Abstract:
A liquid-gas manifold includes a single container of roughly cylindrical overall external shape, designed to define an annular space between a side wall of the container and an interior wall of a heat exchange column. The container also has a perforated bottom and a connection between the container and the interior wall of the column. Gases from the annular space are transferred to a space located above the container.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of matter and/or heat exchange columns, particularly columns for scrubbing or distilling gas mixtures. More specifically, it relates to manifolds that collect the liquid descending down inside these columns and distribute it over the upper surface of the active zone of the column that they overhang. 
     During the processes of separating the various constituents of a gaseous mixture inside a column, it may be necessary to extract the gases ascending up inside this column so as to subject them to a treatment such a heat exchange operation intended to return them to a given temperature. This is the case in particular when scrubbing the ascending gases inside the column using a liquid constituent. As an example of such a method, mention may be made of the operation of separating hydrogen from mixtures containing hydrogen, CO and methane which are obtained by the reforming of methane with steam. During the separation operation aimed at collecting pure hydrogen at the top of the column, the hydrogen may be scrubbed with liquid methane that is introduced into the upper part of the column. 
     For such a scrubbing operation to be as effective as possible, a temperature as close as possible to −180° C. needs to be maintained throughout the column, even though the scrubbing is exothermal. For this purpose, it is a known practice to extract the ascending gases at various points on the column, to pass them through a heat exchanger aimed at cooling them, and to reintroduce them into the column at a level above the level at which they were tapped. The drop in temperature of the collected gases after they have passed through the exchanger causes the less volatile compounds of the gaseous mixture to condense. This condensed liquid is collected by liquid traps which pour it out into manifold containers. These manifold containers have a perforated bottom which allows them to distribute the liquid they contain over the upper surface of an active zone, such as a packing, that they overhang. 
     These liquid trap-manifold assemblies constitute relatively bulky members, the overall height of which can be as much as a few meters. As the column generally has a number of packings and stages where the ascending gases are extracted, cooled and then reintroduced into the column, this construction of necessity entails building very tall columns, therefore having a high cost price. In addition, these liquid trap-manifold assemblies are of complex structure and are in themselves costly to produce. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide users of matter and/or heat exchange columns with liquid-gas manifolds which are appreciably less complicated than the existing manifolds, so as to allow a reduction in the cost of construction of the column, and possibly in its overall height. 
     To this end, a subject of the invention is a liquid-gas manifold for a matter and/or heat exchange column, characterized in that it comprises a single container of roughly cylindrical overall external shape, designed to define an annular space between its side wall and the interior wall of the said column and having a perforated bottom, means for connecting the container to the interior wall of the column, and means allowing the gases to be transferred from the said annular space to the space located above the container. 
     The latter means may consist of openings formed in an upper lip of the said manifold, or in the side wall of the container. 
     As a preference, the container has a narrowing of its internal cross section in its central part. 
     Another subject of the invention is a matter and/or heat exchange column comprising at least one liquid-gas manifold collecting the descending liquid to distribute it to an active zone that it overhangs, characterized in that the said manifold is in accordance with the type described above. 
     According to one variant of the invention, the said means allowing the transfer of the ascending gases from the said annular space into the space located above the container comprise a pipe for tapping the ascending gases from the said annular space and a pipe for reintroducing the said gases into the column above the container. 
     According to another variant of the invention, openings are made in an upper lip of the container, and open into an heat exchanger incorporated into the said column. 
     As will have been appreciated, the invention consists in incorporating into the liquid-gas manifold, a single container of cylindrical overall shape with a perforated bottom, with which no separate liquid trap is associated. According to the various variants of the invention, the container collaborates with the wall of the column to send the ascending gases to undergo a treatment in apparatus located outside or inside the column, or allows the ascending gases to pass through. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from reading the description which follows, which is given with reference to the following appended figures: 
     FIG. 1 which depicts, in longitudinal section, one portion of a gaseous mixture separation column of the prior art; 
     FIG. 2 which depicts, in longitudinal section, one portion of a gaseous mixture separation column equipped with a liquid-gas manifold according to the invention; 
     FIG. 3 which depicts, in longitudinal section, one portion of a gaseous mixture separation column equipped with a liquid-gas manifold according to a variant of the invention; 
     FIG. 4 which depicts, from above, a liquid-gas manifold according to another variant of the invention; 
     FIG. 5 which depicts, in longitudinal section, a portion of a gaseous mixture separation column equipped with a liquid-gas manifold according to another variant of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The portion of gaseous mixture separation column according to the prior art which is depicted in FIG. 1 comprises a cylindrical wall or barrel  1 . It is filled over a portion of its height with a packing  2  constituting an active zone of the column. In the installation given by way of example, the gases leaving the packing  2  are at a temperature higher than the desirable temperature for performing a gas scrubbing operation with the greatest possible efficiency. This is the case, for example, when the column has to treat a hydrogen/CO/methane mixture resulting from a reaction for the reforming of methane with steam, which the column is supposed to separate into pure gaseous hydrogen, on the one hand, collected at the top of the column, and a liquid CO/methane mixture, on the other hand, collected at the bottom of the column. For this purpose, it is often desirable to carry out an operation of scrubbing the ascending gaseous mixture with liquid methane introduced at the top of the column. For this scrubbing operation to have maximum effectiveness, it needs to take place at a temperature close to −180° C. As the gases leave the packing  2  at a temperature slightly higher than the desired temperature, these gases are tapped off using a pipe  3  tapped into the wall  1  of the column. The gases thus collected are sent to a heat exchanger  4  where they are cooled (for example using liquid CO). Once the temperature of the gases has been brought back down to −180° C., the gases and the liquid which has condensed during the heat transfer operation are reintroduced into the column by a pipe  5 . The latter opens into the column at a level higher than the level at which the gas extraction pipe  3  was located. The liquid fraction of the matter reintroduced into the column is collected by a liquid trap  6 . This liquid trap  6  is in the form of a funnel, the circumference of the upper part of which is secured to the periphery of the internal wall  1  of the column at a level located between that of the gas tapping pipe  3  and that of the pipe  5  for reintroducing the gases and condensed liquid into the column. The funnel-shaped part of the liquid trap  6  opens onto a cylindrical portion  7  equipped with a solid bottom  8 . Liquid  9  can thus accumulate in the bottom of the liquid trap  6 . Pipes  10 ,  11  allow this liquid  9  to be introduced into a manifold  12  located under the liquid trap  6 . This manifold  12  may conventionally be in the form of a container of complex shape, the bottom of which has perforations  13 ,  14 ,  15 ,  16 ,  17 ,  18 . The liquid  19  present in the manifold  12  flows through the perforations  13 ,  14 ,  15 ,  16 ,  17 ,  18  of said manifold towards the packing  2 . The heads of liquid  9 ,  19  present in the liquid trap  6  and in the manifold  12  correspond to the pressure drops of the gas between the upper and lower levels of these liquids. The bottom of the manifold  12  is also equipped with domes  20  which have perforations  21  allowing the ascending gases leaving the packing  2  to pass through the manifold  12 . 
     The separation column according to the invention and depicted in FIG. 2 comprises, placed between the respective levels of the gas tapping pipe  3  and the pipe  5  for reintroducing the gases and the condensed liquid, a support  22  which runs around the inside of the wall  1  of the column around its entire circumference. Resting on this support  22  is an upper lip  23  of a container  24  which forms part of a liquid-gas manifold according to the invention. This container  24  has a cylindrical overall shape and its bottom  25  has perforations  26 . Its outside diameter d is smaller than the inside diameter D of the column. These perforations  26  distribute the liquid  27  present in the container  24  over the upper surface of the packing  2  which the container  24  overhangs. The ascending gases leaving the packing  2  pass through the annular space defined, on the one hand, by the internal wall  1  of the column and, on the other hand, by the external wall of the container  24 . They are directed towards the gas tapping pipe  3 , because the support  22  on which the upper lip  23  of the container  24  rests delimits, in collaboration with the side wall of the container  24 , a zone which is impervious to the ascending gases. As in the prior art, these ascending gases pass through a heat exchanger  4  which drops their temperature to the desired level. After they have been reintroduced into the column by the pipe  5 , the cooled gases continue to rise, while the condensed liquid and the scrubbing liquid flow into the container  24 , without a separate liquid trap or any other member comparable to the liquid trap  6  of FIG. 1 being provided. The head of liquid  27  present in the container  24  corresponds to the pressure drop of the gases between the upstream and downstream sides of the container  24 . 
     By comparison with the configuration according to the prior art and illustrated in FIG. 1, the exemplary configuration according to the invention in FIG. 2 is about 1 m less tall, therefore an appreciably reduced height. This makes it possible to give the column height which is smaller than it would usually be, this being all the more advantageous if the stages of extracting, cooling and reintroducing the gases into the column are numerous. 
     As a variant, as depicted in FIG. 3, the container  24  may have a narrowing  28  of its inside diameter in its central part. The amount of liquid  27  retained in the container  24  can thus be reduced. To make the liquid  27  easier to collect, it is also possible to envisage giving the container  24  the shape of a funnel above the narrowing  28  of its cross section. 
     As a variant, as depicted in FIG. 4, the upper lips  23  of the containers  24  may have openings  29 . In collaboration with similar openings made in the supports  22 , these openings  29  allow the gases to rise up inside the column. These openings  29  may thus open into heat exchangers similar in their function to the exchanger  4  of FIGS. 1 to  3 , but incorporated into the wall  1  of the column. Once the gases have passed through these exchangers and have been reintroduced into the column, the liquid which has condensed drops back down to be collected in the containers  24 . 
     The manifolds according to the invention may also be used in scenarios where there is no desire to cause the ascending gases to undergo a particular treatment but where there is simply a desire to distribute the descending liquid uniformly over the surface of the packing (or, in general, the active zone) that the manifold overhangs. For this purpose, it is possible to use the variant of the container  24  which is depicted in FIG.  5 . It is installed in a column, the wall  1  of which has no means for causing the ascending gases to be subjected to a particular treatment, whether outside or inside the column. As in the variants depicted in FIGS. 2 and 3, the annular space between the container  24  and the wall  1  of the column is closed off at its upper end by a lip  22  secured to the wall  1  of the column collaborating with an upper lip  23  of the container, both being devoid of openings through which the ascending gases could pass. By contrast, such openings  30  are to be found on the side wall of the container  24 . In this way, all the condensed liquid descending from the upper stages of the column passes through the container  24 , and does not impede the ascending movement of the gases in the annular space. 
     As a variant, the orifices  30  could be made in the lip  23 .