Abstract:
A centrifugal pellet dryer including a stationary cylindrical screen, a driven elevating rotor in said screen elevating wet pellets inside the screen and imparting radial forces to the wet pellets to impact them against the interior of the screen to enable moisture on the pellets to be separated and discharged through the screen, a housing enclosing the screen and rotor and including an inlet for a slurry of pellets, an outlet for dried pellets and an outlet for water removed from the pellets. The side walls of the housing are constructed of a plurality of relatively large, flat panels made of plastic sheet material are supported in a metal framework to attenuate noise of the dryer produced by rotation of the drier rotor and impact of the wet pellets against the screen. A dewaterer in advance of the dryer also has walls made of plastic sheet material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to centrifugal pellet dryers of the type in which a driven rotor impacts wet pellets exiting an underwater pelletizer against the interior surface of a cylindrical screen which allows water to pass therethrough and the pellets to continue upwardly inside the screen to a discharge outlet. More specifically, the present invention is directed to such a centrifugal pellet dryer in which the housing walls are made of a plastic sheet material to attenuate the noise produced by the centrifugal dryer. 
     2. Description of the Prior Art 
     Centrifugal pellet dryers have been effectively used to separate water and moisture from pellets, such as those formed by an underwater pelletizer in which the pellets and water are discharged from the pelletizer cutting chamber as a water and pellet slurry. The water and pellet slurry exiting the pelletizer is typically fed first through a dewatering screen chamber or other suitable water separating equipment to remove the bulk water from the slurry before entering the centrifugal dryer. 
     Existing centrifugal pellet dryers include an outer housing usually constructed of sheet metal panels, a cylindrical screen oriented in the housing and a driven rotor within the screen for elevating the wet pellets (and entrained water) and impacting the wet pellets against the interior of the screen for separating the water from the pellets so that the water can be discharged through the screen and fall by gravity to a water outlet. The dried pellets are elevated and discharged from an outlet in the area of the upper end of the housing. Existing dewaterers are also constructed with sheet metal panels. 
     Centrifugal pellet dryers of this general type including a dewatering component are disclosed in the following U.S. patents owned by Gala Industries, Inc. (“Gala”), the assignee of this application: U.S. Pat. Nos. 3,458,045; 4,565,015; 4,896,435; 5,265,347; 5,638,606; 6,138,375 and 6,237,244. 
     Centrifugal pellet dryers of this type operate on the principle of impact dewatering by utilizing a driven rotor oriented internally of a stationary cylindrical screen with energy being imparted to the wet pellets (and entrained water) by the rotor. The rotor includes peripheral inclined blades to lift the wet pellets (and entrained water) vertically upwardly inside the screen and also to impact the wet pellets (and entrained water) radially against the interior of the screen with moisture being separated from the pellets and discharged through the screen into the interior of the housing. 
     Centrifugal dryers of this type are quite effective in removing water and moisture from the pellets with the residual heat from the pellets from the pelletization operation further drying the pellets as they are discharged from the upper end of the dryer. Operation of centrifugal pellet dryers of this type, however, produce noise levels that can be objectionable to personnel in the vicinity of the dryers. U.S. Pat. No. 5,265,347 discloses a dryer of this type which is constructed to reduce outward transmission of noise to surrounding areas by constructing the housing with double walls and insulation filling the space between the walls and, preferably, the top and bottom panels of the housing. 
     SUMMARY OF THE INVENTION 
     In order to address the problem of high noise levels associated with existing centrifugal pellet dryers, the walls of the pellet dryer housing of the present invention are constructed of substantially flat plastic panels having sufficient thickness to significantly reduce the noise level caused by operation of the centrifugal dryer. The plastic panel walls are supported in a support framework made of a suitable metal, such as stainless steel and/or aluminum, or other material which is rigid and strong enough to support the operational components of the dryer. The rigid support framework includes generally horizontal top and bottom sections which are interconnected by a series of vertical corner frame members to form the rigid support framework. 
     The vertical side edges of the plastic wall panels are sealingly interconnected to provide a substantially rigid plastic wall assembly, and the top and bottom sections receive the top and bottom edges of the side walls around their periphery to form a watertight housing. It has been surprisingly found that such a plastic wall housing will substantially reduce outward transmission of noise produced by the movement of the wet pellets and components of the dryer and the impact of the wet pellets against the interior of the separating screen. 
     The vertical corner frame members of the support framework are connected to the vertical side edges of the plastic wall panels to support and further rigidify the housing. In a preferred embodiment, the vertical side edges of the plastic wall panels are clamped to the metal corner frame members by corner seal strips bolted to the inside of the vertical corner frame members. The frame members extend below the support framework bottom section to support the housing above a support surface and can extend above the support frame top section to provide structure by which the dryer can be lifted and transported by lift devices engaged with the upper end of the frame members. 
     The plastic wall panels are all preferably made from the same plastic sheet material. It has been found that plastic sheet approximately one inch thick is satisfactory for the housing walls of the present invention to significantly reduce the noise levels when operating a centrifugal pellet dryer of the rotating rotor, impact screen type and to aid in providing a requisite rigidity for the overall housing. It is believed that the plastic sheet for use in constructing the plastic wall panels in accordance with the present invention should be at least three-quarters inch thick to provide the necessary noise attenuation and housing strength and no more than two inches thick due to cost and weight considerations. The plastic material for the present invention can be any suitable polymeric material with or without fiber reinforcement. A preferred material is polypropylene. 
     A dewatering screen chamber is preferably integral with the plastic housing centrifugal pellet dryer for initially receiving the pellet and water slurry and removing a major portion of the water in advance of the centrifugal dryer. In the preferred embodiments the bottom section of the dryer is formed with the bottom of the dewatering chamber as one piece, and the side walls and top wall of the dewaterer are all preferably constructed of the same plastic sheet material as the dryer housing wall panels. The dewaterer housing walls are preferably welded together to form a watertight unit. 
     Because the top and bottom sections and plastic side wall panels are all supported by the vertical corner frame members, the pellet dryer of this invention is “modular” in the sense that the top section can be rotated and the plastic side wall panels shifted during assembly without fabrication modifications. This modular flexibility allows the user to select the best position of these components for the user&#39;s facility. 
     Accordingly, it is an object of the present invention to provide a centrifugal pellet dryer having housing walls constructed of plastic sheet material to attenuate the noise produced by operation of the centrifugal pellet dryer to an acceptable level. 
     Another object of the present invention is to provide a centrifugal pellet dryer housing having side walls constructed of generally flat panels of plastic sheet material, preferably polypropylene, to reduce or break up sound wave transmission from the housing. 
     A further object of the present invention is to provide a centrifugal pellet dryer having a housing with side walls constructed of sound-attenuating plastic material, preferably in the form of generally flat panels, supported in a metal support framework for providing structural integrity to the housing and for supporting the operational components of the dryer. 
     Yet another object of the present invention is to provide a centrifugal pellet dryer with plastic sheet panel side walls supported in a metal framework including top and bottom sections which receive and surround the top and bottom edges, respectively, of the wall panels and vertical corner frame members which connect to the side edges of the wall panels to form a rigid and sealed watertight dryer housing assembly. 
     Still another object of the present invention is to provide centrifugal pellet dryer housing walls of plastic material which reduce the noise level to an average of below about 80 decibels (Dba) at points located centrally of and 36 inches away from each of the walls of the dryer as compared to 90 or more decibels (Dba) produced by a centrifugal pellet dryer having conventional metal walls under the same operating conditions. 
     Still a further object of the present invention is to provide a dewatering screen chamber integral with the centrifugal pellet dryer for capturing a majority of the water from the pellet and water slurry in advance of the dryer in which the walls of the dewatering chamber are also made from the same plastic sheet material as the side walls of the centrifugal dryer. 
     A further object of the present invention is to provide a centrifugal pellet dryer including top and bottom sections and plastic sheet panel side walls all supported by vertical corner frame members in which the top section can be rotated and the position of the plastic side wall panels selected for modular flexibility. 
     Still yet another object of this invention to be specifically enumerated herein is to provide a centrifugal pellet dryer in accordance with the preceding objects which will conform to conventional forms of manufacture, be of simple construction and easy to operate so as to provide a dryer that will be economically feasible, long lasting and relatively trouble free in operation. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of constructions and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. The drawings are intended only to illustrate the present invention and should not be considered to scale. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of one embodiment of a centrifugal pellet dryer with plastic walls constructed in accordance with the present invention. 
         FIG. 2  is a front elevational view of the dryer of  FIG. 1  in which certain internal components are illustrated by broken lines. 
         FIG. 3  is a rear elevational view of the centrifugal pellet dryer of  FIG. 1 . 
         FIG. 4  is a left side elevational view of the dryer of  FIGS. 1–3  illustrating the water and pellet slurry inlet to the dewaterer and an access door to the interior of the dewaterer. 
         FIG. 5  is a right side elevational view of the dryer of  FIGS. 1–3  illustrating the rotor drive motor and dry pellet outlet. 
         FIG. 6  is a partial top perspective view of the housing in accordance with the present invention illustrating the relationship of the top section and the vertical corner frame members of the metal support framework. 
         FIG. 7  is a transverse sectional view, on an enlarged scale, taken along section lines  7 — 7  on  FIG. 6 , illustrating the structure of a vertical corner frame member and the manner in which the plastic panels are connected to the corner frame members. 
         FIG. 8  is a fragmental perspective view of the lower end of the housing in accordance with the present invention illustrating the water outlet. 
         FIG. 9  is a schematic vertical sectional view of the dryer of  FIGS. 1–3 , illustrating the relationship of the operating components of the dryer, the housing and the dewaterer. 
         FIG. 10  is a front elevational view of another embodiment of a centrifugal pellet dryer with plastic side walls constructed in accordance with the present invention. 
         FIG. 11  is a left side elevational view of the dryer of  FIG. 10 . 
         FIG. 12  is a top plan view of the dryer of  FIG. 10 . 
         FIG. 13  is a schematic vertical sectional view of the dryer of  FIG. 10  showing the relationship with the plastic panel side walls. 
         FIG. 14  is a transverse sectional view, on an enlarged scale, similar to  FIG. 7 , illustrating the structure for connecting and sealing the edges of the plastic panel side walls to the vertical corner frame members in the dryer of  FIG. 10 . 
         FIG. 15  is a top plan view of the support ring for holding and supporting adjacent edges of screen sections inside the dryer housing for the pellet dryer of  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although preferred embodiments of the invention are explained in detail, it is to be understood that other embodiments are possible. Accordingly, it is not intended that the invention is to be limited in its scope to the details of constructions and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the preferred embodiments, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     Referring to  FIGS. 1–5  of the drawings, one centrifugal pellet dryer in accordance with the present invention is generally designated by reference numeral  10 . The dryer  10  includes a substantially rigid metal support framework, generally designated by reference numeral  11 , having a metal generally square or rectangular top section, generally designated by reference numeral  90 , and a corresponding metal bottom section, generally designated by reference numeral  35 . The top section  90  and bottom section  35  are preferably made of rigid sheet metal panels welded together. The four corners of the metal top and bottom sections are interconnected by vertical metal corner frame members, generally designated by reference numeral  20 , to form the substantially rigid metal support framework  11 . 
     Supported in the framework  11  are four generally vertical wall panels including a front wall panel  12 , illustrated in  FIGS. 1 and 2 , a rear wall panel  14  illustrated in  FIG. 3 , a left side wall panel  16  illustrated in  FIG. 4  and a right side wall panel  18  as illustrated in  FIG. 5 . Each of the wall panels  12 ,  14 ,  16  and  18  are generally flat and rectangular, and opposing wall panels are generally in parallel relation to each other. 
     Each of the wall panels  12 ,  14 ,  16  and  18  are constructed of a substantially rigid plastic material. The adjacent vertical side edges of wall panels  12 ,  14 ,  16  and  18  are sealed together to form a substantially rigid and watertight wall assembly, generally designated by reference numeral  26 , made of suitable plastic material. When fitted into the framework  11 , the tops of the wall panels seal against the top section  90  and the bottoms seal against the bottom section  35  to form the dryer housing, generally designated by reference numeral  15 . 
     Polypropylene is a preferred plastic material for the wall panels  12 ,  14 ,  16  and  18 . It has been found that polypropylene sheeting approximately 1 inch thick for the wall panels of the wall assembly  26  provides the necessary noise attenuation and strength characteristics for the centrifugal pellet dryer  10  of the present invention. However, other suitable plastic materials could be used in constructing the plastic wall assembly  26 , including fiber reinforced plastic materials, and other sheet thicknesses could be selected within the parameters of the present invention. 
     As illustrated in  FIGS. 6 and 7 , each corner frame member  20  includes a narrow vertical central panel  22  and a pair of narrow vertical side flanges  24  oriented in angular relation to the central panel  22 . The flanges  24  are in general perpendicular relation to each other and engage the wall panels  12 ,  14 ,  16  and  18  near their edges. As shown in  FIG. 7 , the flanges  24  engage the external surfaces  25  of the edge portions of adjacent plastic left side wall panel  16  and rear wall panel  14  of the housing  15 . 
     As also shown in  FIG. 7 , the side edges of adjacent wall panels  14  and  16  are angulated at  17  to abut each other and have holes to receive clamp bolts  30  which extend through the central panel  22  of the frame member  20 . The head  28  of each bolt  30  engages the exterior of center panel  22  and a retaining nut  29  on the inner end of bolt  30  engages the interior of angulated edges  17  of the adjacent panels  14  and  16 . A retaining washer  32  is positioned under the retaining nut  29  to clampingly secure the edges of adjacent panels  14  and  16  to frame member  20 . If desired, a continuous inner frame member may be provided in lieu of the individual washers  32  in order to provide a more positive clamping action throughout the length of the vertical edges of the panels  12 ,  14 ,  16  and  18 . 
     The metal top section  90  is bolted to the corner frame members  20  by bolts  92  in a similar manner to the wall panels. The top section  90  is preferably made of aluminum with its lower edges sealed to the top edges of the wall panels  12 ,  14 ,  16  and  18 . Alternatively, the lower edges of the top section panel can overlie the top edges of plastic wall panels  12 ,  14 ,  16  and  18  with a watertight seal formed therebetween. 
     As shown in  FIGS. 6 and 9 , the top edges of top section  90  are closed by a top panel  34 , also made of aluminum. The periphery of top panel  34  is seated to the top of the top section  90  to provide a rigid assembly. The corner frame members  20  extend above the top of the top section  90  as illustrated in  FIGS. 1–5  and also extend above top panel  34  as illustrated in  FIG. 6 . As shown in  FIG. 6 , the top panel  34  includes an upwardly extending flange  36  around the periphery thereof and a central perforated area  38  to vent the interior of the housing upper end. The ends of the flanges  36  are secured to the flanges  24  of the corner frame members  20  by the use of screw threaded fasteners  40  or the like. 
     The top ends of each corner frame member  20  is provided with an opening  42  to provide points of attachment for a lift device such as a crane or similar equipment in order to lift the dryer and place it in a desired location. The lower ends of the corner frame members  20  extend below the bottom section  35  of the dryer  10 , and each corner frame member  20  includes a bottom plate  44  to support the dryer on a supporting surface. The plate  44  may be provided with openings to receive an anchor device to secure the dryer to the supporting surface. 
     The bottom of plastic wall panels  12 ,  14 ,  16  and  18  extend outside the side walls of bottom section  35 , and bolts  99  adjacent the bottom of vertical corner frame members  20  connect to side walls of the bottom section  35  as well as the bottom of the wall panels (see  FIGS. 2 ,  3 ,  4  and  8 ). Appropriate sealing between the side walls of the bottom section  35  and the wall panels  12 ,  14 ,  16  and  18 , if desired, forms a watertight housing  15 . The bottom section  35  acts like a tub at the bottom of housing  15  to collect and direct the water removed from the pellets in the dryer. 
     The front wall  12  of the dryer  10  includes an enlarged vertically extending access opening  46  closed by a correspondingly shaped plastic closure door  48  made of the same plastic sheet material as the wall panels  12 ,  14 ,  16  and  18 . The plastic panel door  48  has one edge thereof hinged to the front wall panel  12  by a plurality of hinges  50 . The opposite edge of the door  48  is retained in closed position by latches  52  which can be easily latched and unlatched to enable the access door  48  to be opened and closed. A door seal  53  is provided peripherally of the door  48  to maintain the watertight integrity of the housing  15 . 
     The operational components of the dryer  10  are positioned within the housing  15  and include the rotor  54  with inclined blades  56  on the periphery thereof which rotates within a stationary perforated cylindrical screen  58 . The structure and operation of the rotor  54  in a drive chamber  64  at the bottom of housing  15  and screen  58  are similar to the centrifugal dryers disclosed in the aforementioned prior U.S. patents. The rotor  54  is driven by an electric motor  60  mounted exteriorly at the bottom area of side wall panel  18  by a laterally extending bracket structure  62  which adjustably supports the motor from the frame members  20  along opposite edges of the wall panel  18 . The motor  60  includes a belt drive  61  on pulley  63  on the lower end of the rotor  54  in a drive chamber  64  at the bottom of housing  15 . The bracket structure  62  for the motor includes adjustments to enable tension on the belt drive to be adjusted. The structure of the belt drive from the motor  60  to the lower end of a shaft  65  of the rotor  54  may be the same as disclosed in the aforementioned prior U.S. patents. 
     The upper end of the rotor  54  is guided and sealed by bearing structure generally designated by reference numeral  57 . The bearing structure  57  is supported by plate  59  which is, in turn, supported by corner frame members  20 . The plate  59  seals the upper end of the wall assembly. 
     The left side wall panel  16  includes a dewaterer, generally designated by reference numeral  68 , in the form of a plastic housing  69  which is sealed to plastic wall panel  16 . The housing  69  includes a metal slurry inlet  70 , preferably made of stainless steel, in the top wall  71 , a plastic access door  72  in an outer wall thereof, and an aluminum bottom section  82 . The bottom section  82  is rigidly connected to the bottom section  35  of the dryer so that the dewaterer  68  is supported by the dryer bottom section  35  and hence framework  11 . The plastic housing  69  including the three side walls and top wall are all preferably made from the same plastic sheet material as the wall panels  12 ,  14 ,  16  and  18 . 
     The dewaterer  68  receives a slurry of water and pellets from an underwater pelletizer and includes an internal, slanted screen  73  which permits water in the slurry to pass downwardly through the screen to a discharge opening  74  in the bottom of the dewaterer  68 . As illustrated in  FIG. 9 , the screen  73  is typically slanted at about 45°, but the angle can be varied as desired. Pellets in the slurry pass downwardly along the upper surface of the inclined screen  73  which forms the bottom of an inclined chute  75 . The chute  75  conveys the pellets into an opening  77  at a lower area at the bottom end of the screen  58  (and rotor  54 ) to enable the rotor  54  and screen  58  to function in a manner disclosed in the aforementioned U.S. patents. 
     Water removed from the pellets by the action of the rotor  54  and the screen  58  flows down inside the wall assembly  26  (and outside the screen  58 ) toward the bottom section  35 . As also illustrated in  FIG. 9 , an inside bottom panel  79  of bottom section  35  is sloped toward and spaced above the floor  81  of the dewaterer bottom section  82  so that the water passing through the screen  58  also flows into the bottom of dewaterer  68  and out through outlet  74 . As such, outlet  74  is the only water outlet for the dryer  10 . In a preferred embodiment the bottom section  35  of the support framework  11  and the bottom section  82  of the dewaterer are welded together as a one-piece unit. 
     Cut in the wall panel  18  of the housing is a downwardly slanted dried pellet outlet  76  which is rigidly mounted to top section  90  for support therefrom. The pellet outlet  76  communicates with the upper end of the rotor  54  and screen  58  of the dryer by which dried pellets exiting from the screen and rotor are discharged from the dryer. A conveying hose or duct work (not shown) is typically connected to the exit end of outlet  76  in order to convey the dried pellets away from the dryer to storage or further processing. A sight glass window  93  is preferably mounted on a side of outlet  76  in order for an operator to view the flow of material out of the pellet outlet. 
     The rear wall  14  of the housing  15  is provided with a plastic access door  78  and has hinges, latches and handle to provide access to the lower portion of the dryer components within the housing. Also, a large central flanged opening  80  is provided in the rear wall panel  14  above the access door  78  for connection to an exhaust fan and air duct (not shown) to provide air circulation through the housing  10 . This structure provides inflow of air through the dried pellet discharge outlet  76  in countercurrent relation to pellets exiting the dryer. 
     The screen  58  typically can comprise multiple sections, such as upper section  95  and lower section  97 , whose abutting edges are held in place by support ring  96 . The ring  96  is supported by radially extending support members  98  connected to corner frame members  20  to support and stabilize the screen  58  as illustrated in  FIG. 9 , in a manner similar to that disclosed in aforementioned U.S. Pat. No. 6,138,375. 
     The plastic wall dryer of this invention is also modular. Using side wall panel  16  and the dewaterer  68  mounted therein as a reference, the other wall panels  12 ,  14  and  18  with related doors and components can be selectively shifted as specified by the user. For example, the top section  90  could be rotated 90° so that the pellet outlet  76  extends to the rear of the dryer  10 . The right side wall panel  18  can become the rear wall, and the motor  60  with brackets  62  would also be mounted on the rear of the dryer. The rear panel  14  with door  78  and opening  80  might then be shifted to the front of the dryer, and the side wall panel  12  with the door  48  placed into the right side panel position. These side wall panels and related components can thus be moved to any of the three side locations not occupied by side wall panel  16  and dewaterer  68 . 
     In operation, a slurry of water and pellets from the underwater pelletizer is fed to the dewaterer  68  through the flanged inlet  70  by means of a suitable conduit. The dewatering screen  73  permits passage of a large proportion of the water to exit through the outlet  74  at the bottom of the dewaterer  68 . The water removed by operation of the rotor and screen assembly passes outside of screen  58  to the bottom of the housing  15  where it flows to the bottom of dewaterer  68  to also pass out through outlet  74 . 
     The pellets are retained by the dewatering screen  73  and are discharged into the bottom of the cylindrical screen  58  and elevated by the rotor  54 . The rotor  54  also imparts radial movement to the wet pellets for impact against the interior of the screen  58  so that the water or moisture on the pellets is discharged through the screen into the housing  15  for discharge from the bottom of the dryer to the bottom of dewaterer  68 . As the pellets reach the upper end of the screen  58 , the dried pellets exit into the dried pellet discharge  76  for conveyance through a duct work (not shown) connected to the flanged outlet  76 . 
     Another embodiment of a centrifugal pellet dryer with plastic wall panels in accordance with the present invention is illustrated in  FIGS. 10–14 . The numerals designating the components in the embodiment of  FIGS. 10–14  correspond to like numbered components in  FIGS. 1–9 , except the numerals for the former are preceded by the number “1” and are in the 100 series; new components may be numbered in the 200 series. Hence, the centrifugal pellet dryer of the  FIGS. 10–14  embodiment is generally designated by reference numeral  110 , and includes a substantially rigid metal support framework, generally designated by reference numeral  111 . The framework  111  has a metal generally square or rectangular top section, generally designated by reference numeral  190 , and a corresponding metal bottom section, generally designated by reference numeral  135 . The four corners of the metal top and bottom sections are interconnected by vertical metal corner frame members, generally designated by reference numeral  120 , to form the substantially rigid metal support framework  11 . 
     The top section  190  includes a support plate  159  which supports the rotor  154  and related upper bearing assembly  232  and pulley  163 . The plate  159  of top section  190  also supports the dried pellet outlet  176 . Surrounding the rotor  154  is cylindrical screen  158  comprising screen sections  195  and  197  supported at their adjacent edges by support ring generally designated by reference numeral  196 . 
     Four generally flat and rectangular wall panels constructed of substantially rigid plastic material  112 ,  114 ,  116  and  118  are supported in the support framework  111  in generally opposed parallel relation to each other in a manner to be described hereinafter. The metal top section  190  is bolted to the top of corner frame members  120  by bolts  192  or any other suitable fastening element. The metal bottom section  135  is also bolted to the corner frame members  112  by bolts  199  or other suitable fastening element to complete the rigid framework  111 . 
     The wall panels  112 ,  114 ,  116  and  118  are supported in framework  111  by four corner sealing strips  202 . Each corner sealing strip  202  is clamped against the adjacent side edges  204  of adjacent wall panels, such as panels  114  and  116  shown in  FIG. 14 , to support and seal the adjacent side edges  204  and form a sealed wall assembly  126  for dryer housing  115 . The wall panel side edges  204  are preferably beveled, as at  206 , to mate with the beveled side edges  208  of the corner sealing strips  202 , in order to support and attain the desired seal between the adjacent side edges  204  and the corner sealing strips  202 . The corner sealing strips  202  are clamped against adjacent side edges  204  by bolts  210  engaged with corresponding threaded tapped round bar elements  212  fixed in place on the inside surface of the corner frame members  120 , as by welds  214  or the like. As shown in  FIG. 13 , there are preferably four vertically spaced bolts  210  to clamp each sealing strip  202  to the wall panel adjacent side edges  204 . 
     As shown in  FIGS. 11 and 12 , the electric motor  160  is mounted exteriorly adjacent the top of the dryer  110  by bracket structure  162  at the back side of the dryer  110 . The belt drive and belt tensioning device (not shown) and pulley  163  in drive chamber  164  thus drive the upper end of shaft  165  of rotor  154 , in a manner similar to that disclosed in the aforementioned prior U.S. Pat. No. 6,237,244. Mounting the electric motor  160  and the related drive components at the top of the dryer  110  is preferred in order to keep water away from the motor and drive components during cleaning of the dryer or in the event of a dryer leak. 
     As shown in  FIGS. 13 and 15 , the support ring  196  for screen  158  is a generally flat plate  250  having inner and outer circular bands  251  and  252  which engage and support the adjacent circular edges of screen sections  195  and  197  in the manner described in the aforementioned U.S. Pat. No. 6,138,375. The plate  250  has corner sections  254 , each of which is affixed to an angle piece  256  through suitable bolts or other fasteners  258 . The angle pieces  256  are in turn bolted to their adjacent corner sealing strips  202  by suitable fasteners  260 . 
     By attaching the support ring  196  directly to the plastic sealed wall assembly  126 , the noise generated by the pellets impacting the screen  158  and vibration imparted thereto is significantly dampened. Further, the corner sections  254  preferably have an opening  255  to facilitate water passing down past the support ring  196 . 
     In the  FIGS. 10–14  embodiment, the drive chamber  164  is also noise insulated by plastic panel side walls  214 , which are also preferably made from the same plastic sheet material as the wall panels  112 ,  114 ,  116  and  118 . The side panels  214  are assembled onto the corner frame members  120  by bolts  216  or other suitable fasteners. Extending above the top panel  134  are a plurality of eyebolts  218  for lifting the dryer  110  by a suitable crane or other lifting equipment. 
     The outside bottom surface of the bottom section  135  is also preferably covered with a plastic sheet material  220 , such as one-half inch thick polypropylene sheet material, and is affixed to the base of the bottom section  135  by appropriate bolts  222  or other suitable fasteners. 
     As with the  FIGS. 1–9  embodiment, the plastic wall dryer of  FIGS. 10–15  is also modular. With respect to the wall panel  116  and dewaterer  168 , the wall panels  112 ,  114  and  118 , together with their respective components, can be selectively shifted to any other wall location, as desired. The top section  190  would be rotated so that the dried pellet outlet  176  is positioned above wall panel  118 . Similarly, the motor  160  and motor mounting bracket  162  would be shifted with wall panel  114 . 
     Elevational movement and impact engagement of the pellets, the rotation of the rotor and the engagement of the rotor blades with the pellets produces sounds which may exceed acceptable levels for personnel in the vicinity of the dryer, especially when using a housing constructed of relatively large, flat sheet metal panels to form the housing. It has been surprisingly found that the noise level emanating from the dryer can be substantially reduced by using plastic panels of polypropylene or other similar plastic material for the dryer housing side walls and dewaterer walls even though the plastic panels are substantially rigid and provide adequate rigidity for the side walls of the dryer when mounted on the corner frame members in accordance with the present invention. 
     Testing was conducted with a prototype dryer having a frame structure and plastic housing walls similar to that illustrated in  FIGS. 1–9 . The testing was conducted within the confines of a noise absorption chamber using a hand held sound measurement device. The motor and drive unit were exposed. The pellet outlet, pellet recirculation piping and water supply piping were insulated at the time of testing. The testing yielded an average SPL reading of 79.25 decibels (Dba). Testing of a comparable Gala dryer having a conventional metal housing under substantially similar test conditions yielded an average SPL reading of 90 or more decibels (Dba). High decibel levels are often considered undesirable for individuals working in the vicinity of the dryer. 
     All of the plastic wall panels and other components are preferably constructed to seal in relation to each other without the use of silicones or other types of sealant, although sealants could be used as desired. Also, the various door gaskets are preferably an edge mounted resilient member of 0-ring configuration having a transverse section of circular configuration. In addition, all of the doors can be supported by internal hinges and operated by a routed or recessed handle structure to eliminate bolt-on projecting structures. Likewise, all door edges and opening edges could include a smoothly curved or radiused edge to eliminate sharp corner edges and reduce the number of parts used and reduce assembly time. All fasteners could have button heads or be covered to further reduce sharp edges or corners which could cause injury and to provide a streamlined external appearance. 
     An exhaust blower to circulate air through the dryer may be secured directly to flanged opening  80 , or connected thereto by a duct. The blower could therefore be mounted anywhere on housing  15 , or at a separate location, or even eliminated if the user has a central exhaust system to connect up to opening  80 . Also, the dried pellet outlet  76  may be provided with a flanged end and be constructed with dimensions that enables unrestricted discharge of pellets. Top plate  34  could possibly be eliminated and top bearing  57  provided with a protective cover. 
     The foregoing is considered as illustrative only of the principles of the invention. Further, numerous modifications and changes will readily occur to those skilled in the art. For example, the housing  11  is shown as constructed with four vertical walls. Those skilled in the art will readily recognize that other wall configurations, e.g., five-sided, six-sided, etc., can be readily adapted for the present invention. Therefore, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.