Abstract:
A vessel for contacting a plurality of objects with a fluid. An upwardly directed stream of fluid and a portion of the objects are confined in a conduit such that the fluid stream causes the objects to flow upward from a moving bed thereof to a disengaging position from where they fall onto an inclined distribution surface, are fed into an annular channel having at least an inclined section, and move downward through the inclined section to a feed position at the fluid inlet. The vessel may be used for treating electrically conductive objects wherein the fluid is an electrolyte, an electrode is positioned to contact the moving bed, and a counterelectrode is positioned in spaced relation to the vessel, which may be fixed or portable.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/068,498, filed Dec. 22, 1997, and is a Continuation-In-Part of U.S. application Ser. No. 10/176,260 filed Jun. 20, 2002, which was a Continuation of International Application No. PCT/US00/35413 filed Dec. 28, 2000, which was a Continuation-In-Part of U.S. application Ser. No. 09/216,859 filed Dec. 21, 1998, now U.S. Pat. No. 6,193,858 issued Feb. 27, 2001, the entire contents of this patent and these prior applications being expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to the use of spouted beds of particles, pieces, parts and other small objects for the treatment thereof in a liquid or gaseous fluid. The invention has particular application for the electroplating of small parts which are difficult to plate by conventional means. The invention also has application in the fields of wastewater treatment, electrowinning, electrochemical synthesis, anodic electrochemical smoothing, anodizing, electrophoretic polymer coating, and physical coating, as well as in the general field of spouted bed applications.  
       BACKGROUND OF THE INVENTION  
       [0003]     Barrel plating, in which objects are tumbled in a perforated horizontal rotating drum, is a common method of electroplating small parts. Representative technology is disclosed in U.S. Pat. No. 4,822,468 by Kanehiro and U.S. Pat. No. 4,769,117 by Shino, et al. Many very small parts cannot be plated effectively in a barrel due to poor contact with the current feeder or fouling on the interior of the drum. These problems often necessitate the addition of plating media (typically some type of smooth metal shot) to the barrel to improve cathodic contacting and part motion. The use of media significantly increases the required plating time and current because the media is also plated and, therefore, the plating cost per part is increased. Additionally, many small parts are fragile or can interlock and may be damaged by tumbling with heavy media. Consequently, these parts cannot be plated successfully in barrels.  
         [0004]     U.S. Pat. No. 5,487,824 by Greigo discloses an integrated electroplating system designed specifically to electroplate very small parts which employs a horizontal accelerating rotating drum to maintain a packed bed of parts in motion during electroplating.  
         [0005]     U.S. Pat. No. 3,1124,098 by Backhurst et al. and U.S. Pat. No. 3,703,446 by Haycock et al. disclose fluidized bed cathodes. Although fluidized beds have excellent liquid-solid contacting, fluidized bed cathodes suffer from poor electrical contact between the fluidized particles, non-homogeneous electrical potentials and particle segregation effects. Additionally, it is difficult to maintain the entire bed fluidized when the particles are changing in size, and possibly density, due to metal deposition. It is unlikely that the potential benefits of the fluidized bed approach will be realized in a practical electrodeposition system.  
         [0006]     Typical spouted beds consist of a cylindrical vessel with a conical bottom section. The vessel contains a bed of particles which form the spouted bed. Fluid is introduced into the spouted bed vessel at the bottom of the conical section as a jet. This fluid jet penetrates the bed of particles contained in the spouted bed vessel, entraining particles and forming a “spout” of upward moving particles and fluid. The particles disengage from the fluid flow in a region above the particle bed and then fall on top of the downward-moving annular bed. The “pumping action” provided by the spout circulates the particles through the vessel in a torroidal fashion; upwards in the spout and downwards in the annular moving bed. A “draft pipe” may be incorporated into the vessel to assist in the fluid transport of the particles. The draft pipe consists of a tube which is fixed coincident with the location of the spout, directly above and aligned with the liquid jet. The draft pipe delays the dispersion of the liquid jet and allows particle transport over a broader range of fluid velocities while also stabilizing the liquid flow.  
         [0007]     U.S. Pat. No 4,272,333 by Scott discloses the use of a moving bed electrode (MBE), in which conductive particles move downward vertically in a packed bed between two electrodes, the anode being shielded with a membrane. The necessity of using a membrane to shield the anode makes this configuration less attractive for practical applications, since the mechanical abrasion of the moving bed of particles can damage the membrane in a short time. Additionally, metal deposition on the membrane may be a complication.  
         [0008]     An article by Hadzismajlovic et al. published in Hydrometallurgy, Vol. 22, pages 393-401 (1989), and U.S. Pat. No. 1,789,443 by Levin disclose the use of spouted bed cathodes with anodes suspended above the spouted bed surface. Although this configuration may eliminate the complication of shielding electrodes using membranes, several operational problems may be encountered with this configuration. Many electrolytes have poor electrical conductivity; therefore, it is advantageous to have the cathode and anode in close proximity in order to reduce the voltage drop over the cell. This cannot be accomplished in these prior art systems, since the spout would collide with the anode. Additionally, the projected spouted bed geometric surface area is very limited, impairing electrode performance.  
         [0009]     Conventional spouted beds also suffer from a particle recirculation problem commonly referred to as “dead spots”, where a portion of the particle bed is stagnant. Dead spots usually exist at the outer edge of the spouted bed surface and are attributable to a failure of the spout to deposit particles at the circumference of the spouted bed. In an attempt to remedy this problem, spouted beds with very steep bottom cone angles have been adopted. In all cases, the radius of the spouted bed has been strictly limited to the distance to which particles in the spout can be transported radially outward by the fluid flow.  
       SUMMARY OF THE INVENTION  
       [0010]     In the present invention, a distribution means has a solid body with a conical distribution surface extending from the vicinity of the upper edge of a draft pipe downward and radially outward towards the vessel sidewall to an annular channel for forming a downwardly moving annular packed bed, and is used to convey parts, pieces, particles or other small objects to this annular spouted bed by preventing the objects from falling near the center of the spouted bed vessel. Instead, the objects disengage from the spout and are deposited on the upper distribution surface of the distribution body. The objects then move along this surface until they are deposited in the annular channel at or beyond the outside edge of the distribution surface.  
         [0011]     Use of the distribution body totally eliminates stagnant areas at the circumference of the spouted bed. Moreover, the distribution body allows very large diameter spouted beds to be constructed at modest fluid flow rates, since it is no longer necessary to transport objects to the spouted bed circumference dynamically via the fluid flow. The distribution body may comprise an upper shield member as shown in the related applications referred to above and a lower separate spacer member similar to that described below. However, an integral shield and spacer body with an upper distribution surface as specifically described below is preferred. Additionally, when such a distribution body or shield is used, large diameter shallow spouted beds with shallow bottom cone angles may be employed. In this type of bed, the motion of the objects is more radially inward rather than downward. Thus, the annular moving bed of the present invention is particularly advantageous for circulating fragile objects where the weight of a deep, small diameter bed may crush or break the objects, and is particularly useful for spouted beds of conductive or partially conductive parts serving as high performance electrodes where large projected areas and shallow bed depths are desirable.  
         [0012]     A portable electroplating apparatus, which incorporates a pump and a vessel which defines a spouted bed electrolytic reaction chamber, is also provided by the present invention. The portable electroplating vessel can be conveyed from process tank to process tank by hand, automated plating system, or hoist. The spouted bed vessel is mounted on a platform with a pump to provide the necessary electrolyte flow for the spouted bed chamber. It is advantageous to incorporate a liquid by-pass circuit and adjustment valve so that the liquid flow to the spouted bed chamber can be adjusted. The liquid flow to the spouted bed chamber can also be adjusted by electronically controlling the speed of the pump. It is also desirable for the spouted bed vessel to be easily detachable from the portable apparatus and also for the internal components to be easily detachable from the vessel to facilitate access to the vessel interior.  
         [0013]     In a further modification of the invention, each process tank may be equipped with a corresponding pump and control valve having a coupling or docking station to which the spouted bed vessel is easily attached and detached so that a spouted bed vessel without its own pump and valve may be conveyed between process tank docking stations.  
         [0014]     In the practice of the present invention, conductive parts are electroplated while being circulated in a liquid spouted bed, in which the liquid is an electrolyte containing metal ions. The parts form an annular moving packed bed which is maintained under cathodic current by being in contact with a current feeder. The passage of current through the parts causes metal to be deposited from the electrolyte onto the parts as they circulate in the apparatus. Typically, the parts are retained in a non-conductive cylindrical vessel with a conical bottom section, although vessels with other geometries may also be used, provided they also have a downward inwardly inclined bottom section. The vessel may be made of a non-electrically conductive plastic material, for example polypropylene.  
         [0015]     The electrolyte is introduced into the vessel as a jet at the bottom of a conical section into the bed of parts to be plated. The liquid jet entrains parts which disengage from the liquid flow in a region above the jet, then move radially outward to an annular channel, and then move downward and radially inward as an annular moving packed bed of parts. The action provided by the liquid jet thus circulates the parts through the vessel; first upwards and radially outward in the jet and then downward and radially inward in the packed bed. The cathodic connection is made with the packed bed via metallic contacts or a current feeder attached to the outside of the distribution body, or optionally inserted into the packed bed from above or attached to the inside wall of the vessel, to a side surface of a separate distribution shield member or to a side or lower surface of a separate spacer member below the distribution shield member.  
         [0016]     If the surfaces of the parts to be plated are entirely conductive, the current feeder may be small in size with respect to the particle bed. If the parts are partially conductive by having non-conductive elements, as is the case with surface mounted electronic components, it is desirable to employ current feeders with a much larger surface area to insure that electrical contact is made with the conductive portions of the parts during their movement in the moving bed. For example, a majority of the vertical and inclined outer surfaces of the distribution body may be lined with a conductive material and used as a current feeder, or a large internal surface of the vessel below the distribution surface and in contact with the moving bed may be conductive and electrically connected as the cathodic current feeder. Large cathodic current feeders are preferred when plating partially conductive parts even when the parts are mixed with conductive media. Additionally, it is advantageous to use a mixture of conductive media and parts in the present invention when the parts are partially conductive. The counterelectrode (anode) maybe suspended above the moving packed bed in the spouted bed chamber, but preferable is located external to the vessel defining the spouted bed chamber.  
         [0017]     The invention also may use a current feeder with a bumpy or otherwise textured surface to facilitate movement of the objects and to prevent the objects from sticking to the current feeder during electrodeposition. Bumps about the size of the objects are particularly useful for preventing rectangularly shaped objects from jamming together and “tiling” as they slide over the current feeder. Moreover, a bumpy or otherwise textured current feeder surface reduces the contact area between the objects and the current feeder, thereby decreasing the possibility that the objects will become fused to the current feeder during electroplating.  
         [0018]     A “draft pipe” is incorporated into the distribution body to assist in the hydraulic transport of the parts. The draft pipe comprises a passage or conduit in the distribution body that may be cylindrical or have some other shape, and the entrance to which is fixed coincident with the location of the spout, namely, directly above and aligned with the liquid jet. The draft conduit delays dispersion of the liquid jet and allows part transport over a broader range of liquid velocities.  
         [0019]     Additionally, it is preferable to employ a parts deflector located above the draft conduit. The parts deflector is a conical point or a flat disk or a downwardly facing concave surface, which is located above the spout. The deflector prevents the parts in the spout from exiting the chamber by directing the part trajectories toward the sidewall of the vessel. It also prevents the jet of entrained parts from colliding with any overhead components in the chamber. The parts deflector is particularly advantageous in conjunction with the draft conduit, since the presence of the draft conduit strengthens the flow of the spout.  
         [0020]     It is also preferred to employ a distribution surface. The distribution surface may be conical and extend from the vicinity of the upper edge of the draft conduit to an annular space or channel between a wall of the vessel and an opposing surface of the internal spacer member. This surface aids in distributing the parts to the annular spouted bed by preventing parts from falling near the center of the reaction chamber. Instead, these parts move along the distribution surface until they are deposited at the top of the annular moving bed of parts.  
         [0021]     In the present invention, one or more counter electrodes may be used and they are typically anodes. The counter electrodes are preferably located external to the spouted bed vessel, which is at least partially immersed in the electrolyte, and in close proximity to the exterior of the vessel sidewall(s). Openings are provided in the immersed portion of the sidewall(s) and/or bottom wall(s) of the spouted bed vessel to allow the passage of current via the electrolyte from the external counter electrodes to the moving packed bed of objects contained in the spouted bed vessel. The submerged vessel openings may be covered by a fine screen, a mesh, cloth or membrane which allows the passage of electrical current and prevents the loss of the objects from the spouted bed vessel. These openings may also serve as means for the electrolyte to exit the spouted bed vessel.  
         [0022]     Typically, external soluble anodes comprised of the same metal as is dissolved in the electrolyte are desirable in electroplating applications where the spouted bed vessel may be conveyed between a plurality of processing tanks. Although insoluble anodes may also be used for these and other applications of the present invention, they are typically used for precious metal plating.  
         [0023]     The liquid electrolyte is injected into the reaction chamber via a pump and, during operation, this arrangement presents no difficulties. However, when operation of the device is interrupted, the parts from the bed may fall into the outlet of the pump via gravity, effectively fouling the pump. Therefore, a means of retaining the parts in the vessel is provided. One approach is to incorporate a screen at the jet inlet which will not allow the parts to pass. If a screen is used, it is preferable to filter the fluid upstream of the screen to prevent fouling.  
         [0024]     An alternate approach is to utilize a solid “trap” arrangement. This can be a simple “U” pipe on the inlet line, or can consist of two concentric pipes which cause the liquid to reverse direction. In either case, the parts are trapped due to their density difference with respect to the electrolyte. An access port can be incorporated into the trap to allow the parts to be conveniently removed from the spouted bed chamber. Alternately, a gate or slide valve may be used to seal the inlet pipe when the flow is interrupted.  
         [0025]     The present invention may also be practiced using rectangular vessels with inward downwardly inclined (slanted) bottoms. In this case, the distribution shield would be an angled flat plate or plates, and the draft conduit and inlet pipe may be either tubular or rectangular. The present invention also contemplates that the spouted bed vessel may be used in a stationary configuration in which the various cleaning, plating and rinse solutions are sequentially introduced from separate holding tanks, circulated through the reaction chamber for the appropriate time, and then purged from the spouted bed vessel via a manifold piping system connected to solution reservoirs, control valves, control system and pumps. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The invention and its assembly and operation may be further understood from the following description of the preferred embodiments thereof, which are shown by way of example in the accompanying drawings wherein:  
         [0027]      FIG. 1  is a cross-sectional elevational view of a portable spouted bed electrochemical reactor vessel and a stationary electrolyte tank and docking system made in accordance with the present invention;  
         [0028]      FIG. 2  is an exterior top view of a spouted bed plating apparatus as modified to provide a self contained portable unit in accordance with the invention; and,  
         [0029]      FIG. 3  is a cross-sectional elevational view of the apparatus of  FIG. 2  as taken along line  3 - 3  of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]     Turning now in greater detail to the appended drawings,  FIG. 1  shows a detailed cross-sectional view of a portable spouted bed reaction chamber or reactor  1 , removeably situated in a stationary process tank  40 . The stationary process tank  40  is equipped with a pumping system to supply a liquid stream of electrolyte to spouted bed chamber  1 , and is further equipped with stationary electrodes  8 , which are external to the chamber  1  and function as counter electrodes to the objects  3  contained in chamber  1 . When electroplating objects  3 , electrodes  8  function as anodes. Tank  40  may be one of a series of process tanks between which portable spouted bed chamber  1  is conveyed during an electroplating process that will circulate through chamber  1  successive processing solutions, such as cleaning, plating and rinsing solutions. As an alternative, chamber  1  may be fixed to tank  40  and successive processing solutions passed through tank  40  from a plurality of process tanks.  
         [0031]     The spouted bed chamber  1  consists of a cylindrical vessel  2  with a conical bottom  11  and a detachable top or cover  12 . Vessel  2  is made of a material, such as polyethylene, that is not electrically conductive. The vessel  2  of spouted bed chamber  1  is partially immersed in the liquid electrolyte L contained in tank  40 , as is indicated by liquid surface S. The electrolyte is injected into the chamber  1  by an external pump  34  via a ball flow regulating valve  32 , a socketed fitting  30  and an inlet pipe  18  having an attached mesh screen  17 . Pump  34  is connected in a closed loop that is completed by tank  40 , a tank outlet fitting  38 , a liquid strainer  36  and associated plumbing.  
         [0032]     The portable spouted bed chamber  1  may be detachably connected to tank  40  by inserting inlet pipe  18  into socketed coupling  30  as shown in  FIG. 1 . The inlet pipe is connected to the spouted bed vessel  2  via a socketed receptacle  19 . Pin  15  is used to retain inlet pipe  18  in socketed receptacle  19 . Mesh screen  17  is attached to the end of inlet pipe  18  and retains the treated objects in the vessel  2  when the liquid flow through the vessel is discontinued. Pin  15  and inlet pipe  18  and attached mesh  17  can be easily removed to allow the unloading of objects from the bottom of vessel  2  of the spouted bed chamber  1 .  
         [0033]     Liquid enters vessel  2  via the inlet pipe  18  and forms a jet that entrains small parts or other objects and carries them into and through a passage or conduit  4  passing axially through an internal spacer member  9  having an upper portion which forms a shield with a conical distribution surface  20 . Although the spacer member and the distribution shield may be separate components, they are preferably made as a single integral piece as shown in  FIG. 1 . The liquid jet with entrained objects moves through conduit  4  and impinges on a deflector  6  that is suspended from the vessel cover  12  and preferably has a downwardly facing concave surface. Deflector  6  directs the entrained objects radially outward and downward, thereby disengaging the objects from the liquid jet.  
         [0034]     The disengaged objects are deposited on the upper distribution surface  20  of spacer member  9  where they move radially outward and downward until they slide off surface  20  and are deposited in a confining channel  3  that is preferably annular and is formed by opposing surfaces of spacer member  9  and the sidewall of vessel  2 . Both of the opposing surfaces forming annular channel  3  preferably have vertically oriented portions and inward downwardly inclined portions, and the objects deposited in the annulus therebetween form an annular moving bed. However, the opposing surfaces of channel  3  may optionally have only inward downwardly inclined portions resembling a pair of concentric funnels, with the outer funnel being both the side wall and bottom wall of a vessel without a vertical wall portion or having a vertical wall portion at or above the annulus. Also, channel  3  may be only partially annular, such as being an arcuate channel or a channel divided into two or more arcuate segments each of which forms a correspondingly arcuate segment of the downwardly moving bed of small parts.  
         [0035]     The confined bed of the objects moves vertically downward and then radially inward and downward in a moving packed bed towards the gap between the upper end of inlet pipe  18  and the lower entrance end of conduit  4 . The inclined portions of the opposing surfaces, and the conical distribution surface  20 , are inclined at an angle in the range of preferably about 20° to about 80°, more preferably about 30° to about 50°, from the horizontal.  
         [0036]     Spacer member  9  is attached to the cover  12  of vessel  2  by one or more vertical supports  22 . The cover  12 , supports  22 , spacer member  9  and deflector  6  form a detachable assembly which is readily removed by lifting the chamber cover  12  from the spouted bed vessel  2 , thus providing easy internal access to vessel  2 .  
         [0037]     Electrical contact with the annular moving bed of objects is made by an arcuate or annular current feeder  16  that is electrically conductive and is attached to spacer member  9 , preferably so as to form at least a portion of its circumference. Current feeder  16  is connected to an external electrical power supply by a cathodic connection comprising an electrically conductive rod  10  that preferably runs axially through one or more of the supports  22  and is connected to a cathodic connector  23 . The outer surface of current feeder  16  may have bumps, or be roughened or otherwise textured to facilitate movement of the objects thereover.  
         [0038]     In the embodiments shown in the drawings for coating small objects with a metal constituent of the electrolyte, the electrodes in contact with the moving bed of objects are connected to the negative terminal of the power source and function as cathodes, and the counter-electrodes  8  are mounted in the stationary tank  40  in proximity to vessel  2  and are connected to the positive terminal of the power source and function as anodes. Current is conducted from the anodes to the moving objects via one or more openings  25 ,  26  and  27  in the sidewall of vessel  2  and in the bottom wall  11 , these openings being covered by a porous screen, mesh, cloth, membrane or other porous medium for retaining the objects within the vessel while passing current. Liquid pumped into the vessel  2  via inlet pipe  18  exits the vessel primarily via the covered openings  27  that are above the level of the bed  3 .  
         [0039]     In implementing the embodiment of  FIG. 1 , as well as the embodiments of  FIGS. 2-3 , a pumping means and a docking means may be provided for each of a series of process tanks. An automated means for detecting the presence of a reactor vessel in each process tank may also be provided and used to automatically switch on the pump serving the tank. The detection means may be a physical contact switch (not shown) in the tank, or a magnetic hall effect sensor  72  on the outside of the tank and a magnet  73  attached to the inlet pipe  18  of the reactor vessel  2  as shown in  FIG. 1 . The detection means may also include a relay module  74  responsive to inputs from sensor  72  to control an A.C. power supply  76  for operating the pump  34 .  
         [0040]     In the embodiment of  FIGS. 2 and 3 , a sensor like the sensor  72  may be located under the lip  71  in the vicinity of the position for a rail  70  and a magnet like the magnet  73  may be attached to the corresponding rail. For such a physical or magnetic detection means, there may be substituted an optical detector, or any other means which can be effectively implemented to serve this purpose. Thus, it is an object of the present invention that the pump for each tank used with the embodiments of  FIGS. 1-3  may be automatically activated when a reactor vessel is present and deactivated when the vessel is removed.  
         [0041]      FIG. 2  shows a top view of a portable plating apparatus  41  having a spouted bed reactor vessel  50  removably situated in a process tank  87  containing a process solution L with its surface designated by S. The internal components of vessel  50  are preferably the same as those shown for vessel  2  in  FIG. 1 . This apparatus may be used in an analogous manner to a plating barrel or plating rack in that it is designed to be conveyed from tank to tank for circulating through vessel  50  successive processing solutions, such as cleaning, rinsing, and plating solutions.  
         [0042]      FIG. 3  shows a sectional view of apparatus  41  taken along line  3 - 3  of  FIG. 2 . The lower portion of the apparatus is immersed below the surface S of the process solution L, and the entire apparatus is supported by side rails  70 ,  70 , which rest on a sidewall lip  71  of each process tank  87  and are equipped with handles  86 ,  86 . The apparatus includes transverse platforms  52  and  54 , which connect the side rails  70 ,  70 . A submersible head centrifugal pump  88  is mounted on platform  54 . The inlet of the pump is attached via an elbow  94  to a liquid strainer  95 . The outlet  96  of the pump is connected via a short segment of plastic pipe to a plastic T fitting  97 .  
         [0043]     The inlet pipe  98  of the spouted bed vessel  50  is detachably coupled to the T fitting  97 . The third opening of the T fitting  97  is attached via a plastic pipe and elbow  99  and a plastic pipe  60  to a bypass ball valve  90 . The outlet of ball valve  90  returns solution to the process tank  87  via the segments of plastic pipe and elbows shown in  FIGS. 2 and 3 . The amount of solution circulated through the spouted bed vessel  50  can be adjusted by using the bypass valve  90 . The liquid flow to the spouted bed chamber can also be adjusted by electronically controlling the speed of the pump. The spouted bed vessel  50  is open to the atmosphere and has a plurality of mesh covered openings  55  and  56  in the vessel sidewall and a plurality of mesh covered openings  57  in the vessel bottom wall. Solution is returned to the process tank via these mesh covered openings, primarily the openings  55  that are above the level of the annular bed.  
         [0044]     The negative direct current electrical connection (cathode) to the circulated objects in vessel  50  is via an electrical connector  48  passing through cover  12 ′ of vessel  50 . The counter electrodes or anodes  44  are suspended in the process tank  87  in proximity to the vessel  50  by conductive connectors  43  carried by conductive support rods  42 , which are connected to the positive terminal of a direct current power supply. Current passes between anodes  44  and the circulated objects contained in vessel  50  primarily via openings  56  and  57  in vessel  50 .  
         [0045]     Persons skilled in the art, upon learning of the present disclosure, will recognize that various modifications to the components and elements of the invention are possible without significantly affecting their functions. For example, the specific vessel structure described above may be varied widely in accordance with spouted bed technology, and may have shapes other than cylindrical, such as four sidewalls defining a rectangular chamber and either a single rectangular bottom wall inclined downwardly to the vessel inlet or opposing rectangular bottom walls converging downwardly toward the vessel inlet. Also, the confining channel  3  at the edge of the distribution surface may have shapes other than circular, such as rectangular, pentagonal, hexangular or octagonal.  
         [0046]     Similarly, the positions of the anode and cathode may be reversed so that metal objects may be polished by having an outer layer removed electrolytically. Furthermore, the apparatus disclosed may be used with a gaseous fluid in combination with a chemical coating composition in order to coat recirculating objects with the chemical composition instead of a metal, thereby providing a spouted bed coating apparatus of the type represented in general by that disclosed in U.S. Pat. No. 5,254,168 issued Oct. 19, 1993, to Littman, et al., the entire contents of this patent being incorporated herein by reference. Accordingly, while the preferred embodiments have been shown and described in detail by way of example, further modifications and embodiments are possible without departing from the scope of the invention as defined by the claims set forth below.