Abstract
A feeding arrangement for feeding comminuted material to a treatment stage using a plug screw feeder. The invention relates to a design of the inlet to the plug screw feeder wherein, at least 2 chutes (20a,20b) are arranged to feed material to the feed screw (10), and that the cross section of each chute is arranged such that more than 50% of the outlet cross section of a first chute (20a) is located on one side of the feed screw axis (CC) and more than 50% of the outlet cross section of a second chute (20b) is located on the other side of the feed screw axis. In an upgrade version for existing plug screw feeders with large rectangular inlets is an insert body (11a) used filling the rectangular inlet, besides the chutes (20a, 20b) passing through the insert body (11a).
Claims
1. Apparatus for feeding comminuted material to a treatment stage said apparatus comprising a plug screw feeder for feeding the material to the treatment stage, the plug screw feeder comprising a feed screw with a conical part at its outlet end and driven by an independent first motor said feed screw rotating around a first screw axis and a corresponding plug screw housing surrounding the feed screw, a chute for feeding the comminuted cellulose material to the plug screw feeder, said chute being arranged at an angle in relation to the first screw axis), said angle lying in the range of from 30-150 degrees, the chute being arranged to provide the material to an inlet section of the plug screw feeder, said inlet section being arranged in the periphery of the feed screw, said apparatus including at least two chutes arranged to feed the comminuted cellulose material to the feed screw, said at least two chutes comprising a first chute and a second chute, the cross section of each of said at least two chutes is such that more than 50% of the outlet cross section of the first chute is located on one side of the first screw axis and more than 50% of the outlet cross section of the second chute is located on the other side of the first screw axis.
2. Apparatus according to claim 1, wherein each of said at least two chutes includes force feeding means driven by its own independent motor.
3. Apparatus according to claim 2, wherein each of said force feeding means comprises a force feeding screw driven by an independent motor for feeding the comminuted cellulose material to the plug screw feeder.
4. Apparatus according to claim 3, wherein each of said force-feeding screws is arranged essentially in the same horizontal plane as the feed screw, the force-feeding screws feeding the material from the side.
5. Apparatus according to claim 3, wherein each of said force-feeding screws is arranged essentially in the same vertical plane as the feed screw, the force-feeding screws feeding the material either from above or below to the feed screw.
6. Apparatus according to claim 1, wherein a first pair of said at least two chutes are arranged in a staggered relation to a plane orthogonal to the first screw axis, such that the chutes are in a plane parallel to a plane of the flights of the feed screw sweeping over the chute outlets.
7. Apparatus according to claim 6, wherein a second pair of said at least two chutes are arranged in a staggered relation to a plane orthogonal to the first screw axis, such that the chutes are in a plane being parallel to a plane of the flights of the feed screw sweeping over the chute outlets.
8. Apparatus according to claim 1, wherein the plug screw housing surrounding the feed screw has an open inlet covering the entire diameter of the feed screw, and wherein the at least two chutes are connected to flow channels having similar cross section as the chutes said flow channels running through an insert body which otherwise is filling the entire open inlet, enabling the flow of material to be fed directly to the periphery of the feed screw via said flow channels in the insert body.
9. Apparatus according to claim 2, wherein the independent first motor for the feed screw and the independent motors for the force feeding means located in the chutes, are connected to a control unit, such that each motor is adapted to be able to be driven at variable speed by the control unit in relation to preset threshold values stored in the control unit, such that the feed screw is rotated at a first speed, and each force feeding means located in the chute is driven at an individual speed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The invention, together with further objects and advantages thereof, may best be understood by reference to the following description and appended drawings, in which:
[0034] FIG. 1 is a schematic set up of a prior art feeding arrangement using a screw feeder;
[0035] FIG. 2 is a part of a prior art feeding arrangement using a screw feeder and a three feeder feeding from the side;
[0036] FIG. 3 is a detail view of a prior art screw feeder housing;
[0037] FIG. 4 is cross sectional view trough a prior art screw feeder housing;
[0038] FIG. 5a-5c are different views of a first preferred embodiment of the invention;
[0039] FIGS. 6a and 6b are two views of an insert body used in the inlet of the screw feeder in the first embodiment of the invention;
[0040] FIGS. 7a and 7b are different views of a second embodiment of the invention;
[0041] FIGS. 8a and 8b are different views of a third preferred embodiment of the invention;
[0042] FIGS. 9a and 9b are two views of an insert body used in the inlet of the screw feeder in the third preferred embodiment of the invention
[0043] FIG. 10 is a view of an alternative of the third embodiment using force feed screws feeding from the side;
[0044] FIG. 11 is a schematic control system for the independent control of the motors of the plug screw and the force feed screws;
[0045] FIG. 12 is a view of a feeding arrangement as shown in FIG. 10, but being fed from above.
DETAILED DESCRIPTION
[0046] In the drawings, similar or corresponding elements are denoted by the same reference numbers.
[0047] For the purpose of this disclosure, the term longitudinal is meant to be the direction along which a body or part has its greatest extension. When the term is used in connection with the axes of screws, the longitudinal axis corresponds to the rotational axis of the feed screw. [0048] Also, the term force feeding means is used for any active feed of material driven by motors, and could include converging conveyor belts pressing and feeding the material in a nip towards the plug screw. [0049] But in the simplest form could an individual flow control in each chute be obtained by controlling the static head of material in each chute by state of the art level control.
[0050] FIG. 1 is a a schematic set up of a prior art feeding arrangement 100 using a plug screw feeder 40. In the simplest form the plug screw feeder is fed with comminuted cellulosic material from a conveyor belt trough a feeding chute 20. A certain level of material may be stacked in the chute forming a buffer volume for the plug screw feeder. A motor M1 is rotating the plug screw 10 and a plug is formed in the final conical compression section CS, before the material is forced into the subsequent treatment stage 200. The treatment stage is typically pressurized and could as shown in this figure be a treatment tower, but other treatment stages may be possible such as disc refiners, digesters, impregnation vessel etc. [0051] In FIG. 2 is a part of a prior art feeding arrangement shown using a screw feeder 40 and a three feeder 20a connected to a chute 20 feeding from the side of the screw feeder 40. The force feeder is shown split from the screw feeder but typically the force feeder is directly bolted to the inlet 12 of the screw feeder 40. The plug screw housing 11 comprises a first transport section TS in the area of the inlet 12 and a conical final compression section CS in a closed part 50 of the plug screw housing. In FIG. 3 is shown the housing with the conical final compression section CS exposed, with draining apertures in the conical part 50a. In FIG. 4 is shown the housing in cross section over the inlet part 12 of the housing 11. Thus, FIGS. 1-4 disclose in principle the prior art design for feeding arrangements using plug screw feeders.
[0052] In FIG. 5a is shown a perspective view of a first preferred embodiment of the invention. As in other conventional screw feeders a load bearing unit is shown on the left hand side of the inlet section 12 with the screw shaft protruding to the left. On the right hand side of the inlet section 12 is the outlet section arranged with the conical final compression section CS in a closed part 50 of the plug screw housing. The invention is shown as applied in a standard plug screw feeder with a rectangular inlet section 12, and an insert body 11a is mounted in the inlet 12 such that the entire inlet 12 is filled up besides two chute channels 20a and 20b. The insert body is shown in phantom shape partially transparent, but this insert body 11a, is disclosed more in detail with reference to FIGS. 6a and 6b. In FIG. 5b the first preferred embodiment of the invention is shown from above, with the first transport section TS and second compressions section CS marked up. The inventive concept with at least two chute channels 20a and 20b is described in more detail with reference to FIG. 5c. As shown in FIG. 5c are at least 2 chutes 20a 20b arranged to feed material to the plug screw 10, and that the cross section of each chute is arranged such that more than 50%, in the FIG. 100%, of the outlet cross section of a first chute 20a is located on one side of the first screw axis CC and more than 50%, in the FIG. 100%, of the outlet cross section of a second chute 20b is located on the other side of the first screw axis CC. For the most efficient filling of the plug screw it is preferred that each first pair of chutes 20a, 20b are arranged in a staggered relation to a orthogonal plane to the first screw axis CC, such that the center of the chutes are in a plane CP being parallel to a plane FP of the flights of the plug screw 10 sweeping over the chute outlets. The flights of the plug screw transports the material to the right as indicated with white arrows, if the screw rotates as shown on the indicator marking on the left of the bearing part. The upper chute 20a will thus feed to the half of the plug screw that has a motion out of the figure, while the lower chute 20b will feed the half of the plug screw that has an motion into the figure.
[0053] In FIGS. 6a and 6b are shown in perspective views the insert body 11a isolated from the housing. The insert body 11a fills the entire rectangular inlet part of the housing besides the chute channels 20a and 20b, and the clearance between the cylindrical part of the insert body 11a and the screw flights is typically the same as between the housing and the screw flights, i.e. in the range of 0.5-10 mm. The effect of the insert body is that the inflow of comminuted material will be established as separated flows from each chute channel 20a,20b until the flow of material fed out from the chute is caught by the impact of the screw flights.
[0054] In FIG. 7a is shown a perspective view of a second embodiment of the invention, and a detail view is shown in FIG. 7b. The difference here in relation to FIG. 5b is the arrangement of the chute channels 20a, 20b versus the orientation of the screw flights. As shown also in FIG. 7b are at least 2 chutes 20a 20b arranged to feed material to the plug screw 10, and that the cross section of each chute is arranged such that more than 50%, in the FIG. 100%, of the outlet cross section of a first chute 20a is located on one side of the first screw axis CC and more than 50%, in the FIG. 100%, of the outlet cross section of a second chute 20b is located on the other side of the first screw axis CC. In this embodiment is the filling of the plug screw performed such that each first pair of chutes 20a,20b are arranged in a staggered relation to a orthogonal plane to the first screw axis CC, such that the center of the chutes are in a plane CP not being parallel to a plane FP of the flights of the plug screw 10 sweeping over the chute outlets, but instead are in a plane CP arranged at an angle P in relation to a plane FP of the flights of the plug screw 10 sweeping over the chute outlets. The upper chute 20a will thus feed to the half of the plug screw that has a motion out of the figure, while the lower chute 20b will teed the half of the plug screw that has an motion into the figure. [0055] As indicated in FIG. 7b there is a potential in shortening of the screw housing, as the distance HS is not needed for filling the plug screw during the transport section TS.
[0056] In FIG. 8a is shown a perspective view of a third preferred embodiment of the invention. The difference here in relation to FIG. 5a is that a second pair of chute channels 20c and 20d are arranged through the insert body 11b besides the first pair of chute channels 20a and 20b. For the most efficient filling of the plug screw it is preferred that also the second pair of chutes 20c, 20d are arranged in a staggered relation to a orthogonal plane to the first screw axis CC, such that the center of the chutes are in a plane CP2 being parallel to a plane FP of the flights of the plug screw 10 sweeping over the chute outlets. Thus, both chute pairs are arranged in planes CP1 and CP2 being parallel to a plane FP of the flights of the plug screw 10 sweeping over the chute outlets. The embodiment of FIGS. 8a and 8b thus utilize more of the available rectangular inlet section that is filled with the insert body 11b. The first pair of inlet chutes filling the plug screw, here inlet chutes 20c and 20d, could then provide with major part of the filling while the second pair of inlet chutes, here inlet chutes 20a and 20b located closer to the outlet, could then provide with some complementing filling of the screw feeder. [0057] In FIGS. 9a and 9b are shown in perspective views the insert body 11b isolated from the housing of this third embodiment. The insert body 11b fills the entire rectangular inlet part of the housing besides the chute channels 20a, 20b, 20c and 20d, and the clearance between the cylindrical part of the insert body 11b and the screw flights is typically the same as between the housing and the screw flights, i.e. in the range of 0.5-10 mm. The effect of the insert body is that the inflow of comminuted material will be established as separated flows from each chute channel 20a, 20b, 20c, and 20d until the flow of material from the chutes are caught by the impact of the screw flights.
[0058] In FIG. 10 is shown an alternative for the third embodiment including force-feeding screws 20am, 20bm, 20cm and 20dm in each of the four inlet ducts 20a, 20b, 20c and 20d, with force feed from the side and into the plug screw. Individual motors for the force feeding screws are at hand but not shown in this drawing.
[0059] In FIG. 11 is schematically visualized a control system for the independent control of the motors of the plug screw and the force feed screws if using only 2 inlet ducts 20a, 20b. For the third embodiment the control system is similar but with additional 2 chutes and 2 motors for the additional force feed screws. Here a control unit CPU is connected in bidirectional manner to each motor M1, M2 and M3. The CPU could detect the prevailing torque of each motor, which in a conventional manner may be a simple detection of the averaged electrical current (in amperes). Hence, a starting torque could be stored in the CPU while operating the motors with empty chutes, and said starting torque (measured in average ampere) is stored as a first reference for each individual motor and is thus used as a no-load reference. The speed of each motor (and hence the feeding capacity of each screw) is controlled by electrical control, and during operation the speed of the plug screw motor Ml is the primary control target. The speed of the force feeding motors M2 and M3 are the secondary control targets and the speed thereof are increased in steps until the driving torque of screw motor Mi reached a set value above the starting torque thereof and when the torque is stable over time (less variation). Because the force feeding motors are working at different conditions, i.e. against the screw flights or concurrent with the screw flight, could optimal filling effect be obtained from each inlet duct. [0060] Thus, the force-feeding screws 20am and 20bm and optionally the screws 20cm and 20dm are arranged to be rotatable at variable rotational speeds. The plug screw 10 is also arranged to be able to rotate at variable speed, the speeds of the plug screw 10 and each of the force-feeding screws 20am-20dm being variable independently of each other. [0061] The force-feeding screws may be run at over speed, i.e. at a speed resulting in a low degree of filling in the force-feeding screws as such or at under speed i.e. at a speed resulting in a high degree of filling in the force-feeding screws as such. In any case, the rotational speed of the plug screw is kept at a certain driving torque allowing a formation of a stable plug in the outlet thereof. When the driving torque of the plug screw is reaching an upper set value could the speed of the force feeding means be reduced accordingly.
[0062] The feeding arrangement may further comprise (not shown) a volumetric detection of material fed into the force-feeding screw 20. The feeding device sets a predetermined rate of material flow, i.e. the production flow. The rotational speed of the plug screw 10 is then set in relation to the predetermined rate of material flow in order to achieve a predetermined density increase of the material in the plug screw (preferably measured as the prevailing driving torque of the motor in amperes). If the production flow is increased, the rotational speed of the plug screw 10 has to be increased to maintain the same density in the plug screw feeder 40. If the rotational speed of the plug screw 10 is maintained while the production flow increases, the density will increase. By increasing the material density in the plug screw feeder an improved fluid-tight plug flow of the material is created through the plug screw feeder 40, but the plug density may not increase over a certain level where plugging occurs which level is specific for each kind of material being compressed.
[0063] The plug screw 10 and the force-feeding screws 20am-20dm are preferably arranged perpendicular to each other, i.e. having their respective rotational axes perpendicular to each other. In a preferred embodiment, they are arranged with their respective axes essentially in the same horizontal plane, so that the non-wood plant material is fed to the plug screw from the side. Preferably, the inlet section 12 is located close to a first end 13 of the plug screw 10, the first end being the one furthest away from the treatment stage 200. [0064] In FIG. 12 is shown an alternative to FIG. 10 for the third embodiment including force-feeding screws 20am, 20bm, 20cm and 20dm in each of the four inlet ducts 20a, 20b, 20c and 20d, with force feed from above and into the plug screw. Individual motors for the force feeding screws are at hand but not shown in this drawing.
[0065] Although the invention has been described with reference to specific illustrated embodiments, it is emphasized that it also covers equivalents to the disclosed features, as well as changes and variants obvious to a man skilled in the art, and the scope of the invention is only limited by the appended claims. [0066] The embodiments as shown in FIGS. 5a and 8a could also have feeding chutes from opposite side of the housing 11, i.e. with a pair of chutes feeding from below in FIG. 5a or with four chutes from below in FIG. 8a. All chutes may also be arranged in a horizontal plane or alternatively in a vertical plane.
