Patent Publication Number: US-6221265-B1

Title: Method and device for concentrating liquid-drenched material

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for concentrating liquid-drenched material, particularly for de-watering fiber suspensions, in which the material is formed into a string embraced by a straining cloth and rolled while covered with that cloth. The present invention also relates to apparatus suitable for carrying out this method. 
     BACKGROUND OF THE INVENTION 
     A method and an apparatus for concentrating liquid-drenched material by rolling a string of that material while the string is embraced by an endless straining cloth belt are known, for instance, from U.S. Pat. No. 4,017,398. Apparatus of this type which are known are encumbered with certain drawbacks. For instance, a single straining cloth belt which embraces a material string has the tendency to rupture at the edge regions of the string when rolling at high pressure, and generally has a width which is more than twice the breadth of the rolled material string, resulting in large space requirements. 
     An object of the present invention is to provide a novel method and novel apparatus with which the aforesaid drawbacks are avoided at least to a substantial extent. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, this and other objects have now been realized by the invention of a method for the concentration of a dilute material by forming the dilute material into a concentrated layer having a predetermined width, the method comprising enclosing the dilute material between a first straining belt having a first width which is insufficient to completely enclose the concentrated layer and including a pair of longitudinal edges and a center portion, and a second straining belt having a second width which is insufficient to completely enclose the concentrated layer, and including a pair of longitudinal edges, moving the first and second straining belts through first and second endless paths, the first width being greater than the second width, causing the pair of longitudinal edges of the first straining belt to overlap the pair of longitudinal edges of the second straining belt in an initial concentration stage, unfolding the pair of longitudinal edges of the first straining belt, and further compressing the concentrated layer against the first straining belt in a further concentration stage. In a preferred embodiment, the dilute material comprises a fiber suspension. 
     In accordance with one embodiment of the method of the present invention, the further compressing of the concentrated layer comprises compressing the concentrated layer between the first straining belt and a third straining belt having a third width and moving in a third endless path, the third width being greater than the second width. 
     In accordance with another embodiment of the method of the present invention, causing of the pair of longitudinal edges of the first straining belt to overlap the pair of longitudinal edges of the second straining belt comprises folding the central portion of the first straining belt over a first transverse folding edge having a first end and a second end, and folding each of the pair of longitudinal edges of the first straining belt over a second folding edge extending obliquely forward and outward in the direction of movement of the first straining belt and over a third folding edge extending obliquely forward and inward in the direction of movement of the first straining belt, whereby the pair of longitudinal edges of the first straining belt are folded over the first and third folding edges first inwardly over the central portion of the first straining belt and then parallel to the center portion of the first straining belt. 
     In accordance with another embodiment of the method of the present invention, unfolding of the pair of longitudinal edges of the first straining belt comprises folding the pair of longitudinal edges of the first straining belt outward and rearward around a third folding edge and a second folding edge and folding the central portion of the first straining belt back over a first folding edge. 
     In accordance with the present invention, apparatus has also been devised for the concentration of dilute material by forming the dilute material into a concentrated layer having a predetermined width, the apparatus comprising a first straining belt having a first width which is insufficient to completely enclose the concentrated layer, and a pair of longitudinal edges and a central portion, and having a first endless path, a second straining belt having a second width which is insufficient to completely enclose the concentrated layer, and a pair of longitudinally extending edges, and having a second endless path, the first width being greater than the second width, enclosing means for causing the longitudinal edges of the first straining belt to be folded over the longitudinal edges of the second straining belt whereby the first and second straining belts enclose the concentrated layer in an initial concentration stage, and secondary concentration means comprising means for unfolding the longitudinal edges of the first straining belt whereby the concentrated layer is further compressed against the first straining belt in a further concentration stage. Preferably, the dilute material comprises a fiber suspension. 
     In accordance with one embodiment of the apparatus of the present invention, the apparatus includes a third straining belt having a third width and a third endless path, the third width being greater than the second width, and the third straining belt disposed for compressing the concentrated layer between the first straining belt and the third straining belt in the further concentration stage. 
     In accordance with the present invention a method has been devised in which at least a terminating part of the concentration process effected by rolling is carried out with the string of material located between outwardly spread, single sheets of straining cloth, and wherein 
     for the purpose of enclosing the string of material there is used two belts of straining cloth, each travelling in a respective endless path, and each having a width which alone is insufficient to fully enclose the string of material; 
     the string is enclosed by a narrow belt and a broader belt of straining cloth, and the longitudinally extending edge portions of the broader web are caused to overlap the longitudinally extending edge portions of the narrower belt; and wherein 
     at least the broader web is spread out to form a single straining cloth sheet subsequent to the initial stage of the concentration process, and is also used during the remainder of said concentration process. 
     The present inventive method places no great strain on the straining cloth belts, and enables the material to be concentrated at high roll pressures, since the terminating concentration process is carried out with the string of material located between outwardly spread, single sheets of cloth. Only a relatively small amount of space is required, since the broader belt can have a width which is substantially smaller than the circumference of the rolled string. 
     According to the present invention, apparatus suitable for carrying out the aforesaid method while achieving the advantages afforded thereby includes a first stage through which the material is transported in enclosure means during initial concentration of the material to form a string of material and which is comprised of two separately advanced endless belts of straining cloth, and a second stage in which the material is finally concentrated by rolling the string of material as it is transported between two outwardly spread belts of straining material that move in two endless paths, wherein the enclosure means is formed by a narrower and a broader belt of straining cloth, each having a width which alone is insufficient to form said enclosure means, and wherein at least the broader belt also extends through the second stage and, in an outwardly spread state, also forms one of the transport belts used in this stage of the process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in more detail with reference to the following detailed description which, in turn, refers to the accompanying drawings, in which: 
     FIG. 1 is a side, elevational, schematic representation of a first embodiment of the apparatus of the present invention; and 
     FIG. 2 is a side, elevational schematic representation of a second embodiment of the apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Those components that find agreement or general agreement in both Figures have been identified with the same reference numerals. 
     The apparatus for concentrating liquid-drenched material, such as fiber suspensions, and particularly paper pulp suspensions, shown in FIG. 1 includes two belts of straining cloth,  1  and  2 , which are each advanced in a respective endless path and which may comprise a plastic wire cloth. One belt  1  is guided around guide rollers  3 - 11  and is broader than the second belt  2 , which is guided around guide rollers,  12 ,  13  and  14 , and also around the guide roller  8  used to guide the broader belt  1 . The directions in which the belts,  1  and  2 , move are indicated by respective arrows,  15  and  16 . 
     Positioned beneath the guide roller  14  is a known folding device generally referenced  17  (see for instance International Application No. WO 94/12260) that includes a first folding edge  18  which extends transversely to the direction of movement of the belts,  1  and  2 , and over which the central part of the belt  1  is folded. Connected to respective ends of the first folding edge  18  are second and third folding edges,  19  and  20 , which, as seen in the direction of movement of the folded belt  1 , extend obliquely forwards and outwards and obliquely forwards and inwards respectively. The longitudinally extending edge parts,  21  and  22 , of the folded belt  1  are folded over the second folding edges  19  firstly in towards and over the central part of the belt  1  and are then again folded over the folding edges  20 , so that said edges will partially cover and extend parallel with the central part. As the edge parts,  21  and  22 , of the belt  1  are folded, the belt  2 , whose width corresponds generally to the length of the folding edge  18 , is introduced into the folding device  17  in a manner such that the sides of the belt  2  will be overlapped by the edge parts,  21  and  22 , of the belt  1  such as to form from the two belts,  1  and  2 , an enclosure for a slurry of material to be concentrated, which is delivered through a hopper  23  in the direction of arrow  24 . In order to hold the belts  1  and  2  together in a position in which they embrace this material, the belts may be caused to run in a perforated tube (not shown) mounted between the folding device  17  and the guide roller  8 , so as to form a string  25  of partially concentrated material, which is then further concentrated by rolling the material between pressure rolls,  26  and  27 . 
     Before finally concentrating the material between the rolls,  26  and  27 , the edge parts,  21  and  22 , of the belt  1  are spread out in a belt unfolding device generally referenced  28 , including a first folding edge  29  which extends transversely to the direction of movement of the belt  1 . Connected to each end of the first folding edge  29  are respective second and third folding edges,  30  and  31 , which, seen in the direction of belt movement, extend obliquely rearwards and outwards and obliquely rearwards and inwards, respectively. The longitudinally extending edge portions of the belt  1  are therewith unfolded outwards around the third folding edge  31  and then rearwards around the second folding edges  30 , while the central portion of the belt  1  is folded back over the first folding edge  29 . 
     The concentrating apparatus shown in FIG. 1 thus includes a first stage located between the folding device  17  and the unfolding device  28 , in which the material delivered at locations  23  and  24  is concentrated into a coherent string  25  by straining the material through the enclosure formed by belts,  1  and  2 , and a second stage located between the unfolding device  28  and the roller  12  in which the material is finally concentrated by rolling the string  25  situated between the belt  2  and the belt  1  outwardly spread in the unfolding device  28 , the finally concentrated material departing in the direction of arrow  32 . Rolls that operate at moderate pressure or pressures may also be provided in the region between the guide roller  8  and the unfolding device  28 . However, in the case of high pressure rolling of the material, the string of material  25  shall be located between outwardly spread, single sheets of straining cloth. The devices required for collecting and conducting away liquid that drains from the material or is pressed therefrom have not been shown in the drawings, for the sake of clarity. 
     Although not shown in-detail, the belts,  1  and  2 , may be driven by driving one or more of the guide rollers  3 - 14  around which these belts pass. It will be seen from the illustrated arrangement of rolls  9 - 11  that the belt  1  unfolded in the device  28  forms a support for the string  25  immediately as that string exits from the unfolding device. The use of devices  17  and  28  of the kind shown in FIG. 1 is favorable from both the aspect of space and from the aspect of stress, or strain, in comparison to successively shaping belts from a flat to a tubular section in accordance with U.S. Pat. No. 4,017,398, for instance. It will be understood, however, that the invention is not restricted to the use of devices of the kind illustrated in FIG.  1 . 
     As noted above, in the case of the arrangement shown in FIG. 1 the width of the belt  2  corresponds to the lengths of the folding edges,  18  and  29 , so that overall it has the shape of an outwardly spread single sheet. In certain cases, it is desirable that the upper side of the string  25  has a straining belt  33  whose width exceeds the width of the string  25  as the string passes between the roll pairs,  26  and  27 , as shown in the FIG. 2 embodiment, so as to avoid any direct contact between the string material and the upper rolls  26 . 
     Thus, according to FIG. 2, the belt  2  forming part of the enclosure formed in the folding device  17  also passes around and upwards from a guide roller  34  located immediately downstream of the unfolding device  28 , in addition to passing around the guide rollers,  14  and  18 , and, by means of a guide roller  35  located above the guide roller  34 , back towards and around the guide roller  14 . The part of the apparatus in which the material is finally concentrated downstream of the unfolding device  28  uses a further straining belt  33  which, as mentioned above, is broader than the belt  2  and the string  25 , but which is preferably narrower than the belt  1 . The belt  33  extends in an endless path in the direction of arrow  36 , around guide rollers,  12  and  13 , and around two guide rollers,  37  and  38 , located adjacent respective guide rollers,  35  and  34 . 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.