SI21319A - Method for baking and calcinating shaped carbon bodies in an annular furnace - Google Patents

Abstract

The invention relates to a method for calcining and baking shaped carbon bodies, in particular carbon or graphite electrodes in annular furnaces. The method for baking or calcining shaped carbon bodies that are covered with packing coke takes place in an annular furnace at temperatures of over 900 DEG C, whereby the packing coke is additionally covered with a material containing CaO and large amounts of cristobalite and/or tridymite, with a CaO content of between 1.5 and 10 wt % and an SiO2 content of between 90 and 98.5 wt %.

Description

Description

The present invention relates to a process for calcining and firing molded carbon bodies, in particular carbon or graphite electrodes in a circular chamber furnace (Ringkammerofen).

For example, anodes or cathodes for the production of aluminum by the Herault-Hall process in t. im. Circular chamber furnaces are fired in a closed or open structure at temperatures preferably from about 900 ° C to 1300 ° C. Such furnaces consist of a plurality of stationary chambers over which, in general, several circulating fires are arranged, which, inter alia, consist of a combustion apparatus and a cooling device.

The closed-loop circular chamber furnace is e.g. described in WO 92/22780. In order to protect green anodes or cathodes predominantly arranged in chambers in several layers from deformation and abrasion (oxidation), the cavities remaining around them are filled with petroleum coke, metallurgical coke and the like, generally in granulation. from 1 mm to 20 mm (hereinafter referred to as coke). After the firing process, the coke is removed with the help of a suction device and the anodes or cathodes are taken out. The top anode respectively. The cathode blocks are technically conditioned as particularly threatening to the combustion, resulting in a cover layer, usually made of the same material as the coke used, on their surface. For example, in a closed anode furnace, the thickness of the coating layer when using metallurgical coke is about 30 to 40 cm, and when using petroleum coke it is about 55 to 70 cm. In open anode furnaces, compared to a closed furnace, the top anode blocks are covered with a much thicker layer.

Essentially, the cover material in a carbon burner furnace has the following requirements:

- the prevention of slag and crust formation, especially when driving slag-forming coke;

- multiple use;

- a significant reduction in the thickness of the coating layer compared to the coke insert itself;

- there is no negative impact on the quality of the carbon form;

- easy handling;

- a positive economic balance.

It is known from DE 2 314 391 that, in order to prevent oxidation of filler coke, the top surface of the filler coke loaded around the carbon molds is coated with silica sand, naturally occurring (mineralogically composed of quartz), by itself or as with a mixture of coke. However, very strong crust formation proved to be very defective and repeated use was not possible.

DE 2 314 391 proposes a refractory material with a refractory material whose particles (in the form of beads, grains, tablets or cubes) are larger than the particles of the coke, but smaller than about 50 mm. This classification should allow for the subsequent separation and re-use of filler coke and cover material. However, in the examples, interlaced beads of the alumina material group (90 wt% A1 ₂ O ₃ , 10 wt% SiO ₂ , as well as 99 wt% A1 ₂ O ₃ and 1 wt% SiO ₂ ) and mullite ( 31.8 wt.% A1 ₂ O ₃ and 66.2 wt.% SiO ₂ ) are extremely expensive to prepare. According to the file, an additional layer of filler coke, which is placed underneath the refractory material, is urgently needed to prevent the carbon form from being blown off the surface. However, the thickness of this layer of filler coke is not indicated. Particularly when metallurgical coke is used in the additional coke layer, rich slags are formed in the process of burning with iron, which partially scratches the described covering material and causes difficult separation from the rest of the coke by filling and sieving. This post does not report the effects of gaseous constituents that leak in the carbon burning process.

In the experiments contemplated by the present invention, it has been shown that e.g. Aluminum oxide balls are destroyed after two bypasses when inserted into a closed fur chamber furnace.

EP 0 779 258 A2 describes a material for filling cavities between carbon bodies and the walls of individual combustion chambers, consisting of a homogeneous mixture of carbon support and material containing silicon oxide. S1O2 is intended to serve as a donor to absorb the resulting free impurities, especially sodium, during the firing process, thereby reducing the corrosion of the refractory walls of the chamber. An essential advantage of this method of treatment is that recyclable material such as e.g. contaminated carbon-filter powders and crushed used solitary bricks. Examples of mixing ratios of filler material and their preparation are known. Defined reports on the chemical composition of the silicon oxide component are not given. The harmful formation of slag when using coke as a filler material, especially in the upper region of the chamber walls, is pointed out, and the proposed filler material in the patent file is expected to reduce this problem. However, the insert could not prevent the formation of slag on the surface of the bulk, which, especially in the closed circular chamber furnace, firmly adheres to and reacts with the refractory brick material in the upper region of the chamber walls. As a result of urgent mechanical cleaning, the walls are quickly destroyed and need to be repaired. The use of contaminated recycled materials enhances the formation of slag and crust.

It is an object of the invention to improve known methods for calcining or calcining shaped carbon bodies.

The invention therefore relates, inter alia, to a process for calcining or calcining with filler coke-covered molded carbon bodies in a circular chamber furnace at temperatures above 900 ° C, wherein the filler coke is further coated with a CaO-containing material rich in cristobalite and / or tridimite, having a CaO content of 1.5 to 10 wt% and a SiO ₂ content of 90 to 98.5 wt%.

With a particle insert made of cristobalite and / or tridimite-rich CaO-containing material having a SiO ₂ content of 90 to 98.5 wt% and a CaO content of 1.5 to 10 wt% and a granulation content of 2 to 35 mm, we achieved in a surprising way the requirements for covering material described above, in particular the prevention of slag formation and the crust when using slag coke. The cover material is laid over the coke, which surrounds the carbon moldings on all sides.

Thus, according to the invention, we first developed a material by mixing at least one granular refractory with a content of SiO ₂ above 94% by weight, with at least one CaO-rich feedstock and, optionally, binders so that the resulting sowing mass to design. For example, natural quartzite or recyclable material from the furnace liner, e.g. coke ovens, which are assembled so that in the dry weight of 90 to 99 wt.% SiO ₂ , preferably 93 to 95 wt.% SiO ₂ . Lime milk, limestone and / or other calcium compounds are mixed as CaO feedstock to the extent that 1.5 to 10% by weight, preferably 2 to 4% by weight, of the dry weight are present. As binders, for example, sulphite scrap and artificial resins. The raw materials are conveniently assembled so that they have a granular composition of 0 to 10 mm, preferably 0-5 mm.

Prepared mass e.g. they are compressed into square molds, dried and preferably sintered at temperatures between 900 and 1600 ° C. After calcining the mold, the grain thickness from 2 to 35 mm, preferably 6 to 20 mm, is crushed and graded.

According to one embodiment of the invention, the prepared mass is molded into bodies, e.g. cylinders, cubes and the like, having a desired particle size of from 2 to 25 mm after firing, eliminating crushing by subsequent classification.

According to a particular embodiment of the invention, the quartz brick used is e.g. from coke oven furnaces and vaulting melting furnaces for glass having an earlier CaO content of more than 1.5% by weight, is rich in cristobalite and / or tridimite and having a SiO ₂ content exceeding 90% by weight. Such pre-products are ground to a thickness of 2 to 35 mm, preferably 6 to 20 mm.

Apply a layer of, preferably, filler coke to the top surface of the carbon molds to prevent scorching. According to a particular embodiment of the invention, this layer is replaced by a material which, after burning in a circular chamber furnace, exists as a covering material. This is achieved by mixing one or more carbon carriers when mixing the SiO ₂ - and CaO feedstocks, whereby after the formation and subsequent temperature treatment below a preferred 350 ° C there is sufficient strength to be used. When firing in a circular chamber furnace, carbon combusts in a CaO-containing mold, whereby the sintered material can be used as a covering material, and optionally crushing and classification may be necessary.

The invention is further explained by the following embodiments.

The experiments were carried out in a closed circular chamber furnace for the anode firing. The individual chambers were again made up of individual cassettes. The dimensions of the cassette were approximately: 4.64 m deep, 3.8 m long and 1 m wide. We filled machine cassettes A, B, C and D with a metallurgical coke (filler coke) with a granulation of 5 to 12 mm into the cavities around the green anodes that we intended to burn.

A metallurgical coke in a layer thickness of about 45 cm was loaded into the cassette A on the upper anode surface over the entire cross section of the chamber (3.8 m χ 1 m).

A layer of metallurgical coke about 40 cm thick was loaded onto cassette B and a 5 cm thick layer composed of solitary debris 2-12 mm, with about 0.3 wt% CaO, 45 wt% SiO _{2 was} poured into it. and 50% A1 ₂ O ₃ . Such behavior is generally common and significantly reduces the metallurgical coke burst when compared to that in cassette A.

A cassette of about 40 cm thick metallurgical coke layer was also loaded into cassette C and approximately 5 cm thick, consisting of CaO-containing material of the invention, which is rich in cristobalite and tridymite and has a granularity of 2-12 mm. CaO content was about 2.5 wt%, SiO ₂ content was about 94.5 wt. and the content of the sum of tridimite and cristobalite was greater than 80% by weight. The strength of the material was about 3000 N and the bulk density was about 850 g / l.

In cassette D, the metallurgical coke layer on the top anode surface was reduced to 8 cm and loaded with a layer thickness of about 15 cm, the same material of the invention as in chamber C. In cassette D, the total layer thickness above the top anode was about 23 cm, which is about 22 cm less compared to the A, B and C cassettes.

Under the above conditions, green anodes were fired at a firing temperature of approximately 1280 ° C. The materials used in the cassettes behaved as indicated in Table 1. In the cassettes B and D, we further specified the total consumption of metallurgical coke as a benchmark, and the data are also listed in Table 1.

Table 1

Procedure used Cover layer condition, miscellaneous Comparative example, metallurgical coke alone (cassette A) strong annealing of metallurgical coke, formation slag and and baking on the walls of the cassette Comparative example, chamotte debris (cassette B) strong slag and crust formation, baking slag on cassette walls and slag grip to the metallurgical coke that lies beneath it, consumption metallurgical coke about 10 kg / t calcined anodes The process of the invention (cassette C) there is no slag or crust formation, no lingering with metallurgical coke The process of the invention is reduced layer thickness (cassette D) there is no slag or crust formation, no lingering with metallurgical coke, consumption of metallurgical coke approx 1.5 kg / t calcined anodes

The material of the invention may have been taken from the chambers and, following the procedures described above (examples of cassettes C and D), reused as cover material in other cassettes. Even after more than 5 spirits, the material showed no slag or crust formation, and there were no burns on the cassette walls that could react with the refractory brick material, especially in the upper region of the cassette walls. The examples provided illustrate that the use of the material prevents the formation of slag and crust even after repeated use and that the consumption of metallurgical coke is drastically reduced. The refractory brick material in the cassette wall is protected against slag corrosion by the use of cover material, especially in the upper area of the cassette walls.

It is particularly noteworthy in the case of the process in cassette D that, by reducing the overall thickness of the layer above the top anode, it is now possible to burn larger anodes in the furnace without having to change the dimensions of the cassette.

Claims (9)

Patent claims 1. A process for calcining or calcining with filler coke-covered molded carbon bodies in a circular chamber furnace at a temperature above 900 ° C, characterized in that the filler coke is additionally coated with a CaO-containing material rich in cristobalite and / or tridimite, and has a CaO content of 1.5 to 10 wt.% And a SiO ₂ content of 90 to 98.5 wt.%. A process according to claim 1, characterized in that the material has a content of cristobalite and tridymite greater than 50% by weight. Method according to claims 1 to 2, characterized in that the material has a particle size of 2 to 35 mm. Process according to one of the above claims, characterized in that the CaO content is from 2 to 4 wt% and the SiO ₂ content is 93 to 95 wt%. Method according to one of claims 1 to 4, characterized in that the material is made of quartz bricks used. Method according to one of the above claims, characterized in that the material does not form slag. Process according to any one of the preceding claims, characterized in that a carbonaceous material, preferably below 350 ° C, is placed between the carbon molds to be burned and the cover layer, wherein the oxide raw material components have a CaO content from 1.5 to 10 wt.% and SiO ₂ content from 90 to 98.5 wt.%. -1010 A method according to claim 7, characterized in that the material after firing in the circular chamber furnace is used as a covering material. Material according to claim 8, characterized in that a material with a particle size of 2 to 35 mm is used.