Technical progress of blast furnace ironmaking in Xuanhua Iron and Steel Co., Ltd

　　1. Foreword

　　At present, Xuanhua Iron and Steel Co., Ltd. has 3 blast furnaces, 2500m3 × 2+2000m3 × 1。 In recent years, the former process of Xuanhua Iron and Steel Co., Ltd. has taken many measures at the same time to improve the quality of raw fuel into the furnace on the basis of fine material production. Taking the transformation of upper charging system as a breakthrough, it has achieved long-term stable and smooth operation. In view of the reduction of air temperature, it has continuously explored and studied, broken through the technical bottleneck of low air temperature operation, better handled the contradiction between furnace protection and strengthening, continuously improved the utilization coefficient of blast furnace, continuously decreased the fuel consumption index, and made great technical progress.
 

　　2. Improve raw fuel quality

　　2.1 improve coke quality

　　In 2017, the sulfur content of the self-produced coke of Xuanhua Iron and Steel Co., Ltd. was gradually reduced. The ratio of high sulfur coal was reduced from 8% to 4%, the new resource of low sulfur coking coal was added by 15%, and the sulfur content of coke was reduced from 0.90% to 0.83%. At the same time, the coal blending was refined, the coal mining sites were reasonably adjusted, the ash content of coke was controlled not to exceed 13.0%, the average particle size of coke was gradually increased from 50mm to 52mm, the drum strength was increased by 1.4%, and the strength remained above 67% after reaction.

　　2.2 improve sinter quality

　　After the fourth quarter of 2016, the sinter kept its alkalinity stable and gradually reduced SiO2 and MgO. SiO2 decreased from 5.5~6.0% to about 5.3%, MgO decreased from 2.2% to 1.8%, and sinter grade increased from 54.5% to about 56%. The concept was changed. Instead of maintaining high FeO strength, the operation of low water, low carbon and thick material layer was implemented. The FeO content was reduced by 1.4 percentage points, providing a strong guarantee for improving the reduction degree of sinter.

　　After reducing SiO2, FeO and MgO, the metallurgical properties of sinter are improved, and the ore phase composition is improved. The matching relationship between SiO2, FeO, MgO and alkalinity is continuously studied, and the structure of raw materials is optimized. The reduction degree of sinter is increased to 80%~82%.

　　2.3 improving pellet quality

　　Carry out the research on the qualified particle size of green pellets, stabilize the mixing and polishing structure, strengthen the pelletizing operation, stabilize the moisture of the mixture, strictly control the fineness of fine powder into the plant, and the content of 8mm~16mm particle size of green pellets exceeds 82%. The FeO content of pellet is lower than 1.5% by adjusting thermal parameters and increasing oxidation atmosphere.

　　2.4 reduce the content of harmful elements

　　By controlling the harmful elements in the incoming raw materials, controlling the recycling of high zinc materials, and rationally proportioning, the control objectives of incoming zinc load ≤ 350g/t and alkali load ≤ 4kg/t have been achieved, and the harm to the blast furnace has been reduced.
 

　　3. Progress in blast furnace operation technology

　　3.1 transformation of upper charging system of blast furnace

　　Before 2012, the blast furnace distribution mode of Xuanhua Iron and Steel Co. was mainly "central coking". However, due to the influence of raw fuel conditions and operation, this distribution mode did not play a positive role, resulting in high long-term fuel consumption and low output of the blast furnace. In 2012, each blast furnace gradually changed from "central coking" to "platform + funnel" mode, widened the coke platform, stabilized the edge air flow, appropriately reduced the central air flow intensity, and maintained the narrow and strong central air flow. Take 2\\blast furnace of Xuanhua Iron and Steel Co. as an example to illustrate the transformation effect of upper charging system, as shown in Table 4. See Table 5 for the transformation effect of upper loading system

　　3.2 adjustment and optimization of process parameters

　　In order to increase the output, the blast furnace of Xuanhua Iron and Steel Co. actively increased the air volume, and each blast furnace increased the air volume by 100m3/min-150m3/min. After increasing the air volume, the top pressure of two 2500m3 blast furnaces was increased by 10KPA to 15kpa in order to control the air flow velocity in the furnace and reduce the blast furnace fuel consumption. In order to further stabilize the gas flow and reduce the fuel consumption of the blast furnace, by expanding the ore batch, increasing the thickness of the ore bed, adjusting and optimizing the upper and lower charging systems, the CO2 content in the gas was increased to more than 20%, and the utilization rate of the gas was improved.

　　3.3 break through the technical bottleneck of low air temperature operation

　　After adding converter gas to two 2500m3 blast furnaces of Xuanhua Iron and Steel Co., Ltd., due to the high dust content of converter gas, the hot blast furnace lattice brick slagging and gas heat exchanger blockage were caused, and the air temperature was lower than 1000 ℃. After the air temperature drops, the upper and lower operating systems of the blast furnace are adjusted to achieve the purpose of reasonable air supply system and improving the utilization rate of gas:

　　(1) Control of theoretical combustion temperature in front of tuyere. Increasing the oxygen enrichment rate, 1\blast furnace is increased from 3.7% to 4.2%, and 2\blast furnace is increased from 3.5% to 4.5%. Limit the coal ratio. The coal ratio shall not exceed 145kg/t. At the same time, control the bituminous coal ratio. The theoretical combustion temperature in front of the tuyere is 2100 ℃ to 2200 ℃.

　　(2) Lengthen the tuyere length and reduce the tuyere area. The length of tuyere is lengthened from l585mm to l615mm, 17 long tuyeres are used for 1# blast furnace, the tuyere area is reduced from 0.3357m2 to 0.3285m2, and all long tuyeres are used for 2# blast furnace, the tuyere area is reduced from 0.3321m2 to 0.3248m2, and the raceway in front of tuyere extends to the center of hearth.

　　(3) Control of heating system and slagging system. Properly increase the furnace temperature from 0.25%-0.40% to 0.30%-0.45%, and increase the basicity of slag from 1.20 times to 1.25 times to supplement the hearth heat.

　　(4) Adjustment of upper loading system. Develop the central air flow and maintain a certain edge air flow. The edge air flow shall not be excessively suppressed or developed, otherwise it is easy to cause furnace wall bonding. Pay close attention to the changes of furnace temperature and heat load, strengthen furnace type management and adjust in time.

　　Through adjustment, the rationality of raceway of two 2500m3 blast furnaces is shown in Table 6, and the smooth running degree of furnace conditions is improved,

　　3.4 high efficiency comprehensive furnace protection technology of Xuanhua Iron and Steel Co., Ltd

　　Xuanhua Iron and steel 1# blast furnace has been in the late stage of furnace service, and the hearth refractory has different degrees of erosion. The temperature of hearth carbon brick rises, especially in the iron mouth area, which has great potential safety hazards. The water volume of 1\5 blast furnace body of Xuanhua Iron and Steel Co., Ltd. has been used to the maximum, and there is no adjustment allowance. During daily operation, the titanium load was maintained from 8kg/t to 9kg/t, the temperature change of hearth carbon brick was highly valued, and prevention and control were emphasized. Furnace protection measures were taken at the early stage of rapid temperature rise, so as to avoid the increase of operation difficulty of blast furnace with a large increase of titanium load and the decline of technical and economic indicators. In the process of furnace protection, the combination of overall furnace protection and local furnace protection shall be adopted, and a variety of furnace protection measures shall be taken. At the same time, the contradiction between furnace protection and intensified smelting shall be handled well. Furnace protection measures mainly include:

　　(1) Due to the long service time, titanium ore is added to increase the titanium load. The titanium load is increased to more than 9kg/t (FE), and the furnace is protected as a whole. Due to the particularity of the blast furnace process layout of Xuanhua Iron and Steel Co., Ltd., for example, increasing the titanium content by sintering will increase the titanium load of the blast furnace without furnace protection, affecting the operation of other blast furnaces. After adding titanium ore, the disadvantage of "one person catches a cold and the whole family takes medicine" is overcome.

　　(2) Adjust the operation parameters of blast furnace. Pig iron [si] is increased from 0.25%-0.40% to 0.35%-0.50%, slag alkalinity is increased to 1.20 times -1.25 times, titanium reduction is promoted, the sulfur content of pig iron is less than 0.025%, and the first-class product rate of pig iron is ≥ 95%, which is conducive to the formation of protective layer.

　　(3) Strengthen the maintenance of iron mouth. The depth of the iron mouth shall be controlled within 3.0m to 3.2m. It is strictly prohibited to cast iron at the wet iron mouth and conduct the operation of blasting. It is prohibited to burn the iron mouth, maintain the full air high-pressure plugging rate, and maintain the integrity of the iron mouth mud bag.

　　(4) Local furnace protection and tuyere blocking operation. If the temperature of carbon bricks in the hearth continues to rise and the heat flow intensity of the cooling stave at the corresponding part exceeds the control standard, block the tuyere and strengthen local furnace protection.
 

　　4. Conclusion

　　In the second half of 2018, a new hot blast stove will be built for 2\blast furnace, which will be put into use in December. The air temperature has reached 1100 ℃, and the air temperature of 1\blast furnace is between 1000 ℃ and 1050 ℃, and it is at the end of furnace service, which has a great impact on the output and technical indicators of blast furnace.

　　Although Xuanhua Iron and Steel Group has made some progress in ironmaking technology, there is still a significant gap in pig iron output, fuel consumption and application of new processes and new technologies compared with the group's brother units and national advanced units.