Definition
Blast furnace is a kind of iron making equipment, which is used in the first process of iron and steel smelting, that is, iron ore must be smelted by blast furnace to get a variety of uses of pig iron block, or hot metal for steelmaking use.
Blast Furnace Structure
The blast furnace uses steel plate as the shell, and the shell is lined with firebrick. The blast furnace body is divided into five parts from top to bottom: mouth, body, belly, bosh and hearth. Due to the advantages of good technical and economic indicators, simple process, large production capacity, high labor production efficiency and low energy consumption, the iron produced by this method accounts for the vast majority of the world's total iron output.
Blast Furnace Lining
A layer of 345 ~ 1150mm thick firebrick is laid inside the furnace shell to reduce the heat dissipation of the furnace shell, and cooling equipment is set in the brick to prevent the deformation of the furnace shell. In order to prevent the local brick lining from being damaged first and shorten the service life of the blast furnace, different refractory brick lining must be selected according to the factors of damage, cooling and blast furnace operation. High and super high grade clay bricks are traditionally used in the hearth and bottom of the furnace. This part of the brick is gradually melted, due to shrinkage and poor brick quality, used to cause major burning-through accidents. Furnace hearth, furnace bottom mostly use carbon refractories, basically solving the problem of burning through the furnace bottom. There are three types of using carbon bricks in the furnace bottom: all carbon bricks; Around and above the bottom of the furnace is carbon brick, the lower part is clay brick or high aluminum brick; Around and below the bottom of the furnace is carbon brick, and the top part is clay brick or high aluminum brick. The latter two are also called comprehensive furnace bottom. The thickness of the designed furnace bottom has a thinning trend (from 0.5d to about 0.3d or 1/4 thickness of the inner diameter of the furnace shell, d is the diameter of the furnace hearth). The disadvantage of carbon bricks is that they are vulnerable to air, carbon dioxide, water vapor and alkali metal erosion. The furnace belly, especially the brick lining under the furnace body, is easily damaged due to wear, thermal stress, chemical erosion and so on. In blast furnaces with cooling walls, when they are put into operation for about two years, the brick lining at the lower part of the furnace body is often completely eroded. The brick lining of the upper part of the furnace body and the furnace mouth should have the material of anti-wear and thermal stability, and the clay brick should be used. After the brick lining in the furnace bosh is eroded, the production is maintained by "slag skin".
Raw Materials
The raw materials for blast furnace smelting is composed of iron ore, fuel (coke), and slag flux (limestone). Usually, production of 1T pig iron requires 1.5-2T iron ore, 0.4-0.6T coke, and 0.2-0.4T slag flux, in total 2-3T raw materials. Therefore, in order to guarantee the continuous production of blast furnace, the user needs to have sufficient supply of raw material.
Smelting Process
In blast furnace production, iron ore, coke and slag flux (limestone) are loaded from the top of the furnace, and preheated air is blown in from the tuyere located in the lower part of the furnace along the furnace. At high temperatures, the carbon in coke (some blast furnaces also blow auxiliary fuels such as pulverized coal, heavy oil, natural gas, etc.) and oxygen pumped into the air are burned to produce carbon monoxide and hydrogen, and oxygen in iron ore is removed during the rising process in the furnace, thus reducing iron. The molten iron is discharged from the iron tapping mouth. The unreduced impurities in iron ore combine with the flux such as limestone to form slag, which is discharged from the slag mouth. The resulting gas is discharged from the top of the furnace, and after dust removal, it is used as fuel for hot blast stoves, reheating furnaces, coke ovens, boilers, etc. The main products of blast furnace smelting are pig iron, as well as by-products of blast furnace slag and blast furnace gas.
Product
Pig iron is a blast furnace product (refers to the blast furnace smelting pig iron), and the product of bblast furnace is not only pig iron, but also ferromanganese, which belongs to ferroalloy products. Ferromanganese blast furnace does not participate in the calculation of various indexes of ironmaking blast furnace. In the process of blast furnace ironmaking, water granulated slag, slackness wool and blast furnace gas are also produced as by-products.
