(Zhengzhou Annike Industrial Co., Ltd., Zhengzhou 452370, China)

Abstract: This paper describes the current situation of hot blast stove in China, taking the development of top-fired hot blast stove in China as the main line, through the investigation and comparison of the performance of various top-fired hot blast stove burners, combined with the requirements of steel users for high air temperature, high efficiency, long life and low emissions of hot blast stove, using the top-fired hot blast stove test research platform and computer simulation, research and development of cone column rotary cutting top-fired hot blast stove burner high power ceramic technology, the hot blast stove has low NOx combustion technology, and the engineering application practice proves that the cone-column rotary cutting top-burning hot blast stove has the advantages of low investment, low energy consumption, low emission, high air temperature and long life. With the increasingly prominent indicators of environmental protection emissions and energy consumption, Anneke will continue to devote itself to the continuous optimization and improvement of top-burning hot blast stoves and the research and development and production of supporting refractory materials. Through the continuous optimization and upgrading of furnace structure and refractory configuration, it will provide top-burning hot blast stove technology with high temperature, long life, low carbon and consumption reduction, intelligent and intensive for users of China's iron and steel enterprises.

Key words: cone-column rotary-cutting top-fired hot-blast stove; low carbon and consumption reduction; high efficiency and long life; low NOX emission

1 Foreword

The main task of ironmaking blast furnace is to produce molten iron, which plays a vital role in the development of iron and steel industry. As an important auxiliary equipment of ironmaking system, the main function of hot blast furnace is to provide high temperature hot air for blast furnace production.
As the energy conversion equipment of the ironmaking system, the hot blast stove supplies the heat of the blast furnace to account for about ⅓ of the energy consumption of ironmaking production. Since the 20th century, the structural type of hot blast stove has experienced the evolution and transformation process of internal combustion type, external combustion type and top combustion type. The domestic hot blast stove market is basically occupied by the internal combustion hot blast stove of Holland, the external combustion hot blast stove of Nippon Steel in Japan, and the top combustion hot blast stove of Kalugin in Russia, etc., and forms a technical monopoly. Among these three typical hot blast stoves, the top-fired hot blast stove has gradually replaced the internal combustion hot blast stove and the external combustion hot blast stove and has become the mainstream of the new hot blast stove with its compact space, stable structure and small footprint.

2 Development of top combustion hot blast stove

As a more reasonable and advanced furnace type than internal combustion and external combustion hot blast stove, top combustion hot blast stove technology has been recognized by the iron-making industry at home and abroad. Top-burning hot-blast stove technology first appeared in the chemical industry system. Hartmann put forward the idea of applying top-burning hot-blast stove in the 1920 s, but it was not paid attention to until the 1960 s, due to the requirements of high air temperature, the research on top-burning hot-blast stove began.

The pioneers of top-burning technology in China began to study related work in the 1960 s. In 1970, they obtained successful experience in Shougang's 23.5m3 experimental furnace and successfully applied this technology to 1327-2500m3 large blast furnace, which is a precedent in the world for applying top-burning hot blast furnace to blast furnace above 1000 m3. The furnace type is characterized by large hat and high-power short-flame burner (see Figure A), although Shougang type top-fired hot blast stove has achieved high air temperature (1150-1200 ℃) in blast furnace production, the burner nozzle is easy to be damaged under high temperature, which is restricted by the limitations of equipment and materials at that time. Except for Shougang, Shigang and Fujian Sanming Iron and Steel Co., Ltd., it has not been widely used. Its vault and burner design, regenerator lattice brick and siliceous material are used, it laid the foundation for the development of many top-burning hot blast stoves later. [1]

As a Chinese characteristic, the technology of ball hot blast stove began in the late 1950 s and can also be classified as a kind of top-burning hot blast stove. Because of its small investment and simple technology, it has been widely used in domestic small and medium-sized ironmaking blast furnaces. Although in the late 1990 s, relevant domestic institutions made a lot of improvements to ball hot blast furnaces and successfully applied them on 1500m3 blast furnaces, however, with the implementation of the national policy of eliminating backward production capacity equipment and stricter environmental protection standards, coupled with the frequent shutdown of the ball-type hot blast stove for ball change, large temperature difference of hot air temperature, short service life, high energy consumption and other defects, it is difficult to meet the development of large blast furnace ironmaking technology.

In foreign countries, the all-Soviet Metallurgical and Thermal Research Institute of the former Soviet Union conducted a comprehensive study on the top-burning hot blast stove. In 1982, a Kalujin top-burning hot blast stove was built on the 1513m3 blast furnace of the Lower Tagir Metallurgical Company (see Figure B). This hot blast stove absorbed the characteristics of the hemispherical big hat vault of the Shougang top-burning hot blast stove and improved the arrangement structure of the burner, the lower part of the large spherical vault is arranged with a ring structure independent of air and gas, and the ceramic burner built with refractory materials solves the problem of high temperature of the burner of Shougang type top-burning hot blast stove. However, due to its large vault structure, too many burners and complicated design and manufacturing operations, it is impossible to make technical transformation to the existing internal combustion hot blast stove. Only one hot blast stove was built in Russia, and this technical scheme was abandoned later, however, it has accumulated experience in the application of refractory materials, lattice bricks, grates and other related technologies.

A domestic hot blast stove company used the early Kalujin hot blast stove technology as a template to improve the vault shape as a catenary line type big hat. Through applying for a utility model patent, it was also applied to some domestic small and medium-sized blast furnaces (see Figure C). However, due to the large vault size of this type of top-burning hot blast stove, the refractory material consumption was 15%-25% more than that of the small hat-top-top-burning hot blast stove, and was put into operation, it is easy to appear vault collapse, lattice brick sinking, operation difficulties and many other problems, not widely accepted by the market.
Subsequently, Kalugin improved the early annular precombustion chamber hot blast stove, absorbed the vault structure design of the regenerator of Nippon Steel's external combustion hot blast stove, and introduced the small hat Kalujin top combustion hot blast stove (see Figure D). Since 2000, it has been tested in industrial practice in Russia. In 2001, the technology of Russian Kalugin small hat top combustion hot blast stove was introduced into China by Beijing Iron and Steel Design Institute, combined with the domestic metallurgical design, refractory materials and other mature technology and equipment, catch up with the rapid development of China's iron and steel industry construction wave, in the domestic market has been gradually promoted and applied.

In the past 20 years, the wide application of top-burning hot blast furnaces in my country has advanced by leaps and bounds. The top-burning hot blast furnace technology with independent intellectual property rights of major domestic steel design institutes and related companies has also shown a state of blooming and contending. On the one hand, it has independently developed a variety of structural forms of top-burning hot blast furnaces, boldly applied; on the other hand, the introduction, digestion and absorption of foreign advanced technology has achieved gratifying results, especially in the application of large blast furnace, the top combustion hot blast stove technology has entered a new period of development.

In China's current iron and steel enterprises, a variety of top-burning hot-blast furnace furnace type coexist, in the long-term use process, found that there are some shortcomings, urgent need to improve and solve, such as uneven burner airflow distribution, low thermal efficiency, high gas consumption, high NOx emission value, burner nozzle dislocation, hot-blast outlet collapse, lattice brick sinking, hot-blast pipe deformation brick caused by short service life of hot-blast furnace and other issues, only by solving the above problems, the top burning hot blast stove can meet the needs of the current steel users and develop better in the future. [2]

3 Various top-fired hot blast stove burner performance investigation and comparison.

The top-fired hot blast stove has been developed for more than 50 years, and its development process is basically the continuous improvement process of the burner. The top-fired hot blast stove places the burner on the vault of the regenerator of the hot blast stove, uses the vault space as the combustion chamber, and cancels the independent combustion chamber structure. The burner structure has experienced the process from the initial sleeve metal burner to the sleeve ceramic burner, and then to the ceramic burner. The evolution of the shape from the initial hemispherical large vault to the current common hemispherical small vault, the design principles and use of several top-fired hot blast stove burners are compared and analyzed as follows.

Through the analysis of the burner of the hot blast stove with the above structure, combined with the requirements of high air temperature, high efficiency, long life and low emission of the hot blast stove, the design of the new top-fired hot blast stove burner needs to be studied from the following aspects:

1) The ceramic burner adopts a small vault structure to optimize the internal refractory masonry and brick type;

2) The design of ceramic burner nozzle should be optimized to strengthen the cross mixing effect of air flow, ensure the air and gas mixing evenly, and require the gas to achieve complete combustion in the limited vault space;

3) The completely burned high-temperature flue gas can be evenly distributed on the entire heat storage body plane, so that the entire heat storage body section can be evenly heated, and the thermal efficiency of the hot blast stove can be improved;

4) Each orifice in the high temperature area of the hot blast furnace is optimized in structure and material from the steel shell, equipment and refractory composite bricks to prevent the local high temperature of the furnace shell;

5) Using advanced research and development technology, obtaining real and detailed operation information inside the burner, combining computer simulation and experimental means, mastering the influence of the geometry, quantity and arrangement of air gas nozzles on the performance of the burner, and providing the basis for the design and optimization of the new burner;

6) Combining computer simulation and experimental data, research on refractory materials for ceramic burners, supporting materials adapted to working conditions, and formulating a batch of standards suitable for national conditions;

7) Design and improve the burner structure, improve combustion performance, improve the thermal efficiency of combustion equipment, reduce environmental pollution is the focus of the new burner design and development direction.

1 Research and Development and Application of Cone Column Rotary Cutting Top Combustion Hot Blast Stove Technology

Annike Company is a national high-tech enterprise with core business of refractory material manufacturing, blast furnace hot blast stove technology output and EPC engineering service. Since its establishment, Annike has always focused on the independent research and innovation of hot blast stove technology and accumulated more than ten years of hot blast stove technology research and innovation experience. Annike has its product integrated manufacturing and hot blast stove technology advantages, with China Metallurgical Jingcheng, China Metallurgical South, China Metallurgical Sadie, Shougang International and other large domestic metallurgical design institutes, we have carried out strong alliances and actively explored the market. In the field of refractory materials for large blast furnaces above 3000m3 in China, Annike's products The market share has reached more than 86%.

Over the years, Anneke has been adhering to the corporate mission of continuously promoting the technological development of blast furnace hot blast stove and the progress of refractory technology. In order to develop a new top-burning hot blast stove that is more suitable for national conditions and then break foreign technical barriers, the company, together with MCC Jingcheng, has established 11 multidisciplinary R & D teams of metallurgy, materials, thermal engineering and structure, headed by academician Zhou Guozhi of Chinese Academy of Sciences and professor Zhang Bopeng, inventor of Shougang, on the basis of a large number of investigations on the production site of top-burning hot blast stove in domestic iron and steel enterprises, through numerical simulation, cold state and hot state experimental verification, in-depth study of the existing hot blast stove operation data in the market, and combined with customer needs, continuously optimize the top-burning hot blast stove system structure and refractory standardized configuration, successfully developed a more reasonable structure, more efficient cone column rotary cutting top-burning hot blast stove.

2 Research and development of high-power ceramic burner for cone column rotary cutting top-fired hot blast stove

The burner is the most critical equipment of the top-fired hot blast stove, and its performance has a great influence on the thermal efficiency, energy consumption, environmental protection and other economic indicators of the hot blast stove. During the development of the burner, advanced design concepts, theories and methods were used to comprehensively and systematically study the physical and chemical processes such as hot blast stove combustion, gas movement and refractory heat transfer. For the first time, modern research methods such as theoretical research, numerical simulation optimization, cold/hot test, etc. are integrated to develop and apply the ceramic burner of the cone-column rotary cutting top-burning hot blast stove, and achieve a major breakthrough in core key technologies.

Combustion methods include diffusion combustion and power combustion (premixed combustion). The early top-fired hot blast stove burners belong to premixed combustion. Practice has proved that premixed combustion requires high ratio of air and fuel, has limited regulation ratio, is easy to cause backfire, has poor combustion stability, and has great danger for the working condition where the combustion-supporting air is preheated to 500 ℃ ~ 600 ℃. The burner of the cone-column rotary cutting top-burning hot blast stove adopts diffusion combustion. The air and fuel are cross-mixed in three dimensions in the mixing chamber, and the flame combustion process is formed in the combustion chamber. The air and gas have a large adjustment space and strong working condition adaptability. Moreover, there is no safety hazard for the working conditions of high-temperature preheating of combustion-supporting air.

5.1 burner structure

Compared with the previous burner, the cone column rotary cutting top combustion hot blast stove burner in the layout and structure have significant improvements, the advantages are:

1) The burner mixing chamber is a cone-column composite structure, the gas nozzle is distributed in the cone section, the air nozzle is distributed in the cylindrical section, the traditional top-burning furnace burner air gas plane swirl mixed flow field, improved into a three-dimensional space vortex flow field, and reduce the burner vault height, so that low investment, high efficiency.

2) The gas section of the burner mixing chamber is constructed with steel mold to support the overall pouring. The gas ring and gas nozzle are located in the cone section, and the top space is small, which is conducive to nitrogen purging. It avoids the displacement of the nozzle brick caused by the deflagration of the traditional top-fired hot blast stove, avoids the gas residue of the gas ring nitrogen purging, and eliminates the deflagration phenomenon of the gas nozzle. This design makes the conversion of hot blast stove air supply and burning furnace safer and more efficient;

3) The position of the burner mixing chamber is not the highest temperature position, and the highest internal temperature will not exceed 1100 ℃, which prevents the intergranular stress corrosion of the mixing chamber shell, reduces the heat loss and improves the overall thermal efficiency of the hot blast stove;

4) The combustion mode is three-dimensional mixed combustion, and the gas flow and air flow of multiple layers of different radii (less than the radius of the air flow) form a cross three-dimensional mixture of multiple concentric different diameters, which ensures the full mixing and combustion of air and gas, and improves the theoretical combustion temperature, thereby increasing the hot air temperature;

5) Due to the small area of the hollow column, the negative pressure area formed by the mixed air flow after the throat rectification is very small, which ensures the uniform distribution of the flue gas entering the lattice brick and effectively improves the utilization rate of the regenerator.

Low NOx Combustion Technology of 5.2 Cone Column Rotary Cutting Top Combustion Hot Blast Stove

In combustion technology, the rotating jet has the characteristics of rotating steady flow and free jet, which is an effective combustion method to strengthen combustion and organize flame form. In view of the problem of NOx emission, the use of three-dimensional swirl in a reasonable air-fuel ratio technology can significantly reduce the formation of NOx; a significant feature of the three-dimensional vortex burner is the ability to produce a return zone, so that the gas flow back, the intensity of the return flow and the size of the return zone is an important characteristic index to measure the swirl burner. The larger the area of the reflux zone, the stronger the reflux intensity, the closer the location to the flame root, the better the combustion condition, the more uniform the furnace temperature, the less likely to produce local high temperature, from the following aspects to ensure that the generation of NOx is lower than the national ultra-low emission standard.

1) When the vault temperature of the hot blast stove is more than or equal to 1420 ℃, the content of NOX in the burning product rises sharply, which produces intergranular stress corrosion on the steel plate of the hot blast stove shell. The vault temperature of the modern hot blast stove should be controlled below 1400 ℃ to ensure the service life of the steel structure of the hot blast stove.

2) Through the study of NOx generation mechanism, it is concluded that the main NOx produced by blast furnace gas combustion is thermal NOx, and low NOx combustion technology is the main technical measure to reduce the thermal NOx generation of hot blast stoves. [3]

3) The arrangement of multi-layer burners is adopted, and the burners are designed into a cone-column rotary cutting structure to realize three-dimensional vortex strong mixed combustion. Under the condition of realizing the same air temperature, the consumption of CO can be reduced, and the generation of NOx can be reduced, so that the NOx emission of hot blast stove can reach the standard, which not only solves the pollution of CO, but also does not produce new polluting gases, making it an environment-friendly high-friendly air supply equipment.

4) The cone-column rotary cutting top-fired hot blast stove can use 100 percent of blast furnace gas as hot blast stove fuel, double preheating gas and combustion-supporting air, and obtain a supply air temperature of ≥ 1250 ℃ under the condition of vault temperature ≤ 1350 ℃, ensuring NOx emission ≤ 50mg/m3.

Monitoring of NOx content in flue gas of a cone column rotary cutting hot blast stove in Hebei and Shanxi: less than 30 mg/m3

Experimental study and computer simulation of 5.3 cone column rotary cutting top burning hot blast stove

One of the most significant advantages of the cone-column rotary cutting top-fired hot blast stove is the uniform distribution of airflow, and the numerical simulation CFD technology is used to carry out a detailed study and demonstration.

The application of CFD fluid simulation technology can effectively reduce the design cost, it uses numerical calculation method to solve the flow simulation directly, and finds a variety of flow phenomena, including computational aerodynamics, computational combustion, computational heat transfer, computational chemical reaction flow and other research directions. In recent years, we have used simulation technology to study the combustion characteristics and flue gas flow in the vault space of hot blast stoves, and have conducted simulation studies on various top-burning hot blast stoves. At present, the computer numerical simulation method of computational fluid dynamics has been an important means of pre-design of the project, and the distribution of flow field, temperature field and concentration field in the burner is obtained by simulation method, and the optimal scheme is selected as the basis for cold experiment and industrial application.

5.4 measures to improve the thermal efficiency of cone column rotary cutting top combustion hot blast stove

There is a big gap between the difference between the highest vault temperature at the end of combustion and the air supply temperature (temperature efficiency) on many hot blast stoves in active service: in the hot blast stove using traditional burners and large-aperture lattice bricks as heat storage bodies, the temperature difference reaches 150~180 ℃, and the cone column rotary cutting top-burning hot blast stove ensures that the vault temperature is less than 1350 ℃, the difference between the traditional vault temperature and the air supply temperature is reduced to 80 ℃ ~ 100 ℃, and the air temperature can be increased by 30~50 ℃ under the same vault temperature.

Improve the combustion efficiency of the hot blast stove, improve the material of the grate, adopt the grate with composite structure, raise the maximum exhaust gas temperature at the end of the hot blast stove combustion to ~ 450 ℃; use the hot blast stove exhaust gas with higher temperature to preheat the gas and combustion-supporting air to 200~230 ℃ through the heat exchanger. The exhaust temperature of the waste flue gas after preheating the air gas is 120±5 ℃, and the heat carried away by the waste flue gas is reduced as much as possible to avoid the condensation inside the heat exchanger caused by the low temperature of the flue gas to damage the heat exchanger.

In order to protect the hot blast furnace shell and strengthen heat insulation to reduce heat loss, light heat insulation bricks and aluminum silicate fiber board are used outside the working layer, the inner surface of the furnace shell is fully sprayed, and acid-resistant spraying is used in medium and high temperature areas. The design temperature of the furnace shell in the combustion chamber and regenerator section shall be ≤ 80 ℃, the design temperature of the furnace shell in the middle part of the regenerator shall be ≤ 70 ℃, and the temperature of the furnace shell in other parts shall be ≤ 60 ℃.

3 Supporting refractory research and development and standard development

Established a large-scale top-fired hot blast stove refractory material configuration and technical system, formulated "silica brick", "high alumina brick", "hot blast stove with red pillar stone brick", "hot blast stove ceramic burner refractory brick" and other 9 national and industry standards, and created a key refractory material technical standard system. Editor-in-chief of many technical standards, such as "Technical Specification for Energy Saving of Top Burning Hot Blast Stove with High Blast Temperature" (GB/T30163-2013) and "Technical Specification for Refractory Materials for Top Burning Hot Blast Stove" (YB/T4638-2018).

4 Engineering applications

Cone column rotary cutting top-burning hot blast stove has been introduced to the market since 2013. Up to now, more than 180 stoves at home and abroad have adopted this technology. Through PCT patent application, they have obtained patent authorization from Russia, Japan, Ukraine, India and other countries. In particular, in 2021, they signed an EP project with Russia's MMK Steel Group to upgrade the 7# blast furnace-internal combustion hot blast stove into Anike cone column rotary cutting top-burning hot blast stove, as well as India's JSW 5872m ³ blast furnace new top-burning hot blast furnace EP project, marking that the top-burning hot blast furnace technology with China's independent intellectual property rights has reached the international leading level.

Compared with the conventional top burning hot blast stove, the main advantages of the cone column rotary cutting top burning hot blast stove are:

Low investment: in the case of the same furnace capacity, the height of the hot blast stove can be reduced, reducing the project investment by about 10%-18%;

Low energy consumption: compared with the traditional burner, the three-dimensional vortex burner saves 5%-8% of gas;

③ Low emission: when the dome temperature is ≤ 1350 ℃, the air supply temperature is ≥ 1250 ℃, the NOx emission is ≤ 50 mg/m, and the NOx emission is more than 65% lower than the national ultra-low emission standard;

④ High air temperature: the regenerator has high utilization rate for high-temperature flue gas, reducing the difference between the vault temperature and the supply air temperature to 80 ℃ ~ 100 ℃, and increasing the air temperature by 30~50 ℃;

⑤ Long life: Using more than 100 patents and proprietary technologies, the hot blast stove system has been stable and smooth for more than 30 years.

High blast temperature is an important technical feature of modern blast furnace, and increasing the blast temperature is the main technical measure to increase the amount of coal injection, reduce the coke ratio and reduce the production cost. In recent years, the hot air temperature of domestic blast furnaces has gradually increased, and some blast furnace air temperature indicators have reached the international advanced level.

Since its inception, Anneke cone-column rotary-cut top-fired hot blast stove has achieved remarkable economic and social benefits, which is especially suitable for the new construction and transformation of blast furnaces in China. With the increasingly prominent indicators of environmental protection emissions and energy consumption, Anneke will continue to devote itself to the continuous optimization and improvement of top-burning hot-blast stoves and the research and development and production of supporting refractory materials. Through the continuous optimization and upgrading of furnace structure and refractory configuration, Anneke will provide top-burning hot-blast stove technology with high temperature, long life, low carbon and consumption reduction, intelligent and intensive for users of China's iron and steel enterprises.

References:
[1] Zhang Bopeng, Li Fuchao, Wang Lianwei, Development of Top Burning Hot Blast Stove Technology in China, Ironmaking, 2012,P1-6.
[2] Wu Qichang. Discussion on Reducing NOx and CO Emissions from Blast Furnace [C]// 2013 National Metallurgical Energy Environmental Protection Production Technology Conference, P2-3.
[3] Ma Xiaoxi, Liang Shuhua. Formation and control of thermal NOx in gas flame [J]. Environmental Herald, 1997(2):17-20.