CH663610A5 - METHOD FOR PRODUCING SILICON FROM RAW MATERIAL QUARTZ IN AN ELECTRONIC LOWER STOVE. - Google Patents

Description

The invention relates generically to a process for the production of silicon from raw material quartz in an electronic shaft furnace, the raw material quartz in granular form and also reducing agent briquettes of quartz and carbon are introduced into the electronic shaft furnace, which are related to the reaction Si02 + 3C = SiC + 2CO have an excess of carbon, with the quartz in the reducing agent briquettes first being converted to SiC in an upper part of the electronic low-shaft furnace at a temperature of below 1600 ° C. and then in a lower part of the electrical low-shaft furnace Temperature of over 1600 ° C the liquid raw material quartz is reduced. The reducing agent briquettes are preferably produced by hot briquetting and the temperature at which the liquid raw material quartz is reduced is preferably 1800 to 2000 ° C. - raw material quartz denotes all silicon dioxide carriers used for the production of silicon, in particular quartzites and quartz sand. Quartz sand is generally used to produce the reducing agent briquettes. Hot briquetting refers to binder-free briquetting in which the starting materials are based on a

Temperature of 430 to 540 ° C heated and formed into briquettes using pressure (see. DE-PS 1 915 905). Within the scope of the invention, however, it is also possible to work with reducing agent briquettes which have been produced in another way.

In the known generic method (DE-PS 3 032 720), use is made of reducing agent briquettes which, at most, have a slight excess of carbon in relation to the reaction Si02 + 3C = SiC + 2CO. In fact, the aim is to convert the reactants in the specified reaction in the reducing agent briquettes as completely as possible, namely to SiC and CO, and then to reduce the liquid raw material quartz in the lower part of the downhole furnace at the specified 15 high temperatures with the SiC as reducing agent perform. The excess of carbon is only present because the carbon also reacts with oxygen in the reduction of the silicon dioxide in the reducing agent briquettes and is thus lost for the reduction of the silicon dioxide. Within the framework of the known measures, however, the reducing agent briquettes practically consist of silicon carbide after the reduction of the silicon dioxide and no longer of carbon. The known measures have proven themselves, but are in need of improvement with regard to the silicon yield and thus with regard to the energy requirement.

The invention has for its object to carry out the generic method so that a high silicon yield is obtained with reduced energy consumption. 30 To achieve this object, the invention teaches that use is made of reducing agent briquettes which, in relation to the reaction Si02 + 3C = SiC + 2CO, have an excess of carbon of more than 50% by weight that in the upper part of the electronic shaft furnace Reductant briquettes are formed at a temperature of below 1600 ° C next to the SiC activated carbon, the reducing agent briquettes taking on a coke-like structure, and that on the one hand with this activated carbon and on the other hand with the SiC formed, the 40 raw material quartz used in the lower part of the electronic low shaft furnace is reduced. In the context of the invention, preference is given to working with an excess of carbon in the reducing agent briquettes which is less than 90% by weight, preferably about 80% by weight. Optimization is also achieved if the process is carried out overall in such a way that at least 50% by weight of the raw material quartz used in the lower part of the electronic shaft furnace is reduced with the activated carbon. - Overall, the Möller is adjusted so that the material balance is correct. It is not necessary to work exclusively with the reducing agent briquettes of the composition described. Rather, a classic Möller can be added within limits (e.g. from 3 t quartz / 0.41 charcoal / 0.41 peat coke / 0.3 t 55 petroleum coke / 0.5 t low-ash coal), as long as it is only ensured that from the reducing agent briquettes sufficient activated carbon is made available.

As already mentioned, the method of producing the reducing agent briquettes is basically arbitrary for the method according to the invention. However, it must be ensured that the reducing agent briquettes are stable in order to be introduced in the manner described as a Möller together with the raw material quartz in an electronic shaft furnace and to react there in the manner described. According to a preferred embodiment of the invention, the procedure is such that one works with reducing agent briquettes,

which are produced by hot briquetting in the form of egg briquettes or pillow briquettes and which have a size of 15 to 60 cm3. In connection with this, the invention further recommends working with reducing agent briquettes whose carbon content, insofar as is necessary for hot briquetting, consists of baking coal and, moreover, inert carbon carriers such as petroleum coke, anthracite, graphite, brown and hard coal coke. It goes without saying that the process according to the invention for ferrosilicon and for silicon metal can be continued by using suitable substances, e.g. Iron shavings or iron granulate, into the electronic low-shaft furnace.

The invention is based on the knowledge that, in the reduction of silicon dioxide with carbon in the reducing agent briquettes, in addition to the formation of the silicon carbide, active carbon is also formed, which as it were as virgin carbon in the lower part of the electronic shaft furnace, in addition to the silicon carbide, to reduce the Silicon dioxide is available, which improves the yield and reduces the energy consumption. This is explained in more detail below using exemplary embodiments.

example 1

To produce around 600 t of silicon, 1200 t of briquettes were produced, which were used in the electric furnace with an almost equal amount of lumpy quartz.

In the first process step, the briquettes were made from a mixture of

30% baking coal

32% petroleum coke and

38% quartz sand (99.8% Si02)

produced by the hot briquetting process, i.e. the coal was used as a binder at temperatures around 500 ° C. The finished, cooled briquettes were examined and contained

(42 +/- 0.4) Si02 and (52 +/- 0.7) Cfix.

A strength test showed that point compressive strengths of 150 to 200 kg had been reached, which can be explained by the inclusion of the inert substances such as petroleum coke and sand in the melted and cooled coal. Measurement of the inner surface of the briquette showed 0.5 to 1.0 m2 / g. This means that there are no reaction kinetically interesting areas where heterogeneous conversions between gases such as SiO on the one hand and carbon on the other hand can take place with high conversions.

In a second process step, the briquettes were fed to an electronic low shaft furnace. The material was screened off in front of the oven, which had resulted in abrasion and breakage during transport. This fine material was less than 5% in proportion. This is a very good result, since charcoal, peat and coal are destroyed much more. Numbers of more than 10% are known.

663 610

In the electric furnace there was a mixture of lumpy quartz and briquettes with continuous filling, which were heated up and reacted in a statistically good distribution due to similar behavior during pouring.

Consider the blanket response of Si generation

Si02 + 2C = Si + 2CO,

it can be seen from the analysis of the briquettes that the carbon is overdosed in them and only the further reaction with the quartz pieces ensures full conversion. But because of the equation before silicon formation, silicon carbide

Si02 + 3C = SiC + 2CO

arises, the question remains whether there is sufficient carbon in the briquette for this case. The calculation shows that there is around twice as much carbon in the briquette as the reaction requires. This is a molar ratio of 1: 5 to 1: 6. This was aimed at so that the coke structures embossed during hot briquetting are preserved, even if losses occur as a result of reaction to silicon carbide.

Evidence for this view was provided by using thermocouples to find out the temperature zone in which the carbide reaction takes place. Samples were taken in the 1500 to 1600 CC hot material, which clearly demonstrated that the briquettes still have their original shape, although the sales between carbon and silicon had already begun or had completely expired.

Most of the briquettes had a white surface, which means that reactions had taken place here. However, the measurement of the inner surface of the cooled briquettes was more important. The measurement showed a greatly expanded inner surface of 20 to 230 m2 / g.

This leads to a sharp decrease in the amount of Si02 generated in gas cleaning. Energy consumption and silicon yield are closely linked to this. It was measured on the furnace that the power consumption decreased by around 14% and the Si yield increased by more than 20%. An unexpected, but important economic advantage was the halving of the electrode consumption. This decreased from 128 kg / t Si to 59 kg / t Si. The movements of the electrodes were kept to a minimum.

Example 2

The situation is more favorable for the production of ferrosilicon. The losses due to the formation of SiO are lower here.

If one proceeds in the manner described above,

The fact that the piece of quartz and briquette remain in a ratio of 50:50 to each other, and that scrap iron is added to the extent that a 75 alloy is produced, the advantages of the briquettes can still be clearly seen: the power consumption drops by 8% and the yield silicon increases by 12%.

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Claims (5)

663 610 1. A process for the production of silicon from raw material quartz in an electronic shaft furnace, whereby the raw material quartz in granular form and also reducing agent briquettes of quartz and carbon are introduced into the electronic shaft shaft furnace, which have an excess in relation to the reaction Si02 + 3C = 2CO Have carbon, in an upper part of the electronic shaft furnace the quartz in the reducing agent briquettes is first converted to SiC at a temperature of below 1600 ° C and then in a lower part of the electronic furnace at a temperature of over 1600 ° C the liquid raw material -Quartz is reduced, characterized in that one works with reducing agent briquettes which, in relation to the reaction Si02 + 3C = SiC + 2CO, have an excess of carbon of more than 50% by weight that in the upper part of the electronic low-shaft furnace activated the reducing agent briquettes at a temperature below 1600 ° C next to the SiC r Carbon is formed, the reducing agent briquettes adopting a coke-like structure, and that with this activated carbon on the one hand and the SiC on the other hand, the raw material quartz is reduced in the lower part of the electronic downhole furnace. 2. The method according to claim 1, characterized in that one works with reducing agent briquettes which have an excess of less than 90 wt .-%, preferably about 80 wt .-%, of carbon. 2nd PATENT CLAIMS 3. The method according to any one of claims 1 or 2, characterized in that in the lower part of the electronic shaft furnace at least 50 wt .-% of the raw material quartz are reduced with the activated carbon of the reducing agent briquettes. 4. The method according to any one of claims 1 to 3, characterized in that work is carried out with reducing agent briquettes which are produced by hot briquetting in the form of egg briquettes or pillow briquettes. 5. The method according to claim 4, characterized in that one works with reducing agent briquettes whose carbon content, insofar as is necessary for hot briquetting, consists of baking coal and, moreover, of inert carbon carriers such as petroleum coke, anthracite, graphite, brown and hard coal cokes.