In April 2019, the Ministry of Ecology and Environment, the National Development and Reform Commission, the Ministry of Industry and Information Technology, the Ministry of Finance, and the Ministry of Transport jointly issued the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Steel Industry" (hereinafter referred to as the "Opinions"). The "Opinions" put forward that to strengthen source control, blast furnace gas and coke oven gas should implement fine desulfurization, blast furnace hot blast furnaces and steel rolling heat treatment furnaces should adopt low-nitrogen combustion technology; encourage the implementation of sintering machine head flue gas circulation. At the same time, it is stipulated that the emission concentration of particulate matter, sulfur dioxide and nitrogen oxides of blast furnace hot blast stoves shall not exceed 10, 50, and 200 mg/m³ per cubic meter of flue gas, respectively. In June 2019, Henan Yuxing Hot Air Stove Engineering Technology Co., Ltd. (hereinafter referred to as Yuxing Company) commissioned a third-party organization to test 9 Yuxing top-fired hot blast stoves supporting 1260-2850m³ blast furnaces. The results showed that, The nitrogen oxide emissions of these hot blast stoves are only 32.83-mg/m³, which is far below the limit of 200 mg per cubic meter stipulated in the "Opinions". For this reason, "World Metal Herald" interviewed Mr. Liu Shiju, Chairman of Yuxing Company.

Reporter: In order to promote the high-quality development of the steel industry, promote industrial transformation and upgrading, and help win the battle against the blue sky, the state has issued the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Iron and Steel Industry". What impact will it have on the field of blast furnace hot blast stoves?

Liu Shiju: Since the reform and opening up, our country has neglected the protection and management of the ecological environment while the economy has developed rapidly. The people's living environment has been deteriorating, which has brought great harm to the people's lives and health.

In recent years, long-term and large-scale haze weather has appeared in many places in our country, which has seriously affected people's lives. The main source of smog is the industrial greenhouse effect and soot emissions. Therefore, changing the ecological environment must start with industrial emissions, but the governance task is arduous and a long way to go. The iron and steel industry is a high energy-consuming industry, producing pollutants such as nitrogen oxides, sulfur dioxide, and dust particles during the production process. Coal combustion is the main factor that produces sulfur dioxide, dust removal is the main factor that causes dust particles, and the formation of nitrogen oxides is closely related to the mixed combustion temperature and combustion mechanism.

The Ministry of Ecology and Environment of the People's Republic of China conducted in-depth investigations and studies on the pollution of steel enterprises at the grassroots level and steel enterprises, and issued the "Opinions" in April 2019. The "Opinions" put forward indicator limits and control measures for organized emissions, unorganized emissions, and bulk material product transportation based on industry emission characteristics.

In production practice, the actual nitrogen oxide emission value of hot blast stove fluctuates in the range of 100-500mg/m³, while the local emission standard before 2018 was 300mg/m³. The new national standard stipulates more stringent indicators and requires blast furnace hot air The emission limit of furnace nitrogen oxide is 200mg/m³. Some iron and steel enterprises must carry out special desulfurization, denitrification and dust removal in order to make hot blast stoves reach this target. They must pay for the investment of treatment equipment and high operating costs, which will increase the cost of the enterprise and reduce the profit of the enterprise. The low-nitrogen combustion comprehensive technology of Yuxing top-combustion hot blast stove has completely got rid of the dilemma of high nitrogen oxide emissions from hot blast stoves. Under the condition of not investing in denitrification equipment and increasing the operating cost of hot blast stoves, only the hot blast stove itself The structure and optimization of hot blast stove combustion technology can achieve ultra-low nitrogen oxide emissions, and the emission of nitrogen oxides is far below the new limit standard, which effectively reduces the investment and operation and insurance costs of hot blast stoves, and ensures the economic benefits of users.

Reporter: Without adding denitrification equipment, the nitrogen oxide emission of Yuxing hot blast stove can be far below the new limit standard. Could you please introduce how Yuxing hot blast stove achieves ultra-low nitrogen oxide emissions?

Liu Shiju: In 2010, Yuxing Technology R&D Center started research on the key technology of ultra-low nitrogen oxide emissions, namely low-nitrogen combustion integrated technology. There are two types of nitrogen oxide emission control technologies, namely low-nitrogen combustion technology and flue gas denitrification treatment technology. Low-nitrogen combustion technology is to control the formation of nitrogen oxides during the combustion process through various technical means, and control the formation of nitrogen oxides from the source. Yuxing hot blast stove low-nitrogen combustion comprehensive technology is to enhance the heat storage and heat exchange capacity of checker bricks to strengthen the distribution of hot blast stove flue gas flow; set up two and three preheats in the hot blast stove to achieve high temperature and low oxygen; increase the air temperature, Reduce the vault temperature and the air supply temperature difference, and finally reduce the vault temperature and other technologies to reduce the production of nitrogen oxides and achieve ultra-low nitrogen oxide emissions. The specific measures are:

(1) Gas and air enter their corresponding loops. Because the walls and burner loop walls in the air supply and heating periods are in a high temperature state, the gas and air entering the loop are preheated by the wall once. Then, the gas and air are staggered and placed in a pair of oblique opposites on the periphery of the large wall of the regenerator parallel to the regenerator and the lower end of the dome. The gas and air are placed above the dome at a high speed of 25-35m per second. Injecting, because the gas and air is set as a small stream, it is mixed and burned. The mixed gas and air form a low-temperature gas curtain cover. The gas curtain cover just separates the high-temperature area from the refractory lining of the vault and protects the vault lining. While being protected from the effects of high temperature and airflow, the low-temperature air curtain is also preheated by high-temperature radiation heating. This is the so-called three-time preheating process. The preheating temperature of the gas and air curtain layer of the insufficiently mixed part is as high as 500- 1000°C. Through the important third preheating, the theoretical combustion temperature of the sprayed gas and air has been effectively increased, and the air temperature has been increased.

(2) Adopting long flame pre-mixed combustion and upward spraying, through the action of the negative pressure of the chimney, the two kinds of gas sprayed up are sprayed to the top of the vault and turned back down into the bed surface of the regenerator. This process forms a natural vortex. The gas and air sprayed up are mixed with secondary air flow.

(3) In addition to the preheating and vortex mixing performance, the upward spraying process has also specially set the swirl mixing characteristics, and the swirl movement at the top is very intense, due to the use of the secondary gas mixing and swirling of the vortex. The three-time mixing and mixing of the flow makes the gas and air mix more evenly, the flame is shorter, the air excess coefficient is smaller, and the ultimate goal of complete combustion is realized.

(4) While realizing uniform mixed combustion, improving the heat storage and heat transfer capacity of checker bricks and lowering the dome temperature, and implementing high air temperature, it is necessary to reduce the difference between the dome temperature and the air supply temperature. This must be achieved through the use of high-efficiency checker bricks and increasing the lattice temperature. To achieve the brick utilization rate, the measures taken are to reduce the grid hole diameter and increase the unit heat exchange area, and do everything possible to implement the uniform distribution of the flue gas flow field and the cold air flow field of the checker brick section, and the pressure and flow checker brick has such performance. .

Through the above four technical measures, good environmental protection and high wind temperature effects have been obtained in practice. On July 10, 2012, Shanxi Tongcai’s 1860m³ blast furnace Yuxing catenary top-fired hot blast stove was put into operation. In October and November of that year, it created a historical record of monthly average high wind temperature of 1314.7℃ in China, and it has not been exceeded. The average dome temperature is 1409°C, the difference between the dome temperature and the air supply temperature is 94°C, and the dome temperature when nitrogen oxide is generated is greater than 1420°C. Field tests were conducted on this group of hot blast stoves, and the test results showed that the nitrogen oxide generation amount was 83mg/m³, which realized the generation of low nitrogen oxides.

Reporter: After years of development, a large number of blast furnaces have been equipped with Yuxing hot blast furnaces. Could you please introduce the overall situation of the nitrogen oxide emissions of Yuxing hot blast furnaces.

Liu Shiju: In 2012, the successful application of Shanxi Tongcai Yuxing hot blast stove's low-nitrogen combustion technology greatly encouraged and improved the enthusiasm of Yuxing Hot-blast Stove Research Center to continue to optimize low-nitrogen combustion technology towards ultra-low emissions. After several years of development, With hard work, ultra-low nitrogen combustion technology has been implemented in the subsequent construction of Yuxing hot blast stoves.

In order to test the stability of the ultra-low emission data, from June 6th to 14th, 2019, Yuxing Company commissioned a third-party testing agency. The Yuxing top-combustion hot blast stove has been tested on site. The test results show that the vault temperature of the hot blast stove in the burning state is in the range of 1280-1310℃, and the air supply temperature is in the range of 1200-1250℃. The hot air of the three blast furnaces is in the range of 1280-1310℃. The nitrogen oxide concentration in the combustion state of the furnace is all 20-47mg/m³, which is far lower than the national ultra-low emission target. The vault temperature is 1300 ℃, which can achieve an air temperature above 1200 ℃, which is the key technology of Yuxing hot blast stove. The small difference between the vault temperature and the supply air temperature is the key to low nitrogen oxide emissions. Unfortunately, the checker bricks of these hot blast stoves still use ordinary 19-hole 30mm checker brick technology, so there is still room for improvement. Although there is no high-efficiency and high-performance interconnecting checker bricks with holes, compared with the Shanxi Tongcai hot blast stove put into production before, the mixed combustion space is much larger, so that the flue gas flow field is more evenly distributed, which effectively improves the heat storage and exchange. Thermal capacity and combustion capacity, so the nitrogen oxide emission is lower than Shanxi Tongcai hot blast stove.

On June 8, 2019, Yuxing Company commissioned a testing agency to conduct inspections on the No. 6 Yuxing catenary top-fired hot blast stove (reconstructed by cutting the furnace shell) and the No. 7 newly built Yuxing catenary from Hebei Aosen Iron and Steel Company. The top-fired hot blast stove has been tested for flue gas composition. The test results show that the supply air temperature is in the range of 1200-1250 ℃. The NOx measured in one combustion cycle of the No. 6 blast furnace hot blast stove is 52, 42, 42, respectively. 39, 45, 39, 40mg/m3. The nitrogen oxides measured by the No. 7 blast furnace hot blast stove in one combustion cycle in six times are 36, 37, 33, 40, 37, 37mg/m³, which are all lower than the national ultra-low emission index. No. 7 blast furnace is a newly-built blast furnace and a matching hot blast furnace. It is equipped with online detection. The value of the online detection is 37.5mg/m³, which is consistent with the average value of 36.67mg/m³ of the third party commissioned by Yuxing.

Table 1 lists in June 2019 Yuxing Company commissioned a third-party testing agency to test Yuxing hot blast stoves for 9 blast furnaces of 1000-3000m³ in Hebei Province according to the air supply for 60min and the air temperature of 1220-1250℃, every 10min. The result of testing the smoke composition during the combustion emission period. The results showed that the tested nitrogen oxides were all lower than 50mg/m³, with an average of 37.5mg/m³. Liu Shiju finally pointed out that, from the current point of view, Yuxing top-combustion hot blast stove can meet the limit of nitrogen oxide emission of less than 200mg/m³ of blast furnace hot blast stove proposed in the "Opinions" without denitrification treatment. The actual test data on the spot proves that the comprehensive low-nitrogen combustion technology of Yuxing hot blast furnace is successful. It can make the hot blast furnace supporting the ironmaking blast furnace meet the ultra-low emission requirements without adding denitrification treatment, and control the nitrogen oxides from the source. It meets the national environmental protection requirements, saves the cost of flue gas treatment, and can bring economic benefits to users.