RU2058936C1 - Method of making technical silicium in rotary ore-thermic electric furnace - Google Patents

Abstract

FIELD: metallurgy, particularly the invention may be used for producing crystalline silicon in non-ferrous metallurgy and for producing silicium containing ferroalloys in ferrous metallurgy. SUBSTANCE: method comprises steps of melting quartzite in ore-thermic furnaces; before introduction of quartzite into a charge sieving it by two fractions (20-40)mm and (40-120)mm; mixing large-size fraction quartzite with petroleum coke, charcoal, hard coal and wooden chip and loading the mixture on a grate by cones with height 400-500 mm arround electrodes; loading smallsize fraction quartzite by batches at a descending side of the electrode; rotating the furnace upon melting process in such a way, that a revolution number of reverse rotation of the furnace is by 2-10 times more, than its revolution number in forward direction; charging the small-size quartzite upon a period of rotation of the furnace with increased speed only in zones of active descending of the charge. EFFECT: enhanced quality of technical silicium, being produced by such method. 3 cl

Description

 The invention relates to metallurgy and can be used in the production of crystalline silicon in non-ferrous and silicon ferroalloys in ferrous metallurgy.

 Closest to the invention is a melting method comprising dosing, mixing, portioning and continuous melting of a mixture consisting of quartzite, petroleum coke, charcoal and hard coal, characterized in that the mixture is mixed with wood chips before being introduced to the top.

In this method, due to the introduction of 1.5-2.5 t / t of wood chips into the charge, the top is very loosened, becomes more mobile and gas permeable. Gases through the charge layer with this method of melting out more evenly. This increases the completeness of capture of silicon monoxide by reaction
SiO _gas + 2C SiC _t + CO. (one)
At the same time, there is not enough carbon in the furnace top zone to capture all silicon monoxide; part of it condenses by exothermic reactions (2) and (3)
SiO _gas __ → SiО _w (2)
2SiO _gas __ → SiO _2ж + Si _ж (3)
The release of a large amount of heat from reactions (2) and (3) and liquid products causes sintering of the top. With an excess of carbon, the formation of a skeleton of refractory carbide leads to sintering of the top. When introduced into the mixture of wood chips, the pieces of the mixture are mechanically isolated from each other by particles of wood chips. This increases the gas permeability of the mixture, reduces the escape of silicon and sintering of the top (Tolstoguzov N.V. Theoretical foundations and technology of smelting silicon and manganese alloys. M. Metallurgy, 1992, pp. 108-110). This made silicon melting possible in 16.5 and 25 MVA furnaces.

However, even with this method of smelting, large losses of silicon and sintering of the top cannot be avoided. The extraction of silicon usually does not exceed 65-70%
The objective of the invention is to increase the extraction of silicon and improve the use of carbon charge.

 To this end, in a melting method comprising dosing, mixing, loading and continuous melting of a mixture of quartzite, petroleum coke, charcoal and coal and wood chips. Before introducing into the charge, quartzite is dispersed into two fractions of 20-40 mm and 40-120 mm, after which coarse quartzite is mixed with petroleum coke, charcoal and coal and wood chips and loaded onto the top in the usual way with cones 400-500 mm high around the electrodes, and fine quartzite fractions of 20-40 mm are loaded in portions from the runaway side of the electrode.

 In addition, the rotation mode of the furnace is selected in such a way as to accelerate the descent of a small part of quartzite into the furnace of the furnace, and also so that the descending quartzite gets into the sub-electrode space.

 The problem is also solved as a result of the fact that the reverse rotation speed of the furnace is 2-10 times higher than the direct rotation speed of the furnace, and the loading of fine quartzite occurs mainly during rotation of the furnace at an increased speed. Finally, it is also important that increased rotation speed occurs only in areas of active charge gathering.

The main reason for the reduced extraction of silicon during conventional melting is the consumption of a large amount of carbon in the top zone for the formation of carbide by the total reaction
SiO _{2 (t, g)} + 3С SiC _t + 2CO (4)
Its formation sharply reduces the potential of the charge to capture SiO _gas , which leaves in large quantities from the furnace hearth.

 The formation of carbide in the top zone is according to schemes 1 and 2.

Scheme 1: SiO _{2 (t, g)} __ → SiO _gas + 1 / 2O ₂ (O) (5)
1 / 2O ₂ (O) + С __ → СО (6)
SiO _gas + 2С SiC _t + СО (7) __________________________________________________________
SiО _{2 (t, g)} + 3С SiC _t + 2CO (4)
Scheme 2: SiO _{2 (t, g)} __ → SiO _gas + 1 / 2O ₂ (O) (5)
1 / 2O ₂ (O) + 1 / 2SiC __ → 1 / 2SiO _gas + 1 / 2CO (8)
3 / 2SiO _gas + 3C 3 / 2SiC _t + 3 / 2CO (7) _______________________________________________________
SiO _{2 (t, g)} + 3С SiС _t + 2CO (4)
An increase in the size of quartzite in the mixture and an increased rate of vanishing of a small part of quartzite reduces the degree of development of reaction (5) for gasification (evaporation-dissociation) of silica, and thereby releases three moles of carbon for each mole of silica quickly converging into the forge. This creates the possibility of additional capture of 1.5 moles of monoxide from the furnace hearth, that is, the released carbon is used 1.5 times more efficiently.

 The increased rate of descent of a small part of quartzite is achieved both as a result of the fact that quartzite of 20–40 mm is loaded in the form of a “heavy” charge (without additives of light materials), and as a result of loading on the run-down side of the top, where the charge is looser. Naturally, not only loose charge from the downstream side, but also a continuously formed gap between the electrode and the charge on the top contributes naturally to an increase in the rate of quartzite quenching. Therefore, the accelerated descent of a small part of quartzite is ensured as its "heavy" laying, falling into the gap and collapse of the loose part of the top.

 To ensure a high rate of descent of a small part of quartzite, as indicated above, the direction of rotation and its speed periodically change, and the speed of rotation in the opposite direction increases by 2-10 times. Such an increase is possible, since the electrode is located in the cavity in the lower part, and the upper part of the top with such a reciprocating motion does not have time to sinter and does not impede rotation. The rotation of the furnace is carried out, for example, as follows: in the forward direction 1 h, speed 1 r / 100 h, in the opposite direction 0.25 h, speed 1 r / 50 h, in the forward direction 0.25 h, speed 1 r / 50 h. After of which the cycle repeats, that is, the furnace first rotates for an hour in the forward direction at a speed of 1 revolution per 100 hours, etc.

To obtain optimal melting indices, the entire reducing agent is loaded with large quartzite. On the one hand, this eliminates carbon in the hearth, which can reduce the efficiency the use of SiO _gas in the furnace for the destruction of carbide and the production of silicon by reaction (9)
SiO _gas + SiC _t Si _W + 2CO (9).

On the other hand, this increases the potential of the top to capture SiO _gas by reaction (1).

 An increase in the speed of rotation in the opposite direction relative to the initial one in the forward direction is naturally determined by the properties of the mixture and the conditions of its sintering. So, with a loose charge, the speed of rotation in the forward direction can be 0.25-0.5 rpm / day, in the opposite 0.5-2 rpm / day, that is, the reverse speed can grow by 2-10 times. With process disturbances and strong sintering, the reverse rotation speed is only 2-3 times higher than the forward speed. The difference in the speed of forward and reverse rotation also changes with a change in the furnace power, increasing with increasing power.

 PRI me R 1 (analog). Silicon is melted in a 25 MVA furnace with a working power of 17.5 MW and a working current of 67.5 kA. The mixture consists of 300 kg of quartzite, 30 kg of charcoal, 30 kg of petroleum coke, 80-100 kg of coal and 200-250 kg of wood chips. The mixture is mixed on conveyor belts and is fed into the top on the top, periodically puffed and pick up to the electrodes. During melting, the furnace rotates at a speed of 1 revolution per 100 hours. Metal is produced periodically 2-3 times per shift. Extraction of silicon into metal 66.8% energy consumption 16.5-19.5 thousand kWh / t. Electrode consumption 98-125 kg / g, carbon consumption 1537 kg / t. The furnace is overgrown with carbide. Therefore, approximately once a month, it works on a melt. Productivity is reduced by about 2-2.5 times.

PRI me R 2. The proposed method of melting is implemented in the following way. Quartzite with a particle size of 20-120 mm is scattered into two fractions -40 mm 1/3 by weight and +40 mm 2/3 by weight. Then 300 kg of quartzite with a grain size> 400 mm is mixed on a conveyor belt with 45 kg of charcoal, 45 kg of petroleum coke, 90 kg of coal and 200-250 kg of wood chips and loaded onto the top with conventional cones 400-500 mm high around the electrodes. The furnace rotates at a speed of 1 revolution in 70 hours for an hour in the forward direction, then for 15 minutes at a speed of 1 revolution in 20 hours in the opposite direction and 15 minutes at a speed of 1 revolution in 20 hours in the forward direction. Quartzite with a grain size of -40 mm is loaded in portions from the runaway side of the electrode when the furnace is rotated in the reverse and forward direction. Metal is produced 3-4 times per shift. After which the rotation cycle is repeated within 60 ^about .

 The quartzite consumption per ton of alloy is 2650-2750 kg / t, the energy consumption is 14.5-16.5 thousand kWh / t. Extraction of silicon 76-80% carbon consumption 1200-1246 kg / t.

The proposed method allows to obtain the following advantages:
increase silicon extraction by 3-8%;
reduce by 200-250 kg / t the specific consumption of reducing agent;
reduce the specific energy consumption to 14.5-16.5 thousand kWh / t;
increase gas permeability and charge gathering;
facilitate the working conditions of staff.

Claims (3)

 1. METHOD FOR PRODUCING TECHNICAL SILICON IN ROTATING ORE-THERMAL ELECTRIC FURNACES, including dosing of the charge components from quartzite, petroleum coke, charcoal and hard coal and wood chips, loading, melting of the charge, the discharge of the quartz fraction differs in that 40 120 and 20 40 mm, after which the coarse fraction is mixed with petroleum coke, charcoal and coal and wood chips and loaded onto the top with cones around the electrodes, the fine fraction is loaded to the electrodes with on the side of the runaway part of the electrodes, while the rotational speed of the furnace around the vertical axis and its direction are periodically changed.  2. The method according to claim 1, characterized in that the furnace is first rotated in the forward direction, then with a frequency of 2 10 times greater, in the opposite direction, then again in the forward direction with the same frequency, after which the rotation cycle is repeated.  3. The method according to PP.1 and 2, characterized in that the rotation of the furnace in the forward and reverse directions is carried out within the zone of active gathering of the charge.