Abstract:
The bin arrangement is for collecting and discharging smaller ligno-cellulosic material. The bin has a transition part from a circular section of the bin and downwardly to a rectangular section with a long and short side of the rectangular section. The transition part could be built with few wall segments, thus needing less welding. Two rotary pocket feeders, each with at least one shaft extending parallel to the long side, are arranged directly under the rectangular section, enabling a uniform feed from the bin. The use of two rotary pocket feeders with this design directly under the bin does not destroy the even feed of material through the bin part, which otherwise is experienced from using conventional feed screws that feed material in a transverse direction from the bin outlet. The bin does not need to have a complex bin design which converges to a small circular inlet to a conventional rotary pocket feeder.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a bin arrangement for the collecting and discharging of smaller ligno-cellulosic material, preferably in the form of chips. 
       BACKGROUND OF THE INVENTION 
       [0002]    In connection with the manufacture of papermaking pulp, various steps in the process include material being transported in the form of chips or pulp. In certain parts of the process the material must be fed uniformly from bins for storage and/or treatment of the material to a subsequent treatment step. The problem in this case is to bring about a uniform flow through the bin. The material can adhere to the walls of the bin and thereby cause arching and/or ratholing and/or the material can move at different speeds in different parts of the cross-section of the bin. The feed of the material through the bin can thus be stopped, or the retention time of the material in the bin can vary. This is particularly unfavourable when the material is subjected to some kind of treatment in the bin, for example preheating with steam or treatment with chemicals. In this case it is wished that the treatment is made during a predetermined time, which is difficult if different parts of the material move in different ways. 
         [0003]    Many different solutions of the above problem have been suggested. 
         [0004]    U.S. Pat. No. 2,943,752 from 1960 disclose an early chip bin design for bulk feed with a rectangular lower outlet with a transition part down to the lower outlet that promote an even flow through the chip bin as such. This chip bin avoids the extensive welding work necessary to make the transition part. However, directly at the outlet end there is still a single screw feeding the bulk material sidewise, which screw hinders even flow out from the bin as the screw is filled primarily at the distant end as seen from the outlet. 
         [0005]    EP 0 742 854 discloses among others a similar solution, but with one screw. Hence, the same problem with filling the screw from the end of the screws is at hand. 
         [0006]    U.S. Pat. No. 4,958,741 discloses a bin with an upper part having a circular upper edge and an oval lower edge, where the length of the oval is equal to the diameter of the circle, and with a lower part having an oval upper edge and a circular lower edge. This chip bin is expensive to manufacture as a lot of welding work is necessary for each of the wall segments making up the chip bin convergence. 
         [0007]    U.S. Pat. No. 6,336,573 discloses a bin with a cylindrical upper part and a lower part with an upper circular edge and a lower oval edge, where the length of the oval is equal to the diameter of the circle. Feeding out from the bin is made with a screw. Several proposals are mentioned addressing the problem with filling the screw evenly from the whole chip bin, and thus trying to decrease the disadvantages with using a screw. The proposals includes varying shaft diameter, flight diameter and varying pitch of the screw so as to provide a substantial uniform flow along the slot outlet. 
         [0008]    SE 511 519 (=U.S. Pat. No. 6,250,514) and U.S. Pat. No. 6,089,417 shows more complicated solutions of bins per se resulting in a chip bin that is expensive to manufacture as a lot of welding work is necessary for each of the wall segments making up the chip bin convergence. 
         [0009]    U.S. Pat. No. 7,178,698 discloses a bin with an upper cylindrical part and a lower part having a circular upper edge and a rectangular lower edge, where the length of the long side of the rectangle is equal to the diameter of the circle. Feeding out from the bin is made with two counter rotating screws, feeding towards a central circular outlet beneath the screws. However, the problem is that the screws are filled at the end of the screws emptying the chip bin from there, and at the central outlet the screw may not empty the bin in equal volume from the centre of the bin as the screw is already filled. 
         [0010]    The problem with all these chips bins lies in the usage of screw conveyers that pick up bulk material close at wall of chip bin outlet and thus empties the chip bin from that end of screw, but not promoting an even flow through the entire chip bin volume. Even if the bin design per se is promoting even flow downwards, the screw conveyers prevents even flow as they are filled at the distant end as seen from the subsequent outlet. 
         [0011]    In following description is the expression rotary pocket feeder used which is a conventional machine per se in feeding wood chips to a digester. Another name for the rotary pocket feeder is the star feeder. In a rotary pocket feeder are a number of pockets formed between axially oriented vanes on a revolving shaft, feeding comminuted material, for example chips from an upper inlet end to a lower outlet end after a rotation of about 180 degrees. The pockets are simply filled by gravity, and are emptied by gravity. Rotary pocket feeders have been used in conventional piping for feeding chips to digesters. In conventional continuous cooking systems has one rotary pocket feeder, i.e. chip meter, been used for chip volume measurements after the chip bin and a following rotary pocket feeder, i.e. low pressure feeder, has been used as a low pressure sluice feeder ahead of the steaming vessel. These rotary feeders are described more in detail in  Chemical Pulping  Book 6A (ISBN 952-5216-06-03), 1969, in chapter 6, section 3.2 “ Chip metering and feeding into process pressure ”, on pages A522-A514. However, these rotary pocket feeders, especially the chip meter, have had either a circular inlet or have been fed by a screw conveyer from the chip bin, and thus have had no impact on an uniform retention time of chips in the chip bin. 
       SUMMARY OF THE INVENTION 
       [0012]    An object of the invention is to solve the above-mentioned problems with an invention as in the appended claims. The solution is not related to the chip bin per se only or to rotary pocket feeders per se in the outlet, but instead to a combination of a simple and yet reliable chip bin and a rotary pocket feeder at outlet end that supports even flow from the whole arrangement of chip bin and rotary pocket feeder. 
         [0013]    The advantages are that a better uniform material flow than in prior art is provided, where the same flow speed in the entire volume of material kept in the bin will be obtained with much decreased risk of stagnant zones, arches etc. Further, the total height of the bin and rotary pocket feeder may be lower than in prior art, which is cheaper. 
         [0014]    If there is a wish for treatment in the bin, this invention also enables to have a better defined treatment time in a part of the bin, since all the material will spend the same time in said part of the bin. This gives a better result and is cheaper, since the treatment needs to take place in only a limited part of the bin. 
         [0015]    With a rotary pocket feeder at the outlet, there are further advantages, such as an even more uniform material flow through the whole outlet, which flow is not sensitive to different conditions. A rotary pocket feeder treats the material more gently than e.g. a screw conveyor. The energy consumption is also lower. 
         [0016]    Since the flow through a rotary pocket feeder is more well defined than the flow through e.g. a screw conveyor, it is also possible to use the rotary feeder for another function, namely for measuring the flow of the material. This obviates the need for a separate means for measuring the flow of the material. 
         [0017]    The invention relates to a bin arrangement, i.e. a novel combination of a bin design and a rotatry pocket feeder that provide even flow of material through and from the arrangement. 
         [0018]    The bin arrangement is intended for collecting and discharging of smaller ligno-cellulosic material, which bin comprises a cylindrical upper part with an inlet, and a conical lower part with an outlet, which conical lower part comprises a circular upper edge, an essentially rectangular shaped lower edge having two first opposing long sides and two second opposing short sides, and a surface between the upper edge and the lower edge. The bin arrangement is designed such that the opening formed in the lower edge forms a rectangular shape with a ratio of the first long sides to the second short sides in the range of 1.5-4:1, preferably 3:1, and directly below the lower edge is a rotary pocket feeder mounted with an inlet of the rotary pocket feeder having a form congruent to the rectangular shape of the lower edge and an outlet of the rotary pocket feeder on the opposite side of the rotary pocket feeder also having a form congruent to the rectangular shape of the lower edge, said rotary pocket feeder including at least one rotating feeder means with a rotating axis arranged between the rotary pocket feeder inlet and outlet and driven by a motor, with the axis extending in parallel with the first long sides, and with radially open pockets separated by at least 6 vanes on said axis, each vane running from one end of the axis to the other end of the axis and between the second short sides. 
         [0019]    This design of bin and rotary pocket feeder in combination guarantees a uniform flow of material trough the arrangement while using a simple form of chip bin with less welding work for manufacturing. 
         [0020]    In a preferred embodiment the bin arrangement has a rotary pocket feeder including two counter rotating feeder means with vanes arranged to rotate the feeder means so that the material is fed downwards in the pockets of the feeder means and in the middle of the two counter rotating feeder means. 
         [0021]    Preferably the vanes of the rotary feeder are straight along the axis of the rotating feeder means, or alternatively are axially turned around the axis of the rotating feeder means. When using turned vanes, the vanes are turned so that a first end of a first vane and a second end of a second vane is along a line parallel to the axis of the rotating feeder means. These vanes provide a disturbance against the overlying material volume and helps filling of the pockets, and the turned vanes provide for a disturbance that travels from one end of rotor to the other during rotation. 
         [0022]    The bin as such in the bin arrangement has a length of both the first long sides and the second short sides of the essentially rectangular lower edge that are shorter than the diameter of the upper edge. A transition from a large circular bin volume is thus possible. 
         [0023]    Further the surface forming the outer wall of the bin in the transition part comprises two first opposing segments, each first opposing segment being between the upper edge and one of the first long sides of the lower edge; two second opposing segments, each second opposing segment being between the upper edge and one of the short second sides of the lower edge; and four intermediate segments, each of the intermediate segments between the upper edge, the lower edge, one of the first opposing segments and one of second opposing segments. Thus the entire concial transition part is made from only 8 wall segments, and could be welded together by only 8 welding seams. Further, each of the two first opposing segments is flat and essentially triangular with a base of the triangle towards one of the first long sides of the essentially rectangular lower edge. These segments becomes where easy to manufacture. Preferably each of the two first opposing segments has a first angle (α 1 ) of 1-10°, preferably 4-7°, to a thought vertical line. This part of the transition provides for a smaller degree of convergence towards the outlet, different from the convergence of the other parts of the transition. 
         [0024]    Hence, in other parts of the transition the two second opposing segments is flat and essentially triangular with a base of the triangle towards one of the second short sides of the essentially rectangular lower edge. These segments becomes where easy to manufacture as well. Preferably each of the two second opposing segments has a second angle (α2) of 5-20°, preferably 10-14° to a thought vertical line ( 32 ). This part of the transition provides for a larger degree of convergence towards the outlet, different from the convergence of the other parts of the transition. 
         [0025]    Preferably the essentially rectangular lower edge has rounded corners. Sharp corners should be avoided as they may cause disturbance in flow. 
         [0026]    Finally the four intermediate segments needed for the transition part are curved, and the conical transition may be manufactured by only 4 curved segments. 
         [0027]    Further advantageous embodiments of the device according to the present invention and further advantages with the present invention emerge from the detailed description of embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which: 
           [0029]      FIG. 1  is a perspective view of a bin arrangement according to the present invention; 
           [0030]      FIG. 2   a - d  are different views of the bin as such, i.e. two side views, a top view and a perspective view of the bin; 
           [0031]      FIG. 3   a - d  are the same as  FIG. 2   a - d,  but with feeder means in the form of a rotary pocket feeder; 
           [0032]      FIG. 4   a - f  are a perspective view, three side views, a cross section view and a top view of a rotary pocket feeder according to the present invention; 
           [0033]      FIG. 4   g - h  are different side views of different embodiments of a rotary feeder part with straight and turned vanes, respectively. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0034]      FIG. 1  illustrates an embodiment of a bin arrangement  1 , according to the invention, for the collecting and discharging of smaller ligno-cellulosic material, preferably in the form of chips. The bin  1  comprises a cylindrical upper part  2  with an inlet  3  and a conical lower part  4  with an outlet  5 . The inlet  3  and the outlet  5  should preferably be centred with respect to the bin  1 . The bin  1  is provided with a rotary pocket feeder  40  at the outlet  5 , which will be discussed below. 
         [0035]    The bin  1  may also be provided with e.g. a screw conveyor  60  for further distribution of the material. This kind of screw conveyer is typically “starve-fed”, meaning that the volumetric feed capacity of the screw conveyer is larger than the volumetric in feed of material. During operation this is easily implemented by increasing the speed of the screw conveyer. In this way is comminuted material not prevented from flowing through the rotary pocket feeder. However, the rotary pocket feeder could also feed the material straight downwardly to a chute. Further, the bin  1  may be provided with some kind of support  61 . 
         [0036]    It has been realised that in order to obtain a uniform mass flow in a bin, the added compressive stresses should be of such a size and distribution that the resulting shearing stress exceeds the strength of the material. The size of the compressive stresses is proportional to the diameter of the bin. The distribution of the compressive stresses depends much on the shape of the conical part. Simplified, in a conical part, which is symmetrical in all directions, compressive stresses will arise in all directions, while in a conical part as in  FIG. 1 , which is not symmetrical in all directions, compressive stresses will arise from two directions, which also results in a larger shearing stress, which results in that the material flows better through the bin. 
         [0037]    The details of the conical lower part  4  are shown more in detail in  FIG. 2   a - d.  In  FIG. 3   a - d  is shown the same conical lower part  4 , but with a rotary pocket feeder  40 . The conical lower part  4  comprises a circular upper edge  6 , an essentially rectangular shaped lower edge  7  and a surface  8  between the upper edge  6  and the lower edge  7 . The circular upper edge  6  has the same diameter as the cylindrical upper part  2 . The essentially rectangular shaped lower edge  7  has two first opposing long sides  9 ,  10  and two second opposing short sides  11 ,  12 . “Essentially rectangular” means that the rectangle  7  may have straight or rounded sides  9 ,  10 ,  11 ,  12  and/or corners  13 ,  14 ,  15 ,  16 . Preferably, the corners  13 ,  14 ,  15 ,  16  of the rectangle  7  are rounded, in order for the material not to get stuck in the corners  13 ,  14 ,  15 ,  16 . Preferably, however, the sides  9 ,  10 ,  11 ,  12  are straight, for reasons explained below. 
         [0038]    The surface  8  of the conical lower part  4  comprises two first opposing segments  17 ,  18 , two second opposing segments  19 ,  20  and four intermediate segments  21 ,  22 ,  23 ,  24 . Each first opposing segment  17 ,  18  is arranged between the upper edge  6  and one of the first long sides  9 ,  10  of the lower edge  7 . Preferably, each of the two first opposing segments  17 ,  18  is flat and essentially triangular with a base  29  of the triangle towards one of the first long sides  9 ,  10  of the essentially rectangular lower edge  7 . “Essentially triangular” means that the corners  25 ,  26 ,  27  and/or the sides  28 ,  29 ,  30  of the triangle  17 ,  18  may be straight or rounded, but, preferably, the sides  28 ,  29 ,  30  and the corners  25 ,  26 ,  27  of the triangle  17 ,  18  are straight, since that will give cheaper manufacture. Flat opposing segments  17 ,  18  will also cause a better flow, since there will be only one direction of stress in the flow. 
         [0039]    In a corresponding way, each second opposing segment  19 ,  20  is arranged between the upper edge  6  and one of the second short sides  11 ,  12  of the lower edge  7 . Preferably, each of the two second opposing segments  19 ,  20  is flat and essentially triangular with a base  31  of the triangle  19 ,  20  towards one of the second short sides  11 ,  12  of the essentially rectangular lower edge  7 . 
         [0040]    Each of the intermediate segments  21 ,  22 ,  23 ,  24  is arranged between the upper edge  6 , the lower edge  7 , one of the first opposing segments  17 ,  18  and one of second opposing segments  19 ,  20 . Preferably, the intermediate segments  21 ,  23 ,  24  are curved so that a smooth surface  8  is created between the circular upper edge  6  and the essentially rectangular lower edge  7 . 
         [0041]    The length of both the first long sides  9 ,  10  and the second short sides  11 ,  12  of the essentially rectangular lower edge  7  should be shorter than the diameter of the circular upper edge  6 . 
         [0042]    An arrangement of this kind will give smooth borderlines between the different segments, which also will improve the mass flow through the bin. 
         [0043]    Preferably, each of the two first opposing segments  17 ,  18  has a first angle α 1  of 1-10°, 4-7°, to a thought vertical line  32 , while each of the two second opposing segments  29 ,  20  has a second angle α 2  of 5-20°, preferably 10-14° to the thought vertical line  32 . This gives an essentially rectangular shape of the lower edge  7  with a ratio of the first side  9 ,  10  to the second side  11 ,  12  of about 1.5-4:1, preferably 3:1. 
         [0044]    In order to give a uniform flow with the least risk of arching or ratholing, small first angles α 1  and second angles α 2  towards a thought vertical line  32  are better than large angles α 1 , α 2 . Also, having a lower edge  7  with a large cross section area is better than a lower edge  7  with a small cross section area. But, on the other hand, it is wished to have a uniform flow through the whole cross section of the lower edge  7 , which is more difficult to obtain the larger the lower edge  7  is. Further, long cross sections in the conical lower part  4  are better than e.g. circular or square cross sections. But a long lower edge also requires a more expense feeder means. Thus, these are conditions that need weighing up towards each other. 
         [0045]    Preferably, the first opposing segments  17 ,  18  and the second opposing segments  19 ,  20  do not meet on the lower edge  7 , but the intermediate segment  21 ,  22 ,  23 ,  24  is intermediate also on the lower edge  7 , thus shaping round corners  13 ,  14 ,  15 ,  16  of the lower edge  7 . 
         [0046]    For an optimal flow, the friction of the inner wall  33  in the conical part  4  should preferably be as low as possible. E.g. stainless steel will work. The friction of the inner wall in the cylindrical part  2  is less critical and may be higher. 
         [0047]    Not only the shape of the bin  1 , but also the rotary pocket feeder  40  for discharging the material affects the result. In order to have a uniform flow of the material, the rotary pocket feeder  40  should preferably feed the material uniformly from the whole cross section of the lower edge  7  or there is a risk that stagnant zones will occur. In the simplest form of the invention could the rotary pocket feeder include only one rotating feeder means. In the preferred embodiment disclosed in drawings the rotary pocket feeder  40  comprises two rotating means  41 ,  42 , see  FIG. 4   a - h.  It is an advantage to have two rotating means  41 ,  42  that are counter rotating, because the symmetry will increase the probability for a uniform feeding of the material from the whole cross section of the lower edge  7 . 
         [0048]    The opening formed in the lower edge of the bin forms a rectangular shape with a ratio of the first long sides  9 ,  10  to the second short sides  11 ,  12  in the range of 1.5-4:1, preferably 3:1, and directly below the lower edge is a rotary pocket feeder  40  mounted with an inlet IN of the rotary pocket feeder having a form congruent to the rectangular shape of the lower edge  7  and an outlet OT of the rotary pocket feeder on the opposite side of the rotary pocket feeder also having a form congruent to the rectangular shape of the lower edge. 
         [0049]    In  FIG. 4   a - h  is shown a better solution which will be less sensitive for different conditions. There is shown a rotary pocket feeder  40  having two rotating means  41 ,  42  in the form of rotary feeder parts  41 ,  42  with horizontal and parallel axes  43 . The rotary pocket feeder  40  is also provided with a motor  48 . 
         [0050]    Preferably, the rotary pocket feeder  40  has counter rotating rotary feeder parts  41 ,  42  and is arranged to feed the material downwards through the vanes  44 ,  45 . The best result is given if the counter rotating feeder parts  41 ,  42  rotates so that the material is fed downwards in the middle of the rotary pocket feeder  40 , between the feeder parts  41 ,  42 . It would, however, also work, but not as well, to instead feed the material downwards at the peripheries of the rotary pocket feeder  40 . The rotary feeder parts  41 ,  42  should preferably be synchronized, so that they rotate with the same speed, but in opposite directions. This may e.g. be achieved with two motors that are e.g. electronically synchronized, or, as in  FIG. 4   a - h,  having gears  51 ,  52 . 
         [0051]    There are preferably  6 - 12  vanes  44 ,  45 ,  49 ,  50  in each rotary feeder part  41 ,  42 . The vanes form radially open pockets separated by the vanes on the rotary feeder part, each vane running from one end of the axis to the other end of the axis and between the second short sides  11 , 12 . 
         [0052]    In order to feed the material uniformly from the whole cross section of the lower edge  7 , the vanes  44 ,  45  are preferably axially turned around the axis  43  as in  FIG. 4   h , but the vanes  49 ,  50  may also be straight as in  FIG. 4   g . Best result seems to be given by having a first end  46  of a first vane  44  and a second end  47  of a second vane  45  being along a line parallel to the axis of the rotating means  41 ,  42 . Preferably, the first vane  44  and second vane  45  are subsequent vanes  44 ,  45 . This may also be explained as each vane  44 ,  45  is turned around the axis 1/N of a turn, where N is the number of vanes  44 ,  45 . 
         [0053]    A rotary pocket feeder also treats the material more gently than a screw conveyor. Since the flow through a rotary pocket feeder is more well defined than the flow through a screw, it is also possible to use the rotary pocket feeder for another function, namely for measuring the flow of the material. This obviates the need for a separate means for measuring the flow of the material. 
         [0054]    Having also second opposing segments  19 ,  20  enables to have a lower bin  1 , which is cheaper. It also enables a better control of the flow through the bin  1 . It further means that the rotary pocket feeder means  40  need not be so long, which is economical. It also enables to have a standardised size of the lower edge  7 , so that the same rotary pocket feeder  40  may be used for a number of bins  1  having different diameters of the upper edge  6 , which also is economical. In total, the costs both for manufacture and installation will be considerably lower than in prior art. 
         [0055]    Further, since this arrangement will make the mass flow through the bin much more uniform, the retention time of the material in the bin and also in different part of the bin will be much better defined. If there is a wish for treatment in the bin, this invention also enables to have a better defined treatment time in a part of the bin, since all the material will spend the same time in said part of the bin. This means that the bin may have e.g. alkali treatment in only a limited part of the bin and thus operate with a cold top of the bin, which is very economical. The invention shall not be considered limited to the embodiments illustrated, but can be modified and altered in many ways by one skilled in the art, without departing from the scope of the appended claims.