Rapid recovery method for long-term damping down of large blast furnace

Abstract

The invention provides a rapid recovery method for long-term damping down of a large blast furnace, and aims to solve the problems of long reblowing time, high recovery cost loss and the like after long-term damping down of the blast furnace in the prior art. Comprising the following steps: S1, carrying out sectional charging control before damping down: S11, stopping small-size fraction consumption of a blast furnace in 2-2.5 T smelting time before damping down, and increasing the coke ratio in the furnace through natural weight reduction of ore batches; s12, 1.3-1.7 T smelting time before damping down is conducted, the ore batch weight is reduced, the coke amount is not changed, and the coke ratio is increased for the second time; s13, in 1.3-1.7 T smelting time before damping down, the coke amount is changed, the in-furnace coke ratio is increased, and the in-furnace alkalinity is checked according to the preset first molten iron silicon content; s14, 0.6-0.8 T smelting time before damping down is conducted, and two-section type net coke adding is achieved; s15, 0.2-0.4 T smelting time before damping down, the basicity of the slag is checked according to the preset second molten iron silicon content, the raw material structure is adjusted, and the checked final slag basicity is kept unchanged; s2, heat loss control in the damping-down period; and S3, air pressure guided reblowing rapid recovery is carried out.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method for rapid recovery of a large blast furnace after a long-term shutdown. Background Technology

[0002] During the production cycle, blast furnaces often need to shut down due to equipment maintenance, environmental protection restrictions, or sudden malfunctions. For long-term shutdowns exceeding 12 hours, blast furnaces face severe thermal challenges. 1. Huge heat loss: During the shutdown period, combustion stops, but the furnace cooling wall, tuyeres and furnace bottom water cooling system are still running, continuously taking away a large amount of sensible heat. For low silicon smelting blast furnaces, due to their low heat reserves, they are very prone to "furnace cooling", which can lead to the hearth freezing in severe cases, and slag and iron cannot be discharged after the blast is restarted. 2. Deterioration of air permeability: During the shutdown process, as the air stops, the material column loses the support of gas buoyancy and is compressed. The position of the softening zone moves down and solidifies, resulting in a decrease in the porosity of the material layer. In the early stage of re-airing, cold air has difficulty penetrating the dense material column, which can easily lead to excessive edge airflow or local pipes, causing material suspension. 3. Long recovery period: Traditional recovery methods usually require 6 to 12 hours or even longer to restore normal air volume and output. During this period, the coke ratio increases significantly, producing a large amount of substandard pig iron with high silicon and high sulfur content, resulting in huge economic losses. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for rapid recovery of large blast furnaces after long-term shutdown, aiming to solve the problems of long restart time and large cost of blast furnace recovery in the prior art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for rapid recovery of a large blast furnace after a long-term shutdown includes the following steps: S1. Set the blast furnace smelting cycle T 冶 Segmented loading control before ventilation shutdown: S11. 2-2.5 T before the wind stops. 冶 During this period, the consumption of small particles in the blast furnace is stopped, and the coke ratio is increased by naturally reducing the weight of the ore batch while keeping the original coke batch weight unchanged. S12. 1.3 to 1.7 T before the wind stops. 冶 During this period, the ore batch weight is reduced to 90% of the original batch weight without changing the amount of coke, and a second coke ratio increase is carried out. S13. 1.3–1.7 T before the wind stops. 冶 The time was adjusted, the amount of coke was changed, the coke ratio was increased again, and the basicity of the feed to the furnace was checked according to the preset silicon content of the first molten iron, and the raw material structure was adjusted. S14. 0.6–0.8 T before the wind stops.冶 Add time to the first settling, with an interval of 0.1 to 0.3 T. 冶 A second coke removal process is added after a certain time, achieving a two-stage coke removal process. S15. 0.2–0.4 T before the wind stops. 冶 Time, check the slag basicity according to the preset second iron silicon content and adjust the raw material structure to keep the final slag basicity unchanged; S2. Heat loss control during ventilation shutdown: After the blast furnace is shut down, the flow rates of soft water and high-pressure water in the cooling system are reduced in stages according to the duration of the shutdown. S3. Rapid recovery of wind pressure-guided re-airflow: The system rapidly increases air volume by operating according to air pressure, restoring the target air volume within a specified time, and then restores oxygen enrichment and pulverized coal injection based on the probe's movement.

[0005] Furthermore, in step S1, the blast furnace smelting cycle T 冶 = (Blast furnace working volume / (mass of each raw material / specific gravity of each raw material + weight of each fuel / specific gravity of each fuel) / 0.85) / number of batches of materials in the last 24 hours.

[0006] Furthermore, in step S11, after stopping the consumption of small-particle ore, the coke ratio fed into the furnace is increased from 330-340 kg / tFe in normal production to 340-350 kg / tFe.

[0007] Furthermore, in step S12, the coke ratio fed into the furnace is increased to 360-370 kg / tFe.

[0008] Furthermore, in step S13, the coke ratio fed into the furnace is increased to 380-390 kg / tFe.

[0009] Furthermore, in step S13, the preset silicon content of the first molten iron is 0.5 to 0.7.

[0010] Furthermore, in step S14, the two-stage net coke addition method is as follows: First coke cleaning: The amount added is calculated based on the downtime. 1 to 1.2 tons of clean coke are added every hour of downtime, and the clean coke in this section is controlled to reach the lower part of the furnace waist at the time of downtime. Second round of coke cleaning: The amount added is calculated based on the downtime. 0.7 to 0.9 tons of clean coke are added every hour of downtime, and the clean coke in this section is controlled to reach the lower part of the furnace body during the downtime.

[0011] Furthermore, in step S15, the preset silicon content of the second molten iron is 0.3 to 0.4%.

[0012] Furthermore, in step S2, the heat loss control during the ventilation shutdown period includes the following methods: Two hours after the blast furnace is shut down, the soft water flow rate is controlled to 3 / 4 of the normal flow rate, and the high-pressure water flow rate is controlled to 1 / 2 of the normal flow rate. The blast furnace was shut down for 4 hours, and the soft water flow rate was reduced to half of the normal production rate.

[0013] Furthermore, in step S3, the specific operation of restoring the ventilation parameters is as follows: Rapid pressurization phase: Increase airflow rapidly by 50 kPa each time, and the airflow will recover to 75% of normal within 15-25 minutes; Pressure stabilization observation phase: After reaching 75% air volume, run the system stably for a preset time and observe whether the air permeability index is at a normal level. Fine-tuning to reach full production capacity: If the air permeability index is normal, continue to increase the air volume by 10 kPa each time until the normal air volume is reached; Pulverized coal injection recovery: If the probe starts to move during the ventilation period, immediately resume the oxygen-enriched and pulverized coal injection operation.

[0014] The technical solution provided by this invention has the following advantages compared with the prior art: By changing the charging method for the two smelting cycles before the blast furnace shutdown, controlling the position of net coke before the shutdown, changing the amount of heat loss during the blast furnace shutdown, and changing the parameter recovery process after the blast furnace restarts, the rapid recovery of long-term shutdown of large blast furnaces can be achieved. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] This invention provides a method for rapid recovery of a large blast furnace after a long-term shutdown, comprising the following steps: S1. Set the blast furnace smelting cycle T 冶 Segmented loading control before ventilation shutdown; Specifically, T 冶 = (Blast furnace working volume / (mass of each raw material / bulk density of each raw material + weight of each fuel / bulk density of each fuel) / 0.85) / number of batches of materials in the past 24 hours. The smelting cycle is calculated based on 85% of the material in the furnace. The cycle time is calculated based on the actual number of batches of materials in the past 24 hours. For a 3000m³ blast furnace, it is about 6 hours. The blast furnace shutdown time is T. 休 (Time units are all in hours, and long-term shutdown time is 12-48 hours).

[0017] Pre-shutdown sectional loading includes five stages: S11 to S15. S11. 2-2.5 T before the wind stops. 冶 During this period, the consumption of small particles in the blast furnace is stopped. While maintaining the original weight of the coke batch, the coke ratio is increased by the natural weight reduction of the ore batch. The coke ratio will be increased to 340-350 kg / tFe (normal production is 330-340 kg / tFe). By discontinuing the use of small-particle ore, the permeability of the furnace charge column (permeability = air volume / pressure difference) during the shutdown process is increased by 1-3, avoiding changes in the smelting cycle caused by poor permeability before shutdown. This is achieved within 2 T before shutdown. 冶 Stop consuming small-particle ore and reduce costs while meeting ventilation requirements.

[0018] S12. 1.3 to 1.7 T before the wind stops. 冶 During this period, the ore batch weight was reduced to 90% of the original batch weight (the 3000m³ blast furnace was reduced from 100 tons to 90 tons), without changing the amount of coke, and a second coke ratio increase was carried out, raising the coke ratio into the furnace to 360-370 kg / tFe. Continue to increase the coke ratio into the furnace to avoid fluctuations in the coke ratio into the furnace exceeding 20 kg / tFe in the next operation, which would affect the accuracy of the shutdown process calculation. Moreover, by gradually increasing the coke ratio into the furnace through S11 and S12, the heat can be increased. Compared with the traditional method of centrally adding clean coke to the hearth, this can reduce fuel cost waste and ensure that the production parameters of low silicon smelting are under control.

[0019] S13. 1.3–1.7 T before the wind stops. 冶 Adjust the amount of coke and increase the coke ratio in the furnace to 380-390 kg / tFe. Adjust the raw material structure by checking the basicity of the feedstock according to the silicon content of the molten iron (0.5-0.7). Basicity = (CaO per ton of iron) / (SiO2 per ton of iron - Si content in molten iron / 100) 1000 60 / 28); The coke ratio is further increased to over 380 kg / tFe to ensure that all the furnace charge inside the blast furnace is replaced with charge from the resting furnace. The estimated increase in the coke layer thickness at the furnace waist is 0.015–0.020 m, which is conducive to the rapid recovery of parameters during the restart of the blast furnace. Furthermore, the basicity change is checked according to the change in silicon content of molten iron to avoid the impact of slag phase changes on the rapid recovery process of the restart of the blast furnace. The coke ratio is controlled according to the thickness of the coke layer at the furnace waist, which is more accurate than the traditional coke ratio calculation and control.

[0020] S14. 0.6–0.8 T before the wind stops. 冶 The time is added to the first coking process. The amount of coking for the first process is calculated based on the downtime, adding 1 to 1.2 tons every hour, with an interval of 0.1 to 0.3 tons. 冶After a certain time, a second batch of clean coke is added. The amount of the second batch of clean coke is calculated based on the downtime, with 0.7 to 0.9 tons added every hour. The timing of adding clean coke is calculated based on the smelting cycle to ensure that before the blast furnace shutdown, the first clean coke reaches the lower part of the furnace waist (16m from the lower edge of the furnace throat in a 3000m³ blast furnace), and the second clean coke reaches the lower part of the furnace body (12m from the lower edge of the furnace throat in a 3000m³ blast furnace). Precise control of the clean coke position ensures that the first clean coke after the blast furnace restarts improves the permeability of the softening zone, facilitating rapid parameter recovery; the second clean coke increases the heat of the blast furnace hearth, preventing furnace cooling caused by rapid parameter recovery. By adopting a two-stage coke addition method, the minimum cost is achieved while meeting the permeability requirements of the softening zone and replenishing the heat loss after the blast furnace restarts.

[0021] In steps S11 to S13, the physical heat of the hearth has been raised to 1500-1550℃ in conjunction with the adjustment of the injection volume. The heat loss of the hearth is essentially physical heat, not chemical heat. Adding coke to increase the silicon content of the molten iron (chemical heat) is meaningless. Furthermore, the upward furnace temperature after the blast furnace is restored is not conducive to the rapid recovery of parameters. Another reason is that multi-stage coking will have more uncertainties, such as the coking position and changes in local permeability, which will increase the difficulty of process control.

[0022] S15. 0.2–0.4 T before the wind stops. 冶 Time, check the slag basicity according to the preset second iron silicon content and adjust the raw material structure to keep the final slag basicity unchanged; Before the shutdown, the furnace charge structure is planned for the parameter recovery process after the shutdown to ensure that the blast furnace can quickly return to normal production after restarting. Before the shutdown, the charge column in the furnace is adjusted according to the silicon content of the molten iron in two stages. Based on the influence of the shutdown process on the silicon content of molten iron in steps S11 to S13, the silicon content of molten iron in each stage is controlled by adjusting the injection volume. Then, the change of slag phase is calculated based on the silicon content, and the structure is adjusted in advance to stabilize the slag phase, so as to avoid the difficulty of recovery caused by the increase of pressure difference due to overheating in the furnace during the shutdown and restart process.

[0023] S2. Heat loss control during ventilation shutdown: After the blast furnace is shut down, the flow rates of soft water and high-pressure water in the cooling system are reduced in stages according to the duration of the shutdown. Specifically, after the blast furnace is shut down, the soft water flow rate is controlled to 3 / 4 of the normal rate for 2 hours, and the high-pressure water flow rate is controlled to 1 / 2 of the normal rate. After the blast furnace is shut down for 4 hours, the soft water flow rate is controlled to 1 / 2 of the normal production rate to ensure that the heat from the combustion of the clean coke can compensate for the heat loss carried away by the cooling.

[0024] S3. Rapid recovery of wind pressure-guided re-airflow: Increase the air volume rapidly by 50 kPa each time, and the air volume will recover to 75% of the normal level in 15-25 minutes (approximately 4000 m³ / min for a 3000 m³ blast furnace); stabilize for 3 minutes, observe that the permeability index is at a normal level, and continue to increase the air volume by 10 kPa each time until the normal air volume is reached. During this period, the probe will start to move, which means that oxygen enrichment and pulverized coal injection will be restored.

[0025] Using the method of rapid air increase based on air pressure, compared to the method of air volume, can better stabilize the permeability of the furnace within a controllable range (25-35). It avoids the fluctuations in airflow in the furnace caused by the mutual influence between air pressure and air volume when operating based on air volume. Because when operating based on air volume, as the air volume increases, the air pressure increases and the air volume automatically decreases, which may mislead the operator to continue to increase the air volume, making the recovery process difficult to control.

[0026] The technical solution of this application will be described in detail below through a specific implementation case of the applicant: From 7:46 on April 12, 2024 to 18:48 on April 13, 2024, the No. 3 blast furnace was shut down for a long period of 2102 minutes. 1. Furnace temperature control: On the 11th, during the day and afternoon shifts, the furnace temperature is controlled at 0.25% to 0.35%, with a physical heat of ≥1500℃. During the night shift, the furnace temperature is gradually increased, and the final furnace temperature is controlled at 0.35% to 0.40%, with the actual basicity controlled at 1.20 and the physical heat of molten iron above 1500℃.

[0027] 2. Loading during rest period: At 19:00 on April 11, small mines will cease operations. The ore batch size is 94t (originally 98t), and the coke ratio is 347kg / t. Note that the coke batch size remains unchanged. At 22:00 on April 11, the load was reduced to 90t, the coke ratio was increased by 16kg / t (coke ratio 363kg / t), the load was 4.76, the reference coal powder was 40t / h, R2 was controlled at 1.13±0.02, and MgO / Al2O3 was 0.75±0.05. At 1:00 AM on April 12th, the load was reduced, the ore batch was 90t, the coke ratio was increased by 22kg / t (coke ratio 385kg / t), the coke batch was increased by 1300, the load was 4.46, the reference pulverized coal was 35t / h, the batch volume was 82.15, R2 was controlled at 1.13±0.02 (0.6 silicon), MgO / Al2O3 was 0.75±0.05, and the reference furnace charge structure was high alkali 58.3% + low alkali 27.5% + lump ore 14.2%; At 3:00 AM on April 12th, 40 tons of clean coke were added (the clean coke was added in two batches of 20+20 along with the coke batches from 3:00 AM to 3:10 AM, reaching the lower middle part of the furnace body, 16 meters away from the lower edge of the furnace throat, during the shutdown period). After an interval of 493 m³ (approximately 6 batches of material), 30 tons of clean coke were added (the clean coke was added in two batches of 20+10 along with the coke batches, reaching the lower middle part of the furnace body, 12 meters away from the lower edge of the furnace throat, during the shutdown period). After that, about 16 more batches of material were added and the shutdown period was stopped. At 5:00 AM on April 12th, the ore batch was 90 tons, the coke ratio remained unchanged at 385 kg / t, the load was approximately 4.48, R2 was controlled at 1.13 ± 0.02 (0.35 silicon), MgO / Al2O3 was 0.75 ± 0.05, and the reference furnace charge structure was 60.9% high alkali + 24.5% low alkali + 14.6% lump ore.

[0028] 3. Re-ventilation operation (1) At 18:48 on April 13, the air was restored, 4 air outlets were blocked, and the air was quickly added. At 19:11, the air volume was 4200, the air pressure was 275, and the air supply line was 2.5m. (2) 19:33 Air volume 4200, air pressure 310, coal injection; 19:40 Air volume 4500, air pressure 328, oxygen enrichment 2500; (3) 20:04 Air volume 5000, air pressure 333, top pressure 181, full air, open No. 3 iron tap to output iron; (4) On the 14th, wind vents 15#, 23#, 7# and 30# were opened, and wind vent 30# was opened at 6:52 on the 14th, so all wind vents were open.

[0029] In this embodiment, the entire ventilation process takes only 75 minutes, which effectively improves the ventilation efficiency compared to the traditional ventilation shutdown and ventilation method.

[0030] Taking a 3000m³ blast furnace as an example, with a maintenance cycle of 4 months, this method can reduce iron production loss by 1200 tons per blast furnace maintenance. Based on a benefit of 100 yuan per ton of iron, this translates to a benefit of 1200 tons per maintenance. 300 yuan / ton = 360,000 yuan, annual profit 12 5 = 1.8 million yuan / year.

[0031] Moreover, rapid blast furnace recovery can reduce the adverse effects on other processes during the recovery process and reduce the consumption of energy media per ton of iron during the recovery process.

[0032] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rapid recovery of a large blast furnace after a long-term shutdown, characterized in that, Includes the following steps: S1. Set the blast furnace smelting cycle T 冶 Segmented loading control before ventilation shutdown: S11. 2-2.5 T before the wind stops. 冶 During this period, the consumption of small particles in the blast furnace is stopped, and the coke ratio is increased by naturally reducing the weight of the ore batch while keeping the original coke batch weight unchanged. S12. 1.3 to 1.7 T before the wind stops. 冶 During this period, the ore batch weight is reduced to 90% of the original batch weight without changing the amount of coke, and a second coke ratio increase is carried out. S13. 1.3–1.7 T before the wind stops. 冶 The time was adjusted, the amount of coke was changed, the coke ratio was increased again, and the basicity of the feed to the furnace was checked according to the preset silicon content of the first molten iron, and the raw material structure was adjusted. S14. 0.6–0.8 T before the wind stops. 冶 Add time to the first settling, with an interval of 0.1 to 0.3 T. 冶 A second coke removal process is added after a certain time, achieving a two-stage coke removal process. S15. 0.2–0.4 T before the wind stops. 冶 Time, check the slag basicity according to the preset second iron silicon content and adjust the raw material structure to keep the final slag basicity unchanged; S2. Heat loss control during ventilation shutdown: After the blast furnace is shut down, the flow rates of soft water and high-pressure water in the cooling system are reduced in stages according to the duration of the shutdown. S3. Rapid recovery of wind pressure-guided re-airflow: The system rapidly increases air volume by operating according to air pressure, restoring the target air volume within a specified time, and then restores oxygen enrichment and pulverized coal injection based on the probe's movement.

2. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S1, the blast furnace smelting cycle T 冶 = (Blast furnace working volume / (mass of each raw material / specific gravity of each raw material + weight of each fuel / specific gravity of each fuel) / 0.85) / number of batches of materials in the last 24 hours.

3. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S11, after stopping the consumption of small-particle ore, the coke ratio fed into the furnace is increased from 330-340 kg / tFe in normal production to 340-350 kg / tFe.

4. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S12, the coke ratio fed into the furnace is increased to 360-370 kg / tFe.

5. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S13, the coke ratio fed into the furnace is increased to 380-390 kg / tFe.

6. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S13, the preset silicon content of the first molten iron is 0.5 to 0.

7.

7. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S14, the two-stage net coke addition method is as follows: First coke cleaning: The amount added is calculated based on the downtime. 1 to 1.2 tons of clean coke are added every hour of downtime, and the clean coke in this section is controlled to reach the lower part of the furnace waist at the time of downtime. Second round of coke cleaning: The amount added is calculated based on the downtime. 0.7 to 0.9 tons of clean coke are added every hour of downtime, and the clean coke in this section is controlled to reach the lower part of the furnace body during the downtime.

8. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S15, the preset silicon content of the second molten iron is 0.3 to 0.4%.

9. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S2, heat loss control during the shutdown period includes the following methods: Two hours after the blast furnace is shut down, the soft water flow rate is controlled to 3 / 4 of the normal flow rate, and the high-pressure water flow rate is controlled to 1 / 2 of the normal flow rate. The blast furnace was shut down for 4 hours, and the soft water flow rate was reduced to half of the normal production rate.

10. The method for rapid recovery of a large blast furnace after a long-term shutdown according to claim 1, characterized in that, In step S3, the specific operation of restoring the ventilation parameters is as follows: Rapid pressurization phase: Increase airflow rapidly by 50 kPa each time, and the airflow will recover to 75% of normal within 15-25 minutes; Pressure stabilization observation phase: After reaching 75% air volume, run the system stably for a preset time and observe whether the air permeability index is at a normal level. Fine-tuning to reach full production capacity: If the air permeability index is normal, continue to increase the air volume by 10 kPa each time until the normal air volume is reached; Pulverized coal injection recovery: If the probe starts to move during the ventilation period, immediately resume the oxygen-enriched and pulverized coal injection operation.