Abstract: The main experience of blast furnace operation technology and management of Fangda Special Steel in recent years is summarized. By continuously optimizing blast furnace operation, paying close attention to concentrate technology and adjusting the upper and lower parts, the stability of blast furnace ironmaking production has been improved, and achieved The technical and economic indicators continued to improve under the condition of high utilization factor and furnace protection.
Keywords: blast furnace, fuel ratio, mine angle, tuyere, air temperature
1 Introduction
Fangda Special Steel currently has two 1000m3 blast furnaces with an effective volume of 1050m3; there are two iron holes in the south and north, and 20 air outlets. The 1# blast furnace was put into operation in October 2006. The blast furnace adopts high-quality carbon brick ceramic cup integrated furnace bottom, top-fired hot blast furnace, PW type string tank top, belt feeding, and full iron storage type casting iron ditch. The 2# blast furnace was put into operation in December 2011. The bottom of the furnace is made of microporous carbon bricks, ceramic cups, and a closed circulation cooling system for soft water. It is equipped with 3-stage copper cooling walls, a bell-less furnace top, and an infrared camera for gas on the top of the furnace. Sampling, swinging sliding nozzle, 3 top-fired hot blast stoves (No. 1 and No. 3 hot blast stoves are sprayed with energy-saving cladding coatings), cloth bag dust removal and ash cloth bag conveying technology, TRT power generation, Mint method water slag flushing, etc.
2 Technical indicators
2.1 Utilization factor
With CDQ put into production, the coke quality of the factory has been improved, the blast furnace has obtained a stable coke window platform, the dead material column has improved ventilation and liquid permeability, the stability of the furnace condition has been strengthened, and the smelting intensity has increased year by year. At present, the two 1000m3 blast furnaces of Fangda Special Steel are in the smelting state with high utilization factor. The utilization factor of 1# blast furnace is 3.46t/m3.d, and the 2# blast furnace is 3.58t/m3.d. (As of August 2016, the 1# blast furnace has been in production for nearly 10 years, and the iron output per unit furnace capacity has reached 10672.13 tons) (The change trend of the utilization coefficient of Fangda Special Steel's 1000m3 in recent years is shown in Figure 1).
2.2 Coke ratio and coal ratio
The comprehensive coal ratio of Fangda Special Steel's 1000m3 blast furnace has increased from 125 to 130kg/t in previous years to more than 140kg/t, and the high coal ratio has reached 155.88kg/t. At the same time, with the forward progress of furnace conditions and the continuous increase of load, the coke ratio is as low as 338.77kg/t; in March 2016, the low coke ratio was 338.77kg/t, and the fuel ratio was 489.33kg/t (about 1000m3 of Fangda Special Steel). The change trend of coke ratio and coal ratio in several years).
2.3 Key technical and economic indicators
The comprehensive technical and economic indicators of Fangda Special Steel's 1000m3 blast furnace, the production of molten iron has gradually increased, and the fuel ratio has also been reduced year by year. up to 10672.13 tons), and the accumulative fuel ratio of blast furnaces in the whole plant achieved 503.95kg/t.
3 Main technical progress and measures
3.1 Concentrate technology
①Improve the grade of ore into the furnace
Concentrate is the basis of blast furnace ironmaking, and improving the grade of the blast furnace is the core content of the concentrate technology. Fangda Special Steel has always adhered to the policy of combining "concentrated materials as the main material, supplemented by economic materials", and has achieved a gradual improvement in the grade of the furnace.
②Optimize the screening system under the tank
       Strictly control the material flow rate under the tank, and gradually reduce the ore screen mesh under the tank to increase the effective amount of ore entering the furnace and reduce waste. For the screening under the tank and the charging material, a perfect management system and process has been formulated, which is managed as a daily process discipline. At present, the sieve hole of machine burning has been reduced from 4.5mm to 3.5mm, and the sieve hole of raw ore has been reduced from 8 to 10mm to 4.5mm. At the same time, the samples entering the furnace and the size of the returned ore are tested every week, and the ore material flow rate under the control tank is less than or equal to 40kg/s, and the coke material flow rate is less than or equal to 25kg/s, which are measured and adjusted every day.
③Improve the quality of coke
       Fangda Special Steel's self-produced coke volume cannot fully meet the needs of blast furnace production, and 40% needs to be purchased, resulting in large fluctuations in the variety and quality of purchased coke. In order to stabilize the quality of external cokes, the variety of external cokes has been gradually reduced since 2012, from the original number to 4 per month, and A and B cokes with better quality are the mainstream external cokes, and others are supplemented. Different types of coke are stored in separate piles and used in different furnace bases. When the furnace condition is poor, the CDQ emergency with better quality should be used in time.
3.2 The upper operating system
①Large ore lot, big ore angle
Large ore batch smelting can increase the thickness of the coke window at the furnace waist, which is beneficial to reduce the interface reaction, improve the load level and stabilize the gas flow. Since 2012, large batch tests have been gradually carried out in three blast furnaces. At the same time, technicians have been organized to measure the trajectory of the collision point of the material flow, and the upper limit value of the large angle has been established, realizing a reasonable gas flow in which the central gas flow is the main gas flow and the edge gas flow is supplemented. distributed. At present, the 1# blast furnace has been expanded from the original 32 tons to 37-38 tons, and the 2# blast furnace has a large ore batch of 42 tons. The ore coke angle is gradually increased. The large ore angle is 44° and the coke angle is 42°. The ore platform has been widened, and the effect of improving the utilization rate of gas is obvious.
②High top pressure
The high top pressure is beneficial to prolong the contact time between the gas and the charge, and improve the utilization efficiency of the thermal energy and chemical energy of the gas; the 1# blast furnace is gradually increased from the original 190KPa to 207KPa; the 2# blast furnace top pressure is also increased from 198KPa to 215KPa in stages.
3.3 Low silicon smelting
In daily operation, the 1# blast furnace [Si] is controlled by 0.30-0.50%, and the 2# blast furnace is controlled by 0.25-0.45%.
While reducing [Si], appropriately increase the binary basicity of slag to ensure the physical heat and desulfurization effect of molten iron. At the same time, control the Al2O3 content in the slag not to exceed 16.5% during ore blending.
3.4 Technological breakthrough
①A major breakthrough was achieved in the proportion of raw ore used
In August 2015, due to changes in the market, special steel blast furnaces began to use raw ore gradually. Since the 1# blast furnace protects the furnace, the focus is on the 2# blast furnace for proportioning research. The proportion of raw ore used in 2# blast furnace is as high as 27%, which realizes the production of the charge structure that completely replaces pellets, and achieves relatively good economic indicators. With the adjustment of the raw ore into the furnace sequence, the transformation of the screening system under the tank, the development of the lump ore drying process and the lump ore and machine-fired mixing process, etc., the proportion of raw ore used has been greatly increased. The two blast furnaces basically More than 20% can be used stably.
②Plan for quick recovery after wind break
The clean coke of the air blast material is added in stages, and at the same time, the alkalinity and load of the air blast material are strictly calculated to ensure sufficient heat in the hearth after the re-airing. slag-iron fluidity. According to the length of the wind break, consider blocking 2 to 4 air outlets. At present, Fangda Special Steel has basically achieved full-wind and full-oxygen operation within 4 hours after the planned maintenance.
③The 1# blast furnace has achieved 9 years of production without burning out the cooling stave
The 1# blast furnace has always adhered to the operation idea of ​​suppressing the edge airflow and developing the center airflow. From the opening of the furnace to 2015, the furnace wall has never been thick and nodular, and measures such as fluorite cleaning have not been taken. The 1# blast furnace adopts a cooling structure combined with plate and wall, and the formed slag skin 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 recoil in time.
④The effect of the two blast furnace plate preheaters is good, and the air temperature increases year by year
The two 1000m3 blast furnaces both use plate preheaters to preheat the gas and air to 300°C and 200°C respectively. The effect is obvious. When the furnace conditions are favorable, the air temperature is gradually increased by turning off the mixed air operation. The air temperature of 1# blast furnace is stable above 1200℃, and the 2# blast furnace is about 1240℃. Only when the company conducts one-stop maintenance, the air temperature is at a relatively high level, except that the air temperature is greatly reduced due to the oxygen stoppage.
⑤Application of small mine recovery technology
Fangda special steel machine burning capacity is not enough, in order to increase the effective amount of ore into the furnace and reduce waste, in recent years, the screen hole of the screen under the tank has been gradually reduced (4.5mm → 3.5mm), and small ore recovery has been carried out at the same time. The blast furnace return rate dropped from the initial 12% to 15% to 5% to 7%. In addition, the 2# blast furnace adopts the technology of grading into the furnace, and at the same time uses the discharging sequence under the tank to achieve the purpose of optimizing the distribution of gas flow.
⑥Using a long air outlet to facilitate the penetration of the center
The "blow-through center" is a key factor in an active hearth. During the production of 1# blast furnace over the years, the length of the tuyere was gradually adjusted from 420mm at the opening of the furnace to the current 550mm. Due to the thin-walled structure of the copper cooling wall of the 2# blast furnace, when the raw fuel changes frequently, it is easy to cause unstable central airflow, resulting in a large amount of slag peeling off, and even small edge pipes in severe cases; for this purpose, the tuyere was gradually lengthened from 583.5mm to 630mm . After the tuyere was lengthened, the airflow in the center of the 2# blast furnace was stable, and the furnace condition remained in the right direction, and there was no fluctuation for more than half a year. The tuyere lengths of Fangda Special Steel's two 1000m3 blast furnaces are rare among the same type of blast furnaces in the country.
4 Conclusion
Fangda Special Steel has continuously explored the operation technology, through a series of measures such as concentrate level, large ore batch, large angle difference, high top pressure, high air temperature, high oxygen enrichment, large coal injection, etc., as well as strengthening the management inside and outside the furnace. The stable running of the blast furnace and the continuous improvement of technical and economic indicators have achieved good economic benefits.