A method for discharging residual iron from a large submerged arc furnace

Abstract

The present invention relates to the technical field of ferroalloy smelting, and a method for discharging residual iron from a large submerged arc furnace, comprising the following steps: Step 1: Increase the temperature inside the furnace and expand the molten bath inside the furnace; Step 2: Technical requirements during the operation of charging empty materials; Step 3: Determine the position of the residual iron discharge port; Step 4: Residual iron discharge operation. The present invention realizes for the first time that during the major overhaul of a large submerged arc furnace, through the preparation of pre-process operations and the technical cooperation during the empty material process, the bonded substances inside the furnace are melted into a liquid state to the greatest extent, and through the residual iron discharge operation, all the liquid substances inside the furnace are discharged outside the furnace, greatly reducing the difficulty of cleaning the residual substances inside the furnace, shortening the cleaning stage time, and improving the major overhaul efficiency of the submerged arc furnace. Through the implementation of this method, the residual slag and iron inside the submerged arc furnace are reduced from about 800 t of the measured quantity to about 300 t. The workload is reduced by about 2 / 3, and the construction time is shortened by 2 to 3 days.

Description

Technical Field

[0001] The present invention relates to the technical field of ferroalloy smelting, and particularly to a method for discharging residual iron from a large submerged-arc furnace. Background Art

[0002] Two 75MVA ferrosilicon smelting submerged-arc furnaces of our company were introduced from Outotec Company in Finland in 2013. As of September 2022, they have been in operation for eight and a half years. The refractories inside the furnace are severely eroded, and the temperature at the furnace bottom has risen abnormally, indicating that the refractories at the furnace bottom have been eroded more, bringing greater risks to safe production. Since the start of production, the refractories inside the furnace have not been repaired or replaced. To reduce the risk of production accidents and improve production efficiency, it is necessary to carry out a major overhaul of the submerged-arc furnace and replace the refractories inside the furnace. A major overhaul of the submerged-arc furnace is a work with high construction difficulty and long cycle. Especially the cleaning of the residual slag and iron inside the furnace has a small construction space, high temperature, high hardness, and slow progress. Reducing the amount of residual slag and iron inside the furnace is an effective measure to reduce the cleaning stage. This requires discharging the high-temperature molten slag and iron inside the furnace out of the furnace as much as possible when the furnace is shut down. Therefore, the application of the residual iron discharging technology can well solve this problem.

[0003] Through the application of the residual iron discharging technology, the present invention can discharge as much of the residual materials and high-temperature molten slag and iron adhered to the furnace wall and around the electrodes out of the furnace as possible through the preparation in the early stage and the application of the empty charge technology and the specific implementation of the residual iron discharging technology, reducing the workload and difficulty for the subsequent cleaning of the residues inside the furnace, improving the work efficiency at this stage, and significantly shortening the time for the major overhaul of the submerged-arc furnace. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for discharging residual iron from a large submerged-arc furnace in view of the above problems.

[0005] The object of the present invention is achieved as follows: A method for discharging residual iron from a large submerged arc furnace, comprising the following steps: Step 1: Increase the temperature inside the furnace and expand the molten pool inside the furnace: 1) 4 - 8 days in advance, control the silicon content in the ferrochrome water to 6 - 7%; 2) The position of the working end of the electrode is 0.8 - 1.2 m horizontally from the tapping hole; 3) Control the slag melting point at 1680 - 1710 °C; Step 2: Technical requirements for cooperation during the empty charge operation: 1) The coke amount for the auxiliary empty charge reaches 2 - 3 batches, with a total weight of the furnace charge per batch of 1000 - 1500 Kg. Keep 2 - 3 batches of normal materials stored around the electrode, with 1000 - 1500 Kg of materials per batch, and extend the working time of the electrode by 2 - 3 hours to expand the reaction area inside the furnace to extend towards the furnace wall edge; 2) When the resistance of a certain electrode inside the furnace > 2 mΩ, lower the electrode of this item to keep the resistance below 2 mΩ, and at the same time control the furnace bottom temperature ≯ 1000 °C; Step 3: Determine the position of the residual iron tapping hole: Calculate the erosion thickness of the refractory inside the furnace to judge the elevation of the residual iron tapping hole; Measure the furnace shell temperature to further narrow down the range of the residual iron tapping hole and determine the position of the residual iron tapping hole; Step 4: Residual iron discharging operation: When the material level inside the furnace during the empty charge operation drops to the working end of the electrode, on the one hand, organize the last furnace of iron to be tapped from the normal tapping hole, and on the other hand, start drilling the residual iron tapping hole with a pneumatic pick. Stop drilling with the pneumatic pick when the inside of the residual iron tapping hole turns red. After the last furnace of iron is completely tapped from the normal tapping hole, replace the residual iron tapping hole with a large oxygen lance to burn through and start discharging the residual slag and iron inside the furnace; When the residue inside the furnace no longer flows out through the residual iron tapping hole, cut off the power supply inside the furnace and the residual iron discharging operation ends.

[0006] The specific operation of Step 3 is as follows: 1) Measure the erosion thickness of the refractory inside the furnace: Calculate the erosion thickness using Fourier's formula: The remaining thickness ΔΖ = λ 1 *Δt 1 / q, where λ 1 = λ 0 + b*t, λ 1 is the thermal conductivity of the refractory at the eroded part of the furnace bottom after correction, Δt 1 is the temperature difference between the erosion line and the deep point, λ 0 is the thermal conductivity of the refractory above the furnace bottom, b is a coefficient, t is the average temperature between the erosion line and the deep point, and q is calculated from the temperatures of two thermocouples at different depths at the furnace bottom; 2) The furnace bottom refractory structure is two layers of microporous carbon bricks + one layer of magnesia casting layer. Determine the position of the residual iron tapping hole at the junction of the second layer of carbon brick and the magnesia layer, that is, 800 - 1100 mm below the normal tapping hole.

[0007] The beneficial effects of the present invention are as follows: The present invention realizes for the first time that during the major overhaul of a large submerged arc furnace, through the preparation of pre - process operations and the technical cooperation during the empty - charge process, the bonded materials in the furnace are melted into liquid to the greatest extent, and through the operation of discharging residual iron, all the liquid materials in the furnace are discharged outside the furnace, greatly reducing the difficulty of cleaning the residual materials in the furnace, shortening the cleaning stage time, and improving the major overhaul efficiency of the submerged arc furnace. Through the implementation of this method, the residual slag and iron in the submerged arc furnace are reduced from about 800t measured to about 300t. The workload is reduced by about 2 / 3, and the construction time is shortened by 2 - 3 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be further described below in conjunction with the drawings.

[0009] Figure 1 It is the temperature distribution diagram of the furnace shell of the present invention.

[0010] Figure 2 It is the position diagram of the thermocouples at the furnace bottom of the present invention.

[0011] Among them: 1. Tap hole, 2. Carbon brick layer, 3. Position of residual - iron discharge hole, 4. Magnesium layer. SPECIFIC EMBODIMENTS

[0012] The basic idea of the invention technology: Before the operation of discharging residual iron, the temperature in the furnace is increased by 5 - 10% compared with the daily temperature, the size of the working molten pool in the furnace is enlarged, the bonded materials around the furnace wall are melted, during the empty - charge operation, the position of the electrode is lowered in cooperation, the arc is continuously extended horizontally, the melting of the bonded materials in the furnace is expanded, and the liquid state is maintained. Finally, all the melted materials are discharged outside the furnace through the operation of discharging residual iron.

[0013] The specific technical solutions are as follows: The first step: Increase the temperature in the furnace, expand the molten pool in the furnace, and reduce the bonding of materials around the furnace circumference. Specific methods: 1. One week in advance, increase the silicon content in the ferrochrome water from the daily control of 4.0 - 5.0% to 6 - 7%. 2. Adjust the position of the working end of the electrode from 1.5m away from the tap hole to 1.0m. 3. Control the slag melting point, adjust it from 1730°C to 1700°C to improve the fluidity of the slag.

[0014] The second step: The technical requirements for cooperation during the empty - charge operation: 1. The amount of coke for auxiliary empty - charge reaches 2 - 3 batches of the total weight of the furnace charge. To improve the permeability of the molten materials, while maintaining a certain amount of materials stored around the electrode, extend the working time of the electrode, and expand the reaction area in the furnace as far as possible to the edge of the furnace wall. 2. When the resistance in the furnace > 2mΩ, press and release this electrode to keep the resistance below 2mΩ. At the same time, control the furnace bottom temperature ≤ 1000°C.

[0015] Step 3: Determine the position of the residual iron tapping hole. The method is as follows: Calculate the erosion thickness of the refractory in the furnace to judge the elevation of the residual iron tapping hole; further narrow down the range of the residual iron tapping hole by detailed measurement of the furnace shell temperature, and finally accurately determine the position of the residual iron tapping hole in combination with the characteristics of the furnace bottom refractory structure and daily operation experience. 1. Measure and calculate the erosion thickness of the refractory in the furnace. When the temperature of the refractory in the furnace is basically stable, the heat transfer of the refractory in the furnace can be regarded as one-dimensional, and the Fourier formula is used to calculate the erosion thickness. The remaining thickness ΔΖ = λ 1 *Δt 1 / q, where λ 1 = λ 0 + b*t, λ 0 is the thermal conductivity of the furnace bottom refractory, b is the coefficient, t is the average temperature between the erosion line and the deep point, and q is calculated from the temperatures of two thermocouples at different depths at the furnace bottom (calculated using the formula q = λAB*ΔtAB / ΔΖAB, the insertion depths of the thermocouples are known, the temperatures are known, and the thermal conductivity of the refractory at this part is known). 2. Measure the temperature of the outer side of the furnace shell using an infrared thermometer. The temperature distribution is as follows Figure 1 . 3. The furnace bottom refractory structure is two layers of microporous carbon bricks + one layer of magnesia casting layer. During the daily production process, it is found that the temperature of the furnace bottom thermocouple rises abnormally for a short time. After analysis and judgment, it is considered that the molten iron drills into the gaps of the furnace bottom carbon bricks and arches the furnace bottom carbon bricks, and the furnace bottom carbon bricks are eroded at high temperatures. Determine that the position of the residual iron tapping hole is at the junction of the second layer of carbon bricks and the magnesia layer, that is, 1010 mm below the normal tapping hole.

[0016] Step 4: Residual iron tapping operation. When the burden surface in the furnace drops to the working end of the electrode during the empty charge operation, on the one hand, organize the last furnace of iron to be tapped from the normal tapping hole, and on the other hand, use a pneumatic pick to start drilling the residual iron tapping hole. Stop the pneumatic pick drilling when the inside of the residual iron tapping hole turns red. After the last furnace of iron is completely tapped from the normal tapping hole, replace the residual tapping hole with a large oxygen lance to burn through and start discharging the residual slag and iron in the furnace.

[0017] When the residues in the furnace no longer flow out through the residual iron tapping hole, cut off the power supply in the furnace and the residual iron tapping operation ends.

[0018] This technology was successfully implemented during the major overhaul of the 2 # submerged arc furnace in October 2022. The construction time in the cleaning stage was shortened by 3 - 5 days compared with the case without residual iron tapping. Through the implementation of the residual iron tapping technology, the daily adhesives and residual slag and iron in the furnace can be discharged outside the furnace to the greatest extent, reducing the difficulty of cleaning the residues in the submerged arc furnace during the major overhaul, greatly accelerating the construction progress in the cleaning stage, and significantly improving the efficiency of the major overhaul of the submerged arc furnace.

[0019] The specific situation is as follows: One week in advance, control the silicon content in the ferrochrome molten iron to 6 - 7%; adjust the position of the working end of the electrode to 1.0 m horizontally from the tapping hole; control the slag melting point at 1690 - 1710 °C;

[0020] When starting the empty charge operation, add 2 - 3 batches of coke, 1000 Kg per batch, keep 2 - 3 batches of materials stored around the electrode, and extend the electrode working time by 2 - 3 hours; when the resistance of a certain electrode in the furnace > 2 mΩ, press and release that electrode to keep the resistance below 2 mΩ, and at the same time control the bottom temperature of the furnace ≯ 1000 °C.

[0021] Through measurement, the position of the tapping hole for the residual iron is determined to be 1010 mm below the daily tapping hole. When the material surface in the furnace drops to the working end of the electrode, open the residual iron hole and discharge the residual iron in the furnace into the external residual iron pit. About 200 t of residual iron is discharged this time.

[0022] The above are only specific embodiments of the present invention, but the structural features within the protection scope of the present invention are not limited thereto. Any changes or modifications made by any person skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for discharging residual iron from a large submerged arc furnace, Characterized in that: It includes the following steps: Step 1: Increase the temperature in the furnace and expand the molten pool in the furnace: 1) 4 - 8 days in advance, control the silicon content in the ferrochrome water to 6 - 7%; 2) The position of the working end of the electrode is 0.8 - 1.2 m from the horizontal level of the tapping hole; 3) Control the slag melting point at 1680 - 1710 °C; Step 2: Technical requirements for cooperation during the operation of charging empty materials: 1) The amount of coke for auxiliary empty charging reaches 2 - 3 batches, with a total weight of each batch of furnace charge of 1000 - 1500 kg, keep 2 - 3 batches of normal materials stored around the electrode, with each batch of 1000 - 1500 kg of materials, extend the working time of the electrode by 2 - 3 hours, and expand the reaction area in the furnace to extend towards the furnace wall edge; 2) When the resistance of a certain electrode in the furnace > 2 mΩ, lower the electrode of this item to keep the resistance below 2 mΩ, and at the same time control the bottom temperature of the furnace not to exceed 1000 °C; Step 3: Determine the position of the residual iron discharge port: Calculate the erosion thickness of the refractories in the furnace to judge the elevation of the residual iron discharge port; further narrow the range of the residual iron discharge port by measuring the furnace shell temperature, and determine the position of the residual iron discharge port; Step 4: Residual iron discharge operation: When the material surface in the furnace during the empty charging operation drops to the working end of the electrode, on the one hand, organize the last furnace of iron to be tapped from the normal tapping hole, and on the other hand, start drilling the residual iron discharge port with a pneumatic pick. Stop drilling with the pneumatic pick when the inside of the residual iron discharge port turns red. After the last furnace of iron is completely tapped from the normal tapping hole, replace the residual iron discharge port with a large oxygen lance to burn through and start discharging the residual slag and iron in the furnace; When the residues in the furnace no longer flow out through the residual iron discharge port, cut off the power supply in the furnace, and the residual iron discharge operation ends.

2. The method for discharging residual iron from a large submerged arc furnace according to claim 1, Characterized in that: The specific operation of Step 3 is as follows: 1) Measure the erosion thickness of the refractory in the furnace: Calculate the erosion thickness using Fourier's formula: The remaining thickness ΔΖ = λ 1 *Δt 1 / q, where λ 1 = λ 0 + b*t, and λ 1 is the thermal conductivity of the refractory at the eroded part of the furnace bottom after correction, Δt 1 is the temperature difference between the erosion line and the deep point, and λ 0 is the thermal conductivity of the refractory above the furnace bottom, b is a coefficient, t is the average temperature between the erosion line and the deep point, and the unit of q is w / m 2 . Calculate it through the temperatures of two thermocouples at different depths at the furnace bottom; 2) The refractory structure at the furnace bottom is two layers of microporous carbon bricks + one layer of magnesia castable layer. Determine the position of the residual iron tapping hole at the junction of the second layer of microporous carbon bricks and the magnesia castable layer, that is, 800 - 1100 mm below the normal tapping hole.

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