Corrosion Mechanism of Magnesia Carbon Bricks in Working Layer of Converter Lining

Overview

Magnesite carbon brick lining in the rotary kiln plays an important role in protecting it from the thermal erosion caused by slags, coke, crude oil or other high temperature substances. The wear and tear of magnesite carbon brick lining is caused by its erosion from the molten slag, coke and newly burned or hot metal materials, which can reduce the service life of the magnesite carbon brick lining and even reduce the output of the rotary kiln. Therefore, it is of great significance to study the mechanism of thermal erosion of magnesite carbon brick lining in rotary kiln.

Thermal erosion of magnesite carbon brick lining in rotary kiln is mainly caused by the following five aspects:[1]:

1. Chemical interaction between slag and magnesite carbon brick:

According to the nature of the metallic oxide and hydrostatic pressure in the materials sprayed from the nozzle, when the slag penetrates into the magnesite carbon brick lining, chemical reaction takes place between the alkali oxide and SiO2 in the slag and the carbon bonded magnesium oxide in the magnesite carbon brick lining. The reaction mainly consists of high temperature corrosion, reducing intrusion and direct reaction between slag and magnesite carbon brick lining material.

2. High temperature oxidization of magnesite carbon brick lining:

The oxidization of magnesite carbon brick lining will lead to the decrease of MgO content and the decrease of basicity of refractory material. The increase of temperature results in the increase of oxidization degree of magnesia carbon brick lining, because its contact with oxygen molecule in atmosphere forms the magnesia carbide, which affects the physical and chemical properties of magnesia carbon brick lining. It is easy to destroy its matrix structure. And it accelerate the thermal erosion of the magnesia carbon brick lining.

3. High temperature Mechanical erosion:

When the material impacts the magnesia carbon brick lining, part of the energy will be absorbed, part of the energy will be reflected, and the rest energy will be converted into kinetic energy. The kinetic energy will destroy the magnesia carbon brick by producing a local temperature rise, leading to thermal erosion of the magnesia carbon brick.

4. Heat conduction erosion:

The surface energy of magnesia carbon brick is little, and the heat capacity is big. When the magnesia carbon brick is exposed to high temperatures, the heat will penetrate through it, resulting in thermal erosion of the brick.

5. Thermal spalling:

When the magnesia carbon brick is exposed to high temperatures, the coefficient of thermal expansion of magnesia carbon brick is greater than that of slag, which will lead to the stress on its surface. Under the action of the thermal stress, the surface of the magnesia carbon brick will spall and cause the thermal erosion of the magnesia carbon brick.

Conclusion

In view of the mechanism of thermal erosion of magnesia carbon brick lining in rotary kiln, corresponding measures should be taken to optimize the properties and structure of magnesia carbon brick and reasonably select the chemical composition of slag and mechanical properties, in order to protect the lining and reduce the wear and tear of the lining.

The mechanism of Magnesia-Carbon brick wear in converter inclusions

Magnesia–Carbon brick is widely used in converter inclusions,which plays an important role in protecting steel and raises the service life of the furnace. However,with the ever-extending use time, wear and erosion would occur on the surface of Magnesia-Carbon brick, which will eventually lead to its failure.

The reason of Magnesia-Carbon brick wear mainly contains wear from abrasion and corrosion. Abrasion wear is due to the relative mechanical impact between brick wall and slag-metal liquid. With the continuous operation of converter,the surface of Magnesia-Carbon brick wear through the sliding friction between the steel liquid and slag against the brick wall. Meanwhile,the alkaline erosion resulting from alkaline materials contained in the steel liquid would cause Magnesia-Carbon brick the chemical corrosion,which eventually lead to its wear and tear.

With the increase of wear and tear of Magnesia-Carbon brick,its refractory grade slumps,and the strength and wear resistance of converter lining decreases.Which directly affects the service life of converter inclusions and steel conduction capacity.

In order to reduce and prevent the erosion of Magnesia-Carbon brick,we need to shorten the service time of Magnesia-Carbon brick,enhance the hardness of the lining,and improvement of steel refining process. It is necessary that proper treatment of the operating parameters,such as temperature zone,work furnace temperature,eccentricity,O2 blowing power and so on,to give full playof the strength of Magnesia-Carbon brick.