Abstract:
A liquid distributor includes a principal container with a perforated bottom, as well as transport members to transmit, by gravity, the liquid from at least one opening in the perforated bottom, to a supply point not in vertical alignment with this opening.

Description:
The present invention relates to a liquid distributor for distillation columns, of the type comprising a principal volume having in its lower portion outlet openings distributed about a region. 
     Floating petroleum platforms produce residual gases. For environmental and economic reasons, it is more and more necessary to recover these gases. One method consists in their conversion to heavier hydrocarbons, in the form of liquid and hence more easily transportable, by the Fischer-Tropsch process, which consumes large quantities of oxygen. 
     It would be interesting to be able to provide an on-board air distillation column on a floating platform or a barge, but the good operation of such equipment is burdened with serious difficulties. Thus, a first requirement is that the liquid be uniformly distributed at the head of the column over all the cross section of this latter despite the swinging of its axis due to swell. 
     The invention has for its object to provide a liquid distributor whose operation will be less sensitive to such oscillations. 
     To this end, the invention has for its object a liquid distributor of the recited type, characterized in that it comprises a transport member adapted to transmit by gravity the liquid from at least one opening in the perforated bottom to a supply point not located in vertical alignment with this opening. 
     The distributor according to the invention can comprise one or several of the following characteristics: 
     the opening is constituted by a single perforation or by several perforations adjacent each other; 
     the transport member comprises an inlet end located below and in vertical alignment with said opening and spaced from the outlet end of this latter; 
     the transport member comprises an upwardly open conduit in the form of a trough or closed in the form of a tube, this conduit being straight, bent at one or several locations or curved; 
     the transport member comprises at its outlet end a spray device for a spray region whose area is greater than that of said opening; 
     the mean diameter of said region is less than the mean diameter of the surface containing the outlet openings of the transport members, the ratio of the diameters being particularly about 1 to 6; 
     the distributor comprises transport member associated with a group of openings spaced from each other and adapted to carry the liquid flow from these openings substantially to a common supply point not located in vertical alignment with said openings; 
     the transport member comprises several conduits, particularly several tubes, whose inlets are adapted to receive the liquid flow from said openings, these conduits joining in a single conduit for the group of openings; 
     the total flow rate of said flow remains substantially constant when the distributor inclines; 
     the transport member or members associated with two openings substantially diametrically opposed relative to a central axis of said region and of the same area, lead substantially to a common supply point; 
     the liquid flow from at least one opening or group of openings is carried by the transport member or members such that its flow rate becomes greater when the sprayed region is raised under the influence of the inclination and less in the contrary case; 
     the transport member associated with each opening leads to a supply point situated angularly at an angle of 180° from this opening relative to a central axis of the distributor; 
     the openings are disposed in a first substantially horizontal plane in concentric substantially circular crowns each corresponding to a crown of outlet openings disposed in a second substantially horizontal plane located below the first plane and comprising the same number of supply points, and a transport member connected to each point of the first crown at a point associated with the second crown; 
     the couples of associated points are offset angularly by a same angle about the axis of the crowns, the transport member connecting two crowns forming an envelope surface in the shape of a sleeve and the assembly of the transport members forming a series of such envelope surfaces nested within each other; 
     said angular offset is reversed from one envelope surface to the following; 
     said angular offset is comprised between about 80 and 100°; 
     said angular offset is comprised between about 100 and 180°; 
     the outlet ends of the transport members supply the liquid to several secondary distribution receptacles with perforated bottoms. 
     The invention also has for its object a distillation column characterized in that it comprises, at at least one level, a liquid distributor as defined above, above a distillation section. 
     According to other characteristics of this distillation column: 
     the distillation section has cross-corrugated packing; 
     the distributor is a distributor at the head of the column, said principal volume being at least partially disposed within the upper dome of this latter; 
     the transport members deliver directly the liquid onto the distillation section; 
     the column is on-board a floating structure such as a floating petroleum platform or a barge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Examples of embodiment of the invention will now be described with respect to the accompanying drawings, in which: 
     FIG. 1 shows schematically, in axial cross section, a receptacle with a perforated bottom in an inclined position; 
     FIG. 2 shows schematically in perspective a liquid distributor according to the invention, disposed at the head of a distillation column; 
     FIG. 3 is a schematic plan view of the distributor of FIG. 2; 
     FIG. 4 shows schematically a liquid transport member of this distributor; 
     FIGS. 5 and 5A are similar views of two modifications; 
     FIG. 6 shows schematically another embodiment of the liquid distributor according to the invention; 
     FIG. 7 is a schematic perspective view showing the principal of operation of yet another embodiment of the liquid distributor according to the invention; 
     FIG. 8 is a top plan view of a specific embodiment of the second stage of the distributor of FIG. 7; and 
     FIGS. 9 and 10 show schematically two modifications of a detail of the distributor according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There is shown in FIG. 1 a receptacle  1  in the form of a basin whose bottom  2  is perforated with openings  3  and has a circular shape with a normally vertical X—X axis. The openings  3  can particularly be circular holes and, unless otherwise indicated, it will be supposed that such is the case and that the holes are all identical. 
     When the receptacle contains a liquid L and the axis X—X is inclined at an angle α to the vertical, the openings  3  located at a same distance r from this axis supply different flow rates, because they are surmounted by different heights of liquid. 
     Thus, in the inclination plane, which is that of FIG. 1, the upper opening  3 A supplies a flow rate Q A  proportional to the {square root over (h−r sin α)}, whilst the lower opening  3 B supplies a flow rate Q B  proportional to the {square root over (h+r sin α)}. Under conditions of oscillation due to swell, if the receptacle forms a head distributor of an on-board distillation column, with its radius substantially identical to that of the column, the difference of flow rate can be of the order of 10% or more, which is unacceptable to ensure satisfactory operation of the column. 
     FIGS. 2 and 3 show a liquid distributor  4  which comprises a receptacle  1  and which, on the contrary, ensures practically uniform distribution of the liquid over all the cross section of the distillation column  5  no matter what the inclination, under the mentioned conditions of oscillation. As a modification, the receptacle  1  could moreover be replaced by a series of troughs with perforated bottoms, or by a layer of perforated tubes. 
     The distillation column  5  comprises, in its upper portion, a cylindrical collar  6  with an axis X—X, and an upper dome  7 . The column is on board a floating structure schematically shown at S in FIG.  2 . The upper distillation section  8  of the column is constituted by a cross-corrugated packing. 
     As is well known, such a packing comprises a superposition of sections or packs  9  of cross-corrugated packing, of which each has the form of a cylindrical cake occupying all the cross section of the column. 
     Each pack  9  is constituted by a stack of corrugated strips with oblique corrugations. Each strip comprises a generally vertical plane, all the strips have the same height, and the corrugations are alternately inclined in opposite directions from one strip to the next. Thus, the corrugations of adjacent strips touch at a large number of points of intersection. Moreover, the packs  9  are offset angularly by 80% from one pack to the following one, relative to the general axis of the column. 
     The receptacle  1 , upwardly opening and of a diameter substantially less than the internal diameter of the collar  6 , is disposed in the dome  7 . The ratio of the diameters is typically 1 to 6. The bottom  2  of the receptacle  1  comprises as many openings  3  as are desired points of distribution of the liquid over the upper pack  9 , namely typically 1000 to 3000 openings for a column of about 4 meters diameter. 
     The distributor  4  moreover comprises one rectilinear tube  10  per opening  3 . Each tube  10  has an upper inlet opening  11  disposed just below the corresponding opening  3 , and a lower outlet opening  12  disposed just above the upper surface  13  of the upper pack  9 . If r and R designate respectively the distances to the axis X—X of the openings  11  and  12 , then R&gt;r. Moreover, the point  12  is angularly offset by 90° about the axis X—X relative to the point  11 , as is seen in FIGS. 2 and 3. 
     The openings  3  are disposed in a series of concentric crowns. With each crown  14  of mean radius r is associated a crown  15  of mean radius R of the surface  13 , and all the tubes which connect these two crowns are inclined in the same direction. Thus, the assembly of the tubes  10  associated with two homologous given crowns  14  and  15  constitute generatrices of a hyperboloid of revolution  16 . 
     For two adjacent pairs of crowns  14  and  114 , the tubes  10  are inclined in opposite directions, thereby forming two hyperboloids of revolution  16  and  116  nested within each other. The hyperboloid  116  schematically shown in FIG. 2 thus corresponds to the crowns  114  and  115  located immediately within the crowns  14  and  15  mentioned above. 
     The assembly of tubes  10  forms in this way a stack of hyperboloids of revolution whose generatrices are alternately inclined in the two directions. 
     When the axis X—X is vertical, all the tubes  10  supply the same flow rate of liquid because of the symmetry of revolution of the assembly of the distributor  4 . 
     When the axis X—X is inclined, the radius of the receptacle  1 , substantially less than that of the column, has the effect of reducing the differences of flow rate between the openings  3  of its bottom  2 . 
     Moreover, the pairs of substantially diametrically opposite openings belonging to the two adjacent crowns  14 ,  114  are interconnected by their tubes  10  at two points  12 ,  112  adjacent to each other, because they are located substantially in the same radial half-plane passing through the axis X—X and belonging to two adjacent crowns  15 ,  115 . 
     As a result, the region of the surface  13  situated just below the points  12  and  112  will receive the total flow rates emitted by a substantially diametrically opposed pair of openings of the receptacle  1 , which total is practically constant for all the pairs of openings. 
     It therefore suffices that the area of the region in question will be sufficiently small that the two flow rates will be well remixed by the cross-corrugated packing, such that the distribution of the liquid over all the surface  13  remains permanently substantially uniform despite the oscillations of the axis X—X. 
     It should moreover be noted that the structure of the distributor  1  lets the rising gas pass through without substantial pressure drop, between the tubes  10  and about the receptacle  1 . 
     FIG. 4 shows a rectilinear tube  10 , provided at its inlet with a funnel  17  which guarantees the collection of all the liquid from the corresponding opening  3 . All of the funnels  17  are fixed in place by means of a plate  18  with openings of the same diameter as the receptacle  1 , disposed at a small distance below the bottom  2  and fixed to this latter. 
     Moreover, as shown schematically in FIG. 2, all the tubes  10  are positioned relative to each other at an intermediate level between the receptacle  1  and the surface  13 , by a suitable positioning structure  118 . 
     FIG. 5 shows several modifications of the arrangement of FIG.  4 : 
     On the one hand, the funnel  17  is omitted, and the inlet opening  11  of the tube  10 , of a diameter substantially greater than that of the opening  3 , is positioned just below the lower end of this latter, but spaced from the latter, by means of the plate  18  connected to the receptacle  1 . 
     On the other hand, the tubes  10  are incurved, with an upstream portion  20  for acceleration of the liquid, with a steep slope, and a downstream portion  21  with a more gentle slope. 
     Finally, the lower end  12  of the tubes  10  is provided with a spray head  22 , which promotes the spreading of the distribution of the liquid over the surface  13 . Thus, the spray head  22  distributes the liquid over an area of the surface  13  greater than that of the corresponding opening  3 . 
     In this example, the curved tubes associated with the two homologous crowns are wound so as to generate about the axis X—X a surface in the form of a sleeve. Thus, the assembly of the curved tubes forms a series of such surfaces nested within each other, the direction of winding of the tubes being reversed from one surface to the next. 
     The modification of FIG. 5A differs from the preceding one, on the one hand, by the omission of the spray head  22 , and on the other hand by the shape of the tube  10 . Thus, the latter comprises a principal inclined rectilinear portion, as does that of FIG. 4, and is elbowed to form two end portions which are also rectilinear but vertical. 
     FIG. 6 shows another manner of correcting the effects of inclination of the column, by obtaining a liquid distribution which anticipates the poor distribution in the packing due to that inclination. Thus, under the influence of that inclination, the liquid has the tendency to accumulate on one side of the column, whilst the other side progressively dries out. It would therefore be desirable to supply the drying out side with a greater liquid flow rate and the opposite side with a lower flow rate. 
     To do that, the tubes  10 A and  10 B associated with the substantially diametrically opposite openings  3 A and  3 B, lead to points  12 A,  12 B on the surface  13  which are also substantially diametrically opposed but which are reversed relative to the two openings. Thus, the point  12 A (respectively  12 B) is located substantially in the same radial half-plane, relative to the axis X—X, as the opening  3 B (respectively  3 A). This arrangement therefore permits spraying more intensively the regions of the packing that are apt to dry out under the influence of the inclination. However, to obtain as before a structure permeable to rising gas and without crossing between the tubes  10 , the provision of numerous tubes  10  supposes in this case their provision in a complex shape, namely helicoidal, which is more complicated than the embodiment of FIGS. 1 and 2. 
     In the example of FIG. 6, the point  12 A is angularly offset by 180° about X-X′ relative to the point  11 A. For angles comprised between 100° and 180°, there is obtained a greater or lesser effect of correction or of the distribution, the maximum being reached at 180°. 
     The mode of compensation of flow rate of FIGS. 1 and 2 is used in the embodiment of distributor  4  schematically shown in FIG. 7, but in a two-stage distribution configuration. Thus, the receptacle  1 , whose bottom  2  comprises a number n of openings  3  very much less than the total number N of the spray points of the surface  13 , for example 32 openings  3 , forms a precise predistribution stage  104  of the liquid. The openings  3  are disposed in a single crown, adjacent the peripheral wall of the receptacle  1 . 
     At a lower level is located an additional stage  105  for local distribution of the liquid, constituted by n/2=16 secondary receptacles  101  upwardly open and with perforated bottoms  102 , of the same area and the same perforation concentration, regularly spaced over the cross section of the column (only two receptacles  101  have been shown, for clarity). Each bottom  102  is pierced by n′ openings  103  such that (n/2)×n′=N, namely, for example, n′=200, which corresponds to N=3200 holes. 
     Each secondary receptacle  101  is supplied by two tubes  10 A,  10 B themselves supplied respectively by two diametrically opposed openings  3 A,  3 B, as before. There is thus on the one hand a compensation for the inclination of the level of the distribution stage  104 , plus a substantial reduction of the effect of inclination in each secondary receptacle  101 , thanks to the small dimensions of the latter. 
     As a modification, as shown in broken lines in FIG. 7, the arrangement of the openings  3 A and  3 B can be carried out by replacing the two tubes  10 A and  10 B by a single T-shaped tube  110  which receives the flows of liquid from the two diametrically opposed openings and combines them in a single flow in the stem of the T. 
     There is shown in FIG. 7 an assembly of receptacles  101  spaced from each other, to explain the operation of the distributor. However, in practice, there will be used a single receptacle  101  (FIG. 8) having substantially the diameter of the surface  13  and subdivided in an axially symmetrical way into 16 compartments  123  all having the same area and the same perforation density. These 16 compartments can for example be obtained by means of five partitions  23  parallel to each other, forming chords of the receptacle  101 , of which one is a diameter, and by ten partitions 24 perpendicular to the preceding ones. 
     As will be understood, the manner of correction or “over-compensation” of the flow rates schematically shown in FIG. 6 can also be applied to the transportation of liquid from the receptacle  1  to the receptacles  101  or to the compartments  123  in the case of a two-stage distributor. 
     In each of the embodiments described above, each opening  3 , instead of being constituted by a single perforation of a relatively large diameter, could be constituted by a group of perforations  203  of small diameter near each other. The resulting advantage is to permit obtaining a given flow rate of liquid with a height H 2  (FIG. 10) less than the height H 1  necessary in the case of a single perforation (FIG.  9 ), which creates an agitating vortex effect. However, the diameter of the multiple perforations  203  must remain sufficient to avoid any risk of plugging by impurities contained in the liquid to be distilled. 
     As will be understood, the invention is applicable also to the distribution of reflux liquid in a fixed column but whose axis is not perfectly vertical. 
     WO-A-90/10 497 discloses among other things a packing analogous to the above cross-corrugated packings, but perforated in a different manner. The term “cross-corrugated packing” used herein also comprises such a packing, as well as any analogous packing.