Fangda special steel 1000M ³ Progress of blast furnace ironmaking technology

　　Abstract: the main experiences of Fangda special steel in blast furnace operation technology and management in recent years are summarized. Through continuous optimization of blast furnace operation, paying close attention to concentrate technology and upper and lower adjustments, the stability of blast furnace ironmaking production has been significantly improved, and the technical and economic indicators under the condition of high utilization coefficient and furnace protection have been continuously improved.

　　Key words: blast furnace, fuel ratio, ore angle, tuyere, air temperature
 

　　1. Foreword

　　Fangda special steel has two 1000m3 blast furnaces with an effective volume of 1050m3; There are two iron ports in the South and North, and 20 air vents. 1\blast furnace was put into operation in October, 2006. The blast furnace adopts high-quality carbon brick ceramic cup comprehensive furnace bottom, top burning hot blast stove, PW series tank furnace top, belt feeding, and full iron storage pouring iron ditch. 2\blast furnace was put into operation in December, 2011. The furnace bottom adopts microporous carbon bricks, ceramic cups, soft water closed circulating cooling system, and is equipped with three sections of copper cooling staves, bell less furnace top of cascading tanks, infrared camera of furnace top gas, automatic gas sampling, swinging chute, three top burning hot air furnaces (No. 1 and No. 3 hot air furnaces are coated with energy-saving coating), bag dust removal, bag conveying technology, TRT power generation, Mingte method water slag flushing, etc.
 

　　2. Technical indicators

　　2.1 utilization factor

　　With the company's CDQ put into operation, the coke quality of the plant has been improved, the blast furnace has obtained a stable coke window platform, the permeability and liquid permeability of the dead material column have been improved, the stability of the furnace condition has been strengthened, and the smelting intensity has been increased year by year. At present, the two 1000m3 blast furnaces of Fangda Special Steel Co., Ltd. are in the smelting state with high utilization coefficient, and the utilization coefficient of 1# blast furnace is up to 3.46t/m3 d. 2 × blast furnace: 3.58t/m3 d。 (as of August, 2016, the 1\blast furnace has been in production for nearly 10 years, and the iron production per unit furnace capacity has reached 10672.13 tons) (the change trend of utilization coefficient of Fangda special steel 1000m3 in recent years is shown in Figure 1).

　　2.2 coke ratio and coal ratio

　　The comprehensive coal ratio of 1000m3 blast furnace of Fangda special steel has increased from 125 ~ 130kg/t in previous years to more than 140kg/t, and the highest coal ratio is 155.88kg/t. At the same time, the lowest coke ratio is 338.77kg/t with the furnace condition running smoothly and the load increasing; The lowest coke ratio of 338.77kg/t and fuel ratio of 489.33kg/t will be achieved in March 2016 (the change trend of coke ratio and coal ratio of Fangda special steel 1000m3 in recent years).

　　2.3 key technical and economic indicators

　　According to the comprehensive technical and economic indicators of the 1000m3 blast furnace of Fangda special steel, the hot metal output has been gradually increased, and the fuel ratio has also decreased year by year. From January to August 2016, under the condition that the 1\.
 

　　3. Main technical progress and measures

　　3.1 fine material technology

　　① Improve ore grade

　　Concentrate is the basis of blast furnace ironmaking, and improving the grade of feed is the core content of concentrate technology. Fangda special steel has always adhered to the policy of "focusing on refined materials, supplemented by materials" and realized the gradual improvement of furnace grade.

　　② Optimize the screening system under the trough

　　Strictly control the material flow rate under the trough and gradually reduce the ore screen hole under the trough, so as to improve the effective ore quantity into the furnace and reduce waste. For the screening under the trough and charging, a perfect management system and process are formulated as a daily process discipline. At present, the machine fired sieve hole has been reduced from 4.5mm to 3.5mm, and the raw ore sieve hole has been reduced from 8 ~ 10mm to 4.5mm. At the same time, the incoming sample and the returned particle size shall be tested every week to control the flow rate of ore and stone under the tank ≤ 40kg/s and the flow rate of coke ≤ 25kg/s, and the measurement and adjustment shall be carried out every day.

　　③ Improve coke quality

　　The self-produced coke of Fangda special steel can not fully meet the needs of blast furnace production, and 40% of it needs to be purchased, resulting in large fluctuations in the variety and quality of purchased coke. In order to stabilize the quality of external coke, the variety of external coke was gradually reduced in 2012, from several to four per month, and a and B coke with good quality were used as the mainstream external coke, and others were supplemented. Different types of coke shall be stored in different heaps, and the furnace seats shall be used differently. When the furnace condition is poor, the CDQ emergency with good quality shall be adopted in time.

　　3.2 upper operation system

　　① Large ore lot and large ore angle

　　Large batch smelting can increase the thickness of coke window at furnace waist, reduce interface reaction, improve load level and stabilize gas flow. Since 2012, large batch tests have been carried out in three blast furnaces step by step. Meanwhile, technicians have been organized to measure the trajectory of the material flow collision point, and the maximum angle upper limit value has been established, realizing the reasonable gas flow distribution with the center gas flow as the main stream and the edge gas flow as the auxiliary stream. At present, the ore batch of 1# blast furnace has been expanded from 32 tons to 37 ~ 38 tons, and the maximum ore batch of 2# blast furnace has been increased to 42 tons. The ore coke angle has been gradually increased, with the maximum ore angle of 44 ° and coke angle of 42 °. The ore platform has been widened, and the gas utilization rate has been significantly improved.

　　② High jacking pressure

　　High top pressure can prolong the contact time between gas and charge, and improve the utilization efficiency of gas heat and chemical energy; 1. The blast furnace is gradually increased from 190kpa to 207kpa; The top pressure of 2# blast furnace was also increased from 198kpa to 215kpa by stages.

　　3.3 low silicon smelting

　　In daily operation, 1\blast furnace [si] is controlled at 0.30-0.50%, and 2\blast furnace is controlled at 0.25-0.45%.

　　While reducing [si], properly increase the binary basicity of slag to ensure the physical heat of molten iron and desulfurization effect. At the same time, the Al2O3 content in slag shall not exceed 16.5% during ore blending.

　　3.4 technological breakthrough

　　① A major breakthrough has been achieved in the proportion of raw ore used

　　In August 2015, due to market changes, special steel began to gradually use raw ore for blast furnace. Due to the protection of 1\. The proportion of raw ore used in 2\blast furnace is as high as 27%, which realizes the production by replacing the burden structure of pellet ore, and has achieved good economic indicators. With the adjustment of the sequence of raw ore feeding into the furnace, the transformation of the screening system under the trough, the development of lump ore drying process and the mixing process of lump ore and machine firing, the utilization ratio of raw ore has been greatly improved, and the two blast furnaces can basically be used stably for more than 20%.

　　② Plan rapid recovery after wind break

　　The net coke of the off air material is added in sections. At the same time, the alkalinity and load of the off air material are strictly calculated to ensure that the hearth heat is sufficient after re blowing, and the appropriate high furnace temperature and acid slag are controlled to ensure the fluidity of slag iron after re blowing. According to the length of wind off time, it is considered to block 2 ~ 4 tuyeres. At present, Fangda special steel has basically realized all air and oxygen operation within 4 hours after planned maintenance.

　　③ The cooling stave of No. 1 \

　　1\blast furnace has always adhered to the operation idea of restraining the edge air flow and developing the center air flow. From the start-up to 2015, the furnace wall has never been thickened and nodulated, and no measures such as fluorite washing have been taken. 1 \1\blast furnace adopts the cooling structure of plate wall combination, and the slag skin formed is relatively stable. Pay more attention to the management of the cooling system. Once it is found that the local water outlet is small or the water temperature difference is high, take measures such as Backwashing in time.

　　④ The two blast furnace plate preheaters have good effect, and the air temperature has increased year by year

　　The two 1000m3 blast furnaces use plate preheaters to preheat the gas and air to 300 ℃ and 200 ℃ respectively. The effect is obvious. When the furnace conditions are running smoothly, the air mixing operation is fully closed, and the air temperature is gradually increased. The blast temperature of 1 × blast furnace is stable above 1200 ℃, and that of 2 × blast furnace is about 1240 ℃. Only during the one-stop maintenance of the company, the air temperature was at a high level, except that the air temperature was greatly reduced due to oxygen shutdown.

　　⑤ Application of small ore recovery technology

　　The machine firing capacity of Fangda special steel is insufficient. In order to improve the effective amount of ore into the furnace and reduce waste, in recent years, the screen hole of the screen under the tank (4.5mm → 3.5mm) has been gradually reduced, and small ore recovery has been carried out at the same time. The ore return rate of blast furnace decreased from 12% ~ 15% to 5% ~ 7%. In addition, the 2# blast furnace adopts the graded charging technology, and uses the chute discharging sequence to optimize the gas flow distribution.

　　⑥ Long tuyere is used to penetrate the center

　　"Blow through center" is the key factor to activate the hearth. During the production of 1\blast furnace over the years, the tuyere length has been gradually adjusted from 420mm to 550mm. Due to the thin-walled structure of the copper cooling stave, when the raw materials and fuels change frequently, the central air flow is easy to be unstable, resulting in a large number of slag flakes falling off, and even small edge pipes in serious cases; To this end, gradually lengthen the air outlet from 583.5mm to 630mm. After lengthening the tuyere, the air flow in the center of 2# blast furnace was stable, and the furnace condition kept running smoothly without fluctuation for more than half a year. The tuyere length of the two 1000m3 blast furnaces of Fangda special steel is rare in the same type of blast furnace in China.
 

　　4. Conclusion

　　Fangda special steel has realized the stable operation of the blast furnace and the continuous improvement of technical and economic indicators through a series of measures such as continuous exploration of operation technology, fine material level, large ore batch, large angular difference, high top pressure, high air temperature, high oxygen enrichment, large coal injection, and strengthening the management inside and outside the furnace, and achieved good economic benefits.