Abstract:
The contact between, for example, ascending liquid droplets of lighter liquid, as the dispersed phase, and heavier liquid, as the continuous phase, flowing across perforated trays in a flooded liquid/liquid contacting column, is enhanced by providing upstanding baffles on lower trays, interspersed with depending baffles from the trays above. The baffles cause the heavy liquid to flow along an undulating path. Flow distributing partitions extend along the undulating flow path, between the baffles, to distribute liquid flow across the trays. The roles of the lighter liquid and the heavier liquid may be reversed as phases.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a liquid/liquid exchange column.  
         [0002]     Liquid/liquid exchange columns are know in which, for example, a liquid, having a relatively greater density, hereinafter referred to in this patent specification and claims, as the “relatively denser, heavier liquid” or “heavier liquid,” is passed downwardly in an upwardly extending casing, and across a series of upwardly spaced, perforated trays therein, as a liquid layer, ie., a continuous phase, while a relatively less dense liquid forming a dispersed phase, hereinafter referred to in this patent specification and claims as the “relatively less dense, lighter liquid” or “lighter liquid,” has sufficient buoyancy to form, a supernatant layer on the heavier liquid from droplets of the lighter liquid by ascending through the tray perforations and the layers of the heavier liquid. The perforated trays have drainage openings so that the descending heavier liquid will flow back and forth consecutively across the perforated trays. The drainage openings are provided with downcomers forming overflow weirs for providing the layer of heavier liquid on the trays, for the droplets of the lighter liquid to ascend through, and liquid seals between the trays to trap the lighter liquid beneath the perforated trays.  
         [0003]     In other liquid/liquid exchange columns the heavier liquid is the dispersed phase and the lighter liquid is the continuous phase. In these exchange columns, the heavier liquid gravitates from a continuous layer, downwardly through the pores of the trays to form droplets which gravitate further downwardly through a supernatant layer of the lighter liquid flowing between the undersides of the porous trays and the layers of the heavier liquid therebelow. It follows, from the above descriptions of the roles of the heavier and lighter liquids, that the heavier liquid is capable of gravitating downwardly as droplets through a continuous phase layer of the lighter liquid flowing across the undersides of the perforated trays.  
         [0004]     While known liquid/liquid exchange columns are useful, it would be highly desirable to increase the exchange between the liquids by increasing the surface contact between the dispersed phase and the continuous phase, and enhancing scrubbing of the dispersed phase by the continuous phase.  
       SUMMARY OF THE INVENTION  
       [0005]     According to the present invention there is provided a liquid/liquid exchange column, comprising,  
         [0006]     a) an upwardly extending exchange column casing for flooding by the reception of a relatively denser, heavier one of the liquids at, and removal of a relatively less dense, lighter one of the liquids from, an upper end, and the reception of the lighter liquid at, and the removal of, heavier liquid from, a lower end,  
         [0007]     b) a series of perforated trays partitioning the casing at different levels in the column, with adjacent trays provided with liquid openings which are positioned for a first one of the said liquids to cross first sides the trays, as a continuous phase, while a second one of the said liquids permeates the trays from a second side to form globules, as a dispersed phase in the first liquid,  
         [0008]     c) for each liquid opening, a duct comprising, 
        i) a liquid retaining portion, for retaining a layer of first liquid in contact with the first side of the tray containing that liquid opening, and     ii) a liquid conveying portion extending in the opposite direction to the liquid for retaining a layer of the second liquid in contact with the second side of the tray containing that liquid opening, the liquid conveying portion having a flow restricting outlet therefrom, for conveying first liquid to the first side of an adjacent tray, while retaining a liquid seal of the first liquid therein, and for each pair of adjacent trays,        
 
         [0011]     d) at least one depending baffle from the upper one of those trays, and  
         [0012]     e) at least one upstanding baffle on the lower one of those trays, and wherein,  
         [0013]     f) each depending baffle, upstanding baffle, liquid retaining portion, and liquid conveying portion extending between adjacent trays, overlap vertically, and are spaced from one another, to provide, an undulating, first liquid flow paths between those adjacent trays.  
         [0014]     The liquid retaining portions may be upstanding on each tray and the liquid conveying portions extend downwardly from the trays, so that the first liquid is the heavier liquid.  
         [0015]     The liquid retaining portions may depend from the trays, and the liquid conveying portions extend upwardly from the trays, so that the first liquid is the lighter liquid.  
         [0016]     Flow directing partitions may be provided which partition the spaces between the depending and upstanding baffles to form a grid therewith and distribute liquid flow across the trays.  
         [0017]     The liquid conveying portions, when extending downwardly from the trays, may have sloping lower wall portions to gradually reduce the cross-sectional area in a downward direction.  
         [0018]     The liquid conveying portions, when extending upwardly from the trays, may have sloping upper wall portion to deflect descending globules towards the tray immediately therebelow.  
         [0019]     The flow restricting outlets may comprise horizontal slots which form a grill. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     In the accompanying drawings which illustrate, by way of example, embodiments of the present invention.  
         [0021]      FIG. 1  is a schematic side view of a liquid/liquid exchange column,  
         [0022]      FIG. 2  is a schematic plan view along II-II,  FIG. 1 ,  
         [0023]      FIG. 3  is a schematic side view of a portion of the column shown in  FIG. 1 ,  
         [0024]      FIG. 4 , is a schematic side view of a portion of a different column to that shown in FIGS.  1  to  3 ,  
         [0025]      FIG. 5  is a perspective view of a portion of a different column to that shown in FIGS.  1  to  3 , and  
         [0026]      FIG. 6  is a similar view to  FIG. 5 , but of a different column thereto. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     In FIGS.  1  to  3 , there is shown a liquid/liquid exchange column, comprising  
         [0028]     a) an upwardly extending exchange column casing  1 , for flooding by the reception of a relatively denser, heavier one of the liquids at, and the removal of a relatively less dense, lighter one of the liquids from, an upper end, and the reception of the lighter liquid at, and the removal of, the heavier liquid from, a lower end,  
         [0029]     b) a series of perforated trays  2  to  8  partitioning the casing  1  at different levels, with adjacent trays, such as trays  3  and  4 , provided with liquid openings  10  and  12  which are positioned for a first one of said liquids to cross first sides  11  of the trays  2  to  8 , between the liquid openings  10  and  12  as a continuous phase, while a second one of the said liquids permeates the trays  2  to  3  from a second side  13  to form globules, as a dispersed phase in the first liquid,  
         [0030]     c) for each liquid opening, such an opening  10 , a duct  14  comprising, 
        i) a liquid retaining portion  16 , for retaining a layer of first liquid in contact with the first side  11  of the tray  2  to  8  containing that liquid opening  10 , and     ii) a liquid conveying portion  18  extending in the opposite direction to the liquid retaining portion  16  for retaining a layer of the second liquid in contact with the second side  13  of the tray  2  to  8  containing that opening  10 , the liquid conveying portion  18  having a flow restricting outlet  32  therefrom, for conveying first liquid to the first side  11  of an adjacent tray, such as trays  10  and  12 , while retaining a liquid seal of the first liquid therein, and for each pair of adjacent trays  2  to  8 ,        
 
         [0033]     d) at least one depending baffle  20  from the upper one of those trays, such as tray  3 , and  
         [0034]     e) at least one upstanding baffle  22  on the lower one of those trays, such as tray  4 , and wherein,  
         [0035]     f) each depending baffle  20 , the upstanding baffle  22 , and the liquid retaining portion  16 , and liquid conveying portion  18  extending between trays, such as trays  3  and  4 , overlap vertically, and are spaced from one another, to provide, an undulating first liquid flow paths across each of the trays  2  to  8  for the first liquid.  
         [0036]     The liquid retaining portions  16  may be upstanding on each tray  2  to  8 , as shown in FIGS.  1  to  3 , and the liquid conveying portions  18  extend downwardly from the trays  2  to  7 , with the outlets  32  adjacent the lower tray, so that the first liquid fill flow downwardly therein and is the heavier liquid.  
         [0037]     The liquid retaining portions  16  may depend from the trays  2  to  8 , as shown in  FIG. 4 , and the liquid conveying portions  18  extending upwardly on the trays  2  to  7 , with the outlets  32  adjacent the upper tray, so that the first liquid will flow upwardly therein and is the lighter liquid.  
         [0038]     Referring now to FIGS.  1  to  3 , a heavier liquid  36 , and a lighter liquid outlet  38 , are provided at the upper end of the casing  1 , with the lighter liquid outlet  38  at a higher level than the heavy liquid inlet  36 . A lighter liquid inlet  40 , and a heavier liquid outlet  42 , are provided at the lower end of the casing  1 , with the lighter liquid inlet  40  at a higher level than the heavier liquid outlet  42 .  
         [0039]     In the operation of this embodiment, the casing  1  is flooded by  
         [0040]     i) heavier liquid from the inlet  36  so that heavier liquid gravitates down the casing from tray  2  through the openings  14 , by flowing as a layer across each of the trays  3  to  8 , in contact with their first sides  11 , as the continuous phase, to exit from the casing  1  through outlet  42 , and  
         [0041]     ii) lighter liquid, as the second, dispersed phase liquid, entering the inlet  40  passes upwardly, to form a layer of second liquid in contact with the second sides  13  of the tray  2  to  8  and then passes through the pores in the trays  2  to  8  and to form ascending globules in the layer heavier liquid flowing across the first sides of the trays  2  to  8 .  
         [0042]     The globules are buoyed upwardly through the layer of heavier liquid on the trays  2  to  8  to form what is essentially a floating, supernatant layer of lighter liquid adjacent the second sides of the trays  2  to  7 , and then pass upwardly through the pores of the next tray  2  to  7  to form the globules once more.  
         [0043]     In this embodiment, there is a layer essentially of lighter liquid immediately beneath each tray  2  to  8 , and a layer of essentially heavier liquid on each tray  2  to  8  which overflows over the outlets  32  and any lighter liquid that may be entrained in the overflow of liquid over the portions  16  is bourne upwardly from a liquid seal of heavier liquid that collects in the downwardly extending passage portions  18  to join the essentially lighter liquid layer beneath the trays  1  to  7 .  
         [0044]     The heavier liquid that collects in the downwardly extending passage portions  18 , forms a liquid seal therein, and is allowed to flow out of the downwardly extending passages  18 , at a position adjacent the first side  11  of the tray below, at a rate which maintains the liquid seal.  
         [0045]     The heavier liquid flowing out of the downwardly extending passages  18  flows across the trays  3  to  9  and entraining the globules of the lighter liquid, which are bourne upwardly therein, is deflected by the baffles  20  and  22  to flow along an undulating path and this causes the heavier liquid to retain the globules of lighter liquid for a longer period, and also to scrub them to a greater extent, thus enhancing exchange between the heavier liquid and the lighter liquid.  
         [0046]     As is more clearly shown in  FIG. 3 , the descending heavier liquid flows over the retaining portion  16  of the duct  14  and down the liquid conveying portion  18  to exit therefrom through the outlet  32  and flow along the undulating path, over the tray  5  to the next retaining portion  16 . The liquid seal in the liquid conveying portion  18  isolates the lighter liquid from the tray  4  passing to the tray  5 , and so the only way of escape for this lighter liquid is upwardly through the perforations in the tray  4  and to form globules once more on that tray.  
         [0047]     Referring to  FIG. 4 , in this embodiment each duct  14  extends to convey liquid upwardly i.e., the liquid conveying portion  18  extends upwardly to discharge liquid through the outlet  32  adjacent the tray  2  to  7  above, while the liquid retaining portion  16  extends downwardly to retain a layer of liquid immediately beneath each tray  2  to  7 .  
         [0048]     In this embodiment a layer essentially of heavier liquid on each tray  2  to  8  descends through the pores of the trays  2  to  8 , to pass downwardly as globules through a supernatant layer of lighter liquid flowing across and immediately beneath each tray  2  to  7 . A layer of lighter liquid is retained under each tray  2  to  8  by the liquid retaining portion  16  while excess lighter liquid escapes under the liquid retaining portion  16  to float upwardly through the liquid conveying portion  18  and exit through the outlet  32  to form a layer of essentially lighter liquid beneath the next tray  2  to  7  thereabove.  
         [0049]     Thus, in this embodiment, the lighter liquid is the continuous phase and the heavier liquid is the dispersed phase.  
         [0050]     In some embodiments of the present invention, flow directing partitions  44  to  52  (FIGS.  1  to  3 ) may be provide partitioning the spaces between the depending baffles  20  and the upstanding baffles  22  to form a grid therewith and distribute liquid flow across the trays  3  to  8 .  
         [0051]     In  FIG. 5 , similar parts to those shown in FIGS.  1  to  3  are designated by the same reference numerals, and the previous description is relied upon to describe them.  
         [0052]     In  FIG. 5 , the liquid conveying portion  18  has a sloping, lower wall portion  56  to gradually reduce the cross-sectional area therein, in a downwardly extending direction to contain a seal of the heavier liquid, and the outlet  32 , FIGS.  1  to  3 , is replaced by horizontal slots  58  forming a grill.  
         [0053]     The embodiment shown in  FIG. 5  operates in the same manner as the embodiment described with reference to FIGS.  1  to  3 .  
         [0054]     In  FIG. 6 , the conveying portion is uppermost, and has a sloping, upper wall portion  60  to deflect descending globules of heavier liquid towards the tray  3  to  8  immediately therebelow, and contain a seal of the lighter liquid, the outlet  32 ,  FIG. 4 , is replaced by horizontally extending slots  62  to form a grill.  
         [0055]     The embodiment shown in  FIG. 6  operates in the same manner as the embodiment described with reference to  FIG. 4 .  
         [0056]     Exchange columns of the present invention are useful in, for example, the petroleum refining and petrochemical industries.  
         [0057]     While reference has been made to essentially lighter liquid and heavier liquid layers, it will be appreciated that a transitional layer exists between these layers compose of both liquids.  
         [0058]     It will also be appreciated that the baffles, liquid retaining portions, and liquid retaining portions may be inclined vertically or curved and still provide undulating, first liquid flow paths.