Preparation method of fused corundum

Abstract

The invention relates to the field of non-ferrous metallurgy, in particular to a method for producing fused corundum in an electric furnace, and can be used for producing various molten materials. A smelting method of fused corundum comprises the steps that aluminum oxide is loaded into an electric furnace, the furnace shell wall is water-cooled, the aluminum oxide is smelted under the constant electric power condition, and fused corundum melt is discharged from the electric furnace. And after the fused corundum melt is discharged, the electric furnace is restarted, and fused corundum is smelted under the maximum power of the electric furnace. Before smelting, the relation between the thickness of the furnace lining and the temperature of the wall of the furnace shell is calculated; in the smelting process, the power of the electric furnace and the flow of cooling water are adjusted based on the calculated thickness of the furnace lining through temperature reading of a thermocouple installed on the wall of the furnace shell, and therefore continuous heat monitoring on the wall of the furnace lining is achieved. Therefore, the physical dimension of the molten pool can be stably kept in a specified range, so that the energy consumption of a unit product can be reduced, and the production efficiency of the electric furnace can be improved.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of non-ferrous metallurgy, i.e. obtaining fused corundum in an electric furnace, which can be used to obtain various fused materials. BACKGROUND

[0002] Fused corundum is widely used in the production of high-temperature refractory materials, both as a grinding material and filler for individual products and for unshaped refractory materials.

[0003] Corundum is produced by electrically fusing raw materials rich in alumina (e.g. bauxite and alumina). At present, there are three types of corundum: ordinary corundum, which is obtained by reducing smelting of bauxite and contains not less than 87% of alumina, the colour of which varies from grey-brown to dark brown; white corundum (white alumina), which is obtained by re-smelting of pure bauxite and contains not less than 97% of alumina, the colour of which is white or light pink; and single-crystal corundum, which is obtained by smelting bauxite with ferrous sulphide and a reducing agent, followed by extraction of single-crystal corundum, the content of alumina being 97-98%.

[0004] Electric furnaces produce corundum in two ways:

[0005] 1) by continuous reducing smelting of kaolin or bauxite with the addition of carbon, which forms two products: the main product is corundum, and the by-product is ferrous alloy, which are periodically separated from the furnace and discharged into a mould for corundum and into a ladle for ferrous alloy;

[0006] 2) by periodic smelting of bauxite in a furnace with a replaceable hearth or by periodically pouring fused corundum from the furnace into a mould (see A.N. Parada and M.I. Gaisik, Electric Heat Treatment of Inorganic Materials, Moscow, Metallurgiya, 1990, p. 230).

[0007] A method for producing corundum is disclosed (SU 929560, published on 23.05.1982), which comprises reducing arc furnace smelting of raw materials containing alumina in the presence of a carbon reducing agent, with discharge of a high-alumina melt and associated metals from the furnace. In order to reduce the consumption of electric power and increase the efficiency of the electric furnace, the arc furnace smelting and discharge of the high-alumina melt are carried out at a temperature of 2050-2150 K, and an aluminium-iron alloy is added to the melt at the time of or after the discharge of the melt, the amount of the alloy being 6% by weight of the melt. The disadvantage of this method is that additional material is added to the furnace, which increases the cost of producing corundum. In addition, the corundum produced contains various metallic impurities, which are reduced during the reducing smelting.

[0008] A known method for producing corundum (RU 2171225, published on July 27, 2001) includes smelting of bauxite raw material in a furnace, in the presence of a carbon reducing agent, by precisely controlling the charge of the raw material, and separate tapping of corundum and ferroalloy. Raw material with a moisture content of 10-40% is charged into the furnace at fixed intervals at a rate of 10-20% of the total charge. At the same time, the melting time is 9-12.5 hours. If necessary, at the end of smelting, the chemical composition of the melt is corrected by pre-dried bauxite in an amount of 5-30% of the total charge in the furnace. The disadvantage of this method is the use of raw materials with a high moisture content, which increases the cost of production of fused corundum.

[0009] A known method for producing corundum (RU 2347766, published on February 27, 2009) includes a charge composition that includes heat-treated bauxite in the following weight percentages: titanium-containing corundum 88-97, pyrite and rutile 1-4, aluminosilicate glass phase 2-8, and additionally added aluminum oxide in an amount of 40-60% by weight of the charge loaded into the furnace, and the charge is melted in a reducing environment. The disadvantage of this method is that the charge for producing corundum is composed of several components, which increases the cost of producing corundum.

[0010] The most technically close method is the method for smelting corundum in an electric furnace with a corundum lining, which includes charging the electric furnace with aluminum oxide, melting the aluminum oxide at a constant electric power, and tapping the melt from the furnace. The smelting is divided into two stages: the first stage is smelting of fused corundum at full power of the furnace, and the second stage is at a reduced power of the furnace by 8-18%. The duration of the first smelting stage is 43-47% of the total melting time of the fused corundum, and the second stage is 53-57% (patent RU 2784404, published on November 24, 2022).

[0011] From the point of view of the technical essence and common features, this technical solution is considered the closest analogue. The disadvantage of this method is the low productivity of the furnace for smelting fused corundum and the long smelting time. SUMMARY

[0012] The purpose of the present invention is to improve the technical and economic efficiency of smelting fused corundum from aluminum oxide.

[0013] The technical result is the solution of the stated problem, the increase in the productivity of the furnace and the reduction in the specific energy consumption of production.

[0014] The solution to the problem and the technical effect are achieved by the following: in the corundum smelting method, comprising loading the alumina into the electric furnace, using water to cool the furnace shell wall, melting the alumina mainly by constant electric power, and discharging the electrically fused corundum melt outside the furnace, wherein according to the proposed invention, after discharging the electrically fused corundum melt, the electric furnace is restarted, and the corundum melting is mainly carried out at the maximum power of the electric furnace; before melting, the relationship between the furnace shell wall temperature and the skull thickness is calculated; during the smelting process, the electric furnace power and the cooling water flow are adjusted based on the calculated skull thickness through the temperature readings of the thermocouples installed on the furnace shell wall, thereby achieving continuous thermal monitoring of the skull wall.

[0015] The water flow for cooling the skull wall can reach 47-50 cubic meters per minute, which is reduced by 10-45% compared to before the installation of the thermal control system.

[0016] The skull thickness is calculated according to the corresponding relationship values of the furnace shell temperature given in Table 1.

[0017] The values not given in Table 1 but within the specified range can be calculated by linear approximation. These values are obtained by establishing a mathematical model of the convective heat distribution in the furnace bath. In establishing the mathematical model, the geometric shape and material properties of the furnace shell must also be considered. The mathematical model is established at the design stage, and through this model, the dependence between the furnace shell wall temperature and the skull thickness is found. The mathematical model is established using the physical properties of the electrically fused corundum as a lining material (density, thermal resistance, etc.). The water flow is monitored through an independent metering (water circulation) system, with a dedicated metering point for each electric furnace. The water flow is adjusted through valves on the electric furnace, and the electric furnace power is controlled by adjusting the electrode current and the electric furnace transformer voltage. It should be noted that, taking into account the material heat capacity properties and personnel protection requirements, the furnace shell temperature is limited to 500°C and the skull thickness approaches 0 mm (i.e., practically does not exist), since the furnace shell is made of steel with a maximum temperature resistance of 700°C. After stopping at 500°C, the furnace shell temperature will continue to rise to 520-550°C due to thermal inertia, but will not exceed the critical threshold of 700°C.

[0018] Table 1

[0019]

[0020]

[0021] Maintaining the skull wall thickness between 170-210 mm through the thermal control system contributes to the efficient operation of the electric furnace. This is due to the fact that, in accordance with the requirements for the reliability of the electric furnace operation, the maximum effective volume of the melt bath (containing the melt) is fully utilized. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1A thermocouple arrangement on a furnace shell according to the present application is shown. DETAILED DESCRIPTION

[0023] A thermocouple arrangement on a furnace shell is shown in Figure 1 Fig. 1. The thermocouple (1) is mounted on the furnace body (2) below the melt (5) in a position set so that it can monitor the part of the shell most likely to come into contact with the melt. To eliminate the interference of cooling water on the monitored parameter, the thermocouple (1) must be in direct contact with the lining wall and it is mounted in such a way that the boss (3) is welded to the shell and the thermocouple is fixed with the joint (3) in a pre-prepared opening in the shell. After the smelting process is completed, the melt is discharged through the discharge opening (6).

[0024] The self-lining furnace has a number of (usually 2 per furnace zone - main and secondary pipes, located opposite each stage of the electric furnace) curved shell water spray pipes, the regulation of the water flow being achieved by shutting off the water flow into the spray pipes. Disconnection of other pipes reduces the cooling water flow by 10 to 45%.

[0025] During the test, the cooling water flow rate was reduced to 47 to 50 cubic meters per minute (standard flow rate is 80 cubic meters per minute), while the electrical energy consumption was reduced by 500 kWh (standard flow is 8500 kWh per melting), thus effectively utilizing the thermal energy of the melt. The cooling flow rate is monitored by the water flow metering system of each smelting furnace. The electrical energy consumption for melting is determined empirically in the production equipment and is determined at 8500 kWh; tests have shown that when the electrical energy consumption for melting reaches 8000 kWh, the melt approaches the furnace outlet, increasing the risk of uncontrolled discharge from the bath, resulting in further melting inefficiency. The temperature of the shell is monitored using sensors integrated into the thermal control system.

[0026] The ratio of electrical energy consumption and cooling water use is due to the fact that the productivity of the smelting furnace reaches its maximum and the electrical energy consumption per ton of electrically fused corundum is significantly reduced.

[0027] During the smelting process, the thermal control of the lining wall adjacent to the shell ensures that the lateral lining of the bath remains constant in terms of conditions, contributing to the efficient operation of the electric furnace. Maintaining a stable lining thickness depends on the electrical operating conditions and, in the event of a change in the lining, the smelting furnace can adjust the process parameters to restore the lining thickness to its target value.

[0028] Thermal monitoring during smelting stabilizes the process and electrical state, ensuring consistency in smelting characteristics (ingot weight, productivity, etc.), while maintaining electrical parameters, including current, voltage and electrical energy consumption, at a stable level without sudden fluctuations from one smelting cycle to another.

[0029] Power control is mainly achieved by adjusting the electrode current, thus allowing smooth regulation of power during smelting.

[0030] A stable process, free from sudden power adjustments, ensures the long-term maintenance of the molten pool geometry, resulting in positive effects on electric furnace productivity and energy consumption. The geometry of the molten pool containing the melt directly affects the electric furnace productivity and is constrained by the furnace shell. The proposed method maximizes the effective utilization of the furnace bath and increases its effective geometry.

[0031] Examples of method implementation methods

[0032] Testing was conducted in a 6600 kVA industrial furnace used for the periodic smelting of alumina to produce corundum. The furnace operated primarily at electrode voltages of 265–286 V and currents of 12 kA. The average smelting duration was 1.20–1.35 hours. The melt flowed out after consuming 7100–8400 kWh of power, compared to previous operating cycles of 8500–9000 kWh. The furnace lining in the bath was maintained at an optimal thickness of 170–210 mm.

[0033] Example 1 (Prototype method prior to installation of the thermal control system according to the invention)

[0034] The electric furnace operates at a power of 6200kW, a voltage of 286V, and an internal temperature range of 80m. 3 The furnace operated at a cooling water flow rate of 1 / min and a smelting duration of 1.87 hours. The power consumption per smelting cycle was 8500 kWh. A total of 6.5 tons of fused corundum was produced, with a power consumption of 1307 kWh / t and a furnace productivity of 3.48 t / h. The furnace lining thickness was 300 mm before smelting and 280 mm after smelting.

[0035] Example 2

[0036] The electric furnace operates at a power of 6200kW, a voltage of 286V, and a capacity of 50m³. 3 The furnace operated at a cooling water flow rate of 1 / min and a melting duration of 1.3 hours. The power consumption per melting cycle was 8000 kWh. A total of 6.54 tons of fused corundum was produced, with a power consumption of 1222 kWh / t and a furnace productivity of 4.79 t / h. The furnace lining thickness was 200 mm before melting and 177 mm after melting. Before melting, the physically measured furnace lining thickness (using a furnace lining measuring instrument) was compared with the value provided by the thermal control system, and only minor differences were observed. During melting, the furnace relied on system readings to monitor changes in the furnace lining thickness. After the melt flowed out, the physically measured furnace lining thickness was again compared with the thermal control system readings. The temperature control system consisted of temperature sensors, a signal converter (converting voltage to 4–20 mA current), a controller that calculated the furnace lining thickness based on temperature data, and units for data collection, storage, and processing.

[0037] Example 3

[0038] The electric furnace operates at a power of 6200kW, with a voltage of 286V and a temperature of 47–52m. 3 Melting was carried out at a cooling water flow rate of / min for 1.28 hours. The power consumption for each melting cycle was 8000 kWh. A total of 6.72 tons of fused corundum was produced, with a power consumption of 1191 kWh / t and a furnace productivity of 4.33 t / h. The furnace lining thickness was 199 mm before melting and 190 mm after melting. Temperature control was performed in the same manner as in Example 2.

[0039] Example 4

[0040] The electric furnace operates at a power of 6200kW, with a voltage of 286V and a temperature of 60–62m³ / h. 3 Melting was carried out at a cooling water flow rate of / min for 1.5 hours. The power consumption per melting cycle was 8400 kWh. A total of 6.49 tons of fused alumina was produced, with a unit power consumption of 1294 kWh / t and a furnace productivity of 4.33 t / h. The furnace lining thickness was 200 mm before melting and 190 mm after melting. Temperature control was performed in the same manner as in Example 2.

[0041] Example 5

[0042] The electric furnace operates at a power of 6200kW, with a voltage of 286V and a temperature of 65–70m³. 3 Melting was carried out at a cooling water flow rate of / min for 1.68 hours. The power consumption per melting cycle was 8400 kWh. A total of 6.14 tons of fused corundum was produced, with a power consumption of 1369 kWh / t and a furnace productivity of 3.65 t / h. The furnace lining thickness was 210 mm before and after melting. Temperature control was performed in the same manner as in Example 2.

[0043] Example 6

[0044] The electric furnace operates at a power of 3100kW, with a voltage of 218V and a temperature of 56–58m³. 3 Melting was carried out at a cooling water flow rate of / min for 2.6 hours. The power consumption per melting cycle was 7100 kWh. A total of 5.4 tons of fused alumina was produced, with a unit power consumption of 1313 kWh / t, a furnace productivity of 2.1 t / h, and a furnace lining thickness of 208 mm before melting and 190 mm after melting. Temperature control was performed in the same manner as in Example 2.

[0045] Example 7

[0046] The electric furnace operates at a power of 6000kW, with a voltage of 265V and a capacity of 60m³. 3Melting was carried out at a cooling water flow rate of / min for 1.3 hours. The power consumption per melting cycle was 7400 kWh. A total of 5.9 tons of fused alumina was produced, with a specific power consumption of 1254 kWh / t, a furnace productivity of 4.5 t / h, and a furnace lining thickness of 196 mm before melting and 191 mm after melting. Temperature control was performed in the same manner as in Example 2.

[0047] In the initial phase of testing, process control was conducted by comparing values ​​obtained using a test method—measurements of the furnace lining wall via lining gauges. Subsequently, the primary source of parameter control was readings from the thermal control system. This system determines the lining thickness based on the measured temperature. The furnace receives information about the lining thickness at each sensor mounting point, as well as the minimum thickness recorded at all measurement points. The system requires temperature data, which it receives from sensors mounted on the furnace shell. Then, based on a pre-calculated table (developed through mathematical modeling), the system calculates the lining thickness. For operator convenience, current and voltage data are available within the system, with predetermined information thresholds to indicate potential electrical overload conditions. Melting duration and power consumption are monitored by the operator using a process flow diagram and meters mounted on the furnace. New parameters regarding time, power consumption, and melt volume are recorded in the same manner for performance comparison with the corresponding period from September to November 2023.

[0048] Experimental smelting tests involving reductions in power consumption and furnace cooling water flow rate showed that the optimal reduction in power consumption for smelting was 5–6% (Examples 2 and 3), and the cooling water flow rate was reduced to 47 m. 3 / h. This leads to the efficient use of heat from the electric arc and the melt (achieving a stable thermal equilibrium), resulting in a reduction in melting time (because there is no delay in lining recovery when its thickness decreases to a critical level), an increase in furnace productivity, and a reduction in power consumption per ton of molten corundum.

[0049] Reducing power with a smaller margin (Examples 3 and 4) or a larger margin (Examples 5 and 6) does not produce a significant positive effect on reducing power consumption per ton of corundum or increasing furnace productivity.

Claims

1. A method for producing fused alumina, comprising charging alumina into an electric furnace, water-cooling the furnace shell, melting the alumina under constant electric power, and discharging the fused alumina melt from the electric furnace, characterized in that, After the electrofused corundum melt is discharged, the electric furnace is restarted and corundum is smelted at the maximum power of the furnace. Before smelting, the relationship between the furnace shell temperature and the furnace lining thickness is calculated. During the corundum smelting process, the furnace power and cooling water flow rate are adjusted based on the calculated furnace lining thickness by using the temperature readings of thermocouples installed on the furnace shell wall, thereby achieving continuous thermal monitoring of the furnace lining wall.

2. The method according to claim 1, characterized in that, The water flow rate used for cooling the furnace lining is 47-50 cubic meters per minute.

3. The method according to claim 1, characterized in that, The relationship between furnace lining thickness and furnace shell temperature is calculated using a mathematical model of convective heat distribution within the furnace pool.

4. The method according to claim 1, characterized in that, The furnace lining thickness is maintained at 170–210 mm.

5. The method according to claim 1, characterized in that, Thermocouples are preferably placed in areas of the furnace wall that are prone to burn-out.

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