MATERIAL

TECHNICAL FIELD

The present invention relates to a bin for the collecting and discharging of smaller ligno-cellulosic material, preferably in the form of chips.

BACKGROUND OF THE INVENTION

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. Many different solutions of the above problem have been suggested.

US 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. EP 0 742 854 discloses among others a similar solution, but with one screw.

US 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. US 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. An arrangement is made in order to decrease the disadvantages with using a screw. SE 51 1 519 and US 6,089,417 shows more complicated solutions of bins.

SUMMARY OF THE INVENTION

An object of the invention is to solve the above-mentioned problems with an invention as in the appended claims.

The advantages are that a better uniform material flow than in prior art is provided, where the same flow speed in all the material will be obtained with much decreased risk of stagnant zones, arches etc. Further, the height of the bin may be lower than in prior art, which is cheaper.

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.

In embodiments with a rotary 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 feeder treats the material more gently than e.g. a screw conveyor. The energy consumption is also lower. Since the flow through a rotary 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. 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

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:

Fig. 1 is a perspective view of a bin according to the present invention;

Fig. 2a-d are two side views a top view and a perspective view of a bin according to the present invention;

Fig. 3a-d are the same as Fig- 2a-d, but with feeder means in the form of a rotary feeder;

Fig. 4a-f are a perspective view, three side views, a cross section view and a top view of a rotary feeder according to the present invention;

Fig. 4g-h are different side views of different embodiments of a rotary feeder part with straight and turned vanes, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 illustrates an embodiment of a bin 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 be centred with respect to the bin 1 . The bin 1 may be provided with a feeder means 40 at the outlet 5, which will be discussed below. The bin 1 may also be provided with e.g. a screw conveyor 60 for further distribution of the material. Further, the bin 1 may be provided with some kind of support 61 .

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.

The details of the conical lower part 4 are shown more in detail in Fig. 2a-d. In Fig. 3a-d is shown the same conical lower part 4, but with a feeder means 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 sides 9, 10 and two second opposing sides 1 1 , 12. "Essentially rectangular" means that the rectangle 7 may have straight or rounded sides 9, 10, 1 1 , 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, 1 1 , 12 are straight, for reasons explained below. 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 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 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.

In a corresponding way, each second opposing segment 19, 20 is arranged between the upper edge 6 and one of the second sides 1 1 , 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 sides 1 1 , 12 of the essentially rectangular lower edge 7. 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.

The length of both the first sides 9, 10 and the second sides 1 1 , 12 of the essentially rectangular lower edge 7 should be shorter than the diameter of the circular upper edge 6.

An arrangement of this kind will give smooth borderlines between the different segments, which also will improve the mass flow through the bin.

Preferably, each of the two first opposing segments 17, 18 has a first angle a1 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 a2 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 1 1 , 12 of about 1 .5-4: 1 , preferably 3: 1 .

In order to give a uniform flow with the least risk of arching or ratholing, small first angles a1 and second angles a2 towards a thought vertical line 32 are better than large angles a1 , a2. 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.

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, 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.

Not only the shape of the bin 1 , but also the feeder means 40 for discharging the material affects the result. In order to have a uniform flow of the material, the feeder means 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. The feeder means 40 may e.g. comprise one or two rotating means 41 , 42, see Fig. 4a-h or Fig. 5. 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.

One solution may be to have a feeder means 40 in the form of a screw conveyor or preferably two counter rotating screw conveyors. The screw conveyors preferably have conical axes and variable pitch of their screws, in order to increase the probability for a uniform feeding of the material from the whole cross section of the lower edge 7. The conicity, the pitch and the rotation speed should be adapted for the conditions. This works well for well defined conditions. However, if the conditions should change, this solution will not work as well. This makes this an unflexible solution that seldom works really well in practise. In Fig. 4a-h is shown a better solution which will be less sensitive for different conditions. There is shown a feeder means 40 in the form of a rotary feeder 40 having one or preferably two rotating means 41 , 42 in the form of rotary feeder parts 41 , 42 with horizontal and parallel axes 43. The rotary feeder 40 is also provided with a motor 48. Preferably, the rotary 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 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 feeder 40. The rotary feeder parts 41 , 42 should 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. 4a-h, having gears 51 , 52.

There are preferably 6-12 vanes 44, 45, 49, 50 in each rotary feeder part 41 , 42. 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. 4h, but the vanes 49, 50 may also be straight as in Fig. 4g. 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.

A rotary feeder also treats the material more gently than a screw conveyor. Since the flow through a rotary feeder is more well defined than the flow through a screw, 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.

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 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 feeder means 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.

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.