Abstract:
The invention relates to a permeation installation comprising: 
     a single pressure resistant chamber ( 30 ), 
     a plurality of permeation modules ( 34, 36 ) disposed within the chamber, each module being constituted by at least one permeator formed of hollow fibers with porous walls and being disposed within an envelope ( 38 ) provided with perforations placing in communication the external portion of each module and the common gaseous circuit, 
     elements ( 32 ) to supply the installation with the gaseous mixture to be treated, 
     elements ( 46 ) to recover the fraction of the gaseous mixture having passed through the wall of the fibers; and 
     elements ( 44 ) to recover the fraction of the gaseous mixture that has not passed through the wall of the fibers.

Description:
FIELD OF THE INVENTION 
     The present invention relates to permeation installations. 
     BACKGROUND OF THE INVENTION 
     The technique or process of permeation permits the separation of a gas from a mixture of gases in gaseous phase with the help of porous walls. This technique consists in applying under a relatively high pressure of the order of several tens of bars, the gaseous mixture in the environment of a bundle of hollow fibers produced from polymer of a particular type. Under the influence of the pressure and because of the nature of the material, the molecules of a gas will be adsorbed selectively by the material constituting the hollow fibers, passing through the pores of these porous fibers and will be recovered by desorption within the channel of very small size existing in these fibers. On the other hand, the gas or gases corresponding to the other molecules will not pass or will very little pass through the porous wall and will remain outside the bundle of hollow porous fibers. 
     In certain embodiments, a so-called sweeping gas flow, of a different composition than the permeate, is introduced within the fibers, from the side opposite that for recovery of the permeate. This injection has for its object to increase the yield by recuperation of the gas preferentially passing through the fibers. 
     This embodiment somewhat complicates the technique of permeators and is not described in what follows. The invention can also be applied to this type of embodiment. 
     In the accompanying FIG. 1, there is schematically shown a permeator. It comprises an external chamber  10  resistant to pressure, within which is mounted a bundle  12  of hollow porous fibers. The gaseous mixture is introduced by the nozzle  14  disposed at the lower end of the chamber  10 . The gas under pressure surrounds the bundle of hollow fibers. The fraction of the gas which passes through the hollow wall penetrates the channels of the fibers and is recovered at one end of these latter in a chamber  16 , the latter being connected to an outlet conduit  18  for the fraction of the gaseous mixture having passed through the wall of the fibers and which will ultimately be called permeate and indicated by the letter P. On the other hand, the fraction of the gaseous mixture which did not pass through the wall of the fibers is recovered, preferably with a tube provided with perforations  20  which extends axially along the bundle of fibers  12 . This fraction of the gaseous mixture leaves the chamber  10  by the nozzle  22  connected to the perforated tube  20 . The fraction of the gaseous mixture that did not pass through the wall of the hollow fibers will ultimately be called non-permeate and indicated by the letter R. 
     In another embodiment, the gaseous mixture is introduced via the central tube  22  and the non-permeate is recovered in the chamber  20 . 
     As already indicated, the pressure of the gaseous mixture is relatively high, typically in the order of several tens of bars. It is thus necessary that the external chamber  10  with resistance to pressure have a relatively great wall thickness and the different nozzles such as  18  and  22  passing through this wall must also be made precisely to maintain the resistance to pressure of the chamber  10 . 
     It will be understood that it is thus interesting to have several permeators  12  within the same pressure resistant chamber  10 . This has already been proposed, particularly in U.S. Pat. No. 4,874,405, which discloses a permeation module consisting of several individual permeators disposed one above the other, these permeators being disposed in a same pressure resistant chamber. 
     However, it appears that, for reasons both technical and economical, it is difficult to have more than three permeators one above the other within a same chamber. However, there exists a certain number of situations in which it is desired to be able to process volumes of gaseous mixture with relatively high flow rates which are not compatible with the use of three permeators disposed one above the other. 
     To solve this problem, it could be envisaged to arrange within a same pressure chamber (shown at  24  in the accompanying FIG.  1 A), several permeation ensembles, such as  26 , disposed one beside the others. In FIG. 1A, there is also shown the inlet nozzle  28  for the gaseous mixture to be treated in the pressure chamber  24 . However, it is important in such an installation that each permeation module be supplied by a predetermined gaseous flow rate, departing from this flow rate gives rise to a very great decrease in the output of the installation. To solve this problem, there can be envisaged provision of different permeation modules  26  in a pressure resistant chamber  24  of large dimension, such that the flow rates for each permeation module will be substantially the same. It will be understood, however, that such a solution is unacceptable because it leads to a very great increase in the cost of the installation because of the large dimensions of the pressure resistant chamber  24  and hence in particular the increase of the wall thickness of this chamber. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a permeation chamber in which several permeators or several permeation modules are disposed one beside the other within a single pressure resistant chamber whose dimension is reduced whilst permitting an overall higher output from this installation. 
     To achieve this object, according to the invention, the permeation installation comprises: 
     a single pressure resistant chamber, 
     at least two permeation modules disposed within said chamber, each module being constituted by at least one permeator formed of hollow fibers with a porous wall and being disposed within an envelope provided with perforations placing in communication the external portion of each module and the common gaseous circuit, 
     means to supply said installation with a gaseous mixture to be processed, 
     means to recover the fraction of the gaseous mixture that has passed through the wall of said fibers; 
     means to recover the fraction of the gaseous mixture that has not passed through the wall of said fibers. 
     It will be understood that, thanks to the interposition of the perforated envelopes constituting pressure drops in the common gaseous circuit, the modules are supplied with substantially equal flow rates for the different modules and with a good distribution of the flows for each module, thereby permitting the optimum operation of each permeation module and accordingly the optimum operation of the unit. It will be moreover understood that the perforated envelopes are disposed at the interface of two gaseous media whose pressures are not very different. These envelopes can therefore have a relatively simple mechanical construction. 
     According to a first embodiment, the perforators are interposed in the supply circuit of the gaseous mixture to the permeation modules. According to a second embodiment, the perforations are interposed in the recovery circuit of the fraction of the gaseous mixture that has not passed through the walls of the fibers of the permeators (non-permeate). 
     It will be understood that, in these two cases, the pressure drop which results permits substantially equalizing the gaseous flow rate in all the permeation modules. 
     According to a first embodiment of the installation, each permeation module has a generally cylindrical shape, each envelope has a cylindrical shape surrounding said permeation module over all its axial length and said cylindrical envelope is perforated in its lateral portion and is closed at each of its ends by a closed wall. 
     According to a second embodiment of the invention, each permeation module has a generally cylindrical shape, each permeation module is surrounded over all its length by an imperforate cylindrical wall and an imperforate plate closes one end of the imperforate cylindrical wall, another end plate having said perforations. 
     Preferably, the pressure drop created by said perforations is comprised between 10 and 90% of the total pressure drop between the inlet of the installation and the outlet for the fraction of the gaseous mixture that has not passed through the wall of the fibers, and preferably between 15 and 60%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Another characteristics and advantages of the invention will become better apparent from a reading of the description which follows, of several embodiments of the invention, given by way of non-limiting example. The description refers to the accompanying figures, in which: 
     FIG. 1, already described, shows schematically a permeator of the prior art; 
     FIG. 1A, already described, shows in simplified fashion a permeator that can be used with several permeation modules disposed side by side; 
     FIG. 2 is a simplified view of a first embodiment of a permeation installation according to the invention; 
     FIG. 3 shows in simplified manner a second embodiment of the permeation installation; 
     FIG. 4 shows in simplified manner a third embodiment of the permeation installation; 
     FIG. 5 shows in simplified manner a fourth embodiment of the permeation installation; 
     FIG. 6 shows in vertical cross-section a detailed example of embodiment of the permeation installation according to the embodiments of FIG. 3; 
     FIG. 6A is a cross-sectional view on the line A—A of FIG. 6; 
     FIG. 7 is a fragmentary view of FIG. 6 showing the recovery of the permeate and of the non-permeate in a permeation module; and 
     FIG. 7A is a cross-sectional view on the line A—A of FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A permeation installation according to the invention an belong to four different types, on the one hand, according to whether the envelope is perforated in its lateral portion (FIGS. 2 and 4) or at one of its ends (FIGS. 3 and 5) and on the other hand, according to the position of the perforated envelopes relative to the different gas flows, the perforated envelope being interposed within the gaseous mixture to be treated (FIGS. 2 and 3) or in the flow of non-permeate (FIGS.  4  and  5 ). 
     Referring first to FIG. 2, there will be described a first embodiment of the permeation installation. In this simplified figure, there is shown the pressure resistant chamber  30  provided with its nozzle  32  for the introduction of the gaseous mixture F. In each figure, there is also shown two permeators  34  and  36  which could also be permeation modules constituted by several permeators mounted one above the other. Each permeation module  34 ,  36  is disposed within an envelope constituted by a cylindrical wall  38  which extends over all the height of the permeation module and which is closed at its ends by two plates  40  and  42 . The sidewall  38  is perforated, with perforations of calibrated diameters, whilst the plates  40  and  42  are imperforate. In a schematic manner, there is also shown tubing  44  for the recovery of the non-permeate R and the tubing  46  for recovery of the permeate P recovered within the hollow fibers constituting the permeators  34 ,  36 . 
     It will be understood that thanks to the pressure drop resulting from the perforations  38 , the different permeators or permeation modules  34 ,  36  can be supplied with a same perfectly defined flow rate no matter what the pressure drop of the different paths from the introduction nozzle of the gaseous mixture  32  to the permeators  34 ,  36 . It will also be understood that the pressure within the envelope constituted by the lateral walls  38  and the end plates  40  and  42  is only a little less than the pressure of the gaseous mixture in the chamber  30  within the envelopes  38 . These envelopes  38  can thus have a reduced thickness and very much less than the thickness of the external chamber  30 . 
     FIG. 3 shows in a simplified manner a second embodiment of the permeation installation. The latter again comprises the external pressure chamber  30  with its nozzle  32  for introduction of the gaseous mixture to be treated under pressure. There are seen the permeators or permeation modules  34  and  36 . These latter are disposed in individual envelopes constituted by a cylindrical wall  50  extending over all the height of the permeation module, this wall  50  being imperforate. A first end of the lateral  50  is closed by an imperforate plate  52 , whilst its second end is closed by a plate  54  provided with perforations of calibrated dimensions. The same is true for all the permeators or permeation modules contained within the chamber. It will be understood that, as in the first embodiment, the perforated plates  54  divided the entering flow and impose pressure drops which can be adjusted with high precision to obtain for each permeation module a same flow rate corresponding to the optimum operation of the permeation module. As in the case of the first embodiment, the envelopes  50 ,  52 ,  54  can be made with a relatively less thickness, because the pressure on their two surfaces is substantially the same. The non-permeate R is recovered by the tubes  44  and leaves the chamber  30  by the nozzle  55 . 
     In the embodiment shown in FIG. 4, the installation has the same structure as that of FIG.  2 . The difference resides in the circulation of the different gas flows. The gaseous mixture F to be treated is introduced into the permeators through the interior tubes  44 , whilst the non-permeate R is recovered through the outlet nozzle  32  of envelope  30 . The perforated envelope ( 38 ,  40 ,  42 ) is disposed in the flow R of non-permeate leaving the permeators. 
     According to the embodiment of FIG. 5, the installation has the same structure as that of FIG.  3 . Only the circulation of the different gas flows is modified. The gaseous mixture F to be treated is introduced into the chamber through the nozzle  55  and the non-permeate R is recovered through the nozzle  32  after having passed through the perforations of the plates  54 . 
     It follows that the number of permeators or of permeation modules is typically greater than  2 , as is shown in simplified manner in FIGS. 2 to  5 . This number can be equal to  3 ,  5  or  7 , which permits optimum filling of the interior of the chamber  30 . 
     It will be understood that no matter what the embodiment in question, the pressure drop created by each perforated envelope interposed between the introduction nozzle for the mixture into the chamber and each permeation module, or between each permeator and the recovery nozzle of the non-permeate, permits defining very precisely the circulatory flow rate through each permeation module. It will also be understood that this pressure drop can be defined in such a manner as to be very much greater than the pressure drop resulting from the normal circulation of the gaseous mixture within the pressure resistant chamber and at the exterior of the envelope surrounding each permeation module. There can also be a certain number of permeation modules beside each other in a pressure resistant chamber of reduced dimensions. It will also be understood that the pressure on opposite sides of the perforated plates is relatively identical and that the plates can therefore be made of sheet metal of a thickness that is also relatively reduced. 
     Preferably, the pressure drop created by the perforated envelopes is comprised between 10 and 90% of the total pressure drop between the inlet of the installation and the non-permeate outlet. Preferably, this pressure drop is comprised between 15 and 60%. 
     It can also be indicated that, preferably, the total surface of the perforations represents from 0.1 to 3 times the cross-section of the supply nozzle for gaseous mixture (FIGS. 2 and 3) or this same proportion of the cross-section of the outlet nozzle for the non-permeate (FIGS.  4  and  5 ). Again preferably, these ranges are comprised between 0.5 and 2 times the cross-sectional area of the nozzle. 
     The perforations can also be predetermined by the perforation that their total surface represents relative to the total surface of the perforated envelope. This proportion is preferably below 10% and again preferably below 1%. 
     Referring now to FIGS. 6 and 7, there will be described in greater detail a preferred embodiment of the permeation installation according to the principle shown in FIG.  3 . 
     In FIG. 6, there is shown the external pressure resistant chamber  70  of the permeation installation which is constituted by a cylindrical sidewall  72 , by a bolted cover  74  and by a semispherical end cap  76 . 
     The bottom  76  of the pressure chamber is provided with a nozzle  78  for the introduction of the gaseous mixture to be processed. The lower portion of the chamber is separated from the rest of the latter by a plate  80  which thereby defines, at the lower end of the chamber, a single supply chamber  81 . In this figure, there are also shown two permeation modules  82  and  84 , the cross-sectional view of FIG. 6A showing that the installation in fact comprises a third permeation module  86 . Each permeation module comprises three unitary permeators generally indicated at  88 ,  90  and  92 , disposed in series one above the other. Each permeation module is surrounded over all its length by a cylindrical envelope  94  whose upper end is closed by a plate  96  and whose lower end is closed by a lower perforated plate  98  which is connected in sealed fashion to the plate  80  or which is integral with it. Thus, the perforations such as  100  in the perforated plates  98  open directly into the supply chamber  81  and thereby permit creating a pressure drop between the introduction nozzle  78  and each permeation module  82 ,  84  and  86 . As better shown in FIG. 6A, the perforations are preferably disposed on a same circle relative to the longitudinal axis of the permeation modules, thereby permitting providing a homogeneous circulation over all the periphery of the module. 
     The recovery of the permeate P and of the non-permeate R will be better understood with reference to FIGS. 7 and 7A, in which there is shown a portion of a permeation module. More precisely, in FIG. 7, there is shown for example the permeator  90  and the permeator  92  of the permeation module  82 . There is also shown the envelope  94 . At the upper end of the bundle of hollow fibers constituting the permeator  90 , is seen an annular chamber  102  for recovery of the permeate within the hollow fibers. The recovery of the non-permeate is carried out through a perforated tube  104  which is disposed in an axial passage  106  of each permeator. The perforated tube thus permits recovering the non-permeate which arrives at the upper end  108  of the perforated tube  104  above the plates  96  closing the envelopes  94  surrounding each permeation module. The non-permeate thus arrives in the upper space  110  of the external chamber and redescends into the vertical spaces limited on the one hand by the cylindrical sidewall  72  of the external chamber, and on the other hand by the envelopes  94  of the permeation modules. The non-permeate R is recovered through the outlet nozzle  112  disposed at the lower end of the cylindrical sidewall  72  above the plate  80 . 
     It will be understood that thanks to this arrangement, the assembly of the permeation modules is surrounded by a circulation of gas corresponding to the non-permeate which is also located along the external wall of the permeation installation. This circulation permits maintaining a very homogeneous temperature during operation of the modules by preventing any contact between the gas to be treated and the external medium, generally at a substantially lower temperature, thereby to obtain optimum performance. 
     Returning to FIG. 7, it will be seen that the recovery of the permeate is carried out through an axial tube  114  introduced into the perforated tube  104 . At the level of each chamber  102  for recovery of the permeate, tubing  116  connects the tube  114  to the chambers  102 . The upper end of the tube  114  is closed whilst its lower end passes through the bulbous portion  76  of the external envelope to be connected to nozzles  118 . 
     The permeation installations according to the invention can have numerous applications, particularly the purification of hydrogen. 
     The permeate is thus the hydrogen of which it is desired that the purity be above 80% in total moles of permeate, preferably greater than 85%. The installation operates at a temperature comprised between 40 and 120° C. 
     Another installation consists in obtaining a mixture of predetermined composition, of hydrogen and a gas selected from CO, N 2 , Ar, CO 2  and He. In this case, the mixture is the non-permeate R. The installation operates at a temperature comprised between 60 and 90° C.