause the desor-

  tion of the gas 02 which is adsorbed by the adsorbent 21a, and on the other hand the desorbed gas is discharged outside via the collecting pipe 18, the valve 15j, the discharge pipe 4c and the pipe common discharge 7 to then be recovered. In addition, by monitoring and determining when the concentration of this gas 02

249712 (

  11. starts to drop, valves 15j, 29k are closed to

  end the desorption operation, the other functions

  tions of this second preferred embodiment illustrated

  in fig. 4 being identical to those of the first. We no-

  tera that in these two preferred embodiments, one can omit the tank 10 without having a

  disadvantage. Furthermore, and depending on the possibilities

  N2 gas consumption tees, we can also

  omit the tanks 31, 34 without this

disadvantages.

  Having established a comparison between the methods according to the present invention which have been described above and the methods of the prior art by completing each

  adsorption towers of fig. 1 and 2 and ad towers

  sorption of fig. 3 and 4 with 10 kg of adsorbent (Fe-K-Na-A), the results were obtained which are recorded in Table l and Table 2. It will be noted that in the case where

  Fe-K-Na-A is used as an adsorbent (iron having a

  lence of two or more to an industrially pure zeolite

  type A4), the gas constituting the adsorbate is oxy-

  gene 2 and the gas that is not present in the adsorbate

is nitrogen N2.

Table 1

  Test apparatus and method j r- Units Method of the invention Method of the prior art Fig. 3 Fig. 4 Fig. 1 Fig. 2

, ,,,,,,,,, ,,,

1 rea

reading

2 rea

  Readout Desorption by evacuation Desorption by sweep Pressure Pa (. 10Q 5) 6 6 6 6 D ei _ _ _ _ _ _ __ _ _ _ _ _. _ __ _ _. _ _ _ Flow rate Nm3 / h 10 10 10 10 Temperature. c 25 25 25 25

F _. '. ,,

High pressure Pa (.105) 6 6 6 6

Low pressure Pa (.10). 2.7 3- -

  e High pressure Nm / h 5.3 5.3 4.9 4.5

m Low pressure Nm3 / h 2.1 1.9 - -

  Total Nm3 / h 7.4 7.2 4.9 4.5 Concentration in 0,% in vol. 1 or less 1 or less Pressure Pa (.105) 1.2 -> 0.2 1.2 1.2 - 0.2 1.2 Gas .... 0 Flow rate Nm3 / h 2.6 2.8 1.4 1.7 02 .. supplied 02% concentration in vol. 79 73 70 55 fun Flow rate of 02 pure Nm3 / h 2.05 2.04 0.98 0.94 Flow rate of secondary cavity gas Nm3 / h 2.0 2.5 N2 gas supplied oa [minus 1 or minus 1 or

Table 2

  Units Fig. 3 Fig. 4 Fig. 1 Fig. 2 Compressor (2) Kcal / kg 50.1 50.1 50.1 50.1 Difference in enthalpy between an outlet and an inlet in Compressor (14) Kcal / Kg 18.0 21.5

an exit and an entry into--

the case of an adia-

  in the case of an adia change- Vacuum pump (36) Kcal / Kg 48.3 - 48.3 -

  baticque. Compressor (2) Kcal / h 649 / k I 649 / n 649 / i 649 / Election power

  required Compressor (14) Kcal / h 23 / q 35 / i - -

necessary.... . ....

  Vacuum pump (36) Kcal / h 90 / - 48 / -

  Total Kcal / h 762 / q 684 / d 697 / - 649 /% Gas N2 Kcal / Nm3 103/4 90 / h 142/144 / r Energy required per unit 3 02 pure Kcal / Nm 372 /% 335 / n 711 / i 690 / Ii of product volume. 3 Pure N2 + 02 gas Kcal / Nm 81 / q 74 / i 119 / l 119 / w - r%) o M rbo 14. As shown in Table 1, the flow rates of the

  N2 and 02 gas and the concentration of gas 02 supplied are

  compared to the tech- nology process.

previous pic.

  On the other hand, it appears from Table 2 that the power consumed is reduced to about 2/3 of that of the process of the prior art. More specifically, we obtained the results backfilled in 1 Table 2 while the compressor 14 has a differential pressure

  weaker between its exit and its entry than the compress

  sor 2 and the vacuum pump 36 and that its denial iq must be pu-s high, assuming that these yields are identical and by calculating in an ap-roche manner the power required using a di-agra-mae is for air. In this case, it is assumed that the temperature of the raw air which

  is introduced into the pipe 1 is 25 ', that the increase

  The pressure p-invoked by compressor 2 is

  8.5.105 Pa, than the average power required to compress

  sor 14 and the vacuum pump 36 is there! half of the maximum steam, and that the gas outlet pressure 02 is

1.2 x. 105 Pa.

  If we now refer to fig 5, this one represents

  feels a third Dréférê embodiment of the invention

  tion, come; 3osants.denumcues those of the second preferred embodiment (fig. 4) being designated by the same references, and only the parts of the apparatus which are different from those of the second preferred embodiment

  giving rise to an explanation in the following. In this embodiment, the compressor 14 of FIG. 4 is omitted from the

  main discharge pipe 12 and as a result the cell 13b becomes unnecessary. The pipe 12 is discharged outside the system through the outlet 40. For the rest, the components of FIG. 5 are identical to those

* of fig. 4.

  In use, the method of the third embodiment

  reading is identical to that of the second, except that when the adsorption tower 19 has started operation I and that the adsorption tower 21 has started operation II, only 15. the valves 152 and 11 are open while the valve 291 is closed as well as the valves 15i, 15j, 15k, 29i, 29j, 29k and 13a, the valve 13b having been eliminated. During this operation, the cavity gas which is in contact with -5 the adsorbent 21a reaches directly to the reservoir 10 via the main discharge pipe 12 and the valve 11, and because the valve 13b has been eliminated , it suffices to open the valve 13a and to close the valve 11 when the pressures prevailing in the tower 21 and the tank 10 have become equal to start the secondary pressure reduction operation. During this operation, the cavity gas contained in the main discharge pipe 12 is discharged to the outside of the system through the outlet

  40. When the internal pressure prevailing in the ad tower

  sorption 21 is almost equal to the partial pressure of the

  gas 02 contained in the air which is sent to the tower of ad-

  sorption 19, the valve 13a is closed and the series of operations

  pressure reduction is complete. Then, the process continues with the desorption operation in the

  turn 21 by opening the valves 15j and 29k. Natural-

  leraent, at the beginning or during the secondary pressure reduction operation, as soon as the partial pressure of the gas 02 has been reached, the subsequent pressure reduction operation is instantly terminated. As regards the other operating modes of the method, they are identical to those of the first embodiment. However,

  a fourth embodiment can be obtained in modi-

  trusting the process. Thus, instead of sending the cavity gas from only one side of the adsorption tower 21 by opening the valve 152, it can be sent from both sides of the tower and simultaneously by opening the valve 29ú in addition to valve 151, the process being the same as regards

  concerns all of its other aspects. According to another modification

  tion of the process (constituting a fifth embodiment

  tion), we can supply the cavity gas from both

  sides of tower 21 by opening valves 152 and 292 during

  throughout the duration of the pressure reduction operations

primary and secondary.

  16. The results reported in Table 3 were obtained.

  by comparing the method according to the present invention and

  crit with reference to fig. 5 and the processes of the tech-

  previous pic, filling each of the ad towers

  sorption of fig. 1 and 2 and adsorption towers of fig. 5 with 10 kg of adsorbent (Fe-K-Na-A). In that case

  also, as Fe-K-Na-A is used as an adsorber-

  bant, the adsorbate gas is oxygen (02) and the gas

  which is not present in the adsorbate is nitrogen (N2).

Table 3

  Previous process Processes according to the invention FIG. I Fig. 2 Fig. 5 Apparatus and test method Desorption Desorption3ra- 4 reaea Units by par lsation lisation evacuation evacuation sweep evacatio balyage lization lization readout Pressure Pa (.10) 6 6 6 6 6

Air supply

  Flow Nm3 / h 10 10 10 10 10 mentation. Temperature C 25 25 25 25 25 5 .. M High pressure Pa (.10) 6 6 6 6 6 He_ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ Low pressure Pa (.10 - - 2.2 2.7 2.9 Gas N High pressure Nm3 / h 4.9 4.5 4.7 5.9 6.0 Total Nm / h 4.9 4.5 5 , 9 6.2 6.1 Cni., O. _ Less! _O u _o i ns_ __ -oms _uisomn Concentration in 02% in vol. 1 or less I or less 1 or less I or less I or less

_ _ _............

  Gas 02 delivered Pressure _ 1.2 1.2 1.2 1.2 Flow rate Nm3 / h 1.4 1.7 2.6 2.0 2, 1 Concentration of 02% in vol. 70 55 55 62 74 Debit2pu 0 980,4,431,4 25 F Nm3 / h -4. Pa (.10 Il) 112 --_> OP2 Pure O2 flow rate 0.98 0.94 1.43 1.24 1.55 18. It can be seen by examining Table 3 that despite the

  only compressor 2 is used but not the pump

  eg when empty, and therefore the power consumption is lower, the flow rates obtained for N2 gas and for O 2 gas are greater than those obtained with the processes of the prior art, thus reducing the

Fresh from production.

  Regarding the outlet of the cavity gas from the two sides of the adsorption tower, if this is carried out during the hold, the series of reduction operations

  pressure, a higher gas flow 02 can be obtained

  as long and therefore a greater reduction in production costs than when the gas is only extracted during

  the primary pressure reduction operation, This means

  Only in the case where the cavity gas is only extracted from one side (the air supply side

  gross) of the adsorption tower during the third operation-

  pressure reduction, the value obtained is inter-

  to those of the results mentioned above.

  According to the method of the present invention, the flow

  N2 gas is not important, cob-qe described above, and this -

  implies that the concentration of gas 02 in the discharge gas

  managed by the discharge pipes 7, 40 is high. Special-

  ment in the case of the fifth preferred embodiment, the concentration of O gas can reach 74%, this ui 2 pei

  reduces the manufacturing costs of this O2 gas.

  If we now refer to fig. 6 concerning a sixth preferred embodiment of the invention, it will be noted that the components identical to those of the first mode

  (fig. 3) are designated by the same references

  which will only be described in the following

  parts of the device which are different from those of the first

mier embodiment.

  In this embodiment, the compressor 14 of the

  fig. 3 is omitted from the main discharge pipe 12 and the val-

  ve 13b therefore becomes unnecessary. The balance tank

  bre 10 is also omitted from the main cavity gas discharge pipe 8 and as a result the valve 11 is

24971;

19.

  also useless. The pipe 12 opens in this case to the ex-

  inside the appliance via exit 40.

  In all its other aspects, the device represented

  in fig. 6 is identical to that shown in FIG. 3.

  In use, the method of the sixth embodiment is identical to that of the first, except that in this case limits are imposed on the durations allocated.

  to each of the process operations due to the elimination

  balance tank 10. Thus, if the duration ne-

  stopped at the high pressure adsorption operation I is T minutes, that of the primary pressure reduction in operation II is T1 minutes, that of the secondary pressure reduction in operation II is T2 minutes and that of the desorption of the adsorbed gases of operation II is T3 minutes, the sum of T1, T2 and T3 must then be equal to or less than T minutes. If the elapsed time

  for the various parts of operation III is T1 mid-

  nutes for low pressure adsorption and T4 minutes for pressure increase, the sum of T1 and T4 must also be equal to or less than T minutes. The process continues with operation I as for the first mode

  but when tower 21 begins operation

  tion II, only valves 15e and 29P. Font open. This causes the discharge of any residual gas remaining in the

  cavities of the adsorption material 21a through the descent pipe

  main load 12, either via the col-

  reader 18, valve 15Q and pipe 6c, either by the

  end of the collecting pipe 24, the pipe 28c and the valve 29X at the end of the high adsorption operation

pressure.

  At this point, the low pressure adsorption operation takes place in tower 20, the valves 15g and 29f being open so that the low pressure N2 gas flows through the valve 29f, the pipe 26b and the pipe manifold 23 to reach the tower 20 while at the same time the cavity gas contained in the main pipe 12 is directed

  towards tower 20 via the regulating valve

  trice 9, hoses 8 and 5b, valve 15g and hose col-

  20. reader 17. When the internal pressure prevailing in the tower has reached the adsorption pressure at low pressure, the gas 02 contained in the cavity gas is adsorbed by the adsorbent substance 20a while the condensed N2 gas is discharged into the balance tank 34 via the collecting pipe 23, the pipe 26b, the valve 29f and the main pipe 33. When a duration of

  T1 minutes has passed, and when the reduction operation

  preliminary pressure in tower 20 and the opera-

  low pressure adsorption in tower 21 are complete, valve 15g is closed and valve 13a is

  open, causing the cavity gas to discharge

  both in tower 21 outside the system. However,

  if one wishes to extract the gas 02 as a product used

  readable, and depending on the gas concentration 02 'it is also possible to close the valves 13a, 15ú and 29 and open the valve 15j either at the beginning or

  during the secondary cavity gas discharge operation

  to supply some or all of the cavity gas in conjunction with the product gas. Then, with regard to the adsorption tower 21, the valves! S5, 291 and

  13a are closed and the valve 15j is open. Therefore

  quence, an adsorbed gas consisting mainly of gas 02 which has been adsorbed by the adsorbent 21ais desorbed due to the pressure reduction caused by the vacuum pump 36 through the manifold pipe 18,

  the valve 15j, the discharge pipe 4c and the discharge pipe

  main charge 7, and it is discharged outside the system via the common discharge pipe 37. This desorbed gas contains a high concentration of

  gas 02 At the time described above, the operation of

  sorption of the adsorbed gas is finished. On the other hand, in

  with regard to the adsorption tower 20, when the opera-

  low pressure adsorption is complete, the val-

  ves 15g and 29f are closed and valve 29e is open.

  As a result, high pressure N2 gas passing through

  the common outlet pipe 30 reaches the ad tower

  sorption 20 via the valve 29e, the hose

24971,

  21. supply 25b and manifold 23 so as to raise the pressure until it reaches the pressure necessary for the high pressure adsorption operation, and then operation d is terminated pressure rise. Then, the adsorption towers 19, 20 and 21 carry out the above-mentioned operations in turn.

  so that when the adsorption tower 19 starts the

  peration II above, the adsorption tower 20 begins

  operation I and the adsorption tower 21 begins the operation

  ration III, which means that natural air is separated into gas 1q2and into a gas containing a high concentration of gas 02 * While the cavity gas is supplied from

  two sides of the adsorption tower 21 by opening the val-

  ves 152Q and 29U of the adsorption tower 21 and the valve 13a during the secondary pressure reduction operation of the sixth preferred embodiment described above, the

  cavity gas could be extracted from one side only

  lernent of the adsorption tower 21 o the valve is mounted

  i by opening only the valves 15t and 13a (this cons-

  titling the sixth embodiment). In addition, while the cavity gas supplied from the adsorption tower

  21 is sent to the adsorption tower 20 by opening the val-

  ves 152, 29t2, 15g and 29f of the adsorption towers 20 and 21 during the primary pressure reduction operation while the cavity gas supplied by the adsorption tower 21 is discharged to the outside of the system by the common discharge pipe 12, the valve 13a and the outlet pipe 40 during the secondary pressure reduction operation of this sixth preferred embodiment mentioned above,

  there could be a modification consisting in de-

  charge the cavity gas outside the system

  using the valves 15u, 29 and 13a during the primary pressure reduction operation, then by sending the cavity gas into the adsorption tower 20 through the opening of the valves 15k, 29t, 15g and 29f and by the valve closure

  13a during the second pressure reduction operation

  and, as a third operation,

  pressure reduction, by discharging outside the system 22. the surplus cavity gas by closing the valves 15g

  and 29f and opening of the valves 15g, 29t and 13a (this cons-

  constituting an eighth embodiment).

  The results set out in Table 4 were obtained by comparing the processes of the prior art and the

  processes according to the present invention described with reference

  Refer to fig. 6, filling each of the turns with

  sorption of fig. 1 and 2 and adsorption towers of the

  fig. 6. Note that the indication "variant of the 8Q

  reading "concerns the case where, in this eighth reali-

  sation, the apparatus was used by lowering the internal pressure of the adsorption tower at the end of the primary pressure reduction operation so as to eliminate

  the third pressure reduction operation.

Table 4

  Fig. 6 Apparatus and prior art Method according to the present invention test method Units, Variant 6 reali- 7 reali- 8 realides the 8 Fig. I Fig. 2 station station station realization

l t i ,, ..

  Gas supplied Pressure Pa (.10) 6 6 6 6 6 6 per tower Flow rate Nm3 / h 10 10 10 10 10 10 adsorption [Temperature C 25 25 25 25 25 25

,,, ,,

  High 5 pressure Pa (.10) 6. 6 6 6 6 6 Pressure {Low 5 pressure Pa (.10) - 2.5 2.5 1.8 1.2 N2 gas supplied High 3 pressure Nm3 / h. 4.9 6.4 5.4 5.9 5.2 4.8 Low pressure flow Nm3 / h - - 1.1 0.8 0.4 0.2 Total Nm / h 4.9 6, 4 6, 5 6.7 5.6 5.0 Concentration in% by volume. I or less 1 or less I or less I or less I or less 1 or less

. ...,

  Pressure Pa (.10) 1.2-- 0.2 1.2--0.2 1.2--0.2 1.2--0.2 1.2 -) 0.2 1.2 0.2 Gas 02 Flow Nm3 / h 1.4 1.7 2.0 1.8 2.1 2.0 supplied 02% concentration in vol. 70 74 80 75 80 80 Flow rate of 0 pure Nm3 / h 1.0 1.25 1.6 1.38 1.68 1.6 2,., O -0 Il4 24. As shown in Table 4 and despite the fact that

  the conditions for supplying a gas to the adsorption towers

  tion that uses most of the power

  consumed are identical, in all embodiments

  The preferred concentration of the present invention is that both the gas concentration 2 and the flow rate of the supplied gas 2 are improved compared to the prior art methods, and thus the costs can be reduced when

  gas 2 is extracted as a usable product.

  In the sixth preferred embodiment and although the flow rate of N2 gas is the same as with the process of the prior art, both the concentration of O2 and the flow rate of gas 2 supplied are improved and it follows that this mode of realization is suitable for the case ow we extract

  at the same time N2 and 02 gases as used products

  wheat. With respect to the seventh embodiment, although the gas flow 2 is low compared to the sixth preferred embodiment, the obtained gas flow N2 is higher, and as a result, this embodiment is suitable for the case where N2 gas is extracted

as a usable product.

  With regard to the eighth embodiment, although the flow rate of the N 2 gas obtained is lower than that obtained with the sixth and seventh preferred embodiments, the flow rate and the concentration of the gas 2 obtained are improved and it results therefrom that this embodiment

  suitable for extracting gas 2 as a

usable.

  If we now refer to fig. 7 which relates to a ninth preferred embodiment of the invention, it will be noted that the parts identical to those of the sixth preferred embodiment (FIG. 6) are designated by the same references and which will not be described in the following.

  that the parts of the apparatus which are different from that

  those of the sixth embodiment.

  In this embodiment, the balance tank and the shut-off valve 11 are mounted on the outlet pipe 25. main 8. In all other respects, the device shown

  in fig. 7 is identical to that of FIG. 6. In use

  The method of the ninth preferred embodiment differs from that of the sixth embodiment only in that it is no longer necessary to synchronize the low pressure adsorption operation in tower 20 with

  the primary and secondary pressure reduction operations

  in tower 21 because the cavity gas supplied by tower 21 is sent indirectly to tower 20 via the balance tank 10 and the valve

stop 11.

  The incorporation of the balance tank 10 and the

  stop valve there in the pipe 8 also allows modi-

  similarly operating the methods of the seventh and eighth embodiments,

  eliminating the need for synchronization of operations

  rations. We can make changes to this mode

  that are similar to those described above

  above with regard to the seventh and eighth embodiments, this making it possible to obtain tenths and

eleventh embodiments.

  Regarding the ninth, tenth and eleventh preferred embodiments, effects similar to those of the sixth, seventh and eighth can be expected

  embodiments. Furthermore, in these ninth, di-

  tenth and eleventh preferred embodiments, since there is no need to synchronize the operation

  low pressure adsorption with re-

  primary and secondary pressure reduction, there is more freedom to organize these operations. In addition, since the cavity gas can be extracted for a short period of time, the duration can be shortened

  total necessary for operations and we can therefore increase

  ter the quantity of raw air treated per unit of time.

  Although the present invention has been described below

  above in conjunction with various pre-

  it goes without saying that it is not limited to these 26. and that various modifications and design variants

  can be brought to him without departing from his mind.

  For example, the invention can also be applied to the case where carbon dioxide gas is separated from a

  combustion by adsorption. By the way- $, as far as

  identifies the adsorption, one can use apart from Fe-K-Na-A and Fe-Na2X a molecular sieve with carbon (adsorbent

  for oxygen) or an adsorbent suitable for nitrogen.

-.:-- - f 24971x -27.

Claims (10)

R E V E N D I C A T I O N S   1. Process for the separation of a mixed gas by adsorp-   tion, during which there is repeatedly carried out, in several adsorption towers operating alternately, an adsorption operation consisting in supplying a raw gas in an adsorption tower (19, 20, 21) containing a   adsorbent (19a, 20a, 21a) so that the adsorbent ad-   sorbs a gas constituting the adsorbate and to extract a   gas not present in the adsorbate of said adsorption tower   tion, and a desorption operation of reducing   the pressure in said adsorption tower so that the ad-   sorbent desorbs the gas constituting the adsorbate which has been adsorbed by the latter and recovering the gas constituting the adsorbate, characterized in that to start a desorption operation, the mixed gas supplied by a tower   adsorption that has completed adsorption during a   primary pressure reduction period in the   said adsorption tower is sent to another adsorption tower   sorption whose pressure has been raised to an intermediate pressure situated between the adsorption pressure and the desorption pressure, after the end of the desorption operation, by a gas not present in the adsorbate and constituting the result of the low pressure adsorption   and / or a mixed gas supplied during the recovery period   primary pressure reduction, to perform a low pressure adsorption operation during which the gas constituting the adsorbate and contained in said mixed gas   is adsorbed, the result being that one can use ef-   effectively a mixed pressurized gas having a low concentration of gas constituting the adsorbate which is   supplied during the primary pressure reduction period   mayor. 2. A method of separation of a gas by adsorption according to claim 1, characterized in that a tower   adsorption which has completed the primary pressure reduction   the mayor is subjected to a reduction in secondary pressure by placing the interior of said adsorption tower in communication with the atmosphere and further reducing the 28.   pressure in an adsorption tower which has completed the reduction   secondary pressure by means of a vacuum pump   (36), this making it possible to desorb a gas constituting a   adsorbate and which has been adsorbed by an adsorbent.   3. A method of separation of a gas by adsorption according to claim 1, characterized in that the interior   of an adsorption tower which completed the reduction of   primary pressure is subject to a reduction in pressure   condaire which brings it almost to the partial pressure of the gas constituting the adsorbate in the raw gas, and in that in addition the gas constituting the adsorbate which has been   adsorbed by an adsorbent is desorbed by scanning the   inside an adsorption tower which has completed the secondary pressure reduction operation, a gas not present in the adsorbate being released during an operation low pressure adsorption.   4. Method of separation of a gas by adsorption   lon one of claims l to 3, characterized in that a   mixed gas supplied during a reduction operation   secondary pressure increased in pressure until the   low pressure adsorption, then sent to an adsorption tower which has been elevated to low pressure adsorption pressure, either together   with a mixed gas supplied during a reduction period   tion of primary pressure either as a result of said methane gases   diapers to be adsorbed, which makes it possible to increase the production rates of the gases constituting the raw gas present in the adsorbate and not present in the adsorbate, and also   reduce power consumption.   5. Process for the separation of a gas by adsorption   lon one of claims 1 to 3, characterized in that   inside the gas concentration tolerance consti-   kills of an adsorbate in the gas discharged outside the system and rich in a gas constituting the adsorbate, a   part or all of a mixed gas supplied during the   secondary pressure reduction operation is sent outside the system together with the gas supplied by an adsorption tower during a desorption operation, this 2497 120 29.   which increases the rate of production of the gas cons- as an adsorbate.   6. Method of separation of a gas by adsorption   according to one of claims 1 to 5, characterized in that   that an adsorption tower that finished the last operation-   low pressure adsorption is subject to an increase   pressure statement leading to high pressure by means of any or both gases consisting of the raw high pressure feed gas and a portion   a high pressure gas not present in the adsorbate ob-   held during the high pressure adsorption operation.   7. Process for the separation of a gas by adsorption   lon one of claims 1 to 5, characterized in that a   mixed gas obtained during the primary pressure reduction operation and / or the secondary pressure reduction operation is sent to an adsorption tower which performs a low pressure adsorption operation   via a reservoir (10), which allows   eliminate the need to synchronize the adsorption operation   tion at low pressure with reduction operations primary and secondary pressure.   8. Process for the separation of a gas by adsorption   lon one of claims 1 to 7, characterized in that at   during the secondary pressure reduction operation, a mixed gas is supplied from the raw gas supply side (16, 17, 18) of the adsorption tower or both from the side (16, 17, 18) of raw gas supply and on the side (22, 23, 24) of gas outlet not present   in the adsorbate of said adsorption tower.   9. Process for the separation of a gas by adsorption   lon one of claims 1 to 8, characterized in that   the adsorbent (<1a, 20a, 21a) intended to be introduced into the adsorption towers (19, 20, 21) is an adsorbent capable of selectively adsorbing oxygen from air, which is obtained adding at least iron having a valence of two or more to an industrially pure zeolite of type A4.   10. Apparatus for separating a gas mixed by adsorption   30. tion, comprising at least two adsorption towers (19, 20, 21), a main mixed gas supply pipe (1) in which is mounted a compressor (2), and valve connections (3a- 15a-16, 3b-15e-17, 3cl5i-18) at one end of each tower so that the mixed gas can be sent into each tower for the adsorption to be carried out there, characterized in that the towers (19, 20, 21) comprise mixed gas supply pipes (3a 3b-, 3c) and gas outlet pipes (4a, 4b, 4c, 5a, 5bb 5c, - 6a, 6b 6c) of cavities connected via a common collecting pipe (16, 17, 18} at their inlet ends, and pipes (25a, 25b, 25c, 26a, 26b, 26c) for the outlet of the constituent gas as well as hoses (27a, 27b, 27c, 28a, 28b, 28c) for discharging the cavity gas connected by means of a collecting manifold (22, 23, 24) at their outlet ends, surrounding the valves (15a-15L, 29a-29Y) are fitted in all of said pipes   while other equipment such as 6- tanks   balance (10, 31, 34), vacuum pumps (36) and comp.   additional pressers (14) are provided as far as 0   they are necessary for the special conditions of the   specification of mixed gas and supply requirements   constituent gases, and in that the arrangement of the apparatus   reil is such that it can implement a method according to   one of the preceding claims: - f -_