Abstract:
Highly efficient packing bodies are formed by stacking plates having at least 30% open space provided by apertures and rod-like baffle elements which project from a surface of the plate. The panels are latched together into a stack by means of a plurality of latching rods, longer than the baffle rods which are frictionally received into opposed sockets formed in the surface of the adjacent plate. A cover plate with downwardly depending rods and latching sockets disposed to receive the latching rods from the opposed plate is utilized to prevent the exposed rods from engaging the rods of other plates so that voids in a packed tower are avoided.

Description:
CROSS-REFERENCE TO PROVISIONAL APPLICATION 
     This application is based on provisional application Ser. No. 60/092,779 filed Jul. 14, 1998. 
    
    
     TECHNICAL FIELD 
     The present invention relates to fluid contact structures for use in packed towers. 
     BACKGROUND OF THE INVENTION 
     Packed towers are used for mass transfer operations such as absorption, desorption, extraction, scrubbing and the like. The function of the packing is to facilitate mass transfer between two fluid streams, usually moving countercurrent to each other. Efficiency and rate of mass transfer are enhanced by providing large surface area in the packing to facilitate contact of the fluids and by breaking the liquid into very fine droplets to enhance mass transfer to a gas phase. 
     U.S. Pat. No. 4,724,593 describes an improved method for manufacturing high performance, symmetrical, open volumed packing bodies. The high performance packing bodies have performed well and have captured a significant share of the market. An open, non-obstructive structure provides low pressure drop while dispersing and distributing flow in both longitudinal and lateral directions. 
     While the void volume of the interior structure of the packing body is less than prior high efficiency packing bodies, the structure normal to the longitudinal axis is still difficult to provide and manufacture requires several bending and rolling operations to form the sheet material into a packing body. 
     An improved packing body is disclosed in U.S. Pat. No. 5,498,376 issued Mar. 12, 1996, the disclosure of which is expressly incorporated herein by reference. A perforated strip of material is simply rolled into a spiral or into a concentric cylinder structure. The improved packing bodies have a high degree of open space, from 30% to 98%. Surprisingly, the rolled packing bodies are found to provide better mass transfer and efficiency than prior packing body structures. 
     Packing bodies having substantially open structure with good baffling action formed by folding and bending adjacent perforated panels along fold lines to form packing bodies in which the plates are substantially parallel to each other are disclosed in U.S. Pat. No. 5,458,817 issued Oct. 17, 1995. 
     Packing bodies are produced with complex shapes in a simplified manner from separate, perforated plates which are stacked in parallel relation. They are fixed in that relation by spacing means such as projections from the surfaces of the segments or side members such as bent or separate perforated side plates adhered to the side edges of the stacked segments. The plates also include baffle means for increasing disruption of the fluid into droplets. 
     The projections from the surface of the segments can also be used as baffles to disrupt large droplets, to create local turbulence, to increase contact between gas and liquid and to facilitate mass transfer. The projections can be polygonal tabs raised from the surface. The baffle tabs can be diamond, rectangular or circular in shape. Thin cylindrical rod projections from the surface have been found to be very effective in facilitating mass transfer while providing an open volume of above 30% with very low pressure drop. 
     Highly efficient packing bodies have recently been developed which utilize some longer rod projections to space and/or latch adjacent plates together. All of the baffle elements are rod-like projections and are substantially parallel to each other. All of the rod-like elements are releasable from a mold. The panels can be manufactured from a single mold and latched together to form a stacked packing body. The preferred latching means are sockets provided in the bottom surface of the adjacent panel. The latching rods can be tapered and are frictionally engaged in an opposed socket. Adhesive can be used to assure that the panels do not separate. 
     The panels can be successively reduced in size to form packing bodies having complex, polygonal shapes approaching spherical by simply molding a plurality of panels of different shapes and sizes. The panels can be square, rectangular, circular or oval. A differently shaped body can also be provided by cutting a square body across several panels to form a facet shaped member. 
     These packing bodies have a high degree of open space provided by perforations, at least about 30% of the packing body is open space, preferably from 50% to 98% of the body is open space. The rods provide increased surface for fluid contact. 
     The plates can be formed of metal, thermosetting resins, thermoplastic resins or ceramic precursors such as metal oxides dispersed in organic binder resin. The perforated plates are formed by molding organic resin materials. After the plate is in its final configuration, the plate can be fired to cure the resin or convert the precursor to a final ceramic state. 
     These packing bodies can be produced from much simpler starting materials. Even if molds are used to form the plates, the molds are much cheaper and simpler than molds used to form prior high performance packing bodies. Packing bodies can be formed in complex shapes that can not be practically made by other techniques and can be produced at much lower costs. 
     The stacked packing bodies  10  as shown in FIG. 1 (Prior Art) tend to entangle due to open rods  12  projecting from the bottom plate  14  which can enter the openings in the top plate and become entangled with rods in the sides or bottom of an adjacent stacked packing body. 
     STATEMENT OF THE INVENTION 
     An improved, stacked packing body is provided in accordance with this invention which reduces the binding of one stacked packing body to another. A first feature of the improved packing body is the inversion of the last plate to enclose and cap the ends of the rods. A further feature is to add spacing elements to the outside faces of the packing, preferably partial spacers provided on the perimeter of the outside plates and other spacers radially directed from the circumference toward the center of the packing. 
     The plates can have a thickness from 0.1 to 15 mm. In the case of metal, the thickness is usually from 0.2 to 0.4 mm. In the case of plastic, the thickness is usually from 0.5 to 3 mm, preferably 1 to 2 mm and in the case of ceramic, the strip preferably has a thickness from 2 to 8 mm. 
     The packing bodies of the invention are suited for waste water treatment, particularly in bio-film reactors. The high surface area of wavy brush-like packing now in use becomes covered with a layer of bacteria. The tank is periodically cleaned by air shearing to peel-off and dispose of the bacteria. Preliminary tests have been conducted with square stacked packing of the invention. The performance of the stacked packing of the invention was roughly the same in most cases and better in some cases (depending on the type of contaminants in the water). However, the stacked packing of the invention is less expensive and considerably easier to install than the brush packing, especially in large reactors. So on a cost/performance basis the stacked packing is clearly superior. 
     These and many other features and attendant advantages of the invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view with one plate detached of a prior art stacked packing containing a plurality of rod-like projections; 
     FIG. 2 is a top view of a further embodiment of a stacked packing; and 
     FIG. 3 is a view in section taken along line  3 — 3  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 2 and 3, an improved stacked packing body  20  is formed of at least two individual plates  22 ,  24 . The plates are joined into a stack  26  by inserting the tapered end  27  of longer rods  28  from the first plate  22  into an opposed socket  30  on the adjacent plate  24 . The end portions  31  of the longer rods  28  are preferably tapered to facilitate entering the socket  30 . The plate is preferably formed of a flexible, plastic inert to the liquid and gas media in a tower such as polypropylene or various flexible injection moldable fluoropolymers such as Teflon PFA (perfluoroalkyl vinyl ether-tetrafluoroethylene copolymer) and Teflon FEP (tetrafluoroethylene-hexafluoropropylene copolymer). The plastic is flexible and slightly deformable. It can form a secure joint  34  when forced into a socket  30 . The reliability of the joint  34  can be enhanced by the use of adhesive. Liquid adhesive can be injected into the socket before forming the joint. The polygonal plates illustrated in FIG. 2 have a diameter of about 9.5 inches. The length of each segment is about 4 inches. Baffle rods  40  are about {fraction (1/2+L )} inch long. 
     Each plate  22  can have a border  42  formed of equally sized perimeter segment members  44 . The longer rods  28  are placed at least at the corner intersections  46  of the perimeter segment members  44 . The sockets  30  can be formed in top portion  47  of each of the longer rods  28 . 
     The plates  22 ,  24  also contain a grid of cross members  50  and  60 . The cross members  50 ,  60  can be parallel to the side members  44  in case of a rectangular packing or can be at an angle to the side members in case of a polygon such as an octagon. Additional latching rods  28  with sockets  30  can be molded onto interior intersections of the cross members  50 ,  60  and at places in between the intersections. Usually, random packing will have at least two latching joints, generally from 4 to 12 joints, usually from 6-8 joints for packings with 4-6 plates. A stacked packing will have at least 10 to 50 latching points. 
     A plurality of baffle rods  28  depend from the lower surface  72  of the cross members  50 ,  60 . The baffle rods  28  are thin and may be tapered. Generally, the rods are from {fraction (1/32+L )} inch to {fraction (1/4+L )} inch, typically about {fraction (1/8+L )} inch at the base. The baffle rods  28  are usually mounted at each intersection  74  of the cross members and usually also at the mid point  75  between adjacent intersections. 
     The plates  22 ,  24  could be cut or stamped into shaped plates such as round, oval or polygonal and stacked. However, this would weaken the stacked packing body since a portion of the border would be cut away as would some or all of the long rods and sockets which provide latching joints. As shown in FIG. 2, it is preferred to separately mold each plate with a perimeter border  42  and with longer hollow rods  28  with socket  30  and with joints  34  mounted on or adjacent the perimeter border  42 . The perimeter border  42  for the polygon top plates  22 ,  24  can be continuous. The longer rods  28  can be formed opposite an aperture  30  in a longer rod  28  or opposite a cavity formed in a member facing the rod  28 . 
     Referring now to FIGS. 2 and 3, one aspect of the invention is the provision of a terminal cover plate  100  for the last plate  24  of the stack  26 . The cover plate  100  can have the same or different shape than the stack. The cover plate  100  is preferably no larger than the stacked plates to avoid binding to other packing bodies and forming voids in the packed tower. 
     The cover plate  100  also contains an open grid  106  formed of grid members  108 , which extends across the plate and reinforcing cross members  110  which intersect the members  108 . Rod-like baffle elements  112  project downwardly from the edge  114  of the members  108 ,  110 . Small spacer elements  125 , parallel to the baffle elements  112  may be attached to the top face  127  of the plate  100 , preferably, at the intersections  129  of the sides  127 . The spacer elements  125  need not cover the side  127 . The spacer elements  125  need only occupy from 10 to 50% the length of a side  127 . The spacer elements  125  extend vertically from the sides a distance of about 0.05 inch to 0.500 inch, generally about 0.1 inch. 
     Socket members  116  also project downwardly from the cover plate  100  in the form of a short rod  118  containing a cavity  120 . The position of the socket members  116  correlates to the position of the longer latching rods  28  on the adjacent plate  24 . When the rods  28  are inserted into the sockets  116  on the cover plate  100 , the cover plate  100  is latched to the adjacent plate  24  by compression fit and/or adhesive bonding. The spacing between the baffling elements  112  and the opposed plate  24  is less than the height of the stack. 
     Another feature of the invention is the provision of spacer structure on the outside faces of the stack to further prevent undesired stacking of the packing bodies. The spacers can be continuous or discontinuous. Partial spacers  125  can be mounted on the outside face of the perimeter of the terminal plates as previously discussed. Radial spacers  84  can be provided which run from the perimeter segments  127  toward the center of the top plate  100 . The radial ribs are shown connected to a raised square spacer  88  which is one aspect of the mold and is not necessary to the spacing function. The partial spacers  125  mounted on the perimeter can also be connected to the outside surface  90  of the first plate  22  and are identified with the same part numbers. 
     The stacked packing body can have a width and a height from 1 to 20 inches, generally from 3 to 10 inches. Usually, the width to height ratio is about {fraction (1/8+L )} to {fraction (1/4+L )}. The spacing and latching rods are generally longer by at least {fraction (1/8+L )} to {fraction (3/4+L )} of an inch, generally about {fraction (3/8+L )} inch longer. The number of plates is determined by the length of the rod baffles and the spacing between plates. The spacing of the plates is related to packing factor. The plates can have a thickness from 0.1 to 15 mm. In the case of metal, the thickness is usually from 0.2 to 0.4 mm. In the case of plastic, the thickness is usually from 0.5 to 3 mm, preferably 1 to 2 mm and in the case of ceramic, the strip preferably has a thickness from 2 to 8 mm. A packing body will generally have a packing factor from about 3 to 65 per foot and a surface area from about 10 to 200 ft 2 /cu.ft. The rods have a diameter from {fraction (1/16+L )} to {fraction (1/4+L )} inch, generally about {fraction (3/8+L )} inch longer. The rods need not be cylindrical. They can have a square or other polygonal cross-section. The packing body has a polygonal shape such as cylindrical, rectangular, hexagonal or octagonal. Generally, the diameter of each stackable packing body is from 3 inches to 15 inches, generally about 10 inches. The height of a 3 layer stacked packing body can be from 1 inch to 10 inches, generally around 3 inches. 
     The spacing between plates depends on the height of the baffle rods. Generally, the rods have a height from {fraction (1/16+L )} to 2.0 inches and have a tapered end. The rods may project upwardly, downwardly or some may project upwardly and some may project downwardly. The packing body will have at least 2 plates preferably from 2 to 30 plates. Random packing bodies are generally from 1 to 5 inches in nominal diameter, have a height from 1 to 4 inches and baffle rods from {fraction (1/16+L )} to {fraction (3/4+L )} of an inch. The method of the invention could also be used to produce large, modular, structured packing bodies such as cubic or rectangular-shaped modules such as 1 foot×1 foot×1 foot; 2 foot×1 foot×1 foot or 3 foot×1 foot×1 foot. The structured modules are placed one module at a time into a tower until the tower is filled. 
     The packing body can be in the form of a polygon such as a rectangle, hexagon or octagon having parallel side walls. The panels can step down in width in discrete steps. 
     The modular plates can be interconnected into stacks by inserting a longer rod into the opposed socket in the next plate. The plates can be stacked alternating the orientation of the rods from facing axially with the tower to transverse to the axis of the tower. The outside volume of the tower between the stacks of packing and the wall of the tower can be filled with random packing. 
     The plates need not be the same size. When the plates differ in size, they can be stacked to form three dimensional polygon shapes approaching ovoid or spherical shape. 
     It is to be realized that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations are permissible without departing from the spirit and scope of the invention as defined in the following claims.