What Kind of Refractory Castable Material is Best for Coke Oven Doors?
With the development of large-scale blast furnaces and technologies such as oxygen enrichment and coal injection, the stability of the quality of coke used in blast furnaces has become a key factor restricting the stable operation of blast furnaces. The insulation effect and life of coke oven door bricks directly affect the quality of coke on both sides of the coke oven machine and coke. The mechanization and automation of coke oven operation require the longevity of furnace door bricks. In addition, with increasingly stringent environmental protection standards, the previous phenomenon of fire and smoke from coke oven doors will be eliminated. Therefore, coke oven door bricks must not only have good refractory properties, but also have good insulation effects, corrosion resistance, and overall stable performance.
The refractory materials of coke oven door bricks have developed from traditional clay and lightweight insulation materials to cordierite, mullite and cordierite composite materials with better refractory properties. In addition to the performance of conventional refractory materials, furnace door brick refractory materials must also have better refractory properties than furnace wall bricks. Including thermal shock resistance, lower heat transfer coefficient and density, corrosion resistance, and anti-carbonization performance.
Cordierite Refractory Materials for Coke Oven Doors
Cordierite (2MgO·2Al2O3·5SiO2) is an aluminum magnesium silicate mineral. Cordierite in refractory materials is generally artificially synthesized. Cordierite has a low thermal expansion coefficient, a small thermal conductivity, and a strong compressive resistance. It is currently one of the most commonly used refractory materials for coke oven door bricks.
Early cordierite was generally synthesized from industrial alumina, clay, kaolin, talc, bauxite, coke gemstone, etc. Cordierite has excellent thermal stability, but its high temperature load performance is relatively poor. In order to further improve the high temperature performance of cordierite, cordierite composite materials are currently being studied more. Including cordierite-mullite composite materials, clay-fused quartz, magnesium aluminum spinel-cordierite composite materials, mullite-alumina composite materials, etc. The performance of these refractory materials is significantly better than cordierite materials.
The coke oven door is frequently opened during production, the surface temperature is high, and the coke outlet temperature varies greatly. The lining of the traditional coke oven door in China is mostly made of cordierite bricks and clay bricks, but the service life is not long.
The reason is: the products of the coking process of the coke oven door are complex and the chemical erosion of the products is serious. Diffusion through the pores of the bricks to the inside of the bricks, diffusion destroys the lattice structure of the bricks, reduces the performance of the bricks, and shortens the service life. The temperature of the coke oven door varies greatly, and rapid heating and cooling cause cracks on the surface of the lining bricks, and also damage the corners of the refractory bricks.
Refractory Castables for Coke Oven Doors
If refractory castables are used for coke oven doors, the body density cannot be too large. Because the door is too large and too heavy, the thermal conductivity is high when it is opened frequently. However, lightweight castables have the characteristics of low thermal conductivity, small thermal expansion coefficient and elastic modulus, and good thermal shock resistance. However, the strength is not good, the apparent porosity is large, and it cannot meet the needs. If cordierite material is used as castable, cordierite has high strength and strong resistance to acidic gas erosion, but it is expensive, has high masonry requirements, and is difficult to replace after local damage.
Moreover, during the use of the coke oven, tar will firmly adhere to the surface of the lining, and the thick carbon deposit layer will cause the furnace door to be closed loosely, leaking and emitting fire. If the carbon deposits are cleaned, the mechanical force will accelerate the early damage of the furnace door lining bricks. In recent years, the lining of large-volume coke oven doors has been mostly made of refractory castable prefabricated blocks. The material is clay plus fused quartz composite castable. Because of the combination of this composite property, the refractory castable has strong thermal shock stability. It can withstand the thermal shock and frequent opening of the furnace door during the coke oven production process. In addition, fused quartz has strong resistance to acid gas erosion and carbon deposition.
Clay and fused quartz composite castables are used as prefabricated blocks. Clay materials are cheap and have high strength. When manufacturing molding modules or integral casting, the production process is simple and convenient to use. The introduction of fused quartz with extremely low thermal expansion coefficient into clay plays a dual role of reducing the thermal expansion coefficient and increasing microcracks, and the thermal shock resistance will increase. It is fully adapted to the temperature of frequent opening of the furnace door under acidic high temperature. In addition, the bulk density and thermal conductivity of fused quartz are both low. When fused quartz is introduced into clay materials, the thermal conductivity of the castable is low, and the weight of the furnace door is appropriate, which fully meets the performance of the coke oven door.
While the performance of the composite refractory castable meets the use, it is made into a prefabricated block, which is convenient to construct and has a long service life. Therefore, the use of clay and fused quartz composite refractory castables is most suitable for coke oven doors.
