The direct reduction process can be divided into two major categories depending on the use of the reducing agent; a gas-based direct reduction method using a gas reducing agent and a coal -based direct reduction method using a solid reducing agent.
Gas-based direct reduction method, mainly in the wealth of the Middle East, South America and other regions of natural gas resources in these areas in order to process EAF-based steel industry has also been rapid development. Representative processes are shaft furnace method, reaction tank method and fluidization method. The coal-based direct reduction method is mainly distributed in South Africa, India, East Asia, South Asia, New Zealand and other places. The natural gas resources are limited, but there are high-quality iron ore resources and abundant coal resources.
China from the reserves and the rational use of energy considerations, it can not provide enough gas for the production of metallurgical industry, even if gas is available, the cost is too high, the production of one ton of direct reduced iron (DRI), if natural gas to 400-500m3, The cost of the natural gas portion accounts for 600-800 yuan; if gas is used, it costs 1600m3, and the gas cost costs 1600 yuan. Therefore, gas-based direct reduction cannot be considered.
At present, the processes used in China include tunnel kiln process, rotary kiln process and downdraft kiln process, all of which are coal-based reduction methods. The downdraft kiln has developed earlier in China, and its characteristics include: low investment, fast launch, low cost, flexible scale, simple operation, low requirements on raw materials, but its product quality is poor and unstable, production efficiency is low, and energy consumption is high. The labor intensity is high, the operating environment is poor, the environmental pollution is serious, the equipment level is backward, the whole manual operation, no mechanization, but there are some small enterprises in use because of their low investment. However, the state does not advocate the use of it, which is a process of elimination and ban.
The tunnel kiln process has the advantages of mature technology, low investment, quick effect, low cost, high product quality and stability, simple operation, stable equipment operation, low energy consumption, undemanding raw materials, flexible scale, high filling factor, etc. . However, there are also shortcomings of high labor intensity and low degree of mechanization. There are more than a dozen direct reduced iron (sponge iron) plants in use in China. It is a mature and reliable process in China.
The characteristics of the rotary kiln process: high degree of mechanization and low labor intensity, but also high product cost, large investment, prone to ring failure, low product quality, high product differentiation rate, and demanding raw materials and reducing agents. Low production efficiency and low thermal efficiency. There are several used in China, but they are not very successful. In addition, some research institutes in China have conducted experiments and research on other processes, but no effective progress has been made.
In view of the advantages and disadvantages of various processes, combined with China's actual national conditions, our company has developed a new process suitable for China's national conditions: the reduction furnace is a tunnel kiln, and the production capacity can be determined according to the length of the site. , avoiding the short, the process is highly automated and employs less. It is a fine process developed from these several processes and some advanced coal-based direct reduction processes abroad. This process is flexible in scale. The reduction furnace output ranges from 10,000 tons/year to 100,000 tons/year, and the furnace length ranges from 60 meters to 300 meters.
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