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Important route

 Date:2017-05-26 18:07:03
Increasing the coal injection ratio is an important route for the development of ironmaking technology in China
1. The significance of blast furnace coal injection
Blast furnace pulverized coal is the central part of the optimization of the structure of the ironmaking system. It is one of the three important technical routes for the development of iron and steel industry in China. At present, the technical measures to improve the coal injection ratio are: to achieve high wind temperature, high iron grade charge, dehumidification and oxygen-enriched air, improve the permeability of the furnace and blast furnace operation level, preferably coal injection coal, Improve the combustion conditions.
(1) blast furnace pulverized coal, to reduce the coking process of environmental pollution. Blast furnace spray instead of coke, reducing the blast furnace iron ore on the demand for coke, coke oven less production of coke, to reduce the coking process of environmental pollution.
(2) to ease the shortage of China's main coking coal, iron ore system to optimize the energy structure. Coking coal generally requires more than 50% of the main coking coal to meet the blast furnace iron ore quality requirements of the coke. And a wide range of coal injection of coal, can ease the shortage of China's main coking coal, but also can reduce the cost of coal purchase system.
(3) blast furnace pulverized coal can realize the energy saving of the structure of ironmaking system. 2014 China's key iron and steel enterprises coking process energy consumption of 105.93kgce / t, coal injection and injection of energy required in the 20kgce / t-35kgce / t. Blast furnace blowing 1 ton of coal, iron can make the energy-saving system to save about 80kgce / t standard coal.
(4) blast furnace pulverized coal can reduce the investment of ironmaking system. According to statistics, foreign investment in the construction of coal injection plant is coking plant unit investment 25% -30%, converted into metallurgical coke unit investment of 30% -40%. China's coal injection workshop unit investment is coking plant construction unit investment of 12% -16%, for the metallurgical coke part of the investment of 15% -20%. Therefore, in the new and expansion of blast furnace, the construction or expansion of coal injection workshop must be implemented simultaneously, so as to achieve good economic benefits.
(5) coal instead of coke has a huge economic benefits. At present, coke and coal powder per ton spread in the 300 yuan -500 yuan. For example, if the coal injection ratio is over 130kg / t, the annual injection of about 520,000 tons of pulverized coal, instead of the equivalent amount of coke, will reduce the iron cost by about 15.6 million -26 million yuan.
(6) to improve the labor productivity, reduce production costs. The number of coalworkers and the production and operation costs are much less than the coking plants, which can greatly improve the labor productivity of steel enterprises and reduce the production and operation costs.
2. China's coal injection level and the international advanced level there is still a gap
According to statistics, in 2014 China's large and medium-sized iron and steel enterprises blast furnace coal injection than 145.85kg / t, down 2.73kg / t over the previous year. The reason is that the quality of raw materials changes, resulting in a decline in coal injection. Compared with the previous year, 42 enterprises than the decline in coal injection, 27 enterprises to improve the coal ratio. These enterprises by reducing the coke ratio, improve the coal ratio, to achieve the blast furnace optimization operation.
The technical conditions of improving the coal injection ratio are: high air temperature, oxygen enrichment and dehumidification blast. The iron ore grade is high, the slag iron ratio is low, the permeability of the charge is good, the blast furnace operation is optimized and the gas distribution in the furnace is promoted Uniformity; the outlet of the coal injection evenly, the quality of coal injection (grinding, mobility, good combustibility, high carbon content, containing low harmful impurities); ore metallurgical performance is good, so that low melting zone , And so narrow. The ratio of the coal injection ratio must be compatible with the blast furnace production conditions, especially the quality of the original fuel quality. At present, ironmaking enterprises have not simply pursued the indicators of high coal injection ratio, but also pay attention to economic jet ratio, economic fuel ratio and the best economic benefits. See Table 2.
"China Iron and Steel Industry Science and Technology Development Guide (2011-2020)" proposed in the blast furnace coal injection indicators: 2011-2020 national key iron and steel enterprises> 2500m blast furnace coal injection ≥ 160kg / t-200kg / t,> 1000m Blast furnace coal injection ≥ 140kg / t, the use of more than 30% of the multi-metal refractory compound smelting blast furnace coal injection ≥ 140kg / t.
Currently. China's blast furnace jet level and the international advanced level there is still a big gap. The world's leading blast furnace coal injection ratio is 266kg / t, the international advanced level of coal injection ratio of 180kg / t -200kg / t. China 's current new> 2000 m 3 blast furnace, the design of coal injection than the average> 180kg / t, 4000 meters 3 or more blast furnace, designed jetting average> 200 kg / t.
3. The key technology of high coal injection ratio
3.1 keep the hearth heat sufficient technology
Blast furnace ironmaking normal production needs the hearth has plenty of heat to ensure that iron ore reduction, slag flow is good, easy to separate, slag desulfurization rate and good ventilation. The hearth heat is expressed by the theoretical combustion temperature of the hearth. The heat of the hearth is required to have a higher temperature and heat of the furnace, and the theoretical combustion temperature is considered to be reasonable at 2200 ℃ ± 50 ℃.
Pulverized coal need to absorb heat after the outlet. The first is that the pulverized coal is heated, then the volatiles are burned and the carbon is burned. So that each blown l0kg / t anthracite, will make the hearth temperature drop 15 ℃ -20 ℃, l0kg / t bituminous coal will make the furnace temperature drop 20 ℃ -25 ℃. Burning amount> l00kg / t will make the hearth temperature drop 150 ℃ -250 ℃ above, high coal injection ratio will make the hearth temperature drop more. In order to keep the hearth temperature within 2200 ℃ ± 50 ℃ reasonable range, it is necessary to take the technical measures to keep the furnace temperature. Specific methods are:
(1) to improve the hot air temperature: hot air temperature rise l00 ℃, the furnace can be the theoretical combustion temperature increased 60 ℃ -80 ℃, allowing multi-jet coal 30kg / t-40kg / t.
(2) Oxygen-enriched blast: Oxygen-enriched rate increased by 1%, furnace theoretical combustion temperature increased by 45 ℃ -50 ℃, allowing multi-shot coal 20kg / t-30kg / t.
(3) dehumidification blast: blast humidity for every 1g / m3 reduction, the theoretical combustion temperature increased 6 ℃ -7 ℃, hot air temperature increased by 9 ℃, allowing multi-jet coal 3kg / t-4kg / t.
3.2 to improve the pulverized coal combustion rate technology
Pulverized coal combustion in the hearth includes combustion of combustible gases (decomposition of coal from heat) and combustion of solid carbon (residual carbon after coal decomposition). These combustion conditions depend on the temperature, oxygen content, and pulverized coal ratio Surface area and burning time. In addition, the amount of carbon in the dust is also an important indicator of the burning rate of pulverized coal.
The technical measures to improve the burning rate of pulverized coal are:
(1) to improve the hot air temperature. The pulverized coal ratio is required to have a hot air temperature above 1200 ° C at 180 kg / t to 200 kg / t. A blast furnace with a wind temperature below 1000 ° C is not conducive to coal injection.
(2) Oxygen-enriched blast. The oxygen enrichment rate increased by 1%, the pulverized coal combustion rate increased by 1.51%, and the theoretical combustion temperature increased by 45 ℃ -50 ℃ before the outlet, which could increase the coal injection ratio by 12kg / t-20kg / t, increase the yield by 4.79% Calorific value of 3.4%. Reduce the amount of gas, wind diameter need to shrink 1% -1.4%, can improve the hearth temperature, but also improve the role of oxygen combustion agent.
(3) to improve the specific surface area of ​​coal to promote coal combustion. Requires general coal particle size -200 mesh to 50%. The use of bituminous coal and anthracite mixed coal injection, coal particle size -200 mesh to 60% (bituminous coal in the case of high temperature decomposition of volatile, resulting in coal powder burst, increase the specific surface area of ​​coal). Anthracite coal particle size -200 mesh to 70% -80%. Coal water control in 1.5% ± 0.5%, the maximum not more than 2.5%.
(4) dehumidification blast, improve the hearth temperature and blast oxygen content. The wet weight is reduced by 1%, the theoretical combustion temperature is increased by 45 ° C, the coke ratio is reduced by 0.9% and the yield is increased by 3.2%. The blast humidity control in about 6%, dehumidification blast, can achieve the blast of the four seasons of winter air volume of the blast (summer than the winter wind about 14% less).
(5) to improve the roof gas pressure, reduce the gas flow rate, to extend the burning time of coal in the furnace, reducing the gas pressure difference. It is estimated that the pulverized coal in the hearth burning time 0.01s-0 04s, the heating rate of 103k / s-106k / s. Increasing the pressure of the roof gas can promote the production and smelting of the role of low ferrosilicon.
3.3 to improve the material permeability of the column
The normal operation of the blast furnace to maintain a reasonable gas pressure difference, that is, hot air pressure minus the furnace top pressure value. The permeability of the column is determined by many factors, including the quality of the original fuel, the speed of the blast wind, the charging system, etc., only to take comprehensive measures to improve the permeability of the column. High coal-jet ratio conditions, the quality of coke is good or bad (alkali metal on the tamping coke damage, so that the coke easy to powder) on the charge permeability of a great impact should be a high degree of attention.
(1) to improve the blast furnace into the ore iron grade, reduce the amount of slag. Blast furnace gas resistance in the largest place in the melting zone, especially iron ore has just begun to melt, reduced to FeO and the formation of the initial slag, slag has not yet separated, has not yet dropped to the hearth. Zhang Shourong academician special emphasis: If the blast furnace into the furnace grade in more than 59%, tons of slag volume <300kg, the gas resistance will be greatly reduced, will reduce the slag liquid pan phenomenon.
(2) to improve the quality of coke, especially the thermal properties of coke, will greatly improve the permeability of the furnace column. Coke in the role of the blast furnace are: skeleton role, reducing agent, to provide heat, pig iron carburizing, filling the hearth. Especially in the case of high coal than coal ratio, coke skeleton role is even more important. High coal ratio than the requirements of the quality of coke, see Table 3.
(3) charge composition performance is stable and uniform. Stable charge composition refers to the iron ore raw materials, iron and impurities and alkalinity fluctuation range is small. Developed countries require sinter ore iron fluctuations range of ± 0.05%, alkalinity fluctuations 0.03 (times). China's "blast furnace iron ore engineering design specifications" requirement is iron fluctuations ± 0.5%, alkalinity fluctuations ± 0.08 (times).
Charge permeability requirements: to keep the charge of 0.44 space, can make the gas flow. At the same time also requires the uniform size of the furnace, particle size 5mm-10mm charge content of less than 30% (not more than 35%), otherwise it will have a significant impact on the permeability of the charge.
(Sintered, pellets, lumps) such as drum high strength, good thermal stability, good reduction performance, stable performance, etc., can improve the sinter (alkalinity of 1.8 times to 2.0 times) of the alkali change, Blast furnace to create good conditions. Even grate - rotary kiln production of pellet quality and process energy consumption, than the shaft produced by the pellet better.
(4) to optimize the blast furnace operation technology will effectively improve the permeability of the charge. Large blast furnace with large mining approved, so that the thickness of the coke layer in the 0.5m-0.6m, in the change of coke load, do not easily change the coke layer thickness.
Optimize the cloth technology (material batch, material line, cloth way, etc.) and the appropriate drum kinetic energy (adjust the caliber and tuyere length), can achieve uniform distribution of coal gas within the blast furnace, while improving the permeability of the charge.
Stable blast furnace heat system, air supply system, loading system, slagging system active in the hearth, is conducive to high-yield blast furnace, high quality, low consumption, longevity, high coal ratio. To improve the level of modern management, to achieve standardization, standardization, digital management, stable operation of the blast furnace to create a high efficiency of iron.
3.4 to improve the coal charcoal replacement technology
(1) to improve the quality of coal injection. Requires the injection of coal in the harmful impurities, grinding can be good, high carbon content, high calorific value, low ash (coal ash and harmful impurities must be lower than the ash content of coke), low sulfur content, Good, good liquidity and so on. Pulverized coal containing K2O + Na2O the total amount of <3.0kg / t, because K, Na in the blast furnace will cause nodulation and coke, easy to crack, resulting in coke strength decreased.
(2) Pulverized coal injection to achieve uniform and stable flow. The uniformity error of the pulverized coal is <3% and not more than 5%. In order to ensure uniform volume of coal in the air outlet, it is recommended that the pulverized coal dispenser be placed at a high level (recommended in the roof platform), so that the length of the single pipeline is similar. To avoid the phenomenon of individual blistering powder.
(3) the use of bituminous coal and anthracite mixed spray, is conducive to improving the coal ratio and coal replacement ratio. Coal optimization is an important measure to improve the replacement ratio, it is suggested that the proportion of bituminous coal is about 30%.
(4) on the blast furnace jet ratio. Due to the different production conditions of iron-making enterprises, blast furnace limit of high coal injection than the value will be different. But the industry for the injection of coal limit value is consistent: First, while increasing the amount of coal injection, blast furnace fuel ratio did not increase; Second, the blast furnace gas dust in the carbon content did not rise, the washing water is not the same as the oil-like toner. Source: Metallurgical Information Network