Centrifuge with mechanism for inhibiting the migration of separated air-entrained solids
[451 Apr. 29, 1975 CENTRIFUGE WITH MECHANISM FOR INHIBITING THE MIGRATION OF SEPARATED AIR-ENTRAINED SOLIDS Andrcsen et a1 233/7 Lavanchy .1 233/7 Primary E.\&#39;anzinerGeorge H. Krizmanich [75] Inventor: Dieter Hors Home Houston Attorney, Agent, or Firm-Learman &amp; McCulloch [73] Assignee: Baker Perkins Inc., Saginaw, Mich. 221 Filed: Mar. 25, 1974 1571 ABSTRACT A rotary tapering centrifuge bowl within a surround- [21] Appl 454374 ing collecting housing having a solids receiving outlet adjacent the smaller diameter end of the bowl and a [52] U.S. Cl 233/7; 233/27 q i i ing u le jacen the larger diameter [51] Int. Cl B04b 1/20 end f the bowl. A baffle, provided within h h ing [58] Field of Search 233/7. 1 R, 3, 1 A, 27, for substantially isolating the solids outlet, leaves a 233/28 minimal clearance space around the rotary bowl, and an air director moves air in a direction to inhibit the [56] Referen Cited migration of air-entrained solids through the clearance UNITED STATES PATENTS Space- 3,l48,145 9/1964 Reed 233/7 8 Claims, 1 Drawing Figure I 7 7 I I Till In 30 l &#39;00 19 I0 i I 26 2o 24 25 .oc  
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  CENTRIFUGE WITH MECHANISM FOR INHIBITING TI-IE MIGRATION OF SEPARATED AIR-ENTRAINED SOLIDS BACKGROUND OF THE INVENTION In the centrifugal separation of a variety of solids from liquids, centrifugal apparatus, which includes a tapering shell or barrel rotated at a high speed about its longitudinal axis, may be very efficiently employed. In such barrels, the solids are moved toward the small diameter end of the barrel while the liquids discharge through the large diameter end. Centrifuge bowls of this character are normally horizontally disposed in a collecting housing, and a baffle or seal is employed to isolate the solids collecting portion or outlet of the housing from the liquid collecting section or outlet. Centrifuges of this type are particularly well suited, for instance, to use in the rendering industry. One of the problems which has been encountered in the use of such equipment is the migration of light, fluffy solids through the seal, from the solids-collecting portion of the collection housing to the liquid-collecting portion. I have discovered that this occurs because the natural movement of air within the housing is toward the larger diameter end of the centrifuge bowl, and some of the particulate solids tend to become entrained in the air stream and be sucked through the baffle seal.  
  One of the prime objects of the present invention is to obviate this problem in an efficient manner without necessitating the employment of such a snugly fitting seal that undue power is required to revolve the centrifuge bowl at the high separating speeds required.  
  Another object of the invention is to overcome the migration problem without employing a separately powered and expensive collecting device within the liquid collecting housing which would have to be protected from exposure to the liquids separated.  
  Another object of the invention is to utilize the rotary movement of the centrifuge bowl to obviate the problem by fixing fan blades to the exterior of the bowl so that counter-flow air currents are provided which are directed at the baffle seal, and prevent the migration of particles through the seal.  
  A final object of the invention is to provide a construction which accomplishes the desired result in a most economical and reliable manner without adding substantially to the cost of the equipment, or in any substantial way increasing its operating power requirements, and while at the same time considerably improving its operating efficiency.  
 SUMMARY OF THE INVENTION A centrifuge for separating particulate solids from liquid wherein a rotary centrifuge bowl. having a tapering body section with a large diameter end and a small diameter end, is revolved within a collecting housing having a solids outlet adjacent the small diameter end and a liquid outlet adjacent the large diameter end. A baffle, provided within the housing to substantially isolate the solids outlet, leaves a minimal clearance space around the rotary shell, and an air flow director is provided for moving air in a direction to inhibit the normal movement of air-entrained solid particles through the space.  
  Other objects and advantages of the invention will be pointed out specifically or will become apparent from the following description when it is considered in conjunction with the appended claims and the accompanying drawing, in which:  
  FIG. 1 is a schematic, longitudinal, sectional view through the centrifuge.  
  Referring now more particularly to the accompanying drawing, the centrifugal separator includes an essentially tapered, annular centrifugal shell or bowl 10, having a large diameter end 10a and a small diameter end 10b. The shell or bowl is mounted within a collecting housing 11 and, at its small diameter end 1017, is closed by a cover or end plate 12, formed with a central tubular extension 14 to provide a bearing shaft for one end of barrel 10. The shaft 14 is supported for rotation by a suitable bearing such as pillow block 15, and may be driven at desired speeds via a pulley 16, connected to a suitable drive source such as an electric motor.  
  Mounted within the centrifuge bowl 10, to preferably have scraping and bearing engagement therewith, is a solids advancing screw, generally designated 17, which includes a tubular shaft 18 provided with a helical blade 19 of gradually decreasing radial extent toward the small diameter end of the bowl 10 as shown. The shaft 18 may be suitably journaled for rotation by a bearing comprising pillow block 19, supported as is pillow block 15, by a framework structure generally designated F, externally of annular housing 11.  
  A pulley 20, for driving shaft 18, may be connected to a separate electric motor, or may be connected via suitable drive transmission gearing to the same electric motor which drives pulley 16. In centrifugal apparatus of this kind, the barrel l0 and shaft 18 are customarily rotated in the same direction of rotation, at slightly different speeds, so that solid material s in the barrel, separated by the centrifugal action, will be moved by the flight 19 in the direction of arrow x toward the smaller end of the barrel as shown in the drawing, while the liquid l flows in the direction of arrow y toward the other end of the barrel 10, from which it is discharged over barrel lip 10.  
  As indicated earlier, the shaft 18 is tubular and a slurry supply tube 21 extends axially through hollow shaft 14 and a suitable opening in end plate 12 into the open end of shaft 18 to deliver the liquid-solids mixture to the interior tapering surface of barrel 10, via circumferentially spaced openings such as shown at 22. The inner end of shaft 18 may, of course, be journaled by end plate 12. At the discharge end of the tapered barrel 10, which includes a cylindrical end portion 100, circumferentially spaced, radially extending, discharge nozzles 23 are provided which may be held in place by ring or collar parts 24 and 25, preferably bolted together as at 26. The parts 24 and 25 are machined to form nozzle or liner-receiving discharge openings 27. As indicated, the nozzles 23 discharge solids to a solids discharge conduit 28, provided for annular housing 11 at one end thereof, and, as will further be noted, a similar liquid discharge conduit 29 is provided at the opposite end of housing 11 to receive the liquid expressed out the open larger diameter end of centrifuge bowl 10.  
  Provided within the housing 11, to separate or isolate the solids discharge opening 28 from the liquid discharge opening 29, is an annular baffle ring 30 forming a part of a seal interface, generally designated 31. Baffle ring 30 may be welded to a circular rib 32 provided on the interior of housing 11 as shown, and, provided on the centrifuge bowl l0 and fixed thereto in any suitable manner, is a U-shaped seal or eowling 33 having an annular slot 34 which closely receives the internal edge of baffle, but leaves a suitable running clearance 35 therebetween. As earlier noted, it is through this clearance 35 that a migration of solids has been observed to take place. I have discovered that ifl direct a curtain of air, as exemplified by the arrows a, at the seal interface 31, that this migration of solids is greatly inhibited and substantially eliminated.  
  Provided on bowl l0, and fixed to the exterior thereof in a suitable manner, is a ring 36 to which fan blades 37 are welded. Preferably the blades 37 are first welded to ring 36 and then twisted helically in a direction such that, when the centrifuge bowl 10 is revolved, the blades 37 create a curtain of air moving in the direction of arrows a toward the baffle 30 and seal interface 31.  
  ln operation the solids-liquids slurry is delivered through supply tube or pipe 21 to the interior of bowl 10 via openings such as shown at 22, and, at the high speed of rotation of bowl 10, the slurry is thrown to the internal surface of bowl 10. The flights 19 are driven at such a speed that solids are conveyed toward the discharge nozzles 23 while the liquid flows toward the large diameter end 10a of the bowl l and proceeds over the lip provided thereon to the liquid outlet conduit 29.  
  Because the peripheral surface speed of the larger diameter end 10a of bowl 10 is greater than the peripheral surface of the small diameter end, a lower pressure is created adjacent the larger diameter end of the centrifuge bowl 10, which normally causes an air flow from the smaller diameter end of centrifuge 10 toward the larger diameter end, this air flow taking a spiral or vortical path. I have discovered that the fan blades 37 will direct a sufficient flow of air in a counter-flow direction to prevent light, fluffy particles, such as renderings, from being sucked through the clearance space 35, and efficiently and effectively prevent this solids migration. This, of course, has a substantial effect on the operating efficiency of the centrifuge.  
  It is to be understood that the drawings and descriptive matter are in all cases to be interpreted as merely illustrative of the principles of the invention, rather than as limiting the same in any way, since it is contemplated that various changes may be made in various elements to achieve like results without departing from the spirit of the invention or the scope of the appended claims.  
 I claim:  
  1. In a centrifuge for separating particulate solids from liquid; a rotary centrifuge bowl having a tapering body section with a larger diameter end and a smaller diameter end; a drive for rotating said centrifuge bowl at a separating speed; a collecting housing surrounding said centrifuge and having a solids collecting portion and outlet adjacent the smaller diameter end and a liquid collecting portion and outlet adjacent the larger diameter end; a baffle, provided within said housing around said centrifuge bowl to substantially isolate the solids collecting portion, said baffle leaving a minimal clearance space around the rotary bowl; a supply conduit for delivering a solids-liquid slurry to the interior of said bowl; said bowl incorporating means for moving the solids toward the smaller diameter end to be discharged while the liquid proceeds to the larger diameter end; and an air flow director for moving air in a direction to inhibit the normal movement of airentrained solid particles through the space.  
  2. The centrifuge of claim 1 wherein said air flow director is formed on the exterior of said bowl, adjacent the space and on the side of said baffle opposite the solids outlet, to move the air in a direction toward said space. i  
  3. The centrifuge of claim 2 wherein said director comprises fan blades, fixed to the rotary shell at circumferentially spaced intervals and pitched to move air toward the space.  
  4. The centrifuge of claim 1 wherein the means for moving the solids toward the smaller diameter end comprises an advancing screw mounted on an axial shaft extending within said bowl.  
  5. The centrifuge of claim 4 in which said screw comprises a helical solids-advancing flight of decreasing radial extent in a direction toward said smaller diameter end, which is in scraping engagement with the interior wall surface of said body section.  
  6. The centrifuge of claim 4 wherein the shaft and screw are driven in the same direction of rotation as said bowl but at a different speed sufficient to advance the solids axially to the smaller diameter end.  
  7. The centrifuge of claim 1 wherein an annular cowling on the exterior of said shell has an annular slot closely receiving said baffle.  
  8. The centrifuge of claim 1 wherein means are provided for mounting the centrifuge bowl for rotation about a horizontal axis.