The development direction of sponge iron technology in our country

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Sponge iron, also known as directly reduced iron (DIR), is widely used in industries such as metallurgy, weight distribution, and filtration media. Since energy is sourced from other reducing gases and coal rather than coke, this is a new iron-smelting process with a short production cycle and low pollution levels, free of the use of coke. It represents one of the key areas in China’s steel industry for applying high-tech and advanced appropriate technologies to transform traditional industries. However, in recent years China’s steel production is on the verge of exceeding 200 million tons, while the DRI production capacity has remained around 1 million tons, mainly due to the unsatisfactory economic returns of the sponge iron plants in operation. Given the actual conditions in our country, coal-based methods should be vigorously developed. The most important thing is to choose the process route. At present, in China, various processes such as tunnel kilns, rotary kilns, and those using carbon pellets as additives have been developed to maturity. However, the actual performance of these different processes varies, and not all mature processes can yield good results. The only criterion for testing truth is practice. To facilitate the study and comparison of DPI processes and to promote the development of China’s direct reduced iron industry, several key technical and economic indicators for the DRI process have been proposed, based on blast furnace ironmaking technologies that have similar products and processes. These indicators are used to analyze and compare the existing major processes, with a view to identifying directions for process improvement: 1. Developing tankless processes: In the initial stages of use, reduction tanks did indeed improve product quality, provided a stable reduction atmosphere, and increased production to a certain extent. However, with the continuous advancement of technology, the reduction tank has now become a bottleneck restricting the development of this process, and it is necessary to overcome it. If a canless process is used, it not only eliminates the cost of manufacturing cans. At the same time, energy consumption will also be significantly reduced. The typical energy consumption for the tank-type method in tunnel kilns is 800 kg/t, of which the heat storage capacity of the tanks accounts for a significant portion ； 2. Utilization coefficient: (t/d*m3) This is the main indicator for measuring the production efficiency of blast furnace ironmaking. In the past, the utilization factor of blast furnaces was generally around 2.0. In recent years, as ironmaking technology in China has continued to improve, the utilization factor of some large-scale blast furnaces has reached 4.0. The industry average is now around 3.0 as well. In comparison, current coal-based methods are far behind, regardless of the process used. The utilization factor for coal-based rotary kilns is around 0.4, that for coal-based tunnel kilns using the pot-type method is around 0.2, and that for coal-based external-heating vertical furnaces is around 1.3. The top priority is to improve the utilization rate of the kiln, so as to increase productivity ； 2. Energy consumption: (kJ per ton of iron or kGce per t of iron). The energy consumption per ton of iron, expressed in kGce/t, and the coke ratio, expressed in kg/t, are the main indicators of energy consumption in blast furnace iron production. With the optimization of ironmaking technology and the advancement of coal injection technology, this figure has been decreasing year by year; currently, the coke ratio is around 460 kg, and the energy consumption per ton of product is 13 GJ. Since blast furnaces are currently the most industrialized and stable method for iron production, this energy consumption level serves as a standard. Sponge iron also needs to strive to reach this level. However, blast furnace ironmaking uses coke as the main energy source, and due to the high energy consumption in coke production, the energy consumption per ton of iron produced by blast furnace ironmaking is 17 GJ/t. In recent years, the development of the steel industry has led to a shortage of coke, driving up its prices significantly and increasing the costs of iron production in blast furnaces. This thus provides an opportunity for the development of sponge iron. Because the sponge iron process uses ordinary coal or gas for iron production. Since coal is less valuable than coke, it should theoretically be more energy-efficient for iron production in blast furnaces. However, if the requirements for coal quality are too high and the coal consumption is excessive, this advantage is diminished. For example, rotary kilns have very strict requirements for coal. Only coal varieties of high quality such as Shenfu can be used, and the energy consumption ratio is around 1t/t. In this way, the total energy consumption reaches around 25 GJ/t. Although tunnel kilns have low requirements regarding the type of coal used, they consume a lot of energy. Including the reducing agent, it is approximately 1.5 t/t, with energy consumption reaching 45 GJ/t. In this way, what was once an advantage has turned into a disadvantage; it has become urgent to reduce energy consumption ； 3. Product quality: Due to the low reduction temperature of DRI, it is reduced directly to metallic iron in a solid state; therefore, it is not possible to remove sulfur and phosphorus through slag formation as in blast furnace ironmaking. Therefore, to produce sponge iron of high quality, high-grade iron ore or pelletized ore is required, or further processing after extraction is needed to remove impurities. It is essential to choose the appropriate raw materials based on the intended use of the product. For example: for metallurgical powders, iron oxide scale is the best choice; for iron smelting, ordinary iron ore powder will suffice, and for regular magnetization purposes, iron sludge is adequate. Furthermore, the sponge iron produced should strive to have a higher density, as this will enable blast furnaces to achieve higher utilization rates and yields of molten iron ； 4. Investment cost per ton of DIR: (yuan/t). This directly affects the initial investment required by the enterprise as well as the length of the time it takes to recover that investment. It is also an indicator for controlling investment risks. Currently, the static investment for blast furnaces is 700–800 yuan per ton, for rotary kilns it is around 800–900 yuan per ton, while for tunnel kilns using the tank method it is 200–300 yuan per ton. Although the investment in blast furnaces is high, their utilization factor has reached 4.0; therefore, the cost per ton is actually lower than that of rotary kilns ； 5. Make extensive use of favorable resources: Do not limit yourself to high-end resources such as coal, coke, and high-quality iron ore powder. The existing high-quality resources in the region should be fully utilized. For example, when it comes to reducing agents, machine-made charcoal made from straw, rice straw, and the like can be used. It not only reduces costs but also improves product quality, as charcoal itself contains few impurities such as sulfur and phosphorus. In terms of fuel, resources such as biogas can also be utilized. The main component of biogas is methane, and its calorific value is similar to that of natural gas; it can therefore be utilized taking one’s own conditions into account. If there is a coking plant in the vicinity, the coke oven gas produced there can also be utilized. These are all ways to reduce costs. China’s DIR process is already highly mature, but it lags behind shaft furnaces and blast furnaces in terms of certain key technical and economic indicators, which results in products lacking competitiveness in the market, poor economic performance for enterprises, and also hinders the development of the entire industry. Each manufacturer must take into account its own characteristics, draw on blast furnace technology as well as current advanced coke-free ironmaking techniques, and develop a set of processes suitable for its own development. We can only find new paths for the development of the DIR process by continuously exploring new technologies. Phone: 13292586869