WO2008110517A1

WO2008110517A1 - Method and device for the cryogenic grinding of bulk material

Info

Publication number: WO2008110517A1
Application number: PCT/EP2008/052791
Authority: WO
Inventors: Igor Plahuta
Original assignee: New View S.L.
Priority date: 2007-03-09
Filing date: 2008-03-07
Publication date: 2008-09-18
Also published as: EP2136926A1; DE102007011970A1

Abstract

The invention relates to a method for the cryogenic grinding of bulk material, especially bulk material having soft or elastic material properties, for example rubber-elastic properties, under normal conditions. According to said method, the bulk material is embrittled so that the particles of bulk material can then be size-reduced in the embrittled condition. The surface of the particles of bulk material is increased before the step of embrittlement. The invention also relates to an installation (1) for the cryogenic grinding of bulk material, especially bulk material having soft or elastic material properties, for example rubber-elastic properties, under normal conditions. Said installation comprises a cooling section (7) for embrittling the particles the bulk material is constituted of and a size-reduction device (8), mounted downstream of said cooling section, for size-reducing the material embrittled in the cooling section (7). The installation (1) also has a device (2), mounted upstream of the cooling section (7) in the direction of material flow, for increasing the surface of the particles of bulk material.

Description

Method and device for cryogenic crushing of bulk material

The invention relates to a method for the cryogen crushing of bulk material, in particular of bulk material with soft or elastic under normal conditions material properties, such as rubber elastic Eigen- shanks, in which the bulk material is embrittled to then crush the bulk material particles in their embrittled state. Furthermore, the invention relates to a system for cryogen crushing of bulk material, in particular of bulk material with soft or elastic under normal conditions material properties, such as elastomeric properties, with a cooling section for embrittlement of the bulk material forming particles and with a cooling line downstream crushing device for comminuting the embrittled in the cooling section material.

In order to be able to comminute bulk goods whose particles have soft or elastic, in particular rubber-elastic properties under normal conditions (ambient conditions) with conventional comminution devices, for example impact shredders, they are embrittled before the comminution step. For this purpose, the bulk material particles to be crushed pass through a cooling section in which they are cooled down to a temperature such that they are embrittled before their comminution. Typically, liquid nitrogen is used for cooling, which in its evaporation extracts heat from the bulk particles to be cooled, causing it to be cooled. A typical bulk material which is cryogenically comminuted are, for example, motor vehicle tire granules. In the embrittled state, such bulk material particles can readily be supplied to a crushing device, wherein crushing devices are usually mills or disintegrators, such as impact mills.

In an operation of such a cryogenic crushing plant, it is endeavored to keep the coolant consumption low. It has been proposed in DE 103 52 300 A1 to divide the flow of bulk material before the process of embrittlement into individual particle fractions differing in their grain size. This is done with the aim that each particle fraction has a relatively homogeneous particle size distribution having. Each particle fraction is assigned its own cooling section. On account of the homogeneous particle size distribution in each particle fraction, the cooling conditions, ie the use of the coolant quantity and / or the residence time of the particles introduced into the cooling section, can be adapted to the mean particle size of a particle fraction in order to achieve through-and-through embrittlement of the particles with minimal refrigerant consumption to achieve a particle fraction. An embrittlement of particle fractions with a larger grain size can therefore be carried out under different process parameters than an embrittlement of the particle fractions with a smaller grain size.

In this prior art method is considered disadvantageous that in the grain size-dependent fractionation of the bulk material particles before embrittlement tend the sieves with a smaller mesh size to clogging. Also sometimes the necessary provision of several parallel to be operated cooling sections is considered disadvantageous.

Based on this discussed prior art, the invention is therefore based on the object, an initially mentioned method and to provide a corresponding system in which a largely homogeneous embrittlement of the bulk material particles is possible without the bulk material flow must be fractionated in particle sizes.

This object is achieved by an aforementioned method in which the surface of the bulk material particles is increased before the step of embrittlement.

The system-related object is achieved by a plant of the aforementioned type, in which the system comprises a cooling line in the material flow direction upstream device for increasing the surface of the bulk material particles.

In this method, the same applies to the claimed device, the surface of the bulk material particles is increased before the step of embrittlement. The result of increasing the surface area of the individual bulk particles is that the coolant used, for example the liquid nitrogen, has a correspondingly larger surface area compared to those prior to the treatment of the surface enlargement attack the individual embrittled particles and thus can escape heat to be embrittled particles on the enlarged surface. The enlargement of the surface thus has the consequence that a through-and-through embrittlement of the individual bulk material particles takes place rapidly. The process of enlarging the surface of the individual bulk material particles also has the consequence that the individual particles are homogenized with regard to their material thickness. The homogenization of the thickness of the particles in this context does not necessarily mean that they are flattened out, but this may well be the case. Rather, the increase in surface area is to be understood as meaning that when rubber-elastic granules, for example used tires, are used, the original thickness of the granules is reduced and the grains subsequently have a grated structure which may look bloated due to the material properties. Such a habit can also be addressed as a finely structured popcorn structure. The particles then have numerous extensions and constrictions with the result that the material thickness and thus the necessary penetration depth of the refrigerant into the material for embrittlement of the total volume of the original particle is smaller. After the treatment of the bulk material particles to increase their surface area, the particle thickness distribution of the particles forming the bulk material flow is much narrower than before this process step. Due to the more or less homogeneous thickness distribution of the particles to be embrittled. This means that in order to achieve through-and-through embrittlement, the residence time for all particles of the bulk flow in the cooling section, even if they have a very different size before the surface enlargement step, is more or less the same. Thus, with this method or with such a system, with which this method is carried out, bulk material particle flows are basically embrittled in a single cooling section and, despite varying particle size in the starting material, virtually simultaneously achieve a uniform degree of embrittlement.

In addition, it is advantageous in the described method that, as a rule, the process of enlarging the surface also entails macroscopic, microscopic and / or molecular-level introduction into the particle - A -

be installed break points. Although this does not have any direct influence on the embrittlement parameters to be observed, this is advantageous for the comminution of the particles following the embrittlement. Due to the presence of such predetermined breaking points comminution of the bulk material particles already takes place with a lower comminution energy. In particular, this property of embrittled bulk material particles allows the bulk material particles to be comminuted to be comminuted by means of a rolling process. Forced comminution is assisted by the intermeshing of the embrittled particles due to their prescribed structure, which they receive through the surface enlargement process. In contrast to otherwise typically used disintegrators, which are operated at a high rotational speed, the rollers of such a comminution device rotate slowly, and thus also consume less energy. The comminution by means of a crushing device designed as a roller can also be addressed as a forced comminution device, since each bulk material particle is conveyed through the nip. In otherwise typically used disintegrators, the crushing result depends on the probability that a bulk material particle is caught by the percussion chain or hit by particles caught by the percussion chain in order to be crushed by itself. Moreover, the crushing result using a roller is more homogeneous, which affects the particle size distribution of the crushed bulk material particles. When using such a forced shredding device designed as a roller, it can also be operated in such a manner that the brittle is supplied to the brittle bulk material particles in a grain-supported structure. The nip can then be greater than the thickness of the grains to be crushed. Due to the embrittlement and the incorporation of the predetermined breaking points as a result of the increase in surface area, a comminution of the particles fed to such a forced-flow device is then also carried out among each other. Taking advantage of such a grain-fed supply of embrittled bulk material particles, the roll surfaces may have structures to promote introduction of the embrittled bulk material particle stream into the roll nip.

The invention is based on an embodiment below With reference to the accompanying figures. Show it:

Fig. 1: a schematic representation in the manner of a block diagram of a cryogen crushing plant and

2a, 2b: a schematic representation of individual particles supplied to the system (FIG. 2a) and the bulk material stream supplied to the system of FIG. 1 after an increase in surface area of the bulk material particles (FIG. 2b).

A cryogenic crushing plant 1 is used for crushing bulk material, which has soft or rubber-elastic properties under ambient conditions (normal conditions). The plant 1 is thus suitable for crushing the scrap tire granules or the like. The plant 1 is fed in a manner not shown a bulk material flow, for example by means of a conveyor belt or other conveyor. The cryogenic crushing plant 1 comprises a disk mill 2, which is supplied with the bulk material to be comminuted, as indicated by the block arrow. The disc mill 2 is designed so that the supplied bulk material particles in the disc mill 2 are not necessarily physically crushed, but increased in surface area. This is done by grinding the supplied particles. As a result of this rubbing operation, the rubber-elastic granulate particles are rubbed in the same way as an eraser during the process of erasing, resulting in a finely structured popcorn-like structure. This is associated with a significant increase in surface area of the same. The surface enlargement is associated with a reduction in the actual material thickness in the individual sections of the surface-enlarged particle. The self-adjusting material thickness of the particles is predetermined by the gap of the disks 3, 4 of the disk mill 2 working against each other. The disks 3, 4 each sit in opposite directions, as shown by the arrows, rotatingly driven shafts. On each shaft sitting in a parallel arrangement to each other several discs, so that the discs 3, 4 of the two waves mesh like a comb. Such a disk mill is described for example in DE 202 01 979 U1. The discs 4 of the disk mill 2 are provided with a wave contour, so that in this way, at the against each other work of the two discs 3, 4, the gap between the discs 3, 4 oscillated between a minimum width and a maximum width. The disclosure of DE 202 01 979 U1 is hereby made by express reference to the disclosure of this description. The processed by the disc mill 2 bulk material particles then have a, compared to the thickness distribution of the input side, the disk mill 2 acting on bulk material, relatively homogeneous distribution. The material emerging from the disk mill 2 is fed via a collecting funnel 5 to a conveying device 6.

FIG. 2 a shows by way of example a schematic representation of the habit of granulate particles fed by the disc mill 2. These are characterized by a square compact habit. FIG. 2b shows, in a schematic representation, bulk particles P emerging from the disc mill 2. The particles P are shown in a plan view. The plane recognizable in FIG. 2 is that plane in which the grains originally supplied as granulate particles have been deformed as they pass through the disk mill 2. The finely structured popcorn structure described above can be recognized by the numerous bulges and constrictions in FIG. 2b. By comparing the processed bulk material particles P of FIG. 2 b with the representation of the granulate particles supplied to the disc mill 2 according to FIG. 2 a, the elongation and the associated increase in surface area becomes clear. It can also be seen that the particles P processed with the disk mill 2 have a very fissured surface, and therefore also for this reason the surface is considerably enlarged in comparison with the supplied granulate particles (see FIG. In the machined with the disc mill 2 rubber particles due to the ragged surface sometimes holes are incorporated, so that the total number of particles P numerous weaknesses that are addressed in connection with these embodiments as predetermined breaking points have. Some of these predetermined breaking points are identified by the reference symbol S in FIG. 2b. Submitting the bulk material particles of a process for increasing the surface area of the individual particles, as done by the disc mill 2, not only leads to the formation of the above-described predetermined breaking points S, but also to weakening in the case of polymer granules and thus for the installation of predetermined breaking points at the molecular level.

For the above-described process, in particular a disc mill is suitable, as described in DE 202 01 979 U1, since, due to the intermittent gap, a particularly effective squeezing and elongation of the supplied rubber granule particles takes place.

At the output of the disc mill 2, the particles P are fed to the conveyor 6, with which they are transported through a cooling tunnel 7. The cooling tunnel 7 is used to embrittle the particles P. In the illustrated embodiment, it is provided to embrittle the particles P through and through. In order to bring about cooling and embrittlement, the cold tunnel is charged in a manner not shown with a refrigerant, for example liquid nitrogen, as shown diagrammatically by the "refrigerant" designation in Figure 1. The homogeneous thickness distribution supplied to the cooling tunnel 7 Bulk material particles ensure that the bulk material particles guided through the cooling tunnel 7 have a quasi-same degree of embrittlement at the outlet of the same The degree of embrittlement can be through-and-through embrittlement It may also be desired that only a marginal embrittlement The embrittled particles P are then fed to their comminution at the exit of the cooling tunnel 7. The crushing device 8 is a forced comminutor which, in the illustrated embodiment, is designed as a roller mill has two mutually driven rollers 9, 10. The nip 11 between the two rollers 9, 10 is greater than the size of the embrittled particles P. The embrittled particles P are fed to the crushing device 8 in a grain-supported structure 12. Therefore, the individual particles P are based on one another during their feeding into the nip 11. If these are introduced into the nip 11, the particles P break due to the grain-supported structure with each other, in particular at the predetermined breaking points S and introduced at the molecular level weak points. From the nip 11 emerges underside of the crushed material and is collected in a container 13. Instead of the container 13, a conveyor belt or the like can be arranged at the output of the breaking device 8 be.

To feed the embrittled particles P in a grain-protected structure of the crushing device 8, the embrittled particles P are first brought from the conveyor 6 to a further conveyor 14 which is driven at a much slower conveying speed than the conveyor 6. From the conveyor 14 reach the embrittled Particles P in a feed hopper 15 from which these underside then emerge in the desired grain-protected dressing.

Preferably, the conveyor 14 is also located in the cold tunnel 7, so that the out-conveyed from the cold tunnel 7 particles P can keep their cold possible long.

In the illustrated embodiment is located at the exit of the cooling tunnel 7, an otherwise not shown fractionating. In the fractionating unit, the embrittled grains, which in this state are better sieved than under normal conditions, are divided in terms of their grain size into two fractions. The screened over the sieve size particles P are fed via the return line 16 again the disc mill 2. This does not take place for the reason that the particles of this size could not be crushed by the crushing device 8, but to add cold grains to the supplied bulk material flow in order to cool the disc mill 2 with this. For this purpose, the larger grain fraction is used because they can transport more cold via the return line 16 due to their size. Correspondingly better is the disk mill 2 or its disks 3, 4 cooled. Instead of providing a fractionating device at the exit of the cooling tunnel 7, a particle flow division can likewise take place here, so that part of the embrittled material flow is added to the disk mill 2 for cooling the same.

In FIG. 1, in a further development of the above-described Appendix 1, the reference numeral 17 shows an oversize-recirculation via which a correspondingly fractionated oversize grain is conveyed from the outlet of the

Disc mill 2 is returned to the entrance. The fractionating direction is not shown in Figure 1. Similarly, the system 1 can have a further return line 18, via which a grain fraction can be returned, up to the entrance of the disc mill 2. The return line 18 has a return line branch 19, via which a return to the entrance of the cooling tunnel 7 takes place. The return line 18 or 19 is used if a further homogenization of the grain spectrum at the output of the crushing device 8 is to be brought about and the already relatively homogeneous particle size distribution at the output of the crushing device 8 is to be further narrowed.

With the cryogenic crushing plant described and with the described method can be in a particularly effective manner with low energy and refrigerant use such granules mince into small particle sizes that can not be crushed under ambient conditions, at least not in the desired particle size. It is noteworthy in this apparatus and in this method, the relatively narrow particle size distribution of emerging from the crushing device 8 and collected in the container 13 material.

If desired, the material can be fractionated again at the exit of the crushing device 8 in order to obtain particle fractions with even narrower grain distribution spectra.

LIST OF REFERENCE NUMBERS

1 cryogenic grinding plant

2 disc mill

3 disc

4 disc

5 catching funnels

6 conveyor

7 cooling tunnel

8 crushing device

9 Roller 0 Roller 1 Nip 2 Structure 3 Container 4 Conveyor 5 Feed hopper 6 Return line 7 Overshot return 8 Return line 9 Return line branch

P particles

S breaking point

Claims

claims

1. A method for cryogen crushing of bulk material, in particular of bulk material with soft or elastic under normal conditions material properties, such as rubbery properties in which the bulk material is embrittled to subsequently crush the bulk particles in their embrittled state, characterized in that prior to the step of embrittlement the surface of the bulk particles is increased.

2. The method according to claim 1, characterized in that the surface enlargement of the bulk material particle while reducing its thickness are deformed one or two-dimensionally.

3. The method according to claim 2, characterized in that by the process of increasing the surface of the individual bulk material particles macroscopically and / or at the molecular level predetermined breaking points (S) are incorporated into this.

4. The method according to any one of claims 1 to 3, characterized in that the bulk material particles are subjected to increasing their surface before embrittlement a grinding process.

5. The method according to claim 4, characterized in that the grinding of the particles takes place by means of a Reibmahlens.

6. The method according to claim 4 or 5, characterized in that a part of the brittle bulk material particles (P) is again added to the grinding process supplied bulk material particle stream.

7. The method according to claim 6, characterized in that the bulk material particles (P) are fractionated after embrittlement and before the step of crushing with respect to their grain size and the oversize thus obtained is fed again to the milling process.

8. The method according to any one of claims 1 to 7, characterized in that the embrittled bulk material particles (P) are fed to an impact comminution.

9. The method according to any one of claims 1 to 7, characterized in that the embrittled bulk material particles (P) are fed to a forced crushing.

10. The method according to claim 9, characterized in that for forced crushing the embrittled bulk material particles (P) are subjected to a rolling process.

11. The method according to claim 10, characterized in that the embrittled bulk material particles (P) are brought together before rolling, so that the rollers supplied bulk material particle stream having a grain-reinforced structure (12).

12. Plant for cryogen crushing of bulk material, in particular of bulk material with soft or elastic under normal conditions

Material properties, such as rubber-elastic properties, with a cooling section (7) for embrittlement of the bulk material forming particles and with a cooling section (7) downstream crushing device (8) for crushing the embrittled in the cooling section (7) material, characterized in that the plant (1) comprises a device (2) upstream of the cooling section (7) in the material flow direction for enlarging the surface of the bulk material particles.

13. Plant according to claim 12, characterized in that the plant (1) comprises a mill, in particular a disc mill (2) as a surface enlargement device.

14. Plant according to claim 12 or 13, characterized in that the plant (1) has a particle recirculation (16) to act with embrittled bulk material particles (P) before their crushing the surface enlargement means.

15. Plant according to one of claims 12 to 14, characterized in that the plant (1) has a crushing device as an impact crusher.

16. Installation according to one of claims 1 to 14, characterized in that the plant (1) as a crushing device, a rolling or crushing device (8).