Method for Selection of Refractory Material Used for Kiln
Introduction
The raw material kiln temperature is generally between about 1200-1700℃, which is a high temperature environment requiring great refractory materials to have high thermal shock resistance, chemical stability and heat preservation performance, Mechanical strength, and adjustable expansion coefficient. The selection of refractory materials used in kiln must be closely related to the type of kiln. On the one hand, it depends on the characteristics of high-temperature environment, such as temperature and furnace atmosphere, etc; on the other hand, it depends on the product itself and its requirements of the kiln operation conditions. This article explains the method for selection of refractory material used for kiln.
Factors
Furnace Type
Material selection for kiln should be closely related to the combination of furnace type and application. The application and classification of refractories for different furnaces mainly depends on the production intensity of the furnace, the combination of smelting and burning, the energy medium used and the required temperature, the type of kiln. The selection of refractories for the various kilns should be determined mainly by the operating temperature, the chemical composition of the material contained in the furnace atmosphere and the mechanical properties of the refractories, such as compressive strength, abrasiveness, permeability, thermal shock, creep and thermal expansion.
Atmosphere
Furnace atmosphere includes fuel type, dew point, partial pressure of oxygen and other components, corrosion of the lining and other factors. As there are different fuel types, the type of refractories is also different. Refractories with catalytic properties (such as Al2O3-SiC-C, corundum-graphite, corundum-aluminum silicate) are preferred for incinerators attacked by sulphur dioxide SO2 produced while burning dioxide fuels such as heavy oil and coal.
In oxidizing materials such as iron and steel, basic refractories such as magnesia, alumina and magnesia chrome bricks, chrome-magnesia spinel bricks and direct-bonded magnesia-zircon bricks are commonly used. For reduction furnaces, carbon bricks such as magnesia carbon bricks and graphite bricks are commonly used, and heat-insulating refractories can also be used.
Material Property
In order to improve the service life of the kiln, the refractory material should have a good thermal shock resistance, slag corrosion resistance, alkali corrosion resistance, mechanical strength and heat insulation performance, and low thermal linear expansion coefficient. Reasonable selection should also be based on the environmental conditions under which the kiln is used and the product characteristics to be produced.
Thermal Shock Resistance
Thermal shock is one of the main causes of damage to refractory materials in kilns, so it is necessary to select materials with high thermal shock resistance. The most commonly used refractory materials are chromite-spinel, andalusite, corundum and zircon for fuel burning kilns, and dolomite, quartzite, magnesite-chrome brick and quartz brick for air combustion kilns.
Slag Corrosion Resistance
In order to ensure the service life of the kiln, the selection of refractory materials must have good slag corrosion resistance. The common refractory materials used to resist slag corrosion are chrome spinel bricks, magnesia chrome bricks and magnesia carbon bricks, which are widely used in iron and steel smelting kilns.
Alkali Corrosion Resistance
The main alkali corrosion resistant refractory material used in kilns is alumina-chromium brick, which is widely used in kilns with alkali corrosion, such as corner and feed channel of cement rotary kiln and burning zone of lime kiln.
Mechanical Strength
The mechanical strength of refractory material for certain working conditions is determined by the temperature and loading conditions of kiln and the nature of material in kiln. Firebrick and magnesia-chrome bricks are usually used to resist chemical corrosion and protect kiln furnace wall and guard plate in high temperature areas.
Heat Insulation Performance
The selection of insulating refractories used in kilns should take into account the insulation requirements of kiln, the performance of the material and the technical and economic conditions. Common insulating refractories, such as lightweight fire clay bricks, light high alumina bricks, light corundum-graphite bricks, lightweight magnesia and lightweight spinel bricks.
Thermal Linear Expansion Coefficient
The thermal linear expansion coefficient of refractory material used in kiln should be lower than that of kiln lining, because if the thermal linear expansion coefficient of material is larger than that of kiln lining, cracks will appear in the lining due to difference in thermal expansion and contraction, reducing the service life of the kiln. Therefore, it is necessary to select the refractory material with low thermal linear expansion coefficient with appropriate combination of several materials. For example, fireclay bricks combined with high alumina bricks, corundum-graphite combined with magnesite-chrome, etc.
Conclusion
Overall, the selection of refractory material used in kiln should be determined by considering the type of kiln, atmosphere, material performance, mechanical strength and heat insulation performance, and low thermal linear expansion coefficient. The choice of appropriate refractory material can help to improve the service life of the kiln and ensure production efficiency, making full use of refractory material.
