What is blast furnace ironmaking?
It refers to the production process of pig iron smelting with a blast furnace. The blast furnace is the main body of the process flow, which moves downward from the iron ore, fuel and solvent loaded on the upper part, and the air-fuel is blown into the lower part to burn, resulting in a large number of high-temperature reducing gases moving upward. The burden is heated, reduced, melted, slagging, carburizing, desulfurization and a series of physical and chemical processes, and finally produces liquid slag and pig iron.
Sources of Blast Furnace Iron-making Dust
The main dust in blast furnace ironmaking comes from the tapping yard and raw material system.
The pollutants produced in the tapping yard are the smoke and dust produced by blast furnace during tapping and slag discharging, high-temperature molten iron and slag furnace contacting other combustibles. For every ton of iron produced by the blast furnace, the average smoke, and dust emitted by the tapping mill is 2.5 tons. Among them, the smoke and dust produced by the tapping ditch, slag ditch, slag separator, swinging nozzle, and hot metal pot belongs to the primary smoke and dust, accounting for all the smoke and dust. 86% of the dust.
The smoke and dust generated during the opening and closing the iron tap belong to secondary smoke and dust, accounting for 14%. The temperature of smoke and dust from the iron tapping yard is generally higher than 70-200 C. The particle size of smoke and dust generally accounts for 50-60% below 10 microns. The content of Fe2O3, SIO 2 and carbon in smoke and dust is 49.4%, 10.97%, and 15.49%, respectively.
The main places where dust is produced in blast furnace system discharge on the trough, rotation of belt conveyor, screening under the trough, loading truck of raw fuel, aggregate hopper, etc. The concentration of dust is 5-8 g/m. The national standard requires that the belt conveyor be used at all transfer stations, the inlet and outlet of the trough, and the screening facilities under the trough should be equipped with a dust collector purification device. When feeding on the top of the furnace with a belt conveyor, a separate dust removal device should be installed. It requires that the content of the dust-containing gas discharged after all dust removal is less than 50 mg/m_and that the dust content of the air in the working environment is reduced to 10 mg/m_.
The dust of the raw material system usually comes from the dedusting of the ore trough in front of the furnace of the ironmaking plant. It mainly includes the harmful dust produced by raw material fuels such as blast furnace sinter, coke, and miscellaneous ore during transshipment, unloading, feeding, and feeding.
Main Dust Removal Technologies in Ironworks
Dust removal in the tapping yard:
At present, the main way to control the primary smoke and dust is to install a dust-proof cover at the places where the smoke and dust are produced, such as tap hole, iron trench, slag trench, etc. Then the smoke and dust are removed by fan. The smoke and dust are purified by pipe into the bag filter or electrostatic precipitator. The purified gas concentration is less than 50 mg/m。
The secondary dust collector system generally adopts the following three treatment devices:
One is the natural exhaust air curtain type, that is to say, the whole roof is regarded as a general ventilation hood with ventilation curtain exhaust fans around it; the other is the vertical curtain type, which has a ventilation passage composed of movable vertical curtain to extract dust into the dust collector; and the third is to disperse and collect dust at the dust production points of each tap hole, so as to unify the exhaust and dust removal.
Despite the limitation of dust removal technology due to the high temperature limit, treatment technology is being improved with the development of industry and technology, mainly in two parts, including the way of cooling and reprocessing of this part of dust, as well as the research and development of high temperature resistant treatment materials and products.
At present, besides bag filter, a filter cartridge filter is also used in some iron and steel enterprises. This type of filter uses various cylindrical folded filter materials. It can absorb dry dust particles efficiently. The dust removal efficiency is much higher than that of traditional bag filter, which greatly reduces the emission of harmful substances.
Dust removal in the raw material system:
The fundamental measure for dust control of this part of waste gas is to strictly control the powder content of blast furnace raw materials and fuels, especially sinter.
In addition, airtight cover and suction dust removal system can be set up for different dust production points. Local airtight cover (such as belt conveyor transfer point), integral airtight cover (such as vibration screen) or large capacity airtight cover (such as material pit of feeding trolley) can be adopted for airtight cover according to different conditions. The bag dust collector can be used for dust removal.
Dust control in the raw material system usually uses exhaust hood, sealing cover or combination of both to pump dust-laden air through the pipeline to the dust collector for purification, and the purified flue gas is discharged into the atmosphere through the flue tube.
According to the different conditions of the plant, the appropriate dust control methods are selected to meet the new emission standards of the ironmaking plant and reduce the pollution to the atmosphere.
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