Patent Publication Number: US-2009223873-A1

Title: Screening apparatus for a contaminated fibrous suspension and its use

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of PCT application No. PCT/EP2007/007964, entitled “SCREENING APPARATUS FOR A CONTAMINATED FIBROUS SUSPENSION AND ITS USE”, filed Sep. 13, 2007, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a screening apparatus for contaminated fibrous suspensions. 
     2. Description of the Related Art 
     An object of such a screening apparatus is to get undesired contaminants out of an aqueous fibrous suspension which, for example, can be obtained from waste paper. As is known, in addition to the desired fibrous materials, waste paper contains a more or less large quantity of contraries, which must not get into the paper. As a rule, a plurality of separating processes is required in order to remove the various types of contraries in the different sections of the preparation process. In many cases, the occurrence of blockages of the preparation system by contraries can be forestalled only by flushing cycles being set up, which understandably can lead to loading of the preparation operation, to quantity surges and to fiber losses. 
     At the start of the stock preparation, the raw materials are usually mixed with water in a pulper and comminuted to such an extent that they can be pumped out of the pulper as a suspension. Even if, in many cases, pre-cleaning is carried out in the pulper, a considerable quantity of contraries still remain in the suspension that are pumped out and get into the apparatus used for the preparation. 
     In the scientific article, “Erfahrungen mit einem System zur Stofflöserentsorgung” [Experiences with a system for pulper waste disposal] by Hans-Bernhard Winterstein, which appeared in DAS PAPIER vol. 5, 1993, pages 236 to 239, a waste disposal machine having a screen plate at the top is described. The inlet into this machine is oriented downwards, specifically directly in the direction towards the heavy fraction sluice. Lightweight fractions, in particular of plastic foils, accumulate in the housing of the waste disposal apparatus and are flushed out cyclically. To this end, the contents are diluted with washing water until the washing water consistency is approximately reached. 
     German Patent Document DE 198 25 669 A1 shows a screening apparatus for pulping and sorting waste paper, which likewise contains a flat screen located at the top, which is kept free by a rotor. The feed into the housing is carried out tangentially. At the bottom, there is a contraries outlet leading obliquely downwards and having a sluice. 
     What is needed in the art is a screening apparatus with which the contraries can be sorted out successfully and operationally reliably. The intention is for the greatest possible range of contraries to be covered. The screening apparatus is in particular to be suitable for pulping specks and pieces of paper. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention, the rotor movement produces a rotational flow which has an axis of rotation concentric with the rotor axis. This rotational flow in the case of the subject-matter of the invention is not fitted concentrically in the housing but at an oblique angle. It is beneficial if, in addition, an eccentric arrangement of rotor and housing is chosen. 
     The screening apparatus according to an embodiment of the invention is capable of retaining contraries in the housing with the aid of the screen and of removing them from the fibrous suspension. As compared with the prior art, it has the advantage of improving the pulping of specks and paper pieces, also the separation of coatings and printing inks. In addition, lower wear is possible, since there is barely any risk left that heavy fractions will stay for a long time on a circulation path similar to a circle in the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its advantages will be explained by using drawings, in which: 
         FIG. 1  shows a screening apparatus that according to an embodiment of the present invention, sectioned in a side view; and 
         FIG. 2  shows schematics relating to the use of the screening apparatus according to the invention in waste paper preparation. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a screening apparatus of the present invention in a typically upright position of use, although it could also be arranged horizontally or in another orientation. It contains a housing  1 , which includes a main part  7 , a conical adjoining part  8  located above it and a conical part  9  located below main part  7 . The internal volume of main part  7  is considerably more than 30% or even more than half the total internal housing volume. Main part  7  has a cylindrical shape with a centerline  11  which, in relation to axis  12  of rotor  4 , is arranged at an oblique angle α, which can be chosen between 1° and 60°, being illustrated here about 12°. Angle α preferably lies between 5° and 25°. Adjoining part  8  includes a truncated cone which is concentric with axis  12  and widens at the bottom and which adjoins screen  3  at the top and, the bottom of the cone adjoins main part  7  with a transition  14 . Transition  14  runs at right angles to center line  11  of main part  7  and is therefore intersected obliquely by the truncated cone. As a result, there is an eccentricity between main part  7  and the truncated cone. 
     In the position of use of the apparatus, axis  12  can be upright with respect to vertical axis  13  at an angle β which lies between 0° and 30°, and preferably between 10° and 20°, here it is at 15°. Arranged in adjoining part  8  of housing  1  and concentrically with its centerline  12  is a rotor  4 , which is rotatingly driven by a drive set located above, but not shown. Rotor  4  is used both to generate a rotational flow and also for the purpose of keeping screen  3 , situated on the upper part of housing  1 , free of blockages, for which reason rotor  4  is moved along close to the feed side of screen  3 . Screen  3  divides the interior of housing  1  off from the accepts chamber  2  located above, from which the stock accumulated therein can be led out through an accepts outlet  5 . Screen  3  is a planar disc provided with screen openings  17  but can also have the form of a flat truncated cone. In the lower part of housing  1  there is an outlet opening  6  leading obliquely downwards for the contraries. It is beneficial to terminate housing  1  at the bottom towards the outlet opening  6  in such a way that any heavy fractions that have reached the bottom are able to slide out of conical part  9  into outlet opening  6 . In order to keep this region free of deposits, the addition of flushing water through a flushing water connection  27  is provided. 
     At one end of main part  7 , rotor  4  is spaced therefrom at a minimum spacing. The spacing is at most 50% of the diameter of rotor  4 . 
     As a rule, the screening apparatus will be operated with positive pressure, so that the contraries emerge automatically. In this case, the positive pressure can regulate the quantity of contraries drawn off. However, it is also possible to provide the contraries outlet  6  with a shut-off element, not shown, to open and close it cyclically. It is also contemplated that a metering device can be included which conveys a specific quantity continuously out of the interior without any blockages. 
     As already mentioned, there is the possibility of both cleaning and also further pulping of the fibrous suspension fed in, via an inlet connector  10 , with particular advantage in the same apparatus. For instance, it is expedient, in the screening apparatus of the type described here, to perform further comminution of the solid material contained in the suspension, in order to improve the ability to sort the material. In this case, it is necessary to draw a balance between the damage which arises as a result of the comminution or the contraries and the benefit which can be achieved from the higher level of separation of contraries and fibrous webs. This consideration also includes the size of the screen opening  17  chosen in screen  3 . In the cases in which further comminution of defibring of the materials found in the suspension is desired, the result is a very simple possible way of implementing this. Specifically, on the periphery of rotor  4 , provided with vanes  15 , baffle pieces  16  are then fitted which, in interaction with the vane tips, are able to effect gentle comminution. 
     Openings  17  in screen  3  are round with a minimum diameter of between 10 mm to 20 mm. Alternatively, the minimum diameter may lie between 2 mm and 5 mm. 
     The possible uses of the screening apparatus according to the invention are explained by using a plant example, as illustrated in  FIG. 2 . Here, the starting point is pulper  18  in which paper stock, for example waste paper, is mixed with water and changed into a suspension. In its bottom region, pulper  18  is equipped with a screen, not shown, through which part of the suspension passes into an annular chamber  21  and is processed further as fibrous suspension  22 . 
       FIG. 2  also shows the extraction of a contaminated fibrous suspension, which has not passed through the screen of pulper  18 , through a sedimentation tank  20 , and then the forwarding of the suspension freed of coarse heavy fractions  24  in this way into a screening apparatus  19  according to the present invention. Screening apparatus  19  here substantially has the task of pulping the stock further and of separating off a stream  25  of contraries, in order, in this way, to form a clean accepts suspension  26  which has passed through the screen of screening apparatus  19 . The stream  25  of contraries passes into a re-sorting apparatus, for example a sorting drum  23 , in which a separation between contraries  28  and fibrous suspension  30  is carried out, it being possible, for example, for this fibrous suspension  30  to be led back into pulper  18 . 
     It is to be noted that  FIG. 2  is intended to show only one example for the appropriate use of the subject matter of the invention and the possibility of the new apparatus. The diagram illustrates only the most important of the method steps, the apparatuses which are sued for this purpose being only indicated and all of the details of the conveying and regulating devices are not shown. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.