Abstract:
A flow distributor for liquid descending in a vertically elongated process column having an internal space. The distributor is made up of an elongated liquid distribution trough configured and arranged for being mounted in a process column in a position to extend across the internal space thereof. The trough has outer walls defining an elongated, longitudinally extending internal fluid distribution chamber and includes outlet holes which extend through the walls at locations permitting liquid to escape laterally outwardly from the trough. The distributor also includes a baffle distributor structure made up of an elongated, downwardly extending distributor plate member disposed adjacent the trough in a position such that at least a portion of a surface thereof is contacted by liquid escaping from said hole. The distributor also includes an elongated, fluid receiving element attached at a lower edge portion of said plate member presenting an elongated fluid distribution channel extending longitudinally of the plate member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Priority benefits under 35 U.S.C. §119(e) are claimed in this application from provisional application Ser. No. 60/529,509, filed on Dec. 15, 2003, the entirety of the disclosure of which is hereby specifically incorporated herein by this reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to mass transfer and heat exchange columns and, more particularly, to liquid distributors used in such columns and methods of distributing liquid using such liquid distributors. 
     2. The Prior Art Background 
     In mass transfer and heat exchange columns, liquid and vapor streams are brought into contact with each other to effect mass transfer and/or heat exchange between the liquid and vapor. One or more beds of structured or random packing are typically used to facilitate intimate contact between the liquid and vapor and thereby enhance the desired mass transfer and/heat exchange. The liquid stream typically descends through the packing bed while the vapor stream ascends through the packing bed in countercurrent relationship to the flow of the liquid stream. 
     Uneven horizontal distribution of the liquid stream as it enters the packing bed is undesirable because it reduces the area of contact between the liquid and vapor and thus decreases the mass transfer and/or heat exchange between the liquid and vapor. To ensure proper operation of the column, it is also important to ensure that the ratio of liquid to vapor is constant over the cross-section of the column. For this reason, it is important to have an even distribution of liquid as it enters the packing bed. Various types of liquid distributors are used in attempts to facilitate the horizontal distribution of liquid as it enters the packing bed from an overlying region in the column. In general, these distributors deliver the liquid to the packing bed at a number of spaced apart locations, commonly referred to as “drip-points.” The drip-point density is a measure of the number of drip-points per unit area and is commonly used to measure the distribution performance of liquid distributors. 
     One known type of liquid distributor uses a plurality of elongated, parallel troughs to horizontally distribute the liquid to the underlying packing bed. Liquid is distributed to the troughs by a feed box that extends perpendicularly to the parallel troughs. In one arrangement, the feed box is positioned on top of the parallel troughs and delivers liquid to the parallel troughs through a plurality of holes in the floor and/or side walls of the feed box. In another arrangement, the parallel troughs extend outwardly from the sides of the feed box and liquid flows into the parallel troughs through openings in the side walls of the feed box. In one general type of distributor, such as disclosed in U.S. Pat. No. 4,855,089 to Michels and in U.S. Pat. No. 4,816,191 to Berven et al., splash baffles are spaced outwardly from the side walls of the parallel troughs to receive liquid exiting from the parallel troughs. The liquid then flows down the splash baffles and drips into the packing bed along a drip line. It is also known to include a number of horizontally extending corrugations in the splash baffles. In a further type of distributor disclosed in EP 0 42 615 A2, drip tubes descend from the parallel troughs and deliver liquid to a multi-port distributor plate that multiplies the number of drip points into the underlying packing bed. 
     One problem associated with known types of liquid distributors is the difficulty in ensuring uniform horizontal distribution of liquid at low liquid flow rates. A need has thus developed for a liquid distributor that is capable of facilitating uniform liquid mixing and horizontal distribution at low liquid flow rates. 
     SUMMARY OF THE INVENTION 
     In one particular aspect, the present invention is directed to a liquid distribution system comprising an elongated feed box and a plurality of elongated liquid distribution troughs in fluid flow communication with the feed box. The troughs may desirably be spaced apart and preferably lie in a common plane in parallel relationship to each other. In one embodiment, the troughs may underlie the feed box and openings are provided in a floor and/or one or both side walls of the feed box to deliver liquid from the feed box to each of the troughs. In another embodiment, the troughs may extend outward from opposed side walls of the feed box and openings are provided in the side walls to allow liquid to flow from the feed box to the troughs. The troughs may have a square, rectangular, circular, oval or other configuration when viewed in vertical cross section. Each trough may also include openings positioned in a floor and/or one or both side walls of the trough to allow liquid to exit from the trough. A baffle distributor is positioned to receive the liquid exiting from each trough and facilitate the horizontal distribution of the liquid prior to delivery of the liquid to an underlying mass transfer bed, such as a bed of random, structured or grid-type packing. 
     The baffle distributor may desirably comprise a splash plate positioned to receive the flow of at least some of the liquid exiting the associated trough. The splash plate may extend vertically or it may be inclined toward the associated trough in the downward direction. The splash plate may include a liquid spreading surface that functions to deflect the downward flow of liquid and cause horizontal spreading of the liquid as it descends on the liquid spreading surface. Each baffle distributor may also include an elongated channel that is positioned under the troughs in a position to receive liquid from an associated liquid spreading surface. The channels are preferably coplanar and extend parallel to each other. The channels may extend in parallel relationship to the overlying troughs or they may extend at a preselected angle to the longitudinal axis of the troughs. The channels have a plurality of spaced apart liquid discharge holes that deliver liquid to the underlying mass transfer bed at a number of drip points corresponding to the number of liquid discharge holes. A filler formed of a porous liquid permeable material is preferably placed within each channel to facilitate the horizontal distribution of the liquid within the channel prior to entry into the liquid discharge holes. 
     The channels each have an overflow weir, preferably of a saw-toothed design, that provides for the controlled discharge of any overflow of liquid from the channels. A drip edge having a similar saw-toothed design extends downwardly from the trough to receive liquid traveling along the outer surface of the trough. The drip edge is preferably positioned in vertical alignment with the channel so that liquid drips off the drip edge and falls into the channel for horizontal distribution prior to entry into the underlying mass transfer bed. The described liquid distributor provides for good liquid mixing and horizontal distribution of the liquid at low liquid flow rates as well as high liquid flow rates. 
     In one very important aspect thereof, the invention provides a flow distributor for liquid descending in a vertically elongated process column having an internal space. In accordance with this aspect of the invention, the distributor may include an elongated liquid distribution trough configured and arranged for being mounted in a process column in a position to extend transversely of the column in the internal space. Desirably, the trough may include an outer wall structure defining an elongated, longitudinally extending internal fluid distribution chamber and at least one outlet hole extending through the wall structure at a location to permit liquid to escape laterally outwardly from the trough. The flow distributor may also desirably include a baffle distributor structure having (1) an elongated, downwardly extending distributor plate member disposed adjacent the trough in a position such that at least a portion of a surface thereof is contacted by liquid escaping from the hole and (2) an elongated, fluid receiving element attached at a lower edge portion of the plate member. Ideally, in accordance with this aspect of the invention, the fluid receiving element may include an elongated fluid distribution channel extending longitudinally of the plate member. 
     In further accordance with the concepts and principles of the invention, the elongated, downwardly extending distributor plate member may be configured and arranged so as to extend transversely of the column in the internal space thereof in a direction that is in essential parallelism relative to the elongated liquid distribution trough when the distributor is mounted in a process column. Alternatively, the elongated, downwardly extending distributor plate member may be configured and arranged so as to extend transversely of the column in the internal space thereof in a direction that is at an angle relative to the elongated liquid distribution trough when the distributor is mounted in a column. 
     More specifically, the outer wall structure of each trough may comprise a pair of spaced apart upright walls having lower edges and a floor that interconnects the lower edges. In addition, the outlet hole may desirably be positioned in one of the upright walls, and the trough may ideally include a secondary hole positioned at a higher elevation than the outlet hole. 
     Desirably, the channel of the receiving element may be arcuate or perhaps even circular in transverse cross-sectional configuration. Alternatively, the transverse cross-sectional configuration may be of any multi-sided shape such as square, rectangular, triangular, etc. 
     In one particularly preferred form of the invention, the fluid receiving element may have an upwardly extending outer edge disposed at an opposite side of the channel from the lower edge portion of the plate member. Furthermore, the fluid receiving element may include a porous, liquid permeable filler material disposed in the channel. Desirably, the fluid receiving element may also include structure for holding the filler material in place and the channel may be disposed directly beneath the trough for essentially its entire length. 
     Preferably, the fluid receiving element may be essentially coextensive in length with the elongated distributor plate member, the channel may have an open top and the fluid receiving element may include at least one drip hole in the wall structure at a lower portion of the channel. 
     Ideally, the fluid receiving element and the elongated distributor plate member may be integrally connected and formed by bending a metal sheet. Also, the upwardly extending outer edge of the fluid receiving element may comprise an outlet weir for the channel. 
     In accordance with preferred aspects of the invention, the distributor plate member may include a liquid spreading element disposed at a lower area of the surface and positioned beneath the portion thereof that is contacted by liquid escaping from the hole. Desirably the liquid spreading element may comprise a sheet of expanded metal which ideally may have a vertically oriented diamond pattern. 
     In accordance with a further important aspect of the invention, a flow distributor is provided which includes an elongated liquid distribution trough configured and arranged for being mounted in the column in a position to extend transversely of the column in the space. The trough may desirably include an outer wall structure defining an elongated, internal fluid distribution chamber and there may be at least one hole extending through the wall at a location to permit liquid to escape from the chamber and flow downwardly along an outer surface of the trough. In accordance with this aspect of the invention, the flow distributor may also include an elongated drip element carried by the trough. The drip element desirably extends longitudinally of the trough structure and downwardly therefrom, and the same desirably is disposed beneath the hole in the trough and has a lower longitudinally extending drip edge. 
     In accordance with this aspect of the invention, the outer wall structure of the trough comprises a pair of spaced apart upright walls having lower edges and a floor that interconnects the lower edges. The hole in the trough may be either in one of the upright walls or in the floor. When the hole is in an upright wall, the drip element is desirably attached to the same upright wall. Alternatively, when the hole is in the floor, the drip element is desirably attached to the floor. In one particularly preferred form of the invention, the floor is downwardly V-shaped in transverse cross-sectional configuration and the elongated drip element is attached to an apex of the V-shaped configuration. 
     In another important aspect of the invention, the flow distributor includes a trough as described above and a baffle distributor structure made up of an elongated, downwardly extending distributor plate member is disposed adjacent the trough in a position such that at least a portion of a surface thereof is contacted by liquid escaping from the hole. In accordance with this specific aspect of the invention, the distributor plate member includes a liquid spreading element at a lower area of the surface disposed beneath the portion of the surface that is contacted by liquid escaping from the hole. 
     In further accordance with the concepts and principles of the invention, the same provides a flow distributor for liquid descending in a vertically elongated process column having an internal space. In accordance with this aspect of the invention, the flow distributor includes an elongated liquid distribution trough as described above and a baffle distributor structure that includes an elongated, downwardly extending distributor plate member disposed adjacent the trough in a position such that at least a portion of a surface thereof is contacted by liquid escaping from the hole. Ideally, in further accordance with this aspect of the invention, the distributor plate member is disposed so as to extend laterally of the trough. 
     The invention further provides apparatus for feeding liquid descending in an internal space of a vertically elongated process column to a flow distributor. Thus, in further accordance with the invention, the apparatus includes an elongated feedbox structure configured and arranged for being mounted in a process column in a position so as to extend across the interior space of the column. Desirably, the feedbox structure includes an outer wall assembly defining an elongated, longitudinally extending internal fluid distribution zone. At least one outlet hole extending through the wall structure is provided at a location to permit liquid to escape from the zone and flow downwardly in the column. In accordance with this form of the invention, the apparatus also includes a predistributor trough disposed in the zone. This predistributor trough includes a wall arrangement defining an internal area and providing apertures allowing liquid to flow from the internal area and into zone. 
     In yet another form, the invention provides apparatus for feeding liquid descending in an internal space of a vertically elongated process column to a flow distributor. In accordance with this form of the invention, the apparatus includes an elongated feedbox structure configured and arranged for being mounted in a process column in a position to extend transversely of the column in the internal space thereof. The feedbox structure includes an outer wall assembly defining an elongated, longitudinally extending internal fluid distribution zone. The apparatus also includes an elongated liquid distribution trough including a cylindrical outer wall structure defining an elongated, longitudinally extending internal fluid distribution chamber. In accordance with this form of the invention, the trough is arranged to extend through the wall assembly and into the zone, and the same includes an opening positioned to allow liquid to flow from the zone and into the chamber, and at least one outlet hole extending through the wall structure at a location to permit liquid to escape therefrom and flow downwardly in the internal space. In accordance with the specific preferred aspects of the invention, the opening is ideally positioned in a lower area of the outer wall structure and the same is arranged to face generally downwardly so that liquid from the zone flows upwardly into the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side perspective view of a mass transfer column with portions of a shell of the column broken away to show a mass transfer bed and one embodiment of a liquid distributor of the present invention positioned within an open internal region of the column; 
         FIG. 2  is a top perspective view of the liquid distributor shown in  FIG. 1  with a portion of a feed box shown broken away to show liquid exit holes positioned in a floor of the feed box; 
         FIG. 3  is a side elevation view of a fragmental portion of a trough and baffle distributor of the liquid distributor taken along line  3 — 3  of  FIG. 2 ; 
         FIG. 4  is an end elevation view of the trough and baffle distributor of  FIG. 3  taken in vertical section; 
         FIG. 5  is an end elevation view of an alternate embodiment of a trough and baffle distributor taken in vertical section; 
         FIG. 6  is a fragmentary side elevation view of the trough and baffle distributor taken along line  6 — 6  of  FIG. 5 ; 
         FIG. 7  is a top plan view of another embodiment of the liquid distributor of the present invention, with the baffle distributors being shown schematically; 
         FIG. 8  is a fragmentary top perspective view of the liquid distributor shown in  FIG. 7 , with portions broken away to illustrate details of construction; 
         FIG. 9  is a top plan view of a still further embodiment of the liquid distributor of the present invention; and 
         FIG. 10  is a fragmentary top perspective view of a feed box and troughs of the liquid distributor shown in  FIG. 9 , with portions broken away to show construction details. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings in greater detail, and initially to  FIG. 1 , a mass transfer or heat exchange column is designated generally by the numeral  10  and includes an upright cylindrical shell  12  that defines an open interior region  14  in which one or more liquid distributors  16  of the present invention and one or more mass transfer beds  18  are located. The liquid distributor  16  is used to facilitate a more uniform horizontal distribution of one or more descending liquid streams as it enters the upper end of the underlying mass transfer bed  18 . The mass transfer bed comprises one or more types of mass transfer devices, including but not limited to those conventionally known as structured, grid or random packing. 
     Column  10  is of a type used to process liquid and vapor streams, including to obtain fractionation products. Although column  10  is shown in a cylindrical configuration, other shapes, including polygonal, may be used. Column  10  is of any suitable diameter and height, and is constructed from suitably rigid materials that are preferably inert to, or otherwise compatible with the fluids and conditions present within the column  10 . 
     Liquid streams  20  are directed to the column  10  through feed lines  22  and  23  positioned at appropriate locations along the height of the column  10 . Feed line  22  normally carries only liquid and feed line  23  may carry liquid, vapor and a mixture of liquid and vapor. Although only two liquid feed lines  22  and  23  are shown in the drawings for simplicity of illustration, it will be appreciated by those of ordinary skill in the art that additional liquid feed lines may be utilized if desired. Similarly, only one vapor feed line  24  carrying a vapor stream  26  is illustrated, but additional vapor feed lines can be included if necessary or desired for the vapor and liquid processing occurring within the column  10 . It will also be appreciated that the vapor stream  26  can be generated within the column  10  rather than being introduced into the column  10  through the feed line  24 . The column  10  further includes an overhead line  28  for removing a vapor product or byproduct  30  from the column  10 . A bottom stream takeoff line  32  is provided for removing a liquid product or byproduct  33  from the column  10 . Other column components such as reflux stream lines, reboilers, condensers, vapor horns and the like may be present but they are not illustrated because they are conventional in nature and are not believed to be necessary for an understanding of the present invention. 
     Turning additionally to  FIGS. 2–4 , the liquid distributor  16  in one embodiment of the present invention includes an elongated central feed box  34  that receives liquid from a descending liquid stream, such as the liquid stream  20  that has been delivered by the liquid feed line  22  to the open internal region of the column  10 . It will be appreciated that the feed box  34  need not receive liquid directly from the outlet of the liquid feed line  22 , but the liquid may instead be first subjected to one or more processing steps and then collected by a collector (not shown) for delivery to the feed box  34 . The feed box  34  extends horizontally in a first direction and is of a length corresponding to the diameter of the column  10  or at least a substantial portion thereof. The feed box  34  is preferably positioned along the column diameter, but it will be understood that more than one feed box  34  can be used and positioned at preselected locations. 
     The feed box  34  comprises a pair of spaced apart side walls  36  and  38  that are connected at their lower edges by a floor  40  and at their ends by end walls  42  and  44 . An optional cover (not shown) may connect the upper edges of the side walls  36  and  38  to prevent liquid from spilling over the side walls  36  and  38 , such as when the column  10  is subjected to a rocking motion in off-shore applications. If the cover is used, a suitable opening is provided in the cover to permit liquid to be delivered to the feed box  34 . 
     The feed box  34  feeds liquid to a plurality of elongated troughs  46  that preferably extend generally parallel to each other in a direction that is at an angle, preferably perpendicular, to the orientation of the feed box  34 . The troughs  46  may desirably, but not necessarily extend across the entire cross section of the column  10 , and the number of troughs  46  is selected to provide the desired drip-point density in the underlying mass transfer bed  18 . The troughs  46  are constructed in a manner similar to the feed box  34  and have spaced apart side walls  48  and  50  that, in one embodiment, are connected by a floor  52  and end walls  54  and  56 . In the illustrated embodiment, the feed box  34  is positioned on top of the troughs  46  and liquid flows downwardly into the troughs  46  through openings  58  in the floor  40  of the feed box  34 . Openings may be provided in the side walls  36  and  38  of the feed box  34  to provide an additional or alternative route for liquid to exit the feed box  34  and flow into the troughs  46 . 
     Rather than having the feed box  34  positioned in overlying relationship to the troughs  46 , the troughs  46  and feed box  34  may be arranged in coplanar relationship with the troughs  46  extending outwardly from the side walls  36  and  38  of the feed box  34 . In this coplanar arrangement, openings are provided in the side walls  36  and  38  of the feed box  34  to allow liquid to flow from the feed box  34  to the troughs  46 . It will be appreciated that other methods of delivering liquid to the troughs  46  can be used and are within the scope of the present invention. 
     A plurality of primary openings  60  are provided in at least one of the side walls  48  or  50  of each trough  46  to allow liquid to exit from the trough  46 . The primary openings  60  are positioned at a preselected height above the floor  52  of the trough  46  and the same are spaced apart a preselected distance from each other along the length of the trough  46 . The primary openings  60  can be of any desired shape, such as circular, triangular or vertically elongated. The number and size of the openings  60  may be selected to accommodate the anticipated flow rate of liquid through the liquid distributor  16 . A series of secondary openings  62  are positioned in the side wall  48  or  50  containing the primary openings  60 . The secondary openings  62  are positioned near the top of the side wall  48  or  50  and have a total open area greater than the open area of the underlying primary openings  60 . The secondary openings  62  allow for a controlled release of liquid from the trough  46  in the event the liquid flow rate exceeds that which can flow through the primary openings  60 . A triangular shape is normally utilized for the secondary openings, but other configurations can be used instead. 
     In accordance with the present invention, each trough  46  has a baffle distributor  64  that extends along and is spaced outwardly from one or both of the side walls  48  or  50  of the trough  46 . The baffle distributor  64  comprises a splash plate  66  positioned to receive the flow of liquid from the primary openings  60  in the trough  46  and a channel  68  positioned under the splash plate  66  to receive the flow of liquid after it impacts against the splash plate  66 . The splash plate  66  is preferably coextensive in length with the longitudinal length of the trough  46  and preferably has a vertical height sufficient to receive liquid flow from the secondary openings  62 . The splash plate  66  also extends downwardly a sufficient distance to position the attached channel  68  a preselected distance below the floor  52  of the trough  46 . The splash plate  66  may extend in parallelism relative to the adjacent side wall  48  or  50  of trough  46 , or it may be inclined toward the side wall  48  or  50  in the downward direction. 
     One or more brackets  70  are used to mount the baffle distributor  64  to the side wall  48  or  50  of the trough  46 . Preferably, at least two spaced apart brackets  70  are used to mount the baffle distributor  64  and are constructed to permit vertical adjustment and leveling of the baffle distributor  64 . In the illustrated embodiment, the brackets  70  are formed by severing the splash plate  66  along two spaced apart line segments that extend downwardly from the top edge of the splash plate  66 . The portion of the splash plate  66  bounded by the severed line segments is then bent away from the plane of the splash plate  66  and then bent again to form an attachment segment  72  that is parallel to the plane of the splash plate  66 . A vertically elongated hole  74  is then formed in the attachment segment  72  and an aligned hole  76  is formed in the adjacent side wall  48  or  50  of the trough  46 . A nut and bolt assembly  78  extends through the aligned holes  74  and  76  to secure the splash plate  66  to the trough  46 , with the vertically elongated hole  74  allowing for adjustment and leveling of the baffle distributor  64 . Other methods of attaching the splash plate  66  to the trough  46  can be used and are within the scope of the invention. 
     The splash plate  66  has a liquid spreading surface  80  that faces the trough  46  and receives the flow of liquid therefrom. The liquid spreading surface  80  may be integrally formed with the splash plate  66  or it may be formed separately and subsequently attached to the splash plate  66 . The liquid spreading surface  80  functions to enhance the horizontal spreading of the liquid as it flows downwardly along the splash plate  66 . It will be appreciated that this function can be performed in many different ways. For example, as can best be seen in  FIG. 3 , the liquid spreading surface  80  can be a separate sheet of expanded metal having a vertically oriented diamond pattern that serves to disrupt the downward flow of liquid and redirect it in a lateral direction. Other examples include grooves, projections and the like that are formed in the splash plate  66  and also cause lateral spreading of the liquid. The specific construction of the liquid spreading surface  80  can assume many different forms and remain within the scope of the invention. 
     The channel  68  that receives liquid from the splash plate  66  is horizontally oriented and preferably extends in parallelism relative to and is coextensive in length with the associated trough  46 . The channel  68  is preferably formed by bending a lower portion of the splash plate  66  into a partially circular or at least arcuate transverse cross-sectional configuration. The channel  68  is open at the top to allow entry of liquid from the overlying trough  46 , and the same has a plurality of spaced apart discharge holes  82  in the bottom to allow liquid to flow downwardly from the channel  68  into the underlying mass transfer bed  18  at a plurality of spaced apart locations or drip-points. The discharge holes  82  are preferably formed by punching in the direction from the upper surface to the undersurface of the channel  68  so that the raised perimeter that surrounds the punched hole  82  as a result of the punching operation is on the undersurface of the channel  68  where it does not impede entry of liquid into the hole  82 . The size and number of discharge holes  82  are selected to provide the desired liquid flow and drip-point density into the underlying mass transfer bed  18 . Likewise, the size of the channel  68  is selected to accommodate the desired liquid flow rate. Although the channel  68  is illustrated as having a substantially circular or arcuate shape, other configurations can be used instead. The channel  68  also need not be formed integrally with the splash plate  66 , but can be formed as a separate piece and attached by welding or other means to the splash plate  66  and/or trough  46 . Preferably, the ends of the channel  68  are closed by end walls  83 . 
     The channel  68  includes a filler  84  formed of a porous and liquid permeable material that facilitates the horizontal distribution of liquid within the channel  68 , particularly under low liquid flow rates. The filler  84  can be formed from various materials having a preselected porosity and liquid permeability. For example, woven materials such as rolled wire gauze, gasket rope, rolled cross-woven gasket tape, and combinations thereof can be used for the filler  84 . Other materials, including non-woven materials, can be used provided they are compatible with the liquid and have the necessary porosity and liquid permeability. In applications with low liquid flow rates, the filler  84  preferably may have wicking characteristics so that the liquid can be horizontally distributed by capillary action. 
     The filler  84  is retained within the channel  68  by a series of hold-down brackets  86  that are welded or otherwise secured to the channel  68 . The hold-down brackets  86  preferably exert a downward force on the filler  84  to cause it to conform to the configuration of the channel  68  to reduce the quantity of liquid that is able to flow along the upper surface of the channel and enter the discharge holes  82  without first entering the filler  84 . The splash plate  66  is preferably aligned with the channel  68  in a manner to cause liquid to drip from a lower edge of the liquid spreading surface  80  onto the filler  84  to facilitate horizontal spreading of the liquid prior to entry into the discharge holes  82 . 
     As can best be seen in  FIG. 3 , the channel  68  includes an overflow weir  88  opposite from the splash plate  66 . The weir  88  preferably has a saw-toothed profile to facilitate a uniformly horizontally distributed overflow of liquid over the weir  88  at high liquid flow rates that exceed the flaw capacity of the discharge holes  82 . A saw-toothed drip-edge  90  extends downwardly from the side wall  48  or  50  of the trough  46  to facilitate the horizontal distribution of liquid that flows down the outside of the side wall  48  or  50  after exiting through the primary openings  60 , such as at low liquid flow rates, and the secondary openings at higher liquid flow rates. Preferably, the drip-edge  90  is vertically aligned with the channel  68  so that the liquid drips from the drip-edge  90  into the channel  68  for further horizontal distribution before it drips into the underlying mass transfer bed  18 . In the event liquid overflows through the secondary openings  62  in the troughs  46 , a portion of the liquid is able to bypass the liquid spreading surface  80  by flowing through the cut-out in the splash plate  66  at the location of the brackets  70  and then flowing down the outer face of the splash plate  66 . 
     Returning to  FIG. 2 , a pair of parallel beams  92  are equally spaced on opposite sides of the feed box  34  and are secured by welding or other means to the top edges of the troughs  46 . The beams  92  serve to support and align the troughs  46 . Vertically adjustable support clips  94  are positioned on the ends of the beams  92  and feed box  34  to allow the liquid distributor  16  to hang from a support ring (not shown) or other structure mounted on the column shell  12 . The beams  92  and support clips  94  are not shown in  FIG. 1  to better illustrate the construction of the liquid distributor  16 . Other methods of supporting the liquid distributor  16 , such as grid supports placed on the underlying mass transfer bed  18 , can be used instead. 
     It can be seen that the baffle distributors  64  operate to create a more uniform horizontal distribution of liquid into the underlying mass transfer bed  18 . Liquid that enters the feed box  34  from an overlying zone undergoes an initial mixing and horizontal distribution as it accumulates within the feed box  34 . Liquid descends through the openings  58  in the floor  40  of the feed box  34  and enters the underlying troughs  46 . As liquid accumulates within the troughs  46 , it undergoes further mixing and is horizontally distributed in a direction at a 90° or other preselected angle to the horizontal distribution provided by the feed box  34 . Liquid exiting from the primary openings  60  in the troughs  46  enters the channels  68  of the baffle distributors  64 , either by first descending along the drip edge  90 , descending directly into the channels  68  through the spacing between the splash plate  66  and the trough  46 , or by flowing down the liquid spreading surface  80  of the splash plate  66 . Both the drip edge  90  and the liquid spreading surface  80  further the horizontal distribution of the liquid prior to entry into the channels  68 . Once the liquid enters the channels  68 , the filler  84  causes further horizontal distribution of the liquid prior to discharge through the discharge holes  82  in the bottom of the channels  68 . As liquid accumulates within the channels  68 , it undergoes further mixing and horizontal distribution prior to discharge. The discharge holes  82  provide numerous drip points for well-mixed and well-distributed liquid to enter the underlying mass transfer bed  18 , thereby enhancing the mass and or heat transfer occurring within the mass transfer bed. While the baffle distributors  64  have particular applicability in applications where there is a low liquid flow rate, they may also be used at high liquid flow rates as well as at rates in between. At higher liquid flow rates, liquid is able to exit the troughs  46  through the secondary openings  62  and travel downwardly along the same paths as liquid exiting through the primary openings  60 . The liquid exiting the secondary openings  62  may also bypass the channels  68  by passing through the cutouts in the splash plates  66  at the locations of the brackets  70 . If liquid should overflow the channels  68 , the overflow weirs  88  facilitate a more uniform discharge of liquid into the mass transfer bed  18 . The positioning of the baffle distributor  64  in relation to the associated trough  46  and the use of the drip edge  90  impede vapor entry into the spacing between the splash plate  66  and the trough  46  where it could cause undesired entrainment of the liquid in the vapor stream. 
     Variations of the troughs  46  and the baffle distributors are possible and remain within the scope of the present invention. For example, in the embodiment illustrated in  FIGS. 5–6 , a trough  146  has side walls  148  and  150 , end walls  154  and  156 , and a centrally sloping generally V-shaped floor  152  rather than the flat floor illustrated with reference to troughs  46 . A plurality of primary openings  160  are provided at a preselected elevation in the sloping floor  152  to allow liquid to exit the trough  146  after it has accumulated to a preselected level within the trough  146 . This trough design allows solids and other debris that may be present in the liquid to accumulate in the valley created by the sloping floor  152  without plugging the primary openings  160 . 
     A baffle distributor  164  similar to the one previously discussed is used in conjunction with troughs  146 . The baffle distributor  164  has a splash plate  166  connected to a channel  168  at its lower end and mounted at its upper end to one of the side walls  148  or  150  by a nut and bolt assembly  78 . A liquid spreading surface  180  is provided on the splash plate  166  to receive and horizontally distribute liquid exiting the troughs  146  through the primary openings  160 . The splash plate  166  delivers liquid to a filler  184  in the channel  168  that serves to facilitate the horizontal distribution of liquid in the manner previously described. Discharge holes  182  are provided at the low point in the channel  168  to allow liquid to drip from the channel at preselected drip-points and descend into the underlying mass transfer bed  18 . The channel  168  preferably includes end walls  183  that facilitate the accumulation of liquid within the channel  168  to further the mixing and horizontal distribution of the liquid prior to discharge through the discharge holes  182 . Hold-down brackets  186  and overflow weirs  188  of the types previously described are also provided with baffle distributors  164 . A saw-toothed drip edge  190  is also mounted to an undersurface of the floor  152  of trough  146  at a location to receive liquid flowing along the undersurface of the floor  152  and distribute it to either the liquid spreading surface  180  or the filler  184 . The operation of the baffle distributor  164  will be readily understood from the previous description with respect to baffle distributor  64 . 
     Turning now to  FIGS. 7 and 8 , a predistributor trough  200  is provided within the feed box  34  previously described. The predistributor trough  200  has a plurality of slots  31  formed in its side walls  33  and  35  to calm and facilitate the horizontal distribution of liquid as it flows into the feed box  34 . The feed box  34 , in turn, feeds liquid to the troughs  46  and the baffle distributors  64  which are illustrated schematically. 
       FIGS. 7 and 8  also illustrate an alternate arrangement of the baffle distributors  64  in relation to the troughs  46 . Rather than extending parallel to the troughs  46  as was the case with the previously described arrangements, the baffle distributors  64  extend transversely, preferably perpendicularly, across two or more troughs  46  to facilitate a horizontal distribution of liquid in the transverse direction, thereby allowing mixing of liquid from two or more troughs  46  prior to distribution to the underlying mass transfer bed  18 . In addition, by extending the baffle distributors at an angle to the troughs  46 , the number of baffle distributors  64  may be more or fewer than the number of troughs  46 . In the arrangement illustrated in  FIGS. 7 and 8 , the primary openings  60  are provided in the floor  52  of the troughs  46  and the drip edges  90  are spaced from the baffle distributors  64  on the opposite side of the primary openings  60 . Again, the splash plate  66  of each baffle distributor  64  may extend vertically or at an angle to the vertical. 
     A still further variation of the present invention is illustrated in  FIGS. 9 and 10  in which a liquid distributor  216  has cylindrical troughs  246  that extend horizontally through the side walls  236  and  238  of the feed box  234 . Each cylindrical trough  246  is closed on its ends by caps  254  and  256  and has a bottom cutout  251  in that portion of the trough  246  positioned within the feed box  234 . The cutout  251  allows for liquid in the feed box  234  to enter the cylindrical trough  246  and then exit the cylindrical trough  246  through a plurality of longitudinally spaced apart primary openings  260  located in the bottom of the cylindrical trough  246  outside of the feed box  234 . In this manner, liquid exiting the cylindrical troughs  246  through the primary openings  260  is more uniformly horizontally distributed across the underlying mass transfer bed  18 . If desired, baffle distributors  64  of the type previously described may extend transversely across two or more cylindrical troughs  246  to further facilitate a horizontal mixing and distribution of the liquid. 
     From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objectives hereinabove set forth, together with other advantages that are inherent to the structure described and disclosed. 
     It will be understood that certain features and subcombinations are of utility and may be employed separately and without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     Since many possible embodiments may be made of the invention disclosed herein without departing from the scope thereof, it is to be understood that all matter set forth herein or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.