EP0675762B1 - Method and plant for grinding old brasques and similar products - Google Patents

Description

Old pot liners are carbon products that come from the demolition of the lining of the walls and the bottom of the tanks electrolysis of the alumina constituting the cathode. This coating wears out and gets deteriorates and it is necessary to replace it periodically with a coating new. The operation of demolishing the coating, called debridging, is performed by pneumatic tools and produces large blocks may contain inclusions of metals such as iron or aluminum. These blocks are then reduced by conventional means to a size which allows passage through a square trunk grid of approximately 400 mm.

Old pot lining is heavily impregnated with products harmful, such as fluorides and cyanides. Until now, they were landfills, but new regulations on pollution and environmental protection means treating them, for example calcining them, to eliminate harmful products and possibly allow recovery carbon constituents.

The invention relates more particularly to factories aluminum production in which the treatment of old pot lining requires a prior reduction of these potlaces into pieces whose size does not exceed a few millimeters, and relates to a process and a grinding plant to achieve this result with only two reduction stages and screening.

However, we know from document US-A-3,606,176 a process for the grinding of old pot lining comprising, inter alia, a crushing operation, carried out in a cone crusher, an operation of screening and a grinding operation.

However, the grinding operation is not carried out with a apparatus for providing a high reduction ratio so as to ability to obtain grains of sufficient fineness directly. It is also note that these are crushed again in the following. This document is in fact mainly on the subsequent physico-chemical treatment of the grains.

We also know from GB-A-2,056,425 a grain reduction process of old pot lining. Matter is everything first crushed in a cone crusher and passed through a crusher rollers before being separated to be shredded again or undergo further treatment.

As for the previous American document, the process described mainly relates to the planned physico-chemical operations later.

• ladite opération de criblage permet de séparer du produit concassé les grains ayant les dimensions du produit fini,
• ladite opération de broyage est effectuée dans un broyeur vibrant à cône, et présentant un rapport de réduction de l'ordre de 20,
• ladite opération de broyage permet de réduire les produits du criblage aux dimensions du produit fini,
• les dimensions des grains du produit fini n'excèdent pas 2,5 à 3 mm.

The present invention relates to a method for grinding old pot lining, or similar products polluted by metals and / or harmful products, said method comprising a crushing operation, a screening operation, and a grinding operation, characterized in that:

• said screening operation makes it possible to separate the grains having the dimensions of the finished product from the crushed product,
• said grinding operation is carried out in a vibrating cone crusher, and having a reduction ratio of the order of 20,
• said grinding operation makes it possible to reduce the screening products to the dimensions of the finished product,
• the grain dimensions of the finished product do not exceed 2.5 to 3 mm.

The process which is the subject of the present invention is characterized in that that it involves a crushing operation in which the old pot lining are reduced to pieces whose dimensions do not exceed 50 mm, a screening operation to separate the grains having a size of a few millimeters and constituting the finished product, and a grinding operation allowing to reduce the rejection of screening to the dimensions of the finished product. Of preferably, the grains of the finished product will all have dimensions less than 2.5 to 3 mm. The products of the grinding operation may be returned to screening.

The present invention also relates to the use of a grinding plant for old pot lining, or similar products polluted by metals and / or harmful products, including a crusher, a screen, the mesh size corresponds to that of the finished product, a vibrating mill cone, means for transporting the products leaving the screen to the screen crusher and possibly those coming out of the crusher and means for send the screen rejects to the entrance of the crusher, for the implementation of the process described above.

The vibrating cone crusher is a crusher in which the cone or the tank is placed vibrations, the other element, tank or cone, of the mill being fixed or mobile. The shredders of this type are capable of a high reduction ratio compared to cone crushers classics whose movements of the cone are controlled by an eccentric.

The crusher may be a jaw crusher in which the jaws form between them an angle less than 20 °. This reduced angle promotes the taking of reputable products soapy like old pot lining.

Instead of the jaw crusher, an autogenous or semi-autogenic grinder can be used with peripheral output.

La figure 1 est le schéma d'une installation de broyage de vieilles brasques conçue selon l'invention;

La figure 2 est une vue en coupe verticale d'un broyeur vibrant à cône; et

La figure 3 est le schéma d'une autre installation conforme à l'invention.

Other characteristics of the invention will appear on reading the description which follows and refers to the accompanying drawings which show, by way of nonlimiting example, two embodiments of the invention. In these drawings:

FIG. 1 is the diagram of an installation for grinding old pot lining designed according to the invention;

Figure 2 is a vertical sectional view of a vibrating cone crusher; and

Figure 3 is the diagram of another installation according to the invention.

The installation of Figure 1 consists essentially of a feed hopper 10, jaw crusher 12, vibrating cone crusher 14, screen 16, two endless belt conveyors 18 and 20, an elevator 22, a dust filter 24 and a silo 26.

The hopper 10 is provided with a vibrating extractor 28 which makes it possible to load the blocks of which it is filled on the conveyor 18 supplying the crusher 12. Separators magnetic 30 and eddy current separators 31, to eliminate scrap and other metal parts, are placed on the conveyors 18 and 20 and / or at their jetty.

Crusher 12 is a single acting jaw crusher. This device is classic construction except for the angle α formed by the jaws between them which is approximately 16 ° and significantly lower than that usually adopted for this type of crusher. This reduced angle favors the taking of reputed soapy products such as old brasques.

The inlet opening of the crusher 12 is sufficient to absorb blocks passing through through a 400 mm square mesh grid and its outlet opening is sized to that the blocks are reduced to pieces having practically all smaller dimensions about 50 mm.

This result, which corresponds to a reduction rate of around 8, is achieved not only through proper sizing of the inlet and outlet openings, but also thanks to the fact that we adopt a stroke of the movable jaw so that the throughput of the crusher is significantly lower than that of a conventional cone crusher of same dimension, for example 10T / H instead of 50-60 T / H.

The crushed product is loaded on the transporter 20 and transported by it and the elevator 22 to the screen 16. This is equipped with a mesh grid of a few millimeters aside, for example 3 mm. The products having passed through this grid are stored in silo 26.

The screen 16 is also equipped with a 50 mm mesh upper grid which allows recover and eliminate any unbelievable, mainly pieces of aluminum, allegedly crushed and rejected by the crusher 14.

Refusals from screen 16, whose dimensions are greater than 3 mm, are sent to a buffer hopper 32 which feeds the crusher 14 and allows it to be kept charged permanence, which is an essential condition for its effectiveness.

The grinder 14, shown in FIG. 2, is made up, like the cone grinders conventional, by a frame 40 carrying at its upper part a tank 42 in which is fixed a wear part 44 in the form of a hollow cone trunk, called a concave, and by a cone 46 placed inside the concave and resting on a spherical surface whose center is located on the axis of the concave and which allows the cone to rotate around its axis and to perform a movement roundabout inside the concave. Whereas in conventional cone crushers, the cone movements are controlled by an eccentric, in the grinder 14 these movements are caused by an eccentric mass 48 rotatably mounted on the tail of the cone and driven in rotation by a motor 50. This mill has a reduction ratio of the order of 20, significantly higher than that of a conventional cone crusher.

The products leaving the mill 14 are loaded onto the conveyor 20 and transported, with the products leaving the crusher 12, up to the screen 16.

Although in the example described, it is the cone of the mill that is vibrated at the by means of a rotating eccentric mass, the name vibrating cone crusher used in this description covers all cone crushers where one of the elements, cone or tank, or the two are vibrated by any appropriate means, not imposing a trajectory predetermined to said element.

The jaw crusher could be replaced by other devices capable of reduce 400 mm blocks into pieces of 50 mm or smaller. We could, in In particular, use an autogenous or semi-autogenic mill with peripheral output. This device, which consists of a drum with a horizontal axis whose diameter is greater than the length and which is rotated about its axis, by appropriate means, is supplied with through a central opening provided on one of the bottoms and has on its wall, near the other bottom, openings whose dimensions are chosen to let pass only the pieces whose size is less than the maximum size desired.

Figure 3 shows the diagram of an installation including an autogenous grinder designated by the reference number 12 '. All other devices in this installation are designated by the same reference number as in Figure 1. In the installation shown, the crusher 12 'has on one of its bottoms a central opening into which opens a feed chute 28, and openings are provided on its cylindrical wall, near on the other bottom, for the evacuation of crushed products. These openings are surrounded by a annular casing provided at its base with an airlock for the evacuation of crushed products and connected to the suction of a fan through the filter 24. The fine fraction of the ground product is driven by the air current flowing in the grinder and recovered in the filter. Alternatively, fine crushed products could be pneumatically discharged through an opening center of the bottom of the mill adjacent to the peripheral openings.

The autogenous shredder 12 'reduces the blocks of 400 mm into pieces whose size is around 30 mm and the vibrating cone crusher 14 operates in open circuit (without screening crushed products and recycling of rejects), the crushed products practically all having a size less than 3 mm.

It is understood that any modifications which may be made to the shapes described above by the use of equivalent technical means fall under the part of the invention.

Furthermore, the invention is not limited to the grinding of old pot lining but applies also to similar materials, polluted by metals and / or harmful products, such as cyanides, fluorides, etc., for example in briquetting or refractory linings of blast furnaces steel or metallurgical furnaces.

Claims (6)

1. Process for grinding spent potlinings, or similar products contaminated by metals and/or harmful substances, the said process comprising a crushing operation, a screening operation enabling the grains having the dimensions of the finished product to be separated from the crushed product, and a grinding operation, characterised in that

   the said grinding operation is carried out in a vibratory cone grinder having a comminution ratio in the order of 20 ;

   the said grinding operation enables the screening products to be reduced to the dimensions of the finished product ;

   the dimensions of the grains of the finished product do not exceed 2.5 to 3 mm.
2. Process according to claim 1, characterised in that the products of the grinding operation are also subjected to the said screening operation.
3. Use of a plant for grinding spent potlinings, or similar products contaminated by metals and/or harmful substances, comprising a crusher (12, 12'), a screen (16) the mesh size of which corresponds to that of the finished product, a vibratory cone grinder (14), means (20, 22) for transporting to the screen the products that leave the crusher and, possibly, those that leave the grinder, and means for returning the rejects of the screen (16) to the input of the grinder (14), for implementing the process according to claim 1.
4. Use according to claim 3, characterised in that the crusher is a jaw crusher (12) the jaws of which form between them an angle of less than 20° and, preferably, an angle equal to 16°.
5. Use according to claim 3, characterised in that the crusher is a peripheral output type autogenous or semi-autogenous grinder (12').
6. Use according to any one of claims 3 to 5, characterised in that the said plant comprises a hopper (32) that feeds the grinder (14) and keeps it constantly under load.

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