Abstract:
A streamer trap assembly for collecting streamers from a flow of polymer pellets includes a housing comprising an inlet, an outlet, and an opening bounded by a sealing surface; and a streamer trap positioned in the housing through the opening. The streamer trap comprises a screen sized to collect the streamers at the screen and to allow the polymer pellets to pass through the screen, a guide positioned to guide the flow of polymer pellets from the inlet to the screen and from the screen to the outlet, and a cover adapted to engage the sealing surface and cover the opening.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a method and apparatus for removing contaminants from polymer pellets. In particular, the present invention relates to a method and apparatus for removing streamers from a flow of polymer pellets. 
       BACKGROUND OF THE INVENTION 
       [0002]    A pneumatic conveying system is generally used to convey polymeric pellets, for example from a rail car or truck to a receiving container. When pneumatically conveying pellets, it is usually necessary to use a high transport velocity to prevent settling and to maintain movement of the pellets. Unfortunately, such a high transport velocity tends to cause frictional heat to build up as the pellets travel and contact a tube or conduit wall, and can cause melting of some of the pellets. The melted portions of the pellets can adhere to the tube or conduit wall in a thin polymeric layer, which can eventually break loose from the wall, travel with the pellets, and contaminate the process downstream. These thin strips of polymeric material, which are deposited on the walls of the tube or conduit by the moving pellets, are considered contaminants and are referred to by various names such as streamers, snakeskin, angel hair, etc. 
         [0003]    Accordingly, a need exists for a method and apparatus that efficiently removes streamers from a flow of pellets. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention solves the above need. In particular, the invention provides a streamer trap assembly for collecting streamers from a flow of polymer pellets. The assembly comprises a housing which comprises an inlet, an outlet, and an opening bounded by a sealing surface, and a streamer trap positioned in the housing through the opening. The streamer trap comprises a screen sized to collect the streamers at the screen and to allow the polymer pellets to pass through the screen, a guide positioned to guide the flow of polymer pellets from the inlet to the screen and from the screen to the outlet, and a cover adapted to engage the sealing surface and cover the opening. 
         [0005]    The invention also provides a method of collecting streamers from a flow of polymer pellets. The method comprises providing a housing comprising an inlet, an outlet, and an opening bounded by a sealing surface, positioning a streamer trap in the housing through the opening, the streamer trap comprising a screen sized to collect the streamers at the screen and to allow the polymer pellets to pass through the screen, a guide positioned to guide the flow of polymer pellets from the inlet to the screen and from the screen to the outlet, and a cover adapted to engage the sealing surface and cover the opening, connecting the inlet to a supply of polymer pellets, and applying a vacuum to the outlet such that the polymer pellets proceed in the inlet, through the screen, and out the outlet, and such that the streamers are collected at the screen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a streamer trap assembly according to an embodiment of the present invention. 
           [0007]      FIG. 2  is a perspective view of a streamer trap according to an embodiment of the present invention. 
           [0008]      FIG. 3  is a cross-sectional perspective view of a streamer trap assembly according to an embodiment of the present invention. 
           [0009]      FIG. 4  is a perspective view of a streamer trap assembly according to another embodiment of the present invention. 
           [0010]      FIG. 5  is a perspective view of a streamer trap according to another embodiment of the present invention. 
           [0011]      FIG. 6  is a perspective view of a streamer trap housing according to an embodiment of the present invention with the streamer trap and tray removed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIGS. 1 ,  3 , and  6 , housing  1  of the streamer trap assembly  38  comprises an oblong box  10  having first and second opposed rectangular sidewalls ( 3 ,  4 ), third and fourth opposed rectangular sidewalls ( 5 ,  6 ), a rectangular bottom wall  7 , and a rectangular open top  61  opposed to the bottom wall  7  and defined by the top edges of each of the first through fourth sidewalls ( 3 ,  4 ,  5 ,  6 ). The first and second opposed sidewalls ( 3 ,  4 ) preferably have a width in the transverse direction  37  of about 8 inches and a height in the vertical direction  35  of about 10 inches. The third sidewall  5  preferably has a length in the longitudinal direction  36  of about 12 inches and a height in the vertical direction  35  of about 10 inches, and the fourth sidewall  6  preferably has a length in the longitudinal direction  36  of about 12 inches and a height in the vertical direction  35  slightly less than about 10 so that the fourth sidewall  6  defines an optional slot  62  in the oblong box  10  as discussed in more detail below. The bottom wall  7  is preferably about 8 inches wide in the transverse direction  37  and about 12 inches long in the longitudinal direction  36 . The walls of the oblong box  10  are preferably aluminum plates welded together. 
         [0013]    The first sidewall  3  includes a centrally located circular inlet opening  8 . An inlet tube  12  is attached to the outer surface of the first sidewall  3  at the perimeter of the circular inlet opening  8 , preferably by welding. The inlet tube  12  has an inside diameter approximately the same size as the diameter of the circular inlet opening  8 . The inlet tube  12  is configured to connect with a polymer transport line such as the outlet of a rail car or truck or other storage or transportation facility. The connection may be made by slip fit or other connection mechanism. Preferably, four inlet tube braces  11  are equally spaced around the outer surface of the inlet tube  12  and are each attached to the inlet tube  12  and the first sidewall  3 , preferably by welding. Each inlet tube brace  11  has a first edge attached to the outer surface of the first sidewall  3  and extending from the inlet tube  12  approximately toward a corner of the first sidewall  3 , and a second edge attached to the outer surface of the inlet tube  12  and extending from the first sidewall  3  toward the free end of the inlet tube  12  in the longitudinal direction  36 . The inlet tube  12  and inlet tube braces  11  are preferably made of aluminum. 
         [0014]    The second sidewall  4  includes a centrally located circular outlet opening  9  that is axially aligned with and has approximately the same diameter as the circular inlet opening  8 . An outlet tube  14  is attached to the outer surface of the second sidewall  4  at the perimeter of the circular outlet opening  9 , preferably by welding. The outlet tube  14  has an inside diameter that is approximately the same size as the diameter of the circular outlet opening  9 . The outlet tube  14  is configured to connect with a conduit that is operatively connected with a vacuum source. Four outlet tube braces  13  are equally spaced around the outer surface of the outlet tube  14  and are each attached to the outlet tube  14  and the second sidewall  4 , preferably by welding. Each outlet tube brace  13  has a first edge attached to the outer surface of the second sidewall  4  and extending from the outlet tube  14  approximately toward a corner of the second sidewall  4 , and a second edge attached to the outer surface of the outlet tube  14  and extending from the second sidewall  4  toward the free end of the outlet tube  14  in the longitudinal direction  36 . The outlet tube  14  and outlet tube braces  13  are preferably made of aluminum. 
         [0015]    The third sidewall  5  extends in the vertical direction  35  from the open top  61  to the bottom wall  7 . The fourth sidewall  6  extends in the vertical direction  35  from the open top  61  to a position in the vertical direction  35  approximately flush with or slightly lower than the respective lowermost attachment points ( 15 ,  17 ) of the inlet tube  12  and the outlet tube  14  to the first and second sidewalls ( 3 ,  4 ). An optional slot  62  in the oblong box  10  is thereby defined by the lower edge of the fourth sidewall  6 , an edge of the bottom wall  7 , a lower portion of an edge of the first sidewall  3 , and a lower portion of an edge of the second sidewall  4 . The optional slot  62  allows an optional tray  18  to be removably received in the housing  1  as discussed in more detail below. In the case that the slot  62  and tray  18  are not desired, the fourth sidewall  6  can be extended in the vertical direction  35  from the open top  61  all the way to the bottom wall  7 . 
         [0016]    Referring to  FIG. 2 , streamer trap  2  of the streamer trap assembly  38  comprises a cover  16 , a support plate  22  attached to the cover  16 , a screen  26  attached to the support plate  22 , and a guide trough  27  attached to the support plate  22 . The streamer trap  2  is removably received in the housing  1  through the open top  61  as discussed in more detail below. 
         [0017]    The cover  16  comprises a rectangular plate that is longer and wider by approximately 1 inch than the length and width of the open top  61 . The dimensions of the cover  16  thus provide for about a ½-inch wide lip, which overhangs the perimeter of the open top  61 . As seen from  FIG. 6 , the box  10  also can also have a lip  63  around the circumference of the open top  61 . The lip on the cover  16  and the lip  63  on the box  10  allow for a good vacuum seal between the cover  16  and the housing  1 . The cover  16  has a surface that faces away from the housing  1 , i.e., an upper surface  21 , and a surface that faces the housing, i.e., a lower surface  29 . A gasket (not shown), preferably of rubber, plastic, or foam, may be attached at the perimeter of the lower surface  29  of the cover  16  and/or on the lip  63  of the open top  61  to provide for a vacuum-tight sealing engagement between the housing  1  and the cover  16 . When the cover  16  is engaged with the open top  61 , the position in the vertical direction  35  of the streamer trap  2  relative to the housing  1  is thus fixed. 
         [0018]    A rectangular support plate  22  is perpendicularly attached to the lower surface  29  of the cover  16 , such that the support plate  22  is directed downwardly in the vertical direction  35  into the housing  1 . The support plate  22  extends downwardly from the cover  16  toward the bottom wall  7  in the vertical direction  35  to a position slightly lower in the vertical direction  35  than the respective lowermost attachment points ( 15 ,  17 ) of the inlet tube  12  and the outlet tube  14  to the first and second sidewalls ( 3 ,  4 ). The support plate  22  extends across the interior of the housing  1  in the transverse direction  37  approximately from the third sidewall  5  to the fourth sidewall  6 . The support plate  22  is positioned such that it is between and parallel to both of the first and second sidewalls ( 3 ,  4 ), and is closer to the second sidewall  4  than the first sidewall  3 . Two triangular support braces ( 23 ,  24 ) are preferably positioned proximate the fourth and third sidewalls ( 6 ,  5 ), respectively. The support braces ( 23 ,  24 ) each have an edge that is attached to and extends along the surface of the support plate  22  facing the first sidewall (hereinafter the support surface  30 ) in the vertical direction  35 , and an edge that is attached to and extends along the lower surface  29  of the cover  16  in the longitudinal direction  36 . The cover  16 , support plate  22 , and support braces ( 23 ,  24 ) are preferably aluminum plates attached to each other by welding. 
         [0019]    Located in the support plate  22  is a circular support opening  25  that axially aligns with and is approximately the same diameter as the inlet and outlet openings ( 8 ,  9 ). A screen  26  is attached to the support surface  30  of the support plate  22  such that it completely covers the support opening  25 . The screen  26  is preferably comprised of a crisscross of stainless steel strands that form a grid of square openings sized in the range of about ¼ inch×¼ inch to about 1 inch×1 inch. Preferably, the openings are about ½ inch×½ inch. The grid spacing is configured to be large enough that polymer pellets are allowed to pass through without deforming and small enough that the screen  26  collects the majority or most of streamers in the flow of polymer pellets. The screen  26  may be attached to the support plate  22  by any attachment means such as welding or bolts or both. In one embodiment, the screen  26  is welded to a flat piece of metal that is bolted onto the support plate  22 . The support plate  22  may also include horizontally or vertically disposed bars (not shown) on the outlet side of the opening  25  to support the back side of the screen  26 . 
         [0020]    A guide trough  27 , preferably of aluminum, is attached to the support plate  22 , preferably by welding. The guide trough  27  resembles a tube split longitudinally approximately in half with a concave surface facing the open top. The guide trough  27  is positioned relative to the support plate  22  such that a primary portion  19  of the guide trough  27  extends in the longitudinal direction  36  from the support surface  30  to a position approximately flush with the first sidewall  3 , and a secondary portion  20  of the guide trough  27  extends in the longitudinal direction  36  from the surface (not shown) of the support plate  22  facing the second sidewall  4  to a position approximately flush with the second sidewall  4 , the primary and secondary portions ( 19 ,  20 ) thus fixing the position in the longitudinal direction  36  of the streamer trap  2  relative to the housing  1 . The primary and secondary portions ( 19 ,  20 ) can either be unitary or separate. The guide trough  27  has a curvature that approximately aligns with and matches the respective lower halves of the curvatures of the support opening  25 , inlet opening  8 , outlet opening  9 , inlet tube  12 , and outlet tube  14 . The guide trough  27  is attached to the support plate approximately at the lower half of the perimeter of the support opening  25 . The two longitudinal free edges  28  of the guide trough  27  are flared outward such that they extend to a position approximately flush with the third and fourth sidewalls ( 5 ,  6 ), respectively, the outwardly flared edges  28  thus fixing the position in the transverse direction  37  of the streamer trap  2  relative to the housing  1 . The flared edges  28  help to prevent polymer pellets from falling down under the guide trough  27 . 
         [0021]    Referring back to  FIGS. 1 ,  3 , and  6 , removably positioned within housing  1  through the optional slot  62  is the optional tray  18 . The tray  18  includes a rectangular catch plate  32  sized and positioned to rest upon and approximately overlap the entirety of the bottom wall  7  of the housing  1  when the tray  18  is positioned in the slot  62 . The tray  18  also includes a rectangular outer wall  31 . When the tray  18  is positioned in the slot  62 , the outer wall  31  of the tray  18  lies approximately in the same plane as the fourth sidewall  6  of the housing  1 , extends vertically from the catch plate  32  approximately to the bottom edge of the fourth sidewall  6 , and extends longitudinally between lower portions of edges of the first sidewall  3  and the second sidewall  4 . The tray  18  also includes side walls  33  and a rear wall  34  extending from side and rear edges of the catch plate  32  toward the open top  61  in the vertical direction  35 . The tray  18  seals with the housing  1  in a vacuum-tight arrangement. The perimeter of the inner surface of the tray outer wall  31  and/or the perimeter of the slot  62  may be provided with a gasket to improve the seal around the slot  62 . 
         [0022]      FIG. 4  shows another embodiment of the streamer trap assembly  38  according to the invention. This embodiment is like the one shown in  FIG. 1 , except that it has a handle  41  attached to the cover  16  to facilitate removing the streamer trap  2  from the streamer trap housing  1 , and a handle  42  attached to the tray  18  to facilitate removing the tray  18  from the housing  1 . The handles  41  and  42  are preferably made of aluminum or steel and can be attached to the cover  16  and tray  18 , respectively, by any attachment means such as welding, bolts, or screws. This embodiment also preferably incorporates a vacuum break  43  in outlet tube  14 . The vacuum break  43  allows air to come into the outlet tube  14  if the vacuum is too high to prevent collapsing the downstream conveying tubes. 
         [0023]      FIG. 5  shows the streamer trap from  FIG. 4 , which is like that of  FIG. 2  except with handle  41 , detached from the housing  1 . 
         [0024]    The streamer trap assembly  38  according to the invention can be operated as follows. With the streamer trap  2  and tray  18  in place in the housing  1 , the inlet tube  12  is connected to a supply of polymer pellets, such as a container of a rail car. The outlet tube  14  is connected to a conduit that is operably connected to a vacuum source and that leads to a receiving container. The vacuum source is activated, and polymer pellets are pulled in the inlet tube  12 , are guided by the guide trough  27  through the screen  26 , and are pulled through the outlet tube  14  and into the receiving container. In the meantime, streamers in the flow of polymer pellets are collected at the screen  26 . 
         [0025]    When it is desired to remove the streamers collected at the screen  26 , for example, after the desired amount of pellets has been received in the receiving container, or if the screen  26  has become clogged with streamers, the vacuum source is deactivated and the user manually removes the streamer trap  2  from the housing  1  so that the collected streamers can be removed from the screen  26  and subsequently discarded, separately collected for recycling, or otherwise disposed of as desired. While the streamer trap  2  is being removed from the housing  1 , leftover polymer pellets which may have settled in the guide trough  27  are carried by the guide trough  27  out of the housing  1 . Some of the leftover polymer pellets may fall off the guide trough  27  and back into the housing  1  during removal of the streamer trap  2 , and these polymer pellets are caught in the tray  18 , which can then also be removed from the housing  1 . The leftover polymer pellets carried by the removed guide trough  27  and tray  18  can then be returned to the rail car, deposited with the delivered polymer pellets, or otherwise disposed of as desired. 
         [0026]    The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.