Abstract:
A conveying system ( 22 ) transports loose particulate material past a radiation source ( 200 ). A feed system ( 20 ) discharges particulate material onto the conveying system ( 22 ). A pneumatic system with an inlet manifold ( 14 ) and tubes ( 16 ) provides air through which the particulate material is fluidly transported to the feed system ( 20 ). A receiving hopper ( 24 ) receives the particulate matter from the conveying system ( 22 ). A dump hopper ( 10 ) dumps the particulate material into the pneumatic system. A discharge manifold ( 18 ) separates the particulate material from air. A metering gate ( 70 ) is located at a base of a hopper ( 69 ), which controls the layer of particulate material deposited onto said conveyor. A second inlet manifold ( 26 ) and tubes ( 28 ) adjacent the receiving hopper entrains the particulate material in air. A receiving station ( 32 ) receives the particulate material from a second discharge manifold ( 30 ).

Description:
This application claims priority from Provisional Application Ser. No. 60/122,678, filed on Mar. 3, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the art of material treatment. It finds particular application with a vacuum pneumatic conveying system to deliver plastic pellet material to a belt conveyor. The pellets are carried on the belt conveyor past an electron beam source for irradiation treatment. It is to be appreciated that the present invention is also applicable to the treatment of other materials, such as grains, seeds, other polymers, and the like. 
     Currently, plastic pellets are loaded in trays to be conveyed through an irradiation unit. Typically, the trays are raked and sent through the unit again for retreatment until an appropriate total radiation dose is reached. This prior system has drawbacks including the large amounts of manual labor, consistent dose assurance, and problems attributable to heating of the polymer material of the pellets. 
     The present invention contemplates a new and improved apparatus and method which overcome the above referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, an apparatus is provided for irradiating particulate material. The particulate material is suspended in a moving fluid and conveyed to a source of radiation. The pelletized material is passed at a controlled rate through the radiation. The pelletized material is fluidized and conveyed from the radiation, the fluidizing concurrently cooling the pelletized material. 
     In accordance with a more limited aspect of the present invention, the pelletized material is deposited in a layer of uniform thickness on a belt conveyor prior to passing through the radiation and is removed from the belt conveyor and refluidized after irradiation. 
     In accordance with another more limited aspect of the present invention, the pellets are a polymeric material which pass through the radiation at a known rate to achieve a preselected polymerization reaction. 
     In accordance with another aspect of the present invention, the fluidized particulate material is passed through the radiation while suspended in the fluid. 
     In accordance with yet another aspect of the present invention, fluids themselves, such as liquid sewage, waste water, stack gasses, and the like, are treated by the radiation beam. 
     A principle advantage of the present invention is the provision for transporting loose particulate material passed an irradiation source at a controlled rate. 
     Another advantage of the present invention is that plastic pellets are treated with an accurately controlled dose of radiation. 
     Still another advantage of the present invention is manual labor and human process variations are minimized. 
     Yet another advantage of the present invention is that particulate material is entrained, irradiated and recollected into the same container, all without human intervention. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding of the following detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIG. 1 is a top elevational view of the plastic pellet vacuum system in accordance with a preferred embodiment of the present invention; 
     FIGS. 2A,  2 B, and  2 C are top and two-side elevational views of a dump hopper of the system of FIG. 1; 
     FIG. 3 is an expanded side perspective view of the vacuum take-off box of the dump hopper of FIG. 2; 
     FIGS. 4A and 4B are top and side elevational views of the dumping work platform of the system of FIG. 1; 
     FIGS. 5A and 5B are top and side elevational views of the ladder and work platform of FIG. 4; 
     FIG. 6 is a top elevational view of the pipes and diverter valves of the system of FIG. 1; 
     FIG. 7 is a side elevational view of the belt feeding system of the system of FIG. 1; 
     FIGS. 8A and 8B are top and side elevational views of the cyclone hopper of the system of FIG. 7; 
     FIGS. 9A,  9 B and  9 C are top and two side elevational views of the surge hopper of the system of FIG. 7; 
     FIGS. 10A,  10 B and  10 C are top and two side elevational views of the metering gate of the system of FIG. 7; 
     FIGS. 11A and 11B are two side elevational views of the receiving hopper of the system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A containment room is defined by a series of walls which are impermeable to radiation. An access entrance is defined by a tortuous path of radiation impermeable walls such that scattered irradiation does not escape the containment room. Exterior to the containment room, particulate material, such as polymeric pellets, are emptied from large shipping containers onto a conveying system for conveying the particulate material into the containment room. More specifically to the preferred embodiment, the plastic pellets are fluidized in air and pneumatically conveyed into the containment room. In the containment room, they are separated from the air flow and passed at a metered room through the radiation. More particularly to the preferred embodiment, the particles are formed into a layer of selected thickness and passed at a known rate through an electron beam of selected energy. After being irradiated, the particulate material is recollected and conveyed out of the containment room and repackaged in the original shipping containers. In the preferred embodiment, the plastic pellets are again entrained in air and conveyed pneumatically from the containment room. 
     With reference to FIG. 1, a dump hopper  10  is adjacent a dumping work platform  12 . The bottom of the hopper is connected to a pneumatic tubing inlet manifold  14  (shown in FIG. 6) which in turn feeds into a series of pneumatic tubes or pipes  16 . Five pipes  16  are shown in FIG. 1, but a different number of pipes may be used. Preferably, the tubes or pipes  16  are fabricated from stainless steel. The pipes  16  form a path through which air is blown to entrain and convey particulate material, such as plastic pellets, through the path. Air is blown into the system from outside the system. The air is fed into the inlet manifold  14  and is controlled by a diverter valve (not shown). The diverter valve sets the flow rate of air. As additional pellets are needed, the flow rate is increased. If too many pellets are being fed through, the flow rate is decreased. 
     The pneumatic tubing  16  feeds into a discharge manifold  18 . The manifold  18  in turn feeds the pellets into the belt feeding system  20 , which is discussed in more detail below. From the belt feeding system  20 , loose pellets are discharged from a stream of air and are formed into a layer on a belt conveyor  22 . The pellets are then transported on the belt conveyor  22  passed a radiation source  200  and are irradiated. Preferably, the radiation source is a 5 MeV electron beam. A magnetic accelerator  202  accelerates electrons to form an electron beam. A deflection circuit  204  sweeps the beam back and forth across the belt  22 . The beam deflector is located above the conveyor belt  22  such that the beam is directed vertically downward. 
     Alternately, depending upon irradiation time, the pellets remain fluidized into the air flow, or pushed by the air, moved by vibration, and the like, through the electron beam. 
     The irradiated pellets from the conveyor are received in a receiving hopper  24  which is located at the other end of the conveyor belt and below the belt. Below the hopper  24 , the pellets are entrained in flowing air and distributed by a second inlet manifold  26  into another series of pneumatic pipes  28 . 
     The air also serves to cool the pellets which were heated by the electron beam. Heating of the pellets, which are preferably a polymer, can affect the properties of the pellets. 
     The pellets are then carried through the pipes  28  to a second discharge manifold  30  which in turns separates the pellets from the air into a receiving station  32  for packaging or bagging. 
     Referring now to FIGS. 2A,  2 B and  2 C, a funnel  40  is located at the bottom of the dump hopper  10  to feed pellets into a pneumatic interface  42 . Preferably, the interface  42  comprises a vacuum take off box  44 , as shown in detail in FIG.  3 . The pipe interface  42  feeds the manifold  14 . 
     The vacuum take-off box  44  comprises a tube  46  and a box  48 . Preferably, the tube  46  has one or more slots  50  which control the volume or rate at which the pellets enter the tube  46 . 
     Referring now to FIGS. 4A,  4 B,  5 A and  5 B, the dumping work platform  12  consists of steel tubing, platforms and railings. Stairs  52  provide attendant access to the platform. Boxes or polyethylene bags of pellets can be lifted with a hoist over the hopper  10  for dumping. The stairs provide human access, as necessary, to guide the dumping or remedy any malfunctions. 
     As the pellets are deposited into the dump hopper  10 , they flow to the take-off box  44 . The inlet manifold  14  feeds the pellets into one or more pneumatic pipes or tubes  16 . The entrained pellets travel with the air flow to the belt feeding system  20 . The air flow is provided by a source (not shown). A diverter valve (not shown) is used to control the air flow rate. 
     Referring now to FIG. 7, the belt feed system  20  includes two cyclone hoppers  60 ,  62  which are shown in more detail in FIG.  8 . At the top of the hoppers  60 ,  62  is a tangential inlet  67  which carries the air and pellets into the hoppers. Centrifugal force urges the heavier pellets radially outward. As the velocity of the pellets is reduced, they fall to the bottom of the hopper. Excess air is discharged through an air outlet  64  at the top center  66  of the hoppers  60 ,  62 . 
     As shown in FIG. 7, slide gate assemblies  68  are located at the bottom of the hoppers  60 ,  62  and above a surge hopper  69 . The two cyclone hoppers  60 ,  62  feed into and are mounted above the surge hopper  69 , which is shown in more detail in FIGS. 9A,  9 B and  9 C. 
     At the bottom of the surge hopper  69  is a metering gate  70 , shown in more detail in FIG.  10 . The surge hopper  69  feeds onto the belt conveyor  22 , as shown in FIG.  7 . The metering gate is set to a fixed, but adjustable, level above the belt  22  to control the thickness of the layer of pellets deposited on the belt conveyor. 
     Sensors  80  placed adjacent a top surface and bottom surface of the hoppers  60 ,  62  are used to monitor the level of pellets within the hoppers. The slide gates  68  are responsive to the sensors  80  and open and close through the use of a metering valve  72  as additional pellets are required to maintain the pellet pressure head in the hopper  69  if the pellets run dry. 
     The pellets feed into the surge hopper  69  and onto the conveyor belt  22 . The metering gate  70  opens when the level of pellets is high and closes when the level is too low. A small gap  74  can exist between the gate  70  and the conveyor belt  22  to allow movement of the pellets onto the conveyor and to prevent excess pellets from being deposited onto the conveyor belt  22 . 
     After the pellets are deposited loose onto the conveyor belt  22 , they travel passed and are irradiated or cured by a radiation beam from vertically above the conveyor belt  22 . The beam is monitored to control the rate at which the pellets are irradiated. An interlock is provided between the belt conveyor and beam to ensure coordination between the operation of the two systems. 
     After the pellets are irradiated or cured, they are received by the receiving hopper  24  located below the belt conveyor, which is shown in detail in FIGS. 11A and 11B. The pellets fall from the end of the conveyor belt  22  (shown in phantom in FIG. 11B) into a hopper  92 . A metering device or valve  94 , which is located below the hopper  92 , has a plurality of vanes  95  that define chambers or pockets to control the amount of pellets flowing through the hopper. The vanes prevent air from blowing back up into the hopper. The valve  94  also reduces noise associated with the air and pellet flow. A fresh air inlet  96  provides air flow to the pipe  98  to entrain the pellets. 
     Referring again to FIG. 1, the cured pellets are fed from pipe  98  into a pipe inlet  26  and then into pipes or tubes  28  to the fourth manifold  30  to the filling or receiving station  32 . The filling station  32  also has two cyclone hoppers  100 ,  102  which are arranged and used in a similar manner to the hoppers  60 ,  62  of the belt feeding system  20 , as described above. 
     Preferably, a vibratory screener (not shown) is positioned below the cyclone hoppers  100 ,  102  of the receiving station. This screen aids in controlling the rate and amount of pellets being fed into the surge hopper. The pellets initially contact the screen and then as the screen vibrates, the pellets slip through openings in the screen. The vibrating screen keeps any pellets which fused together from entering the packaging boxes. The pellets are deposited into the same box or bag that was used initially to bring them into the system. The boxes or bags are placed onto a conveyor system and are moved out of the way from other boxes or bags. The pellets are boxed or bagged and are then ready for use. 
     When the pellets are entrained in the moving air, the entrained pellets are treated as a fluid. Consequently, other fluids, such as liquid sewage, waste water of other types, stack gases, and the like can be treated with an analogous system. 
     An alternative embodiment of the present invention includes a thermal sensor downstream of the electron beam to monitor the temperature of the pellets. If the pellets were coming out of the electron beam too warm, the system could be shut down to determine where a malfunction is occurring or the beam energy, thickness of the pellet layer, and belt conveyor speed is adjusted. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalent thereof.