WO2008135487A1

WO2008135487A1 - Method and system for cryogenically crushing pourable material

Info

Publication number: WO2008135487A1
Application number: PCT/EP2008/055325
Authority: WO
Inventors: Igor Plahuta
Original assignee: New View S. L.
Priority date: 2007-05-02
Filing date: 2008-04-30
Publication date: 2008-11-13
Also published as: DE102007020520A1

Abstract

Disclosed is a method for cryogenically crushing pourable material, especially pourable material that has soft or elastic, e.g. rubber-elastic, properties in normal conditions. Said method comprises an embrittling step, whereupon the embrittled particles are crushed. In a first step of said method, the grain size spectrum of the delivered particle flow is spread during a grinding process to obtain a fine fraction and a coarse fraction. The fine fraction is then separated from the particle flow. The particles of the remaining coarse fraction are embrittled and are then once again delivered to the grinding process. A system for carrying out said method comprises a grinder (2) as a crushing device, downstream of which a particle flow separation device (8) is mounted to separate the fine fraction from the particle flow that is discharged from the grinder (2). A cooling section (9) to which the coarse fraction formed by separating the particle flow is fed is mounted downstream of the particle flow separation device (8). The outlet of the cooling section (9) is connected to the inlet of the grinder (2) in order for the particles that are embrittled in the cooling section (9) to be delivered to the grinder (2) for crushing purposes.

Description

Process and plant 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 elastomeric Eigen- shafts, the method comprises a step of embrittlement to subsequently reduce the embrittled bulk material particles in their embrittled state. Furthermore, the invention relates to a plant for cryogen crushing of bulk material.

In order to be able to comminute bulk goods whose particles have soft or elastic, in particular rubber-elastic properties under normal conditions (environmental conditions) with conventional comminution devices, for example impact crushers, they are embrittled before the comminution step. For this purpose, the bulk material particles to be comminuted undergo a cooling section before being comminuted, in which they are cooled down to a temperature such that they are embrittled. Typically, liquid nitrogen is used for cooling, which, when it evaporates, extracts heat from the bulk particles to be cooled, causing it to cool down. 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. For this purpose, 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 which differ in their particle size. This is done with the aim that each particle fraction has a relatively homogeneous particle size distribution. Each particle fraction is assigned its own cooling section. Due to the homogeneous particle size distribution in each particle fraction, the cooling conditions, ie the use of the amount of coolant and / or the residence time of the introduced into the cooling section particles be adapted to the average particle size of a particle fraction in order to achieve a through-and-through embrittlement of the particles of a particle fraction with minimal refrigerant consumption. An embrittlement of particle fractions with a larger particle size can therefore be carried out under different process parameters than an embrittlement of the particle fractions with a smaller particle size.

Even if bulk materials consisting of particles with rubber-elastic properties can be comminuted as intended by this prior art method, the equipment required for carrying out the method is not inconsiderable.

Based on this discussed prior art, the invention is therefore the object of developing an aforementioned method and also an aforementioned device in such a way that this is possible with less equipment.

This object is achieved by a method in which in a first step, the grain size spectrum of the supplied particle stream is spread by forming a fine fraction and a coarse fraction by way of a grinding process, then the fine fraction is separated from the particle stream, subsequently the particles of the remaining Coarse fraction embrittled and the embrittled particles are fed again to the grinding process.

The device-related object is achieved by a Kry- ogenzerkleinerungsanlage with the features of claim 6.

In this method and the same also applies to the claimed system, the equipment required for crushing bulk solids, the particles under normal conditions soft and / or elastic properties, with a very low cost of equipment possible. According to this method, the supplied bulk material flow is processed in a mill, preferably an attrition mill, in a first step. In this first process step, the material behavior of the soft and / or elastic properties of the particles to be comminuted under normal conditions is utilized. These are processed in one Mill lengthened; Consequently, the surface and the grain size of the particles is increased. At the same time a certain fine-grained abrasion arises. The consequence is that the grain spectrum of the bulk material fed to the mill, which typically corresponds to a Gaussian normal distribution, is spread. The attrition produced during the milling step has a relatively small particle size. On the other hand, the particles which are enlarged with respect to their surface by the grinding process have a grain size which is relatively large in comparison to the abrasion and which is larger than their original size. The particle flow exiting the mill then typically has two maxima with regard to the particle size distribution contained therein, the one maximum representing the abrasion produced during grinding and the particles possibly already being introduced in this particle size. The other maximum represents the average grain size of the particle size of the bulk material stream fed to the mill as a result of the grinding, with respect to its grain size.

Downstream of the milling process, the bulk material leaving the mill is divided by separating those particles belonging to the smaller particle size fraction from those belonging to the larger particle size fraction. This is done, for example, by sieving. It is also possible to blow out the fine particles. The mesh size of the sieve used for this purpose corresponds to a particle size between the Gaussian distribution maxima representing the two particle size fractions, for example the minimum. To improve the screening process, it may be appropriate to shift the mesh size of the screen from the actual minimum towards the Gaussian distribution maximum of the larger grain fraction. Screening of this particle stream, which is spread with respect to its particle size distribution, can be carried out, largely without the problems otherwise encountered when sieving elastomers. The reason for this is that in the particle stream to be screened, the proportion of particles having a size approximately in the region of the mesh size of the sieve is only very small. The particles passing through the meshes of such a sieve are therefore for the most part much smaller than the mesh size. For the particles that do not pass through the mesh, the reverse applies. The size of these particles is not significantly larger than the mesh size of a - A -

such a sieve. Consequently, they can easily slip on the top of such a screen, unroll or otherwise be transported away.

The fine fraction created in the course of the division of the particle stream is expediently provided in a particle size which corresponds to that desired by the comminution process. Thus, this grain fraction is preferably already a finished product.

The non-separated by the process of particle flow separation from the mill fed bulk material particles are then fed to a cooling tunnel for embrittlement thereof. Such a cooling tunnel is a commercially available cooling tunnel that is operated using a refrigerant, for example liquid nitrogen. The embrittled particles are then fed back to the mill. The embrittled particles introduced into the mill break during the milling process, such breakage typically causing the particle size of the fragments of such a fractured particle to be smaller than the mesh size of a screen used for particle flow division. Consequently, these particles are separated from the particle flow as a result of the particle flow downstream of the mill and not fed again to the cooling tunnel. The feeding of the embrittled particles into the mill not only has the purpose to bring the particles to be comminuted into a state that they can be broken, but also that the mill or their grinding tools are cooled by the supply of cold particles ,

In this method, and also in the case of the above-described plant, only a comminution tool is thus used in a skillful manner in order to effectively comminute the particles of a supplied bulk material stream to the desired extent, in order to obtain a fine, relatively finely divided product with respect to its grain size ,

The invention is described below with reference to an embodiment with reference to the accompanying figures. Show it: 1 is a schematic representation in the manner of a block diagram of a cryogen crushing plant,

2a, 2b: a schematic representation of individual particles supplied to the plant (FIG. 2a) and the particles (FIG. 2b) processed by a milling process and FIG

3a, 3b show the particle size spectrum of a particle stream fed to the cryogen grinding plant (FIG. 3a) and the particle size distribution spectrum of the particle flow after carrying out a milling process (FIG. 3b).

A cryogenic grinding plant 1 is used for crushing bulk material having soft or rubbery properties under ambient conditions (normal conditions). The cryogenic crushing plant 1 is therefore suitable for comminuting, for example, used-tire granules or the like. The cryogen removal unit 1 is supplied with a stream of bulk material in a manner not shown, for example by means of a conveyor belt or another conveyor.

The cryogenic crushing plant 1 comprises an attrition mill 2 which is supplied with the bulk material to be comminuted, as indicated by the block arrow. The attrition mill 2 is designed so that the bulk material particles fed through the bulk material flow are not necessarily physically comminuted, but increased in their surface area. This is done by grinding the supplied particles. As a result of this rubbing process, the rubber-elastic granulate particles are rubbed in the same way as an eraser during the process of etching, resulting in a finely structured, popcorn-like structure. This is associated with a significant increase in surface area and increase in the particle size of the particles. Associated is the enlargement of the particles with a reduction of the actual material thickness, which is defined by the inside width of the grinding gap of the mutually-working discs 3, 4 of the friction mill 2. In the process of milling the particles supplied, these particles are not only increased in terms of their surface area and grain size due to the aforementioned material properties, but it also creates a fine-grained abrasion.

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

FIG. 3 a shows the particle size distribution of the particles fed to the attrition mill 2 through the bulk material flow. The grain size distribution in this embodiment corresponds to a Gaussian normal distribution curve. As a result of the process of grinding the particles fed in, fine-grained abrasion results on the one hand as described above, and on the other hand an increase in grain size takes place. The particle flow emerging from the attrition mill 2 then has a relation to the supplied bulk material. Current spread grain size spectrum, as shown by way of example in Figure 3b. The particle size distribution spectrum shown in FIG. 3b shows a first maximum 5, which represents the fine grain fraction at the exit of the attrition mill 2. This fine fraction comprises the abrasion formed in the course of grinding and, of course, those particles which have already exhibited this grain size in the fed bulk material flow. As a result of the grain enlargement through the grinding process, another maximum 6 representing the coarse fraction can be seen in the particle size distribution spectrum of FIG. 3b. The two maxima 5, 6 are separated by a region 7 in the particle size distribution spectrum. The exiting at the output of the attrition mill 2 particle flow has only a relatively smaller number of particles having this grain size. The change of the grain size spectrum from that corresponding to FIG. 3 a to that corresponding to FIG. 3 b is understood in the context of these explanations as spreading.

Downstream of the attrition mill 2 is a screening device 8 (cf., FIG. 1) with which the particle flow leaving the attrition mill 2 is divided. A funnel T serves to supply the particles emerging from the attrition mill 2 to the sieve device 8. The fine fraction is separated off from the particle flow with the sieve device 8. The mesh size of the sieve 8 associated sieve corresponds to a grain size in the region 7 of the grain size distribution spectrum of Figure 3b and is characterized therein by the reference numeral M. The mesh size of the screen is not found in the illustrated embodiment in the actual minimum of the range 7 of the grain size distribution spectrum, but is shifted to the maximum fraction 6 representing the coarse fraction.

The fine fraction separated by the screening device 8 has a particle size spectrum which corresponds to the nominal particle size of the product to be produced by the reduction process. Consequently, the separated fine fraction is to be addressed as a finished product. The coarse fraction formed by the screening device 8 is then fed to a cooling section 9 in which the particles of this fraction are embrittled. The cooling section 9 is a cooling tunnel. To induce cooling and embrittlement, the cooling tunnel is not closer shown manner with a refrigerant, such as liquid nitrogen, as schematically indicated by the label "refrigerant" in Figure 1, applied. The exit 10 of the cooling section 9 is connected to the inlet 1 1 of the attrition mill 2. The particles embrittled in the cooling section 9 are returned to the attrition mill 2 via a return line 12. The embrittled particles entering the attritor 2 break down as a result of the grinding process. The resulting fracture typically has a grain size corresponding to the fine fraction. The embrittled particles are mixed in the area of the inlet of the attrition mill 2 with the flow of bulk material fed to the attrition mill 2. The feeding of the embrittled particles into the attrition mill 2 also serves to cool the disks 3, 4.

In the described embodiment, an attrition mill has been used to realize the milling process. The milling process can be realized equally with a disk mill, for example, such as is described in DE 202 01 979 U1.

LIST OF REFERENCE NUMBERS

1 cryogenic grinding plant

2 friction mill

3 disc

4 disc

5 maximum

6 maximum

7 area

8 screening device

9 Cooling section 0 Output 1 Input 2 Return line

M mesh size

T funnel

Claims

claims

1. A method for cryogen crushing of bulk material, in particular bulk material with soft or elastic under normal conditions material properties, such as rubbery properties, the method comprises a step of embrittlement to subsequently reduce the embrittled bulk material particles in their brittle condition, characterized in that in a first step, the grain size spectrum of the supplied

Particle stream is spread by forming a fine fraction and a coarse fraction by way of a grinding process, then the fine fraction is separated from the particle stream, then embrittled the particles of the remaining coarse fraction and the embrittled particles are fed to the grinding process again.

2. The method according to claim 1, characterized in that the grinding of the particles of the supplied bulk material flow takes place by means of a Reibmahlens.

3. The method according to claim 1 or 2, characterized in that the separation of the fine fraction from the particle stream after the step of milling is carried out by way of a screening process.

4. The method according to any one of claims 1 to 3, characterized in that the particles of the separated by the process of separating fine fraction have a particle size of the desired particle size corresponding grain size.

5. The method according to any one of claims 1 to 4, characterized in that in the caused by the process of milling grain enlargement predetermined breaking points are installed on the macroscopic and / or microscopic level in the enlarged particles.

6. plant for cryogen crushing of bulk material, in particular of bulk material with soft or elastic under normal conditions material properties, such as rubbery properties, with a cooling section (9) for embrittlement of supplied bulk material particles and one of the cooling section (9) downstream crushing device for crushing in the cooling section (9 ) embrittled material, characterized in that the crushing device is a mill (2) that the device (1) via a mill (2) downstream particle flow divider (8) for separating a fine fraction from the particle flow has, which

Particle stream part means (8) downstream of the cooling section (9), which is supplied to the coarse fraction formed by the particle flow division, and that the output of the cooling section (9) is connected to the input of the mill (2), so that in the cooling section ( 9) embrittled particles for crushing the same of the mill (2) are supplied.

7. Plant according to claim 6, characterized in that the particle flow divider device is a sieve device (8).

8. Plant according to claim 6 or 7, characterized in that the separated from the particle flow fine fraction has a grain size corresponding to the desired particle size spectrum.