A COMMINUTION DEVICE

Abstract: Apparatus for comminuting or finely dividing waste material, such as food waste and/or domestic waste, in water to form a slurry. The apparatus includes a tubular wall (11) whose inner surface has an axis about which the inner surface is rotationally symmetrical. The inner surface has disposed around the periphery of the wall slot-like sieve openings which are generally similarly orientated in relation to each other, wherewith the wall delimits a comminuting chamber which includes a rotationally-driven knife carrier which is adapted to rotate about the axis (2) of the wall (11), and which carries a cutting edge (41). The cutting edge (41) is adapted to move tightly adjacent the inner surface of the wall (11) and to sweep over the slot openings (8). The cutting edge (41) defines an angle in the region of 10-80 DEG relative to the length axis of respective swept slots, as seen in the inner surface of the wall (11), wherein the direction of rotation of the cutting edge deviates from the length axis of said slots by at least 10 DEG .

Description: A comminution device The present invention relates to an apparatus of the kind defined in the preamble of Claim 1, for comiTiinuting, or finely dividing, food wastes in water to form a mixture or slurry. The slurry shall be suited for biogas-winning and will preferably also have a high dry solids content. After having been prepared, the slurry is led to a fermentation tank in which biogas is acquired. After winning biogas, the solid rests in the slurry are made hygienic, i.e. heat- treated, the thickness of the solid rest particles preferably being at most about 10 mm. It is well known to comminute food wastes in water to form a slurry, for instance as illustrated in U.S. 4,034,422, U.S. 4,128,210, U.S. 4,183,470 and U.S. 4,917,311. Basically, a known apparatus of this kind comprises a tubular wall which has a rotational- symmetrical inner surface with sieve openings distributed around the wall periphery, wherewith the inner surface of the wall delimits a comminuting chamber that includes a rotationally driven impeller which is coaxial with the wall and which includes a cutting edge, wherein the comminuted or finally divided waste material is able to pass through the openings into a collection chamber. One problem with earlier known constructions is that the wall openings frequently become clogged and are difficult to clean. In the case of this earlier technology, circular holes have been used typically in said wall. In the case of apparatus constructed in accordance with the earlier technology, the holes often become clogged by parts of the waste being processed, such as salmon skin and the like. Moreover, the earlier apparatus normally operate with slurries that have relatively low dry solid contents slurry, meaning that relatively large biogas production tanks are required and that relatively large amounts of energy are consumed in rendering the waste hygienic subsequent to winning said biogas and/or for de-watering in connection with dumping the solid rests. Accordingly, one object of the invention is to provide an apparatus that will operate effectively with slurries that have a relatively high dry solids content and also to enable troublesome types of waste products to be disintegrated effectively, such as fish skin, salmon skin, and the like. This object is achieved with an apparatus according to the accompanying independent Claim 1. Other embodiments of the apparatus will be apparent from the accompanying dependent Claims. In accordance with the invention, the cutting edge shall be arranged to sweep closely adjacent to a wall surface that includes slot-like openings, wherein said cutting edge is adapted to define an angle in the region of 10-80° relative to the longitudinal direction of the slots swept by said cutting edge, said slots being essentially similarly orientated in relation to each other. The angle is chosen so as to establish a clipping effect between the cutting edge and one long edge of respective slots. The cutting edge is conveniently disposed on a knife that is generally parallel with the inner surface of said wall and moves adjacent thereto. The cutting edge and the slots suitably have opposite slopes in relation to a line on the surface of the inner wall that extends parallel with the axis. The slots may have a length/width ratio in the order of 1 :3, wherewith the slots may have a width of about 1 cm and a length of about 3 cm, for instance. The cutting edge and the slots are conveniently arranged so that when sweeping over a slot the cutting edge will cross said slot at a point which is displaced progressively along the slot, preferably upwards in the arrangement. The length direction of the slots deviates from the rotational direction of the cutting edge suitably by at least 50°. The chamber has a generally vertical axis, wherewith the slots and the cutting edge are orientated to have an intersection point that moves upwards in the chosen direction of rotation of the cutting edge. The apparatus also includes means for supplying water and waste to the chamber continuously, wherein said means can be set to produce a slurry that has a dry substance content of at least 5%, preferably at least 10%, more preferably at least 15% and even more preferably about 20% or higher. The apparatus may include a chamber for collecting the slurry that passes through the slots, said chamber being connected to a feraientation tank for winning biogas. The invention will now be described in more detail by way of example and with reference to the accompanying drawing. Fig. 1 is a schematic axial section view of an inventive apparatus. Fig. 2 is a schematic section view taken on the line II-II in Fig. 1. Fig. 1 shows a container 1 which receives, via respective conduits 20, 30, water and food waste/domestic waste in proportions chosen in relation to each other,. Each conduit is shown to include a respective valve 21 and 31 and is also shown to be connected to a respective pump 22 and 32, wherein the apparatus is adapted to establish in the container a slurry that has a chosen dry solids content. The illustrated container is essentially rotational-symmetrical about a vertical axis 2 and has a downwardly narrowing diameter, including a generally cylindrical wall section 11. Located immediately beneath the bottom edge of said section 11 is a bottom plate 3 which is rotatable about the axis 2 and which carries at its periphery a knife 4. The wall section 11 forms part of a ring-shaped collecting box 5 which includes an outlet pipe 6 that leads to a tank 7. The wall section 11 includes transit openings 8, which are disposed in rows that lie respectively in a plane normal to the axis 2. The openings 8 in respective rows are preferably similarly orientated in relation to each other. The knife 4 of the illustrated embodiment has a forwardly extending cutting edge 41 which lies closely adjacent the inner surface of the wall section 11 and which defines a line 42 that forms an angle β with a line 50, which is parallel with the axis 2 and lies on the inner surface of the wall section 11. It will also be seen that the wall 41 slopes upwardly and rearwardly in relation to its movement direction 43, which lies in a plane normal to the axis 2. It will also be seen that the openings 8 have a generally elongate slot-like form. In one preferred embodiment, the slots 8 have a length/width ratio of 3: 1, wherewith the width is about 10 mm and the length about 30 mm. As shown, the slots 8 and the cutting edge 41 are generally straight in their longitudinal direction, and curved extensions are possible provided that the inventive clipping effect is achieved. The slots 8 are orientated so that their long axes 81 will define an angle α relative to the axis 50, said angle preferably being about 30°. α + β is greater than 10° and preferably greater than 20°. α + β is suitably 70° at the highest. Preferably, α + β is in the range of 20-60°, for instance about 40°, although the clipping angle α + β may, of course, be chosen with respect to the clipping effect desired in respect of material that is difficult to disintegrate or shred. The cutting blade 4 is suitably generally parallel with the inner surface of the wall 11. The bottom plate rotatably driven about the axis 2 may, of course, carry a plurality of knives 4. The angle γ between the direction of movement 43 of the knife and the length direction of the slot will preferably be at least 10° and more preferably about 60° in the illustrated case. This angle shall be chosen so as to prevent pieces of material from being displaced along respective slots without being clipped or cut against the long edges of the slots. Although the wall section 11 is shown to be generally cylindrical, it will be evident that the generatrix of the wall section 11 may be inclined to the axis 2. As shown in Fig. 1 , the collecting box 5 has a corner gap, which is sealed by the edge of the bottom plate disposed adjacent thereto with a small clearance. However, it will be obvious that the collecting box 5 may have a generally closed cross-sectional profile whose inner wall is provided with the slots 8 that are swept by the knife 4. Fig. 2 shows the slots 8 disposed in two mutually parallel rows, wherewith the slots 8 in both rows are mutually aligned in pairs. The slots may be included in fewer or more rows.

Claims: CLAIMS 1. Apparatus for comminuting or finely-dividing waste material, such as food waste and/or domestic waste, in water such as to form a slurry, wherein said apparatus includes a tubular wall (11) that has an inner surface which includes an axis about which the surface is rotationally symmetrical, wherein the inner surface has- disposed around its periphery slot-like sieve openings (8) which are orientated generally similarly in relation to each other, wherein the wall delimits a comminution chamber which includes a rotationally driven knife carrier (3) which is rotatable about the axis (2) and carries a knife (4) that has a cutting edge which is adapted to move tightly adjacent the inner surface of the wall (11) so as to sweep across the slot-like openings (8), characterised in that the cutting edge (41) defines an angle of 10-80° with the length direction of respective swept slots (8), wherein the length direction of respective slots (8) defines an angle of at least 10° with the direction of rotation (43) of the knife. 2. Apparatus according to Claim 1, characterised in that knife (4) includes a cutting blade that extends in a plane which is generally parallel to and lies adjacent the inner surface of said wall. 3. Apparatus according to Claim 1 or 2, characterised in that the cutting edge (41) and the length direction (81) of respective slots have opposition inclinations relative to a line (50) in the inner wall surface parallel with the axis (2). 4. Apparatus according to any one of Claims 1-3, characterised in that the angle between the length direction of respective slots and the cutting edge is at least 20° and preferably at least 30°; and in that said angle is less than 70°, preferably less than 60° and more preferably less than 50°. 5. Apparatus according to any one of Claims 1-4, characterised in that the axis of the wall (11) is essentially vertical; and in that the direction of rotation of the knife carrier is chosen to cause the point of intersection between the cutting edge and respective slots to move upwards. 6. Apparatus according to Claim 5, characterised by means (21, 22; 30, 31, 32) for supplying water and waste material to said chamber, wherein said means can be set to establish in the container (1) a slurry that has a chosen dry solids content of at least 10%, preferably of at least 15% and more preferably of around 20%. 7. Apparatus according to Claim 6, characterised by means (20-22; 30-32) for supplying water and waste material to the material for maintaining a slurry that has a chosen, generally constant dry solids content in the container (1). 8. Apparatus according to any one of Claims 1-7, characterised by a collecting chamber (5) which receives the slurry departing via the slots and which surrounds said wall section (11); and in that the collecting chamber can be connected to a tank (7) via a conduit (6), for winning biogas by fennentation of the slurry. 9. Apparatus according to any one of Claims 1 -8, characterised in that the slots (8) have a length/width ratio in the region of 2 : 1 to 5 : 1 , preferably about 3 : 1 ; and in that the slots have a width in the region of 0.5-1.5 cm, preferably about 1 cm. 10. Apparatus according to any one of Claims 1-9, characterised in that the length axis of the cutting edge (41) defines an angle of roughly 60° with the length axis of respective swept slots (8); and in that the length axis of the cutting edge defines an angle of roughly 60° with the rotational direction (43) of said knife.

Inventors: OEHRN GUNNAR, OEHRN, GUNNAR
Applicants: OEHRN GUNNAR, OEHRN, GUNNAR
Application year: 2001
Main classification: B02C18
IPC codes: B02C18