WO2004016356A1

WO2004016356A1 - Method and device for grinding bulk materials

Info

Publication number: WO2004016356A1
Application number: PCT/FR2003/002012
Authority: WO
Inventors: Mathias Falkenberg
Original assignee: Alidomi Environnement Sarl
Priority date: 2002-07-30
Filing date: 2003-06-30
Publication date: 2004-02-26
Also published as: DE10234763A1; AU2003260638A1; EP1558394A1

Abstract

The invention relates to a method and device for grinding bulk materials (2) which have very flexible granules and a loose and very compressible bulk structure (5). Said coarse granulation materials are transported to a grinding device (1) which transforms the materials in such a way that the granulation thereof becomes finer. For this purpose, the generic type device (1) comprises at least one grinding unit (16). In order to grind the bulk materials (2) with a defined low dispersion granulation by means of less sophisticated equipment, the bulk structure is compressed prior to grinding in such a way that the thus obtained granulation thereof is finer. Said grinding unit is embodied in the form of a cutting tool to which the bulk material having the bulk compressed structure is transported.

Description

Method and device for grinding bulk materials

The invention relates to a method and an apparatus for grinding bulk materials with very flexible granules and a loose bulk structure which is very compressible, and which are brought under coarse granulation to a grinding apparatus, with the help of which the bulk material bulk is processed to obtain finer granulation. For this, an apparatus of the known generic type comprises at least one grinding mechanism.

In the present description, the expression “bulk material” designates a material in small pieces, in bulk and which is usually transported without packaging. The smallest unit of bulk material is here - regardless of its shape or structure - called "granulated"; an averaged measure of particle size calculated from many pellets is called "granulation" of the bulk material. The "bulk structure" describes the position of the granules of a bulk material in relation to each other.

Waste in the form of films or sheets, in particular that which is made of plastic and originating, for example, from bags used in commerce, pieces of "blister" packaging or large format films with air bubbles are designated as granules as defined above. As another example of loose material in the above sense, one can cite the piled fall foliage, as it occurs in large quantities at a seasonal rate. The individual sheets or pieces of these sheets are here called granules.

In a bulk structure of these materials, there are formed - which is favored by the sheet form of the individual granules and their irregular arrangement with respect to each other - hollow cavities filled with air whose volume far exceeds the volume of the granules themselves. In the bulk materials mentioned by way of example, the granule is very flexible: it does not offer any particular resistance to its deformation - buckling, bending or flattening in the direction of elongation. Such a bulk structure is highly compressible, even at a relatively low pressure, insofar as the air can generally escape from the hollow cavities which have formed therein, and from the volume of the bulk structure.

The usual methods and apparatus for grinding bulk materials are used in particular in the preparation of film waste collected for their thermal exploitation in industrial combustion ovens. Grinding the pieces of film to a defined granulation is a necessary condition for this use. On the one hand, large format pieces are very exposed to convective effects because of the sheet form, so that the place of combustion is barely predictable. On the other hand, it is only at the cutting edges of the pieces of film that the surface required for the supply of oxygen required relative to the material burned is available. At a distance of only a few millimeters from the edges of the pieces, regular and complete combustion is not achieved at the temperatures that usually prevail in industrial ovens, but the pieces are consumed in a "smoldering" fire - undesirable for reasons energy.

In general, processes and apparatuses of the known generic type are known which act essentially by smashing, tearing or shredding individual granules of the bulk material. For example, hammer mills are used provided with a cylinder housed in a cylindrical drum, which is rotatable in the direction of the axis of the drum and to which hammers are fixed by articulations. Bulk material is fed to the drum, individual granules are crushed and smashed between the wall of the drum and the hammers, and the pieces are evacuated through the wall of the drum made as a screen.

Furthermore, there is also known an apparatus equipped with a cylinder also housed in a cylindrical drum, which is rotatable in the direction of the axis of the drum and which is provided with cutting edges essentially placed in the axial direction and radially in projection. The individual granules are cut by these cutting edges on counter knives which are also arranged radially projecting in the wall of the drum. Here too, the wall of the drum is made like a screen and the size of the screen perforations then determines the granulation of the bulk material generated in the device.

In the above techniques, the treated granules are exposed incidentally to the grinding tool - regardless of their current size - and are removed when they pass below the size of the perforations of the screen-shaped wall . The residence time of a granule in the process can thus only be determined statistically; the performance of the device is not exactly adjustable, and the desired granulation is not achieved without fail.

In addition, these techniques require a large complex apparatus and cause in particular with hammer mills, the emission of considerable noise as well as the wear of the grinding tools. In addition, the performance of known devices can only be adopted by adapting the speed of rotation of the cylinder. In addition, in the apparatus described with cutting edges on the cylinder, there is regularly observed during increases in the working speed, or when the drum is overloaded, an increase in the friction effects of the granules on the walls of the drum. and between them, and, consequently, an increase in the working temperature which represents in extreme cases a significant fire risk. The quality, efficiency and safety of the incineration of waste, industrial, household or other waste are dependent on the homogeneity of the product to be incinerated. Usually, the waste burns badly, because its composition is irregular, which gives great variations in quality

(mixture of plastic, paper, cardboard, rags, wood, etc.). After treatment of these products according to the process of the invention, or by the device (the system cuts the products and does not chop them like the known systems), regular quality is obtained. The waste can be reduced to a particle size which varies between 0.1 and 20 mm, preferably 0.1 and 2 mm, and obtain perfect homogeneity.

The combustion is regular by its constant calorific value.

One can use the product obtained alone or mixed with products to be incinerated, or inject it in surplus to regulate combustion. The present invention relates to a method and an apparatus for grinding bulk materials, allowing the grinding of bulk material to a defined granulation, with the lowest possible dispersion, and this with a little complex apparatus.

Starting from the known methods, this objective is achieved in accordance with the invention insofar as the bulk structure is compressed before grinding and the bulk material is treated in the compressed state. This makes it possible to obtain a finer granulation, by cutting. An apparatus according to the invention is characterized, in addition to the generic characteristics of the known apparatuses, by the fact that the grinding tool is a cutting tool towards which the bulk material can be brought in the form of a bulk structure compressed and treated using this tool to obtain fine granulation, by cutting. In a compressed bulk structure, the bulk density is, in comparison with a loose bulk structure, on the one hand generally higher, and on the other hand, locally homogenized. In this state, the bulk material can be transformed as a solid material: thanks to homogenization, the grinding of the bulk material can be controlled and controlled much more easily, in comparison with known methods; moreover because of its higher density, the bulk material is easier to convey when the grinding tool penetrates, and does not escape from it as easily. The invention will be better understood on reading the following description and in view of the appended figures.

FIG. 1 represents a schematic view of an installation according to the invention.

2 shows a schematic side view, in section, of an installation according to the invention.

Figures 3 and 4 respectively represent a schematic top view and side view of an installation according to the invention.

The cutting methods used in accordance with the invention allow, with at least one cutting edge on a cutting surface, a defined sectioning of a "piece" of the compressed bulk material.

The term “cutting process” includes, in particular, both the use of knives and the shearing processes with counter knives. If the "piece size" is less than the granulation of the bulk material being fed, the individual granule of the compressed bulk material is cut, thereby producing finer granulation. The selection, on the one hand of the speed of advance of the compressed bulk material, and on the other hand of the cutting frequency, allows a particularly easy adjustment of the desired fine granulation. The process according to the invention can be used in a particularly advantageous manner for grinding the loose material in the form of sheets, the granules of which have only a very small elongation in one dimension. Such bulk materials are, in particular, sorted plastic film waste. Controlled crushing of such sheet-like bulk material in a loose bulk structure has hitherto been practically impossible. On the other hand, - with the process according to the invention, it is possible to achieve practically a predetermined desired granulation. Thus, loose materials in the form of sheets can also be treated for their thermal exploitation.

The cutting tool used is advantageously provided with several cutting edges, each with a small width, which are placed in the cutting plane next to each other and at a distance from each other, and which penetrate into the material in bulk compressed. The length of the cut pieces of the bulk material is then limited in the direction of the cutting edges essentially to their length. In addition, the neighboring cutting edges can be arranged offset in the cutting direction, and the impact generated by the penetration of the cutting tool into the bulk material is significantly reduced. This effect can be obtained by juxtaposing a plurality of discs of substantially the same diameter, provided with teeth on their axial surface, thus forming a rasp. For example, the discs can be 2 to 4 mm thick. As a result, the mechanical stress of oscillation and impact of the cutting tool is reduced, as is that of all the components of the equipment on which this stress is reflected, in particular, the connection and mounting elements. This reduces, therefore, on the one hand, the requirements to be placed on these components, and, on the other hand, also directly the development of noises in operation. This is why a rasp is preferably used as a cutting tool in the apparatus according to the invention - a tool provided with numerous narrow cutting edges, arranged one behind the other and next to each other in the direction cutting. As an alternative, it is also possible to use, in place of several cutting edges of a small width, a single cutting edge which extends over the entire cutting surface. Admittedly, continuous cutting edges have, in principle, advantages in terms of manufacturing and maintenance. However, if the structure or position of the bulk material is unfavorable, it is possible that cut pieces may form whose length reaches the width of the cutting surface or even clearly exceeds it, when bending in the material to be cut. . The cutting tool in an apparatus according to the invention is then, for example, an isolated shearing tool or a series of shearing tools arranged one behind the other. The mechanical relief described above of the apparatus according to the invention is obtained by the use of shearing tools distributed transversely over the entire surface of the cut and arranged at an angle with respect to the cutting direction.

Preferably, in the process of the invention, the bulk material is conveyed to the apparatus in the form of a loose bulk structure. Then, the method can be implemented, for example, without storage or intermediate treatment, directly after sorting the bulk material. However, bulk materials transported or temporarily stored in different dimensions and shapes can be dispersed by means of generally known devices, and then led to the process according to the invention without further pretreatment. Then, the bulk material is transported in the form of a loose bulk structure to the apparatus according to the invention, in a manner known to those skilled in the art, for example, with belt conveyors or chutes. Alternatively, the apparatus according to the invention is provided with a compression mechanism with the aid of which the bulk material can be compressed and at the outlet from which the bulk material can be brought directly to the cutting tool .

Preferably, the process is implemented continuously, within the framework of processes with regular and automated progress on industrial ovens. This can advantageously be obtained using the apparatus according to the invention, when a loose bulk structure of bulk material is transported to a hopper which narrows in the direction of conveying. The loose, rod-like structure that escapes from the end of the hopper is then compressed relative to the incoming bulk material. This effect is favored when the hopper is installed vertically, its outlet being directed downwards. The bulk material which enters it then compresses by its weight the bulk structure which is below. The walls of the hopper are advantageously provided with a perforation allowing the air which is trapped in the loose bulk structure to escape.

A discontinuous compression mechanism can be, for example, a compression chamber which is limited on the sides and which can be filled with loose loose material. As soon as the filling level reaches a predetermined value, the feeding is interrupted and the bulk material is compressed using a first buffer arriving, for example, from the top, then pushed towards the cutting tool. by means of a second buffer as soon as the compression is completed. Such a machine is shown in Figures 3 and 4, with two pistons, a different number of pistons can however be used.

The compression effect is further increased considerably by a conveying mechanism which allows the bulk material to be transported to the compression mechanism. Preferably, the conveying is equipped, in an apparatus according to the invention, with at least one roller rotating perpendicularly to the conveying direction. The loose material is brought to the upper envelope surface of the roller, and moved in the peripheral direction of the roller due to the forces of adhesion to this surface. Several rollers can be used arranged one behind the other in the conveying direction and / or placed one opposite the other on the material flow.

Alternatively, the two effects of compression and conveying of the bulk material are obtained using a worm device, illustrated in FIG. 2.

Alternatively, the bulk material can be brought to an apparatus according to the invention in an already compressed state, in the form of a boot or continuous roll for example. Then, the apparatus of the invention need only be provided with a guide or support mechanism which prevents the bulk material from deflecting as the cutting tool enters it.

The distribution of particle sizes which it is possible to target with a method according to the invention can be homogenized in a particularly advantageous manner by a sorting device mounted downstream. The various particle sizes can be separated, for example, by grids with different perforation or by centrifuges, in the manner known to those skilled in the art. The process according to the invention can easily allow the bulk material, the dimensions of which are insufficiently reduced, to be recycled to the cutting tool. An embodiment is illustrated below in a schematic representation by way of explanation of the invention.

The figure shows an apparatus 1 according to the invention for grinding the bulk material 2. The bulk material 2 is a mixture of pieces of plastic films which are not shown individually, as they are made available in bundles in the form of a boot - which are not represented either - by the devices for recycling residual materials, after rough sorting of packaging waste, for thermal exploitation as the main fuel for ovens industrial. The size of the pieces of film lies in a range from a few square centimeters to several square meters, and their thickness varies between a few hundredths and several tenths of a millimeter.

The bulk material 2, for example delivered in packages, is transported to the apparatus 1 in the form of a loose loose structure 5 with an average dumping height 6, in the usual way, not shown, that is to say under dispersed form and by means of a belt conveyor 3, the conveying direction 4 is horizontal. In order to protect the device 1 from damage, the bulk material 2 is conveyed on the belt conveyor 3 and passes under a metal detector 7, optionally. If an unrepresented metallic foreign body is detected, the unrepresented drive of the belt conveyor 3 can be immobilized by a signal from the metal detector 7, which allows this foreign body to be removed manually. The device 1 has, after the belt conveyor 3, an inlet orifice 8, open in the direction opposite to the conveying direction 4 and whose cross section is essentially rectangular. A domed guide plate 9 in the form of an upwardly directed funnel guarantees that the pieces of film which clearly exceed the average discharge height 6, will be transported surely towards the inlet orifice 8.

Behind the inlet 8 is a conveying mechanism 10 consisting of two rollers 11, placed one opposite the other, which rotate in opposite directions, and by means of which the bulk material 2 is transported to a compression mechanism 12 in the form of a channel 13 which is shrinks like a funnel. It is through this channel 13 - using the conveying mechanism 10 - that the bulk material 2 is continuously compressed and pressed in the form of a rod. To avoid an obstruction of the compression mechanism 12, the upper wall 14 of the channel 13 is mounted with an elastic suspension directed upwards

(not shown). In this way, it is also possible to convey into the compression mechanism 12 the pieces of film which offer a high resistance to their compression.

The bulk material 2 which leaves the compression mechanism 12 in the form of a rod, in a compressed bulk structure 15 and practically without air pockets, is led directly to the grinding mechanism 16. The grinding mechanism 16 comprises a grater cylindrical 18 which rotates around a horizontal axis 17 and which consists of coarse saw blades with open teeth, not shown individually and stacked on top of each other.

The grinding mechanism 16 is installed inside a casing 19 in the form of a box which is provided on the bottom 20 with a horizontal mesh 21. The mesh width of the mesh 21 corresponds to the maximum admissible particle size which must be generated with the device 1. The granules deposited above the mesh 21 are again led to the device 1 by a return flow 22 (not shown). The granules which pass through the grate are annexed to a combustion furnace (not shown) by means of an exhaust air flow 23.

The device 1 shown makes it possible to bring the bulk material 2 to a defined granulation, which can be between approximately 0.1 to several millimeters, and this with little equipment and low energy expenditure. The dispersion of the particle size is extremely reduced.

Due to the simple structure, it is possible to have a combination of several devices 1 for supplying fuel to an industrial oven. In the event of a line failure - for example, due to the detection of a metallic foreign body in the bulk material 2 - it is possible to ensure the supply by temporarily increasing the performance of the other lines. Unlike known devices, increasing the performance of device 1 poses no problem, even over wide ranges: in comparison, the flow rate of device 1 is already high, even when the rasp 18 is running at low speed. In the apparatus 1, the performance is more limited by the power of the compression mechanism 12 than by that of the grinding mechanism 16. Similarly, the apparatus 1 can also be used for grinding paper, cardboard, wood or plastics which are not in film form.

As the device 1 only consists of a limited number of moving parts, wear and maintenance work are excessively reduced. If the individual saw blades are damaged or worn, they can be replaced or reworked simply. Furthermore, saw blades manufactured in large quantities can be used, and represent a low cost factor.

As an indication, the possible uses of the fuels obtained according to their particle size are given below. With a particle size of less than 2 mm, the fuels can be used as the main fuel, for example in coal ovens where it is injected, or in any incinerator, as a regulating fuel. For particle sizes of the order of 2 to 25 mm, the fuel obtained can be used as secondary fuel and combustion regulator for example in precalcination stages, in cement works in particular.

With grain sizes of the order of more than 25 mm, the fuels can be used as secondary fuels. Thus, the product obtained according to the present application can be used not only as the main fuel, but also as a combustion regulating fuel and combustion additive in particular in high temperature ovens (temperatures above 850 ° C) such as cement kilns and hot kilns, household waste incinerators (IOM Incinerator of Household Waste), steel mills, thermal power plants, sugar factories and the glass industry.

Example:

An uncompacted mixture of plastic, paper and textile is introduced into a worm press which, by its degressive curve system, pushes the product at a pressure of around 3 MPa towards a shrinking mechanism. Thus, in Figure 2, is shown schematically or in partial section, an apparatus according to the invention.

A worm screw 30 is housed in a coaxial sheath 32 provided with a feed chute 34 at one end of the worm screw, chute 34 through which the bulk material is introduced, according to arrow 36. The material is entrained towards the frustoconical end-piece 38 of output placed at the other end of the worm 30 which opens at its end 40 on the cylinder 42 whose axis is perpendicular to the axis of the worm. The cylinder 42 carries the knives or the teeth, not shown. The cylinder 42 is formed of a plurality of concentric metal discs of the same diameter and a thickness of 2 mm, the axial length of the coincident cylinder being at least equal to the corresponding dimension of the end 40 of the frustoconical endpiece. The discs forming the cylinder 42 carry, at least on the part of the cylinder disposed opposite the end 40, teeth which cut the compressed material at its exit from the frustoconical end 38.

As shown in FIG. 2, the frustoconical end piece 38 is provided with smooth walls up to the end 40. The shrinking mechanism, here frustoconical end piece 38, is designed so that the plastic / paper mixture / textile is pushed outwards without reducing or slowing the flow towards the knives and without causing blockage by reducing the diameter. Preferably, perforations are provided to facilitate compression.

To absorb the radial forces which can be exerted on the helical screw, for example due to pieces of wood or textile, the screw used is preferably hollow and has large roller bearings due to its large diameter. These two characteristics make it possible to avoid its deformation.

The plastic, paper and textile mixture exits at the end 40 through an opening 15 mm high and 526.2 mm wide. In the installation schematically shown in Figure 2, the discs all have substantially the same diameter of the order of 22 to 24 cm and are arranged in sufficient number to have a cutting width of at least 53 cm. The end 40 is not contained in a plane, but in a cylinder coaxial with the cylinder 42. In front of the end 40, the knives of the cylinder 42 are arranged to pass as close as possible to the mouth 40 and cut the mixture precompressed. The frustoconical shrink fitting 38 is provided with four rollers, not shown, capable of rolling on the surface of the cylinder 42. They are movable so as to be able to obtain and modulate the exact distance during cutting. The distance between the cylinder 42 carrying the blades or teeth relative to the end 40 is adjusted with traction hooks, the adjustment operations using torque wrenches. The knives used are made of special steels for cutting tools. For the rest, the installation comprises at least the same components as those of the installation shown diagrammatically in FIG. 1. With such an installation, even when working 24 hours a day (3 exposures), the knives are replaced annually, with lubrication regular.

The particle size modulation of the plastic, paper and textile mixture is obtained by modulating the speed of rotation of the knives, with constant supply of the helical screw. For the final adjustment, the cylinder 42 is provided with an auxiliary motor, not shown, which allows the adaptation of the speed of rotation of the knives using an annex adjustment unit.

The helical screw drive motor has a power of 37 kW. The knife drive motor has a variable power, with maximum values of the order of 160 kw and operating powers between approximately 75 kw and 100 kw. The cutting cylinder 42 is driven by a belt, and rotates at a speed of 300 to 800 rpm, for example 400 rpm. The machine presented here produces 5 T / h and these quantities can be increased. Alternatively, in the installation shown in Figures 3 and 4, the compression of the bulk material is carried out hydraulically. Two pistons 41 and 43 make it possible to compress the material introduced according to the arrow 46 which passes through the narrowing duct 48. At the outlet of this duct 48, at the end 50, the bulk material is cut by the teeth of the discs forming the cylinder 52, driven by the motor 53 by the belt 55.

The orders of magnitude of the powers, pressure, and dimensions of the discs, ends are given here for information. Smaller or larger facilities may be provided.

Claims

claims

1. Process for grinding bulk materials with very flexible granules and a highly compressible loose bulk structure, which are brought under coarse granulation to a grinding apparatus, with the help of which the bulk material is transformed into granulation finer, characterized in that the bulk structure is compressed before grinding and that the bulk material is transformed in this state by cutting to obtain the finest granulation.

2. Method according to the preceding claim, characterized in that the compressed bulk material is cut by means of several cutting edges of a small width which are placed in the cutting plane next to each other and at a distance from each other others.

3. Method according to one of the preceding claims, characterized in that the bulk material is conveyed to the device in the form of a loose bulk structure.

4. Method according to one of the preceding claims, characterized in that the bulk material is continuously pressed in the form of a rod and is cut in this state.

5. Method according to one of the preceding claims, characterized in that the bulk material produced after grinding is sorted according to the granulation.

6. Apparatus (1) for grinding loose material (2) with very flexible granules and whose loose loose structure (5) is very compressible - the loose material (2) can then be transported to the apparatus (1 ) under coarse granulation and transformed using a grinding mechanism

(16) to obtain a finer granulation, characterized in that the grinding mechanism (16) is a cutting tool to which the bulk material (2) can be conveyed in the form of a compressed bulk structure (15) and at by means of which it can be transformed by cutting to obtain the finest granulation.

7. Apparatus (1) according to claim 6, characterized in that the grinding mechanism (16) comprises a grater (18).

8. Apparatus (1) according to either of Claims 6 and 7, characterized by a compression mechanism (12) which makes it possible to compress the bulk material (2) and at the outlet of which the bulk material ( 2) can be transported directly to the grinding mechanism (16).

9. Apparatus (1) according to claim 8, characterized by a conveying mechanism (10) using which the bulk material (2) can be conveyed to the compression mechanism (12).

10. Apparatus (1) according to claim 9, characterized in that the conveying mechanism (10) comprises at least one cylinder (11) rotating perpendicularly to the conveying direction (4).