Shougang's 3#4000m3 blast furnace was put into operation on January 8, 2010. At present, due to the serious erosion of the furnace lining, it brings hidden dangers to the production safety, and because of the long-term addition of titanium furnace protection, the activity is reduced. In order to completely eliminate safety hazards, further achieve production and reduce consumption, at the end of June 2022, the 3# blast furnace will be organized to carry out maintenance operations, and Huaxi Technology Group will carry out maintenance projects such as furnace body spraying and lining.

1 Stop the wind and reduce the level operation

1.1 Make preparations before the wind stops

One week before wind maintenance, due to the decline of coke quality, the relationship between the pressure in the furnace is tight. Through active adjustment, the central gas is channeling, the furnace condition is stabilized, and the furnace temperature and physical heat are sufficient before the wind is stopped. Considering the residual iron situation, adding manganese ore to ensure the fluidity of hot metal. On June 26, when the load of the first step is withdrawn, the amount of 2t/ batch is added, and the manganese content in iron is controlled according to about 0.50%; When the full coke load is removed, the amount of 4t/ batch is added, and the manganese content is controlled according to about 0.80%. The adjustment in the furnace before wind shutdown is shown in Table 1.

1) Use of titanium ore. In order to ensure the effect of releasing residual iron, stop titanium ore in advance. After the titanium ore is stopped, the thermocouple temperature on the side wall of the furnace cylinder increases slightly, and the temperature at the bottom of the furnace rises by 10℃.

2) Fluorite usage. 72h before the start of the reduction level, 0.7t/ lot was added, and the CaF2 in the slag was 1.23%; When 0.8t/ lot was added 24h before the start of the falling level, the CaF2 in the slag was 2.67%, lower than the calculated value of 3.5%. Add 0.9t/ batch when the full coke load is reduced, and add 1.1t/ batch when the load is reduced to 2.5T. The maximum CaF2 in the slag was 3.1% during the process of lowering the feed level.

3) Usage of manganese ore. When 2t/ batch is added, [Mn] in iron is about 0.52%, reaching the calculated value of 0.5%. When adding 4t/ lot, the [Mn] in iron is about 1.0%, which is higher than the calculated value of 0.8%.

4) Coke usage. In June, the coke structure was 90% primary dry coke +10% Yaxin dry coke. Change to 100% wet coke when the full coke load is removed. In order to reduce the central coke pile tip, the charge is adjusted when the surface coke is capped to reduce the central coke amount.

5) Oxygen usage. With the reduction of blast furnace load, oxygen is gradually reduced from 24000m3/h to 8000m3/h in order to ensure reasonable combustion temperature. At 10:45 on the 29th, due to the high calorific value of gas nitrogen oxides exceeded the standard, oxygen was reduced to 5000m3/h. At 11:23, oxygen is off.

6) Equipment condition. Before dropping the material level, the spray nozzle is tested, and the average flow rate of a single tube is about 18.5t/h, and the actual maximum water pumping capacity is above 220t/h. The nitrogen routing was reformed, the flow meter data was connected to the duty room, and the nitrogen volume in the furnace was 1140m3/h.

1.2 Falling level process

At 8:25 on June 29, after adding the cover coke, the material level began to fall; At 11:23, the feed line entered the middle and lower part of the furnace body and stopped oxygen; At 14:20, the material line entered the furnace waist, and the nitrogen injection volume reached a maximum of 5500m3/h. Based on the results of gas composition analysis and radar probe data, the material surface position is determined. When H2% rises close to the CO2% value (FIG. 1), the feed surface is under the furnace body; When H2%>CO2%, the material surface enters the furnace waist; When CO2% rises, the feed surface enters the furnace belly and drops to the middle of the furnace belly. At 21:28, change to normal pressure to stop gas; At 3:18 on the 30th, the wind stopped and the work of lowering the material level was successfully completed.

The drop level began at 8:25 and changed to normal pressure at 21:28, and the total air consumption reached 3.51×106m3, accounting for 78.07%, taking 13h3min. The total air consumption of the atmospheric pressure section is 0.99×106m3, accounting for 21.93%, and takes 5h50min. A total of 18h53min was spent on the lowering of the material level.

The top temperature of the shutdown furnace is controlled at about 300-350℃, the minimum air volume of normal pressure is reduced to 1300m3/h, the wind pressure is reduced to 0.45kg/cm2, and the top pressure is reduced to 0.25kg/cm2.

This time, the air temperature of the high pressure section was reduced from 1121℃ to 900℃, and the air temperature of the normal pressure section was gradually increased, with the highest air temperature of 1002℃.

The relationship of pressure and volume is well controlled in the whole process of falling surface. The control is carried out in strict accordance with the curve of material line and air volume, and the detonation condition is avoided by timely active air reduction adaptation, and the material line is lowered to the lower part of the furnace belly with ideal effect.

1.3 Iron output

This drop surface adopts double iron field zero interval iron discharge. There are 9 times of iron pumping during the drop level, including 8 times in the high pressure section and 1 time in the normal pressure section. A total of 1723 tons of iron were produced in the first five times, after which no iron was found (Table 2).

1.4 Summary of falling level

After the full coke load is removed, the full wet coke is used to reduce the shutdown cost. High air volume oxygen enrichment method is adopted in the high pressure section before the material reduction, and the air volume top pressure matching is reasonable, which greatly speeds up the process of the material reduction surface and reduces the total air volume consumption. Furnace top water and top temperature control is ideal, the whole process does not occur knocking phenomenon.

Before the material reduction, in order to ensure the heat of the furnace cylinder, the load is removed in time. After the full coke load is removed, the operating parameters in the furnace are reasonable, the furnace temperature and iron temperature are suitable, and the furnace temperature in the whole process of falling level is sufficient. After the addition of manganese ore, the manganese content in iron reached the planned value, which improved the fluidity of hot metal and laid a foundation for the clean discharge of residual iron.

2 Discharge residual iron operation

2.1 Preparations

The maximum erosion depth of the furnace cylinder is calculated according to the temperature of each layer of the cooling wall, and the erosion is verified by the temperature measurement of the furnace skin. By calculating the amount of residual iron and combining with the actual situation on site, the elevation and Angle of the residual iron eye are determined.

2.2 Process of releasing residual iron

At 3:18 on the 30th, the blast furnace stopped blowing and began to cut the furnace skin.

At 20:38, the remaining iron was boiled and the remaining iron flowed out. Hot metal temperature 1120℃, the highest 1237℃.

23:55, plugging the residual iron eye, the residual iron work is finished.

The whole process takes 3h17min, and the residual iron released is estimated to be 700t.

3. Spray lining of furnace body

3.1 Construction process

Shougang 3#4000m3 blast furnace spraying adopts the sixth generation wet spray lining technology of West China Science and Technology, adopts 3D laser scanning of Beijing University of Science and Technology, analyzes the reasons for the corrosion of resistant materials of each part of the blast furnace according to different working conditions of each part of the blast furnace, and uses the upper and lower spray materials of the blast furnace lining in a targeted way. The spraying takes 48 hours to complete. Successfully completed the 3#4000m³ blast furnace repair project of Shougang Co., LTD. The construction not only restored to the designed furnace type, but also realized the purpose of fast slag hanging and rapid production. All the construction staff of Huaxi Technology, full of enthusiasm, high morale, pragmatic work style has been highly praised by customers, and won the "excellent Organization Award" of the project.

3.2 Advantages of the sixth generation wet jet lining technology

(1) The sixth-generation wet spray lining technology of Huaxi Technology completely uses sol bonding, so that the combination of materials has affinity, and the material structure is further optimized, abandoning the traditional water-adding bonding process, and completely solving the phenomenon of poor water-material bonding in the traditional process and easy to fall off after bonding.
(2) According to the construction feedback over the years, the construction rebound rate is less than 5%, and no dust and toxic and harmful gases are produced during injection, and no environmental pollution is caused, so as to avoid the normal operation of TRT due to dust.
(3) The lining formed by high pressure injection, the formation of a high density lining in the blast furnace lining, low porosity, high density, erosion resistance and wear resistance, so as to achieve the purpose of rapid slag hanging and rapid production.
(4) Stabilizing the edge gas flow and improving the smelting intensity of the blast furnace has an obvious effect.
(5) Rapid recovery of reasonable furnace type, increase output, reduce energy consumption, is one of the most efficient and effective methods for blast furnace longevity.
(6) Intelligent lining, energy saving and consumption reduction lining, after the blast furnace is opened, nitrogen will be produced, and the furnace wall is combined twice to continuously intelligently maintain the furnace lining, so that the gas flows to the center of the blast furnace, so as to achieve the effect of energy saving and consumption reduction. According to the production data statistics of iron and steel enterprises, the coke reduction ratio of the sixth generation wet spray lining technology in West China can reach up to 7%, the utilization coefficient is improved, and the average direct profit benefit of hot metal is nearly 50 million yuan!

3.3 Theron high strength compound injection material research and development concept

(1) The use of metal (Si/Al) ductility to achieve plastic molding, using the nitriding and reduction atmosphere in the blast furnace to achieve the use of the original synthetic high temperature reinforcement phase (Si3N4/SiAlON), and non-oxide substrate to form a perfect inlay structure, while achieving:
◆ Excellent resistance to chemical erosion

◆ It has self-repair function during use

◆ Good thermal shock resistance

(2) Based on the metal-non-oxide composite material system, through the non-oxide surface modification, the sol-gel molding process is used to achieve:
◆ Good liquidity

◆ Fast drying performance

◆ Overall stability after drying

The sixth generation Silon high-strength composite spray material of Huaxi Technology solves the defects of traditional cement combined spray coating. It has excellent wear resistance, good chemical stability, higher bending strength, better thermal conductivity, and high-quality slag making ability.

4 Open the furnace for air supply operation

4.1 Prepare for air supply

At 0 o 'clock on August 2, the 3# blast furnace officially began to bake.

At 10:10 on the 6th, the oven was completed, and the blast furnace was cooled, loaded and compressed.

At 9:28 on the 9th, the loading and opening of the charge began. Coke is filled from 1.5m below the center line of the tuyere to the center line of the tuyere, and 31 batches of clean coke, 29 batches of empty coke and 17 batches of normal material are added above the center line of the tuyere. The coke ratio of the whole furnace is 3.07t/tHM, the total slag ratio is 782kg/tHM, the total iron content is 605t, the total slag content is 473t, the alkalinity R2=0.72, Al2O3= 19.94%, MgO=3.54%, CaF2=4.66%.

4.2 Air Supply Operations

At 21:6 on the 9th, the blast furnace began to resume air supply.

Before air supply, 8 air outlets are blocked, and the air supply area is 0.3618m2. When supplying air, use the vent valve to control the air pressure and air volume. At 21:25, the 11# and 12# tuyere see light; 22:30, the tuyere all see light; At 2:18 on the 10th, the gas composition was qualified and the gas was pumped. At 2:27, the air volume increased from 2300m3/min to 2500m3/min, and the top pressure was automatically adjusted. At 3:33, the air was increased to 3600m3/min, and then the air volume stabilized at 3600m3/min. After 8 o 'clock, with the formation of the soft melting zone, the pressure relationship is gradually tightened, the pressure difference in the furnace is controlled (≯ 0.8kg /cm2), and the top temperature is gradually increased. After 14:00, the soft melt zone basically formed, and the cumulative air supply volume was 2.956 million m3. The composition of gas during the formation of soft melt zone is shown in Figure 2.

At 21:51 on the 10th, the cumulative air volume reached 4.4 million m3, and the first iron was produced as planned. Iron production time is 61min, iron output is 227t. 31min after slagging, the slag flow is good, and the first iron is washed with water. The maximum physical heat of hot metal is 1497℃, and the maximum furnace temperature is 4.45%. With the increase of air volume and the increase of load, the level of furnace temperature decreases gradually. During the day of the 11th, the furnace temperature began to drop below 2%, and the recovery rhythm accelerated. 10:58, the tuyere is fully opened, and the air volume is increased to 5200m3/min; At 18:46, the air volume increased to more than 6300m3/min, so that the 3# blast furnace took 45h40min to reach the full air. At 2300 hours, the load increased to 4.06. The control of Si content in hot metal in the air volume recovery stage is shown in Figure 3.
4.3 Air Supply summary

1) The opening process of the 3# blast furnace is smooth. The full blast furnace production was realized after 45h40min, indicating that the opening plan was reasonable, fully considered and strictly implemented in the recovery process. This furnace opening practice provides important reference for future related work.

2) The rhythm of adding air and stabbing tuyere in the air supply process is well mastered. According to the temperature level of the furnace, the wind speed is strictly controlled to ensure the rapid and stable air supply process, and there is no pipeline, suspension and other accidents, and no bad tuyere phenomenon.

3) Iron slag fluidity is better in the first furnace opening. The hot metal goes directly into the torpedo tank, the slag washes away, and the furnace temperature is sufficient and reasonable. The reasonable addition of fluorite ensures the normal flow of slag iron and provides an effective guarantee for rapid recovery.

4) Supply air recovery air volume and load match well. The better matching between the two is conducive to the stable and slow decline of Si content in iron, and speeds up the recovery progress of air volume.