Size reduction device and method for the size reduction of solid particles

Abstract

A size reduction device and method for solid particles, which are conveyed as a suspension in a liquid flow. The device includes a housing, at least two counter-rotatable size reduction components disposed in the housing, each including a plurality of cutting elements, disposed on a common rotatable shaft with a longitudinal axis. The flow direction of the suspension is at right angles to the longitudinal axes of the shafts of the size reduction components. Two mutually opposite guide rails with a longitudinal axis parallel to the shafts are assigned to components. Each guide rail includes a base plate, on which ribs with channels are constituted parallel to the flow direction on the side of the base plate towards the component.

Claims

1. A size reduction device for solid particles conveyed as a suspension in a liquid flow through the size reduction device, the size reduction device comprising: a housing which is at least partially open at opposite sides for the purpose of introducing and discharging the suspension in a flow direction; at least two counter-rotatable size reduction components disposed in the housing, wherein each size reduction component comprises a plurality of cutting elements, which are each disposed on a common rotatable shaft, wherein each shaft has a longitudinal axis, wherein the flow direction of the suspension is at right angles to the longitudinal axes of the shafts of the size reduction means; two mutually opposite guide rails with in each case a longitudinal axis parallel to the longitudinal axes of the shafts of the size reduction means are assigned to the size reduction means, wherein each guide rail comprises a base plate, on which ribs with channels lying in between are constituted parallel to the flow direction on a side of said base plate that points towards the size reduction means, wherein the liquid flow and the solid particles entrained therein having a maximum size predetermined by the width of the channel can be conveyed through the channels, and wherein the ribs each cover only a partial region of a width of the guide rails parallel to the flow direction.

2. The size reduction device according to claim 1, wherein the ribs each comprise two aligned partial ribs, wherein a central, essentially unstructured intermediate region is constituted between aligned partial ribs, in which central region a second size reduction process of small solid particles takes place.

3. The size reduction device according to claim 2, wherein the partial ribs each comprise side faces parallel to the flow direction which are broadly constituted as isosceles triangles, wherein the base of the isosceles triangles is disposed on the base plate of the guide rail and wherein the tip of the triangle lying opposite the base and pointing in the direction of the size reduction means is rounded off.

4. The size reduction device according to claim 3, wherein the partial ribs are each constituted, in their region lying adjacent to the intermediate region, first more sharply and then less sharply inclined towards the intermediate region, so that a broadly U-shaped valley is constituted in the intermediate region between the two aligned partial ribs.

5. The size reduction device according to claim 4, wherein the base plate of the guide rail comprises a central recess symmetrical with a central longitudinal axis of the guide rail parallel to the longitudinal axes of the shafts of the size reduction means, and wherein the cross-sectional area of the central recess has the shape of an isosceles trapezium, wherein the shorter base side of the trapezium forms the central region of the recess.

6. The size reduction device according to claim 5, wherein the vertex of the U-shaped valley is identical to the center point of the shorter base side of the trapezium.

7. The size reduction device according to claim 3, wherein the aligned partial ribs are constituted mirror-symmetrical with the central longitudinal axis of the guide rail parallel to the longitudinal axes of the shafts.

8. The size reduction device according to claim 3, wherein the respective distance between the two triangular side faces of a partial rib narrows from the base in the direction of the tip.

9. The size reduction device according to claim 2, wherein the longitudinal axes of the shafts of the size reduction means are orientated vertical and the ribs of the guide rails are orientated horizontal and wherein the respective uppermost and the lowest rib comprises only one partial rib on the discharge side of the housing and comprises a lengthened essentially unstructured intermediate region in the region of the introduction side.

10. The size reduction device according to claim 1, wherein a valley between the totality of the aligned partial ribs of a guide rail is constituted in a central region of the guide rails parallel to the longitudinal axes of the shafts of the size reduction means.

11. The size reduction device according to claim 1, wherein the liquid flow and solid particles entrained in the liquid flow which do not exceed a maximum size, in the partial region of the width of the guide rails not covered by ribs, can be transferred from a channel constituted between two ribs into a channel constituted between two other ribs, and wherein the suspension comprising liquid flow and entrained solid particles, in the intermediate region between aligned partial ribs of a rib, can be transferred from a channel constituted between two ribs into another channel constituted between two ribs.

12. The size reduction device according to claim 1, wherein different partial regions with different flow velocities of the suspension comprising liquid flow and entrained solid particles are assigned to the guide rails of the size reduction device, wherein the suspension flows through the partial regions one after the other in the flow direction, and wherein, in a first partial region comprising ribs, the cross-sectional area through which the suspension flows is reduced and the flow velocity of the suspension is increased compared to an entrance velocity of the suspension into the size reduction device, wherein, in a second partial region comprising no ribs, a cross-sectional area through which the suspension flows is increased compared to the cross-sectional area in the first partial region and the flow velocity of the suspension is reduced compared to the flow velocity in the first partial region, wherein, in a third partial region comprising ribs, a cross-sectional area through which the suspension flows is reduced compared to the cross-sectional area in the second partial region and the flow velocity of the suspension is increased compared to the flow velocity in the second partial region and wherein a cross-sectional area through which the suspension flows is increased compared to the cross-sectional area in the third partial region and the exit velocity of the suspension from the size reduction device is reduced compared to the flow velocity in the third partial region, and wherein the flow velocity in the first partial region roughly corresponds to the flow velocity in the third partial region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of embodiment of the invention and its advantages will be explained in greater detail below with the aid of the appended figures. The size ratios of the individual elements with respect to one another in the figures do not always correspond to the actual size ratios, since some forms are represented simplified and other forms are represented enlarged in relation to the other elements for the sake of better illustration.

(2) FIGS. 1A-C show a size reduction device with lateral guide rails according to the prior art.

(3) FIGS. 2A-E show in each case different representations of a guide rail according to the invention for a size reduction device.

(4) FIGS. 3A-D show in each case diagrammatically the through-flow of the suspension in the various representations of a guide rail according to the invention according to FIG. 2.

(5) FIG. 4 shows a cross-section A-A (similar to FIG. 1) through a size reduction device with guide rails according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) Identical reference numbers are used for identical or identically acting elements of the invention. Furthermore, for the sake of a clearer view, only reference numbers are represented in the individual figures that are required for the description of the respective figure. The represented embodiments merely represent examples of how the device according to the invention or the method according to the invention can be embodied and do not represent a conclusive limitation.

(7) FIG. 1 show a size reduction device 1 with lateral guide rails 7 according to the prior art. In particular, FIG. 1 shows a complete size reduction device 1, wherein the front side wall is not represented. This and the opposite side wall contain the inlet opening and respectively outlet opening for the suspension containing the solid particles. Two size reduction means 3 are disposed in housing 2 represented in cross-section. Said size reduction means each comprise a plurality of cutting discs 4, which are disposed as a stack upon one another. Cutting discs 4a of size reduction means 3a are disposed on a common shaft 5a and cutting discs 4b of size reduction means 3b are disposed of a second common shaft 5b. In the present case, second common shaft 5b is the drive shaft, which is driven by a drive, for example a motor M. First common shaft 5a is a driven or follower shaft 5a, which rotates around its longitudinal axis in the opposite direction with respect to shaft 5b.

(8) Cutting discs 4 are each separated from one another by spacer elements 6, wherein spacer elements 6 preferably have the same thickness as cutting discs 4, so that spacer elements 6a of size reduction means 3a lie in the same plane as cutting discs 4b of size reduction means 3b. In this way, a cutting disc 4a of a size reduction means 3a, together with spacer element 6b of the other size reduction means 3b, forms a pair of size reduction members operating with one another.

(9) Guide rails 7 are disposed in housing 2 at the side of size reduction means 3. Said guide rails can for example comprise triangular projections 7* at their opposite ends, said projections serving as diversion elements for diverting solid particles towards the front edges of the cutting teeth of cutting discs 4. An exemplary embodiment of a guide rail 7 known from the prior art is represented in FIG. 1B and FIG. 1C shows a cross-sectional representation through a size reduction device 1 according to FIG. 1A with a guide rail 7 according to FIG. 1B. Guide rail 7 comprises ribs 8, between which slots 9 are constituted. Ribs 8 and slots 9 extend parallel to the flow direction of the liquid with the solid particles to be sized-reduced. The side of ribs 8 that points towards size reduction means 3 is in each case constituted as a concave arch, in particular broadly in a form-fit manner with the external periphery of cutting discs 4 of size reduction means 3. Furthermore, guide rail 7 is disposed next to size reduction means 3, but at a certain distance from the latter, so that small solid particles can pass through, although the passage of large solid particles is not possible. Furthermore, the distance between ribs 8 of guide rail 7 is so small that the flow passage arising between ribs 8 prevents the passage of non-size-reduced waste material, but permits the passage of small solid particles of the solid waste with the through-flowing liquid. The non-size-reduced waste material is thus diverted and has to pass between the two size reduction means 3a, 3b, wherein it is suitably size-reduced.

(10) FIG. 2 shows in each case different representations of a guide rail 10 according to the invention for a size reduction device 1 according to FIG. 1A. In particular, such a size reduction device 1 comprises in each case two mutually opposite guide rails 10, which lie adjacent to the rotating cutting mechanism comprising size reduction means 3a and 3b of a two-part size reduction device 1 (see FIG. 1). With a vertical arrangement to shafts 5a, 5b of size reduction means 3a, 3b, guide rails 10 are disposed between the upper and the lower part of housing 2. With a horizontal arrangement of shafts 5a, 5b of size reduction means 3a, 3b, a guide rail 10 is assigned to the upper side wall of housing 2 and a guide rail 10 is assigned to the lower side wall of housing 2. In particular, guide rails 10 are disposed at inner sides of housing 2 parallel to longitudinal axes L.sub.5a, L.sub.5b of shafts 5a, 5b of size reduction means 3a, 3b (see also FIG. 1).

(11) FIG. 2A show as a perspective view of a guide rail 10, FIG. 2B shows a plan view, FIG. 2C shows a view from in front and FIG. 2D shows a side view.

(12) Guide rails 10 also comprise ribs 12, which—similar to the prior art—serve to ensure that the flow passage arising between ribs 12 prevents the passage of non-size-reduced solid particles, but permits the passage of small solid particles with the through-flowing liquid. The through-flow of the liquid is thus increased and at the same time the size reduction effect is increased.

(13) In contrast with the prior art represented in FIG. 1, however, ribs 12 comprise a number of structural differences. In particular, their geometrical shape displays the following properties: ribs 12 are not constituted continuous over the entire width B.sub.10 of guide rail 10, but rather are each divided into two partial ribs 13a, 13b with a so-called rib-free central region 14.

(14) The totality of all partial ribs 13a constituted mountain-like forms a first mountain chain and the totality of all mountain-like partial ribs 13b forms a second mountain chain. A valley is constituted between the latter by the totality of all rib-free central regions 14, said valley essentially extending along a central longitudinal axis L.sub.10 of the guide rail parallel to longitudinal axes L.sub.5a, L.sub.5b of shafts 5a, 5b of size reduction means 3a, 3b (see also FIG. 1).

(15) Furthermore, base plate 11 of guide rail 10, on which ribs 12 are disposed, comprises a central recess 15 parallel to longitudinal axes L.sub.5a, L.sub.5b of shafts 5a, 5b of size reduction means 3a, 3b (see also FIG. 1). Rib-free central region 14 between aligned partial ribs 13a, 13b forming a rib 12 is in each case disposed in particular in central recess 15 of base plate 11. As will be explained in greater detail in connection with FIG. 3, rib-free central region 14 forms a turbulence zone with a lower flow velocity v3, in which solid particles 30 are size-reduced by impact against the rotating cutting edges of cutting discs 4 (see FIGS. 1 and 4).

(16) Furthermore, ribs 12 comprise a symmetrical lateral bevel on both sides for exerting a directional influence on the solid particles in the liquid flow onto partial sections. Partial ribs 13a, 13b have in particular a broadly isosceles triangle shape, wherein base 16 of the triangle is assigned to base plate 11 and tip 19 lying opposite the base has an angle γ, preferably a rounded-off obtuse angle γ.sub.(ST).

(17) As can also be seen in particular in FIGS. 2A, 2D and 2E, partial ribs 13a, 13b of ribs 12 narrow from base 16 of partial ribs 13a, 13b in the region of base plate 11 towards their rounded tip 19. This means that thickness D.sub.16 in the region of base 16 is greater than thickness D.sub.19 in the region of tip 19.

(18) Furthermore, partial ribs 13a, 13b are constituted first more sharply and then less sharply inclined in their region 18a, 18b adjacent to central region 14, so that a U-shaped valley 17 is constituted in each case between the two aligned partial ribs 13a, 13b of a rib 12.

(19) FIG. 3 show in each case diagrammatically the passage of the suspension with solid particles in flow direction SR in various representations of a guide rail 10 according to the invention according to FIG. 2. Flow velocities v are represented pictorially in particular in FIG. 3.

(20) FIG. 4 shows a cross-section A-A (similar to FIG. 1) through a size reduction device 1* with guide rails 10 according to the invention, in particular the arrangement of two size reduction means 3a, 3b between two guide rails 10 according to the invention. Solid particles 30, 30.sub.G to be size-reduced are conveyed as suspension S in a liquid flow FS through size reduction device 1*.

(21) Constituted between adjacent ribs 12 of a guide rail 10 is a channel 20, into which only small solid particles 30.sub.K with a defined maximum size can enter. Larger solid particles 30.sub.G are directed back into the main liquid flow and thus between cutting discs 4 of size reduction means 3a, 3b. The flow line of a small solid particle 30.sub.K, which enters into a channel 20 constituted between two adjacent ribs 12, tends to follow the geometrical profile of ribs 12.

(22) As already described in connection with FIG. 2, the profile structure of each partial region 13a, 13b of ribs 12 makes provision such that thickness D of partial ribs 13a, 13b narrows, starting from base 16 at the lateral parts towards the rib height or rounded tip 19. The cross-sectional area of the flow or of channel 20 narrowing towards base 16 of ribs 12 makes it possible for smaller solid particles 30.sub.K to follow liquid flow FS without problem. On the other hand, the cross-sectional area of channel 20 widens at tips 19 of partial ribs 13a, 13b. This causes a locally raised flow velocity v+ in the immediate proximity of rotating cutting discs 4 (see in particular FIGS. 3A and 4), the effect of which is that larger solid particles 30.sub.G in flow channel 20 pass almost inevitably into the cutting mechanism of size reduction device 1* constituted by size reduction means 3a, 3b.

(23) The flow line also follows the profile because the side walls of partial ribs 13a, 13b each have a tendency to reduce the wall thickness or thickness D of partial ribs 13a, 13b of ribs 12, and because, in a flow field, the flow line is always tangential to flow direction SR at an arbitrary point of the field. In central region 14 of rib 12, in which ribs 12 are not constituted continuous, small solid particle 30.sub.K experiences different changes in flow direction SR. A flow region with an increased degree of freedom is found in central region 14. Small solid particle 30.sub.K, which is constrained to be transported onwards in flow channel 20 of a rib 12 on the same side of partial ribs 13a, 13b, can however also switch in central region 14, by means of a brief change in flow direction SR into a flow direction SR1, from one side of partial region 13b to the other side of aligned partial region 13a of the same rib 12. Solid particle 30.sub.K can thus change in central region 14 into different directions preferably at an acute angle α to flow direction SR into other channels 20.

(24) Since the flow velocity in channels 20 between partial ribs 13a, 13b of ribs 20 is, viewed relatively, higher than outside size reduction means 3a, 3b and since solid particle 30.sub.K has a relatively small mass, as a result of which the influence of gravity is almost negligible, solid particle 30.sub.K can change, on account of turbulent flow SR2, also into channels 20* of guide rail 10 at a higher level (see also FIG. 2A in connection with an arrangement according to FIG. 1A).

(25) In particular, four velocity changes Δv can be ascertained in the control volume, which comprises the section from entrance edge 40 to exit edge 42 of guide rail 10 including all ribs 12 present therein. These are illustrated in FIG. 3B.

(26) A first velocity change Δv1 from v1 to v2 occurs with the entry into a section II, in which channels 20 are constituted between partial ribs 13b of ribs 12 which are parallel to flow direction SR. When account is taken of the continuity equation (with retention of the mass) with
v1×cross-sectional area of the inflowing suspension in section I=v2×cross-sectional area of channel 20 in section II

(27) and the Navier-Stokes equation (amount of movement), it is then possible to resolve the latter according to the velocity field and the pressure field. The available area is thus reduced and the velocity is correspondingly increased, i.e. flow velocity v2 in section II is greater than flow velocity v1 in section I. After passage through section II, partial ribs 13b of ribs 12 end and the suspension passes into section III, which in particular comprises central region 14 between aligned partial ribs 13a, 13b of a rib 12. The suspension experiences here a second change of velocity Δv2 from v2 to v3. With the change of velocity Δv2, velocity v2 of the suspension is reduced to velocity v3, since the cross-section of the through-flow is increased again.

(28) When the suspension enters into following section IV into channels 20 between partial ribs 13a of ribs 12, the velocity changes again. With the change in velocity Δv3 from v3 to v4, the flow velocity in turn increases, wherein velocity v4 in section IV tends to correspond roughly to velocity v2 in section II. When the suspension then finally exits from channels 20 formed by ribs 12, exit velocity v5 of size reduction device 1* (see FIG. 4) is established, with the change in velocity Δv4, at a lower velocity than v4.

(29) The embodiment of partial ribs 13a, 13b in regions 18a, 18b adjacent to central region 14 (see FIGS. 2A and 2F) leads to the formation of a U-shaped recess in central region 14, in particular a U-valley 17. In particular, this is also assisted by a central recess 15 of the base plate of guide rail 10 indicated in FIG. 2E. Eddies 45 are formed in the U-shaped recess in central region 14 on account of flow velocity v3 and the flow properties of the suspension. U-shaped valley 17 initiates the formation of eddies 45 taking account of the flow forces, the surface tension and the entrainment effect, which then in turn causes turbulence and increases the probability of solid particles 30, 30.sub.K entrained in the suspension being repeatedly advanced towards cutting discs 4.

(30) The invention is based on the use of the mechanical flow properties, in order thus to generate a zone for an additional size reduction of solid particles 30, 30.sub.K. An improvement in the basic size reduction properties of the currently available double-shaft size reduction devices is thus intended to be achieved. In principle, a corresponding adaptation of the guide rail also to multi-shaft size reduction devices is conceivable.

(31) The first size reduction process takes place as soon as solid particles 30, 30.sub.G, 30.sub.K enter into the suction region of size reduction device 1* and are diverted there in the direction of cutting discs 4 on account of laterally bevelled partial rib 13b, in particular along the equilateral side 22. When solid particles 30, 30.sub.G, 30.sub.K then flow along, following flow direction SR, in channels 20 between partial ribs 13a, 13b of ribs 12, flow velocity v2 in partial section II, i.e. before reaching central region 14 of ribs 12, increases. As soon as the suspension has reached central region 14 between aligned partial ribs 13a, 13b of a rib 12, its flow velocity v3 diminishes on account of the increased cross-sectional area. In addition, this shaping stimulates the formation of eddies 45.

(32) Solid particles 30, 30.sub.K entrained in the suspension tend under these conditions to be fed in central region 14 more often towards cutting discs 4. A secondary cutting process or size reduction process is thus enabled, which in fact is an impact with the cutting edges of cutting discs 4 and brings about a further size reduction of solid particles 30, 30.sub.K. Solid particles 30, 30.sub.K then pass into partial section IV, in which channels 20 are again constituted between partial ribs 13a of ribs 12, after which they then completely leave the size reducer.

(33) Especially in FIGS. 3B and 3D, it can also be seen that uppermost and lowest rib 12* in each case comprise only one partial region 13a with adjacent lengthened central region 14*. In particular, uppermost and lowest rib 12* do not comprise any partial regions 13b aligned with partial region 13a. As a result of this design measure, a passage of larger solid particles is prevented in the region of the shaft seal.

(34) The invention has been described by reference to a preferred embodiment. The person skilled in the art can however envisage that modifications or changes can be made to the invention without thereby departing from the scope of protection of the following claims.

LIST OF REFERENCE NUMBERS

(35) 1 Size reduction device 2 Housing 3 Size reduction means 4 Cutting disc 5 Shaft 6 Spacer element 7 Guide rail 7* Projection 8 Rib 9 Slot 10 Guide rail 11 Base plate 12 Rib 13 Partial rib 14 Central region 15 Central recess 16 Base 17 U-valley 18 Region adjacent to the central region 19 Tip 20 Channel 22 Side 30 Solid particle 40 Entrance edge 42 Exit edge 45 Eddy α Angle B Width D Thickness Δv Change in velocity FS Liquid flow γ Angle L Longitudinal axis S Suspension SR Flow direction v Velocity I (partial) section II (partial) section III (partial) section IV (partial) section V (partial) section