RU73865U1 - MIXTURE PREPARATION LINE FOR SILICON Smelting in an Ore Thermal Electric Furnace - Google Patents

Abstract

The technical solution relates to non-ferrous metallurgy, in particular, to the electrothermal production of technical silicon. The technical solution allows to increase the technical and economic indicators of production of technical silicon due to the involvement of small fractions of petroleum coke in the production. The technical essence is as follows. The batch preparation line for silicon smelting in an ore-thermal electric furnace includes receiving bins 2, 3, 4, 5, 6, 7 for quartzite and various carbon materials, including petrocoke and wood chips, weight batchers 9, 10, 11, 12, 13 , 14 with vibration feeders 8 installed under each receiving hopper and a belt conveyor 1 located below them, above which, in the direction of the conveyor belt 1, there is a receiving hopper 6 with petroleum coke fraction 0.12-12 mm and a moisture content of 6-8%, and after there is a receiving hopper 5 for wood chips. 1 ill.

Description

The proposed solution relates to non-ferrous metallurgy, in particular, to the electrothermal production of technical silicon.

At present, on an industrial scale, industrial silicon is obtained by high-temperature reduction of silica with carbon in an arc furnace with direct carbothermic reduction. Silica is mixed with the reducing mixture, and the mixture thus obtained is loaded onto the top of the ore-thermal furnace, and from there uniformly in small portions it is immersed in the furnace.

In the furnace, the process of reducing silica proceeds in the following stages: the formation of silicon monoxide due to the evaporation of silica in a reducing atmosphere; the interaction of silicon monoxide with carbon with the formation of silicon carbide with silica and silicon monoxide with the formation of elemental silicon.

When loading the mixture, the mixture is rapidly sintered in the zone of its active heating (the zone between the electrodes and the skull) and the mixture freezes, which impairs the gas permeability of the mixture and reduces its descent into the reaction zone. This leads to the formation of burnouts and fistulas on the top, which leads to irretrievable losses of silicon in the form of silicon monoxide with exhaust gases, a decrease in the extraction of silicon and an additional energy consumption.

The degree of reduction of SiO ₂ to Si in smelting is determined by several factors:

First, the conditions for the reduction of SiO ₂ . The greater part of SiO ₂ will be restored in the lower high-temperature zone of the hearth, the higher will be the extraction of silicon, higher melt and grade, lower consumption of electric energy.

Secondly, the higher the reactivity of the reducing agent, the greater part of SiO will be reduced to Si and the smaller part will be carried out by gases in the form of monoxide.

Thirdly, the higher the filtration and adsorption capacity of the mixture (reducing agent) will be at the top, the greater part of SiO, as well as Si and SiO ₂ , will be captured and returned to the high-temperature zone for further restoration.

One of the main factors determining the effective reduction of silicon is the use of carbon-containing reducing agents:

- the suitability of the reducing agent for high temperature conditions

process - heat resistance - while maintaining technological properties

before it enters a higher temperature zone, where the recovery process takes place directly at a temperature> 2500 ° C

- high reactivity (PC), providing fast and complete recovery of silica to silicon, which determines the high extraction of silicon in a commercial product;

- the minimum content of determining impurities, regulated by the specifications of consumers for the quality of technical silicon, is determined by the difficulties with the implementation of refining processes;

- low scarcity and reasonable cost of reducing agent in

conditions of modern production;

The above requirements in the world practice of silicon production, including Russia, meets charcoal - a product of wood pyrolysis. It most fully meets the requirements for it and firmly maintains the reputation of one of the best technological reducing agents in the production of silicon. However, a significant increase in silicon production in recent years has led to an increase in demand for charcoal, its scarcity and a sharp rise in price, which negatively affected the technical and economic indicators of silicon production and led to the need for its partial or even complete replacement with other carbon materials

Working on mixtures of various reducing agents is a forced decision. The replacement has not been completely resolved either theoretically or practically and is fraught with many difficulties.

The following carbon materials are used as reducing agents in the global silicon production: charcoal, wood chips, petroleum coke, coal, peat briquettes and peat coke, anthracite, semi-coke, pitch, legnin, cellolignin coke, brown coal, lump raw wood and other carbon materials.

The decrease in the share of charcoal, as the most expensive reducing agent, in the charge during silicon smelting should be accompanied by a thorough study of the effect of each new component replacing charcoal, taking into account the mutually exclusive properties and the optimal dosage of each.

One of the substitutes for at least part of charcoal is petroleum coke, which is used to reduce the total cost of the reducing agent and to increase the grade of commercial silicon in the form of an additive to the reducing mixture. It is the lowest ash of all reducing agents used in the production of silicon, and contains the largest amount of carbon. Its average composition (%): carbon 90-95; ash 0.17-0.6; volatile 3,5-13. The raw materials for the production of petroleum coke are heavy residues formed as a result of atmospheric and vacuum oil refining (fuel oils, semi-tars, tars), cracking - residues from thermal cracking of fuel oils and tars, heavy gas oils

catalytic cracking, residues of oil production (asphalt propane deasphalting tar, extracts of phenolic refining of oils and the process of duosol, mixtures thereof, etc.). When coking these heavy oil residues, which are carried out at a temperature of 450 to 550 ° C and a pressure of atmospheric to 6 kg / cm ² , a solid product is obtained - petroleum coke (carbon residue).

Currently, petroleum coke has found wide application (due to the high carbon content) in the production of industrial silicon as one of the constituent components of reducing agents. This is confirmed by a significant number of copyright certificates and patents obtained in Russia (about 80) on the use of petro-coke as one of the components of the recovery mixture.

At the same time, for all the advantages of petroleum coke, which has a high carbon content of 90-95%, a low ash content of 0.17-0.6%, volatile 3.5-13%, etc. it has the main significant drawback - low reactivity , which prevents the use of petroleum coke in significant quantities instead of charcoal in the production of technical silicon.

When smelting silicon requires careful preparation of the mixture for melting. This is determined by three specific features of the silicon arc furnace:

- a small living section of the ring hearth for loading the mixture;

- high speed of reaction gases in the furnace and blowing of dust and charge fines;

- the tendency of the mixture to sintering and hovering with subsequent deterioration of smelting.

Based on the requirements of the melting technology, the mixture should be sufficiently dry, optimal in size, well mixed, contain the necessary amount of reaction carbon.

The composition and quantity of the mixture must satisfy the following requirements during melting:

- Do not burn on top and do not blow out;

- provide the necessary gas permeability to remove gases;

- have a large resistivity;

- minimally sinter on the top and continuously descend into the lower high-temperature zone;

- to provide gas filtration from dust and adsorption of vapors, dispersions of silicon and its oxides.

The well-known "Method of smelting silicon" according to the patent of Russia No. 2062799, M. C. С22В 5/10 dated June 29, 94

The essence of the invention lies in the fact that in the process of smelting silicon in an ore-thermal furnace, a reducing mixture containing mass% is used:

Charcoal 25-35

Coal 20-25

Petroleum Coke 30-40

Wood chips 10-15

For all the advantages of this reduction charge used in this "Method ...", it has a major drawback.

In the process of preparation on the charge line for smelting silicon, all components of the reducing agents undergo a significant number of overloads. So, for example, quartzite, petroleum coke, charcoal and wood chips are overloaded 10-12 times before dosing and 8-10 times after dosing. One can only imagine how much over-crushed reducing agent and, in particular, petroleum coke enters the furnace top, which is removed from the furnace top or burns on it, leading to overhead, excessive consumption of carbon and electricity. All these factors affect the instability of the electric furnace on a charge of non-optimal composition for reaction carbon.

The closest in its technical essence and the achieved result to the proposed technical solution is the "Line for the preparation of the mixture for smelting silicon in an ore-thermal furnace" (see OMKatkov "Smelting of technical silicon" study guide, 2nd edition, Irkutsk publishing house State Technical University, 1999, pp. 120-124).

This line includes receiving bins for quartzite and various carbon materials of pre-prepared fractions, including petroleum coke and wood chips, weighing batchers with vibration feeders installed under each receiving bunker, and a belt conveyor located below them. The work of the dosing line is set so that each subsequent type of material in movement of the conveyor belt lies on the previous one along the entire length of the conveyor belt. In general, a layered cake is formed, which is poured into one furnace pocket, thereby ensuring the unity of the charge composition in one pocket.

This line has the same disadvantages indicated above. The objective of the proposed solution is to increase the technical and economic indicators of production of technical silicon.

The technical result of this solution is to improve the quality of the reduction mixture due to the involvement of small fractions of petroleum coke in the production.

The technical result is achieved by the fact that in the preparation line of the charge for silicon smelting in an ore-thermal electric furnace, including receiving bins for quartzite and various carbon materials, including petrocoke and wood chips, weighing batchers with vibration feeders, which are installed under each receiving hopper and a belt located under them conveyor, receiving hopper with petroleum coke waste is located after the receiving hopper for wood chips along the belt conveyor.

The technical essence is as follows.

In the process of production of petroleum coke, as well as in the process of preparing it to obtain a reduction mixture from various carbon materials, a significant amount of coke breeze is formed, which could not be used in the production of silicon. The main reason is that petroleum coke fines, as a rule, were carried out or burned at the top without having fulfilled their function of carbon reducing agent.

It was proposed that petroleum coke wastes, and this small change in the 0.12-12 mm fraction moistened to a moisture content of 6-8%, be fed to wood chips. The petrocoke fines, hitting wood chips, which themselves have high humidity up to 40%, adhere to it with a sufficiently high coefficient of adhesion. Thanks to this, it became possible to deliver petroleum coke fines to the reaction zone of the ore-thermal furnace, thereby reducing the loss of fines from removal from the furnace and its combustion at the top.

Comparison of the proposed technical solution and the prototype shows that the line for the preparation of the mixture for melting silicon in an ore-thermal furnace have common features, namely:

- the presence of a receiving hopper for quartzite;

- the presence of receiving bins for various carbon materials, including petroleum coke and wood chips;

- the presence of weight batchers with vibration feeders installed under each receiving hopper;

- the presence of a conveyor belt located under each receiving hopper.

The salient features of the proposed solution compared to the prototype:

- location in the line of the receiving hopper with petroleum coke waste, after the receiving hopper with wood chips along the belt conveyor;

This is the conformity of the technical solution to the criterion of a utility model - “novelty”.

Comparison of the proposed technical solution not only with the prototype, but also with other solutions in this area from the patent and scientific and technical information did not reveal similar features stated in the distinguishing part of the utility model formula.

At the same time, the combination of features in the proposed technical solution, both known and unknown, declared in the formula of the object of protection, allows to achieve:

- reduction of expenditure ratios of reducing agents by 0.5-1%;

- Involvement of petroleum coke wastes in the production of silicon in the form of small fractions previously unused, together with industrially applicable, at present, fractions from 5 mm to 12 mm and above;

- ultimately, increase the technical and economic indicators of silicon production.

The technical essence of the proposed solution is illustrated by the figure, which shows the "Line of preparation of the mixture for smelting silicon in an ore-thermal electric furnace." The line along the belt conveyor 1 includes a receiving hopper 2 for quartzite, a receiving hopper 3 for coal, a receiving hopper 4 for charcoal, a receiving hopper 5 for wood chips, a receiving hopper 6 for petroleum coke, a receiving hopper 7 for additional coal (the placement of receiving bins with carbon materials is arbitrary in the line, except for the placement of receiving bunkers 5 with petroleum coke and bunker 6 with wood chips, and may depend on specific technological instructions for each production ). In addition, the line includes vibration feeders 8 installed under the receiving hoppers 2, 3, 4, 5, 6, 7 and under the weight batchers 9, 10, 11, 12, 13, 14 for each carbon material.

Industrial applicability was confirmed by positive test results at Silicon CJSC.

Claims (1)

A batch preparation line for silicon smelting in an ore-thermal electric furnace, including receiving bins for quartzite and various carbon materials, including petroleum coke and wood chips, weighing batchers with vibration feeders installed under each receiving bunker and a belt conveyor located under them, characterized in that along the way of the conveyor belt movement, a receiving hopper with petroleum coke waste is located after the receiving hopper for wood chips.