Practice of technological progress in Longgang ironmaking

　　Abstract: This paper analyzes and summarizes the technical progress of blast furnace in Ironmaking Plant of Longgang company from 2015 to 2019. Through scientific production organization, optimization of burden structure, improvement of raw fuel quality, detailed management of furnace conditions, safe maintenance of hearth, application of advanced technology and other practices, the blast furnace has achieved long-term cycle stability, and various indicators have been greatly improved.

　　Key words: ironmaking; Technological progress; practice
 

　　1. Overview

　　There are two 1280M iron making plants at Longgang ³ Blast furnace, 3 sets 1800m ³ The blast furnace produces 7.2 million tons of molten iron annually. From 2015 to 2020, the ironmaking plant of LongSteel Corporation learned advanced experience through external benchmarking and strengthened internal detailed operation management, and achieved remarkable results in raw fuel quality improvement, burden structure optimization, furnace condition management, equipment upgrading, scientific furnace protection, and new technology application, laying a solid foundation for the improvement of blast furnace indicators. Especially since 2019, all technical and economic indicators have achieved historic breakthroughs. The average coke ratio from January to February 2020 is 375kg/tfe, The fuel ratio is 515kg, and the average utilization coefficient is 2.81t/m3d, achieving the best level in history.

 

　　2. Ironmaking technology progress and system upgrading

　　2.1 scientific and systematic planning to realize rapid start-up and intensification of large and medium-sized maintenance of blast furnace

　　From 2015 to 2019, a total of 15 times of large and medium-sized maintenance and furnace closure for more than three months have been carried out for the blast furnace, all of which have been safely and smoothly shut down and started up, and the production and efficiency have been achieved within one week after the start-up. By summing up the experience of shutdown and start-up, a blast furnace overhaul technical system with independent intellectual property rights has been established. In particular, the 4\furnace in April 2018, the 3\furnace in January 2019, and the 1\furnace in December 2019 will quickly achieve stable production and low consumption after overhaul and startup. In 2019, the annual coke ratio of 3# furnace will be 370kg, achieving the lowest annual coke ratio in the ironmaking history of Longgang.

　　2.2 increase equipment upgrading and improve the overall level of equipment

　　Over the years, the ironmaking plant of Longgang has insisted on improving the equipment level, and has successively implemented more than 100 modifications and new equipment in sintering machine and blast furnace by relying on introduction and independent innovation, which has promoted the long-term stability of the production system.

　　2.2.1 the sintering has implemented air leakage control, heightening the breast board, adding water, improving the fan frequency, and applied new equipment and materials such as large air volume, ring cooling waste heat power generation, anti sticking and blocking of furnace bars, energy-saving ignition furnaces, ceramic wear-resistant elbows, and the overall equipment operation rate has been improved.

　　2.2.2 the blast furnace has implemented on-line monitoring of hearth water temperature difference, furnace shell temperature measurement, improvement of cooling capacity and sectional control of cooling water volume; Slag iron ditch process transformation; Upgrading of screening system; Transformation of intelligent injection, intelligent furnace burning, furnace replacement, double preheater of hot blast furnace, TRT online descaling, etc; Automatic remote control technology of opening machine and clay gun; The application of new equipment and materials such as pellet ring cooling, high-strength ceramics and high thermal conductivity carbon bricks has significantly improved the support capacity and automation control level of blast furnace equipment.

　　2.3 relying on scientific and technological progress to promote the technological upgrading of pre Railway

　　2.3.1 insist on technology introduction and innovation. Since 2015, thick bed sintering, small ball sintering, low carbon and low silicon sintering, high and low alkalinity sintering, lump ore bedding and material surface heating technology have been applied in sintering; Steam preheating and ore return technology; Mixture temperature rise technology; Waste heat utilization technology of ring cooling; Mixture granulation technology; New technologies and processes such as thick bed sintering have carried out micro-control research on sintering end point, exhaust gas temperature, laying thickness, charge surface heating, etc., and achieved a significant increase in sintering capacity. The output of finished ore has increased from 35000 tons to 39000 tons, and the sinter feeding rate has increased from 68-70% to 75-76%.

　　The blast furnace has realized the technologies of dedusting, recovery and air supply of pressure equalizing gas at the top of the furnace; Blast furnace top infrared ray, laser charge level imaging, coal injection imaging, hearth erosion model and other monitoring technologies.

　　2.3.2 after 2018, relying on the newly built metallurgical realization room in front of tieqian, the dream of independently testing the metallurgical properties of sinter, lump ore and pellet has been realized. At present, the research on the properties of sinter, pellet, lump ore, Indian powder and ultra-fine powder and the proportioning standards have been realized. Professional experimental standard systems, such as thermal explosion index of iron ore, low-temperature pulverization, reduction performance, soft melting temperature, droplet dissolving performance and sintering test cup, have been gradually established, providing scientific and accurate technical support for sintering and pellet optimization.

　　2.3.3 over the years, through production practice and accumulated experience in large and medium-sized maintenance of sintering machine and blast furnace, ironmaking plants have successively applied for more than 16 authorized patents, published more than 200 professional papers, and implemented more than 1000 job innovations. In 2018, "blast furnace cooling intensity subsection control technology" won the second prize of Shaanxi Metallurgical Science and technology.

　　2.4 use comprehensive strengthening and maintenance means to realize the effective connection between blast furnace protection and stable production and low consumption

　　2.4.1 adhering to the idea of paying equal attention to high production and furnace protection of blast furnaces and long-term furnace protection, by continuously improving the furnace protection control system and standardizing the operation and adjustment, under the premise of stable production and low consumption, the overall decrease and basic control of the side wall temperature of 5 hearth have been realized successively. The 4 blast furnaces have achieved safe furnace production to overhaul, and the furnace service has been extended for 8-10 months.

　　2.4.2 by means of overhaul and daily maintenance, the two 1800 blast furnaces have all realized the subsection control technology of hearth cooling and the improvement and transformation of cooling capacity, so as to solve the hidden dangers of unreasonable distribution of cooling water between blast furnace shaft and hearth and insufficient hearth cooling intensity.

　　2.4.3 highlight the control of key parts. With the further release of production capacity and the high load operation of the equipment, various blast furnaces have successively encountered major safety hazards such as furnace crack and the continuous rise of hearth temperature. The requirements for safety control of furnace crack and the requirements for safety control of abnormal blast furnace hearth temperature have been improved. The management and control measures have been implemented from six aspects: operation environment, on-site operation, hidden danger monitoring, hidden danger rectification, post standard operation and post emergency operation, Effectively control hidden dangers.

　　2.5 implement index benchmarking based on industry gap

　　Over the years, the iron making blast furnace index of Longgang has remained at the middle and lower level of the industry. It has gone out for benchmarking for more than 40 times, absorbed advanced concepts and experience of the industry, and optimized blast furnace operation.

　　2.5.1 reduce the area of air outlet. According to the actual conditions of 80% of raw fuels purchased by Longgang, many varieties and unstable quality, measures have been taken to reduce the air supply area and increase the wind speed year by year. The wind speed has increased from 200m/s to more than 230m/s. The hearth center has been further opened, the air volume has increased, the air flow distribution is more reasonable, and the coal gas utilization rate has increased from 46.5-46.8% to more than 47.1%. Change of tuyere area:

　　2.5.2 optimize the distribution system: for years, the blast furnace has poor stability, frequent fluctuations and poor airflow stability. From 2018 to 2019, an attempt was made to optimize the distribution system in the blast furnace. By adjusting the distribution angle, the same angle of ore and coke, increasing or decreasing the number of distribution circles, canceling or reducing the central coking and other measures, the stability of furnace conditions was improved, the output, quality, coke ratio and fuel ratio of the blast furnace were significantly improved, and long-term stable production and smooth operation with low consumption were realized.

　　2.5.3 optimize coal injection structure. In 2019, the injection structure adjustment will be implemented in the blast furnace. The proportion of anthracite will be increased from 35% to 80%, the fixed C of mixed coal will be increased from 73.8% to over 79.5%, and the coke load will be significantly increased from less than 4.0 times to more than 4.25 times, and the maximum will be more than 4.45 times. At the same time, the coal ratio is increased to more than 150kg, realizing the increase of output and the overall decrease of coke ratio and fuel ratio.

　　2.5.4 keep your eyes inward and stick to the intensive operation.

　　(1) Adhere to full air temperature air supply. From 2015 to 2019, blast furnace air temperature continued to rise, reaching an average of above 1185 ℃ in 2019.

　　(2) Implement high coal ratio. In view of the problems of low coal ratio, high coke ratio and high cost over the years, the coal ratio research has been carried out since January 2019, and the coal ratio has increased from 121kg in 2015 to 149kg.

　　(3) Oxygen enrichment. According to the large amount of coal injected into the blast furnace and the adjustment of the injection structure, the oxygen enrichment of the blast furnace has increased from 25000m3/h in 2015 to more than 37000m3/h. At present, it has reached more than 39000m3/h, and the oxygen enrichment rate has increased from 2.30% to more than 3.1%.

　　(4) Low silicon smelting. Adhere to the operation concept of low silicon smelting, aim at [si] control of 0.30-0.40%, and achieve a breakthrough in furnace temperature stability and silicon deviation. The average silicon is within 0.40%, and the silicon deviation is reduced from 0.16% to 0.13%.

　　2.6 further stable improvement of peripheral supply guarantee capacity

　　By strengthening the concept of "one family working together and integrated management", the peripheral supply guarantee capacity has been further improved and stabilized.

　　(1) Improve the refractory quality, transform the pouring process of the main ditch, increase the thickness and depth of the iron ditch, increase the refractory thickness of the ditch side by 150mm, and greatly increase the iron content of the single channel. The iron flux of 1800 blast furnace has reached 190000 tons, the iron flux of single pouring has increased by 60000 tons, the service life has increased from 50-55 days to 65-70 days, and the pouring times have been reduced by 2-3 times a year.

　　(2) Adapt to the high smelting strength of blast furnace and the increase of production capacity, timely adjust the formula of blast mud, and improve the strength and supply of blast mud. There was no blast furnace condition fluctuation and peripheral accidents caused by blast mud quality fluctuation throughout the year.

　　(3) Using low-temperature and high-strength ceramic wear-resistant materials to extend the maintenance period of the granulation tower of the blast furnace from 3-5 months to more than 8 months, while eliminating the problems that the previously cast graphite is easy to fall off, which is easy to frequently block the slag flushing pipeline and a large amount of slag.

　　(4) The high-strength ceramic precast block is used in the slag flushing tank, which fundamentally solves the problems of damage, collapse and slag discharge of the cast iron slag flushing tank.

　　(5) Through the capacity expansion and energy-saving transformation of the cooling water pump, the water supply capacity has been increased from 4300m3/h to more than 4600m3/h, the inlet water temperature has been reduced from 43 ℃ to less than 40 ℃, the water speed has been increased from 1.6-1.8m/s to more than 2.0m/s, up to more than 2.2m/s, and the cooling quality of the blast furnace has been significantly improved.

　　(6) Reasonable ingredients continuously reduce harmful elements. From 2015 to 2019, the load of harmful elements showed a downward trend as a whole.

　　2.7 grasp the basis of raw materials and create conditions for capacity and quality improvement

　　(1) Adhere to advanced management, pay attention to batching, operation and equipment, and successively complete the technical transformation and process optimization of pelletizing shaft furnace. The operation rate of pelletizing equipment has reached more than 98%, the output has increased from 3800 tons in 2015 to more than 5300 tons, and the proportion of self-produced pellets has increased from 11% to more than 15%, laying a foundation for the stability of blast furnace burden structure.

　　(2) Through the medium maintenance of sintering machine, the fence plates of 265, 400 and 450 sintering machines were raised and transformed. The material layer was raised from 750mm and 800mm to 850mm and 900mm, realizing the control of super thick material layer, and the ore yield was increased by 3-5%.

　　(3) The optimization of sintering raw materials has been preliminarily realized, and the number of sintering raw materials has gradually stabilized from more than 15 to 6-8; Through tackling key problems and stacking optimization, the number of stacking layers of raw material 1 and 2\\system was increased from 240 and 300 layers to 340 and 450 layers, realizing the continuous stability of the quality of sinter mixed ore.

　　(4) Through the transformation of lump ore screening system, the lump ore supply capacity and screening quality have been improved, and the demand of 18-20% of blast furnace lump ore has been realized.

　　(5) All coke of Longgang is purchased. With the strengthening of blast furnace and the impact of environmental protection and production restriction, the regional mainstream coke supply is insufficient. It has been expanded to both inside and outside the province, and as many as 14 new resources have been introduced. In order to ensure the stability of incoming coke quality to the greatest extent, a special regulation and reaction mechanism for coke supply of large blast furnace mainstream coke + small blast furnace non mainstream coke + micro regulation of physical quality was established. By matching different varieties of incoming coke with CSR ≥ 60% and non mainstream coke with small materials, the blast furnace burden structure, furnace condition stability and economic indicators were greatly improved.

　　2.8 strengthen the improvement and standardized management of internal procedures and systems

　　Adhere to benchmarking with the industry's advanced, based on the industry's advanced experience and development direction, and strengthen the improvement and standardized management of internal procedures and systems.

　　(1) The blast furnace protection and control system has been improved, the hearth safety control system and furnace type management system have been improved, and the blast furnace emergency plan and daily monitoring and control system have been revised to achieve no blind zone control of the blast furnace.

　　(2) Revise and improve the process and technical operation procedures of blast furnace and auxiliary units, and add and improve the operation procedures of air supply and induced gas, pressure equalizing operation of furnace top gas and gas recovery.

　　(3) Strengthen the inspection and correction of process system implementation, parameter control, process control, log recording, project promotion, etc. of blast furnace, sintering machine and auxiliary units.

　　(4) Revise and improve the emergency plan for blast furnace operation in combination with on-site environmental protection treatment.

　　3. Conclusion

　　From 2019 to 2020, the blast furnace of Longgang has maintained a long-term stable and smooth operation of furnace conditions and achieved a breakthrough in indicators. However, there is still a gap with the industry in terms of the stability of raw fuel quality and the refinement and adjustment of furnace conditions.

　　(1) Insist on improving the quality of raw materials and fuels, take stabilizing the burden structure and reducing the load of harmful elements into the furnace as a breakthrough, and create conditions for the stable and smooth operation of the blast furnace.

　　(2) Explore the operation system of different raw materials and fuels at different times, reasonably optimize the charging system, achieve the upper stability and lower activity, and ensure the long-term stable and smooth operation of the blast furnace and the improvement of technical and economic indicators.

　　(3) The furnace condition management must meet the requirements of the cooling system. The cooling system cannot be used to adjust the furnace condition for a long time. Meanwhile, the equipment leakage must be treated in time. It is forbidden to maintain the tuyere sleeve for a long time. Continue to improve the daily operation management and improve the operation and management level.

　　(4) To protect the blast furnace, it is necessary to stabilize the furnace condition, increase the wind speed, reasonably use oxygen, increase the titanium content in molten iron, and control the reasonable smelting intensity. Regularly organize experts or professionals to conduct "physical examination" for hearth safety.