EP0366759B1 - Process for size reduction of brittle grinding material - Google Patents

Abstract

The invention concerns a process for size reduction of brittle grinding material. To enhance the overall cost-effectiveness of processes in which only individual particles and the bed of particles are size reduced in a first size reduction stage, the invention proposes a preliminary size reduction of the grinding stock to a relatively coarse, defined particle size during the first size reduction stage, so that the subsequent steps can be carried out on the basis of this defined particle size. As a result, less specific work is required for a given quantity of grinding stock.

Description

The invention relates to a method for comminuting brittle regrind according to the preamble of claim 1.

Such a continuous process is known from DE 36 09 229 A1. This known method according to the prior art is based on the objective of improving a comminution process as described in EP 0 084 383 A1, with the latter method already performing a single grain and material bed comminution. This improvement consists above all in that the regrind agglomerates present after comminution of the material bed are brought to dissolution. In this way, the aim is to remove the fine material content contained in the agglomerates by means of a sifting process, so that the overall process can be made more economical, including the subsequent comminution.

The good-bed roller mills usually used for simultaneous single-grain and good-bed grinding have the advantage that they can be used to grind relatively fine-grained and regrind particles <2 mm are possible. In addition to the previously mentioned disadvantage of agglomeration, the fact that coarser ground material particles also pass through the material bed roller mill appears even more serious. In addition, a material bed roller mill requires a relatively high investment compared to other mills or crushers.

However, the coarse particles passing through the material bed roller mill make it necessary that, for. B. the downstream comminution by means of a gravity mill and in particular a tube mill must also be equipped with grinding media of relatively large diameter. Large steel balls are therefore also required due to the coarse particles that pass through a material bed roller mill. If the degree of filling of a tube mill is reduced, care must be taken to ensure that the relatively large steel balls do not smash the cladding panels, the slotted and end wall panels.

These disadvantageous aspects of the operation of the Gutbett roll mill and the required grinding media size mean that even taking into account the degree of filling with regard to the total energy consumption, a comparatively poor efficiency, as in known systems, is achieved.

From US Pat. No. 4,398,673 a method for classifying and comminuting gypsum ores in particular is known, in which the ore pieces are fed to a first centrifugal crusher after pre-comminution. After a sieving process and air separation, the remaining residue is fed to a second centrifugal crusher. The design and dimensioning of the centrifugal crusher and the speed of the feed plate determine the degree of separation and comminution of the ore components. The use of a tube or roller mill is not intended for this process.

The present invention is therefore based on the object of designing the generic method in such a way that, on the one hand, the specific energy requirement for a specific quantity of regrind is improved, and furthermore the overall economy is significantly increased by a sharp reduction in investment costs, and the method should also be flexible in design.

This object is achieved in a generic method by the features of the characterizing part of claim 1.

An essential core idea of the invention can be seen in the fact that the first comminution process of the regrind is no longer carried out with a relatively expensive material bed roller mill, but with a primary crusher and in particular a centrifugal crusher. When using this primary crusher, it is consciously accepted that the regrind particles leaving the primary crusher are not broken up as finely as, for example, in a material bed roller mill. However, less coarse material is produced with significantly reduced coarse material, which would otherwise hinder the comminution of the coarse material in a second crushing stage due to its buffering effect.

According to the invention, the first comminution is followed directly by a sieving process, with which undesired oversize particles can be fed back into the first comminution in the cyclic process. The fine grain obtained is fed to the second comminution. This eliminates the previously serious disadvantage that relatively large particles are fed to the subsequent processing stages in a fine material bed.

According to the invention, the second comminution takes place in a downstream tube mill, which is designed for the grain size of the screenings with regard to the size of the grinding media and can be operated with a degree of filling of less than 30%.

With the method according to the invention it is thus possible to achieve a defined feed material at the exit of the primary crusher. However, since the feed material is not so fine, the diameter of the grinding media used can now be kept smaller in the second comminution stage, for which a ball or tube mill with grinding media is particularly suitable, so that the pre-comminuted material is specifically stressed and thus the degree of filling can be reduced.

For example, with a defined coarse grain smaller than 3 mm at the outlet of the centrifugal crusher used as a primary crusher in a first chamber of a tube mill, it is possible to use, for example, 40 to 60 mm steel balls. Steel balls in the range from 15 to 30 mm can then be used in the second chamber of the tube mill, for example. Since it is also possible to lower the filling level in a targeted manner, the energy requirement for operating the tube mill is greatly reduced. This measure is supplemented by feeding the semolina obtained at the discharge of the tube mill or the coarse grain in a circuit to a classifier, the grains of which are again fed to the tube mill. The fine particle-air mixture at the outlet of the tube mill can be passed through a downstream filter so that the fine particles can be discharged together with the fine material obtained in the classifying process.

By using grinding media with a smaller diameter in the tube mill, less wear is achieved than is necessarily the case with larger steel balls. The measure of using a centrifugal crusher as a primary crusher, which is inherently independent in character, with which one deliberately goes from the previous idea of the finest possible size reduction in the first stage and takes a comparatively contrary measure, brings the advantage of lower investments. On the other hand, a centrifugal crusher is usually significantly less maintenance and easier to maintain than a material bed roller mill, which is usually designed with oil hydraulics for generating high pressures. In addition, according to the invention, a relatively low construction of the plant can also be achieved. In this way, not only is a cost-effective method implemented in terms of plant technology, but the specific work and energy requirements can also be considerably reduced. Experimentally, values in the range of 2 to 2.5 kWh / t were achieved.

When the pre-broken ground material is fed directly into the tube mill as the second comminution stage, the size or the coarse particles of the screening process are suitably returned to the second comminution stage.

If a single-grain and good-bed comminution is already available, for example by means of a good-bed roller mill, the material to be discharged, which is essentially in the form of agglomerates (slugs), can additionally be fed to a downstream centrifugal crusher for deagglomeration and coarse material comminution in order to be available for further treatment without agglomerates.

Another advantage of the method is that no agglomerates (slugs) are produced in the centrifugal crusher. This also enables problem-free separation of the pre-shredded goods into coarse and fine goods (e.g. by sifting). The fine material is drawn off before the second size reduction and thus the economy is further increased, since no unwanted fine material gets into the second size reduction.

It is particularly advantageous that the first comminution is followed directly by a sieving process, so that undesired oversize particles can be fed back into the first comminution in the cyclic process. This ensures that only the desired fine material is fed to the ball or tube mill.

Fig. 1

die Prinzipdarstellung einer Anlage zur kontinuierlichen Zerkleinerung von Mahlgut, in der einer ersten Zerkleinerungsstufe eine zweite Zerkleinerungsstufe nachgeschaltet ist;

Fig. 2

einen Verfahrensablauf mit den vergleichbaren Anlagenteilen nach Fig. 1, wobei jedoch vor der zweiten Zerkleinerungsstufe ein Sichtvorgang zwischengeschaltet ist und

Fig. 3

einen erfindungsgemäßen Verfahrensablauf nach dem nach einer ersten Zerkleinerung eine Siebung durchgeführt wird und nur das Mahlgut bis zu einer bestimmten Partikelgröße der zweiten Zerkleinerungsstufe zugeführt wird.

The invention is further explained below with the aid of schematic drawings. Show it:

Fig. 1

the schematic diagram of a system for the continuous comminution of regrind, in which a second comminution stage is connected after a first comminution stage;

Fig. 2

a process sequence with the comparable plant parts of FIG. 1, but before the second crushing stage, a visual process is interposed and

Fig. 3

a process sequence according to the invention after which a screening is carried out after a first comminution and only the ground material up to a certain particle size is fed to the second comminution stage.

In Fig. 1, a process flow is shown in a schematic representation, in which the ground material, e.g. Can be cement clinker, the entire system 1 is fed from a feed bunker 2 via a scale 3. A time-metered supply can be carried out by means of the scale 3. Following the balance 3, the ground material is fed to a primary crusher 4, which is preferably a centrifugal crusher.

In the example according to FIG. 1, the material comminuted up to a relatively defined maximum grain size in the centrifugal crusher 4 is passed directly over a section 5 into the second comminution stage, which is designed here as a two-chamber tube mill 6. The first chamber 7 of the tube mill 6 has, for example, steel balls as grinding media with diameters in the range from 40 to 60 mm. The second chamber 8 adjoining the intermediate wall 9, on the other hand, is provided with steel balls in the range from 10 to 30 mm and preferably with diameters in the range from 15 to 30 mm. At the discharge 10 of the tube mill 6, the coarse material is discharged downwards and passes via a conveyor line which is provided with a bucket elevator 11, and the line 17 into a classifier 18. For the classifier 18, a crossflow classifier is particularly suitable, the size of which is via the coarse material outlet 20 and the line 21 of the tube mill 6 are fed as a second comminution stage.

The fines particles discharged into the fines outlet are withdrawn from the process cycle via a removal section 16.

The air-fine particle mixture at the outlet 23 of the tube mill 6 is fed via a line 12 to a filter 13 in which the fine particles are separated from the air. The fine material particles are fed to the removal section 16 via the fine material outlet 15, while the air is discharged via the air outlet 14 may be returned to the process cycle.

The regrind 4 comminuted at the exit of the relatively low investment has a well-defined grain size, in which there are largely no larger regrind particles beyond the desired size range. This makes it possible to work with steel balls of reduced diameter in the second downstream comminution stage for which the two-chamber tube mill is provided, the degree of filling of the tube mill also being below the usual values; in particular less than 30%.

In this way, on the one hand, less wear occurs in the tube mill. On the other hand, however, the energy requirement is also improved by the smaller filling and the reduced overall weight. Compared to the prior art, in which steel balls of 90 size are used in the first chamber of the tube mill, it is now possible to use grinding media with a diameter range of 40 to 60 mm, which can be reduced to 15 to 30 mm in the second stage .

FIG. 2 shows a variant of the system according to FIG. 1. Corresponding reference numerals relate to the same parts of the system. The difference in comparison to the embodiment according to FIG. 1 lies in the fact that the centrifugal crusher 4 of the first size reduction stage is immediately followed by the classifier 18.

This ensures that the fine material can already be withdrawn from the process circuit via the fine material outlets 19 and thus no longer stresses the tube mill 6 as the second comminution stage of the ground material. Since the material throughput of the tube mill 6 is reduced, reached this is yet another improvement in the efficiency of the entire system.

The grit of the classifier 18 in the example according to FIG. 2 is now fed via the coarse material outlet 20 and the line 21 in the circuit of the tube mill 6, the equipment of which with grinding media is corresponding to the embodiment according to FIG.

3 shows a process sequence according to the invention. The same reference numerals as in the previous figures denote the same units. In order to ensure that a pre-comminuted ground material up to a certain particle size is fed to the second comminution stage, in the example according to FIG. 3, a screening process is followed by the pre-crushing. The ground material leaving the centrifugal crusher 4 is therefore passed through a sieve 35. The oversize particles obtained in the sieve 35 either reach the bucket elevator 11 via the line 36a and are recirculated there or are fed to the centrifugal crusher via the line 36b. On the other hand, the ground material, which is obtained up to a desired particle size, is fed via line 37 to the tube mill 6 for further comminution.

In the example according to FIG. 3, the material fed to the bucket elevator 11 passes into the sifter 18. The coarse material obtained after the sifting process is again guided into the second comminution stage 6 via the return line 41a.

In this way it can be ensured that no oversize of the pre-comminuted ground material gets into the tube mill 6, so that the second comminution stage can be optimally designed with regard to the size of the grinding media and the degree of filling.

The scope of the method according to the invention relates not only the grinding of cement clinker, but can also be used with comparable materials such as limestone, ores, coal, quartz sand or grit, these details being understood only as examples.

Overall, therefore, the method according to the invention and the plant alternatives provided therefor reduce the specific work required per intended quantity of regrind, this being supplemented by wear reductions at least on the second size reduction stage. In addition, lower investment costs are required than in comparable systems based on the prior art.

Claims (7)

1. Method for the comminution of brittle dry material for grinding, such as e.g. cement clinker, in which

   (a) the material for grinding firstly undergoes a first comminution,

   (b) subsequently it is supplied to a further, second comminution in a tube mill,

   (c) the oversize material obtained after the second comminution is supplied to a classifying process and

   (d) the fine material particles from the classifying process and the second comminution are led out as fines,

   characterized in that

   (e) the first comminution of the material for grinding is performed as a precrushing operation in a centrifugal crusher to a substantially defined grain size,

   (f) oversize material is removed in a screening process and is led back in a cyclic process to the centrifugal crusher and

   (g) concerning the grinding element size the succeeding tube mill is designed with respect to the grain size of the screening material and is operated with a degree of filling of under 26 to 30 %.
2. Method according to claim 1,
   characterized in that
   the oversize material obtained from the second comminution is supplied in a cyclic process to the classifying operation, whose oversize material is fed to the second comminution process.
3. Method according to claims 1 or 2,
   characterized in that
   the second comminution is performed in a two-stage tube mill, using grinding elements with a diameter in the range of 40 to 60 mm in the first stage and grinding elements with a diameter in the range of 10 to 30 mm in the second stage.
4. Method according to one of the claims 1 to 3,
   characterized in that
   the fines discharge provided after the second comminution undergoes a filtering or a cyclone separation.
5. Method according to one of the claims 1 to 4,
   characterized in that
   the classifying process is performed by transverse flow classifying.
6. Method according to one of the claims 1 to 5,
   characterized in that
   the oversize material obtained from the screening process is supplied in a cyclic process either indirectly or directly to the first comminution process.
7. Method according to one of the claims 1 to 6,
   characterized in that
   the precrushed grinding material is supplied to a classifying process.

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