METHOD AND APPARATUS FOR SEPARATING WETTABLE AND NON-WETTABLE PARTICLES

Abstract: Wettable and non-wettable particles contained in a slurry are separated by flowing the slurry over a rotating disk (12) having a central zone (14), a distinct outside corner (16), and a skirt (15). As the slurry flows in a film over the corner (16), the unwettable particles leave the film and are prevented from rejoining the film by a shelf (19). The process and apparatus are useful in recycling fibre products such as paper and paperboard.

Description: METHOD AND APPARATUS FOR SEPARATING WETTABLE AND NON-WETTABLE PARTICLES Background of the Invention 1. Field of the Invention This invention relates to separation of wettable and non-wettable particles. It has particular value in paper and paperboard recycling wheren the recycled material is reduced to fibres and suspended in aqueous liquid for use- in making fresh paper and/or paperboard. Unfortunately a. portion of the recycled raw material contains contaminants such as hot melt adhesives, pressure sensitive adhesives, waxes, resins, etc. These contaminants, known in the art as ."stickies" greatly reduce the. quality of the product. ' uhtΪT the present " invention, ' there was ' no- economical way to separate fibres contaminated by stickies * from uncontaminated fibres. 2. Prior Art Prior attempts to remove contaminated fibres from uncontaminated fibres based on differences in density, such as by centrifugal cleaners were unsuccessful, because contaminated and uncontaminated fibres have the same densitiy. The stickies have nearly the same density as water. Thus the porous and denser-than-water fibre particles wetted by water, stickies, or both result in all particles having similar densities. Screening was also unsuccessful because fibres of all sizes are contaminated. Hence segregating particles based on size does not solve the problem. A continuously curved spinning disk has been used for separating fibres according to size and for removing non-fibrous materials, such as sand, from the fibre slurry, but removal of fibres contaminated by the stickies is apparentl not accomplished. See Moller et al, Tappi Vol. 63, No. 9 pps 89 to 91 (Sept. 1980) and Moller et al, Paper Technology and Industry, April 1979, pps 110 to 114. These prior-art disks lack certain features critical to the present invention, which are discussed later. Summary of the Invention One aspect of my invention is the discovery that fibres contaminated by stickies are relatively unwettable compared with uncontaminated fibres, and that a rotating disk having certain features can be used to separate relatively wettable and unwettable fibres. Another aspect of my invention is a disk shape especially use ul for removing contaminated ' f bres from a slurry with low energy consumption. More specifically, on aspect of the invention comprises a method for sepa-rating -particles- that are relatively wettable by a liquid from particles that are relatively unwettable, said particles being contained in a slurry of said liquid, comprising the steps of: (a) providing a disk having an outside surface, said outside surface comprising a central zone and a peripheral skirt zone, said zones being joined to form a. distinct annular outside corner, (b) flowign said slurry onto said central zone, (c) rotating said disk about an axis at a speed sufficient to cause a film of liquid and relatively wettable particles to flow over said outside corner and skirt zone and to propel relatively unwettable particles from said film as said film flows over said corner, and (d) preventing relatively unwettable particles propelled from said film from rejoining the slurry contained in said film. Another aspect of the invention comprises apparatus for separating particles that are relatively wettable by a liquid from particles that are relatively unwettable, said particles being contained in a slurry of said liquid, comprising: (a) a disk having an outside surface, said outside surface comprising a central section, a peripheral skirt section, and an intermediate section, said central and intermediate sections being joined to form a distinct annular outside corner, and said intermediate and skirt sections being joined to form a distinct annular inside corner, • . •» (b) means.for flowing slurry . onto . said central section, (c) means for rotating sai * disk about an axis at speed sufficient to cause a film of slurry and relatively wettable particles to flow over said outside corner, intermediate section, inside corner, and skirt section, and to propel relatively unwettable particles from said film as said film flows over said outside corner, and (d) means for preventing relatively unwettable particles, propelled from said film from rejoining tfϊe slurry contained in said film. Brief Description of the Drawings Fig. 1 is a vertical sectional schematic of apparatus for practicing the inventive process. Fig. 2 is a vertical sectional schematic of another embodiment of apparatus for practicing the inventive process. Fig. 3 is a vertical sectional view of a disk in accordance with the invention. OMPI Description of the Preferred Embodiment Recently Oroskar has devised a specially shaped disk for separating fibres according, to size. See Oroskar, Ph.D. Thesis in Chemical Engineering entitled "Spray Fractionation", deposited at the University of Wisconsin Library November, 1982. Surprisingly, the disdk of Oroskar can be used to remove unwettable fibres from a slurry. Referring to Fig. 1, a slurry containing contaminated and uncontaminated cellulose fibers is continuously supplied by pipe 10 from a slurry tank or other source, not shown. Although a process for separating contaminated and uncontaminated cellulose fibers contained in an aqueous slurry, i.e. one in ■which a major portion of the liquid is water-, will be discussed, it is understood that the invention is operable in any situation where relatively wettable and -unwettable- articles contained in-a slurry are to be separated. Pipe 10 flows the slurry onto disk 11, which has an outside surface 12. The outside surface is the side of the disk over which slurry flows as described' later. Outside surface 12 has a central zone 14 and a peripheral skirt zone 15. Preferably the disk is symmetrical about a central axis A. Hence in all of the figures, rotation of the illustrated sectioned apparatus around axis A through 180 degrees would generate the apparatus in 3 imensions.Skirt zone 15 and central zone 14 are joined so as to form distinct outside corner 16. In 3 dimensions, corner 16 is annular, i.e. ring shaped. The term "outside corner" means that the apex of the corner points to the outside of the disk, i.e. the side of the disk over which slurry flows. rø /j * -*. Preferably central zone 14 is flat, as shown in Fig. 1. However, concave or convex central zones are operable. Preferably skirt zone 15 is straight in cross-section, as shown, but non-straight shapes are operable. Note that shape variations in the skirt and central zones must not render the outside corner indistinct. For example, disk 12 may not be a continuous curve in cross-section, such as the arc of a circle or ellipse. Such configurations would not provide a distinct outside corner. With flat central zone and straight skirt zone as shown in Fig. 1, it is preferred that the central ans skirt zones form an inside angle 17 of more than 90 and less than 180 "degrees, more preferably 110 degrees to 160 degrees. Disc lϊ is mounted on shaft 18, which is connected to means, not shown, for rotating the disk -and shaft, such an electric motor. A circular shelf 19, who's purpose is described presently, is provided near shoulder 16. The apparatus of Fig. 1 functions as follows. Pipe 1 flows slurry onto central zone 14 of disk 11. Shaft 18 and disk 11 rotate about axis A at such speed that a film 9 of liquid and relatively wettable fibres flows over corner 16 and skirt 15 and downward as shown by arrows B. However, a .large portion of the relatively unwettable fibres, i.e.those contaminated by the stickies, are propelled from the slurry film as it flows over corner 16. The reason for the unwettable fibre's leaving the film is that their unwettability makes them unable to remain in the slurry as they undergo the change in direction while trying to turn the corner at 16. In other words, the inertial and centrifugal forces acting on unwettable firbres at 16 are greater than the surface tension forces tending to hold them in the slurry. Unwettable fibres propelled from the slurry at corner 16 are represented by arrows C. Shelf 19 prevents the unwettable particles propelled from the slurry from rejoining the slurry. Ideally the operation is performed in a spray chamber, such as those used in conventional spray drying operations. A chamber for this operation would have a lower chamber below shelf 19 for collecting slurry and uncontaminated fibres and an upper chamber above shelf 19 for collecting contaminated fibres. The speed of rotation of the disk depends on the disk's size and shape, and slurry flow rate, and the nature -of the slurry and particles. Optimum rotation ' speed,"which will vary from system to system, . is easily determined experimentally by use of a variable speed drive on the motor driving shaft 18. The disk should rotate fast enough to propel- unwettable fibres from the slurry at corner 16, but not so fast that slurry and a substantial amount of wettable fibres leaves the film at the corner. Orientation of the -apparatus with respect to gravity is of little consequence, since gravitational forces are not involved in the separation. Fig. 2 shows apparatus wherein the slurry flows onto the bottom of the disk. In this case, unwettable fibres, represented by C* would fall to a lower spray chamber (not shown) below shelf 19, and wettable fibres and slurry, represented by arrows B', would collect in the upper spray chamber (not shown), above shelf 19. Fig. 3 is a vertical sectional view of a disk designed to allow maximum separation forces to occur at the outside corner with least energy consumption and without causing excess slurry and wettable fibres to leave the film at that point. Special disk 30 has outside surface 20, which has a central section 21, a peripheral skirt section 22, and an intermediate section 23. Central section 21 and intermediate section 23 meet to form distinct annular outside corner 24. Intermediate section 23 and skirt section 22 meet to form distinct annular inside corner 25. Disk 30 is shown mounted on shaft 18 for rotation about axis A, as in Figs. 1 and 2. Disk 30 is operated similarly to disk 11. Disk 30 could be substituted for disk 11 in Figs. 1 or 2. Rotation of disk 30 causes a film of slurry to flow over corner 24, intermediate section 23, corner 25, and skirt 22. As in Figs. 1 and 2, unwettable fibres are propelled from the film at the outside corner. For disk 30-, it is 'preferred that central section 21 be flat and that intermediate a:nd skirt sections 23 and 22 be straight in cross section as shown. Preferably, inside angle 26 at outside corner 24 ■ is more than 90 and less than 180 degrees, and outside angle 27 at inside corner 25 is more than 90 and less than 180 degrees. To improve the mechanisl efficiency of-disk 30, it is preferable to slightly roughen the outside surface around corner 24 to prevent slippage of the film in the circumferential direction, thereby causing greater.inertial forces to act on the particles as they turn outside corner 24. The following guides containing a broad range, believed operable, and more preferred quantities should be helpful in designing disks in accordance with Fig. 3. FOR A DISK HAVING TOTAL DIAMETER d OF ABOUT 241 MM: Total amount of solids in the feed slurry: 0.1 to 10% broadly OMH- ■ WIPO 0.5 to 2.5% preferred Feed rate: 10 to 1,000 Ib/hr broadly 200 to 3200 lb/hr preferred 1200 to 1500 lb/hr more preferred Temperature of feed: ambient, not believed critical Disk speed: 100 to 20,000 ' rp broadly 2000 to 3000 rpm preferred Length 1 of intermediate section: 1 to 10 mm broadly 1 to 1.5 mm preferred Length m of skirt; 3 to 100 mm broadly . " 25 to 76 ' preferred - FOR A DISK HAVING DIAMETER d OF ABOUT 1 METER: ■ Total amount of- solids in feed.slurry; 0.1 to 10% broadly 0.5 to 2.5% preferred Feed rate: 10 to -66,000 lb/hr.broadly 1300 to 5300 lb/hr preferred Temperature of feed; ambient, not believer critical Disk speed; 10 to 5000 rpm broadly 300 to 1000 rpm preferred Length 1 of intermediate section: 1 to 60 mm broadly 1 to 9 mm preferred Length m of skirt: 3 to 400 mm broadly 25 to 76 mm preferred . EXAMPLE OMPI Apparatus resembling that of Fig. 2 was used in an attmept to separate contaminated fibres from a slurry. The disk had diameter e of 241 mm., and lip length h of 51 mm. The inside angle f at the outside corner was 152.5 degrees. The disk speed of rotation was 320Q rpm. The feedrate was 1300 lb/hr of slurry containing 0.8% solids. The feed initially contained 1615 ppm of stickies contaminating the fibres. After flowing the feed over the rotating disk in accordance with the invention it was found that 86.1% of the contaminated solids were propelled from the film at the outside corner. Yet only 9.9% of the total solids in the feed came out of the slurry at the corner. Hence the slurry' in the top chamber contained 90.1% of the original .solids and only 13 * 9% of the original contaminated fibers, showing a very significant improvement in the quality of the fibres remaining in the slurry film. . - If better results are desired, the slurry from the. top spray chamber could be passed over another rotating disk in accordance with the invention.

Claims: WHAT IS CLAIMED IS: 1. A method for separating particles that are relatively wettable by a liquid from particles that are relatively unwettable, said particles being contained in a slurry of said liquid, comprising the steps of: (a) providing a disk having an outside surface, said outside surface comprising a central zone and a peripheral skirt zone, said zones being " joined to form a distinct annular outsidecorner, (b) flowing slurry onto said central zone, (c) rotating said disk about an axis at a speed sufficient to cause a film of liquid and relatively ' wettable particles to flow over said outside corner * and skirt- zone and- to propel relatively unwettable particles from said film as said film flows over said corner, and (d) preventing the relatively unwettable particles propelled from said film from rejoining the slurry contained in said film. 2. The method of claim 1 wherein said central zone is flat- and said skirt zone is stra-ight iri cross-section and wherein said skirt and central zones form an inside angle of more than 90 and less than 180 degrees at said outside corner. .3. The method of claim 2 wherein said particles are cellulose fibres and the major portion of said liquid is water. 4. The method of claim 2 wherein said inside angle is from about 110 to 160 degrees. 5. The method of claim 4 wherein said particles are cellulose fibres and the major portion of said liquid is water. 6. Apparatus for separating particles that are relatively wettable by a liquid from particles that OMPI are relatively unwettable, said particles being contained in a slurry of said liquid, comprising: (a) a disk having an outside surface, said outside surface comprising a central section, a peripheral skirt section, and an intermediate section, said central and intermediate sections being joined to form a distinct annular outside corner and said intermediate and skirt sections being joined to form a distinct annular inside corner, (b) means for flowing slurry onto said central section, (c) means for rotating said disk about an axis at speed sufficient to cause a film of slurry and relatively'wettable particles to flow over said outside corner, intermediate section, inside corner and skirt section when slurry flows onto said central " section " , and to propel relatively unwettable particles from said film as said film flows over said outside corner, and (d) means for preventing relatively unwettable particles propelled from said film from rejoining the slurry contained in said film. ' 7. "■ The apparatus ' of claim 6- wherein said ' * central section is flat and said intermediate and skirt sections are straight in cross-section, and wherein the central and intermediate sections form an inside angle ■ of greater than 90 and less., than 180 degrees at said , outside corner and said intermediate and skirt sections form an outside angle of more than 90 and less than 180 degrees at said inside corner. 8. The apparatus of claim 7 whereinsaid disk is roughened at said outside corner. 9. A process for separating particles that are relatively wettable by a liquid from particles that are relatively unwettable, said particles being contained in a slurry of said liquid, comprising the steps of: (a) providing a disk having an outside surface, said outside surface comprising a central zone, a peripheral skirt zone and an intermediate zone, said central and intermediate zones being jointed to form a distinct annular outside corner and said intermediate and skirt zones being jointed to form a distinct annular inside corner, (b) flowing slurry onto said central zone, (c) rotating said disk about an axis at a speed sufficient to cause a film of liquid and relatively wettable particles to flow voer said outside corner, intermediate zone, inside corner, and skirt zone, and to propel relatively unwettable particles from said film as said film flows over said outside corner, and . - • ■ (d) preventing the relatively unwettable particles propelled from said film from rejoining the slurry contaied in said film. 10. The process of claim 9 wherein said central zone is flat and said intermediate and skirt zones are straight in cross-section and wherein the central and " intermediate zones form-an inside * ang-le -of more than 90 and less than 180 degrees at said outside corner and said intermediate zone and skirt zone form an outside angle of more than 90 and less than 180 - degrees at said,, inside corner. 11. The process of claim 10 wherein said particles are cellulose fibres and the major portion of said liquid is water. OMPI

Inventors: KLUNGNESS JOHN H, KLUNGNESS, JOHN, H.
Applicants: KLUNGNESS JOHN H, KLUNGNESS, JOHN, H.
Application year: 1984
Main classification: B03B5
IPC codes: B03B5, D21B1