NL8600089A - Reinforcing cavities in green carbon bodies during calcination - using a rigid organic foam body, esp. for anodes prodn. for melt electrolysis mfr. of aluminium - Google Patents

Abstract

A filler medium for mechanically stabilising cavities in green carbon bodies, in at least the first phase of the calcining process, esp. in plugholes and ventilation ports in anodes for the prodn. of A1 by melt electrolysis, comprises a rigid organic foam which does not react with carbon, and which stands in contact with the side wall(s) and bottom surface of the cavity to maintain the shape of the cavity. The foam is e.g. of phenolic or polyurethane foam material which opt. contains a passive carbon filler such as coke or anthracite with a particle size up to 10 mm.

Description

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Reg 7583

Filling mass for green carbon bodies with at least one recess.

The invention relates to a filling mass for green carbon bodies with at least one recess, for the mechanical stabilization of the recess, respectively recesses during at least the first phase of the calcination process, in which the surface hardening occurs, in particular for plug - scavenging of anodes for the production of aluminum by means of melt flow electrolysis, respectively.

There are no fundamental differences when calcining anodes and other carbon bodies with a filling compound according to the invention in the recess or recesses.

Anodes for the aluminum industry are calcined by two different types of methods: - in ring chamber furnaces, stacked on top of each other, surrounded by fire shafts, which are fired by oil and gas.

15 The burners are moved at regular intervals.

- In tunnel kilns, in which the anodes are struck in one or more layers on wagon bridges stacked by a burner tunnel.

In both methods, the anodes are enveloped with filler material, which protects them from oxidizing atmospheric atmospheres.

This granular filling material has the following other functions: - supporting the anodes, in particular in the temperature range, in which the bonding mass of the anode is plastic, - transferring heat from the fire shaft or the side wall of the wagon pressure to the anode, - possibility of avoiding the pitch vapors, - preventing the anodes from baking together or with the furnace wall, and - thermal insulation of the upper range of the anodes by a layer of filler material.

As fillers, in particular, petroleum coke, metallic coke and / or anthracite are used.

The experiences in calcining anodes have shown that the plugs and scuppers of anodes must also be filled with a filling material. In addition to maintaining geometrical dimensions of the holes, a number of other aspects must also be taken into account r '' - -

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4 r -2-, in particular, - that the plug or scavenging holes can be easily cleaned after calcining and t - the influence of the filling mass on the plug or scavenging holes 5 on the furnace filling material, because both masses are joined during cleaning.

Cleaning the plug or scavenging holes is, among other things, not easy, because the anodes are often superimposed such that the openings are covered by the anodes lying above. The pitch vapors formed during the calcination process are difficult to escape from the plug or scavenging holes in such an arrangement and thus favor undesired packing.

The anodes can be placed or arranged in the fire oven in such a way that the plug or scupper holes point outwards. However, this leads to another problem: the filling mass partly flows from the plug or scavenging holes. In practice, in this case the plugs or scuppers filled with plaster mass are closed with plaster. However, this method is very expensive, because it has to be done mainly in manual labor.

Numerous other attempts have been made to stabilize the blow holes or plug holes of green anodes in a simple and cost-effective manner during calcination: moistening the plug or blow holes respectively with water, whereby the vapor which escapes during the calcination is combined. to prevent packing. However, the intended goal has not been achieved.

Cover the plugs and scuppers with aluminum foil and fill with anthracite. No better results have been achieved with greater costs.

- Filling with pebble or sand into the plug or drain holes.

The mixing of sand or pebble with the filling mass of the oven when cleaning the holes has led to unacceptable consequences.

The object of the invention is to provide a filling mass for green carbon bodies of the type referred to above, which can be easily introduced into the plug or scavenging holes, respectively.

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-3- it gives a mechanical support, can be removed with little effort and low-emission and is favorable in cost »

This object is achieved according to the invention in that the filling mass consists of a rigid, non-carbon-reacting organic foam 5, which engages with the side wall, respectively with the side walls and the bottom surface of the recess.

The foam provides the recesses of the green carbon body in the first stage of the calcination with sufficient protection against mechanical deformations. Once the carbon body is externally hardened, it no longer deforms. It is therefore irrelevant if the organic foam crumbles or burns out at a later stage of the calcination process with coke. Residues that are released can always be easily removed after the calcination, are low-emission and do not contaminate the furnace filling material.

According to a first preferred embodiment of the invention, the filling mass consists of a foam block pre-formed in accordance with the dimensions of the recess. After insertion, which can take place by machine or by hand, this is rigidly fitted in the recess. On the non-carbon-contacting side, the foam block 20 is preferably dimensioned such that it is substantially aligned with the respective surface of the carbon body.

The recess in the carbon block may have recesses, grooves, holes or the like, which, however, make up only a small portion of the side and bottom surfaces of the recess. In this case, a foam block is expediently preformed, which leaves these recesses, grooves, holes or the like. The aid function is therefore not disadvantaged. When making anodes with round plug holes, the side wall can be provided with several spiral grooves in a known manner. The foam block to be introduced is preferably designed as a cylinder, the spiral grooves remain free.

The foam block used as a filling mass expediently consists of a phenol-formaldehyde or polyurethane foam.

The foam filler material may contain a solid carbonaceous filler material, which in particular consists of coke or anthracite.

This filler preferably has a grain size of up to about 10 mm.

With recesses with a large cross-section or with anodes •; ./ v -4- with a low surface-to-volume ratio, it may be disadvantageous that the tar fumes can only escape through the anode bodies, not through the foam.

The vapors condense on the transition phase from carbon to foam-5. This drawback can be overcome by the fact that the foam block, with or without filler mass, has passed through at least one bore not adversely affecting the mechanical stability in the vertical or substantially vertical direction relative to the cover surface of the carbon body. These relatively small holes in diameter allow the escape of pitch vapors 10 through the foam block.

According to another variant of the invention, the filling mass is a locally produced two-component foam, which substantially fills the recess with respect to the surface of the carbon body. This variant has the advantage that the foam material is deformed by the contours of the recess and thus all floors, grooves, holes or the like are filled without any problem.

Compared to the preformed foam block, however, certain problems also arise: the recess must be dry, otherwise the water will act as the third reaction component and have an adverse effect.

The nozzles can become clogged if they are not blown clean for longer work interruptions.

- The foam must not partially condense and form droplets before hardening, this would lead to deformations in the recess.

Moving the foaming takes place without any problem if the requirements known to the skilled person are adhered to. The choice of foam making components also depends on the geometry of the recess.

The two-component foam is preferably made from phenol-formaldehyde resins and expanding reagents or isocyanate polyetherol.

In all variants of the invention, the foam can be open or closed-pored.

The invention is further elucidated with reference to the drawing as example 35. In these diagrams: Fig. 1 shows a perspective representation of an anode for the ma- »,« Λ Λ. «Η Γ1 ^:; fig. 2 a round plug hole in an anode, and fig. 3 an insulated foam block with a filling mass.

The anode 10 shown in Fig. 1 has on the cover side two rectangular cross-sections 12 in cross section. Two foam blocks 14 exactly corresponding to the scoops 12 in their dimensions are ready for insertion. They are pushed in by a machine not shown for simplicity.

The round plug hole 10 16 in the anode 10 shown in horizontal section in FIG. 2 is filled with a cylindrical foam block 18 in engagement. The three spiral grooves 20 remain empty. Although the recess is not completely filled, the foam block 18 can practically fully observe its mechanical support function. Pitch vapors can escape better through the non-foam-filled spiral grooves 20 and the bores 26 through the foam block 18.

The partial vertical section through an anode 10 shown in Figure 3 shows a plug hole 16 filled with a foam block 18, which in turn contains a filler 22 of granular anthracite. The outwardly facing surface of the foam block 18 with the filler body 20 and the respective cover surface 24 of the anode 10 are formed in alignment.

Claims (10)

Filling compound for green carbon bodies (10) with at least one recess (12, 16), for mechanically stabilizing the recess, respectively recesses during at least the first stage of the calcination process, in particular for plug or blowdown 5 holes of anodes for the production of aluminum by melt flow electrolysis, characterized in that the filling mass consists of a rigid, non-carbon-reacting organic foam (14/18), which, with the side wall, side walls and bottom surface respectively, of the recess (12, 16) is in form-fitting engagement. Filling compound according to claim 1, characterized in that it consists of a preformed foam block (14) which fits rigidly into the recess (12, 16) and preferably with the respective covering surface (24) of the carbon body (10) approximately is aligned. Filling compound according to claim 2, characterized in that it does not fill depressions, grooves (20), holes or the like formed in the recess (12, 16). Filling compound according to claims 2 or 3, characterized in that it consists of a phenol-formaldehyde or polyurethane foam. Filling compound according to any one of claims 2-4, characterized in that foam (14) contains a passive carbonaceous filler (22). Filling compound according to claim 5, characterized in that the filler. (22) consists of coke or anthracite. Filling compound according to claims 5 or 6, characterized in that the filler (22) has a grain size of up to 10 mm. Filling compound according to any one of claims 2 to 7, characterized in that the foam block (14, 18) in vertical or substantially vertical direction relative to the covering surface (24) of the carbon body (10) by at least one of the mechanical stability non-disadvantageous bore (26) has gone through. Filling compound according to claim 1, characterized in that it consists of a locally produced two-component foam which substantially fills the recess with respect to the covering surface of the carbon body. a λ fï λ V «« * ·> \ J Ö - 7- Filling compound according to claim 9, characterized in that it consists of phenol-formaldehyde resin and expander reagent and isocyanate polyetherol.