The status quo and development of direct reduction

I. Overview

Typically steel enterprise system consists of iron coke, sinter, blast furnace process composition, large investment, long process, high energy consumption which is a common problem. Especially the use of coke, coking coal worldwide only about 10% of the total reserves of coal, with high consumption has now been Leinian scarcity. According to a survey by the United Nations Environmental Protection Organization, the traditional steel industry is a serious source of pollution, and the harmful gases (CO ₂ , CO, NOx, SO ₂ ) emitted by the United Nations have caused a greenhouse effect that will warm the world and expand the ocean. In the 21st century, more stringent international emission standards will be introduced, and coking pollution will threaten the survival of the blast furnace! In recent years, people have been working on the development of using bituminous coal or natural gas as a reducing agent, without coke and huge blast furnace, and iron ore in the solid state. Reducing to sponge iron (SpongeIron), this method of iron making is called direct reduction, and the resulting product is called Direct Reduction Iron DRI (DirectReduction Iron).

Second, the direct reduction development overview

Direct reduction industrialization experiments began in the 1950s, and many processes and methods emerged, but few were successful, and they were in a state of paralysis. After the 1960s, natural gas was extensively mined. In 1968, the US law succeeded, and direct reduction was rapidly developed. . In 1970 global production is only 800,000 t, in 1999, global production reached 38.6 million t, 30-year increase of nearly 50 times (Figure 1), which is rare in the history of metallurgy.

Figure 1 World DRI production in recent years

The objective reasons for the direct reduction of the production of sponge iron are:

1. Most countries in the world are seriously lacking coking coal. Many of them have high-quality iron ore and natural gas and bituminous coal resources. They use local resources to develop direct reduction plants, such as Venezuela, Indonesia, Mexico and other countries with rich natural gas and high-quality iron ore. The main development of gas-based shaft furnace, according to the statistics of 1995, the output reached 28.29 million t / a, accounting for 92% of the total output of direct reduced iron. South Africa, India and New Zealand are rich in bituminous coal and high-quality iron ore. The direct reduction is mainly based on coal-based rotary kiln. Although the output is only 2.46 million t/a, from the recent development trend, large-scale coal-based rotary kiln method Direct reduction plants are being established, and India's Goldstar has established a direct reduction plant with a capacity of 220,000 t/a. The Corex method is adopted: South Africa's Iscor has established a direct reduction plant with a production capacity of 7.23 million t/a. The SLPRN method; the New Zealand plant has established a direct reduction plant with a capacity of 900,000 t/a, using the SLPRN method.

2. With the development of electric furnace short-flow production lines, the output of electric furnace steel is increasing. In 1997, world steel production was 780 million tons, oxygen converter steel accounted for 57%, electric furnace steel accounted for 30%, and open hearth steel accounted for 13%. In recent years, the continuous casting ratio in the world's steel production has increased rapidly, accounting for 72.7%. The high-quality scrap steel in the iron and steel complex has been reduced. Due to the shortage of scrap steel in developing countries, it is bound to develop direct reduction. The use of coated steel in developed countries is increasing, so that the demolition returns. Harmful impurities should be diluted and must be diluted with 30% to 50% sponge iron.

3. In the past ten years, the steel industry has been challenged by polymer materials and silicate materials. The world steel output has stagnated. Since 1988, it has reached 783 million tons, and there has been no breakthrough. However, small steel mills that have won with quality and variety of products have flourished. The choice of raw materials for electric furnace steel is naturally preferred for direct reduction of iron. For example, stainless steel plants first select low-carbon sponge iron produced by low-carbon iron or coal-based rotary kiln as raw materials. In order to develop fine products and increase added value, direct reduction of low carbon sponge iron is used for direct production of electrical iron, ferrite and industrial iron.

4. The demand for steel in developing countries has increased rapidly, and it is required to accelerate the development of the domestic steel industry. The direct reduction-electric steelmaking new process provides a way for countries with limited capital and natural resources and lack of complex technical foundations to replace the traditional blast furnace converter process and develop steel production based on abundant natural gas, non-coking coal energy and iron ore resources in the region. New process.

5. Direct reduction technology and short process of steel production consisting of electric furnace and continuous casting technology can select the process according to domestic capital, energy and demand, establish appropriate economic scale, short construction period, investment and production flexibility, and easy to adjust according to the market. Product type and quantity. Not only does it have great appeal to developing countries, but also developed countries to solve regional steel demand and variety adjustments, there are also small steel mills that actively develop short steel processes.

6. A new breakthrough in direct reduction technology has prompted its development. Problems such as the ring problem of the rotary kiln for many years and the utilization of waste heat are expected to be solved recently. The improvement of shaft furnace waste heat treatment technology requires more sulphur content of natural gas.

Third, the main indicators of the DRI method and the superiority of the technical economy

From the development of direct reduction, gas direct reduction method is dominant in terms of production and production capacity, about 90%; coal-based direct reduction method accounts for about 10% (as shown in Figure 2). The gas-based direct reduction methods mainly include: Midrex method, HYL method and Fior method; coal-based direct reduction methods mainly include: rotary kiln method (including SLPRNI method, Krupp method, Corex method, DRC method, ACCAR method), shaft furnace method, All have entered the stage of mature technology and steady development. There are also coal-based Inmetco, Fastmet and Comet processes, gas-based Finmet and iron carbide processes.

Figure 2 DRI distribution map produced by different methods (1997)

It can be seen from the following table that the use of coal-based and gas-based steelmaking has the following economic advantages: 1. The content of harmful elements Sn, Sb, As and Bi in steel is greatly reduced, which improves the fracture toughness, hot working plasticity and cold working plasticity of steel. . 2. The content of S and P in steel is reduced, the impact toughness of steel is improved, and the temperature of brittle transition point is lowered. 3. Shorten the refining period of the electric furnace and increase the yield of valuable elements such as Ni and Mo. 4. Reduce the [H] and [N] contents in the steel. 5, DRI refined high-quality alloy steel deformation ability is good, suitable for deep-drawn steel. 6. The production of DRI by coal-based rotary kiln method can directly improve the electric furnace productivity and reduce the electricity consumption per ton of steel without cooling.

Coal-based DRI and gas-based DRI indicator

Fourth, the world's direct reduction production status

From the data collected by the direct reduction company, global direct reduced iron production is growing faster than global steel production. This shows that direct reduced iron has increasingly become an important raw material for the steel industry. In 1999, the global total production of direct reduced iron reached 38.6 million tons, an increase of 4.4% over 1998. This shows that the global production of direct reduced iron has climbed for seven consecutive years. Mexico's output this year was as high as 6.2 million tons, an increase of 500,000 tons compared with 1998, ranking first in the world for two consecutive years. India and Venezuela were both unchanged from 1998, with 5.2 million tons and 5.1 million tons respectively, ranking second and third. Iran’s production also increased slightly, to 4.1 million tons (3.7 million tons in 1998). In 1999, the direct reduced iron produced by the Midrex method accounted for 67%. Since 1987, it has exceeded 60% for 13 consecutive years; the HYLIII method accounted for 21%, and the other methods accounted for 12%. As before, gas-based technology still dominates, accounting for 92%, and coal-based accounts for 8%. Among them, HBI accounts for 16%. Figure 3 shows the production in various regions of the world in the last three years. In 1999, a number of direct reduced iron plants were completed and put into operation. Among them, the Sadreha Steel Company of South Africa and the IspatDRI of Trinidad were used in the Midrex model. The direct reduced iron plant of Sol2danha Company used Corex tail gas as the reducing agent for the first time in the world. IspatDRI is the world's largest single mode direct reduction iron plant with a production capacity of 1.36 million tPa. The Alexandria National Steel Company of Egypt also built a Midrex plant at the end of the year. In addition to the Midrex method, factories using other processes have also started production in Russia, Australia, Saudi Arabia, Trinidad and the United States.

Figure 3 Distribution of global DRI production areas from 1997 to 1999

V. Status and development of direct domestic reduction

(1) Favorable conditions for the direct reduction of China's development

1. With the adjustment of steel product structure, steel quality optimization, environmental protection requirements and the gradual improvement of power supply, the short process of electric furnace will inevitably develop rapidly. However, there are not many scrap resources in China, and there is a shortage of high-quality scrap steel resources, which seriously affects the development of high-quality and multi-species electric furnace steel. Therefore, there is a large potential market for direct reduced iron.

2. Although China lacks rich iron ore resources for direct reduction, many areas in China such as Jilin Huadian, Liaoning Benxi, Liaoyang Kezuo, Hebei, Qian'an, Shandong Luzhong, Anhui, Hubei, etc. The iron grade is 67%-70%, the S and P are low, and the residual elements are few. It is suitable for producing high-quality iron concentrate with high quality direct reduced iron, and the price is cheap. The use of fine concentrate as raw material will be the direct reduction feature of China.

3. Resource survey shows that China has abundant natural gas resources, but from the perspective of energy reserves and rational utilization, it cannot provide sufficient natural gas energy for metallurgical production. Even in the inland areas where natural gas supply is sufficient, the supply of high-quality iron ore is also a problem; The production cost of purchased iron ore is increasing. For the direct reduction industry as a raw material industry, its economic rationality is difficult to establish, so it is less likely to develop direct reduction of gas base. However, China's coal resources are abundant, and many areas have non-coking coal resources suitable for direct reduction. Therefore, based on domestic development, the development of coal-based direct reduction has important advantages and significance.

(2) Production status

In recent years, China's direct reduction and development has been rapid. In 1994, China's first direct reduction rotary kiln was completed and put into operation in Kezuo County, Liaoning Province. In October 1996, the direct reduction plant of Tianjin Steel Pipe Company was completed and put into operation. At the end of 1997, Luzhong Metallurgical Mine Company 50,000 t/ a coal-based cold-consolidated pellet rotary kiln direct reduction device was built. In 1998, there was a 62,000 t/a one-step rotary kiln direct reduction device and a 2,500 t/a two-step direct reduction rotary kiln in Jilin Huadian. A number of direct reduction tunnel kiln have been built in many areas of China; the slope furnace process, CRIMM process and rotary furnace direct reduction device have also been developed and constructed. In 1997, 500,000 t/a direct reduced iron production capacity was formed, and the actual output was about 100,000 tons. Direct reduced iron was no longer imported from abroad. So far, China's DRI production has entered industrial production, with a production capacity of more than 600,000 t/a. In 1998, the actual output has exceeded 200,000 tons. Domestically produced direct reduced iron has also been widely tested and promoted in many electric furnace steel mills and machinery manufacturing plants, successfully smelting steel for nuclear power plants, steel for petroleum pipelines, steel for high pressure boilers, steel for chemical hydrogenation reactors, steel for motor rotors. In addition, instead of importing, good results have been achieved, and conditions have been created and experiments have been accumulated for direct reduction development and use in the future. However, it should be clearly seen that there are still some problems in the production and construction of the current direct reduction iron plant. The quality of the products is unstable, the raw materials, energy consumption are high, the productivity is low, the labor intensity is high, and the environmental protection level is low.

(3) New processes and new methods

In view of the lack of cheap natural gas and rich ore resources for direct reduction in China, DRI production in China, except for the use of imported ore, is a coal-based direct reduction method using high-grade concentrate powder as raw material. In order to adapt to the resource conditions, China's DRI production process is diversified, and new processes are constantly emerging. At present, industrial production methods have been implemented: downdraft kiln method, tunnel kiln method, cold-solidified pellet rotary kiln method, rotary kiln one-step method (chain kiln-rotary kiln method), and traditional tunnel kiln The slope furnace method (XSH-A method) combined with the characteristics and advantages of the rotary kiln, and the rotary kiln method using lump ore. There are also a number of methods that are being built or undergoing development research, such as: self-consolidating pellet rotary kiln method (CRIMM method), rotary kiln two-step method, rotary hearth method, improved rotary hearth method, continuous furnace method, Fe ₃ C method using metallurgical plant tail gas (CO ₂ +CO+H ₂ +N ₂ ) as raw material gas, self-heating coal mine pellet method, coal-based fluidized bed method, coal gas-fired shaft furnace method, coal-water slurry gas-making shaft furnace Method, carbon-containing pellets (clamping method), and the like.

6. World direct reduced iron production and market prospects

According to the latest forecast of Midrex, the annual output of direct reduced iron in the world will reach 60 million tons in 2005 and reach 75 million tons in 2010. The main driving force for these growth is: 1 The scale of electric arc furnace steelmaking in various countries is expanding. 2 Electric arc furnace steel producers are increasingly demanding product quality; 3 scrap steel supply is relatively insufficient; 4 commercial pig iron supply is relatively reduced. The company believes that DRI, HBI and commercial pig iron will account for more than 20% of the EAF steelmaking charge.

According to the analysis of Dastur International.Inc, the total annual output of crude steel in the world will reach 798 million tons by 2002, which is basically the same as the 7.9 million tons in 1997. By 2005, the annual output of crude steel is expected to reach 839 million tons. By 2010, it reached 882 million tons. The proportion of electric furnace steel will also increase on the basis of 33% in 1997, reaching 38% in 2002, 40% in 2005 and 43% in 2010. The proportion of oxygen-blown steel in the same period will fall from 58% in 1997 to 55% in 2010. In anticipating the future demand for DRIPHBI, Dasturco considered that pig iron as a metallization charge will increase, possibly from 7 million tons in 1997 to 13 million tons in 2010. At the same time, considering the amount of scrap that may be available, the demand for DRIPHBI will reach 62 million tons in 2002, 82 million tons by 2005, and more than 100 million tons by 2010. In 1997, the global consumption of DRIPHBI was only 36 million tons.

At present, the global DRIPHBI production capacity is about 46 million tPa, and another manufacturer with a production capacity of 16 million tPa is under construction or brewing. Therefore, in the next few years, the production capacity of DRIPHBI will reach 58 million tons in 2002 and reach 62 million tPa in 2005. The shortage of direct reduced iron production will reach 4 million tons in 2002, 20 million tons by 2005, and 40 million tons in 2010. These larger deficit productions will likely be supplemented by Asia with greater production potential, followed by the United States and Europe.

references

1 Zhao Qingjie et al. Direct reduction rotary kiln technology. Beijing: Mechanical Industry Press, 1990

2 Li Zhengbang. Frontier technology of iron and steel metallurgy. Beijing: Metallurgical Industry Press, 1997

3 Shi Zhanqi et al. Accelerate the direct reduction and development of China. Proceedings of the National Conference on Direct Reduction Iron Production and Application, 1999

4 Li Yongquan. Status of production and research of sponge iron abroad. Steel World, 1996, (4): 82

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