Strengthening raw material and fuel quality management
Stabilize the quality of raw materials and fuel entering the furnace
The quality of raw materials entering the furnace has a great impact on the furnace condition of the blast furnace. The stability of raw materials quality is the basis for the smooth operation of the blast furnace.
Blast furnace No. 1 adopts a charge structure of sintered ore + alkaline balls + lump ore. The proportion of pellets accounts for 52% to 65% of the charge structure, and the grade of the charge is 61.4%.
In the daily production of No. 1 blast furnace, great attention is paid to the quality management of raw materials. Online sampling is carried out every 4 hours for raw material quality inspection, and the inspection results are uploaded to the iron-front MES data system, which is convenient for the blast furnace to track the quality of raw materials in time, predict the furnace condition, and take measures in advance.
The quality parameters of raw materials entering the No. 1 blast furnace are shown in Tables 1 to 3. The coke adopts the full dry coke process, and the coke has good quality and high strength, which can meet the production needs of large blast furnaces.
By establishing an integrated iron-front system, the ore and coal distribution structure is stabilized and optimized to ensure the long-term stability of the quality of sintered ore, pellets and coke entering the furnace.
Strengthen screening management
According to the calculation results of Ergun formula, the particle size has a great influence on the pressure difference in the blast furnace. When the particle diameter is less than 5mm, the pressure difference in the furnace will rise sharply, affecting the furnace condition. Strengthening screening management can effectively reduce the small particles in the raw materials and the powder generated during transportation from entering the furnace, and improve the pressure-volume relationship in the furnace.
In daily management, before starting the feeder, start the vibrating screen 3s in advance. After stopping the feeder, delay 30s before stopping the vibrating screen. By adjusting the start and stop time, the vibrating screen can be vibrated without load before the heavy vehicle runs, which can effectively avoid the accumulation of materials on the screen surface after stopping the feeder, and increase the opening rate of the screen to more than 90%.
By optimizing and improving the “Screen Inspection Regulations for the Loading Team”, the 4th shift and the day shift personnel are required to check all the screens once every shift, implement daily inspection and maintenance of the working status of the screens, clean and maintain the screens in time, ensure the long-term clean surface of the screens, avoid the blockage of the screens before screening, and increase the screen opening rate to more than 98%.
Increasing the screen opening rate can effectively improve the screening effect under the silo, reduce the small particles and powder entering the furnace, and improve the air permeability of the upper area of the blast furnace. While maintaining the screen, the feeding amount of various raw materials is also strictly controlled. The feeding amount of coke is less than 30kg/s, the feeding amount of sintered ore is 60kg/s, and the feeding amount of pelletized ore is less than 70kg/s to prevent the accumulation of raw materials from affecting the screening effect. In the management system, you can also query the screening flow rate of the past 10 times, and the material flow rate compliance rate for the whole day can be calculated to fully ensure the quality of the raw fuel entering the furnace.
Control harmful elements entering the furnace
During the blast furnace smelting process, the entry of harmful elements such as alkali metals and zinc into the furnace and their circulation and enrichment in the furnace have a significant negative impact on the blast furnace and its smelting process. Alkali metals can reduce the softening temperature of the ore, causing abnormal expansion of the pellets and causing them to become severely pulverized. Strengthening the gasification reaction capacity of coke will cause the strength of the coke to drop sharply after the reaction and cause pulverization, endangering the normal blast furnace smelting. By optimizing the ore blending, using highly harmful ore powder with low harmful ore powder, optimizing the dust removal ash blending mechanism, strictly controlling the blast furnace alkali metal <3kg/t, and the zinc load <150g/t (see Figure 1), the impact of harmful elements entering the furnace on blast furnace production can be reduced.
Optimize the charging system
As one of the four major operating systems of the blast furnace, the charging system is an important factor in regulating the distribution of upper coal gas flow and affecting the shape of the soft melting zone in the furnace. Appropriate coke distribution helps to improve the distribution of coal gas flow and form a reasonable shape of the soft melting zone, which is beneficial to the preheating and reduction of ore and the improvement of coal gas utilization.
The No. 1 blast furnace currently adopts a high-proportion pellet smelting process, with the highest proportion of pellets reaching 65%. Compared with sintered ore, pellets have high sphericity and good rolling properties, and have a small natural stacking angle in the furnace. After charging, the charge surface is flatter, and the charge tends to be heavier in the center and edge of the blast furnace. In order to alleviate the impact of the increase in the proportion of pellets on the charge distribution, and to improve the comprehensive charge metallurgical properties by the interaction between sintered ore and pellets, the blast furnace charging and charging system are optimized.
The blast furnace adopts ore mixing, and the sintered ore and pellets are mixed by belt feeding to reduce the rolling effect of the pellets in the furnace and enhance the stability of the charge surface. Due to the interaction between different metal materials, the softening temperature reduction and the expansion of the melting temperature range after mixing are alleviated, the charge softening temperature range is reasonable, and the permeability of the middle and lower areas remains at a normal level. After the proportion of pellet ore increases, it has a strong inhibitory effect on the center gas of the blast furnace. The blast furnace charging system control follows the principle of “opening the center, stabilizing the edge; stabilizing the center, taking care of the edge”, and adopts the edge platform + center coking charging method. The ore batch weight is controlled according to the principle of large ore batch, and the batch weight is 182-188t. Through the adjustment of the charging system, the blast furnace gas distribution is more reasonable, among which the edge temperature is controlled at 70-100℃, the W value is 0.4-0.6; the center temperature is 300-600℃, and the Z value is 8-12 (see Figure 2).
Optimize air supply system
The air supply system affects the size and shape of the tuyere whirlpool area in the blast furnace, and affects the initial distribution of the blast furnace gas flow. Reasonable wind speed and kinetic energy are crucial to improving the initial gas distribution of the blast furnace, increasing the activity of the furnace, and maintaining the long-term stability of the furnace condition. Blast furnace No. 1 is equipped with 42 tuyere and the basic air volume is set at 8300m3/min. By continuously optimizing the air supply area (0.5587m2→0.5555m2→0.5546m2→0.5536m2→0.5519m2→0.5498m2), the blast furnace maintains an actual wind speed of 235~255m/s and a blast kinetic energy of 12500~14500kg·m/s (see Figure 3). This can ensure that the initial gas distribution is uniform and reasonable, maintain appropriate wind speed and kinetic energy so that the length of the tuyere vortex zone is appropriate, which can not only blow through the furnace of the giant blast furnace, but also make the edge and center gas distribution reasonable, and obtain ideal gas utilization rate.
Increase oxygen enrichment rate
Oxygen-enriched blast is to add industrial oxygen to the blast furnace to make the oxygen content of the blast exceed the oxygen content of the atmosphere, thereby improving the production efficiency of the blast furnace and reducing the coke ratio and the production cost per ton of iron. From the perspective of smelting, the main effect of blast furnace oxygen enrichment is to increase production. The main effects of oxygen-enriched blast on blast furnace smelting are:
1) Improve the smelting intensity in the blast furnace. As the oxygen content in the wind increases, the amount of air required to smelt each ton of iron decreases. If the amount of air entering the furnace remains unchanged, the smelting intensity can be increased. Studies have shown that theoretically, if the oxygen enrichment rate increases by 1%, the blast furnace can increase production by 4.76%. The actual increase in production is lower than this value. As the oxygen enrichment increases, the increase in blast furnace production decreases.
2) Increase the furnace temperature. As the temperature of the combustion zone increases, the heat exchange between the coal gas and the charge in the lower part of the blast furnace is significantly improved, so that the heat of the blast furnace is concentrated in the lower part. Compared with ordinary blasting, the temperature level from the furnace to the furnace belly area is significantly improved, which is conducive to the reduction of some difficult-to-reduce elements such as silicon and manganese.
3) Increase the content of CO and H2 in the coal gas. After oxygen-enriched blasting, the amount of CO in the coal gas increases due to the high oxygen content and reduced nitrogen content in the wind. When oxygen-enriched blasting is combined with fuel injection, the fuel injection amount can be increased, so that the amount of CO and H2 in the coal gas increases, which is beneficial to the development of indirect reduction.
4) Reduce the temperature of the upper part of the blast furnace. After oxygen enrichment, although the temperature of the combustion zone increases, the amount of gas per unit of pig iron is reduced, the gas-water equivalent is reduced, and the heat that the gas can transfer to the charge is correspondingly reduced, making the heat exchange intensity much greater than that of ordinary blasting. Therefore, the gas is rapidly cooled by the charge after leaving the combustion zone, and its temperature drops rapidly, and the furnace top temperature is significantly lower than that of ordinary blasting.
Blast Furnace No. 1 uses a combination of oxygen addition before the blower and oxygen addition after the blower to control the oxygen content. From October to November 2022, the oxygen enrichment rate of the blast furnace gradually increased from 7.0% to 8.0%, and in January 2023 it increased to 8.2%. At present, the oxygen enrichment rate of the blast furnace is stable at 8.2%, as shown in Figure 4.
Increase oxygen enrichment rate
High blast temperature is an important measure to achieve energy conservation in ironmaking blast furnaces[8]. Blast temperature is one of the important heat sources for blast furnace ironmaking, accounting for 20% to 30% of the total heat input of the blast furnace. The high or low blast temperature level has a great influence on the coke ratio and theoretical combustion temperature.
When the hot blast temperature increases by 100°C, the coke ratio for ironmaking can be reduced by 15 to 20 kg/t, and the theoretical combustion temperature of the tuyere can be increased by 60 to 80°C. No. 1 blast furnace is equipped with four “Kalukin-type” top-fired hot blast furnaces with a designed blast temperature of 1300°C. In July 2022, after the overhaul of No. 2 hot blast furnace, the blast temperature has been below 1220°C. In January 2023, the overhaul of No. 2 hot blast furnace was completed and put into use, and the blast temperature was gradually increased from 1220°C to 1250°C (see Figure 5). After the blast temperature increased, the furnace condition was stable, the smelting intensity of the blast furnace was improved, and the fuel ratio was reduced by about 5 kg/t.
Increase top pressure
High pressure operation is one of the means of strengthening smelting in blast furnaces. High pressure operation has the following advantages:
1) Strengthen the smelting process and increase output.
2) Reduce coke consumption to a certain extent.
3) Reduce the amount of furnace dust blown out.
4) Energy can be recovered.
5) Reduce the silicon content of pig iron.
Increasing the top pressure can reduce the coke ratio to a certain extent, and at the same time, it can also reduce the silicon content of pig iron, which indirectly reduces the fuel ratio. In October 2022, the No. 1 blast furnace proposed the target parameter of high top pressure. The top pressure was gradually increased under the premise of the smooth and stable blast furnace. The top pressure value was gradually increased from 0.278MPa to 0.282MPa. After continuous exploration, the top pressure has been maintained at around 0.28MPa (see Figure 6). After the top pressure is increased, the gas flow rate is reduced, the residence time of the gas in the furnace is increased, and the indirect reduction of the ore is increased, which reduces the fuel ratio.
Maintain appropriate molten iron temperature and strengthen iron tapping management
The long-term smelting practice of No. 1 blast furnace has proved that maintaining appropriate silicon content and temperature of molten iron plays an important role in the active furnace state.
In daily operation, No. 1 blast furnace pays attention to furnace temperature management, controls w (Si) at 0.3% to 0.4%, and molten iron temperature> 1500℃. From October 2022 to March 2023, the average w (Si) was 0.34%, and the average iron temperature was 1506℃, meeting the production needs of large blast furnaces.
For extra-large blast furnaces, slag iron discharge plays an important role in the stable and smooth operation of the blast furnace. The timely discharge of slag iron provides effective space for the continuous smelting of the blast furnace.
Continuous and stable slag iron discharge and timely discharge of clean slag iron can effectively avoid the blast furnace from being blocked due to “slag iron deficiency” in the blast furnace, which is crucial for the long-term stability of large blast furnaces. The reasonable iron-tapping system of the blast furnace has a positive impact on stabilizing the state of the furnace, alleviating the erosion of molten iron in the area in front of the iron mouth, and extending the service life of the furnace in the iron mouth area. The quality of the tapping mud is strictly controlled in front of the iron of the No. 1 blast furnace, the reasonable iron-tapping interval is planned, and the appropriate drill bit size is selected to ensure that the furnace door depth is qualified and the iron-tapping flow rate is stable. The number of iron-tapping times is controlled at 12 to 14 times/d, the furnace door depth control range is 3.8 to 4.2m, and the furnace door depth qualification rate and iron-tapping punctuality rate are kept stable at more than 90%.
Blast furnace production
By stabilizing the quality of raw materials and fuels, optimizing the charging and air supply system, insisting on full air volume, high air temperature, high oxygen enrichment and high top pressure smelting, maintaining the appropriate molten iron heat and optimizing the iron-making system, the No. 1 blast furnace has now achieved smooth and stable operation. From October 2022 to March 2023, the average utilization coefficient of the blast furnace was 2.48t/(m3·d), the coke ratio was 264.5kg/t, the coal ratio was 201.1kg/t, and the fuel ratio was 514.1kg/t (see Table 4).
Conclusion
1) By strengthening the quality management of raw materials and fuels and controlling the harmful elements entering the furnace, it provides an important guarantee for the blast furnace to achieve high-yield and low-consumption smelting.
2) Combined with the practice of high-proportion pellet smelting, by optimizing the blast furnace charging system, adopting the charging mode of adding coke at the edge platform center, stabilizing the edge, developing the center, and controlling the reasonable gas distribution, it is beneficial to improve the permeability of the blast furnace and maintain a high gas utilization rate.
3) Adhere to the operating concept of high wind temperature, high oxygen enrichment and high top pressure, and maintain reasonable wind speed and kinetic energy. Maintaining a reasonable molten iron temperature range and optimizing the iron-discharging system is conducive to activating the furnace state and ensuring smooth smelting of the blast furnace.
4) By optimizing the basic operating system, the No. 1 blast furnace achieves high-yield and low-consumption smelting, and the utilization coefficient is maintained at about 2.48t/(d·m3), the coke ratio is 264.5kg/t, the coal ratio is 201.1kg/t, and the fuel ratio is 514.1kg/t.
