blast furnace

blast furnace

This data is reviewed by the project of data compilation and application of Science Encyclopedia of science popularization in China.

The steel plate is used as the shell of the blast furnace, which is lined with firebrick. From top to bottom, the blast furnace body is divided into five parts: furnace throat, furnace body, furnace waist, furnace belly and hearth. Because of the advantages of blast furnace ironmaking, such as good technical and economic indicators, simple process, large production capacity, high labor efficiency and low energy consumption, the iron produced by this method accounts for the vast majority of the world's total iron production.

During the production of blast furnace, iron ore, coke and slag making flux (limestone) are loaded from the top of the furnace, and preheated air is blown into the tuyere at the lower part of the furnace along the circumference of the furnace. At high temperature, the carbon in coke (some blast furnaces also inject coal powder, heavy oil, natural gas and other auxiliary fuels) is burned with the oxygen blown into the air to generate carbon monoxide and hydrogen. During the rising process in the furnace, the oxygen in iron ore is removed, and iron is obtained by reduction. The molten iron is discharged from the taphole. The unreduced impurities in iron ore combine with limestone and other fluxes to form slag, which is discharged from slag port. The gas produced is discharged from the top of the furnace and used as fuel for hot blast furnace, heating furnace, coke oven and boiler after dust removal. The main products of blast furnace smelting are pig iron, blast furnace slag and blast furnace gas.

origin

The emergence and development of blast furnace in China is an important contribution to human material life.

About 40000 years ago, the cave people had used hematite as pigments and decorations.

Hematite is the most reducible iron ore, and its entry into human life indicates the invention of iron smelting in the future. The pottery kiln unearthed from the Banpo site in Xi'an 6000 years ago shows that our ancestors had mastered the use of fire at that time.

The firing temperature of hard pottery in Shang Dynasty reached 1180 ℃.

This high temperature provides good conditions for metal smelting. The progress of copper smelting technology in Shang Dynasty was more decisive to the emergence of blast furnace. 1、 Blast furnaces were set up in copper smelting furnaces. The raw materials for copper smelting in early China were oxide ores, including malachite.

In the excavated copper smelting sites of the Shang Dynasty and the spring and Autumn period, copper and hematite are put together, and the iron oxide content in the copper slag is very high, some of which reach about 40 PA.

These relics confirmed that during the copper smelting process, the easily reducible iron ore was once brought into the furnace. In the literature Shanhaijing of the Warring States period, it has been recorded many times that copper ore is associated with iron ore: Baimashan is "rich in iron and red copper" and Bingshan is "rich in gold, copper and iron".

This associated phenomenon may be the reason for the earliest use of copper bearing iron ore in copper smelting furnace. The melting point of pure copper is 1083 ℃. The higher the iron content in copper, the higher the melting point. The temperature of copper smelting furnace is low in the initial stage, so it is impossible to reduce a large amount of iron in raw materials. With the increase and expansion of the copper smelting furnace, the burden is fully preheated in the furnace, and the furnace temperature increases gradually. If the temperature exceeds 1300 ℃, pig iron may be produced.

Smelting equipment

history

The oldest blast furnace is the furnace of the Western Han Dynasty (1st century BC). Cast iron was found in the Chinese cultural relics in the 5th century B.C., which shows that smelting has been applied in this era. In the early stage, the inner wall of the furnace was covered with clay, which was used to refine phosphorous iron ore. The earliest melting pot in the West appeared in Sweden from 1150 to 1350. The melting pots of the two countries developed by themselves and did not communicate with each other.

The modern blast furnace using charcoal appeared in 1709. At that time, the multi-purpose deforestation in Europe led to the reduction of charcoal production, forced to develop the iron making method using charcoal, resulting in the emergence of new technologies, which greatly increased the iron making efficiency.

The first modern blast furnace in Japan is the Takahashi blast furnace. Designed by Gao Ren of Oshima, it was ignited on November 26, 1857, and the first batch of iron was produced on December 1. This day is also designated as Japan's iron industry anniversary.

brief introduction

A shaft furnace with a circular cross section. The steel plate is used as the furnace shell, and the refractory brick lining is built inside the shell. From top to bottom, the blast furnace body is divided into five parts: furnace throat, furnace body, furnace waist, furnace belly and hearth. Because of the advantages of blast furnace ironmaking, such as good technical and economic indicators, simple process, large production capacity, high labor efficiency and low energy consumption, the iron produced by this method accounts for the vast majority of the world's total iron production. During the production of blast furnace, iron ore, coke and slag making flux (limestone) are loaded from the top of the furnace, and preheated air is blown into the tuyere at the lower part of the furnace along the circumference of the furnace. At high temperature, the carbon in coke (some blast furnaces also inject coal powder, heavy oil, natural gas and other auxiliary fuels) is burned with the oxygen blown into the air to generate carbon monoxide and hydrogen. During the rising process in the furnace, the oxygen in iron ore is removed, and iron is obtained by reduction. The molten iron is discharged from the taphole. The unreduced impurities in iron ore combine with limestone and other fluxes to form slag, which is discharged from slag port. The gas produced is discharged from the top of the furnace and used as fuel for hot blast furnace, heating furnace, coke oven and boiler after dust removal. The main products of blast furnace smelting are pig iron, blast furnace slag and blast furnace gas.

Raw materials and basic principles

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

Generally, smelting 1 ton of pig iron requires 1.5-2.0 tons of iron ore, 0.4-0.6 tons of coke, 0.2-0.4 tons of flux, and 2-3 tons of raw materials in total. In order to ensure the continuity of blast furnace production, it is necessary to supply enough raw materials.

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

Because the production of blast furnace is continuous, the first generation blast furnace (from start-up 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 top (generally, the top is composed of material type and hopper, and modern blast furnace is bell valve top and bell less top). Hot air (1000 ~ 1300 ℃) is blown into the tuyere at the bottom of the blast furnace, and fuel such as oil, coal or natural gas is injected. The iron ore loaded into the blast furnace is mainly a compound of iron and oxygen. At high temperature, carbon in coke and injection and carbon monoxide generated by carbon combustion capture oxygen from iron ore to obtain iron. This process is called reduction. Pig iron is produced from iron ore by reduction reaction, and molten iron is released from taphole. The gangue in iron ore, the ash in coke and the injection are combined with the limestone and other flux added into the furnace to form slag, which is discharged from the taphole and slag outlet respectively. The gas is exported from the top of the furnace and used as industrial gas after dust removal. Modern blast furnace can also make use of the high pressure of the top of the furnace to generate electricity with part of the gas.

Feeding and batching system

Blast furnace charging is the most important part of the blast furnace system. Timely and accurate batching and charging is the premise to ensure the blast furnace output and product quality. According to the requirements of modern blast furnace, the feeding control system needs to print report forms of automatic feeding and loading data, which reflects the stability, advanced nature and economic practicability of the system. Therefore, from the initial stage of the design to the completion of the application stage, advanced control schemes and hardware control systems are needed to complete the important system. There are two commonly used batching methods in China, volume batching method and weight batching method. Volume batching method is a method to control the volume of materials by using the bulk specific gravity of materials and feeding equipment to achieve the required proportion of materials. This method has the advantages of simple equipment and convenient operation. The disadvantage is that the bulk specific gravity of the material is affected by the moisture content, composition and particle size of the material. Therefore, although the gate opening size remains unchanged, if the above properties change, the feeding amount is often different, resulting in batching error. Weight proportioning method is a method of proportioning according to the weight of materials. This method realizes automatic proportioning with the help of electronic belt scale and quantitative feeding automatic adjustment system.

Blast furnace lining

A layer of 345-1150 mm thick refractory brick is built inside the shell of blast furnace to reduce the heat dissipation of shell. Cooling equipment is set in the brick to prevent shell deformation. The damage mechanism of each part of the blast furnace brick lining is different. 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 damage, cooling and operation of the blast furnace. High grade and super grade clay bricks are traditionally used for hearth and bottom. Because of shrinkage and poor quality of brickwork, it used to cause major burn through accidents. The hearth and bottom were mostly made of carbon refractory materials, which basically solved the problem of furnace bottom burn through. There are three types of carbon bricks used in the furnace bottom: all carbon bricks; carbon bricks around and above the furnace bottom, clay bricks or high alumina bricks at the lower part; carbon bricks around and below the furnace bottom, clay bricks or high alumina bricks at the upper part. The latter two are also called integrated furnace bottom. The design furnace bottom thickness has a thinning trend (from 0.5 < I > d < / I > right to 0.3 < I > d < / I > or 1 / 4 of the inner diameter of the furnace shell, < I > d < / I > is the hearth diameter). The disadvantage of carbon brick is easy to be eroded by air, carbon dioxide, water vapor and alkali metal. The furnace waist, especially the brick lining under the furnace body, is easy to be damaged due to wear, thermal stress and chemical erosion. When the blast furnace with cooling staves is put into operation for about two years, the brick lining at the bottom of the furnace shaft is often completely eroded. The upper part of the furnace body and the lining of the furnace throat should be made of materials with abrasion resistance and thermal stability, and clay brick is suitable. After the bosh brick lining is eroded, the production is maintained by "slag skin".

In recent years, the application of gunning technology to repair brick lining has been quite common. Gunning high alumina refractory (containing alumina 340-60%) has a service life of 3 / 4 of lining.

product

Pig iron is the product of blast furnace, and the product of blast furnace is not only pig iron, but also ferromanganese. Ferromanganese blast furnace does not take part in the calculation of various indexes of ironmaking blast furnace. In the process of blast furnace ironmaking, by-products such as water slag, slag cotton and blast furnace gas are produced.

Characteristics of blast furnace ironmaking: large scale, no matter in other countries or in China

Chinese PinYin : Gao Lu