Production practice of Xingcheng 3200m3 blast furnace

　　Abstract: the production practice of Xingcheng 3200m3 large blast furnace in the past 31 months has been summarized. Through more than 2 years of hard exploration, the operation skills and management ability have been steadily improved, the blast furnace production has developed steadily, no serious abnormal furnace conditions have occurred, and the technical and economic indicators of the blast furnace have been stable at a high level for a long time.

　　Key words: large blast furnace; Gas utilization rate; Fuel ratio

　　From 2002 to September 2009, Xingcheng Special Steel has produced three small blast furnaces, two 450m3 blast furnaces and one 530m3 blast furnace respectively. At the end of September, 2009, the first 3200m3 blast furnace with national industrial and chemical equipment was put into operation, but there was still no coking production, and all raw fuels were supplied externally. After more than two years of hard exploration, the operation skills and management ability have been steadily improved, the blast furnace production has developed steadily, no serious abnormal conditions have occurred, and the technical and economic indicators of the blast furnace have been stable at a high level for a long time.
 

　　1. Blast furnace production

　　1.1 supporting conditions of blast furnace

　　The 3200m3 blast furnace was put into operation on September 25th, 2009, with 4 tapholes and 32 tuyeres. Single burning of blast furnace gas, double preheating of gas and combustion supporting air, and rotary cutting top burning hot blast stove with patented technology; The furnace bottom hearth adopts microporous carbon brick + ceramic cup structure, the furnace hearth section 2, the furnace waist and the middle and lower sections of the furnace body adopt copper cooling staves, the water cooling pipe at the furnace bottom, the large and medium sleeve of the tuyere and the cooling stave adopt soft water closed circulation, and the small sleeve of the tuyere adopts open circuit circulation of industrial water; Bell less furnace top for belt conveying and tumbling tank; Hydraulic opening machine and clay gun in front of furnace; Gravity dedusting + bag dry gas dedusting and purification system; TRT residual voltage power generation system; Steam blower; The new processes and technologies, such as bottom filtration water slag washing system and sintering step-by-step furnace feeding, are all localized.

　　1.2 development of blast furnace production

　　3200m3 blast furnace operators are young and have no experience in large-scale blast furnace operation. Although under the guidance of experts in the same industry, the technology of large-scale blast furnace operation has been quickly mastered, and the technical and economic indicators of blast furnace have been continuously improved, due to lack of operation experience, compared with the same level blast furnace of domestic brother units, Xingcheng large-scale blast furnace still has many differences in operation and technical and economic indicators. To this end, we have been trying to find ways to optimize blast furnace operation. The following is a brief review and summary of the production and operation practice since the blast furnace was put into operation (October 2009 April 2012).

　　(1) Production indicators. Since putting into operation, the utilization coefficient of 3200m3 blast furnace has changed, the charging coke ratio, coal ratio, coke Ding ratio and fuel ratio have changed, and the furnace top temperature and TRT ton iron power generation have changed.

　　Since 3200m3 blast furnace was put into operation for 31 months, no abnormal furnace condition has occurred. After december2009, the utilization coefficient was stable at 2.35~2.50, the coke ratio and coal ratio indicators were steadily improved, maintained at 300~320kg/t and 165~175kg/t respectively, and the fuel ratio was maintained at 510 ~ 520kg/t. After december2011, the utilization coefficient of blast furnace further increased, reaching an average of more than 2.50, with coke ratio of 295~305kg/t and fuel ratio of 505~510kg/t. In april2011, the blast furnace was planned to be repaired for 3 days a year, and the utilization coefficient decreased significantly in that month. The average power generation of TRT tons of iron is 44.46kw · h/t. After deducting the impact of two factory inspections, the average power generation is 45.61kw · h/t. After october2011, with the substantial increase of gas utilization rate, the furnace top temperature decreased significantly, and the power generation per ton of TRT iron decreased, maintaining at 42.0~43.5kw · h/t.

　　(2) Changes in production conditions. As there is no own mine and coking plant, the furnace grade and coke quality are unstable. Through the capacity expansion and reconstruction of sinter blending yard, the time for changing stockpiles was extended from 4 days to 7 days, and a certain proportion of pre changing stockpiles were added to reduce the fluctuation of sinter quality caused by changing stockpiles; The coke is directly supplied to the blast furnace ore tank on board to reduce the damage in the process of reshipment; At the same time, strictly control the t/h value, strengthen the cleaning of screen surface, reduce the powder into the furnace and a series of strengthened management measures to control the fluctuation range of raw fuel within the minimum range.

　　The overall smelting intensity is controlled at 0.70 ~ 0.75, and the comprehensive smelting intensity is controlled at 1.10 ~ 1.20. During the production of blast furnace, the operation index is not optimized by simply increasing the smelting intensity. Too high or too low smelting intensity is not conducive to the optimization of fuel consumption index. The relationship between smelting intensity and fuel ratio of 3200m3 blast furnace is controlled within a good range, but there is a large deviation in some months.
 

　　2. Basic principles and technical route of blast furnace operation

　　2.1 basic principles of blast furnace operation

　　(1) The most basic principle is to stabilize the smooth behavior of blast furnace.

　　(2) Focusing on fuel consumption, any measures to strengthen smelting should not be taken at the expense of fuel ratio.

　　(3) Reduce the amount of coal in the belly of a ton of iron furnace, improve the utilization rate of gas, make full use of the heat and chemical energy of blast furnace gas, and reduce the fuel ratio.

　　(4) Adjust the blast furnace material structure and reduce the raw material cost. On the premise of ensuring coke quality, more tamping coke is prepared to reduce coke cost.

　　2.2 basic technical measures for blast furnace operation

　　(1) Full air volume and high air temperature operation.

　　(2) Dredge the center control edge to find the appropriate two air streams.

　　(3) Adhere to low [si] smelting.

　　(4) Large ore batches are distributed in thick material layer to reduce ore coke interface layer and pressure difference.

　　(5) Prevent all kinds of fluxes from entering the furnace through reasonable ore blending.

　　2.3 production operation management of blast furnace

　　(1) During the production process of blast furnace, the equipment management shall implement the spot inspector system, adhere to the participation of all personnel, and "the integration of operation and inspection".

　　(2) Standardized operation shall be carried out for blast furnace production, the planned operation value system shall be adhered to, and the post operation observation system shall be implemented.

　　(3) Equipment management and production operation shall follow the "three delicacies" policy.

　　2.4 actual operation of blast furnace

　　(1) Adjustment and improvement of air supply system. ① Selection and adjustment of tuyere area and length. When starting 3200m3 blast furnace, the tuyere selected is Φ 120mm × 550mm × 32, the air supply area is 0.3619m2; After that, gradually adjust the air outlet configuration to Φ 130mm × Mainly 600mm, Φ 120mm × 600mm is used as a means to adjust the air outlet area, and the air supply area is maintained at about 0.417m2 for a long time. ② Air temperature, humidity, oxygen content and injection volume. During the production of 3200m3 blast furnace, high air temperature shall be used; Through the operation of dehumidification or humidification system, the stable blowing humidity is 10 ~ 12g/m3; In the operation process, do not pursue too high oxygen enrichment, and stabilize the gas volume of ton iron furnace belly as the starting point; An appropriate high coal ratio is pursued, but when the coal ratio reaches more than 180kg/t, the coke saving effect decreases significantly. When the coal ratio is 160 ~ 165kg/t, the coke ratio and fuel ratio decrease at the same time. ③ Theoretical combustion temperature before tuyere TF. The appropriate theoretical combustion temperature can limit the reduction of silicon in front of the tuyere, which is an important factor affecting low silicon smelting. TF shall be controlled at 2200 ~ 2300 ℃, and the methods mainly include humidification or dehumidification, oxygen enrichment and coal injection.

　　(2) Adjustment and improvement of loading system. ① Ore coke batch weight adjustment. Large ore batch distribution increases coke layer thickness, improves gas flow distribution and increases gas utilization. Since the start-up, the sinter has been fed into the furnace by classification, and the ore batch with the same weight is used during charging. Taking the adjustment in 2011 as an example, before the adjustment, the coke batch weight ≤ 16.2t, and the load ≤ 5.33; After adjustment, coke batch weight ≥ 17.3t, load ≥ 5.57. Adjustment steps: first, under the condition of maintaining the coke load unchanged, the ore batch weight is gradually increased from 85t to 95t, and the coke batch weight is gradually increased to 17.0t; Second, under the condition of maintaining the same coke batch weight, gradually increase the ore batch to 95 ~ 105T and increase the load to 5.57 (see Table 1 for the comparison of relevant parameters before and after adjustment). With the expansion of ore and coke batch weight, the material layer is thickened, the number of material column interfaces is reduced from 44 to 34, the pressure difference of blast furnace is reduced, and the thickness of coke layer is increased, which makes the air flow path smooth, improves the utilization rate of gas, and creates favorable conditions for increasing the load. ② Gear angle and matrix change. The distribution matrix of 3200m3 large blast furnace is set to maintain light load at the edge and center, and maintain "two channels and keep the center". After the furnace is opened, the angle of the 2m feed line section is properly adjusted. After the distribution angle is increased, the radius of the material flow mass center is less than the 9th gear to close to the 10th gear, achieving the purpose of adjustment.

　　In order to find the most economical charging system, the charging system of increasing the edge coke and reducing the ore discharging at the edge, the charging system of increasing the center coke and reducing the ore loose center, and the charging system of simultaneously contracting and developing two gas streams at the edge center have been adopted successively, but both have brought fluctuations in the blast furnace condition. The technology of replacing the central coking with the central coking in the fifth gear was adopted. Through the adjustment of the number of distribution rings and distribution amount of coke in the throat area, the central coke addition amount was reduced from 21.2% to 14.75%. The intensity of the central air flow of 3200m3 blast furnace was effectively controlled, and the central point temperature was reduced from 650 ℃ to 550 ℃. At the same time, the furnace top temperature is reduced from 140 ℃ in the south to 90~110 ℃, the content of CO in the gas is increased from 20.5% to more than 21.5%, and the utilization rate of the gas is more than 48.5%.

　　(3) Adjustment of slagging system. The adjustment of slag making system is mainly based on the following principles: ① when the amount of slag is large and the content of alkali metal is high, the basicity R2 of slag is appropriately reduced and controlled at 1.05 ~ 1.10, taking into account the alkali discharge while ensuring the quality of pig iron; When the slag quantity is small and the alkali metal content is not high, the slag basicity R2 is appropriately increased and controlled at 1.10 ~ 1.15. ② The content of (MgO) in slag shall be controlled within 8.0% ~ 9.0%, the content of (Al2O3) shall be controlled within 15.5%, the ratio of (MgO) / (Al2O3) shall be controlled between 0.55 ~ 0.65, and the ratio of (Al2O3) / (SiO2) shall be controlled within the range of 0.35 ~ 0.45, [si] is generally 0.35%~0.4%, and the hot metal temperature has been maintained at about 1490 ℃.

　　(4) Increase the proportion of tamping coke. In August, 2011, after the use of super grade coke was cancelled, the second iron making branch carried out "fine" management of coke. Issue the coke use proportion sheet every day, take preventive measures in advance and track the coke use to ensure the stability of the coke structure for blast furnace. Due to the management measures in place and the support of the company, under the unfavorable conditions of canceling the special grade coke and increasing the proportion of tamping coke, the operators of the large blast furnace of No. 2 iron making plant overcame a series of problems existing in the tamping coke on the large blast furnace, achieved the success of the long-term use of 4.3m tamping coke in the 3200m3 blast furnace, and quickly explored a set of operation methods and skills suitable for the use of high proportion of tamping coke in the large blast furnace of the plant in the shortest time, Achieve stable and high production of blast furnace and continuously improve production indicators.

　　In 2012, the production of 3200m3 large blast furnace continued to maintain a stable and smooth trend, and various indicators reached a new level: the average daily production of molten iron was more than 8200t/d, the utilization coefficient was more than 2.56, the coke ratio was 304kg/t, the coal ratio was 163kg/t, the fuel ratio was 500 ~ 510kg/t, [si] remained 0.35% ~ 0.40%, the silicon deviation was 0.066, the CO2 content in the top gas reached more than 23.0%, and the average gas utilization rate reached 50.5%.
 

　　3. Problems existed since the blast furnace was put into operation

　　(1) The unplanned wind rest rate is high. Taking 2011 as an example, due to various reasons, the blast furnace has been shut down for as many as 34 times, and the annual average shut down rate has reached 3.316%, which is nearly 2.0% ~ 2.5% higher than that of peers in the same industry, resulting in the phenomenon that the actual daily output is high, but the monthly average daily output is low. The high rate of blowing out has seriously restricted the improvement of blast furnace production index.

　　(2) The quality of raw fuels fluctuates greatly between batches. Without its own coking enterprises and mines, all raw fuels required for production are purchased, which is basically "eating a hundred meals". The quality of various raw fuels is uneven and fluctuates greatly, so the consumption cannot achieve stable supply. The capacity of sinter mixing and stacking is still insufficient, and the frequency of sinter production is high, resulting in the periodic fluctuation of sinter quality; The ore concentrate for pelletizing has large fluctuation in composition, coarse particle size, large amount of binder and low grade.

　　(3) Furnace body temperature is unstable. Since the blast furnace was put into operation, the temperature of the furnace body, especially the temperature of the cooling staves in the 10th ~ 12th section, has been unstable and fluctuated greatly. At present, no solution has been found.

　　(4) There is no standard for tamping coke quality evaluation. The top charging coke standard can be borrowed for a small amount of use, but borrowing the top charging coke standard after a high proportion of use can not guide the production operation, which is manifested in the deviation between the coke index and the actual production index. For example, the particle size of tamping coke is small, the average particle size is 8 ~ 10mm smaller than that of top charged coke, and the pressure difference of blast furnace is higher than that of blast furnace with top charged coke. It is difficult to take out the sample for M40 strength test, so M25 can only be used for evaluation, which can not be compared with M40.

　　(5) The grade base of large blast furnace is uncertain. Due to the influence of market change factors, the feeding grade of small and medium-sized blast furnaces has been greatly reduced, and the feeding grade of 3200m3 blast furnace has also been reduced to about 58.0%. At present, the smooth running of blast furnace and fuel consumption have not been damaged, but the base line needs to be further explored.
 

　　4. Conclusion

　　(1) After Xingcheng 3200m3 large blast furnace was put into operation, the production was stable, and the technical and economic indicators continued to improve.

　　(2) It is feasible to produce large blast furnace equipment nationwide, and the equipment operation is stable and reliable.

　　(3) It is feasible to use tamping coke of small coke oven successfully in large blast furnace. In a short time, a set of operation methods and skills suitable for the use of high proportion tamping coke in the large-scale blast furnace of the plant were successfully explored, which realized the stable production of the blast furnace and achieved good economic benefits.

　　(4) Under the condition that the quality of raw materials and fuels declines, the blast furnace can be strengthened without increasing the fuel ratio by optimizing operation and reasonable ore blending.

　　(5) By pursuing the reasonable distribution of gas flow in the furnace, it is possible to further improve the utilization rate of gas and reduce the fuel consumption of blast furnace ironmaking.

　　(6) The basic measures to reduce consumption and save energy are the distribution of large ore batches, the increase of coke layer thickness, the improvement of gas flow distribution and the improvement of gas utilization rate.