Abstract:
The invention relates to a vaporizer-condensor ( 4 ) of the bath type, comprising at least one heat exchange body ( 13 ), having a multitude of flat passages ( 18 ) for the countercurrent circulation of two fluids in a same direction, and a sealed chamber ( 14 ) for confining a fluid containing the or each heat exchange body, the confinement chamber comprising a central section ( 50 ) of generally cylindrical shape along a longitudinal axis (Y—Y). 
     The longitudinal axis of the central section of said or each confinement chamber is orthogonal to the direction of countercurrent circulation of the fluids in the flat passages of the corresponding heat exchange body. 
     Use in double column air distillation installations.

Description:
FIELD OF THE INVENTION 
     The present installation relates to a vaporizer/condenser of the bath type, comprising at least one heat exchange body, having a multitude of flat passages for the countercurrent circulation of two fluids, from one or several distillation columns, in a same direction, and at least one sealed chamber for confining a fluid containing the or each heat exchange body, the confining chamber comprising a central section of generally cylindrical shape along a longitudinal axis, the longitudinal axis of the central section of said or each confinement chamber being substantially orthogonal to the direction of countercurrent circulation of the fluids in the flat passages of the corresponding heat exchange body. 
     The term “substantially orthogonal” comprises spacings up to 30°, or 20°, or preferably 10° from strict orthogonality. 
     It is sometimes necessary to orient the vaporizer so as to facilitate draining of the liquids. 
     BACKGROUND OF THE INVENTION 
     A vaporizer-condenser of this type is known from DE 1152432, in which the confinement chamber is limited in part by the heat exchange body, the liquid bath of the vaporizer being located exclusively outside the confinement element. 
     The invention is applicable in particular to double column air distillation installations, which is to say with a medium pressure column thermally connected to a low pressure column, provided with vaporizers-condensers of mentioned type. 
     In such installations for the distillation of air, the liquid oxygen which is in the base of the low pressure column is vaporized in the vaporizer-condenser by heat exchange with gaseous nitrogen from the head of the medium pressure column. 
     For a given operating pressure of the low pressure column, the temperature difference between the oxygen and the nitrogen rendered necessary by the structure of the vaporizer-condenser dictates the operating pressure of the medium pressure column. 
     It is therefore desirable that this temperature difference be as small as possible, so as to minimize the expenses connected with the compression of air to be treated injected into the medium pressure column. 
     The reduction of the temperature difference between the nitrogen and the oxygen requires, to preserve the heat exchange capacity of the vaporizer-condenser, increasing the heat exchange surface in this latter. 
     A first solution would consist in increasing the height of the heat exchange body of the vaporizer-condenser to increase the heat exchange surface. However, such an increase of height leads to a hydrostatic overpressure in the oxygen passages which tend to increase the temperature difference and which would impede the good operation of the vaporizer-condenser. 
     Another solution would consist in multiplying the number of passages dedicated to the oxygen and to the nitrogen, for example by increasing the number of the juxtaposed heat exchange blocks which constitute the exchanger body and which operate in parallel in the vaporizer-condenser. 
     Generally speaking, in double column distillation installations, the low pressure column surmounts the vaporizer-condenser which itself surmounts a medium pressure column. The central section of the sealed chamber of the vaporizer-condenser is thus constituted by a sleeve with a vertical axis of revolution. This sleeve is preferably of the same diameter as the sleeves delimiting the medium pressure and low pressure columns. 
     The use of the second solution to increase the heat exchange surface in such a distillation installation would thus require having a vaporizer-condenser sleeve of a diameter greater than those of the medium and low pressure columns. 
     The cost of construction of such an installation would thus be relatively high, particularly because of the large diameter of the sleeve of the vaporizer-condenser and the particular connection pieces to be provided between the sleeve of the vaporizer-condenser and the sleeves of the medium and low pressure columns. 
     SUMMARY OF THE INVENTION 
     The invention has for its object to solve this problem by providing a vaporizer-condenser of the mentioned type, which can function with reduced temperature differences and which permit particularly building double column air distillation installations that are relatively simple and of low cost to construct. 
     To this end, the invention has for its object a vaporizer-condenser of the mentioned type, characterized in that the chamber is located outside of any distillation column and is adapted to contain a bath of liquid to be vaporized. 
     According to particular embodiments, the vaporizer-condenser can comprise one or several of the following characteristics, taken alone or according to any possible technical combination: 
     said or each chamber is formed such that in use, a bath of liquid can surround at least the lower part of the heat exchange body and preferably overflow the upper edge of the latter; 
     said or each heat exchange body comprises several juxtaposed heat exchange blocks along the longitudinal axis of the central section of the corresponding confinement chamber; 
     said or each heat exchange body comprises inlet and outlet connections for fluids, these connections communicate with flat passages of the heat exchange body and are assigned pair-wise to a fluid, the connections of each pair of inlet and outlet connections assigned to a same fluid being disposed substantially symmetrically relative to a longitudinal and median plane of said heat exchange body; 
     said or each of said heat exchange bodies comprises at least one inlet collector and an outlet collector connected respectively to a pair of inlet and outlet connections assigned to a same fluid; 
     for said or each heat exchange body, the outlet or inlet collector or collectors are supported by a same region, particularly the longitudinal end, of the corresponding confinement chamber; 
     for said or each confinement chamber, the central section has a general shape of revolution about its longitudinal axis and preferably the chamber is cylindrical; 
     said or each confinement chamber is or is not delimited, at the level of its central section, in part by the corresponding heat exchange body; 
     said heat exchange body comprises inlet and outlet connections for fluids communicating with the flat passages of said heat exchange body, and these connections are disposed outside said confinement chamber; 
     said or each heat exchange body comprises inlet connection for a gas communicating with passages of the heat exchange body, said heat exchange body comprising means for introduction into these passages of the condensed gas present in said inlet connections; 
     the flat passages of the at least one body are oriented transversely relative to the longitudinal direction of the confinement chamber. 
     the vaporizer comprising at least two bodies, one having flat passages or oriented transversely relative to the longitudinal direction of its confinement chamber and the other having flat passages oriented parallel relative to the longitudinal direction of its confinement chamber. 
     The invention moreover has for its object an installation for the distillation of air, characterized in that it comprises a vaporizer-condenser as defined above, and in that the longitudinal axis of the central section of said or each confinement chamber of the vaporizer-condenser is substantially horizontal. 
     “Substantially horizontal” means “horizontal or having departures up to 30°, preferably 10°, from the horizontal”. 
     Obviously, the heat exchanger within the chamber must remain horizontal so that its operation will be ensured. 
     According to modifications: 
     the installation comprises a medium pressure column, a low pressure column, nitrogen from the head of the medium pressure column and oxygen from the bottom of the low pressure column being placed in heat exchange relation by the vaporizer-condenser; 
     said or each confinement chamber is disposed beside medium pressure and low pressure columns; 
     at least a portion of the vaporizer-condenser is disposed at a level intermediate those of the bottom of the low pressure column and the top of the medium pressure column; 
     the chamber contains a liquid oxygen bath in which the body is submerged in use and 
     the installation comprises a principal heat exchange line to cool the air to be distilled, and the vaporizer-condenser surmounts the principal heat exchange line, the vaporizer-condenser and the principal heat exchange line having if desired parallel axes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from a reading of the description which follows, given solely by way of example and with respect to the accompanying drawings, in which: 
     FIG. 1 is a schematic view of an air distillation installation according to the invention, 
     FIGS. 2 and 3 are schematic perspective views showing respectively the oxygen confinement chambers and the heat exchange body of the vaporizer-condenser of the installation of FIG. 1, 
     FIG. 4 is a schematic half view in vertical transverse section of the vaporizer-condenser of the installation of FIG.  1  and shows particularly the structure of a nitrogen passage, 
     FIG. 5 is a schematic view in vertical transverse cross-section, showing an oxygen passage of the vaporizer condenser of the installation of FIG. 1, 
     FIGS. 6 and 7 are views analogous to FIG. 4 showing two modifications of the invention, and 
     FIG. 8 is a view similar to FIG. 5 showing the structure of an oxygen passage for the modification of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows schematically an installation  1  for the distillation of air, which comprises essentially: 
     a double distillation column which comprises a medium pressure column  2 , a low pressure column  3  and a vaporizer-condenser  4  of the bath type, 
     a principal heat exchange line  5 , 
     an air compressor  6 , 
     an air purification apparatus  7 , and 
     a pump  8 . 
     The low pressure column  3  surmounts the medium pressure column  2 . A vertical sleeve  10  maintains the top of the medium pressure column  2  spaced from the bottom of the low pressure column  3 . 
     The principal heat exchange line  5  comprises, in the illustrated example, five heat exchange blocks  11 . These heat exchange blocks  11  are connected in parallel to the rest of the installation  1  but, for greater clarity, the connections of only a single one of these blocks have been shown in FIG.  1 . The nature of these connections will become more clear during the description of the operation of the installation  1  which will be made later. 
     As shown in FIGS. 1 to  4 , the vaporizer-condenser  4  comprises two identical heat exchange bodies  13  (FIG. 3) of brazed aluminum, which are disposed each in a sealed and cylindrical chamber  14  for confinement of oxygen, in stainless steel or aluminum (FIG.  2 ). A single heat exchange body  13  and a single oxygen confinement chamber  14  are shown in FIG.  1 . 
     It will be understood that a vaporizer-condenser according to the invention can comprise only a single heat exchange body and hence a single confinement chamber or at least three heat exchange bodies, each having its own chamber. Each body  13  has a height between 400 and 1400 mm. 
     The vaporizer-condenser  4  being symmetrical relative to a vertical plane P whose trace is visible on FIG. 4, only a half of the structure of this vaporizer-condenser  4  will be described below. Thus, a single heat exchange body  13  and a single sealed chamber  14  will thus be described in what follows. 
     The heat exchange body  13  has a generally elongated shape along a horizontal or substantially horizontal longitudinal axis X—X and comprises, in the illustrated example, five heat exchange blocks  16  with analogous and joined brazed plates. The five blocks  15  are substantially identical; their number is selected as a function of the size of the vaporizer, thereby facilitating the dimensioning, because identical blocks will be mass-produced. Thus, there can be at least five or more than five blocks  15 . The heat exchange body  13  is symmetrical relative to a longitudinal, vertical and median plane Q whose trace is visible on FIG.  4 . 
     Each heat exchanger block  16  comprises a stack of parallel rectangular brazed plates  17  which define two-by-two passages designated alternately to nitrogen and oxygen. The spacing between the parallel plates  17  is fixed by corrugated partitions which also fulfill the function of thermal fins. The flat passages of the blocks are oriented transversely relative to the longitudinal dimension of the chamber  14 . 
     The passage  18  dedicated to nitrogen is visible in FIG.  4 . 
     This passage  18 , as all the passages  18  dedicated to nitrogen, is rectangular and comprises a principal central heat exchange region  19 , two inlet distribution regions  20  and two outlet collecting regions  21 . 
     The principal heat exchange region  19  comprises a corrugated spacer with vertical generatrices. Each inlet distribution region  20  is in the form of a right angle triangle, disposed in an upper corner  22  of the passage  18  and comprises a corrugated partition with horizontal generatrices. The two inlet distribution regions  20  reunite at the level of the median plane Q, the large bases of these right triangular regions  20  being horizontal. 
     The structure and arrangement of the outlet collection regions  21  is similar to that of the inlet distribution regions  20 , these regions  21  each being disposed at the level of a lower corner  23  of the passage  18 . 
     The passage  18  is closed over all its periphery by vertical and horizontal bars except for a portion at the level of the small vertical bases  24  of the inlet triangular regions  20  and the small vertical bases  25  of the triangular outlet regions  21 , and on the other hand, at the level of liquid nitrogen introduction means, which will be mentioned later. 
     The small bases  24  and  25  of the inlet regions  20  and outlet regions  21  of the five heat exchange blocks  16  form, on each side of the heat exchange body  13 , respectively a series of inlet windows and a series of outlet windows for nitrogen, aligned horizontally. 
     Each series of inlet windows  24  is capped hermetically by an inlet box  28  of a semicircular cross-section, which extends along the five heat exchange blocks  16 . 
     Each inlet box  28  is disposed adjacent upper corners  22  of the nitrogen passages  18  and at a height along the vertical substantially greater than that of the small bases  24  of the inlet distribution regions  20 . 
     Each nitrogen passage  18  moreover comprises adjacent the lower edge of each box  28 , introduction means  30  in the liquid nitrogen passage  18  present in the bottom of the box  28 . These means  30  are in the form for example of a triangular region communicating with the bottom of the inlet box  28 . Such a triangular region converges toward the plane Q and comprises a corrugated partition with oblique generatrices inclined downwardly and toward the interior of the passage  18 . According to a modification (not shown), such liquid nitrogen introduction means  30  need have no corrugation to guide the liquid nitrogen or can be constituted by a bar regularly pierced with openings. 
     Each series of outlet windows  25  of the passages  18  dedicated to nitrogen, is hermetically capped by an outlet box  32 , of semi-circular cross-section of a radius less than that of the inlet boxes  28 . Each outlet box  32  extends longitudinally along five heat exchange blocks  16 . Each outlet box  32  is disposed adjacent lower corners  23  of the passages  18  dedicated to nitrogen and at a height, along the vertical, less than that of the small bases  25  of the outlet collector regions  21 . 
     FIG. 5 is a vertical transverse cross-sectional view showing the structure of a passage  34  of the heat exchange body  13  dedicated to oxygen. Such a passage  34 , as are all the passages  34  dedicated to oxygen, comprises a single corrugated partition  35  with vertical generatrices. This passage  34  is closed on its sides by two vertical bars  36  and opens outwardly at the level of its upper and lower horizontal edges  37  and  38 , respectively. 
     The exchanger body  13  also comprises, at the level of its front end (to the right in FIGS. 1 and 3) a gaseous nitrogen inlet collector  39 , symmetrical relative to the plane Q. This inlet collector  39  comprises a rectilinear and horizontal inlet conduit  40 , and two elbowed outlet conduits  41  each connected to the front end of an inlet box  28 . 
     Each outlet box  32  comprises, at the level of each heat exchange block  16 , a vertical connection sleeve  42 . Two conduits  44  for collecting incondensable rare gases, extend horizontally on opposite sides of the heat exchange body  13  and along the latter. Each collection conduit  44  is located at an intermediate level between the inlet box  28  and the corresponding outlet box  32 . These conduits  44  are connected to the upper ends of the sleeves  42  and open, at the level of the forward end of the heat exchange body  13 , into a collector conduit  45  for the outlet of incondensable rare gases. This outlet collector conduit  45  is horizontal and symmetrical relative to the plane Q. 
     Transverse elbowed conduits  46  (FIGS. 1 and 4) are disposed below the heat exchange body  13  and connect the lower ends of the connection sleeves  42  to a horizontal liquid nitrogen outlet collector conduit  48  which extends horizontally practically over all the length of the heat exchange body  13 , symmetrically relative to the plane Q. This outlet collector conduit  48 , like the inlet conduit  40  and the outlet collector conduit  45 , projects forwardly relative to the heat exchange body  13 . 
     As shown in FIGS. 1 and 2, the sealed chamber  14  comprises a central portion  50  of generally cylindrical shape, in the form of a metallic sleeve with an axis of revolution Y—Y. This sleeve  50  is sealingly closed at the level of its forward end by a forward partition  51  and, at the level of its rear end by a rear partition  52 . These partitions  51  and  52  have a concavity directed inwardly of the chamber  14 . 
     The chamber  50  has, in its forward partition  51 , three circular passages disposed one below the other, respectively  54 ,  55  and  56 , whose cross-sections correspond respectively to those of the inlet conduit  40  of the gaseous nitrogen inlet collector  39 , of the incondensable rare gas outlet collector conduit  45 , and of the liquid nitrogen outlet collector conduit  48 . 
     Another liquid oxygen supply passage  57  is provided in this forward partition  51  between the passages  54  and  55 . 
     A passage  58  (FIG. 1) for liquid oxygen withdrawal is provided in the rear partition  52 . 
     A purge  59  is provided in the bottom of the central section  50  of the sealed chamber  14 . 
     The heat exchange body  13  is disposed in the sealed chamber  14 , their longitudinal axes X—X and Y—Y being parallel. The inlet conduit  40 , the outlet collector conduit  45  and the outlet collector conduit  48  pass to the exterior of sealed chamber  14  respectively through the passages  54 ,  55  and  56 . 
     As shown in FIG. 2, the two sealed chambers  14  are disposed with their longitudinal axes Y—Y parallel and horizontal. The sealed chambers  14  are symmetrically connected relative to the plane P to a common pipe for the evacuation of gaseous oxygen, which extends above the sealed chamber  14 , parallel to their longitudinal axes Y—Y. 
     The vaporizer-condenser  4  is disposed beside the medium pressure column  2  and low pressure column  3 , above the principal heat exchange line  5  whose height has been reduced in FIG. 1 to facilitate illustration. The vaporizer-condenser  4  is supported by the heat exchange line  5  by means of partitions (not shown). A portion of the heat exchange body  13  of the vaporizer-condenser  4  is disposed at an intermediate level between the bottom of the low pressure column  3  and the top of the medium pressure column  2 . 
     The operation of the installation  1  will now be described. 
     Air to be distilled, first compressed by the compressor  6  and purified by the apparatus  7 , passes through the heat exchange line  5  to cool to its dew point. This cooling is ensured in parallel by the heat exchange blocks  11 . Then the cooled oxygen is injected into the bottom of the medium pressure column  2 . 
     The gaseous nitrogen from the head of the medium pressure column  2  is introduced by inlet collectors  39  into the two inlet boxes  28  of each heat exchange body  13 . This gaseous nitrogen is distributed, by distribution regions  20 , uniformly over all the width of the passages  18  dedicated to nitrogen of this heat exchange body  13 . The nitrogen then flows vertically downwardly in the regions  19  of the passages  18  while progressively condensing. 
     Liquid nitrogen that may be present in the bottom of the inlet boxes  28  is introduced into the regions  19  of the passages  18  by the introduction means  30 . This liquid nitrogen then flows vertically downwardly with the nitrogen condensed in the regions  19 . 
     The liquid nitrogen is collected at the bottom of the regions  19  of the passages  18  by means of outlet collector regions  21  and then returned to the two outlet boxes  32 . The incondensable fraction contained in this nitrogen flow is sent by collector conduits  44  and outlet collector conduit  45  to the outside atmosphere. The condensed nitrogen emerging from the passages  18  is itself collected by transverse conduits  46  and by the outlet collector conduit  48  and then returned to the head of the medium pressure column  2 . 
     Liquid oxygen from the bottom of the low pressure column  3  is introduced into each oxygen-confining chamber  14  by means of passages  57  provided in their forward partitions  51 . This liquid oxygen forms a bath in each chamber  14  which fills most of the internal volume of this sealed chamber  14 . The upper surface of the corresponding heat exchange body  13  projects slightly above the liquid oxygen path. 
     Liquid oxygen from the bath circulates vertically upwardly in the passages  34  of the heat exchange body  13  in question while vaporizing countercurrent to the nitrogen circulating in the passages  18 . 
     The oxygen vaporized by each heat exchange body  13  is then returned by means of the nozzle  60  to the bottom of  25  the low pressure column  3 . 
     “Rich liquid” LR (liquid enriched in oxygen), from the bottom of the medium pressure column  2 , is expanded in an expansion valve  61  and then injected at an intermediate level into the lower pressure column  3 . 
     “Poor liquid” LP (somewhat pure nitrogen), from the head of the medium pressure column  2 , is expanded in an expansion valve  62  and then injected at the top of the low pressure column  3 . 
     Impure or “residual” nitrogen NR, withdrawn from the top of the low pressure column  3 , is reheated by passing through the principal heat exchange line  11 . 
     Gaseous oxygen, from the head of the low pressure column  3 , is reheated in the principal heat exchange line  5 . Liquid oxygen, withdrawn from the passages  58  of the sealed chambers  14  and the pump, is vaporized by passing through the principal heat exchange line  5 . 
     Purges  59  permit evacuating impurities which accumulate in the bottom of the oxygen confinement chambers  14 . 
     The structure of the vaporizer-condenser  4  and the position of the sealed chambers  14  permit achieving relatively great heat exchange surfaces by juxtaposition of heat exchange blocks  16 . 
     Moreover, the cost of such a vaporizer-condenser  4  is relatively reduced because of the relatively small diameter of the central sections  50  of the oxygen confinement chambers  14  and by the simplicity of the structure of these chambers  14 . The size of the vaporizer-condenser  4  is also relatively small because of the small diameter of the central sections  50  of the chambers  14 . 
     Moreover, because of the position of the vaporizer-condenser  4 , the circulation of the different fluids between the head of the medium pressure column  2  and the bottom of the low pressure column  3  and the vaporizer-condenser  4  can be ensured while limiting the pumping means. 
     It will also be seen that, for a given air distillation capacity, the length and the ground surface of the heat exchange line  5  are comparable to those of the vaporizer-condenser  4 . Moreover, the height of the medium pressure column  2 , and hence the height at which the vaporizer-condenser  4  must be positioned, corresponds practically to the height of the principal heat exchange line  5  added to the height necessary for the various connections of this line with the rest of the installation  1 . Thus, the height of the support partitions of this vaporizer-condenser  4  is limited. 
     It will be noted that the symmetry of the structure of the heat exchange bodies  13  permits decreasing the height of the inlet distribution regions  20  and outlet collecting regions  21  and hence, for a given exchange height, minimizing the hydrostatic overpressure which is harmful to obtaining a small temperature difference. 
     Moreover, in the case in which the oxygen confinement chambers  14  and the heat exchange bodies  13  will be of different metal requiring the use of mixed junctions, the structure and the presence for each heat exchange body  13  of the inlet connector  39 , of the single outlet collector  45  and of the outlet collecting conduit  48 , permit limiting the number of these junctions. Thus, it is not necessary to provide such junctions but at the level of the inlet conduit  40  of the inlet collector  39 , of the outlet collector  45 , and of the forward end of the outlet collector conduit  48 . 
     The fact that the inlet collector  39 , the outlet collector conduit  45  and the outlet collector conduit  48  are carried by a same region of the forward partition  51  of each oxygen confinement chamber  14 , also permits limiting the inconvenience connected with the difference of the coefficients of thermal expansion between the chambers  14  and the heat exchange bodies  13 . 
     A satisfactory circulation of liquid oxygen in the bath of each chamber  14  is ensured by the fact that the liquid oxygen supply and withdrawal passages  58  are located at opposite ends of each chamber  14 . 
     Finally, to provide vaporizer-condensers  4  of different capacities as a function of specific needs of different air distillation installations  1 , it suffices to modify the number of heat exchange blocks  16 , the number and the diameter of the different connections, and the length of the sleeves  50 . 
     FIG. 6 shows a modification of the invention which is distinguished from that of FIGS. 1 to  5  particularly by what follows. 
     A portion of  70  of the internal flank of the central section  50  of each chamber  14  is constituted by a flank  71  of the corresponding heat exchange body  13 . The general cylindrical shape of the central sections  50  is thus no longer one of revolution. 
     Each heat exchange body  13  no longer has a symmetrical structure and comprises, for each passage  18  dedicated to nitrogen, a single triangular inlet distribution region  20  and a single triangular outlet collection region  21  each of which extends over all the width of the passage  18  in question. 
     A single inlet box  28  and a single outlet box  32  are connected to each heat exchange body  13  on its flank  71 . These boxes  23  and  25  are located outside the corresponding oxygen confinement chamber  14 . 
     Gaseous nitrogen is supplied from the head of the medium pressure  2  to the two inlet boxes  28 , by means of a common inlet collector conduit  73  and two series of transverse conduits  74 . The inlet collector conduit  73  is horizontal and symmetrical relative to the plane P. Each series of conduits  74  comprises transverse conduits  74  regularly spaced from each other and supplying a same inlet box  28 . 
     Similarly, an incondensable rare gas outlet collector conduit  75 , common to the two outlet boxes  32 , extends horizontally and symmetrically relative to the plane P. 
     This outlet collector conduit  75  is connected to each outlet box  32  by a series of transverse conduits  76  regularly spaced from each other. 
     Similarly, a condensed liquid nitrogen outlet collector conduit  77 , common to the two outlet boxes  32 , extends horizontally and symmetrically relative to the plane P. 
     This outlet collector conduit  77  is connected to each outlet box  32  by a series of transverse conduits  78  regularly spaced from each other. The condensed nitrogen is thus returned to the head of the medium pressure column  2  by means of the outlet collector conduit  77 . 
     The supply of liquid oxygen for each oxygen confinement chamber  14  is ensured by an inlet collector conduit  80  disposed in the chamber  14  in question, parallel to the axis Y—Y, and regularly pierced by distribution openings. Withdrawal of liquid oxygen from each chamber  14  is ensured by a series of transverse conduits  81  opening into the bottom of the chamber  14  and by a horizontal outlet collector conduit  42  which is symmetrical relative to the plane P and common to the two chambers  14 . 
     The fact that the inlet boxes  28  and outlet boxes  32  of each heat exchange body  13  are situated outside the oxygen confinement chambers  14 , permits improving the safety of the vaporizer-condenser  4 . It is thus no longer necessary to take into account a possible malfunction of the connections to determine the thickness of the wall of the central body  50  of each oxygen confinement chamber  14 . 
     The modification of FIG. 6 also permits simplifying the structure of the heat exchange bodies  13  and their connections to the rest of the installation  1 . 
     Moreover, the inlet collector conduit  80 , the transverse conduits  81  and the common outlet collector conduit  82  permit ensuring a good circulation of liquid oxygen in the bath of each chamber  14 . It is to be noted that such conduits can also be provided in the modification of FIGS. 1 to  5 . 
     FIGS. 7 and 8 show another modification of the invention which is principally distinguished from that of FIG. 6 by what follows. 
     For each oxygen confinement chamber  14 , a portion of body  85  of the central body  50  of the chamber is formed by the lower wall  86  of the corresponding heat exchange body  13 . Each outlet box  32  has a section covering the three quarters of a circle and covers a lower corner  23  of the corresponding heat exchange body  13 . 
     As shown in FIG. 8, each passage  34  dedicated to oxygen has an inlet distribution region  87 . This region  87  is in the form of a right triangle, and is disposed at the level of the lower edge  38  of the passage  34  and extends over all the width of this passage  34 . The region  87  converges toward the flank  71  of the heat exchange body  13 . The small face  88  of the inlet distribution region  87  is located at the level of the flank  89  of the heat exchange body  13  opposite the flank  71 . The passage  34  is closed on its lateral sides by two vertical bars  36 , except at the level of the small base  88  of the inlet distribution region  87 , and by a horizontal bar  90  at the level of the lower edge  38  of the passage  34 . 
     The liquid oxygen supply and withdrawal of each chamber  14  are ensured as in the case of FIGS. 1 to  5 . 
     As in the case of the modification of FIG. 6, this modification permits simplifying the structure of the heat exchange bodies  13  and their connections to the rest of the distillation installation  1 .