Summary of large blast furnace ironmaking technology

　　Abstract: large blast furnace is the development trend of blast furnace ironmaking in the world and the centralized representative of advanced ironmaking technology. Large blast furnace has the advantages of low energy consumption, environmental protection and high labor productivity. In order to provide reference for China's large blast furnace enterprises, the technical indexes of some large blast furnaces in the world are selected for analysis and comparison, and analyzed from the aspects of raw fuel, operating parameters, technical characteristics and so on.

　　Key words: technical characteristics of large blast furnace for iron making
 

　　1. Foreword

　　Large blast furnace is the development trend of iron making technology. Large blast furnace has the advantages of high production efficiency, low fuel consumption, environmental protection and long life. In the early 1960s, the world's largest blast furnace volume was 2000m3. Around the 1970s, people called blast furnaces above 2000m3 large blast furnaces and blast furnaces above 4000m3 giant blast furnaces. With the continuous development of blast furnace ironmaking technology, the volume of blast furnace is also expanding. In june2013, the 1\. According to gb50427-2008 code for design of blast furnace ironmaking process: a blast furnace with a volume of 4000-4999 m3 is defined as a 4000 m3 blast furnace; A blast furnace with a volume of 5000-5999 m3 is defined as a 5000m3 blast furnace. In this paper, the technical characteristics of some blast furnaces with a volume greater than 4000m3 in the world are analyzed, which provides reference for the technical personnel of domestic ironmaking plants.
 

　　2. Distribution of large blast furnaces worldwide

　　2.1 4000m ³ Distribution of class large blast furnaces

　　According to the author's statistics, by the end of 2016, there were 57 4000m3 blast furnaces in operation worldwide, including 17 in China, 14 in Japan, 7 in South Korea, 4 in India, 2 in Germany, the United States, Russia, Ukraine, the Netherlands, France and Brazil, and 1 in Italy, the United Kingdom and each.

　　The large-scale blast furnace in China started from the production of Baosteel Group in september1985. After entering the 21st century, a large number of large-scale blast furnaces have been built. According to statistics, by the end of 2016, there were 17 blast furnaces with an effective furnace capacity of 4000m3 in service in China.

　　2.2 world 5000m ³ Distribution of class large blast furnaces

　　There are 28 blast furnaces with a volume of more than 5000m3 in the world, including 13 in Japan, 5 in China, 7 in South Korea, and 1 in Germany, Russia and Ukraine.

　　In the 1970s, countries represented by Japan successively established a batch of large blast furnaces with a capacity of more than 5000m3, leading the development trend of large-scale blast furnace ironmaking in the world [1]. On September 29th, 2004, Sumitomo Metal Kajima plant put into operation 5370m ³ The new No. 1 blast furnace is the only large-scale blast furnace newly built in Japan in the past 25 years. The No. 2 blast furnace of Nippon Steel large branch was overhauled and expanded to 5775m in may2004 ³， The daily output reached 13500 tons, making it the world's largest iron making blast furnace at that time. After overhaul, the No. 1 blast furnace of the Nippon Steel plant was also expanded to 5775m ³， These old blast furnaces still have high production efficiency after continuous overhaul and transformation.

　　The volume of No. 1 blast furnace put into operation by POSCO Guangyang steel plant in june2013 is 6000m ³， It is by far the largest blast furnace in the world. Although China's steel output has surpassed that of Japan since 1996, ranking first in the world, the crude steel output in 2008 exceeded 500 million tons, equivalent to four times that of Japan. But before 2009, there were only 10 4000m ³ Among the large-scale blast furnaces above grade, the largest one is Baosteel's No. 1 blast furnace (the third generation) put into operation in february2009, with an effective volume of 4966m ³。 Since there are a large number of small blast furnaces with high pollution and high energy consumption in China, the blast furnace elimination standard was reduced from 300m when the iron and steel industry revitalization plan was formulated in early 2009 ³ Increase to 1000M ³， Directly reduce the backward steel production capacity by more than 180million tons. Therefore, since 2009, China's large-scale iron making blast furnaces have entered a climax of construction, and the output of crude steel has increased from 355million tons in 2005 to 823 million tons in 2014 [2]. On may21,2009, the newly built No. 1 blast furnace (5500m) of Shougang Jingtang company located in Caofeidian Industrial Zone, Tangshan ³) The successful ignition indicates that the development of China's super large blast furnace has entered a new stage. On October 21 of the same year, Shagang 5860m ³ The blast furnace was put into operation and became the largest blast furnace in the world at that time.
 

　　3. Technical and economic indexes of large blast furnace

　　The large-scale blast furnace adopts the thin-wall lining technology of enhanced cooling, pays attention to the convergence of blast furnace design furnace type and operation furnace type, changes the traditional design concept of thick wall lining blast furnace type, and no longer relies on erosion of lining to form a reasonable blast furnace operation furnace type. The furnace type design is based on the stable and smooth operation of blast furnace, improving the permeability of charge column, improving gas distribution and restraining the development of edge gas flow. When the effective height of the blast furnace changes little, reducing the bosh angle is conducive to the smooth discharge and rise of the bosh gas, and is conducive to the formation of a stable protective slag skin in the bosh area, the protection of the cooler in the bosh area and the extension of the service life of the bosh area.

　　As an important index of the scale effect of large blast furnace, the utilization coefficient of blast furnace has always been concerned by everyone, but there is a certain difference between the utilization coefficient of large blast furnace and that of small blast furnace. Comparing the shape parameters of large blast furnace and small blast furnace, it is found that there is no symmetrical proportional relationship between blast furnace volume and hearth area, and the proportion of hearth area corresponding to unit furnace capacity of small blast furnace is significantly larger than that of large blast furnace. According to the ratio and daily iron production of blast furnace, the utilization coefficient of 500m3 blast furnace is 4.0t/ (M3 · d), which is equivalent to about 2.1t/ (M3 · d) of 4000m3 blast furnace. Therefore, the utilization coefficient of large blast furnace for intensified smelting is generally controlled at 2.2~2.4t/ (M3 · d).

　　During the operation of Nippon Steel's large blast furnace, it not only pursues high coal ratio, but determines the coal injection amount according to the situation of the plant. However, the new coal injection device usually selects a high design coal ratio. The proportion of burden structure is very important in the running of large blast furnace. The current proportioning policy of Nippon Steel is to appropriately increase the proportion of lump ore under the condition that the proportion of sinter is 70~80%.

　　The South Korean POSCO blast furnace uses the technology of large coal injection, and the coal ratio is 160-180kg/thm. Like Nippon Steel, South Korea POSCO appropriately increased the proportion of lump ore in the blast furnace burden structure, reducing the production cost.

　　Shagang 5800m ³ The blast furnace was ignited and started on October 20, 2009. The design index was reached in May, 2010. By December, 2010, the utilization coefficient of the blast furnace was up to 2.27t/ (M3 · d), the lowest fuel ratio was 492kg/thm, and the highest coal ratio was 165kg/thm.

　　The No. 1 blast furnace of Jingtang company of Shougang was opened for ignition on may21,2009. By taking measures such as fine charging, exploring a reasonable charging system, air supply system, slag iron tapping system, increasing furnace top pressure and oxygen enriched high air temperature, various production indicators have been continuously improved. After two months of operation, the utilization coefficient of the high furnace has reached more than 2.0t/ (M3 · d). In december2009, the utilization coefficient of Jingtang 1# blast furnace of Shougang reached 2.308 t/ (M3 · d), reaching the design level. In March, 2010, the utilization coefficient of 1\blast furnace reached 2.37 t/ (M3 · d), the coke ratio (including coke Ding) reached 306kg/t, the coal ratio reached 175 kg/t, and the fuel ratio reached 481kg/t. All indicators reached the best level since the commissioning.

　　The piling construction of No. 1 blast furnace of Zhanjiang iron and steel started on May 17, 2013 [3], and was successfully put into operation on September 25, 2015. Since the high-speed furnace began to increase production, the daily output has gradually increased from 8500t/d in November 2015 to 12000t/d in March 2016. By increasing air volume and starting oxygen enrichment and other technical means, the blast furnace has shifted from low utilization factor to high utilization factor production, and the output has increased significantly (by 40%). After the air volume and oxygen enrichment rate are greatly increased, the air flow distribution, temperature field distribution, soft melt zone shape, hearth thermal state, etc. will change greatly, so the operation must be adjusted accordingly. No. 1 blast furnace expanded the tuyere area, increased the air volume and stabilized the air speed, increased the ore batch weight, maintained a reasonable feed rate, reduced the initial feed angle by 10 °, and expanded the feed gear angle difference by 10 °. Through operation adjustment, the utilization coefficient at this stage was gradually increased from 2.0 t/ (M3 · d) to 2.3t/ (M3 · d) in March 2016, the oxygen enrichment rate was 4.2%, and the coal injection ratio was more than 170kg/thm, while maintaining a high gas utilization ratio and a low fuel ratio.
 

　　4. Technical characteristics and Prospect of large blast furnace

　　4.1 concentrate is the basic condition for normal production of large blast furnace

　　These enterprises with super large blast furnaces are well aware of the importance of fine materials, and they have all equipped super large blast furnaces with high raw and fuel conditions. The ore grade of extra large blast furnace is higher, about 2% higher than that of key enterprises in the same period. At present, the sinter ratio of domestic blast furnaces, including super large blast furnaces, is about 70%. This is due to the basicity of sinter and the matching of sintering blast furnace. All super large blast furnaces use high basicity sinter with high sintering grade. Large sintering machines are equipped with super large blast furnaces with advanced production technology, which is necessary to ensure the metallurgical properties and strength of sinter. In general, high-quality raw materials and fuels can basically meet the needs of large-scale blast furnaces, ensure the smooth running stability of large-scale blast furnaces, and achieve better indicators.

　　The quality of coke used in super large blast furnaces is high, and the ash content of coke has certain advantages. In 2016, the ash content of 4000m3 blast furnace was 0.23% lower than that of small and medium-sized blast furnaces, and the ash content of coke used in large blast furnaces was about 12%. In 2016, Benxi Iron and Steel Co., Ltd. had the highest ash content of coke used in large blast furnaces, followed by Maanshan Iron and Steel Co., Ltd. and Shagang, both of which were 12.28%. Baosteel and Zhanjiang blast furnaces have the lowest ash content, about 11.6%. From the perspective of pulverized coal quality, the pulverized coal quality of large blast furnaces is generally excellent. In 2016, the average ash content of pulverized coal was 9.57%, 2~3% lower than that of coke. This can make the coal coke replacement ratio equal to or close to 1, so that the coal injection and fuel ratio can be reduced synchronously, which is conducive to reducing the amount of slag. The blast furnace of Benxi Iron and Steel Co., Ltd. has the highest ash content of pulverized coal, up to 11.06%; The blast furnace of Anyang Iron and Steel Group has the lowest ash content, reaching 8.53%.

　　4.2 wide application of oxygen enriched large coal injection technology

　　Oxygen enriched large coal injection technology and low-cost smelting technology have become the pursuit goals of blast furnace operators. In 2016, the average coal ratio of domestic blast furnaces above 4000m3 reached 156kg/t, of which the highest was Jingtang blast furnace, with a coal ratio of 193kg/t; The lowest is Baotou Iron and steel blast furnace, and the coal ratio is only 121kg/t. The average oxygen enrichment rate reaches 3.57%, the highest oxygen enrichment rate is Shagang blast furnace, which reaches 6.37%, followed by WISCO blast furnace, which reaches 6.12%; The lowest is Meigang and Bayuquan, both about 2.0%. With the continuous improvement of oxygen enriched and coal injection technology, the distribution of blast furnace gas flow will change to a certain extent. "Abundant and stable central gas flow and moderately controlled edge gas flow" are typical characteristics of gas flow distribution in large blast furnace during intensified smelting and large coal injection operation. For large blast furnaces, the adjustment of gas flow must follow the mode of "based on the appropriate air supply system at the lower part, and the distribution system at the upper furnace top matches the cooling system at the middle part", so as to realize the reasonable distribution and stability of blast furnace gas. In addition, due to the distribution characteristics of gas flow in large blast furnaces, the utilization degree of gas in large blast furnaces is small, and the blast furnace has obviously jumped to a new level.

　　Although the oxygen enriched large coal injection technology adopted by large blast furnaces has been recognized and popularized as the effect of cost reduction, efficiency increase, energy conservation and environmental protection, the implementation of oxygen enriched large coal injection technology requires certain conditions. High quality and stable coke and low slag ratio are the premise and foundation for the successful implementation of oxygen enriched and large coal injection technology in large blast furnaces. In the process of oxygen enrichment and coal injection in large blast furnace, the "skeleton" role of coke is particularly prominent. The strength and ash content of coke, as the key indicators of coke quality, must be guaranteed. There is still a certain amount of unburned pulverized coal during the implementation of oxygen enriched and large coal injection technology in large blast furnaces. Therefore, controlling the low slag ratio of blast furnaces can not only effectively improve the permeability of charge column, but also ensure the liquid permeability of hearth Coke Column and the overall activity of hearth.

　　4.3 large modern raw fuel production equipment provides strong support for large-scale blast furnace

　　Large blast furnaces have played an active role in eliminating backward equipment, improving environmental conditions, improving product quality, reducing energy consumption and improving market competitiveness. The design of large blast furnace is reflected in many aspects, such as fine material, high air temperature, large coal injection, high efficiency and long life, environmental protection and energy conservation, improving equipment localization rate, reducing investment and shortening construction period [4]. The construction of large-scale blast furnaces needs to be supported by the design and manufacturing technology of large-scale equipment, on the premise of stable large-scale raw fuel supply, and the matching hardware conditions such as raw fuel (sinter, pellet and coke) processing technology and equipment. At the same time, it needs software conditions such as the understanding of the smelting law of large-scale blast furnaces, the improvement of operation technology and high-level management. The large-scale blast furnace is a concrete embodiment of a country's comprehensive industrial level [5]. The large-scale blast furnace does not only refer to the blast furnace smelting process, but also includes the systematic coordination of pre iron processes such as raw material preparation in the stockyard, sintering, pelletizing and coking. The process of large-scale blast furnace is a process of continuously accumulating and summarizing the smelting law and smelting performance. Only through technological innovation can the long-term smooth and stable production of blast furnace be realized. In the long run, the competitiveness of blast furnaces is not only reflected in the current iron making cost control ability, but also in the future energy conservation, emission reduction and environmental protection. Large blast furnaces have more advantages and competitiveness.

　　The completion and operation of large blast furnace has realized the upgrading of equipment, but the improvement of soft power needs a long time to explore. The first large-scale blast furnace (furnace capacity of 4036m3) in China has experienced arduous exploration from commissioning to stable operation, but it has also obtained relatively complete large-scale blast furnace operation technology, created many advanced blast furnace smelting technical and economic indicators, and showed strong competitiveness. Shougang Jingtang company put into operation the first domestic blast furnace with a furnace capacity of 5500m3 in 2009. The large-scale blast furnace is not only the expansion of blast furnace capacity, but also the hardware equipment and application technology for all processes before ironing. Jingtang company of Shougang has large equipment such as a pellet belt roaster with a roasting area of 504m2, a 550m2 sintering machine and a coke oven with a carbonization chamber height of 7.63m, so as to meet the requirements of large blast furnaces for the quantity, quality and stability of incoming raw fuels, so that the blast furnaces can obtain good operation indicators.

　　4.4 optimizing design and improving service life is the inevitable trend of large blast furnace development

　　Under the condition that the construction investment of large blast furnace is about 7 times higher than that of small blast furnace, the goal of high efficiency and low cost of large blast furnace must be achieved by prolonging the service life of blast furnace as much as possible. Therefore, it is another complete system engineering to realize the longevity of large blast furnace. Under the premise of no medium maintenance, the long-life goal of large blast furnace can be basically achieved only after the blast furnace has been in service for more than 15 years and the iron production per unit furnace capacity is more than 10000t/m3. The realization of long life of large blast furnace must be the comprehensive result of design and manufacturing, construction and maintenance, operation and maintenance, etc. While striving for the stability of the daily operation of the blast furnace and the maintenance technology at the later stage of furnace service to bring positive effects on the longevity of the blast furnace, the longevity technology at the upper and lower parts of the large blast furnace used in the design of the blast furnace is the basis and condition for realizing the longevity goal of the blast furnace. Prolonging the service life of blast furnace is the development trend of modern blast furnace technology. Shougang Jingtang 5500m ³ The design life of the large blast furnace is 25 years, and the iron production of the first generation furnace is more than 20000t/m3. In the design of Jingtang blast furnace of Shougang, the modern blast furnace longevity technology theory is applied, the international advanced blast furnace high-efficiency longevity comprehensive technology is adopted, the reasonable blast furnace type is determined, the non superheater cooler and pure water closed circulation cooling technology are adopted, the lining structure of the furnace body is optimized, and the perfect high-speed furnace automatic detection and control system is set to realize the stable and smooth operation, long-life and high-efficiency of blast furnace production.

　　Bosh angle and height diameter ratio are the main parameters that must be paid great attention to in the design of large blast furnace. Whether the parameters are reasonable or not will directly affect the stability of furnace conditions and the improvement of indicators after the blast furnace is put into operation. The bosh angle and height diameter ratio of large blast furnaces are lower than those of small blast furnaces. For large blast furnaces, the bosh angle is generally controlled at 80.5~82.5 ° and the height diameter ratio is 1.95~2.20. For large blast furnaces of the same level, the selected bosh angle range is obviously more dispersed than the height diameter ratio, that is, large blast furnace enterprises have some differences of opinion on the selection of bosh angle on the basis of basically agreeing with the moderately short and fat type. Taking the selection results of Baosteel's large blast furnace as an example, the selected bosh angle and height diameter ratio are within the average line area. At the same time, the bosh angle and height diameter ratio of Baosteel's blast furnace also have a moderate downward trend, which is mainly related to the deterioration trend of raw fuel conditions. The number of tapholes in front of the furnace must be designed according to the furnace capacity and the enhanced smelting capacity of the blast furnace [6].
 

　　5. Summary

　　(1) The large-scale blast furnace is the development trend of iron making technology. Large-scale blast furnace has the advantages of high production efficiency, low fuel consumption, environmental protection and long life.

　　(2) At present, there are 57 4000m3 blast furnaces in operation worldwide, and 28 blast furnaces with a volume of more than 5000m3 are in operation.

　　(3) Good economic indicators have been achieved after large blast furnaces have been put into operation, with coke ratio reaching 300kg/t, coal ratio reaching 180kg/t and fuel ratio lower than 500kg/t.

　　(4) The main technical features of large blast furnace include: fine material, oxygen enrichment, large coal injection, long life and environmental protection, large-scale raw fuel equipment, etc.