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The principle and the main control points of the converter brick repair furnace and the specific operating steps of the brick repair furnace.
BOF brick repair furnace
In the BOF steelmaking process, caused by molten iron and steel scrap hitting the lining, lining abrasion during molten steel and slag melting, and cinder-based chemical erosion, the lining of the BOF will be subject to a range of degrees of damage during use. causing the lining to gradually become thinner. When the lining has been thinned to a certain level of thickness, the damaged lining section must be repaired promptly. To help improve BOF running, the principle of rapid sintering of magnesia-carbon ladle bricks and converter residual slag at high temperature is used to boldly innovate and improve the existing furnace repair technology, The use of brick repair instead of material repair, which significantly reduces the time and cost of stove repair.
Brick repair is a low cost, short cycle protection method. After the converter has been completed, none or less slag is poured, and the ladle remnants that meet the furnace repair requirements are poured into the position in the furnace that is in need of repair. The residual heat in the slag after steel tapping is used to quickly sinter the slag and the ladle residual at the damaged position of the converter to achieve the purpose of repairing the furnace lining.
Refractory brick repair furnace protection principle and key control points
1. Principle of brick repair sintering
The residual slag of the converter has a high heat, the temperature is 1400 ℃ ~ 1500 ℃, and the magnesia carbon ladle brick is mainly composed of fused magnesia and asphalt binder. At high temperature, during the softening and sintering process of the ladle brick, the asphalt will form a carbon-bonded skeleton and a mesh structure to consolidate the magnesia particles, and evenly adsorb on the surface of the magnesia, and finally obtain a high-strength sintered body. However, the temperature should not be too high. Too high a temperature will accelerate the erosion of the furnace lining. When the steel tapping temperature is controlled at 1650 ℃, it can meet the heat requirements of slag sintering.
2. Control of slag basicity
In order to ensure the effect of brick patching, the slag needs to have a certain viscosity to ensure good adhesion between bricks and furnace linings, and between bricks. The higher the slag basicity, the greater the viscosity of the slag. In the steelmaking process, with the addition of lime, high-melting-point C2S and C3S are formed in the slag. This high-melting-point substance has good refractoriness. Therefore, from the perspective of furnace protection, the higher the basicity, the greater the slag viscosity, the better the refractoriness, and the more conducive to protecting the furnace lining.
However, in actual production, excessive basicity will lead to reduced slag fluidity, and the "drying back" phenomenon is prone to occur during the blowing process. In order to ensure the effect of dephosphorization and desulfurization, it is necessary to increase FeO in the slag by controlling the gun position and adding iron-containing coolants to achieve the purpose of slag reduction. However, low-melting-point substances such as calcium ferrite mainly composed of FeO appear, which affects the adhesion effect of the slag. After sampling and analyzing the final slag of 100 converters, the slag basicity was controlled between 3.0 and 4.0, and the slag had a good adhesion effect with the residual bricks of the ladle.
3. Control and optimization of MgO in slag
MgO solid can only be precipitated in the slag when the solubility of MgO in the slag is greater than the supersaturated solubility. The supersaturated solubility is affected by temperature, alkalinity, and w(TFe) content. The calculation formula is:
w(MgO)=0.4×(T-1650)+0.28×w(TFe)-2×R+9.5
According to the actual production data, the supersaturated solubility of MgO is 9%, so when the content of MgO in the slag is above 9%, MgO in the slag precipitates from the slag, which is beneficial to the maintenance of the furnace lining. However, considering the metallurgical properties of the slag, when the MgO content in the slag is above 15%, the melting point of the solid solution is too high, which is not conducive to slagging and dephosphorization. The MgO content in the slag is in the range of 9% to 14%, which can effectively increase the precipitation of MgO, thereby facilitating the slag hanging on the furnace wall and increasing the life of the furnace lining.
Brick repair furnace specific operations
Brick repair furnace is a low-cost and short-sintering cycle furnace protection method. That is, after the converter has finished steel production, no slag or less slag is used to pour the ladle bricks that meet the repair requirements into the position in the furnace that needs to be repaired. The residual heat in the slag after steel production is used to quickly sinter the slag and the ladle remnants at the damaged position of the converter to achieve the purpose of repairing the furnace lining.
Specific operation steps of brick repair furnace
(1) The size of the ladle bricks used for brick repair is 30-200 mm. The brick body must be dry, oil-free, and free of debris. 1 t of ladle bricks is used for each 1m2 of repair position, and the maximum amount cannot exceed 2 t.
(2) For each furnace repair, adjust the amount of lime and light burner added, control the slag alkalinity at 3.0-4.0, and the MgO content at 9%-14%; the steel production temperature is controlled at 1650 ℃ to ensure the sintering temperature.
(3) For the furnace repair, after the molten steel is discharged, there is no slag splashing. A part of the slag is poured out according to the amount of slag, and 3 to 6 tons of slag is left in the furnace. The specific amount of slag is determined by the weight of the bricks used. It is best to have the slag just cover the bricks. If there is residual molten steel, the residual molten steel must be discharged again at the outlet before the furnace repair operation can be performed.
(4) After leaving the slag, shake the furnace body to the charging side, use the scrap steel bucket to add the ladle bricks into the furnace, and shake the furnace repeatedly according to the repair position until the ladle bricks are evenly covered on the repair position. Let it stand and sinter for 20 to 30 minutes until all the slag is sintered and solidified.
Analysis of effects
Each converter is repaired in the middle and late stages of the furnace service, and the on-site brick repair data and material repair data are analyzed. The repair frequency of brick repair is lower than that of material repair, and the average repair time is shorter. From the repair effect, the average thickness of the furnace lining at each furnace age stage is better than that of the furnace lining repaired with bricks.
Practice has proved that the method of repairing the furnace lining with ladle bricks has produced obvious economic benefits. It not only reduces the cost of furnace maintenance, but also saves 30 minutes each time of furnace repair, which greatly improves the efficiency of steelmaking operations, especially in the later stage of furnace campaign.
