Construction method for prolonging service life of large titanium slag smelting furnace

Abstract

The application discloses a construction method for prolonging the service life of a large titanium slag smelting furnace, and belongs to the technical field of smelting production equipment maintenance and repair processes. The method is convenient to operate, can effectively guarantee the repair quality, and can effectively prolong the service life of the electric furnace by 3-5 years. The method comprises the following steps: discharging molten iron, slag and a dead iron layer with a specified thickness before stopping power supply and furnace, reinforcing the furnace body, removing a sealing steel platform on an upper furnace shell and corresponding auxiliary dust removal pipelines, protectively removing the furnace shell, furnace wall lining and furnace bottom lining that need to be replaced, manufacturing a new furnace shell, sequentially assembling and welding the new furnace shell, protectively recovering the furnace bottom lining and the furnace wall lining, finally recovering the sealing steel platform around the upper furnace shell and the auxiliary dust removal pipelines, and performing the normal metallurgical production after furnace baking, preheating and slag hanging, so that the repair work of prolonging the service life of the titanium slag smelting furnace is completed.

Description

Technical Field

[0001] This invention relates to a construction method, and more particularly to a construction method for extending the service life of large titanium slag smelting furnaces, belonging to the field of smelting production equipment maintenance technology. Background Technology

[0002] A titanium company owns multiple 25.5MW large-scale electric arc furnaces for titanium slag smelting. The process involves mixing a reducing agent and titanium concentrate in a specific ratio and adding the mixture to the furnace. The smelting is then carried out by heating with the furnace electrodes to produce titanium slag and molten iron. The core equipment, the furnace body, mainly consists of a refractory lining, electrodes, a steel furnace shell structure, instrumentation, and an electrical system. The refractory lining, enduring high temperatures and chemical corrosion over a long period, shows significant wear and tear in the later stages of its first furnace life, posing serious safety hazards and hindering safe production. This necessitates a shutdown to end the first furnace life, requiring the dismantling of the furnace body and auxiliary equipment, and reconstruction of the equipment structure. A first furnace life refers to the actual operating time from the completion of furnace drying and entry into production to a major overhaul, typically around 8 years.

[0003] The factors affecting the lifespan of a furnace mainly include furnace design, refractory lining materials, lining construction and drying quality, slag and smelting media, power supply and thermal regime, operation and running behavior, and equipment and cooling system conditions. Even shutdown, startup, and maintenance, production management, and personnel skill levels can directly or indirectly affect the furnace lifespan. When the furnace lifespan meets the design lifespan, and the process, operation, and equipment are stable and orderly, the condition of the "furnace lining itself" determines the final furnace lifespan.

[0004] Improving design and construction standards through major overhauls is characterized by high investment (around 79 million RMB), long duration (110 days), and certain risks associated with adapting to production processes. Continuous optimization of daily maintenance and long-life operation techniques also faces bottlenecks. The optimal choice is to utilize special processes and replace some refractory linings to adapt to the production process in the later stages of the first-generation furnace lifespan, extending the lifespan of large titanium slag smelting electric furnaces by 3 to 5 years with relatively low maintenance costs. However, there are no existing domestic or international technologies for extending the lifespan of similar circular and large submerged arc furnaces. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a construction method for extending the service life of large titanium slag smelting furnaces that is convenient to operate, can effectively guarantee the quality of repair, and can effectively extend the service life of electric arc furnaces by 3-5 years.

[0006] The technical solution adopted to solve the above-mentioned technical problems is: a construction method for extending the service life of a large titanium slag smelting furnace, comprising at least an electric furnace body equipment system, a water cooling system, and a slag and iron tapping system. The electric furnace body equipment system includes at least a water-cooled furnace cover, a furnace shell, a refractory brick lining, and electrodes. The slag and iron tapping ports of the slag and iron tapping system are set on the furnace shell at specified positions. The water-cooled exhaust duct of the water cooling system is connected to the water-cooled furnace cover. A semi-molten dead iron layer is arranged in the furnace shell below the iron tapping port through the refractory brick lining. The construction method includes the following steps. a. The last batch of molten iron and slag generated during the production period before furnace repair is discharged through the slag outlet and iron outlet. b. Open the residual iron tap to confirm the erosion of the furnace wall below the dead iron layer, and discharge the dead iron layer of the specified thickness through the newly built discharge hole with the assistance of electrodes. Then, shut down the power and furnace to proceed to the cold furnace process. c. During the cold furnace process, air cooling is used for temperature reduction through natural cooling in conjunction with water-cooled exhaust ducts. Simultaneously, the furnace body is reinforced with the help of the upper furnace shell. d. Remove the sealed steel platform and corresponding auxiliary dust removal pipes around the specified elevation position of the upper section of the furnace shell, and protectively remove the furnace shell that needs to be replaced, the furnace wall lining, and the furnace bottom lining at the corresponding positions. At the same time, fabricate a new furnace shell to replace the old furnace shell section. e. Assemble and weld a new furnace shell onto the existing furnace shell. f. Use new furnace lining bricks to protectively restore the furnace bottom and wall linings within the new furnace shell. g. Restore the sealed steel platform around the upper furnace shell and the associated dust removal ducts. h. The large titanium slag smelting furnace underwent repair work to extend its service life by employing a uniform micro-heating process for furnace drying, preheating, and slag application, followed by normal metallurgical production operations. In the process of protectively dismantling and replacing the furnace wall and furnace bottom linings, and protectively restoring the furnace wall and furnace bottom linings, waterless operation and / or waterless mortar are used.

[0007] Furthermore, the furnace is powered by electrodes, and before drying, auxiliary materials for drying are laid inside the furnace according to the following requirements. Lay 30-50 tons of magnetic material on the dead iron layer, then add 50 tons of mixed material, followed by at least 8 tons of large coke blocks 200-300 mm thick. Finally, lay titanium slag material with a height of not less than 1000 mm at the edge of the furnace wall according to the natural stacking angle of titanium slag in the furnace to complete the laying of furnace drying auxiliary materials.

[0008] The preferred method for the above scheme is to control the baking time of the uniform micro-heating process oven to 24-26 days. The process of the uniform micro-heating process oven baking is as follows: The furnace lining temperature rise at each stage is strictly controlled at ≤1℃ / h. For the first 10 days of furnace drying, the rate is 10-15℃ / day, and for days 11-25, it is 20-25℃ / day. When the average temperature of the second and third layer thermocouples reaches 105℃, the furnace is shut down for 24-48 hours of heat equalization. When the temperature of the fourth layer thermocouples reaches 300℃, the furnace is shut down for 24-48 hours of heat equalization. If the temperature rise of any layer thermocouple is >30℃ / 24h, the furnace is shut down for 24 hours of heat equalization. The temperature is increased again only after the average temperature of the second layer thermocouples reaches 105℃ and the furnace gas humidity measured for two consecutive days is consistent, until the operating temperature during normal production is reached. During the furnace drying process, the heating rate of new and old bricks is strictly controlled to keep the heating rate as consistent as possible. After the furnace drying is completed, the furnace is shut down for 48 hours of temperature equalization.

[0009] Furthermore, the discharge of molten iron and slag is carried out in the following steps: First, during production, an iron discharge trough with a slope of 8% is constructed, with a steel structure trough as the outer shell and clay bricks and CO2-cured iron ramming material as the inner lining. Then, multiple collection pits for storing residual iron are built in the adjacent ground sand mold pit, which are large enough to accommodate the discharged molten iron and slag and are lined with clay bricks and CO2-cured iron ramming material as the inner lining. After the production of molten iron is completed, the residual molten iron mixed with slag at the bottom of the furnace is discharged through the iron discharge trough. After the residual molten iron mixed with slag is cooled to room temperature, it is hoisted to the designated location by the plant crane to complete the discharge of molten iron and slag.

[0010] The preferred method of the above scheme is to open the taphole at least 400mm below the center of the taphole, based on the electric furnace electrode descent limit, and observe and confirm the erosion of the furnace wall under the dead iron layer. After the molten iron and slag have been discharged, the furnace shell corresponding to the 1000×600mm taphole groove is removed by gas welding. Standing outside the taphole groove, two furnace lining bricks are manually removed to the depth of the groove, extending the refractory lining inside the taphole groove to the refractory lining inside the electric furnace. The coke and slag filler between the original refractory lining inside the furnace and the furnace shell is then constructed with refractory bricks. CO2-cured iron ramming material dries quickly and forms a solidified iron trough. Then, the electrode power is increased and the electrode is gradually lowered to begin melting the dead iron layer below the taphole line. Check and confirm the connection between the refractory lining in the iron discharge trough and the refractory brick lining in the electric furnace. Determine the center of the hole position at the refractory brick lining in the electric furnace. At the same time, mark the residual iron elevation line next to the furnace shell. Use oxygen blowing pipes to burn residual iron discharge holes with a diameter of not less than 60mm on the furnace wall. Then, discharge the dead iron layer in the furnace according to the production iron discharge method until the specified thickness of dead iron layer molten iron flows out to complete the discharge of dead iron layer molten iron.

[0011] Furthermore, the air-cooling process shall last no less than four days. During air-cooling, the pores in the refractory brick lining at the slag and taphole shall be enlarged manually to increase the natural cooling airflow and accelerate the air-cooling process. After the specified air-cooling period is reached, the removal of the furnace cover cooling water ingress into the sealed steel platform and the corresponding auxiliary dust removal pipes shall be stopped. During the removal of the sealed steel platform and the corresponding auxiliary dust removal pipes, it is strictly prohibited for residual water from the electrodes, furnace cover, and related water-cooled components to enter the furnace body. The removal of the furnace wall lining and furnace bottom lining shall be carried out in the following steps: First, according to the access conditions on site, channel holes shall be opened on the furnace shell at the corresponding locations. Then, the furnace wall lining at the channel hole location, the furnace wall lining at the location to be replaced, and the furnace bottom lining shall be removed. Finally, the furnace shell segments at the corresponding locations shall be removed. During the removal of the furnace wall lining at the channel hole location, the furnace wall lining at the location to be replaced, and the furnace bottom lining, water cooling and water-cooled dismantling shall be strictly prohibited. The "rooting" base surface shall be removed from the remaining dead iron layer, furnace bottom lining, and furnace wall lining at the location.

[0012] The preferred method of the above scheme is that, when making the furnace shell, the height of the furnace shell segment to be replaced is determined, and each segment of the furnace shell is made in two sections along the vertical direction. At the same time as making each segment of the furnace shell, the expansion compensation connecting plate to be replaced at the corresponding position is made by preheating in a heating furnace and hot pressing with a special mold. The specific process is as follows: first, a pre-top pressure is applied evenly to make the blank initially adhere to the mold. After the outline is basically formed, the pressure is gradually increased and finally stabilized and held for 15 minutes to ensure the geometric accuracy of the expansion compensation connecting plate.

[0013] Furthermore, the replacement of the furnace shell is carried out according to the following steps: Installation of the lower furnace shell below the taphole → Installation and fixing of the lower ring plate of the middle furnace shell → Installation and temporary positioning of the wall panels → Alignment and tack welding of the upper and lower sections of the new furnace shell → Installation and fixing of the stiffening plates → Welding of the vertical welds of the wall panels → Welding of the horizontal welds → Welding of the outer stiffening plates → Installation and welding of the outer spring plates → Vibration aging to relieve stress → Cutting of the taphole / slag outlet → Installation of outer furnace shell accessories → Painting → Handover and acceptance. During installation, the misalignment of the butt welds must be strictly controlled within 2mm, and the bevel and assembly gap must meet the specified requirements. Welding should be carried out in the order of welding the vertical welds first and then the horizontal welds. After welding, each furnace shell segment should be subjected to vibration stress relief treatment using intelligent vibration aging equipment.

[0014] The preferred method of the above scheme is that the restoration of the furnace bottom lining and the furnace wall lining are both carried out on the dismantled "rooting" base surface. The new furnace bottom lining is made of bottom clay bricks and furnace bottom magnesia bricks with magnesia dry powder as mortar. The new furnace wall lining is made of aluminum silicate fiberboard, coke and high magnesia bricks with magnesia dry powder as mortar. During the masonry process, a protective masonry process that prohibits water cooling and wet dust removal is adopted.

[0015] Furthermore, the dismantled "rooting" base surface has staggered surfaces with inconsistent elevations in various places, and the magnesia powder is 180 mesh magnesia powder. The restoration of the furnace bottom lining and furnace wall lining shall be carried out according to the following steps. The masonry work begins with the lowest base surface of the furnace wall. First, fiber felt is pasted onto the furnace shell using a transparent water glass solution, and then compacted and evenly pressed to eliminate air bubbles and bulges. After each layer of masonry at the same elevation is completed, the next layer of masonry is built on top. After three layers of wall bricks are built, coke alumina aggregate is filled in. The furnace bottom lining and furnace body lining are completed in this order. The preparatory work before masonry is as follows: First, the "rooting" base surface is carefully cleaned and confirmed to ensure that the mortar joints and mud at the junction of the new and old brick linings are full. At the same time, at least 16 thermocouple temperature measuring points are added outside the furnace shell at the specified elevation of the junction. Then, the lumps or sintered refractory mortar on the surface of the old bricks at the "rooting" base surface of the new furnace wall are cleaned and polished to the original color of the refractory bricks using an angle grinder, disc polisher and / or hand chisel. At the same time, according to the actual site conditions at the junction of the magnesia bricks at the furnace bottom, each magnesia brick is processed by dry cutting, disc polisher and / or manual processing to complete the preparatory work before masonry. During the masonry process, wet masonry is used for the steps of new and old bricks, the joints of bricks at the bottom of the furnace, and the first brick and the first layer of bricks for "rooting". The mortar is fully filled and the mortar joints meet the standards. Except for high alumina bricks, clay bricks and masonry in specified locations and quantities, which are wet masonry, all other magnesia bricks and new brick masonry are dry masonry using 180-mesh magnesia powder.

[0016] The beneficial effects of this invention are as follows: The technical solution provided in this application is based on a titanium slag smelting furnace nearing the end of its lifespan. The titanium slag smelting furnace includes at least an electric furnace body equipment system, a water cooling system, and a slag and iron tapping system. The electric furnace body equipment system includes at least a water-cooled furnace cover, a furnace shell, a refractory lining, and electrodes. The slag and iron tapping ports of the slag and iron tapping system are positioned on the furnace shell according to regulations. The water-cooled exhaust duct of the water cooling system is connected to the water-cooled furnace cover. A semi-molten dead iron layer is arranged within the furnace shell below the iron tapping port through a refractory brick lining. Before shutdown, the last batch of molten iron and slag generated during production before furnace repair is discharged. Then, after confirming the erosion of the furnace wall under the dead iron layer, a dead iron layer of a specified thickness is discharged through a newly constructed discharge hole with the assistance of electrodes. Power is then cut off, the furnace is shut down, and the process enters the cold furnace phase. Following this, the process continues... In the preparatory stage, with the cooperation of the upper furnace shell, the furnace body equipment system is reinforced, the sealing steel platform around the specified elevation position of the upper furnace shell and the corresponding auxiliary dust removal pipes are removed, the furnace shell that needs to be replaced, the furnace wall lining and the furnace bottom lining at the corresponding position are protectively removed, and at the same time, a new furnace shell is made to replace the old furnace shell of the corresponding segment. Then, the new furnace shell is assembled and welded in sequence, the furnace bottom lining and the furnace wall lining are protectively restored, and finally the sealing steel platform around the upper furnace shell and the auxiliary dust removal pipes are restored. After the furnace is baked, preheated and slag is applied using a uniform micro-heating process, the furnace is transferred to normal metallurgical production operations to complete the repair work to extend the service life of the large titanium slag smelting furnace. In addition, the protective removal of the furnace wall lining and the furnace bottom lining that need to be replaced and the protective restoration of the furnace wall lining and the furnace bottom lining are all carried out using waterless operation and / or waterless mortar. The above-mentioned construction method of this application, combined with the requirements of furnace lining materials, adopts protective measures when removing the old furnace lining and replacing the furnace lining, and uses waterless operation and / or waterless mortar. Furthermore, since the technical solution of this application only removes the parts related to the repair during the repair construction, the technical solution provided by this application is not only convenient to operate, but also can effectively ensure the repair quality, thereby achieving the goal of effectively extending the service life of the first generation electric furnace by 3-5 years. Attached Figure Description

[0017] Figure 1 This is a front view of the large titanium slag smelting furnace involved in the construction method for extending the service life of a large titanium slag smelting furnace according to the present invention. Figure 2 This is a schematic diagram of the supporting operation involved in the construction method of the present invention for extending the service life of a large titanium slag smelting furnace. Figure 3 This is a schematic diagram of the furnace shell removal area at the inlet and outlet, which is involved in the construction method of the present invention for extending the service life of a large titanium slag smelting furnace. Figure 4 This is a schematic diagram of the furnace shell replacement area involving the tapping spout and slag outlet, which is part of the construction method for extending the service life of a large titanium slag smelting furnace according to the present invention. Figure 5 This is a schematic diagram of the iron removal, slag removal process and furnace lining structure involved in the construction method of the present invention for extending the service life of a large titanium slag smelting furnace. Figure 6 This is a schematic diagram illustrating the process of constructing the furnace wall lining and furnace bottom lining involved in the construction method of the present invention for extending the service life of a large titanium slag smelting furnace. Figure 7 This is a schematic diagram showing the completed construction of the furnace wall lining and furnace bottom lining involved in the construction method of the present invention for extending the service life of a large titanium slag smelting furnace. Figure 8 This is a schematic diagram illustrating the process of furnace lining construction at the slag opening and taphole involved in the construction method of the present invention for extending the service life of large titanium slag smelting furnaces.

[0018] The markings in the diagram are: 1. Water-cooled furnace cover; 2. Furnace shell; 3. Refractory brick lining; 4. Slag outlet; 5. Iron outlet; 6. Dead iron layer. Detailed Implementation

[0019] like Figures 1 to 8 This invention illustrates a construction method for extending the service life of large titanium slag smelting furnaces. This method is convenient to implement, effectively ensures repair quality, and can extend the life of the electric arc furnace by 3-5 years. The titanium slag smelting furnace involved in the construction method includes at least an electric arc furnace body equipment system, a water cooling system, and a slag and iron tapping system. The electric arc furnace body equipment system includes at least a water-cooled furnace cover 1, a furnace shell 2, a refractory brick lining 3, and electrodes. The slag outlet 4 and iron tapping outlet 5 of the slag and iron tapping system are positioned on the furnace shell 2 according to regulations. The water-cooled exhaust duct of the water cooling system is connected to the water-cooled furnace cover 1. A semi-molten dead iron layer is arranged inside the furnace shell 2 below the iron tapping outlet 5 through the refractory brick lining 3. The construction method includes the following steps: a. The last batch of molten iron and slag generated during the production period before furnace repair is discharged through slag outlet 4 and iron outlet 5. b. Open the residual iron tap to confirm the erosion of the furnace wall below the dead iron layer, and discharge the dead iron layer of the specified thickness 6 through the newly built discharge hole with the assistance of electrodes. Then, shut down the power and furnace to proceed to the cold furnace process. c. During the cold furnace process, air cooling is used for temperature reduction through natural cooling in conjunction with water-cooled exhaust ducts. Simultaneously, the furnace body is reinforced with the help of the upper furnace shell. d. Remove the sealed steel platform and corresponding auxiliary dust removal pipes around the specified elevation position of the upper section of the furnace shell. Protectively remove the furnace shell 2 that needs to be replaced, the furnace wall lining, and the furnace bottom lining at the corresponding positions. At the same time, fabricate a new furnace shell to replace the old furnace shell section. e. Assemble and weld the new furnace shell onto the existing furnace shell 2. f. Use new furnace lining bricks to protectively restore the furnace bottom and wall linings within the new furnace shell. g. Restore the sealed steel platform around the upper furnace shell and the associated dust removal ducts. h. The large titanium slag smelting furnace underwent repair work to address its extended service life by employing a uniform micro-heating process for furnace drying, preheating, and slag application, followed by transitioning to normal metallurgical production operations. In the protective dismantling and replacement of furnace wall and bottom linings, and / or protective restoration of furnace wall and bottom linings, waterless operation and waterless mortar are used. The technical solution provided in this application is based on a titanium slag smelting furnace nearing the end of its generation of service life. The titanium slag smelting furnace includes at least an electric furnace body equipment system, a water cooling system, and a slag and iron tapping system. The electric furnace body equipment system includes at least a water-cooled furnace cover, furnace shell, refractory lining, and electrodes. The slag and iron tapping ports of the slag and iron tapping system are set on the furnace shell at specified positions. The water-cooled exhaust flue of the water cooling system is connected to the water-cooled furnace cover. A semi-molten dead iron layer is arranged in the furnace shell below the iron tapping port through the refractory brick lining 3. Before shutting down the furnace, the last batch of molten iron and slag generated during the production period before the furnace repair is discharged. Then, under the condition of confirmed erosion of the furnace wall under the dead iron layer, a dead iron layer 6 of specified thickness is discharged through the newly built discharge hole with the assistance of electrodes. After that, the power is turned off and the furnace is shut down to enter the cold furnace process. Then, in the cold furnace process, the upper With the cooperation of the furnace shell section, the furnace body equipment system is reinforced, the sealing steel platform around the specified elevation position of the upper furnace shell section and the corresponding auxiliary dust removal pipes are removed, the furnace shell that needs to be replaced, the furnace wall lining and the furnace bottom lining at the corresponding position are protectively removed, and at the same time, a new furnace shell is made to replace the old furnace shell of the corresponding segment. Then, the new furnace shell is assembled and welded in sequence, the furnace bottom lining and the furnace wall lining are protectively restored, and finally the sealing steel platform around the upper furnace shell section and the auxiliary dust removal pipes are restored. After the furnace is baked, preheated and slag is applied using a uniform micro-heating process, it is transferred to normal metallurgical production operation to complete the repair work to extend the service life of the large titanium slag smelting furnace. In addition, the protective removal of the furnace wall lining and the furnace bottom lining that need to be replaced and the protective restoration of the furnace wall lining and the furnace bottom lining are all carried out using waterless operation and / or waterless mortar. The above-mentioned construction method of this application, combined with the requirements of furnace lining materials, adopts protective measures when removing the old furnace lining and replacing the furnace lining, and uses waterless operation and / or waterless mortar. Furthermore, since the technical solution of this application only removes the parts related to the repair during the repair construction, the technical solution provided by this application is not only convenient to operate, but also can effectively ensure the repair quality, thereby achieving the goal of effectively extending the service life of the first generation electric furnace by 3-5 years.

[0020] Accordingly, in order to improve the repair effect and submit the repair operation and efficiency as much as possible, the discharge of molten iron and slag in this application is carried out in the following steps: First, during production, a discharge trough with a slope of 8% is constructed, with a steel structure trough for the outer shell and clay bricks and CO2-cured iron ramming material for the inner lining. Then, multiple collection pits for storing residual iron are built in the adjacent ground sand mold pit, which are large enough to contain the discharged molten iron and slag and are lined with clay bricks and CO2-cured iron ramming material for the inner lining. After the production of molten iron is completed, the residual molten iron mixed with slag at the bottom of the furnace is discharged through the discharge trough. After the residual molten iron mixed with slag is cooled to room temperature, it is hoisted to the designated location by the plant crane to complete the discharge of molten iron and slag. When opening the taphole for residual iron, this application specifies that the taphole should be opened at least 400mm below the center of the taphole, based on the electric furnace electrode descent limit. The erosion of the furnace wall below the dead iron layer should be observed and confirmed. After the molten iron and slag have been discharged, the furnace shell 2 corresponding to the 1000×600mm taphole groove is removed using gas welding. Two furnace lining bricks are manually removed from outside the taphole groove to the depth required to extend the refractory lining inside the taphole groove to the refractory brick lining 3 inside the electric furnace. The area between the original refractory brick lining 3 and the furnace shell 2, where the slag filler was located, is then constructed using refractory bricks. Finally, CO2 is used to solidify the refractory lining. The rammed iron in the iron-melting trench dries quickly and is then shaped. The electrode power is increased and the electrode is gradually lowered to begin melting the dead iron layer below the taphole line. The connection between the refractory lining in the iron discharge trench and the refractory brick lining 3 in the electric furnace is checked and confirmed. The center of the hole is determined at the refractory brick lining 3 in the electric furnace. At the same time, the residual iron elevation line is marked next to the furnace shell 2. Oxygen is blown through the oxygen pipe to burn residual iron discharge holes with a diameter of not less than 60 mm on the furnace wall. Then, the residual iron in the dead iron layer in the furnace is discharged according to the production iron discharge method until the residual iron of the dead iron layer of the specified thickness flows out, thus completing the discharge of the molten iron in the dead iron layer. Furthermore, the air-cooling duration is set to be no less than four days. During air-cooling, the three holes in the refractory brick lining inside the furnace at the slag and taphole are enlarged manually to increase the natural cooling airflow and improve the air-cooling rate. After the air-cooling period reaches the specified duration, the removal of the furnace cover cooling water entering the sealed steel platform and the corresponding auxiliary dust removal pipes is stopped. During the removal of the sealed steel platform and the corresponding auxiliary dust removal pipes, it is strictly forbidden for residual water from the electrodes, furnace cover, and corresponding water-cooled components to enter the furnace body. The removal of the furnace wall lining and furnace bottom lining is also carried out. The following steps are to be followed: First, according to the passage conditions on site, make passage holes on the furnace shell 2 at the corresponding positions. Then, remove the furnace wall lining at the passage hole, the furnace wall lining at the position that needs to be replaced, and the furnace bottom lining. Finally, remove the furnace shell segments at the corresponding positions. During the removal of the furnace wall lining at the passage hole, the furnace wall lining at the position that needs to be replaced, and the furnace bottom lining, it is strictly forbidden to use water for cooling and protective removal. The "rooting" base surface is removed from the remaining dead iron layer 6, the furnace bottom lining, and the furnace wall lining at the position.In manufacturing furnace shell 2, the proposed solution is to manufacture each segment of furnace shell 2 in two vertical sections, based on the height of the segment to be replaced. Simultaneously, during the manufacturing of each segment, a preheating furnace and a special mold hot-pressing process are used to fabricate the corresponding expansion compensation connecting plates. Specifically, a pre-pressure is applied evenly to initially adhere the billet to the mold; after the outline is basically formed, the pressure is gradually increased, and finally, the pressure is stabilized and held for 15 minutes to ensure the geometric accuracy of the expansion compensation connecting plates. The specific process for replacing furnace shell 2 is as follows. Installation of the lower furnace shell below the taphole → Installation and fixing of the lower ring plate of the middle furnace shell → Installation and temporary positioning of the wall panels → Alignment and tack welding of the upper and lower sections of the new furnace shell → Installation and fixing of the stiffening plates → Welding of the vertical welds of the wall panels → Welding of the horizontal welds → Welding of the outer stiffening plates → Installation and welding of the outer spring plates → Vibration aging to relieve stress → Cutting of taphole 5 / slag outlet 4 → Installation of outer furnace shell accessories → Painting → Handover and acceptance. During installation, the misalignment of the butt welds must be strictly controlled within 2mm, and the bevel and assembly gap must meet the specified requirements. Welding should be carried out in the order of welding the vertical welds first and then the horizontal welds. After welding, each furnace shell segment should be subjected to vibration stress relief treatment using intelligent vibration aging equipment.

[0021] Furthermore, as a crucial step in the repair work of this application, to maximize the repair effect, the restoration of both the furnace bottom lining and the furnace wall lining is carried out on the removed "rooting" base surface. The new furnace bottom lining is constructed by dry-laying bottom clay bricks and furnace bottom magnesia bricks with magnesia powder as mortar. The new furnace wall lining is constructed by dry-laying aluminum silicate fiberboard, coke alumina, and high magnesia bricks with magnesia powder as mortar. During the construction process, a protective masonry technique is employed that prohibits water cooling and wet dust removal. Specifically, the removed "rooting" base surface has staggered surfaces with varying elevations, and the magnesia powder used is 180-mesh magnesia powder. The restoration of the furnace bottom lining and the furnace wall lining is carried out according to the following steps. The masonry work begins with the lowest base surface of the furnace wall. First, fiber felt is pasted onto the furnace shell 2 using a transparent water glass solution, and then compacted and evenly pressed to eliminate air bubbles and bulges. After each layer of masonry at the same elevation is completed, the next layer of masonry is built on top. After three layers of wall bricks are built, coke alumina aggregate is filled in. The furnace bottom lining and furnace body lining are completed in this order. The preparatory work before masonry is as follows: First, the "rooting" base surface is carefully cleaned and confirmed to ensure that the mortar joints and mud at the junction of the new and old brick linings are full. At the same time, at least 16 thermocouple temperature measuring points are added outside the furnace shell 2 at the specified elevation of the junction. Then, the lumps or sintered refractory mud on the surface of the old bricks at the "rooting" base surface of the new furnace wall are cleaned and polished to the original color of the refractory bricks using an angle grinder, disc polisher and / or hand chisel. At the same time, according to the actual site conditions at the junction of the magnesia bricks at the furnace bottom, each magnesia brick is processed by dry cutting, disc polisher and / or manual processing to complete the preparatory work before masonry. During the masonry process, wet masonry is used for the steps of new and old bricks, the joints of bricks at the bottom of the furnace, and the first brick and the first layer of bricks for "rooting". The mortar is fully filled and the mortar joints meet the standards. Except for high alumina bricks, clay bricks and masonry in specified locations and quantities, which are wet masonry, all other magnesia bricks and new brick masonry are dry masonry using 180-mesh magnesia powder.

[0022] More fundamentally, repairing the furnace shell and lining is only a basic means of extending the furnace's service life. To achieve an even longer service life after repair, furnace drying is an indispensable step. Therefore, this application provides the following furnace drying procedure: furnace drying is performed using electrode-powered heating. Before drying, auxiliary materials for furnace drying are laid inside the furnace according to the following requirements. First, lay 30-50 tons of magnetic material on the dead iron layer 6, then add 50 tons of mixed material, followed by a 200-300mm thick layer of at least 8 tons of large coke blocks. Finally, according to the natural stacking angle of the titanium slag in the furnace, lay titanium slag at the edge of the furnace wall to a height of no less than 1000mm to complete the laying of the furnace drying auxiliary materials. The furnace drying time is controlled at 24-26 days, using a uniform micro-heating process. The process is as follows. The furnace lining temperature rise at each stage must strictly adhere to ≤1℃ / h. For the first 10 days of furnace drying, the rate should be 10-15℃ / day, and for days 11-25, it should be 20-25℃ / day. When the average temperature of the second and third layer thermocouples reaches 105℃, the furnace should be shut down for 24-48 hours of heat equalization. When the temperature of the fourth layer thermocouples reaches 300℃, the furnace should be shut down for 24-48 hours of heat equalization. If the temperature rise of any layer thermocouple exceeds 30℃ / 24h, the furnace should be shut down for 24 hours of heat equalization. The temperature should only be increased after the average temperature of the second layer thermocouples reaches 105℃ and the furnace gas humidity measurements are consistent for two consecutive days, until the operating temperature during production is reached. During the furnace drying process, the heating rate of new and old bricks should be strictly controlled to maintain a consistent heating rate. After the furnace drying is completed, the furnace should be shut down for 48 hours of heat equalization.

[0023] In summary, the technical solution provided in this application also has the following advantages: This method for extending furnace life is the first of its kind in China and has been used continuously for 3 years and 3 months. Currently, the 25.5MW large titanium slag smelting electric arc furnace is operating normally. This proves that, in the later stages of the first-generation furnace life, it is feasible to extend the furnace life of the 25.5MW large titanium slag smelting electric arc furnace by 3 to 5 years, or even 11 to 13 years, by adopting the provided process and replacing some refractory linings to adapt to the production process, at a relatively low cost. This improves the furnace life and achieves the company's expected efficiency gains. It has promotional value and reference significance for extending the life of similar large-scale submerged arc furnaces in China, reducing costs, and ensuring safe production.

[0024] Example 1 The purpose of this invention is to analyze the factors affecting the lifespan of a first-generation furnace. When the furnace lifespan meets the design lifespan, and the process, operation, and equipment are all stable and orderly, the condition of the furnace lining itself determines the final furnace lifespan. In the later stages of the first-generation furnace lifespan, special processes are adopted to replace parts of the refractory lining that are adapted to the production process, thereby extending the lifespan of the first-generation large-scale submerged arc furnace by 3 to 5 years at a relatively low cost, achieving the goal of extending the lifespan of large-scale submerged arc furnaces and increasing enterprise efficiency.

[0025] To clearly illustrate this method, we will now use a successful case study of a 25.5MW large titanium slag smelting electric furnace in its later stages of life, where the refractory lining was replaced to adapt to the production process, and the furnace shell at the slag and taphole was replaced, extending the furnace life of the large titanium slag smelting electric furnace by more than 3 years.

[0026] 1. The 25.5MW large-scale titanium slag smelting electric furnace consists of the furnace body equipment system, charging system, flue gas system, water cooling system, nitrogen generation system, purification system, power supply system, automatic control system, slag tapping and iron tapping system, etc. The furnace body equipment system consists of water-cooled furnace cover, furnace shell, refractory lining, and electrodes.

[0027] 2. Shut down the furnace, remove the dead iron layer and residual iron, and cool the furnace. In electric arc furnace (EAF) production processes, slag is typically removed first, followed by iron. The taphole is 1105mm from the pot-shaped dismantling point. Below the taphole is a semi-molten dead iron layer (the temperature decreases to approximately 900℃ from the center line of the taphole to the bottom of the pot). Corrosion of the furnace wall is relatively minor in this area. Corrosion is more significant at the taphole and slag outlet (actual data from previous overhauls and dismantling). The upper section of the furnace wall above the taphole and slag outlet, in addition to being subjected to the chemical reaction of slag and iron, high temperatures, and high-temperature radiation from electrode heating, experiences particularly severe corrosion. The height of the molten dead iron layer is determined based on the electrode descent limit. Generally, the residual iron outlet is opened 400-500mm below the center of the taphole (it can be deeper, depending on the EAF electrode descent limit). The purpose is to check and confirm the corrosion of the furnace wall below the dead iron layer, creating conditions for the treatment of the furnace lining below the slag and taphole.

[0028] During production, an 8% slope iron discharge trench (with a steel structure outer shell and clay bricks and CO2-cured iron trench ramming material for quick-drying molding) is constructed. Sixteen pits lined with clay bricks and CO2-cured iron trench ramming material for quick-drying molding are built in nearby sand mold pits to collect residual iron. After the residual iron cools to room temperature, it is lifted by a factory crane to a designated location.

[0029] Once the iron discharge facilities and residual iron collection pit in the sand mold pit are completed; slag and iron are discharged using the original production equipment; the furnace shell corresponding to the 1000×600mm (a×b) residual iron trough is removed using gas welding; two bricks are manually removed from outside the iron trough; the refractory lining in the residual iron trough is extended into the refractory lining inside the electric furnace (the coke and slag filler between the original electric furnace lining bricks and the furnace shell must be constructed with refractory bricks before the iron trough ramming material can be quickly dried and formed using CO2); the electrode power is increased and the electrode is gradually lowered to begin melting the dead iron layer residual iron below the taphole; the connection between the refractory lining in the iron discharge trough and the lining bricks inside the electric furnace is checked and confirmed, and the center of the hole is determined at the electric furnace lining brick (at the same time, the residual iron elevation line is marked next to the furnace shell); oxygen blowing is carried out using oxygen blowing pipes to burn through the approximately Ф60 hole in the furnace wall, and the dead iron layer residual iron inside the furnace is discharged according to the production iron discharge method until an appropriate amount of molten iron flows out.

[0030] After the planned residual iron is discharged from the furnace, the electric furnace is shut down and the power is turned off; the bell valve on the top of the water-cooled flue is opened to exhaust the gas; the electric furnace is switched to natural cooling (water cooling is strictly prohibited); the original slag tap and taphole opening and blocking equipment and auxiliary pipe network are removed; the furnace lining holes at the slag and taphole are manually chiseled to enlarge (to increase the natural cooling air volume).

[0031] 3. After natural cooling for 4 days, shut off the cooling water to the furnace cover, remove the auxiliary charging pipes on the furnace cover, the water-cooled flue on the furnace cover and its fixed position on the upper platform, and the furnace cover (including the auxiliary platform suspension and furnace shell cantilever). At the same time, raise the electrodes to their upper limit and rigidly fix them with steel pipe sleeves and install the iron removal facilities. During construction, it is strictly forbidden for residual water from the electric furnace electrodes, furnace cover, and other water-cooled components to enter the furnace.

[0032] 4. Remove the taphole and slag outlet of the furnace shell and clean them up promptly. 4.1 Protectively dismantle the 7.3-meter sealed steel platform around the furnace shell to avoid damaging the preserved structure; protectively dismantle the auxiliary dust removal pipes that affect the removal of the furnace shell, and mark the pipe interface locations (to provide a basis for restoration); prepare to open a temporary inlet and outlet in the middle section of the west side of the furnace shell to ensure unobstructed access for the removal and installation of the furnace lining refractory materials.

[0033] 4.2 Furnace body reinforcement To prevent instability and deformation of the upper section structure during the dismantling of the middle section furnace shell, steel supports (four points vertically symmetrical on the +7.3-meter platform) were used to temporarily reinforce the upper section furnace shell.

[0034] 4.3 Furnace Shell Removal Process The replacement area is the middle and lower layers of the furnace shell. Because the segments are flexibly connected by expansion-compensation plates, the overall rigidity is weak, requiring complete removal and replacement of the entire segment. An external safety operating platform was erected, and the outer reinforcing plates were cut, marking the cut lines at the specified height. After the furnace lining refractory material was removed below the cut lines, the furnace shell was cut inside. A winch and pulley system were used to hoist the cut furnace shell segments to the transport channel for loading. Thermocouples and sheaths were protectively removed before dismantling. After dismantling, the 7.2m platform was enclosed with steel plates, and safety railings were installed at the edges to prevent objects from falling.

[0035] 4.4 Replacement of prefabricated furnace shell in the replacement area A. Segmented Production The original central furnace shell was 4830mm high. Due to limited on-site facilities, it was fabricated in the on-site workshop and then transported to the site. To prevent deformation during overall transportation, hoisting, and installation, and considering the erosion and deformation characteristics of the old furnace shell, the central furnace shell was optimized into a two-section structure (the upper section retains the original furnace shell, only the lower section is replaced). The lower section below the taphole was fabricated according to the original drawings.

[0036] B. Fabrication of Expansion Compensation Connecting Plate The process employs a preheating furnace and a special mold hot pressing process: a 320t hydraulic press is used in conjunction with an ejector for pressing. Key points of process control: first, apply pre-extrusion pressure evenly to allow the blank to initially adhere to the mold; after the outline is basically formed, gradually increase the pressure; finally, stabilize and hold the pressure for 15 minutes to ensure the geometric dimensional accuracy of the connecting plate.

[0037] C. Central Furnace Shell Assembly During the assembly phase, the vertical stiffening plates at the interface and the horizontal stiffening plates at the top will not be installed (in order to reduce resistance when the new and old furnace shells are aligned). They will be installed after the new and old furnace shells are aligned and welded.

[0038] 5. Remove the burned furnace walls and linings. Following the principle of removing furnace wall lining bricks and associated slag from top to bottom and from outside to inside, remove them sequentially down to the height of the residual iron layer. Check the width of the furnace wall at this point. The erosion height of the furnace wall is uneven around the perimeter; generally, the erosion width around the perimeter of the furnace wall above the dead iron layer is 200-350 mm, while the erosion width around the perimeter of the furnace wall below the dead iron layer is generally 20-30 mm. Erosion is severe at the taphole and slag outlet (consistent with production process characteristics). Stop removing the furnace wall lining when the width reaches the specified position. This serves as the base surface for the new furnace wall to "root." The furnace wall at the taphole and slag outlet needs to be removed further downwards. If the width of the new furnace wall "root" base surface is insufficient, use oxygen blowing pipes to cut the residual iron at the edge of the dead iron layer until the furnace wall "root" width meets the specified requirements. Water cooling is prohibited throughout the entire process.

[0039] 6. Furnace shell installation 6.1 Installation sequence Installation of the lower furnace shell (below the taphole) → Installation and fixing of the lower ring plate of the middle furnace shell → Installation and temporary positioning of the wall panels → Alignment of the upper and lower sections (misalignment < 2mm), tack welding → Installation and fixing of the stiffening plates → Welding of the vertical welds of the wall panels → Welding of the horizontal welds → Welding of the outer stiffening plates → Installation and welding of the outer spring plates → Vibration aging to relieve stress → Cutting of the tapping / slag outlets → Installation of external furnace shell accessories (such as air-cooled pipe interfaces) → Painting → Handover and acceptance.

[0040] 6.2 Quality Control (1) Beveling: Beveling shall be carried out in accordance with the specified requirements, and the beveling gap and furnace shell ellipticity shall be controlled in accordance with the requirements of the "Standard for Acceptance of Construction Quality of Steel Structure Engineering".

[0041] (2) Misalignment: The misalignment of butt welds shall be strictly controlled within 2mm.

[0042] 6.3. Welding Process (1) Materials and equipment: The furnace shell material is Q245R (original 20g), the welding wire is φ1.2mm H08Mn2SiA flux-cored welding wire; the shielding gas is CO2 (purity ≥99.5%, moisture ≤0.5%), and it is drained before use; the outer root welding rod is E4315 (baked at 150℃ for 1-2 hours before use, and placed in a heat preservation container for use as needed).

[0043] (2) Welding sequence: weld the vertical weld first, then weld the horizontal weld.

[0044] (3) Horizontal weld: The horizontal welds of the three furnace shells are divided into 6 sections, and 6 welders on the inner and outer sides perform symmetrical and synchronous welding (manual rooting on the outer side → CO2 shielded welding filling on the inner side).

[0045] (4) Weld inspection: Butt welds are qualified by ultrasonic testing (UT) Level II, and fillet welds are qualified by surface dyeing testing (PT) Level II.

[0046] (5) Stress relief: The LM-ZN K4(WD) ​​intelligent vibration aging equipment is used to perform vibration stress relief treatment on each piece of furnace shell.

[0047] 6.4 Rust removal and painting 7. Restoration of furnace lining and accessories 7.1 Furnace Lining Restoration The new furnace lining and walls are constructed on a base surface that retains the dead iron layer, bottom magnesia bricks, clay bricks, and some magnesia bricks on the furnace walls, with varying elevations at different locations. The base surface must be carefully cleaned and verified; the mortar joints and mud saturation at the junction of the new and old brick linings must be ensured; and 16 thermocouple temperature measuring points should be added to the outside of the furnace shell at the junction elevation (see reference for horizontal positions). Figure 3Temperature monitoring is required. For the old bricks at the "rooting" base of the new furnace wall, any lumps or sintered refractory mortar on the surface must be cleaned and polished to the original color of the refractory bricks using an angle grinder, disc polisher, and hand chisel. At the junction with the magnesia bricks at the furnace bottom, bricks must be processed according to the actual site conditions, using dry cutting, disc polishing, and manual processing. Water cooling and wet dust removal are prohibited in all of the above. The steps between new and old bricks, the joints of the furnace bottom bricks, and the first brick and the first layer of bricks at the "rooting" base must be laid wet with full mortar, and the mortar joints must meet standards. The remaining magnesia bricks (except for a small amount of wet-laid high-alumina bricks and clay bricks) must be laid dry using 180-mesh magnesia powder. The masonry work begins at the lowest base of the furnace wall. First, fiber felt (bonded with transparent water glass solution, compacted and evenly pressed to eliminate air bubbles and bulges) is applied to the furnace shell. Only after each layer (at the same elevation level) is completed can the next layer be laid. After three layers of bricks, coke alumina aggregate is filled in. The furnace body and lining are constructed in this sequence. The furnace body and lining construction must strictly adhere to the drawings, the "Code for Construction and Acceptance of Industrial Furnace Masonry Engineering" GB50211-2014, and the "Standard for Quality Acceptance of Industrial Furnace Masonry Engineering" GB50309-2017.

[0048] 7.2 Restoration of auxiliary systems such as furnace cover Restore the auxiliary platform suspension, furnace shell cantilever, and furnace cover (with the electrode steel pipe sleeves being removed and rigidly fixed); conduct insulation tests; repair cooling water system connections; repair water-cooled flue on the furnace cover; and repair auxiliary feeding pipes on the furnace cover.

[0049] 8. Oven and production linkage 8.1 After checking that the furnace is ready for drying, lay the furnace drying auxiliary materials. Lay 30-50 tons of magnetic material on the dead iron layer, then add 50 tons of mixed material, and finally lay about 8 tons of large coke blocks 200-300mm thick; lay titanium slag about 1000mm high at the edge of the furnace wall according to the natural angle of titanium slag accumulation inside the furnace.

[0050] 8.2 The oven is heated by electrodes.

[0051] 8.3 Furnace drying for 25 days. Due to the complex working conditions such as partial replacement of the furnace lining, retention of the furnace bottom lining, residual dead iron layer in the furnace bottom, and combination of new and old bricks, the furnace drying process has special and stringent requirements (not the traditional furnace drying process for newly built furnaces). The following process is adopted: the furnace lining temperature rise at each stage is strictly ≤1℃ / h; for the first 10 days of furnace drying, it is 10-15℃ / day; for days 11-25, it is 20-25℃ / day; when the average temperature of the second and third layer thermocouples reaches 105℃, the furnace is shut down for 24-48 hours of heat equalization; when the temperature of the fourth layer thermocouples reaches 300℃, the furnace is shut down for 24-48 hours of heat equalization; when the temperature rise of any layer thermocouple is >30℃ / 24h, the furnace is shut down for 24 hours of heat equalization; when the average temperature of the second layer thermocouples reaches 105℃ and the furnace gas humidity (measured for 2 consecutive days) is consistent, the temperature is then increased again until the working temperature during production; during the furnace drying process, the heating rate of new and old bricks is strictly controlled to keep the heating rate as consistent as possible; after the furnace drying is completed, the furnace is shut down for 48 hours of heat equalization.

[0052] 8.4 After the electric furnace is baked, preheating and slag hanging are carried out. After the preheating and slag hanging are completed, normal production is resumed.

[0053] 9. Implementation Results: This method for extending furnace life is the first of its kind in China. It has been used continuously for 3 years and 3 months to date, and the 25.5MW large titanium slag smelting electric arc furnace is currently operating normally. This proves that, in the later stages of the first-generation furnace life, it is feasible to extend the life of the 25.5MW large titanium slag smelting electric arc furnace by 3 to 5 years at a relatively low cost by adopting special processes and replacing parts of the refractory lining to adapt to the production process. This improves the furnace life and achieves the company's expected efficiency gains. It has promotional value and reference significance for extending the life of similar large-scale submerged arc furnaces in China, reducing costs, and ensuring safe production.

Claims

1. A construction method for extending the service life of a large titanium slag smelting furnace, comprising at least an electric furnace body equipment system, a water cooling system, and a slag and iron tapping system. The electric furnace body equipment system comprises at least a water-cooled furnace cover (1), a furnace shell (2), a refractory brick lining (3), and electrodes. The slag outlet (4) and iron tapping outlet (5) of the slag and iron tapping system are set on the furnace shell (2) at specified positions. The water-cooled exhaust flue of the water cooling system is connected to the water-cooled furnace cover (1). A semi-molten dead iron layer is arranged in the furnace shell (2) below the iron tapping outlet (5) through the refractory brick lining (3). The method is characterized by: The construction method includes the following steps: a. The last batch of molten iron and slag generated during the production period before furnace repair is discharged through the slag outlet (4) and the iron outlet (5). b. Open the residual iron outlet to confirm the erosion of the furnace wall under the dead iron layer (6), and discharge the dead iron layer (6) of the specified thickness through the newly built discharge hole with the help of electrodes. Then, stop the power and shut down the furnace to enter the cold furnace process. c. During the cold furnace process, air cooling is used for temperature reduction through natural cooling in conjunction with water-cooled exhaust ducts. Simultaneously, the furnace body is reinforced with the help of the upper furnace shell. d. Remove the sealed steel platform and corresponding auxiliary dust removal pipes around the specified elevation position of the upper section of the furnace shell, and protectively remove the furnace shell (2) that needs to be replaced, the furnace wall lining and furnace bottom lining at the corresponding positions. At the same time, make a new furnace shell to replace the old furnace shell of the corresponding segment. e. Assemble and weld a new furnace shell onto the existing furnace shell (2). f. Use new furnace lining bricks to protectively restore the furnace bottom and wall linings within the new furnace shell. g. Restore the sealed steel platform around the upper furnace shell and the associated dust removal ducts. h. The large titanium slag smelting furnace underwent repair work to extend its service life by employing a uniform micro-heating process for furnace drying, preheating, and slag application, followed by normal metallurgical production operations. In the process of protectively dismantling and replacing the furnace wall and furnace bottom linings, and protectively restoring the furnace wall and furnace bottom linings, waterless operation and / or waterless mortar are used.

2. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 1, characterized in that: The drying oven uses electrode-powered heating. Before drying, the auxiliary materials for drying the oven should be laid inside the oven according to the following requirements. 30-50 tons of magnetic material are laid on the dead iron layer (6), then 50 tons of mixed material are added, followed by at least 8 tons of large coke with a thickness of 200-300 mm. Finally, titanium slag material with a height of not less than 1000 mm is laid on the edge of the furnace wall according to the natural stacking angle of titanium slag in the furnace to complete the laying of furnace drying auxiliary materials.

3. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 2, characterized in that: The oven drying time using the uniform micro-heating process is controlled at 24-26 days. The process flow for the uniform micro-heating oven drying is as follows. The furnace lining temperature rise at each stage is strictly controlled at ≤1℃ / h. For the first 10 days of furnace drying, the rate is 10-15℃ / day, and for days 11-25, it is 20-25℃ / day. When the average temperature of the second and third layer thermocouples reaches 105℃, the furnace is shut down for 24-48 hours of heat equalization. When the temperature of the fourth layer thermocouples reaches 300℃, the furnace is shut down for 24-48 hours of heat equalization. If the temperature rise of any layer thermocouple is >30℃ / 24h, the furnace is shut down for 24 hours of heat equalization. The temperature is increased again only after the average temperature of the second layer thermocouples reaches 105℃ and the furnace gas humidity measured for two consecutive days is consistent, until the operating temperature during normal production is reached. During the furnace drying process, the heating rate of new and old bricks is strictly controlled to keep the heating rate as consistent as possible. After the furnace drying is completed, the furnace is shut down for 48 hours of temperature equalization.

4. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 1, 2, or 3, characterized in that: The discharge of molten iron and slag is carried out in the following steps: First, during production, an iron discharge trough with a slope of 8% is constructed. The outer shell is made of steel structure trough, and the inner lining is made of clay bricks and CO2-cured iron ramming material that is quick-drying. Then, multiple collection pits for storing residual iron are built in the nearby ground sand mold pit. These pits are lined with clay bricks and CO2-cured iron ramming material that is quick-drying. After the production of molten iron is completed, the residual molten iron mixed with slag at the bottom of the furnace is discharged through the iron discharge trough. After the residual molten iron mixed with slag cools to room temperature, it is hoisted to the designated location by the plant crane to complete the discharge of molten iron and slag.

5. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 4, characterized in that: When opening the taphole, the opening should be made at least 400mm below the center of the taphole according to the lower limit of the electric furnace electrode. The corrosion of the furnace wall under the dead iron layer should be observed and confirmed. After the molten iron and slag are discharged, the furnace shell (2) corresponding to the 1000×600mm taphole groove is removed by gas welding. The depth of two furnace lining bricks is manually removed from outside the taphole groove. The refractory lining in the taphole groove is extended to the refractory brick lining (3) inside the electric furnace. The coke and sapphire filler between the original refractory brick lining (3) inside the electric furnace and the furnace shell (2) is then constructed with refractory bricks. After that, CO2 is used to solidify the filler. The rammed iron material in the iron smelting trough is quickly dried and formed. Then, the electrode power is increased and the electrode is gradually lowered to begin melting the dead iron layer below the taphole line. Check and confirm the connection between the refractory lining in the iron discharge trough and the refractory brick lining (3) in the electric furnace. Determine the center of the hole at the refractory brick lining (3) in the electric furnace. At the same time, mark the residual iron elevation line next to the furnace shell (2). Use oxygen blowing pipes to blow oxygen to burn out residual iron discharge holes with a diameter of not less than 60 mm on the furnace wall. Then, discharge the dead iron layer in the furnace according to the production iron discharge method until the dead iron layer residual iron of the specified thickness flows out to complete the discharge of the dead iron layer molten iron.

6. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 5, characterized in that: The air cooling time shall not be less than four days. During the air cooling, the refractory brick lining (3) holes at the slag opening and iron taphole shall be enlarged by manual chiseling to increase the natural cooling air volume and improve the air cooling speed. After the air cooling reaches the specified time, the furnace cover cooling water entering the sealed steel platform and the corresponding auxiliary dust removal pipes shall be shut down. During the dismantling of the sealed steel platform and the corresponding auxiliary dust removal pipes, it is strictly forbidden for residual water in the electrodes, furnace cover and corresponding accessories to enter the furnace body. The removal of the furnace wall lining and the furnace bottom lining is carried out in the following steps: First, according to the passage conditions on site, a passage hole is opened on the furnace shell (2) at the corresponding position. Then, the furnace wall lining at the passage hole is removed, the furnace wall lining at the position to be replaced, and the furnace bottom lining are removed. Finally, the furnace shell segment at the corresponding position is removed. Among them, when removing the furnace wall lining at the passage hole, the furnace wall lining at the position to be replaced, and the furnace bottom lining, it is strictly forbidden to use water cooling and water dismantling for protective removal. The "rooting" base surface is removed from the remaining dead iron layer (6), the furnace bottom lining, and the furnace wall lining at the position.

7. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 6, characterized in that: When making the furnace shell (2), the height of the furnace shell segment to be replaced is determined according to the height of the segment. Each segment of the furnace shell (2) is made in two sections along the vertical direction. While making each segment of the furnace shell, the expansion compensation connecting plate to be replaced at the corresponding position is made by preheating the heating furnace and hot pressing the special mold. The specific process is as follows: first, apply the pre-top pressure evenly to make the blank initially adhere to the mold. After the outline is basically formed, gradually increase the pressure and finally stabilize and hold the pressure for 15 minutes to ensure the geometric accuracy of the expansion compensation connecting plate.

8. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 7, characterized in that: The replacement of the furnace shell (2) is carried out according to the following steps: Installation of the lower furnace shell below the taphole → Installation and fixing of the lower ring plate of the middle furnace shell → Installation and temporary positioning of the wall panels → Alignment and spot welding of the upper and lower sections of the new furnace shell → Installation and fixing of the stiffening plates → Welding of the vertical welds of the wall panels → Welding of the horizontal welds → Welding of the welds of the outer stiffening plates → Installation and welding of the outer spring plates → Vibration aging to relieve stress → Cutting the taphole (5) / slag outlet (4) → Installation of the outer accessories of the furnace shell → Painting → Handover and acceptance During installation, the misalignment of the butt welds must be strictly controlled within 2mm, and the bevel and assembly gap must meet the specified requirements. Welding should be carried out in the order of welding the vertical welds first and then the horizontal welds. After welding, each furnace shell segment should be subjected to vibration stress relief treatment using intelligent vibration aging equipment.

9. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 8, characterized in that: The restoration of the furnace bottom lining and furnace wall lining was carried out on the removed "rooting" base surface. The new furnace bottom lining was made of bottom clay bricks and furnace bottom magnesia bricks with magnesia dry powder as mortar. The new furnace wall lining was made of aluminum silicate fiberboard, coke and high magnesia bricks with magnesia dry powder as mortar. During the masonry process, a protective masonry process was adopted that prohibited water cooling and wet dust removal.

10. The construction method for extending the service life of a large titanium slag smelting furnace according to claim 9, characterized in that: The dismantled "rooting" base surface has staggered surfaces with inconsistent elevations in various places. The magnesia powder is 180-mesh magnesia powder. The restoration of the furnace bottom lining and furnace wall lining shall be carried out according to the following steps. The masonry work begins from the lowest base surface of the furnace wall. First, use transparent water glass solution to paste fiber felt on the furnace shell (2), and compact and evenly press it to eliminate air bubbles and bulges. After each layer of masonry at the same elevation is completed, the next layer of masonry is built. After three layers of wall bricks are built, coke gemstone aggregate is filled. The furnace bottom lining and furnace body lining are completed in this order. The preparatory work before masonry is as follows: First, the "rooting" base surface is carefully cleaned and confirmed to ensure that the mortar joints and mud at the junction of the new and old brick linings are full. At the same time, at least 16 thermocouple temperature measurement points are added outside the furnace shell (2) at the specified elevation of the junction. Then, the lumps or sintered refractory mud on the surface of the old bricks at the "rooting" base surface of the new furnace wall are cleaned and polished to the original color of the refractory bricks using an angle grinder, disc polisher and / or chisel. At the same time, according to the actual situation of the magnesia brick joint at the furnace bottom, each magnesia brick is dry-cut, disc polisher and / or manually processed to complete the preparatory work before masonry. During the masonry process, wet masonry is used for the steps of new and old bricks, the joints of bricks at the bottom of the furnace, and the first brick and the first layer of bricks for "rooting". The mortar is fully filled and the mortar joints meet the standards. Except for high alumina bricks, clay bricks and masonry in specified locations and quantities, which are wet masonry, all other magnesia bricks and new brick masonry are dry masonry using 180-mesh magnesia powder.

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