1 Introduction
With the rapid development of China's iron and steel industry, the demand for raw materials growing iron, ore imports accounted for a considerable amount. At present, the domestically imported mineral powder is mainly Australian mine and Indian mine. The content of Al 2 O 3 in these two kinds of mineral powder is generally high. The average content of Al 2 O 3 in the blast furnace slag of Shandong Taishan Iron and Steel Group (referred to as Taigang) is about 18.2%, and the highest can reach 22%. When the content of slag Al 2 O 3 is high, the fluidity and stability of the slag will be deteriorated, which will easily cause the bonding of the furnace wall and the accumulation of the hearth, destroying the normal process of smelting smelting, and bringing a series of problems to the operation of the blast furnace. If scientific guidelines and methods are not formulated, it will cause unsatisfactory furnace conditions and affect production and quality. Therefore, the slag with high Al2O3 content seriously restricts the normal production of the blast furnace.
Effect of 2 Al 2 O 3 content on slag properties
Al 2 O 3 is neutral, but it can be considered as an acidic substance in blast furnace smelting. Its melting point is 2050 ° C. It also produces high melting point (1545 ° C) after mixing with SiO 2 in blast furnace smelting, which makes the slag iron flow poor. It is difficult to separate. When a basic substance such as CaO or MgO is added, although the melting point of CaO is 2570 ° C and the melting point of MgO is 2800 ° C, a substance having a low melting point (less than 1400 ° C) is formed in combination with SiO 2 and Al 2 O 3 in a blast furnace. The inside melts to form a slag with good fluidity, which separates the slag and iron and ensures the normal production of the blast furnace.
2.1 When Al 2 O 3 is less than 15%, the stability of slag can be improved. <br> When the content of Al 2 O 3 is 5% to 20% and the content of MgO is less than 20%, it is melted in a region where CaO/SiO 2 is about 1.0. The temperature is lower; when the content of Al 2 O 3 is low, the melting temperature of slag increases rapidly with the increase of alkalinity; when the content of Al 2 O 3 is more than 10%, the melting temperature increases and the melting temperature slows down as the alkalinity increases. As the area expands, the viscosity of the slag also decreases with the change of alkalinity, and the stability of the slag increases. It is believed that the presence of Al 2 O 3 impairs the effect of changes in CaO/SiO 2 .
2.2 Adverse effects of high Al 2 O 3 slag on blast furnace smelting
When Al 2 O 3 is less than 15%, the stability of the slag can be improved, which is advantageous for blast furnace operation, but the Al 2 O 3 content in the slag is generally 15% to 18% because the high Al 2 O 3 slag is difficult to melt and the viscosity is increased. Large, poor liquidity will have the following negative effects:
(1) high Al 2 O 3 slag clogging the gap between primary slag charge the material column permeability deteriorates, increasing resistance through the coal gas. At the same time, the slag is easily formed into a furnace in the furnace wall of the furnace in the blast furnace, causing the furnace material to fall unsatisfactory, forming a collapsed material, suspending material, and destroying the smelting process. [next]
(2) Since the high Al 2 O 3 slag is too viscous, the fluidity of the final slag is poor, which is not conducive to the diffusion of the desulfurization reaction, and the desulfurization effect is deteriorated. Generally, when Al 2 O 3 is more than 18%, the desulfurization ability of the slag is greatly reduced.
(3) The high Al 2 O 3 slag final slag has poor fluidity, and it is easy to block the hearth. It is not suitable to flow out of the hearth, so that the wall of the hearth is thick, and the volume of the hearth is reduced, which makes the operation of the blast furnace difficult. In severe cases, it will also cause a large amount of burnout of the tuyere and slag.
(4) When the content of Al 2 O 3 in the blast furnace slag is 10% to 15%, it is beneficial to improve the stability of the slag, but when the Al 2 O 3 content continues to increase, the stability of the slag deteriorates. When the furnace temperature is insufficient, the fluidity is drastically deteriorated, and not only is it smooth, but it is also difficult to discharge iron. Therefore, when the furnace temperature is insufficient, it is easy to cause slag iron accumulation in which the furnace temperature is insufficient.
3 Countermeasures <br> When the content of Al 2 O 3 in the blast furnace slag is high, its fluidity and stability are deteriorated, which will seriously restrict the normal smelting of the blast furnace and affect the blasting and yield increase of the blast furnace. However, the supply of raw materials for blast furnace ironmaking is currently tight, and fundamental improvements cannot be achieved in a short period of time. Therefore, only improve the operation of the blast furnace, analyze the impact of various properties of the original fuel on the blast furnace, comprehensively explore the adaptability of various smelting systems, and formulate a reasonable and scientific operation policy to make the furnace condition stable and direct, in order to obtain the best smelting index. .
3.1 Properly reduce the alkalinity of slag and increase the temperature of the furnace <br> When the content of Al 2 O 3 in the slag of the blast furnace is 15% to 18%, the melting temperature of the slag increases obviously, the viscosity increases, and the fluidity deteriorates. Blindly reducing the furnace temperature level, pursuing low-silicon smelting, it is easy to cause the furnace to accumulate. When the slag binary alkalinity CaO/SiO 2 is about 1.0, the fluidity of the slag is the best. The reduction of the alkalinity of the slag is not conducive to desulfurization. Therefore, the furnace temperature should be appropriately increased to make the slag have sufficient physical heat to meet the desulfurization capacity of the slag. This is an important means for high-alloy Al 2 O 3 slag smelting to achieve stable blast furnace antegrade. Shaoguan Iron and Steel Group Co., Ltd. implements sulfur operation in medium silicon according to the high content of Al 2 O 3 in its slag, and appropriately reduces the alkalinity of slag to 0.95~1.03, ensuring good physical and chemical properties of slag and proper control of pig iron. The silicon content is between 0.45% and 0.65% to ensure the physical heat and desulfurization capacity of the slag, and an ideal smelting index has been obtained.
3.2 Appropriately improve blast kinetic energy and improve the working condition of the hearth <br> The lower adjustment agent should ensure reasonable blast kinetic energy, make the hearth fully active, eliminate the dead zone, and reduce the high Al 2 O 3 slag due to the deterioration of fluidity. The possibility of furnace accumulation. In the 450m3 blast furnace of Taigang, due to the unstable Al 2 O 3 content in the slag, the ¢110mm vents were all replaced with ¢105mm vents, and the furnace condition was gradually changed. The blast furnace utilization coefficient was 2.9t/m 3 .d Increase to 3.5t/m 3 .d. In addition, efforts should be made to increase the air temperature level. The monthly average wind temperature level of the 450m 3 blast furnace in Taigang has reached 1000°C. High air temperature can make the hearth full of heat, so high air temperature utilization level should be ensured during operation. [next]
3.3 Improve the quality of the furnace and reduce the amount of slag
The amount of slag directly affects the venting and liquid permeability of the blast furnace soft melt zone. When the slag amount is low, the gas permeability of the blast furnace is improved, and even if the slag viscosity of the blast furnace is high, the influence on the gas permeability and liquid permeability of the column is small.
3.4 Appropriately increase the content of MgO in the slag When the MgO is high, the viscosity of the slag is lowered, the fluidity of the slag is improved, and the desulfurization ability of the slag can be improved. When the content of Al 2 O 3 in the blast furnace slag is high, the role of MgO is particularly important. When the content of Al 2 O 3 in the slag is more than 15%, the content of MgO is raised to about 11%, and the physical and chemical properties of the slag are improved.
3.5 improve the strength properties and high temperature metallurgical coke into the furnace <br> blast furnace coke is the most important liquid-permeable and air-permeable material. With the increasing smelting strength, the role of the soft-melt coke layer in the blast furnace is more and more obvious, which is the key to maintaining the internal gas permeability of the blast furnace. At the same time, in the lower part of the blast furnace, coke pulverization is the source of deterioration of the gas permeability and liquid permeability in the lower part of the blast furnace. Therefore, it is necessary to improve the strength properties and high temperature metallurgical coke.
After the block zone, the coke undergoes the carbon meltdown reaction and the higher and higher heat effect. The surface structure of the coke is destroyed, and the M40 and M10 indicators have lost their effect. The coke in the furnace has good reaction strength in the lower part of the blast furnace. (CSR) and low reactivity (CRI) are key. The improvement of the quality of the coke in the furnace slows down the negative influence of the high Al 2 O 3 content in the slag on the permeability of the lower part of the blast furnace.
3.6 Strengthen the management of raw fuel in the furnace and reduce the amount of powder in the furnace
Formulate a reasonable screening system and strictly implement it to ensure the screening quality of sinter, coke, pellets and raw ore. First, strict management of the tank position into the furnace, strict control of the low tank phenomenon of less than 5mm; second, strict control of the screening speed; third, strict implementation of the cleaning screen system.
4 Conclusions <br> When the content of Al 2 O 3 in the blast furnace slag is high, the fluidity and stability of the slag are reduced, the desulfurization ability is lowered, the gas permeability of the blast furnace is deteriorated, the furnace condition is easily caused, and the furnace is easily caused. The wall thickness and the accumulation of the furnace are abnormal. In view of the fact that this kind of raw material cannot be fundamentally improved in a short period of time, only a scientific and reasonable operation system can be established to reduce the adverse effects of high Al 2 O 3 slag on blast furnace smelting, so that the blast furnace is stable and smooth, and excellent Smelting indicators.
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