Blast furnace is an iron smelting furnace in which preheating, indirect reduction, direct reduction, melting, slag iron dripping, slag iron separation, combustion and gas production are carried out in the same furnace. Its production principle is: iron ore with iron content of 50-60% is made into pellets from mineral powder by pelletizing process or sintered into so-called sinter which is most suitable for blast furnace smelting in a proper proportion, and the flux (mainly limestone, silica and fluorite) is added to remove impurities, and then layered and charged into the blast furnace together with coke. Coke is not only a heat source, but also a reducing agent, and it also plays a supporting role in maintaining ventilation. The high-temperature hot air from the tuyere of blast furnace makes the coke in the furnace burn, and the oxidation reaction takes place in a certain interval near the tuyere to generate carbon monoxide. The coke layer and ore layer alternately charged from the top of the blast furnace are heated and reduced by the high-temperature carbon monoxide gas rising from the bottom of the blast furnace, thus softening a little and gradually decreasing. When the ore descends to the cone-shaped softening melting zone, the ore is reduced. The softening and melting zone begins to melt around 1200℃, and iron and slag melt and drop with the increase of temperature. Molten iron and slag flow through this droplet area and concentrate at the bottom of blast furnace. Because of the different specific gravity, slag is above and molten iron is below, and they are stacked in layers in the furnace.

Smelting principle of blast furnace ironmaking (most commonly used)

Blast furnace smelting raw materials

The raw materials for blast furnace smelting are mainly composed of iron ore, fuel (coke) and flux (limestone).

General smelting 1 ton pig iron requires 1.5-2.0 tons of iron ore, 0.4-0.6 tons of coke and 0.2-0.4 tons of flux, which requires a total of 2-3 tons of raw materials. In order to ensure the continuity of blast furnace production, sufficient raw materials are needed.

Therefore, it is particularly important to purchase raw materials for both pig iron production enterprises and steel mills.

Although the principle of pig iron smelting is the same, the process flow is different because of the different methods and smelting equipment. Let's briefly introduce them respectively.

Blast furnace production is continuous. The first generation blast furnace (from blowing-in to overhaul and shutdown) can be continuously produced for several years to more than ten years. During production, iron ore, coke and flux are continuously loaded from the furnace top (generally, the furnace top is composed of materials and hoppers, while the modern blast furnace is bell-shaped valve top and bell-less top), hot air (1000 ~ 1300℃) is blown from the tuyere at the lower part of the blast furnace, and fuels such as oil, coal or natural gas are injected. The iron ore charged into the blast furnace is mainly a compound of iron and oxygen. At high temperature, the carbon in coke and injection and carbon monoxide produced by carbon combustion take away the oxygen in iron ore and get iron. This process is called reduction. Iron ore is refined into pig iron through reduction reaction, and molten iron is discharged from the taphole. Gangue in iron ore, ash in coke and injection are combined with flux such as limestone added into the furnace to generate slag, which is discharged from the taphole and slag outlet respectively. The gas is led out from the top of the furnace and used as industrial gas after dust removal. Modern blast furnaces can also use the high pressure at the top of the furnace and some derived gases to generate electricity.

Pig iron is the product of blast furnace (refers to the smelting of pig iron in blast furnace). Besides pig iron, there are ferromanganese, which belongs to ferroalloy products. Calculation of indexes of ferromanganese blast furnace without ironmaking. In the process of blast furnace ironmaking, by-products such as water slag, slag wool and blast furnace gas will also be produced.

Features of blast furnace ironmaking: large scale, and the volume of blast furnace is constantly expanding in other countries and China. For example, China Baosteel's blast furnace is 4,063 cubic meters, with a daily output of more than 4,000 tons of pig iron 10000, slag and coke consumption of more than 4,000 tons.

At present, the blast furnace volume of a single pig iron production enterprise in China has reached about 500 cubic meters, but most of them still remain between 100-300 cubic meters, and there are even small blast furnaces with high energy consumption and high pollution below 100 cubic meters. The quality of their products is uneven, scattered and out of scale, which cannot be compared with international steel mills.