The hearth is used to contain molten iron and slags and produce coke combustion gas to provide reducing atmosphere for the blast furnace. It is one of the weakest points of the blast furnace and determines the service life of the blast furnace. 

The working conditions of the hearth are the worst. It, especially the tuyere zone, has the highest temperature in the furnace, about 1700-2000℃. Besides, it is also subjected to chemical attack and erosion of iron slags. Since the part is not easy to repair, it always determines the service life of the blast furnace. Refractory materials used in this part are required to have good corrosion resistance iron slags and alkalis and high thermal conductivity. 

 

The main damages of the hearth include:

1) The erosion of slags and molten iron;

2) The corrosion of alkali metals;

3) The erosion of high temperature coke gas;

4) The damage of the thermal stress;

5) The oxidization and corrosion of the CO2, O2 and H2O.

 

The damage of the hearth is caused by many factors, chemcial factors, thermal factors and mechanical factos. So, the basic requirements for the refractory materials used here include:

1) Good high temperature resistance, the temperature of mlten iron is 1500℃ and the temperature of slags is higher;

2) Good corrosion resistance to slags, especially the alkali metals and oxides, and mlten iron as well as CO, CO2 and H2O;

3) Good ressitance to erosion and wear;

4) Good resistance to penetration;

5) High thermal conductivity.

 

Tradtionally, the carbon refractories are mainly used in the hearth. With the development of the blast furnace technology, the hearth is subjected to more serious working conditions. New refractories are developed such as sintered carbon brick, hot pressed carbon brick, microporous carbon brick, ultra microporous carbon brick, carbon composite SiC brick and semi-graphite self-baked carbon brick. 

 

There are mainly three types of structures of the modern blast furnace hearth: carbonaceous hearth lined with microporous carbon bricks, ceramic cup hearth lined with ceramic materials and composite hearth lined with hot pressed carbon brick + ceramic material. These three structures all have their pros and cons. Microporous carbon bricks can effectively prevent the penetration of molten iron, but cannot prevent the eorsion of alkalis. The ceramic lining has many advantages. The ceramic materials can protect the carbon brick and improve its resistance to penetration and mechancial erosion. The low thermal conductivity of the ceramic materials can make the distribution of the temperature rational in the hearth, prevent the erosion of alkalis and reduce the energy consumption.