The Main Technical Measures For Low-Cost Ironmaking

With the rapid development of my country's steel industry, my country's annual pig iron output reached 660 million tons in 2012, accounting for nearly 60% of the world's annual output. This has led to an increasingly tight supply of mineral resources and rising prices of raw materials and fuels; on the other hand, the contradiction of overcapacity has become increasingly prominent and market competition has become increasingly fierce.

The profit margin of iron and steel enterprises is gradually shrinking, and the situation of operation and development has become increasingly severe. Iron and steel enterprises rely on scientific management methods and scientific and technological methods to tap their internal potential, optimize product structure, reduce system costs, and improve corporate efficiency. Scientific and technological methods must be reflected in technological progress and technological innovation. Advanced technology is the guarantee for low-cost ironmaking. .

Optimization of raw fuel structure

The quality of raw materials and fuels is the prerequisite for blast furnace ironmaking production and the essential connotation of refined material technology; the cost of raw materials and fuels accounts for 2/3 of the cost of ironmaking. Therefore, it is necessary to rely on technological progress, technological innovation, and adopt advanced technical means to optimize the structure and composition of raw fuels and process technology. Through related experiments and practices, it is necessary to influence factors such as physical and chemical properties of different raw fuel structures, metallurgical properties, and blast furnace operation. Comprehensive analysis of its cost performance, so as to achieve low-cost ironmaking under the premise of ensuring and improving the level of concentrates, and obtain maximum economic benefits.

1. Optimization of coke coal blending structure

The role of coke in blast furnace smelting is the charge skeleton, reducing agent, heating agent and carburizing. Under the current smelting conditions of large-scale blast furnace and high coal injection ratio, the role of coke skeleton is particularly important, not only for cold machinery The strength requirements must also meet the requirements of the blast furnace coke thermal performance. The quality of coke is guaranteed by the blending amount of main coking coal, and the cost of coke is mainly reflected in the blending of coal. Therefore, relying on advanced technical means, optimizing coal preparation, coal blending, and coking technology, under the premise of ensuring the quality of blast furnace coke, it is an effective technical measure to reduce coke costs by purchasing low-quality coal or reducing the proportion of coking coal in coal blending.

2. Optimization of injection coal structure

Blast furnace coal injection technology has become a widely adopted technical measure for modern blast furnace ironmaking to save coking and increase iron, reduce costs and increase efficiency, improve the smelting process, and promote blast furnaces to move forward. With the scarcity of traditional anthracite resources and rising prices, the highly volatile and highly explosive bituminous coal injection technology has developed rapidly, and more and more blast furnaces have begun to inject bituminous coal, lignite and other coal types. Broaden the low-price and abundant coal injection coal sources, and scientifically evaluate the cost-effectiveness of various blended coals through the mixing and matching of bituminous coal, lignite, lean and lean coal, anthracite, and blue coal, and optimize the injection coal blending structure , Improve the blast furnace smelting process, reduce the coke ratio, so as to achieve the purpose of reducing costs and improving technical and economic indicators.

3. Optimization of sintering and ore blending structure

With the development of my country's iron and steel industry, domestic iron ore resources are increasingly scarce. There are many types of imported and domestic ore, with different prices and quality. Scientific and comprehensive evaluation of sintering performance and economic value for various iron ore, rational use of various iron ore resources at home and abroad, optimizing the sintering structure, increasing the proportion of low-quality and low-priced minerals, and reducing the cost of sintering. At the same time, improving the performance of sinter is an important technical issue we face.

In addition, in order to produce high-quality sintered ore with low slag ratio under the condition of low-priced ore mix, foreign steel companies proposed MEBIOS (Mosaic Iron Ore Sintering) technology, and conducted a large number of laboratory basic research, and achieved certain As a result, there are already industrial production examples at home and abroad.

Optimization of Blast Furnace Operation Index Parameters

Today, as the level of blast furnace ironmaking technology and equipment is increasingly developed, blast furnace operators are based on refined material technology and make full use of advanced technology such as oxygen enrichment, high pressure, coal injection, and high air temperature to adjust stable and reasonable operating systems and optimize Blast furnace operation index parameters, maintain reasonable blast furnace operation type, maintain blast furnace stable and smooth, improve blast furnace technical and economic indicators, so as to realize the technical policy of "high efficiency, high quality, low consumption, long life, and environmental protection" of modern blast furnace. To fully realize the modern blast furnace technology policy, blast furnace operation must be changed from extensive to fine, scientific smelting concept should be established, operation concept should be changed, evaluation index should be optimized, low fuel ratio and low cost smelting can be realized, and both economic and social benefits can be obtained. .

1. Optimization of smelting intensity index

Smelting intensity is an evaluation index of the degree of smelting intensification of blast furnace. Practice shows that it has a U-shaped curve relationship with the coke ratio (or fuel ratio). The lowest point of the curve corresponds to the appropriate smelting intensity at the lowest coke ratio. Increase or decrease the smelting intensity. The intensity will increase the focal ratio. However, with the improvement of the application level of advanced technologies such as concentrate, oxygen enrichment, high pressure, coal injection and high air temperature, and the improvement of smelting conditions, the curve will shift to the lower right to varying degrees, and the minimum coke ratio will gradually decrease while allowing suitable smelting The strength gradually increases, and the blast furnace utilization factor is further improved. This is the reason why most people in the industry have long advocated the use of medium smelting intensity and adapting to the smelting conditions.

The smelting intensity is an enhanced index based on the volume utilization coefficient. It was introduced from the former Soviet Union in the 1950s. The volumetric combustion intensity is used to measure the intensity of the blast furnace. To a certain extent, it misleads people to adopt an extensive operation method. More blast, more coke, and more iron are used as indicators to measure the productivity of the blast furnace; at the same time, due to historical reasons, in the period of strong steel demand, insufficient production capacity, and large profit margins for steel products, one-sided pursuit of high smelting intensity High volume utilization coefficient, mostly heavy production, light energy consumption, heavy coefficient, light coke ratio, resulting in a long-term high fuel ratio. As my country's economic transformation and development put forward higher requirements on the iron and steel industry, the corresponding evaluation standards also need to change accordingly.

Therefore, the method proposed by Academician Xiang Zhongyong, based on the utilization coefficient of hearth area, to measure the degree of blast furnace strengthening with the gas volume index of the hearth is more scientific and more in line with the essence of blast furnace smelting. The practice of Baosteel's blast furnace by reducing the gas volume per ton of iron hearth to achieve intensification shows that reducing fuel is the most effective way to reduce costs and increase efficiency. Increasing the oxygen enrichment rate and furnace top pressure is a suitable choice for strengthening the blast furnace.

2. Optimization of coal injection ratio index

Coal injection is a major technical measure for energy saving and cost reduction in blast furnace ironmaking. The significance of blast furnace ironmaking is to replace coke with coal, reduce coke ratio, save investment and energy consumption in coke production, and alleviate the contradiction of shortage of main coking coal; , It can improve the smelting operation of the blast furnace, and promote the stability of the blast furnace. Therefore, some companies blindly pursue high coal injection ratio regardless of their own wind temperature and fine material level, resulting in over-injection, lower replacement ratio, and higher fuel ratio, so that the carbon content in the furnace dust even exceeds 50%.

The theory of economic coal injection ratio proposed by Professor Xu Manxing points out that the coal injection ratio corresponding to the lowest coke ratio, the lowest fuel ratio and the highest utilization coefficient is sought to be calculated at different stages of the blast furnace, which is the economic coal injection ratio of the blast furnace at a certain stage. The premise of the economical coal injection ratio is that the increase of the coal injection ratio does not cause an increase in the fuel ratio and the carbon content of the blast furnace dust (under normal circumstances ≤ 20%).

Concluding remarks

Under the situation of increasingly tight raw and fuel resources, obvious overcapacity, and severe requirements for energy conservation and emission reduction, low-cost ironmaking is an inevitable way for steel enterprises to survive and develop. The specific method is: relying on advanced technology to optimize the structure of raw materials and fuels, improve the level of refined materials, and reduce the cost of raw materials and fuels; optimize the operating index parameters of the blast furnace, establish a scientific view of smelting enhancement, and overcome the unilateral pursuit of high production indicators (high smelting intensity, high utilization factor) , High coal injection ratio, etc.), maintain the gas volume in the hearth suitable for the smelting conditions, achieve the high efficiency of the blast furnace, maintain the economical coal injection ratio suitable for the smelting conditions, and achieve the purpose of increasing the replacement ratio and reducing the fuel ratio.

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