IMPROVED RECOVERY OF FINE FIBERS FROM SUSPENSIONS CONTAINING FIBERS AND CONTAMINANTS

Abstract: There is disclosed herein methods and apparatuses for the improved recovery of fine fibers from a feed suspension consisting of long fibers, medium fibers, fine short fibers, contaminants and liquid carrier. In the preferred embodiment, a feed suspension is provided to a first filter in which it is separated into first and second fractions. The first fraction consists of fine fibers, contaminants and liquid carrier which have passed through the first filter. The second fraction consists of fibers, fine fibers and liquid carrier which have been retained on the surface of the first filter. The second fraction is then removed from the first filter for further processing or use in the paper-making process. The first fraction is then provided to a second device for separation into third and fourth fractions. The third fraction consists of fine fibers and liquid carrier which do not pass through the second filter. The fourth fraction consists of contaminants and liquid carrier which pass through the second filter. The third fraction represents fine fibers which would otherwise have been lost in the production process. The third fraction is then returned to the first filter at a location wherein the second fraction has formed. The fiber mat which forms the second fraction assists the first filter in retaining the fine fibers present in the third fraction while the liquid carrier passes through the second fraction and first filter and into the first fraction once again.

Description: IMPROVED RECOVERY OF FINE FIBE RS FROM SUSPENSIONS CONTAINING FIBERS AND CONTAMINANTS Field of the Invention The present invention relates to methods and apparatuses for the recovery of fibers from suspensions containing long fibers, medium fibers, fine short fibers, contaminants and liquid carrier. Background of the Invention In the prior art, it is well known that suspensions containing long fibers, medium fibers, fine short fibers, contaminants and liquid carrier may be separated in order to recover at least a portion of the fibers and fine fibers contained therein. For example, there is shown in Figure 1 such a prior art device known as a drum washer 100. In operation, a filtration drum 102 rotates within a vat 104, containing a feed suspension 106 of fibers and contaminants suspended in a fluid medium such as water. Further, the feed suspension 106 may also be sprayed onto the surface of the drum 102 as by nozzle 108 by a different prior art device known as a FLUIDIZED DRUM WASHER™ (a trademark of Celleco Hedemora, Inc. of Lawrenceville, Georgia) . The drum 102 is driven in direction 107 such as by a motor driven gear 109 which engages a toothed wheel and/or belt drive 111 attached to the drum 102. The drum 102 is supported by an axle 113. Thus, the drum 102 can be rotated in direction 107 through the vat 104 and through the feed suspension 106 contained within the vat 104. The drum 102 is porous with the pore size being selected to be larger than the size of typical contaminants, but smaller t h a n the fibers sought to be recovered. Thus, upon the passage of the drum 102 through the suspension 106 in the vat 104, or spraying of the suspension 16 onto the surface of the drum 102, the operation of hydrostatic pressure will cause fibers to be retained on the outer surface 110 of the drum 102 as a second fraction 112, while contaminants and the fluid medium will pass through the outer surface 110 of the drum 102 to form a first fraction 114 within the interior 116 of the drum 102. This process will continue with the second fraction 112 forming an ever thickening mat on the outer surface no of the drum 102. This mat will further serve to retain fine fibers in the second fraction 112, while contaminants continue to pass into the interior 116 of the drum 102 to form the first fraction 114. However, this process results in the loss of some fine fibers, which undesirably reduces the tonnage yield of the fiber recovery process. At the introduction points of the suspension 106 onto the drum 102 which occur before a mat has formed thereon, fine fibers as well as contaminants pass through the filter material and into the first fraction 114, whereas where a mat has formed, the mat serves to trap fine fibers while the contaminants pass through the mat and filter material. Thus, while a portion of the fine fibers present in the suspension 106 are trapped on the outer surface 110 of the drum 102 by the mat in cooperation with the drum 102 and are included in the second fraction 112, some portion of the fine fibers in the suspension 106 pass through into the first fraction 114, which reduces the yield of fine fiber recovery. A different prior art embodiment of a fiber recovery system is shown in Figure 2. In this prior art embodiment, an endless belt 200 is provided on conveyor rollers 202. The belt 200 is made of a porous filter material which has a pore size selected to retain fibers on the surface of the belt 204, while allowing contaminants and liquid to pass through. In operation, a suspension containing fibers, fine fibers and con t aminants provided in a liquid medium is sprayed, or otherwise deposited onto the surface of the belt through a head box. Fine contaminants and the liquid carrier will pass t h roug h t h e belt 200 due to the action of gravity to form a first fraction 208 in a vat 210. Due to the filtering action of the belt 200, fibers will be retained on the surface 204 of the belt, to form a second fraction 212. The belt is moved by a motor driven gear 214 engaging a toothed wheel 216 and/or belt drive on one conveyor roller 202, which in turn causes the conveyor roller 2 0 2 to rotate in direction 218. As the second fraction 212 reaches the end of the belt 200, it is deposited into a conduit 22 0 for further processing or use. The first fraction 2 08 is drawn out of vat 210 through a drain 222 for processing as a waste stream. As was the case with the prior art embodiment described in Figure 1, fine fibers will pass through the belt 20 0 prior to the formation of the second fraction 212 thereon. The loss of fine fiber results in a reduced yield of usable fiber in the recovery process; thus decreasing the overall efficiency of the recovery process. The lost fiber must be addea from other sources which increases the costs of the recovery process. Additionally, in the recycling process, the loss of fiber results n an overall lower recycling efficiency which results in a greater volume of waste, or a greater use of raw natural resources; both such results are contrary to the goals of recycling and virgin pulping processes. It is therefore an object of the present invention to provide a method and apparatus for the recovery of fine fibers typically lost in prior art fiber recovery processes. It is a further object of the invention to provide a method and apparatus for the recovery of fine fibers which significantly improves the yield of the fiber recovery process. It is yet a further object of the present invention to provide a process for the improved recovery of fine fibers while maintaining the effectiveness of removal of contaminants. It is another object of the present invention to provide an apparatus for the recovery of fibers and improved recovery of fine fibers from a suspension containing fibers and contaminants for an increased yield over prior art fiber recovery devices. fliimma y of the Invention The above and further objects are realized in methods and apparatus practiced in accordance with the preferred embodiments of the present invention. In a preferred embodiment, there is provided a method and apparatus for the improved recovery of fine fiber from feed suspensions containing long fibers, medium fibers, fine short fibers, contaminants and liquid carrier. In accordance with this method, the feed suspension is provided to a first filter which separates the feed suspension into first and second fractions. The first fraction consists of fine fibers, contaminants and liquid carrier which have passed through the first filter. The second fraction consists of fibers, fine fibers and liquid carrier which have been retained on the surface of the first filter. The second fraction is then removed from the first filter for further processing or use in the paper-making process. The first fraction is then provided to a second filter for separation into third and fourth fractions. The third fraction consists of fine fibers and liquid carrier which do not pass through the second filter. The fourth fraction consists of contaminants and liquid carrier which pass through the second filter. The fourth fraction typically constitutes a waste stream and is disposed of in an appropriate manner. The third fraction represents fine fibers which would otherwise have been lost in the production process. The third fraction is then returned to the first filter at a location wherein the second fraction has formed. The fiber mat which forms the second fraction assists the first filter in retaining the fine fibers present in the third fraction while the liquid carrier passes through the second fraction and first filter and into the first fraction once again. In the preferred embodiments, the first filter may be a Fluidized Drum Washer™, a belt thickener, screw press, any type of dewaterer, bowscreen, pressure or gravity screen, hydrocyclone, or a variety of screen type filters. In the preferred embodiments, the second filter can also be selecte d from the same previously listed group of filters as the first filter or may be a SPRAYDISC™ filter manufactured by Celleco Hedemora of Lawrenceville, Georgia, U.S.A. In a further embodiment, the second fraction is provided to a third filter, or dewaterer, and is separated into fifth and sixth fractions. The sixth fraction consists of fibers, fine fibers and a portion of the liquid carrier that had remained in the second fraction. The fifth fraction consists of fine fibers and liquid carrier. In this embodiment, the fifth fraction is added to the first fraction prior to introduction of the first fraction into the second filter. In this manner, any fine fibers present in the fifth fraction are recovered during processing of the first fraction by the second filter. In additional embodiments, methods and devices are provided for transporting the various fractions throughout the system. In one further embodiment, the second filter is provided at an elevation above that of the first filter. The first fraction exits the first filter and drains, by force of gravity, into a tank positioned at an elevation below that of the first filter. The discharge from this tank is then provided to a pump which pumps the first fraction to the second filter. A conduit leading from the second filter to the first filter provides a pathway for the third fraction to flow, by force of gravity, to the first filter which is lower in elevation than filter 2. In another embodiment, the second filter is provided at an elevation below that of the first filter. A conduit directs the first fraction, which flows by force of gravity, from the first filter to the second filter. The third fraction then flows by force of gravity to a tank disposed at an elevation lower than that of the second filter. The discharge of this tank is provided to a pump, which then pumps the third fraction through a conduit to the first filter. In yet another embodiment, the first fraction flows by force of gravity to a tank positioned at an elevation lower than that of the first filter. The discharge of this tank is provided to a pump which pumps the first fraction through a conduit to the second filter. The third fraction flows by force of gravity through a conduit to a second tank which is positioned at an elevation lower than that of the second filter. A second pump is provided at the discharge of the second tank to pump the third fraction through a conduit to the first filter. In further embodiments of the present invention, the re¬ entry location of the third fraction into the first filter is controlled. In one such embodiment, the third fraction is reintroduced below the level of feed suspension in a vat in which the first filter is disposed. The third fraction flows through a nozzle directed to the first filter at a location whereupon a mat o f t h e second fraction has formed. m another suc h embodimen t , the third fraction is reintroduced to the f irst filter a t locations above and below the level of f ee d suspension. O nce again, nozzles direct the flow of the third fraction towar d t h e first filter. In yet another such embodiment, w h erein the first filter is of the belt thickener type, the third fraction is reintroduced at a point downstream of the introduction point of the feed suspension. Brief Description of the Drawings Figure 1 is cross-sectional diagram of a prior art Fluidized Drum Washer™; Figure 2 is a cross-sectional diagram of a prior art belt thickener; Figure 3 is a block diagram of a system for the recovery of fine fibers; Figure 4 is a block diagram of a system for the recovery of fine fibers incorporating a dewaterer; Figure 5 is a cross-sectional diagram showing the components of the present invention, wherein a Fluidized Drum Washer™ is utilized; Figure 6 is a cross-sectional diagram showing the components of the present invention, wherein a belt thickener is utilized; Figure 7 is a side, cross-sectional view of a SPRAYDISC™ filter used in the present invention; Figures 8 - 11 are a cross-sectional views of modifications of a fluidized drum washer used in various embodiments of the present invention; Figures 12 - 14 are a block diagrams showing flow control components used in various embodiments of the present invention; Detailed Description of the Preferred Embodiments As was described in the previous sections, the use of drum washers, disc washers, belt recovery systems, pressure or gravity screen, hydrocyclones, screw or belt presses, dewaterers and a variety of other methods to separate fibers from fine contaminants and water are well known in the art. In all of the prior art techniques, a waste stream consisting of fine contaminants and water is formed during the separation process. In these techniques, a medium is used to separate the fibers from the fine contaminants and a portion of the water used to transport the material. Typically, the medium will consist of a mesh or a porous material having a mesh or pore size selected to retain the fibers while allowing the liquid carrier and fine contaminants to pass therethrough. In operation, as a feed suspension is first introduced to the medium, it is directed to the bare, or submerged, medium and, in addition to the fine contaminants and the liquid medium, smaller fibers will pass through the medium and become part of the waste stream. However, as a mat forms on the medium, the mat itself acts as a filter material as well as the medium and fine fibers typically will be retained in the mat, while the fine contaminants and liquid will continue to pass therethrough. The embodiments discussed below describe a method and apparatus for recovering fine fibers from the waste stream and, in preferred embodiments, utilizing t h e formed fiber mat as a filter material for the passage of recovered fine fibers through the first separation process. With reference to the figures, in which like reference numerals indicate like or corresponding features throughout the figures, Figure 3 shows a block diagram of a system use d to practice the present invention. A first filter device 300 separates a feed suspension (shown as an input to the filter device 300 on line 302) into a first fraction (shown exiting the filter device 300 on line 304) and a second fraction (shown exiting the filter device 300 on line 306) . The first fraction consists of the liquid medium, fine contaminants and fine short fibers not retained in the second fraction. The second fraction consists of long fibers and medium fibers retained by the first filter device and fine fibers which are either retained by the first filter device itself or the first filter device in cooperation with the second fraction formed thereon. The second fraction leaves the first filter device 300 on line 306 for further processing and use. The further processing may include additional washing, dewatering, bleaching or, ultimately, use in the paper making process. The first fraction on line 304 is directed to a second filtering device 308 for recovering fibers from the first fraction. It should be noted that the primary consideration in selection of the two filtering devices 300 and 308 is the nature of the material to be separated and the nature of the input material. For example, the first filter device 300 would probably be selected with a filter medium that has a larger mesh, pore size, hole or slot than that of the second filter device 308, because the input material to the first filter device 300 will include larger material than the first fraction will contain. Thus, if a fine mesh, pore size, hole or slot were selected for first filter device 300, clogging could occur which would reduce the filtering and washing efficiency. However, since the coarse material has already been filtered out of the first fraction, the second filter device 308 could have a smaller mesh or pore size to allow the recovery of finer fibers while still allowing the passage of fine contaminants and liquid. The second filter device 308 separates the first fraction into third and fourth fractions. The third fraction exits the second filter device on line 310 while the fourth fraction exits on line 312. The filter medium used in the second filter device 308 is selected so as to provide for the separation of a substantial percentage of fine fibers from fine contaminants and liquid. Thus, the fourth fraction will consist of contaminants and a portion of the liquid carrier medium, while the third fraction will consist of fine fibers and a portion of the liquid carrier medium (or will have liquid carrier medium added to allow for easy transport of the third fraction) . The fourth fraction constitutes a waste stream and may be further processed for discharge or may simply be discarded. It should be noted that the third fraction may be treated with a hydrocyclone, screen device, or chemical addition to enhance the stream prior to its return to the first separator, in any embodiment shown. The third fraction is then returned on line 310 to the first filter device 300. Preferably, introduction of the third fraction into the first filter device 300 is carried out within a portion of the first filter device 300 upon which a mat of the second fraction has formed. Thus, the mat in cooperation with the filter medium will retain fine fibers present in the third fraction in or on the second fraction, while any remaining liquid medium or fine contaminants pass into the first fraction Figure 4 s a block diagram showing a modification of the preferred embodiment in which the second fraction is further processed. Various fractions are discussed in terms of their consistency to provide information as to the type of separation conducted at each stage. The feed suspension enters the first filter device on line 302. Typically, the feed suspension will have a consistency in the range of about 0.1% to 5%. The second fraction, having a consistency in the range of about 4% to 30%, exits the first filter device 300 on line 304 and is provided to a processing device 316. This processing device 316 is typically a dewaterer of a type known in the art. Screw and belt presses, side hill screens, incline screws or paper machine formers could each be used as the processing device 316. Typically, in operation, the processing device 316 generates a fifth and sixth fraction from the second fraction. All of the dewatering devices described above exert some form of external pressure on the second fraction. As a result, fine contaminants, liquid medium (water) and some amount of fibers will form a fifth fraction in the nature of a liquid stream from the processing device 316. The sixth fraction consists of the remainder of the second fraction after processing by the processing device 316 and will typically have a consistency in the range of about 35%. The sixth fraction exits the processing device 316 on line 318 for further processing or use. For example the fibers present in the sixth fraction on line 318 may be bleached and then used in the paper making process, or they may be otherwise processed and used. The fifth fraction exits the processing device on line 320. The remainder of the system shown in Figure 4 operates in the same manner as was previously described with respect to Figure 3. The first fraction exits the first filtering device on line 306 to which line 320 is connected. Thus, the fifth fraction from the processing device 316 is added to the first fraction and the combined material is provided to the second filter device 308 for recovery of fine fibers. The second filter device 308 separates the input material (provided on line 306) into third and fourth fractions with the recovered fine fibers making up the third fraction and the contaminants and a portion of the liquid medium making up the fourth fraction. The third fraction is then returned via line 310 to the first filter device 300 , prefera b ly at a point where a mat ma d e o f th e secon d fract i on has formed, for further processing. Referr i ng now to Figure 5, a particular em b o d iment of the system d escribed m Figure 3 will be descri b e d . The f irst filter i ng device 300 consists of a fiber d rum washer, which i s typical in the fiber recovery art. A fee d suspension 3 2 2 is provided to a vat 324, such as by spray nozzle 3 2 6 and condu i t 3 28. The feed suspension contacts a hollow drum 3 30 , the surface 3 32 of which is made of a filter medium. The d rum 330 is ma d e to rotate i n direction 329 such as by a motor 331 driving a toothe d gear 333 an d /or belt drive, which engages a toothe d gear 335 mounte d on the d rum. The filter medium of t h e surface 332 of t h e drum 330 i s selected to have a mesh or pore size which will reta i n fibers on the exterior of the drum, b ut allow fine contam i nants, and liquid to pass therethrough. B y the operation of hydrostatic pressure, the feed suspension 3 2 2 will contact the surface 33 2 of the drum 330 and will be separate d into components by the filter action of the drum. Fine contaminants, liqui d medium (water) and some fine fibers will pass into the interior of the drum 330 and form a first fraction 33 4. Fibers will b e retained on the surface 332 of the drum 330 an d form a secon d fraction 336, which typically manifests as a mat of fi b ers forming on the outer surface 332 of the d rum 330 . The formation of the second fraction 336 on the drum 330 also occurs when the feed suspension 322 is sprayed onto the outler surface 322 of the drum 330, such as through spray nozzle 326. It should be noted that material in the feeα suspension 322 passes through the filter medium of the drum 330 more easily on portions of the drum on which no mat has formed. On such portions of the drum 330, fine fibers may pass through the filter medium as will fine contaminants and liquid. By the operation of the feed suspension 322 being filtered by portions of the drum 330 upon which no mat of the second fraction 336 has formed, some amount of fine fibers will enter the first fraction 334. However, where a mat of the second fraction 336 has formed on the drum 330, the mat itself acts to filter the feed suspension and helps to retain fine fibers. The second fraction 336 is moved by motion of the drum 330 out of the vat 324 and into an exit conduit 338. The second fraction 336 is then further processed for use. The first fraction 334 is drawn out of the interior of the drum 330 through a take up 340 and provided as an output on line 306. The first fraction is then provided to a second filtering device 308, which separates the first fraction into third fraction 344 and fourth fraction 346. The second filtering device 308 may be a variety of filtering devices well known in the art. In the preferred embodiment, the second filtering device is a SPRAYDISC™ filter manufactured by Celleco Hedemora, Inc., of Lawrenceville, Georgia, U.S.A. The sole criteria for selection of the type of filtering device to be used as the second filtering device 308 the capability of separating fibers from fine contaminants and liquid. Preferably, this second filtering device 308 will be selected to recover fine fibers from t h e first fraction while allowing fine contaminants and liquid to pass through. Thus, the fourth fraction 346 will consist of fine contaminants and liquid medium and exit the second filtering device on line 312. The fourth fraction 346, which is consi d ered a waste stream, is routed on line 312 for disposal or further processing. The third fraction 344 is provided as output on line 310 which returns the third fraction to the first filtering device 300. In a preferred embodiment, the second filtering device will consist of nozzles 348 which spray the first fraction 334 onto a filter disc 350. This filter disc 350 rotates so that material retained thereon is moved radially outward on the disc 350. As the retained material reaches the bottom of the arc of the disc 350, it is removed from the disc, such as by a mechanical scraper or a water stream. The retained material forms the third fraction 344. The material which passes through the disc 350 constitutes the fourth fraction 346. A more detailed description of a preferred second filter device 308 is provided with reference to Figure 7, below. In the embodiment shown in Figure 5, the third fraction 344 is returned to the vat 324 for reintroduction into the feed suspension 322. A nozzle 352 reintroduces the third fraction 344 into the vat 324 at a point near the drum 330 on which a mat of the second fraction 336 has formed. Thus, the second fraction 336 in cooperation with the filter medium on the outer surface 332 of the drum 330 serves to act as a filter to retain the fine fibers present in the third fraction 344, which had previously passed through the outer surface 332 of the drum 330 and into the first fraction 334. It should be noted that any type of drum washer may be use d in the place of that described above as the first filter device 300. For example, a preferred drum washer may be of the type described in U.S. Patent Application Serial Number 08/444,607, entitled "Fiber Suspension Thickener Having Improved Discharge Consistency," filed on May 19, 1995, the entire disclosure of which is incorporated herein by reference thereto. T h e drum washer of that application includes a turbulence generator which disturbs the formed mat to improve the discharge consistency of the second fraction. A further embodiment, showing the use of a different type of first filtering device 300, is shown in Figure 6. In this embodiment, the first filtering device 300 is a belt thickener as described with respect to the prior art in Figure 2 . Th e f eed suspension 322 is deposited onto an endless belt 356 of filter material from a head box. The second fraction 336 forms on t h e surface of the belt 356 and consists of a mat of retained fibers. The first fraction 334 passes through the belt 3 56 and is collected in a tank or vat 358. The first fraction 3 34 is collected by a take up 360 in the vat 358 and is carrie d via line 306 to a second filtering device 308. As was previously described, the first fraction is separated by t h e secon d filter device 308 into third fraction 344 and fourth fraction 346. The fourth fraction 346 is then provided as a waste stream output on line 312 for disposal or further processing. The third fraction 344 is provided on line 310 for return to the first filtering device 300. Line 310 is provided as an input to nozzle 360. Nozzle 360 is positioned at a point downstream of the head box, at a point over the belt 356 on which a mat of the second fraction 336 has already formed. Thus, the second fraction 336, in cooperation with belt 356, acts to recover fibers present in the third fraction 344, while any remaining fine contaminants and liquid medium pass through the mat of second fraction 336 and belt 356 to become again a part of the first fraction 334. The second fraction 334 is then exits the first filtering device via conduit 362 for further processing as was described above. With the exception of the substitution of a different filtering device for the first filtering device 300, the operation of the system shown in Figure 6 is identical to that shown in Figure 5. Figure 7 shows a preferred second filter device 308. In a preferred embodiment the second filter 308 may comprise a filter which is sold by Celleco Hedemora, Inc., of Lawrenceville, Georgia, U.S.A., under the trademark SPRAYDISC. Figure 7 shows the components of this type of filter device in cross section. Support members 702 support a rotatable axle 70 . Attached to the axle 704 are filter discs 706, 708 and 710. These discs are made of a metal or synthetic support frame 712 which supports filter material 714. A motor 716, with any appropriate gearing, drives axle 704 which rotates as indicated by arrow 718. Nozzle support members 720 and 722 are likewise supported by axle 70 4 , but preferably are decoupled from the rotation of axle 704 so that the filter discs 706, 708 and 710 move relative to the nozzle supports 720 and 724. Nozzle supports 720 and 722 support a number of spray nozzles 724 which are directed toward the filter material 7 14 o f the filter discs 706, 708 and 710. The first fraction 33 4 is supplied to the nozzles 724 via line 306. The first fraction 334 is then sprayed onto the filter discs 706, 708 and 7 1 0 through nozzles 724. Fibers and fine short fibers present in the first fraction 334 are retained on the filter material 7 1 4 and drop to collection sumps 726 to form a third fraction 3 44 . The fine contaminants and a portion of the liquid carrier pass through the filter material 714 and collect in the interior of the filter discs 706, 708 and 710 to form a fourth fraction 346. The third fraction 344 is drawn from the sumps 726 and is output on line 310. The fourth fraction 346 is drawn from t h e interior of the discs 706, 708 and 710 and provided as output on line 3 12. In general, the filter material 714 can be finer than the filter material used in the first filter device 30 0 ( previously described) since most of the coarse fibers will have b een remove d in the previous filtering step. Thus, the filter material 714 of the second filtering device may be finer without concern for clogging due to the accumulation of coarse fi b ers. In this manner, fine fibers which may have passed nto th e first f rac t ion dur i ng processing m the first filter device may b e recovere d b y the second filter device. F i gures 8 - 11 show alternative embodiments of the present invent i on with a variety of different first filtering d evices 300 an d points of reintroduction of the third fraction 344 . Not shown in these Figures is the processing of the first fraction 3 3 4 into the third and fourth fractions 3 4 4 , 346 . This processing may be identical to that described with respect to Figures 5, 6 and 7. Figure 8 shows a similar fiber drum was h er for t h e f irs t filter dev i ce 3 00 as was described with reference to Figure 5. As was the case with the embodiment of Figure 5, a h ollow d rum 33 0 is prov i ded in a vat 324. A feed suspension 3 22 consisting of fibers, fine fibers, fine contaminants and liqui d carrier is introduced into the vat such as by conduit 3 2 8 an d nozzle 326 . The outer surface 332 of the drum 330 is made of an appropriate filter material. By operation of motor and gearing (shown in Figure 5 ) the drum 330 is caused to rotate as indicated by the arrow 329. By the action of hydrostatic pressure, fine contaminants and liquid carrier, along with some portion of fine fibers, are drawn into the interior of drum 330 to form a first fraction 33 4. Concurrently, a mat of fibers forms on the outer surface 33 2 of the drum 330 to form a second fraction 336. The first fraction 334 exits the drum 330 through take up 340 and is output on line 306. The second fraction 336 is provided to conduit 338 for output. As was previously described, the first fraction is separated into third an fourth fractions by a second filter device (shown in Figure 3). The third fraction 344 consists of fine fibers and liquid carrier, while the fourth fraction represents a waste stream of fine contaminants and liquid carrier. T h e thir d fraction 344 is returned to the first filter device 3 0 0 on line 310, which supplies two nozzles 352 and 35 4 with the third fraction 344. One nozzle 352 is provided in the vat 3 2 4 and is directed to a portion of the drum 330 upon which a mat of the second fraction 336 has already formed. The second nozzle 35 4 is directed to spray the third fraction 3 44 directly onto t h e ou t er surface 332 of the drum 330 at a location upon which the fee d suspension 322 has already been sprayed on the drum 330 through nozzle 326. Figure 9 shows a further alternative first filtering device 300. This first filtering device 300 is an example of a drum washer which forms a mat over the top of the drum 330 as opposed to underneath. In this embodiment the drum 330 is caused to rotate in the direction of arrow 802 as by a motor and suitable drive gearing (shown in Figure 5) . The outer surface 332 of the drum is covered with a suitable filter material as was previously described. Feed suspension 322 is provided to a vat 804 such as b y a nozzle 806. It should be noted that t h e nozzle 806 coul d b e directed to spray the feed suspension 322 directly onto the drum 330 . As the feed suspension 322 contacts the outer surface 33 2 o f the drum 3 30, hydrostatic pressure forces liquid carrier an d fine contaminants to pass into the interior of t h e drum 3 30 to form a first fraction 334. This first fraction 334 is drawn out of the drum 330 by take up 340 and provided as output on line 3 06. Concurrently, a mat consisting of fibers forms on the outer surface 332 of the drum 330 to form a second frac t ion 336 . This second fraction 336 is then provided to an exit con d uit 338 f or further processing or use. Once the first fraction 334 has been drawn off from the first filtering device 300, it is provided on line 306 for processing by a second filtering device (shown in Figure 3) for separation into third and fourth fractions. The third fraction consists of fine fibers and liquid carrier while the fourth fraction consists of fine contaminants and liquid carrier, while the fourth fraction comprises a waste stream which may be further processed or discarded. The third fraction 3 4 4 is returned to the first filter device 300 on line 31 0 . Line 310 feeds a nozzle 808 which is positioned to spray the third fraction 344 onto the drum 330 at a point whereupon a mat of the second fraction 334 has previously formed. Thus, the action of the mat of second fraction 334 in cooperation with the outer surface 332 of the drum 330 will serve to retain the fine fibers present in the third fraction 344 on the drum 330. While not shown, the processing of the first fraction into third and fourth fraction is substantially the same as was described with respect to the previous embodiments. Figure 10 shows yet another first filter device 300 in which a mat of second fraction 336 forms on the underside of a drum 330; however, in this case, the mat does not form below the level of liquid in a vat. In the embodiment shown in Figure 10 a drum 330 having an outer surface 332 covered with an appropriate filter material rotates in the direction of arrow 810; the drum is driven by a motor with appropriate gearing and coupling (shown in Figure 5) . The feed suspension 322 is sprayed onto the drum 330 by nozzles 812 and 814 and, thus, is provided to the outer surface 332 of the drum 330 and to a vat 816. By the action of gravity and hydrostatic pressure, fine contaminants and liquid carrier pass through the filter material of the outer surface 332 of the drum 330 and form a first fraction 334 in the interior of the drum. A second fraction 336 consisting of fibers forms on the outer surface 332 of the drum 330 and is moved by the motion of the drum to an exit conduit 818 for further processing or use. The first fraction is drawn off by take up 340 and is provided on output on line 306. Once the first fraction 334 has been drawn off from the first filtering device 300, it is provided on line 306 for processing by a second filtering device (shown in Figure 3) for separation into third and fourth fractions. The third fraction consists of fine fibers and liquid carrier while the fourth fraction consists of fine contaminants and liquid carrier. The fourth fraction comprises a waste stream which may be further processed or discarded. The third fraction 344 is returned to the first filter device 300 on line 310. A nozzle 820 is fed from line 310 and is positioned so as to deposit the third fraction 344 into the vat 816 at a position whereupon a mat of the second fraction 336 has already formed. Thus, the mat of second fraction 336, in cooperation with the filter material on the outer surface 332 of the drum 330, serves to retain fine fibers present in the third fraction 344. Figure ll shows an embodiment of a first filter device 300 similar to that described with respect to Figure 10. The feed suspension 322 is sprayed onto the outer surface 332 of a drum 330 which is covered with filter material by nozzles 819 and 821. Fine contaminants, liquid carrier and some fine fibers pass through the filter material and into the interior of the drum 330 to form first fraction 334. Fibers present in the feed suspension 322 are retained on the outer surface 332 of the drum 330 to form a second fraction 336. The motion of the drum in the direction indicated by arrow 822 will force the mat of second fraction 336 into an exit conduit 824, where the second fraction 336 will be removed for further processing or use. A vat 826 contains the second fraction 336 which does not remain on the surface 332 of the drum 330 during its rotation. The first fraction is drawn out of the interior of the drum 330 by take up 340 and is provided as output on line 306. Once the first fraction 334 has been drawn off from the first filtering device 300, it is provided on line 306 for processing by a second filtering device (shown in Figure 3) for separation into third and fourth fractions, which have been described previously. The third fraction 344 is returned to the first filter device 300 on line 310 which feeds a nozzle 82 8 . This nozzle 828 is positioned so as to deposit the third fraction 344 into the vat 826 at a position whereupon a mat of the secon d fraction 336 has already formed. Thus, the mat of secon d fraction 336, in cooperation with the filter material on the outer surface 332 of the drum 330, serves to retain fine fi b ers present in the third fraction 34 4 . Referring now to Figures 12 - 14, block diagrams of preferred implementations of the above describes systems are described. The block diagrams of Figures 12 - 1 4 are designed to show the location of necessary auxiliary devices such as tanks and pumps and the relative elevations of components to attain the implementation the above described embodiments with the desired flow characteristics. Figure 12 shows an embodiment of the present invention wherein gravity flow and pumping is combined to cause the various fractions to flow in desired paths. In a manner similar to that previously described, the feed suspension is provided to a first filter device 300 on line 302. The source of the fee d suspension is preferably elevated above the first filter device 3 0 0 so that gravity will provide the necessary impetus for flow into the first filter device. The first filter device 30 0 separates the feed suspension into first and second fractions as has been described. The second fraction exits the first filter device 300 on line 304 for further processing or use. The first fraction exits the first filter device 300 on line 306a and empties into a tank 900 situated at a relative elevation lower than that o f the first filter device 300. Thus, gravity provides the flow of the first fraction through line 306a to the tank 900. A d ischarge located at the bottom of the tank directs the second fraction to a pump 902 which then pumps the second fraction through line 3 0 6b to the second filter device 308. The second filter device 3 0 8 is positioned at a relative elevation higher than the first filter device 300. The second filter device 308 separates the second fraction into third and fourth fractions. The fourth fraction exits the second filter device 308 through line 312 for disposal or further processing; the fourth fraction may flow either by gravity, or a pump external to the second filter device 308. The third fraction exits the second filter device 308 on line 310 and flows by gravity to the first filter device 300, where it is processed as was previously described. Figure 13 shows a different combination of gravity feed and pumping. As was previously the case, the feed suspension 302 is provided to the first filter device 300, either under a gravity feed or through pumping. The first filter device separates the feed suspension into first and second fractions and the second fraction exits the first filter device on line 304 for further processing or use. The first fraction exits the first filter device 300 under the influence of gravity on line 306 where is proceeds to the second filter device 308, which is positioned at a relative elevation lower than that of the first filter device 300. The second filter device 308 separates the first fraction into third and fourth fractions as was previously described and the fourth fraction exits the second filter device 308 on line 312, either under the influence of gravity or with the use of an external pump. The third fraction exits the second filter device on line 310a under the influence of gravity and is deposited into a tank 904 situated at a relative elevation lower than that of the second filter device 308. The third fraction is discharged from the tank and provided to a pump 906 which pumps the third fraction along line 310b to the first filter device 300 where it is processed as was described previously. Figure 14 shows an embodiment employing two sets of tanks and pumps. As was previously the case, the feed suspension enters the first filter device 300 on line 302. The first filter device 300 separates the feed suspension into first and second fractions and the second fraction exits the first filter device on line 304 for further processing or use. The first fraction exits the first filter device on line 306a and empties into a tank 908, which is preferably positioned at a relative elevation lower than the first filter device 300 so that gravity will cause the first fraction to flow through line 306a. The first fraction is discharged from the tank 908 and provided to a pump 910 which pumps the first fraction along line 306b to the second f ilter device 308. At the second filter device 308 the first fraction is separated into third and fourth fractions and the fourth fraction exits the second filter device 308 on line 312 for further processing or disposal; the fourth fraction may flow on line 312 either through the force of gravity or by a pump external to the second filter device 308. The third fraction exits the second filter device 308 on line 310a and empties into a tank 912, which is preferably positioned at a relative elevation lower than the second filter device 30 8 so that the third fraction flow on line 310a due to the force of gravity. This tank 912 discharges into a pump 914 which pumps t h e third fraction along line 310b and back to the first filter device 300 for processing as was described above. The above described methods and apparatuses provide for an effective and efficient method for recovering fine fibers which normally are wasted as part of the paper pulp processing arts. Generally, a certain loss of fine fiber was accepted as part of the process of recycling paper or increasing the consistency of a fiber/water slurry. However, as recycling efforts increase and processors attempt to minimize demand for raw fiber resources, fiber losses must be kept to a minimum and yield must be maximized. The above described inventions provide methods and apparatuses which will substantially increase the fiber yield in fiber recovery processes, and yet will operate at typical processing speeds and conditions. In fact, all of the components needed to practice the inventions are available off-the-shelf which will allow for the relatively inexpensive implementation of the invention. The foregoing detailed description of the preferred embodiments was for the purpose of illustration of the invention and should not be construed as limiting the scope of the invention as set forth in the claims. The invention is capable of numerous substitutions, modifications, addition and deletions without departing from the scope of the claims. For example, while preferred first and second filter devices were described above, any device capable of separating a slurry of fibers, contaminants and liquid carrier into fractions could be substituted. In fact, any type of slusher deinker, fluidized drum washer, bow screen, pressure screen, hydrocyclone, screw or belt press, dewaterer or other filter may be substituted for either the first or second filter devices as described as long as they are adapted to provide the separation described above. Additionally, the methods and systems described above can be incorporated into larger paper processing methods or systems. In fact, it is anticipated that the above described invention will be practiced in an overall paper making environment comprising many additional steps beyond the separation of fiber from other components.

Claims: Cla ims : 1. A process for the recovery of fibers from a feed suspension including coarse fibers, the coarse fibers comprising long and medium fibers, fine short fibers and contaminants in a liquid carrier comprising the steps of: providing the feed suspension to a first filter; separating said feed suspension into two fractions, a first containing contaminants and fine short fibers and another fraction containing coarse, medium and short fibers, wherein this second fraction forms a mat on said first filter and wherein said first fraction passes through said first filter; providing said first fraction to a second filter; separating said first fraction into third and fourth fractions, said third fraction comprising said fine short fibers and said fourth fraction comprising said contaminants; applying said third fraction to a location on the first filter upon which said mat has formed, wherein said fine short fibers are deposited on said mat; and removing said second fraction from said first filter for further processing, whereby said second fraction comprises the coarse fibers and recovered fine short fibers from the feed suspension. 2. The method of claim l wherein said step of separating said feed suspension into first and second fractions comprises the following further steps: providing a drum washer for fiber having a hollow drum that is exterior covered in filter material and an interior in a vat; providing said feed suspension to said vat; forming said second fraction on said exterior of said washer through hydrostatic pressure wherein said first fraction forms within the interior of said drum after passing through said exterior of said drum. 3. The method of Claim 2 comprising the further step of maintaining a relatively constant level of the feed suspension within said vat. 4. The method of Claim 3 wherein said step of applying said third fraction to said first filter further comprises returning said third fraction to a location within said vat below the level of the feed suspension. 5. The method of Claim 3 wherein said step of applying said third fraction to said first filter further comprises applying said third fraction to first and second locations on said first filter, said first location located above the level of the feed suspension and the second location below the level of the feed suspension. 6. The method of Claim 1, said step of separating said first fraction into third and fourth fraction further comprising the following steps; providing a surface of filter material adapted to allow passage of said fourth fraction therethrough while preventing passage of said third fraction therethrough; spraying said first fraction onto said surface of filter material wherein said third fraction will not pass through said filter material and said fourth fraction will pass through said filter material; collecting said third fraction; and collecting said fourth fraction after it has passed through said filter material. 7. The method of Claim 1, said step of providing said first fraction to a second filter comprising the further steps of: providing a conduit between said first and second filters; and positioning sa d second filter at an elevation lower than the elevation of said first filter, wherein said first fraction will flow by the force of gravity through said conduit between said first and second filters. 8. The method of Claim 1, said step of providing said first fraction to a second filter comprising the further steps of: providing a tank having an inlet and discharge positioned at an elevation lower than the elevation of said first filter; providing a first conduit between said first filter and said tank wherein said first fraction will flow by the force of gravity through said first conduit into said tank; providing a pump connected to said discharge of said tank; providing a second conduit between said pump and said second filter; pumping said first fraction from the discharge of said tank to said second filter. 9. The method of Claim 1, said step of returning said third fraction to said first filter comprising the further steps of: providing a conduit between said second and first filters; and positioning said second filter at an elevation higher than the elevation of said first filter, wherein said third fraction will flow by the force of gravity through said conduit between said second and first filters, and into or before the first filter. 10. The method of Claim l, said step of returning said third fraction to said first filter comprising the further steps of: providing a tank having an inlet and discharge positioned at an elevation lower than the elevation of said second filter; providing a first conduit between said second filter and said tank wherein said third fraction will flow by the force of gravity through said first conduit into said tank; providing a pump connected to said discharge of said tank; providing a second conduit between said pump and said first filter; pumping said third fraction from the discharge of said tank to said first filter. 11. The method of Claim l wherein said step of returning said third fraction to said first filter further comprises: placing a nozzle at a location within said first filter wherein said second fraction has formed; directing said nozzle to spray in the direction of said second fraction; providing said third fraction to said nozzle; and spraying said third fraction from said nozzle. 12. The method of Claim l comprising the further steps of: providing said second fraction to a dewaterer; dewatering said second fraction to form a fifth fraction comprising said coarse fibers and a first portion of said fine short fibers and a sixth fraction comprising fine short fibers; and adding said sixth fraction to said first fraction prior to provision of said first fraction to said second filter. 13. An apparatus for the recovery of fibers from a feed suspension containing coarse fibers, fine short fibers, fine contaminants and liquid carrier comprising: first separating means for separating the suspension into first and second fractions, said second fraction forming a mat at a location therein, wherein said first fraction comprises contaminants and a first portion of the fine short fibers and said second suspension comprises coarse fibers and at least a second portion of the fine short fibers; a second separating means for separating said first fraction into third and fourth fractions, said third fraction comprising at fine short fibers and said fourth fraction comprising contaminants; means for applying said third fraction on said location in said first separating means upon which said mat has formed. 14. The apparatus of Claim 13 wherein said first separating means comprises a drum washer. 15. The apparatus of Claim 13 wherein said first separating means comprises a belt thickener. 16. The apparatus of Claim 13 wherein said first separating means further comprises: (a) a vat; (b) a hollow filter assembly disposed within said vat and including walls composed of a filter material; (c) means for rotating said hollow filter assembly about a horizontal axis; (d) feed suspension delivery means adapted for furnishing the feed suspension to the vat at the descending side of said hollow filter assembly, thereby forming a pool of feed suspension in which said hollow filter assembly partly submerges, whereby gravity forces water and fine particulates within the fiber suspension through the filter material and into the interior of said hollow filter assembly, thereby creating said second fraction fiber in the vat; (e) second fraction delivery means for collecting and delivering said second fraction further comprising discharge means for discharging said second fraction from the vat at the ascending side of said hollow filter assembly; and (f) a turbulence creating means, disposed within said vat outside and at the ascending side of said hollow filter assembly, for mixing the second fraction. 17. The device of claim 16, wherein said hollow filter assembly comprises a cylindrical filter positioned such that the central axis of said cylindrical filter coincides with said horizontal axis. 18. The device of claim 16, wherein said discharge means comprises an overflow conduit coupled to said vat for receiving the thickened fiber suspension. 19. The device of claim 16, wherein said turbulence creating means is positioned between said vat and the exterior of said hollow filter assembly. 20. The apparatus of Claim 13 wherein said applying means further comprises a nozzle directed toward said second fraction. 21. The apparatus of Claim 13 further comprising: said first separating means further comprising: (a) a vat; (b) feed suspension level control means for controlling the level of feed suspension within said vat; (c) a filter body positioned within said vat such that at least a portion of said filter body extends below the level of said feed suspension within said vat and at least a portion of said filter body extends above the level of said feed suspension within said vat; and (d) drive means for rotating said filter body around a horizontal axis relative to said vat, wherein portions of said filter body will alternatingly rotate from a position above the level of said feed suspension within said vat, to a position within said feed suspension within said vat; and said applying means further comprising: (a) a first header with nozzles located above the level said feed suspension within said vat and directed toward said filter body; and (b) a second header with nozzles located below the level of said feed suspension within said vat and directed toward said filter body. 22. The apparatus of Claim 13 further comprising a first fraction delivery means comprising: a tank positioned at a relative elevation lower than said first separating means, said tank having an inlet and an outlet; a first conduit between said first separating means and said inlet of said tank; a pump connected to said outlet of said tank; and a second conduit connected between said pump and said second separating means, wherein said first fraction flows from said first separating means through said first conduit to said tank due to the force of gravity and said first fraction flows from said tank to said second separating means through said second conduit due to the force supplied by said pump. 23. The apparatus of Claim 22 further comprising: said second separating means positioned at a relative elevation higher than said first separating means; and a third fraction delivery means for directing said third fraction comprising a third conduit connected between said second separating means and said first separating means, wherein said third fraction will flow from said second separating means to said first separating means through said third conduit due to the force of gravity. 24 - τhe apparatus of Claim 13 further comprising a third fraction delivery means comprising: a tank positioned at a relative elevation lower than said first second separating means, said tank having an inlet and an outlet; a f rst conduit between said second separating means and said inlet of said tank; a pump connected to said outlet of said tank; and a second conduit connected between said pump and said first separating means, wherein said third fraction flows from said first separating means through said first conduit to said tank due to the force of gravity and said third fraction flows from said tank to said first separating means through said second conduit due to the force supplied by said pump. 25. The apparatus of claim 24 further comprising: said first separating means positioned at a relative elevation greater than that of said second separating means; and a first fraction delivery means for direction said first fraction comprising a third conduit connected between said first separating means and said second separating means, wherein said first fraction will flow from said first separating means to said second separating means through said third conduit due to the force of gravity. 26. The apparatus of Claim 13 further comprising: a first fraction delivery means comprising: (a) a first tank positioned at a relative elevation lower than said first separating means, said first tank having an inlet and an outlet; (b) a first conduit between said first separating means and said inlet of said first tank; (c) a first pump connected to said outlet of said first tank; and (d) a second conduit connected between said first pump and said second separating means, wherein said first fraction flows from said first separating means through said first conduit to said first tank due to the force of gravity and said first fraction flows from said first tank to said second separating means through said second conduit due to the force supplied by said first pump; and a third fraction delivery means comprising: (a) a second tank positioned at a relative elevation lower than said first second separating means, said second tank having an inlet and an outlet; (b) a third conduit between said second separating means and said inlet of said second tank; (c) a second pump connected to said outlet of said second tank; and (d) a fourth conduit connected between said second pump and said first separating means, wherein said third fraction flows from said second separating means through said third conduit to said second tank due to the force of gravity and said third fraction flows from said second tank to said first separating means through said fourth conduit due to the force supplied by said second pump. 27. The apparatus of claim 13 further comprising: dewatering means for separating said second fraction into fifth and sixth fractions, said fifth fraction comprising contaminants and a first portion fine short fibers and said sixth fraction comprising the coarse fibers and a second portion of the fine short fibers; and fifth fraction delivery means connected between said dewatering means and said second delivery means for receiving said fifth fraction from said dewatering means and adding said fifth fraction to said first fraction prior to separation of said first fraction by said second separating means. 28. The apparatus of claim 27 wherein said dewatering means 5 comprises a screw dewaterer. 29. The apparatus of claim 27 wherein said dewatering means comprises a press. 30. The apparatus of claim 27 wherein said dewatering means comprises a side hill screen. ° 31. The apparatus of claim 27 wherein said dewatering means comprises a paper machine former.

Inventors: FJAELLSTROEM ROLAND, SMITH RYAN M, FJAELLSTROEM, ROLAND, SMITH, RYAN, M.
Applicants: ALFA LAVAL AB, FJAELLSTROEM ROLAND, SMITH RYAN M, FJAELLSTROEM, ROLAND, SMITH, RYAN, M.
Application year: 1997
Main classification: D21D5
IPC codes: D21D5, D21F1