FI76056C - Process for producing silicon from raw material quartz in an electric low shaft furnace - Google Patents

Description

76056

The present invention relates to a process for producing silicon from a quartz raw material further formed from a quartz raw material in a low shaft electric furnace, wherein the reducing agent briquettes with an excess of carbon relative to the reaction SiC> 2 + 3C = 10 SiC + 2CO, first converting the quartz in the reducing agent briquettes to SiC at a temperature below 1600 ° C at the top of the low shaft electric furnace and then exceeding 1600 ° C at the bottom at a temperature of, preferably at 1800 to 2000 ° C, the liquid quartz raw material is reduced. The reducing agent briquettes are preferably prepared by a hot briquetting process. - Quartz raw material here means all silica-containing materials used in the manufacture of silicon, in particular quartzite and 20 quartz sand. Quartz sand is usually used to make reducing agent briquettes. By hot briquetting is meant binder-free briquetting in which the starting materials are heated to 430-540 ° C and formed into briquettes using pressure (cf. DE patent-25 publication 19 15 905). However, reducing agent briquettes prepared in another way can also be used within the scope of the invention.

A known process of this type (DE patent publication 30 32 720) uses reducing agent briquettes with at most a slight excess of carbon relative to the reaction SiC> 2 + 3C = SiC + 2CO. In fact, during said reaction, the aim is to convert the reactants in the reducing agent briquettes, namely SiC and CO 2, as completely as possible, in order to then carry out the liquid reduction of the quartz raw material at a given high temperature in the lower shaft furnace as a SiC reducing agent. Excess carbon is present only because carbon reacts with the oxygen in the reduction of the silica in the reducing agent briquettes and to that extent is lost from the reduction of the silica. However, according to known procedures, the reducing agent briquettes after the reduction of silica are practically formed from silicon carbide and no longer from carbon. Known methods have proven to be useful, but still require improvements in droplet yield and, with it, energy requirements.

The object of the invention is to carry out such a method in such a way that a high silicon yield is obtained with a lower amount of energy.

This object is solved according to the invention by using reducing agent briquettes with an excess of more than 50% by weight of carbon relative to the reaction S1O2 + 3C = SiC + 2CO, so that in the lower part of the low shaft electric furnace in the reducing agent briquettes below 1600 ° C carbon, whereby the reducing agent briquettes have a coke-like structure, and that the activated carbon on the one hand and the SiC formed on the other hand reduce the quartz raw material added at the bottom of the low shaft electric furnace. Within the scope of the invention, an excess of carbon of preferably less than 90% by weight, preferably about 80% by weight, is used in the reducing agent briquettes. In this case, the optimum can also be obtained in such a way that the entire reaction is carried out by reducing at least 50% by weight of the added quartz raw material with activated carbon in the lower part of the low-shaft electric furnace. - In total, the ore mixture 11 3 76056 is adjusted so that the balance of substances is correct. Thus, it is not necessary to use exclusively reducing agent briquettes of the composition described. Rather, within certain limits, a classical ore-5 mixture may be added (eg comprising 3 t quartz / 0.4 t charcoal / 0.4 t peat coke / 0.3 t crude oil coke / 0.5 t low-ash coal) as long as it is ensured that a sufficient amount of activated carbon is provided from the reducing agent briquettes.

As already mentioned, the method and means for producing reducing agent briquettes can be freely chosen in the process according to the invention. However, it must be ensured that the reducing agent briquettes are correspondingly stable, so that they can be added as described as an ore mixture together with the quartz raw material to a low-shaft electric furnace and allowed to react as described there. According to a preferred embodiment of the invention, the procedure is then to use reducing agent briquettes prepared by hot briquetting into fist briquettes or briquette pads, their size 3 being 15 to 60 cm. In this connection, according to the invention, it is further recommended to use reducing agent briquettes whose carbon content, as far as is necessary for hot briquetting, consists of clumping coal, and otherwise inert carbon materials such as crude oil coke, anthracite, graphite, lignite and coal. - It is clear that the process according to the invention can be extended to Ferro-silicon and silicon metal by adding suitable substances, e.g. iron chips or granular iron, to the low-shaft electric furnace 30 in addition to the quartz raw material.

The invention is based on the finding that in the reduction of silica with carbon, in addition to the formation of silicon carbide, there is also the formation of activated carbon in the lower part of the low shaft electric furnace, which in some way acts as a virgin to reduce silica and lead to improved energy yield. This will now be illustrated in detail by way of working examples.

Example 1

To obtain about 600 t of silicon, 1200 t of briquettes were composed of 30% caking coal, 32% crude oil coke and 38% quartz sand (99.8% S1O2) in an electric furnace together with almost the same amount of lump quartz. In the first stage, the reaction was carried out in an upper shallow shaft furnace at a temperature of 1500-1600 ° C and in the second stage at a temperature of 1800-1900 ° C, whereby in the first stage the briquettes contained more than twice as much carbon as the reaction.

SiO 2 + 3C - SiC + 2CO

required. This is overcome by a simple stoichiometric calculation procedure. To demonstrate this, gmoles are used in the above reaction equation.

30 (SiC> 2> + 18 (30 * 20 (SiC) + 28 (2CO)

In the first reaction step, the briquettes do not decompose. A coking, i.e. porous conglomerate with SiC and residual carbon is formed. At the temperatures above 1600 ° C in the lower part of the electric furnace, the remaining carbon still reacts, according to the following reaction formula S1O2 + C * SiO + CO.

SiO is gaseous at the bottom temperatures of the electric furnace, CO also. In addition, the reaction 2SiC + S1O2 - 3Si + 2CO also occurs at the bottom of the electric furnace.

Il 5 76056

Gaseous SiO rises in an electric furnace. There, coke conglomerates first have a physical effect: due to their large surface area, they greedily bind S1O2. At the bottom of the electric furnace, they also work chemically, as follows 2SiO + 3C * SiC + 2CO

At the bottom of the electric furnace, the remaining carbon of the conglomerates continues to react, as mentioned above.

The thermodynamics of the connections are obtained from the known heat amounts of the reactions. In connection with the above-mentioned embodiment, the following results are obtained: Electricity consumption was reduced by about 14% and Si yield increased by more than 20%. In addition, the consumption of the electrodes decreased by half, i.e. from 128 kg / t Si to 59 kg / t Si. Electrode movement was reduced to a minimum.

The decrease in electricity consumption and the increase in Si yield depend on each other: Since SiO is no longer wasted, no energy is wasted previously used to produce the effluent SiO according to the following scheme S1O2 + 2C = SiO + CO.

Example 2:

The situation is more favorable in the production of ferrosilicon. In this case, the losses are smaller due to the formation of SiO.

If the procedure described above is such that the ratio of lump-quartz to briquette addition remains 50:50 and scrap iron is added in such an amount that a 75-alloy is formed, the advantages of briquettes are still clearly identifiable, i.e. power consumption is reduced by 8% and the drop yield increases by 12%.

Claims (3)

6,76056 Claims p A method for producing silicon from a quartz raw material in a Mata lacquer electric furnace, comprising introducing a quartz raw material in granular form into the low-gap electric furnace and further reducing quartz and carbon reducing agent briquettes having an excess of C At this temperature, the quartz in the reducing agent briquettes is converted to SiC, and the liquid quartz raw material is then reduced in the lower part of the low shaft electric furnace at a temperature above 1600 ° C, preferably 1800-2000 ° C, characterized in that reducing agent briquettes using SiO 2 + 3C SiC In addition to + 2CO, an excess of carbon in excess of 50% by weight but less than 90% by weight, preferably about 80% by weight, of activated carbon on the top of the low shaft electric furnace in reducing agent briquettes at a temperature below 1600 ° C in addition to SiC, the reducing agent briquettes acquire a coke-like structure, and that with this activated carbon SiC, on the one hand, and SiC, on the other, are reduced by at least 50% by weight of the added quartz raw material in the lower part of the low shaft electric furnace. Method according to Claim 1, characterized in that reducing agent briquettes prepared by the hot briquetting process in the form of fist briquettes or briquette pads are used * Process according to Claim 2, characterized in that reducing agent briquettes are used, the carbon content of which, in so far as it is necessary for hot briquetting, consists of agglomerating coal and other inert carbon materials such as crude oil coke, anthracite, graphite, brown and coal coke. Il