Abstract:
A hybrid method for processing papermaking fibers to remove high density stickies typically includes utilizing a multistage array of forward cleaners coupled with a flotation cell which increases overall efficiency of the system. In a preferred embodiment, a first rejects aqueous stream from a first stage bank of centrifugal cleaners is treated in a flotation cell before being fed to a second stage bank of centrifugal cleaners. With the improved technique, the accepts from the first stage bank of centrifugal cleaners may be combined with the accepts from the second stage bank of centrifugal cleaners and fed forward to a thickening device, for example. The technique is also suitably employed for removing stickies from material which has already been screened with a fine screen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM FOR PRIORITY 
     This application is a divisional application of U.S. patent application Ser. No. 10/099,610, filed Mar. 15, 2002, now U.S. Pat. No. 7,063,770 which is a continuation-in-part application of application Ser. No. 09/772,395, filed Jan. 30, 2001, now U.S. Pat. No. 6,416,622, which in turn is based upon Provisional Application Ser. No. 60/180,348, filed Feb. 4, 2000. The priority of the foregoing applications is hereby claimed and their disclosures are incorporated herein by reference thereto. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to papermaking fiber processing and more particularly to a method useful for removing stickies from secondary or recycle paper pulp by incorporating a hybrid multistage forward cleaner system with an integrated flotation cell. The method is particularly effective for removing stickies that have already passed through a screening stage. 
     BACKGROUND 
     Processing of papermaking fibers to remove contaminants is well known in the art, including the use of forward cleaners and flotation cells. Such technology is used, for example, to treat secondary (recycle) fiber sources for re-use in paper products such as towel and tissue, paperboard, coated writing and printing papers and so forth. Equipment utilized includes screening devices, flotation cells and the like as may be seen, for example, in U.S. Pat. No. 4,272,315 to Espenmiller; U.S. Pat. No. 4,983,258 to Maxham; U.S. Pat. No. 5,240,621 to Elonen et al.; and U.S. Pat. No. 5,693,222 to Galvan et al. 
     Recycling paper into secondary pulp suitable for re-use in high quality products is a relatively complex, capital intensive undertaking as will be appreciated from U.S. Pat. No. 5,587,048 to Streisel et al. The basic cleaning sequence of the &#39;048 patent is as follows: (1) detrashing—the detrasher contains 6 mm (¼ inch) holes and retains large contaminants, such as plastic bags, pieces of wood, large staples, pieces of metal and packing tape, detrashing typically takes place at 3-5% solids; (2) high-density cleaning—heavy, coarse contaminants, such as bolts, staples and rocks are removed, high density cleaning typically takes place at about 3-4% solids; (3) primary coarse screening—primary coarse screens contain holes 2-3 mm in size, preferably 2.4 mm, for removing medium-sized contaminants, such as small fragments of wood, tape and styrofoam, coarse screening at this stage protects fine slotted screens downstream from being overwhelmed by contaminants that are large relative to the slot width, and results in improvement in quality and production rates, coarse screening typically takes place at about 2.5-3.5% solids; (4) secondary coarse screening—the rejects from the primary coarse screening may be screened again using holes of the same size, but at a lower consistency, about 1.5-2.5% solids; (5) sand cleaning (centrifugal)—sand cleaning at this stage protects the fine slotted screens downstream from excess wear, waste corrugated paperboard contains relatively large amounts of sand, cleaning ahead of the screen increases the cost of the system, and increases the requirements for hydraulic capacity, sand cleaning typically takes place at about 1% solids; (6) screening—fine slotted screens are used with a width of 0.008 inch (0.20 mm), rather than 0.012 inch previously used for corrugated paperboard, the fine screens remove plastic slivers, wax and stickie agglomerates, screening takes place at less than 1% solids, preferably less than 0.9%; (7) Lightweight Cleaning (Gyrocleaning)—lightweight cleaning preferentially removes materials with a specific gravity below 1.0, such as plastics, waxes and stickies, not heretofore removed, lightweight cleaning is performed at about 0.8% solids. 
     It should be appreciated from the &#39;048 patent that existing methods for handling stickies removal were based on removing light contaminants having a density generally less than the fiber being cleaned. Such methods have been found inadequate when a significant amount of heavy stickies are present. 
     The disclosures of the foregoing patents are hereby incorporated by reference. 
     SUMMARY OF INVENTION 
     In the past there were mainly small light weight stickies that managed to get through screens, and most of these small light weight stickies were subsequently removed by the gyro-cleans. More recently, heavy weight stickies started becoming a problem; presumably because some of the new pressure sensitive adhesives tend to form heavy weight stickies. The small heavy weight stickies, which managed to get through screens, were also accepted by the gyro-cleans or reverse cleaners, but they were subsequently rejected with alot of fiber by the forward cleaners. Since the heavy weight stickies from the forward cleaners are still hydrophobic, it is possible to selectively remove them with a flotation cell after the hydrophobic particles attach themselves to air bubbles in the flotation cell. 
     The heavy weight stickies are difficult to remove by flotation if they lose their hydrophobic properties during the deinking process (e.g., due to the addition of dispersing chemicals) or if the flotation cell is operated inefficiently (e.g., at too high a consistency or with insufficient air bubbles or due to inadequate contact between stickies and air bubbles). 
     One advantage of having the flotation cell on the forward cleaner rejects is that it is possible to keep the consistency low, since only 10-30% of the total flow is being treated (the percentage depends on reject flow amount). If all the stock is treated in a flotation cell, the tendency is to raise the consistency from 0.5-0.6% to 1% or higher to keep the size and cost of the equipment down. If the design consistency is already 1%, the heavy weight stickies removal efficiency becomes even worse when the consistency rises above 1% due to production increases. By installing a flotation cell on the forward cleaner rejects in an existing process, it is possible to design the hybrid cleaner flotation cell system at 0.5-0.6% consistency and obtain improved heavy weight stickies removal efficiency. 
     The present invention generally includes a method of processing secondary fiber to remove high density stickies which have a density generally greater than the fiber including: (a) processing a fiber feed stream to generate a rejects stream enriched in high density stickies and (b) treating the rejects stream enriched in high density stickies with a flotation stage to generate an intermediate flotation purified stream with a reduced high density stickies content. Preferably, the feed stream is initially processed by way of a centrifugal separation technique, such as feeding the stream to a bank of hydrocyclones, which generate a rejects stream enriched in high density stickies. The high density stickies typically have a characteristic area (that is, projected maximum cross-sectional area) of less than about 0.5 mm 2 , and usually less than about 0.3 mm 2 . The treatment by the flotation stage is effective to remove at least about 40 percent of the high density stickies present and, in most cases, at least about 50 percent. The high density stickies are believed to be derived from pressure sensitive adhesives. 
     In another aspect of the invention there is provided a method of thin stock processing secondary fiber to remove high density stickies having a density generally greater than the fiber includes the steps of: (a) processing a feed thin stock stream at a consistency of less than about 2.5%, preferably less than about 1%, to generate a thin stock accepts stream and a thin stock rejects stream, the thin stock rejects stream being enriched in high density stickies; and (b) treating the thin stock rejects stream enriched in high density stickies to generate an intermediate flotation purified stream. 
     The present invention provides in still another aspect a hybrid system for processing papermaking fibers and includes a multistage array of forward cleaners coupled with a flotation cell which increases overall efficiency of the system. In a typical embodiment, a first rejects aqueous stream from a first stage bank of centrifugal cleaners is treated in a flotation cell before being fed to a second stage bank of centrifugal cleaners. The accepts stream of the first stage bank of centrifugal cleaners is fed forward as is the accepts stream of the second stage bank of centrifugal cleaners. Preferably, the two accepts streams are combined. 
     One advantage of feeding the second accepts stream forward is that it does not have to be returned to the first bank of cleaners for re-cleaning. This reduces the size of the first bank of cleaners or allows an existing installation to operate at a lower consistency. (The cleaners operate more efficiently at a low consistency of 0.5% than at 0.8 or 1%). Another advantage is that the flotation cell typically operates at greater than 60% efficiency on removing hydrophobic contaminants from the first cleaner rejects, while another cleaner stage removes less than 50% of the hydrophobic contaminants. As a result a large quantity of hydrophobic contaminants are removed in the flotation stage, which makes the remaining cleaner stages work more efficiently with less good fiber loss. 
     As will be appreciated by one of skill in the art, the size and cost of a flotation stage for treating secondary fiber can be reduced by up to 75% if it is installed in centrifugal cleaner system as compared to a full scale treatment of the stock by flotation. The centrifugal cleaner system modeling indicates a 34% reduction in ink speck area of total centrifugal cleaner system accepts by removing ink specks from the first stage rejects with 80% efficiency in a flotation stage and then feeding the flotation accepts forward after centrifugal cleaning of the second stage. (24% reduction if second stage rejects are treated in a similar manner). The ability to feed the centrifugal cleaner rejects forward (after the flotation stage and additional centrifugal cleaning in the next stage) reduces the stock consistency in the first stage, thereby improving the efficiency of the first stage. The capacity of the system is also increased by feeding the second stage centrifugal cleaner accepts forward. The other centrifugal cleaner stages can also be operated more efficiently since more than 50% of the ink in the first stage centrifugal cleaner rejects has been removed in the flotation stage. When the centrifugal cleaner accepts are thickened in a press, a large amount of ink ends up in the pressate. This ink can also be removed by using the ink-laden pressate as dilution water for the centrifugal cleaner rejects going to the flotation stage. 
     A conventional centrifugal cleaner system (as shown in  FIG. 1 ) normally consists of several stages, whereby the rejects of each centrifugal cleaner stage are diluted for cleaning in the next stage and the centrifugal cleaner accepts are fed backwards to the feed of the previous stage. The ink speck removal efficiency of the centrifugal cleaner is usually much less than 50% on toner inks in office waste paper. As a result the total centrifugal cleaner system ink speck removal efficiency can drop to 30% or less on a furnish containing a large proportion of office waste. 
     By sending the first or second stage centrifugal cleaner rejects to a flotation stage (as shown in  FIG. 2 ) it is possible to remove a much higher percentage of the ink specks in office waste. (It was possible to obtain 80% removal of ink specks during a pilot plant trial with a flotation cell operated on second stage centrifugal cleaner rejects.) If the accepts of the flotation cell are cleaned in the next centrifugal cleaner stage, the centrifugal cleaner accepts from that stage can then be fed forward to the thickener. Sending centrifugal cleaner accepts forward reduces the load and improves the efficiency of the previous centrifugal cleaner stage. 
     The present invention is particularly useful in connection with removing stickies from a thin stock recycle fiber product stream; likewise, it is believed pitch removal is enhanced. Stickies are generally a diverse mixture of polymeric organic materials which can stick on wires, felts or other parts of paper machines, or show on the sheet as “dirt spots” or holes. The sources of stickies may be pressure-sensitive adhesives, hot melts, waxes, latexes, binders for coatings, wet strength resins, or any of a multitude of additives that might be contained in recycled paper. The term “pitch” normally refers to deposits composed of organic compounds which are derived form natural wood extractives, their salts, coating binders, sizing agents, and defoaming chemicals existing in the pulp. Although there are some discrete characteristics, there are common characteristics between stickies and pitch, such as hydrophobicity, low surface energy, deformability, tackiness, and the potential to cause problems with deposition, quality, and efficiency in the process. Indeed, it is possible with the present invention to reduce stickies by 50%, 80% or even more by employing a flotation cell in a multistage forward cleaner system as hereinafter described in detail. The rejects from the flotation stage are so full of ink, ash and stickies that they can be rejected without any further treatment. 
     As will be appreciated from the discussion which follows, a preferred method of cleaning recycle pulp includes combining the accepts from a first centrifugal stage with the accepts from a second centrifugal stage which is fed with the flotation-purified rejects of the first stage. The process is particularly effective for removing relatively heavy weight (small size) hydrophobic stickies that have already passed through a screening stage. This will increase productivity of a paper machine utilizing the pulp and decrease paper machine downtime and converting downtime. Stickies build up on wires or fabrics and cause holes to form in the sheet requiring downtime on the paper machine to remove them. Stickies also build up on doctor blades in paper machines and get into the dewatering felt and so forth. In converting, they can cause problems such as sheets sticking together. They clog emboss rolls and interfrere with the proper operation of other rolls, cause holes in the sheet and so on. Solvents are typically required to remove stickies from equipment and this can lead to environmental issues. 
     In recent years, stickies removal from recycle fiber has become more difficult in many cases. Without intending to be bound by any theory, it is believed that stickies generated from waste paper including pressure-sensitive adhesives become more flexible at typical operating temperatures (40° C.) of screens and thus tend to pass through even fine screens. 
     The method of the present invention has been employed in a commercial papermill and found to have a dramatic effect on downtime of the mill. Prior to installation and employment of the inventive method of removing contaminants, the plant typically experienced about 10 hours of downtime per month due to stickies. After employment of the claimed process, the plant has run for eight months without a stoppage due to stickies. In preferred embodiments the present invention is thus directed to a method of removing stickies from secondary or recycle fiber. 
     In one preferred mode of practicing the invention there is provided a method of processing papermaking fibers with a multistage array of forward cleaners including a plurality of centrifugal cleaners configured to generate accepts streams and rejects streams which concentrate hydrophobic contaminants including the steps of: (a) feeding a first aqueous feed stream including papermaking fibers to a first stage bank of centrifugal cleaners of the multistage array; (b) generating a first accepts aqueous stream and a first rejects aqueous stream in the first stage bank of centrifugal cleaners, the first aqueous rejects stream being enriched in hydrophobic contaminants with respect to the first aqueous feed stream; (c) supplying the first rejects aqueous stream to a flotation stage; (d) treating the first rejects aqueous stream in the flotation stage to remove hydrophobic waste from the first aqueous rejects stream and produce an intermediate aqueous purified feed stream; (e) feeding the aqueous purified intermediate feed stream to a second stage bank of centrifugal cleaners of the multistage array, the second centrifugal cleaner being configured to generate a second accepts aqueous stream; and (f) combining the first accepts aqueous stream with the second accepts aqueous stream to form a combined accepts stream. A further step involves thickening the combined accepts stream. Generally, the process is carried out at a consistency of less than about 1%; typically at from about 0.3% to about 0.9%, and preferably at from about 0.4% to about 0.7%. The multistage array of forward cleaners comprises at least 3 banks of centrifugal cleaners in one embodiment. 
     Hydrophobic contaminants removed from the first aqueous rejects stream by the flotation stage may include an ink composition, such as a toner ink composition. Typically, the hydrophobic contaminants removed from the first aqueous rejects stream by the flotation stage includes stickies, and may include an ink composition and stickies. The process is also believed unexpectedly effective in removing stickies derived from pressure sensitive adhesives. 
     In yet another aspect of the invention, there is provided a method of thin stock processing of secondary fiber to remove contaminants including the steps of: (a) screening a first aqueous stream including secondary papermaking fibers having a consistency of less than about 2.5% in a screening device with openings having a screening dimension of less than about 10 mils to generate a screened accepts aqueous stream; (b) feeding the screened accepts aqueous stream to a multistage array of cleaners configured to generate centrifugal cleaner accepts streams and centrifugal cleaner rejects stream which concentrate heavy hydrophobic contaminants, the rejects stream of at least one centrifugal cleaner being fed to another centrifugal cleaner; and (c) processing at least one centrifugal cleaner rejects stream of a centrifugal cleaner of the multistage array with a flotation stage to remove hydrophobic contaminants, the flotation stage thereby generating a flotation purified stream having a reduced hydrophobic contaminants content. 
     Unless otherwise indicated, terminology appearing herein is given its ordinary meaning; %, percent or the like refers, for example, to weight percent and “consistency” refers to weight percent fiber or solids as that term is used in papermaking. “Mils” refers to thousandths of an inch. The banks of centrifugal cleaners are typically hydrocyclone type cleaners. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention is described in detail below with reference to numerous examples and the appended Figures wherein like numbers designate similar parts throughout and wherein: 
         FIG. 1  is a schematic of a conventional multistage forward centrifugal cleaner system wherein each bank of cleaners are designated by a conical element; 
         FIG. 2  is a schematic diagram of a hybrid multistage forward cleaner/flotation apparatus and process of the present invention, wherein a flotation stage is provided to treat the second stage rejects stream; 
         FIG. 3  is a schematic diagram of a hybrid multistage forward cleaner/flotation apparatus and process of the present invention wherein a flotation stage is provided to treat the first stage rejects stream; 
         FIG. 4  is a schematic diagram of a hybrid multistage forward cleaner/flotation apparatus and process of the present invention wherein a flotation stage is provided to treat the first stage rejects and third stage accepts; 
         FIG. 5  is a schematic diagram illustrating an apparatus and process of the present invention wherein the hybrid system has dual forward cleaner banks in series and the rejects stream from both of the forward cleaner banks are provided to a flotation cell; 
         FIG. 6  is a side broken away view of a screen containing a slotted basket; and 
         FIG. 7  is a plot of residual ink concentration versus location in the pulp cleaning system. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is described in detail below for purposes of illustration and exemplification only. Such explanation of particular embodiments in no way limits the scope of the invention which is defined in the appended claims. Referring to  FIG. 1 , there is shown a conventional forward cleaner system  10  of the type employed at a paper mill, for instance, as part of the cleaning process for processing secondary pulp into paper products. System  10  has five stages  12 ,  14 ,  16 ,  18  and  20  of banks of centrifugal cleaners interconnected in the manner shown. Such connections may include suitable piping, mixing tanks, holding vessels and the like (not shown) as may be convenient for operating the system. Pulp is fed at low consistency to the system at  22  to the first bank of cleaners  12  through inlet  24  and centrifugally treated in the first stage by a bank of hydrocyclones, for example, such that the accepts are fed forward at  26  to a thickener (or another cleaning device) at  28  whereas the rejects, concentrating the heavy, hydrophobic waste in the system are fed to second stage  14  at  28  for further treatment in a second stage made up of a second bank of centrifugal cleaners  14 . Diluent water is added to the rejects stream from the first stage as indicated at  30  in an amount suitable for the particular system or operating conditions. Stream  28  (first stage rejects) is thus fed to the second stage cleaners whereupon bank  14  of cleaners generates an accepts stream  32  and a rejects stream  34 . Stream  32  is a recycled to the feed  22  and makes up a portion of the material fed to the first stage bank of cleaners  12 . The first bank of cleaners may be made up of 50 or more hydrocyclones depending on capacity and performance desired. Subsequent stages will each contain fewer cleaners than the previous stage depending upon the amount of rejects, until the final stage contains less than 10 cleaners. 
     Stream  34  is again enriched with respect to heavy components (with respect to stream  32 ) and is fed to the third stage  16  bank of cleaners for further processing. Diluent water may again be added at  36  if so desired to stream  34 . Stage  16  generates another accepts stream  38  which is fed back to the second stage (stream  28 ) and another rejects stream  40  enriched in heavy hydrophobic components. 
     In like fashion, stream  40  is fed to the fourth stage  18  bank of cleaners at  42  where diluent water may again be added. The fourth stage generates another accepts stream  44  and another rejects stream  46 . These streams have the rejects/accepts characteristics noted above. 
     Stream  46  is fed to yet another stage  20  of forward cleaners at  48  wherein stream  46  is divided into an accepts stream  50  and a rejects stream  52  as indicated on the diagram. Accepts stream  50  is recycled to the fourth stage as shown and rejects stream  52  is discarded or further processed if so desired. There is thus described a conventional forward cleaner system utilizing centrifugal cleaners in cascaded/refluxing fashion to concentrate the waste material and purify the pulp which is fed forward at a papermaking process to a thickening device or a cleaning device such as screens or a reverse cleaner. 
     In accordance with the present invention, a flotation stage is advantageously integrated into a multistage forward cleaner system to remove hydrophobic material and increase the cleaning efficiency. Flotation utilizes the phenomenon that the minerals which are present in the ground ore can partially be wetted, i.e., they are hydrophilic, while other parts of the minerals are hydrophobic. Hydrophobic particles have a clear affinity to air. Accordingly, finely distributed air is introduced into the solid-water-mixture so that the air will attach to the hydrophobic particles causing them to rise to the surface of the mixture or suspension. The hydrophobic particles, such as valuable minerals or the above-mentioned contaminants present in repulped stock suspensions, collect as froth at the surface of the suspension and are skimmed off with a suitable means such as a paddle or weir. The hydrophilic particles of the ore or stock suspension remain in the flotation vat. It is also possible to separate two or more useful minerals selectively by the flotation method, for example, in the separation of sulfidic lead/zinc ores. For controlling the surface properties of the minerals small amounts of additives of chemical agents are introduced such as, for example, foaming agents which will help to stabilize the air bubbles, so-called collecting agents which actually cause the hydrophobic effect and prepare the mineral particles for attachment to the air bubbles, and floating agents which temporarily impart hydrophilic properties to the hydrophobic minerals and later return the hydrophobic properties for selective flotation, as mentioned above. The latter are generally inorganic compounds, mostly salts, while the collectors are mostly synthetic organic compounds, and the foaming agents are oily or soapy chemicals such as fatty acid soap. 
     The apparatus of the present invention may utilize a variety of readily available components. The centrifugal cleaners, for example, are available from Ahlstrom (Noormarkku, Finland) or Celleco (Model 270 series) (Lawrenceville, Ga., USA) and are arranged in banks as shown in  FIGS. 2-5 . The flotation stage, which may be multiple cells, are likewise readily available from Comer SpA (Vicenza, Italy). Comer Cybercel® models FCB1, FCB3 and FCB4 are suitable as discussed further herein. 
     There is illustrated in  FIG. 2  an apparatus  100  and method in accordance with the present invention. Apparatus  100  operates similarly to apparatus  10  in  FIG. 1 . Like parts are given like numbers for purposes of brevity and only differences noted from the discussion above. The system  100  of  FIG. 2  operates as described in connection with system  10  of  FIG. 1  and is so numbered in the drawing except that system  100  has a flotation stage  75  for treating the rejects stream  34  of second stage cleaner  14 . Diluent water may be added at  36  as before, and hereafter, stream  34  is treated in the flotation stage to remove hydrophobic material. The accepts from the flotation stage, that is purified as shown by removing hydrophobic waste from stream  34 , is then fed in stream  34 ′ to third stage cleaner  16 . Instead of refluxing the accepts from the third stage back to the second stage, the accepts material is fed forward in a product stream  26 ′ for downstream processing. The hydrophobic rejects ( 31 ′) from flotation stage ( 75 ) are removed from system  100 . 
     In  FIG. 3  there is illustrated another apparatus  200  and method of the present invention. Here again similar functioning parts are numbered as in  FIGS. 1 and 2 , the discussion of which is incorporated by reference here. Apparatus  200  of  FIG. 3  differs from apparatus  10  of  FIG. 1  in that a flotation stage  75  is added to treat the first stage rejects stream  28  to remove hydrophilic waste to produce an intermediate purified stream  28 ′ which is fed to the second stage bank of cleaners  14 . Bank  14  generates a purified accepts stream  32 ′ which is fed forward to the thickening or other device  28  along with stream  26 . The hydrophobic rejects ( 21 ′) from flotation stage ( 75 ) are removed from system  200 . 
     In  FIGS. 4 and 5  there are illustrated alternate embodiments of the present invention. Like components are numbered as in  FIGS. 1-3  above, the discussion of which is incorporated by reference. In the apparatus  300  of  FIG. 4 , there is provided a flotation cell  75  which treats rejects stream  28  from the first centrifugal cleaning stage along with accepts stream  38 ′ from the third centrifugal cleaning stage. Stream  38 ′ is combined with rejects stream  28  and fed to the flotation stage where hydrophobic material is removed and an intermediate purified stream  28 ′ is produced. Stream  28 ′ is fed to the second stage  14  of centrifugal cleaners. The accepts stream from stage  14  is fed forward as stream  32 ″ and combined with stream  26  in thickening device  28 . The hydrophobic rejects ( 21 ′) from flotation stage ( 75 ) are removed from system  300 . 
     Apparatus  400  of  FIG. 5  resembles apparatus  200  of  FIG. 3  except that there is provided a preliminary stage  12 ′ of centrifugal cleaners, the accepts stream  26 ″ of which is utilized as the feed to stage  12 . Rejects stream  28 ″ of stage  12 ′ is combined with rejects stream  28  of stage  12  and fed to flotation stage  75 . Accepts stream  32 ′ of the second stage cleaners is fed forward with accepts stream  26  of stage  12 . The hydrophobic rejects ( 21 ′) from flotation stage ( 75 ) are removed from system  400 . 
     EXAMPLES 
     Pilot plant trials showed that flotation cells such as the Comer Cybercel® can successfully deink secondary centrifugal cleaner rejects, with better results obtained if the consistency is kept close to 0.6%. Consistency refers to weight percent fiber or associated solids such as ash unless the context indicates otherwise. Results on 42% office waste (Grade A) and 100% office waste (Grade B) are shown in Table 1. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Pilot Plant Results for Brightness Gain, Dirt + Ash 
               
               
                 Removal Efficiency on Grades A and B at Halsey 
               
               
                 and Results Used in Simulation Models 
               
             
          
           
               
                   
                   
                 Grade: 
                   
               
             
          
           
               
                   
                 A 
                 B 
                 Model 
               
               
                   
                   
               
             
          
           
               
                   
                 Consistency: 
                 0.69% 
                 0.90% 
                 0.62%   
               
               
                   
                 Brightness Gain: 
                 18.5% 
                  5.3% 
               
               
                   
                 Dirt Removal: 
                 77–89%       
                 65–87%       
                 80% 
               
               
                   
                 Ash removal: 
                   63% 
                   64% 
                 64% 
               
               
                   
                   
               
             
          
         
       
     
     A simulation model was used to calculate the impact of a Comer Cybercel® flotation cell to deink forward cleaner rejects on solids loss, ash removal and on removal efficiency of mid-dirt (&gt;150 microns) from a 1 st  washer to the deinked pulp (while running grade B at 336 tpd at the 1 st  washer): 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Impact of Flotation Cell on Solids Loss, Ash Loss, and 
               
               
                 Mid-dirt Removal Efficiency (according to the Simulation 
               
               
                 Model for 6 different configurations on Grade B) 
               
             
          
           
               
                   
                   
                   
                   
                 Mid-dirt 
               
               
                 Example 
                   
                 Solids loss 
                 Ash loss 
                 Eff. 
               
               
                   
               
             
          
           
               
                 1 
                 No Flotation cell 
                 8.9 
                 tpd 
                 0.8 tpd 
                 96.1% 
               
               
                 2 
                 Flotation cell on 2 nd   
                 2.7 
                 tpd 
                 0.9 tpd 
                 97.0% 
               
               
                   
                 stage Rejects 
               
               
                 3 
                 Flotation cell on 
                 6.7 
                 tpd 
                 1.9 tpd 
                 97.4% 
               
               
                   
                 1 st  stage Rejects 
               
               
                 4 
                 As 3 with 50% eff. in 
                 6.7 
                 tpd 
                 1.9 tpd 
                 97.7% 
               
               
                   
                 1 st  stage 
               
               
                 5 
                 Flotation cell on 1 st   
                 8.9 
                 tpd 
                 1.9 tpd 
                 97.7% 
               
               
                   
                 stage Rejects + 
               
               
                   
                 3 rd  stage accepts, 44% 
               
               
                   
                 eff. in 1 st  stage 
               
               
                 6 
                 Flotation cell on two 1 st   
                 11.8 
                 tpd 
                 2.8 tpd 
                 98.5% 
               
               
                   
                 stages 
               
               
                   
               
             
          
         
       
     
     The following indicators were used to evaluate the performance of the pilot plant:
         feed consistency.   brightness gain of handsheets from accepts compared to feed.   Dirt removal efficiency of small dirt (&lt;150 microns), mid-dirt (&gt;150 microns) and large dirt (&gt;200 microns).   Ash removal efficiency.       

     The results in Table 3 below for examples 7-14 (duplicate runs) show that even at 0.90% feed consistency it was possible to obtain 5.3% points brightness gain, 73% mid-dirt removal efficiency and 64% ash removal on Grade B. Operating the flotation cell at 0.69% consistency on Grade A, it was possible to obtain 8.1% points brightness gain, 79% mid-dirt removal efficiency and 63% ash removal. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Comer Pilot Plant Results on 2 nd  stage Cleaner Rejects 
               
             
          
           
               
                   
                 Feed 
                 Brightness 
                 Dirt + Ash Removal % 
                   
               
             
          
           
               
                 Example 
                 Anal. 
                 Cons. % 
                 Ash % 
                 Gain 
                 Small 
                 Mid 
                 Large 
                 Ash 
                 Comments 
               
               
                   
               
               
                 Grade B 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                  7 
                 1 
                 0.86 
                   
                 3.3 
                 88 
                 71 
                 64 
               
               
                   
                 2 
                   
                 4.4% 
                 5.8 
                 87 
                 74 
                 65 
                 59 
                 Accepts = 90% &gt; 200 m. 
               
               
                  8 
                 1 
                 0.88 
                   
                 5.4 
                 87 
                 74 
                 67 
               
               
                   
                 2 
                   
                 3.9% 
                 4.6 
                 86 
                 69 
                 57 
                 52 
                 Accepts = 99% &gt; 200 m. 
               
               
                  9 
                 1 
                 0.88 
                   
                 6.3 
                 88 
                 78 
                 74 
               
               
                   
                 2 
                   
                 5.9% 
                 5.0 
                 87 
                 73 
                 66 
                 68 
               
               
                 10 
                 1 
                 0.98 
                   
                 5.9 
                 89 
                 74 
                 61 
               
               
                   
                   
                   
                 3.8% 
                 5.7 
                 86 
                 69 
                 63 
                 77 
               
               
                   
                 Average 
                 0.90 
                 4.5% 
                 5.3 
                 87 
                 73 
                 65 
                 64 
               
               
                 Grade A 
               
               
                 11 
                 1 
                 0.53 
                   
                 7.3 
                 — 
                 — 
                 — 
               
               
                   
                 2 
                   
                 15.9% 
                 9.4 
                 92 
                 78 
                 72 
                   
                 Accepts = 95% &gt; 200 m. 
               
               
                 12 
                 1 
                 0.83 
                   
                 4.2 
                 88 
                 70 
                 60 
                 70 
               
               
                   
                 2 
                   
                 17.8% 
                 8.2 
                 87 
                 70 
                 64 
                   
                 Accepts = 90% &gt; 200 m. 
               
               
                 13 
                 1 
                 0.70 
                   
                 8.6 
                 89 
                 88 
                 92 
                 53 
               
               
                   
                 2 
                   
                 16.5% 
                 8.0 
                 89 
                 80 
                 80 
                   
                 Accepts = 74% &gt; 200 m. 
               
               
                 14 
                 1 
                 — 
                   
                 8.7 
                 91 
                 85 
                 87 
                 67 
               
               
                   
                 2 
                   
                 23.8% 
                 10.4 
                 89 
                 85 
                 85 
               
               
                   
                 Average 
                 0.69 
                 18.5% 
                 8.1 
                 89 
                 79 
                 77 
                 63 
               
               
                   
               
             
          
         
       
     
     The effect of incorporating a flotation stage in accordance with the present invention into a multistage forward cleaner system was evaluated with a computer model with respect to the systems illustrated in  FIGS. 1-5 . Results are summarized in the tables below. DIP refers to deinked pulp and DRE refers to dirt removal efficiency. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 System of FIG. 1 - Conventional Multi-Stage Cleaner System 
               
               
                 SUMMARY 
               
             
          
           
               
                   
                 Flow 
                 Cons. 
                   
                 Ash 
                 Ash 
                 Dirt &gt; 150 
                 Dirt &gt; 150 
               
               
                   
                 gpm 
                 % 
                 STPD 
                 % 
                 STPD 
                 ppm/1.2 g 
                 m 2 /day 
               
               
                   
                   
               
             
          
           
               
                 Washer 
                   
                 Thick Stock 
                 540 
                 10.37 
                 335.7 
                 2.53 
                 8.5 
                 720 
                 3310 
               
               
                   
                   
                 DWw 
                 4272 
                 0.03 
                 7.7 
                 7 
                 0.5 
                 1504 
                 158 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.63 
                 9.0 
                 738 
                 3468 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 738 
                 3468 
               
               
                 Dil. Water 
                   
                   
                 4741 
                 0.03 
                 8.5 
                 7.00 
                 0.60 
                 1504 
                 176 
               
               
                   
                 Total in 
                   
                 9553 
                   
                 351.9 
                   
                 9.15 
                   
                 3644 
               
               
                 1 st  Stage Cleaner 
                   
                 Accept 
                 9492 
                 0.60 
                 343.0 
                 2.43 
                 8.34 
                 596 
                 2798 
               
               
                   
                 Total out 
                 Accept 
                 9492 
                   
                 343.0 
                   
                 8.34 
                 596 
                 2798 
               
               
                   
                 Diff. 
                 In-out 
                 60 
                   
                 8.9 
                   
                 0.8 
                   
                 846 
               
               
                 5 th  Stage Cleaner 
                   
                 Rejects 
                 60 
                 2.46 
                 8.9 
                 9.04 
                 0.80 
                 6957 
                 847 
               
               
                   
                 Total 
                 Rejects 
                 60 
                   
                 8.9 
                   
                 0.8 
                   
                 847 
               
             
          
           
               
                   
                   
                 Cleaner to 
                   
                   
                   
                   
                   
                 30.0% DRE 
               
               
                   
                   
                 Press DRE: 
               
             
          
           
               
                 Dil. Water 
                   
                 Out 
                 9334 
                 0.03 
                 16.8 
                   
                   
                   
                   
               
               
                 Press 
                   
                 Out 
                 158.5 
                 35.1 
                 326.2 
                 1.9 
                 6.2 
                 417 
                 1863 
               
             
          
           
               
                   
                   
                 Press to 
                   
                   
                   
                   
                   
                 93.3% DRE 
               
               
                   
                   
                 DIP DRE: 
               
             
          
           
               
                 DIP 
                   
                   
                   
                   
                   
                   
                   
                 28 
                   
               
             
          
           
               
                 PROCESS 
                   
                 Washer - DIP 
                   
                   
                   
                   
                   
                 96.1% DRE 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 System of FIG. 2 - Multi-Stage Cleaner System with Flotation Cell on 2 nd  Stage Rejects 
               
               
                 SUMMARY 
               
             
          
           
               
                   
                 Flow 
                 Cons. 
                   
                 Ash 
                 Ash 
                 Dirt &gt; 150 
                 Dirt &gt; 150 
               
               
                   
                 gpm 
                 % 
                 STPD 
                 % 
                 STPD 
                 ppm/1.2 g 
                 m 2 /day 
               
               
                   
                   
               
             
          
           
               
                 Washer 
                   
                 Thick Stock 
                 540 
                 10.37 
                 335.7 
                 2.53 
                 8.5 
                 720 
                 3310 
               
               
                   
                   
                 DWw 
                 4272 
                 0.03 
                 7.7 
                 0.7 
                 0.1 
                 150.4 
                 16 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.5 
                 708 
                 3326 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 708 
                 3327 
               
               
                 Dil. Water 
                   
                   
                 5666 
                 0.03 
                 10.2 
                 0.70 
                 0.07 
                 150 
                 21 
               
               
                   
                 Total in 
                   
                 10478 
                   
                 353.5 
                   
                 8.62 
                   
                 3348 
               
               
                 1 st  Stage Cleaner 
                   
                 Accept 
                 9492 
                 0.57 
                 327.0 
                 2.25 
                 7.34 
                 461 
                 2063 
               
               
                 3 rd  Stage Cleaner 
                   
                 Accept 
                 927 
                 0.43 
                 23.8 
                 1.39 
                 0.33 
                 373 
                 121 
               
               
                   
                 Total out 
                 Accept 
                 10419 
                 0.56 
                 350.8 
                   
                 7.68 
                 455 
                 2185 
               
               
                   
                 Diff. 
                 In-out 
                 58 
                   
                 2.7 
                   
                 0.9 
                   
                 1164 
               
               
                 Comer 
                   
                 Rejects 
                 42 
                 0.93 
                 2.3 
                 34.77 
                 0.81 
                 32762 
                 1050 
               
               
                 5 th  Stage Cleaner 
                   
                 Rejects 
                 16 
                 0.36 
                 0.3 
                 32.88 
                 0.11 
                 23680 
                 113 
               
               
                   
                 Total 
                 Rejects 
                 58 
                   
                 2.7 
                   
                 0.9 
                   
                 1163 
               
             
          
           
               
                   
                   
                 Cleaner to 
                   
                   
                   
                   
                   
                 30.0% DRE 
               
               
                   
                   
                 Press DRE: 
               
             
          
           
               
                 Dil. Water 
                   
                 Out 
                 10261 
                 0.03 
                 18.5 
                   
                   
                   
                   
               
               
                 Press 
                   
                 Out 
                 158.5 
                 35.1 
                 332.4 
                 1.9 
                 6.3 
                 318 
                 1449 
               
             
          
           
               
                   
                   
                 Press to 
                   
                   
                   
                   
                   
                 93.3% DRE 
               
               
                   
                   
                 DIP DRE: 
               
             
          
           
               
                 DIP 
                   
                   
                   
                   
                   
                   
                   
                 21.3 
                   
               
             
          
           
               
                 PROCESS 
                   
                 Washer - DIP 
                   
                   
                   
                   
                   
                 97.0% DRE 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 System of FIG. 3 - Multi-Stage Cleaner System with Flotation Cell on 1 st  Stage Rejects 
               
               
                 SUMMARY 
               
             
          
           
               
                   
                 Flow 
                 Cons. 
                   
                 Ash 
                 Ash 
                 Dirt &gt; 150 
                 Dirt &gt; 150 
               
               
                   
                 gpm 
                 % 
                 STPD 
                 % 
                 STPD 
                 ppm/1.2 g 
                 m 2 /day 
               
               
                   
                   
               
             
          
           
               
                 Washer 
                   
                 Thick Stock 
                 540 
                 10.37 
                 335.7 
                 2.53 
                 8.5 
                 720 
                 3310 
               
               
                   
                   
                 DWw 
                 4272 
                 0.03 
                 7.7 
                 0.7 
                 0.1 
                 150.4 
                 16 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.5 
                 708 
                 3326 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 708 
                 3327 
               
               
                 Dil. Water 
                   
                   
                 7449 
                 0.03 
                 13.4 
                 0.70 
                 0.09 
                 150 
                 28 
               
               
                   
                 Total in 
                   
                 12261 
                   
                 356.8 
                   
                 8.64 
                   
                 3355 
               
               
                 1 st  Stage Cleaner 
                   
                 Accept 
                 9492 
                 0.50 
                 282.9 
                 2.13 
                 6.04 
                 443 
                 1715 
               
               
                 2 nd  Stage Cleaner 
                   
                 Accept 
                 2679 
                 0.42 
                 67.1 
                 1.12 
                 0.75 
                 191 
                 175 
               
               
                   
                 Total out 
                 Accept 
                 12171 
                 0.48 
                 350.1 
                   
                 6.79 
                 394 
                 1890 
               
               
                   
                 Diff. 
                 In-out 
                 90 
                   
                 6.7 
                   
                 1.85 
                   
                 1465 
               
               
                 Comer 
                   
                 Rejects 
                 74 
                 1.45 
                 6.4 
                 25.91 
                 1.66 
                 15279 
                 1337 
               
               
                 5 th  Stage Cleaner 
                   
                 Rejects 
                 16 
                 0.28 
                 0.3 
                 69.31 
                 0.19 
                 34056 
                 128 
               
               
                   
                 Total 
                 Rejects 
                 90 
                   
                 6.7 
                   
                 1.85 
                   
                 1465 
               
             
          
           
               
                   
                   
                 Cleaner to 
                   
                   
                   
                   
                   
                 30.0% DRE 
               
               
                   
                   
                 Press DRE: 
               
             
          
           
               
                 Dil. Water 
                   
                 Out 
                 12012 
                 0.03 
                 21.6 
                   
                   
                   
                   
               
               
                 Press 
                   
                 Out 
                 158.5 
                 35.1 
                 328.5 
                 1.9 
                 6.2 
                 276 
                 1241 
               
             
          
           
               
                   
                   
                 Press to 
                   
                   
                   
                   
                   
                 93.3% DRE 
               
               
                   
                   
                 DIP DRE: 
               
             
          
           
               
                 DIP 
                   
                   
                   
                   
                   
                   
                   
                 18.5 
                   
               
             
          
           
               
                 PROCESS 
                   
                 Washer - DIP 
                   
                   
                   
                   
                   
                 97.4% DRE 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 System of FIG. 4 - Multi-Stage Cleaner System with Flotation on 1 st  St. Rejects + 3 rd  St. Accepts 
               
               
                 SUMMARY 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                 Dirt &gt; 150 
                   
               
               
                   
                 Flow 
                 Cons. 
                   
                 Ash 
                 Ash 
                 ppm/1.2 g 
                 Dirt &gt; 150 
               
               
                   
                 gpm 
                 % 
                 STPD 
                 % 
                 STPD 
                 Double-dirt 
                 m 2 /day 
               
               
                   
                   
               
             
          
           
               
                 Washer 
                   
                 Thick Stock 
                 546 
                 10.37 
                 339.5 
                 2.51 
                 8.52 
                 1489 
                 6921 
               
               
                   
                   
                 DWw 
                 4266 
                 0.015 
                 3.8 
                 0.7 
                 0.0 
                 300 
                 16 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 1476 
                 6937 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 1476 
                 6937 
               
               
                 Dil. Water 
                   
                   
                 7543 
                 0.015 
                 6.8 
                 0.70 
                 0.05 
                 300 
                 28 
               
               
                   
                 Total in 
                   
                 12355 
                   
                 350.1 
                   
                 8.60 
                   
                 6965 
               
               
                 1 st  Stage Cleaner 
                   
                 Accept 
                 10100 
                 0.46 
                 279.2 
                 2.15 
                 6.01 
                 816 
                 3118 
               
               
                 2 nd  Stage Cleaner 
                   
                 Accept 
                 2104 
                 0.50 
                 62.9 
                 1.16 
                 0.73 
                 346 
                 298 
               
               
                   
                 Total out 
                 Accept 
                 12204 
                 0.47 
                 342.2 
                 1.97 
                 6.74 
                 729 
                 3416 
               
               
                   
                 Diff. 
                 In-out 
                 151 
                   
                 8.0 
                   
                 1.9 
                   
                 3549 
               
               
                 Comer 
                   
                 Rejects 
                 143 
                 0.91 
                 7.8 
                 23.75 
                 1.85 
                 31464 
                 3347 
               
               
                 5 th  Stage Cleaner 
                   
                 Rejects 
                 8 
                 0.41 
                 0.2 
                 7.68 
                 0.02 
                 72988 
                 202 
               
               
                   
                 Total 
                 Rejects 
                 151 
                   
                 8.0 
                   
                 1.9 
                   
                 3549 
               
             
          
           
               
                   
                   
                 Cleaner to 
                   
                   
                   
                   
                   
                 30.0% DRE 
               
               
                   
                   
                 Press DRE: 
               
             
          
           
               
                 Dil. Water 
                   
                 Out 
                 12045 
                 0.015 
                 10.8 
                   
                   
                   
                   
               
               
                 Press 
                   
                 Out 
                 158.5 
                 35.1 
                 331.3 
                 1.9 
                 6.3 
                 511 
                 2316 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Double-dirt 
               
             
          
           
               
                   
                   
                 Press to 
                   
                   
                   
                   
                   
                 93.3% DRE 
               
               
                   
                   
                 DIP DRE: 
               
             
          
           
               
                 DIP 
                   
                   
                   
                   
                   
                   
                   
                 34 
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Double-dirt 
               
             
          
           
               
                 PROCESS 
                   
                 Washer - DIP 
                   
                   
                   
                   
                   
                 97.7% DRE 
               
               
                   
               
               
                 Note: 
               
               
                 Mid-dirt level at the Gyro was doubled from 738 to 1476 ppm in this simulation, which results in double-dirt figures at the press and in the DIP. (Divide by 2 for comparison with simulations in Tables 4–6). 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 System of FIG. 5 - Multi-Stage Cleaner System with Flotation Cell on both 1 st  Stage Rejects. 
               
               
                 SUMMARY 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                 Dirt &gt; 150 
                   
               
               
                   
                 Flow 
                 Cons. 
                   
                 Ash 
                 Ash 
                 ppm/1.2 g 
                 Dirt &gt; 150 
               
               
                   
                 gpm 
                 % 
                 STPD 
                 % 
                 STPD 
                 double-dirt 
                 m 2 /day 
               
               
                   
                   
               
             
          
           
               
                 Washer 
                   
                 Thick Stock 
                 546 
                 10.37 
                 339.5 
                 2.51 
                 8.5 
                 1489 
                 6920 
               
               
                   
                   
                 DWw 
                 4266 
                 0.015 
                 3.8 
                 0.7 
                 0.0 
                 300 
                 16 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.3 
                 2.49 
                 8.5 
                 1476 
                 6935 
               
               
                 Gyro 
                   
                 Accept 
                 4812 
                 1.19 
                 343.4 
                 2.49 
                 8.55 
                 1476 
                 6937 
               
               
                 Dil. Water 
                   
                   
                 7431 
                 0.015 
                 6.7 
                 0.70 
                 0.05 
                 300 
                 27 
               
               
                   
                 Total in 
                   
                 12243 
                   
                 350.0 
                   
                 8.60 
                   
                 6964 
               
               
                 1 st  Stage Cleaner 2 
                   
                 Accept 
                 8417 
                 0.44 
                 223.0 
                 1.89 
                 4.21 
                 523 
                 1596 
               
               
                 2 nd  Stage Cleaner 
                   
                 Accept 
                 3619 
                 0.53 
                 115.3 
                 1.36 
                 1.56 
                 388 
                 612 
               
               
                   
                 Total out 
                 Accept 
                 12036 
                 0.47 
                 338.3 
                   
                 5.77 
                 477 
                 2208 
               
               
                   
                   
                   
                 12036 
                 0.55 
                 400.0 
               
               
                   
                 Diff. 
                 In-out 
                 208 
                   
                 11.8 
                   
                 2.8 
                   
                 4756 
               
               
                 Comer 
                   
                 Rejects 
                 192 
                 0.99 
                 11.4 
                 24.65 
                 2.81 
                 28167 
                 4389 
               
               
                 5 th  Stage Cleaner 
                   
                 Rejects 
                 16 
                 0.39 
                 0.4 
                 8.54 
                 0.03 
                 71490 
                 367 
               
               
                   
                 Total 
                 Rejects 
                 208 
                   
                 11.8 
                   
                 2.8 
                   
                 4756 
               
             
          
           
               
                   
                   
                 Cleaner to 
                   
                   
                   
                   
                   
                 30.0% DRE 
               
               
                   
                   
                 Press DRE: 
               
             
          
           
               
                 Dil. Water 
                   
                 Out 
                 11856 
                 0.015 
                 10.7 
                 0.70 
                 0.1 
                   
                   
               
               
                 Press 
                   
                 Out 
                 180.0 
                 35.16 
                 327.6 
                 1.74 
                 5.7 
                 334 
                 1497 
               
               
                   
                   
                   
                   
                   
                 379.5 
                   
                   
                 double-dirt 
               
             
          
           
               
                   
                   
                 Press to 
                   
                   
                   
                   
                   
                 93.3% DRE 
               
               
                   
                   
                 DIP DRE: 
               
             
          
           
               
                 DIP 
                   
                   
                   
                   
                   
                   
                   
                 22 
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 double-dirt 
               
             
          
           
               
                 PROCESS 
                   
                 Washer - DIP 
                   
                   
                   
                   
                   
                 98.5% DRE 
               
               
                   
               
               
                 Note 
               
               
                 Mid-dirt level at the Gyro was doubled from 738 to 1476 ppm in this simulation, which results in double-dirt figures at the press and in the DIP. (Divide by 2 for comparison with simulations in Tables 4–6). 
               
             
          
         
       
     
     The process of the present invention is particularly useful in connection with thin stock processing of recycle fiber, wherein the aqueous stream has a consistency of less than about 1% during such processing. Thin stock processing is employed in connection with commercial recycling operations, following pulping, thick stock cleaning and washing prior to thickening and bleaching, for example. In a preferred thin stock process in accordance with the invention, the thin stock is screened in a screening device with a screening dimension of less than about 10 mils to generate a screened accepts aqueous stream which, in turn, is fed to a hybrid sytem such as shown in  FIG. 4 , for example. The screening dimension of the screening device is the slot width of a slotted screen basket, or could be the hole diameter of an alternate screening device. 
     Slotted screening devices are preferred and are well known. There is shown in  FIG. 6  such a slotted screening device  500  provided with a feed port  510 , a screen  520  provided with a plurality of elongated slots such as slots  530 , a rejects outlet  540  as well as an accepts outlet  550 . A feed stream is fed at  510  while the rejects stream is withdrawn at  540  and the screened accepts aqueous stream  560  exits outlet  550 . Accepts stream  560  may then be fed forward to a first stage bank of centrifugal cleaners for further dilution and processing as described above. 
     Slotted screens having a slot width of 8 mils or less may be employed. In commercial processes, fine slotted screens of 6 mils are frequently employed. 
     A commercial operation utilizing thin stock processing as part of its secondary fiber processing was operated with a hybrid system as shown and described in connection with  FIG. 4  above. The multistage array of forward cleaners was fed with thin stock which had been screened with 6 mil slotted screens prior to being fed to the forward cleaners. The particular arrangement included in sequence fine slotted screens, gyrocleans followed by the forward cleaner/flotation cell system. The flotation cell employed was a Comer-Cybercell™ device which is preferably operated without diffuser plates. The system was installed along with expansion of a disk thickener downstream of thin stock processing of the fiber. As a result of this project the cleaners started performing better (improved dirt removal efficiency) and the hybrid cleaner-flotation cell removed approximately 80% of the dirt, 63% of the stickies and 53% of the ash in the Comer feed with a brightness increase of 2.4% points. Process mid dirt removal efficiency increased 2.4% (from 96.9% to 98.3%) when running mixed office waste (“MOW”) recycle fiber at 540 ton per day (tpd) input rate. The paper machines have run without stickies problems for 8 months since the Comer cell came on line. 
     The new treatment protocol operated well on a furnish containing 100% mixed office waste (MOW) as shown in Table 9, which compares mid dirt removal efficiency (MDRE)&gt;0.02-0.5 mm 2  before and after Comer flotation cell start-up: 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Mid Dirt Removal Efficiency Before and After Start-up 
               
               
                 of Hybrid Cleaner - Comer Flotation Cell on a Furnish 
               
               
                 Containing 100% Mixed Office Waste (MOW) 
               
             
          
           
               
                   
                 Mid Dirt Removal Efficiency of Dirt &gt; 0.02–0.5 mm 2   
               
             
          
           
               
                 Time 
                   
                   
                 Comer- 
                   
                 Dis- 
                 Disperger - 
               
               
                 Period 
                 Process 
                 Cleaner 
                 Cleaner 
                 Thickener 
                 perger 
                 DIP 
               
               
                   
               
               
                 Before 
                 96.4% 
                 45% 
                 53% - 
                 21% 
                 74% 
                 70% 
               
               
                 Hybrid 
                   
                   
                 clnr 
               
               
                 After 
                 97.7% 
                 50% 
                 79% 
                 13% 
                 78% 
                 73% 
               
               
                 Hybrid 
               
               
                   
               
             
          
         
       
     
     The Effective Residual Ink Concentration (ERIC) also improved throughout the whole deinking system as can be seen in  FIG. 7 . ERIC levels in the deinked pulp dropped from 76 ppm without the inventive thin stock cleaning method to 21 ppm with the hybrid fiber when running MOW fiber at 365 tpd. 
     The performance of the hybrid cleaner—flotation cell is summarized in Table 10. It shows 2.4% points brightness increase, 82% total dirt removal efficiency (TDRE) and 53% ash reduction across the combination. The quality of the 2 nd  stage cleaner accepts was even better than the first stage cleaner accepts. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Hybrid Cleaner - Flotation Cell Results Operating On 1 st  Stage Cleaner Rejects 
               
             
          
           
               
                 Unit 
                 Feed 
                 Brightness 
                 Dirt Removal Efficiency 
                 Ash 
               
             
          
           
               
                 Operation 
                 Cons 
                 Ash 
                 Br.* 
                 Gain 
                 Small 
                 MDRE 
                 TDRE 
                 Removal 
               
               
                   
               
               
                 Comer 
                 0.65% 
                 2.0% 
                 70.9% 
                 2.0% pts 
                 78.8% 
                 64.3% 
                 71.0% 
                 50% 
               
               
                 St. 2 Cleaner 
                 0.58% 
                 1.0% 
                 72.9% 
                 0.4% pts 
                 47.2% 
                 51.2% 
                 49.7% 
                 10% 
               
             
          
           
               
                   
                 Accepts 
                   
                   
                   
                   
                   
               
             
          
           
               
                 Comer-clnr 
                 0.49% 
                 0.9% 
                 73.3% 
                 2.4% pts 
                 85.3% 
                 79.1% 
                 82.0% 
                 53% 
               
               
                   
               
               
                 *Br. Is brightness of feed and accepts, MDRE is mid dirt removal efficiency and TDRE is total dirt removal efficiency. 
               
             
          
         
       
     
     In the plant, the number of stickies in the deinked pulp are counted 3 times per shift by screening a 150 gram sample of deinked pulp on a flat screen with 0.006 inch slots. The count for MOW based fiber averaged 3.3 stickies per 150 grams before installation of the hybrid system and improved to ˜1.3 stickies per 150 grams after implementation of the process. 
     The area of stickies retained on a Pulmac® screen with 4 mil slots was also measured for selected samples. The uncompressed stickies are then counted using a microscope equipped with a grid to estimate the size of the stickies. Two sets of samples were obtained at 4 locations in the overall pulp-cleaning process at a first date, prior to installation and operation of the hybrid cleaner system (Data Set A), at 12 locations at a second date, also prior to installation of the hybrid cleaner system (Data Set B) and again at 8 locations in the process at a third date while the hybrid system shown in  FIG. 4  was operating (Data Set C). The average results of 20 gram stock samples for each location are shown in Table 11. The improvement in total stickies removal efficiency from 95.0% to 98.5% is attributed in part to the improved operation of the hybrid forward cleaning system over forward cleaners alone. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Comparative Stickies Removal 
               
             
          
           
               
                 Process Location and 
                 Pulmac Stickies (mm 2 /100 grams) 
                 Total Removal 
               
             
          
           
               
                 Data Set 
                 Small 
                 Large 
                 X-Large 
                 Total 
                 Efficiency 
               
               
                   
               
             
          
           
               
                 Data Set A 
               
             
          
           
               
                 High Density Cleaner 
                 72 
                 219 
                 119 
                 409 
                   
               
               
                 1 st  Washer - out 
                 76.9 
                 51.3 
                 10 
                 138 
                 1 st  washer -DIP = 85.3% 
               
               
                 Disperger - in 
                 49.1 
                 0 
                 0 
                 49 
               
               
                 Deinked Pulp 
                 20.3 
                 0 
                 0 
                 20 
                 HDCl-DIP = 95.0% 
               
             
          
           
               
                 Data Set B 
               
             
          
           
               
                 1 st  Washer - out 
                 64.0 
                 13.3 
                 0 
                 77 
                 1 st  washer -DIP = 91.0% 
               
               
                 Fine Slotted Screens - out 
                 50.8 
                 3.1 
                 0 
                 54 
               
               
                 St. 1 Cleaner - in 
                 42.9 
                 0.5 
                 0 
                 43 
               
               
                 St. 1 Cleaner - out 
                 36.9 
                 2.8 
                 0 
                 40 
               
               
                 St. 2 Cleaner - out 
                 43.6 
                 0 
                 0 
                 44 
               
               
                 Disperger - in 
                 48.9 
                 2.7 
                 0 
                 52 
               
               
                 Disperger - out 
                 31.9 
                 0 
                 0 
                 32 
               
               
                 Deinked Pulp 
                 6.8 
                 0 
                 0 
                 7 
               
             
          
           
               
                 Data Set C 
               
             
          
           
               
                 High Density Cleaner 
                 102 
                 168 
                 37 
                 306 
                   
               
               
                 1 st  Washer - out 
                 54.7 
                 10.9 
                 0 
                 66 
                 1 st  washer -DIP = 93.0% 
               
               
                 Fine Slotted Screens - out 
                 53.1 
                 0 
                 0 
                 53 
               
               
                 Comer cell - Feed 
                 48.8 
                 0 
                 0 
                 49 
                 Comer in-out = 62% 
               
               
                 Comer Cell - Accepts 
                 18.1 
                 0.6 
                 0 
                 19 
               
               
                 Disperger - in 
                 35.9 
                 0 
                 0 
                 36 
                 Disp. in-out = 34% 
               
               
                 Disperger - out 
                 21.6 
                 0 
                 0 
                 22 
               
               
                 Deinked Pulp 
                 4.6 
                 0 
                 0 
                 5 
                 HDCl-DIP = 98.5% 
               
               
                   
               
               
                 (Small stickies = &lt;0.28 mm 2 ; Large stickies = 0.28–1.47 mm 2 ; X-Large stickies = &gt;1.47 mm 2 ) 
               
             
          
         
       
     
     It can be seen from Table 11 that the Comer cell was particularly effective in removing small stickies, removing over 60 percent of the stickies in the feed to the flotation cell. 
     While the invention has been illustrated in connection with numerous embodiments, modifications to those embodiments within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to those of skill in the art.