The CDQ furnace masonry is a vertical kiln structure, which is a cylindrical upright masonry under positive pressure. The furnace body is divided into the pre-storage section, the ramp area and the cooling section from top to bottom. The entire CDQ furnace is surrounded by an iron shell, and the inner layer is built with different refractory bricks. Some parts also use refractory castable materials.
(1) Refractory materials for the pre-storage section
The upper part of the pre-storage section is the cone top area. Due to the large temperature change before and after coke loading, its entrance is also greatly worn by coke. This part is made of mullite-silicon carbide masonry with good erosion resistance, wear resistance, rapid cooling and heating resistance and high flexural strength. The middle part of the pre-storage section is a straight section of solid refractory brick masonry, which must withstand the thermal expansion generated by the loading of red coke and the impact and wear of the coke. This part is made of high-strength wear-resistant A-type mullite bricks with good rapid cooling and heating resistance. The lower part of the pre-storage section is an annular flue, which is divided into two annular masonry structures, the inner wall and the outer wall. The inner wall must withstand the impact and wear of the coke, and must also prevent leakage between the pre-storage section and the annular flue due to the pressure difference. Therefore, A-type mullite bricks with grooves and tongues are also used for masonry.
(2) Refractory materials for the inclined section
The bricks in the inclined section are cantilevered layer by layer to support the load of the upper masonry. The temperature fluctuates frequently, and the circulating gas carries coke dust, which causes intense erosion of this part. Therefore, mullite and silicon carbide bricks with good thermal shock resistance, wear resistance and flexural resistance are used for masonry in the inclined section.
(3) Refractory materials for the cooling section
Although the straight section refractory brick masonry of the cooling section has a simple structure, its inner wall refractory brick masonry is one of the most vulnerable parts because it has to withstand the intense wear when the coke flows downward. Therefore, B-type mullite bricks with high strength, wear resistance and good resistance to rapid cooling and heating are used.
1. Types of CDQ refractory materials and their application areas
(1) Furnace mouth Type B mullite silicon carbide bricks, mullite silicon carbide fireclay.
(2) Pre-storage chamber Type A mullite bricks, mullite fireclay, dense clay bricks, clay fireclay.
(3) Inclined channel Type A mullite silicon carbide bricks, mullite silicon carbide fireclay, dense clay bricks, lightweight insulation bricks, ceramic fiber felt.
(4) Annular air duct Type B mullite bricks, dense clay bricks, mullite fireclay, lightweight insulation bricks and others.
(5) Cooling chamber Type B mullite bricks, dense clay bricks, mullite fireclay, wear-resistant castables.
(6) Other high-temperature sections Heavy high-aluminum castables, lightweight high-aluminum castables.
2. Performance of CDQ refractory materials
(1) Mullite bricks
Mullite is the only stable binary mineral phase in the Al2O3-SiO2 binary system. Its chemical formula is 3Al2O3·2SiO2. Mullite refractory materials are refractory products with mullite as the main crystal phase, made from artificially synthesized mullite (or naturally purified mullite) as raw materials. They belong to a series of products. When the content of the product is lower than the theoretical composition of mullite, it also contains a small amount of cristobalite; when the content is higher than the theoretical composition of mullite, it contains a small amount of corundum. The high-temperature spiral deformation resistance of mullite products is much higher than that of other ordinary high-alumina bricks, including special high-alumina bricks. Its high-temperature performance is comparable to some properties of silica, magnesia, and corundum products. It has the characteristics of good chemical stability, low thermal expansion coefficient, thermal shock stability, and strong resistance to acid and alkaline slag corrosion. Its resistance to acidic and low-alkalinity slag corrosion is higher than that of magnesia products, but not as good as that of corundum products.
(2) Silicon carbide bricks
Silicon carbide materials are advanced refractory materials produced with silicon carbide as raw materials. They have the advantages of good wear resistance and corrosion resistance, high high temperature strength, high thermal conductivity, small linear expansion coefficient, and good thermal shock resistance. According to the amount of SiC content and the type and amount of binder, silicon carbide materials can be divided into many varieties, but the quality of the material depends to a large extent on the condition of the binder. Mullite-silicon carbide bricks are one of them. They have a very low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance, and high high temperature strength. They will not soften even after long-term use at high temperatures, are not corroded by any acid or alkali, have good salt resistance, are not wetted by metals and slag, and are light in weight. They are high-quality high temperature resistant materials. The disadvantage is that they are easily oxidized at high temperatures and are not suitable for use in oxidizing atmospheres.
The flexural performance and thermal shock stability of the mullite-silicon carbide bricks currently in use are unstable. It is possible to consider using bricks with superior performance indicators and higher stability, such as silicon nitride combined with silicon carbide, silicon oxynitride combined with silicon carbide, and sialon combined with silicon carbide, whose high-temperature flexural strengths reach 40MPa, 30MPa, and 60MPa, respectively. In the performance improvement of the current mullite-silicon carbide bricks (including annular airways), consider improving the load softening temperature>1550℃, increasing the high-temperature flexural strength>25MPa, improving the thermal shock stability (1100℃ water cooling)>60 times, and assessing the wear resistance<5.0Crn3 and other main indicators.
Pure Al2O3, Fe2O3 and calcium oxide decompose with silicon carbide at 1100~1150℃, resulting in slag formation and expansion, so impurities must be controlled.
(3) Other silicon carbide products
① Oxide-bonded SiC
With Al2O3-SiO2 silicate as the bonding phase, including clay-bonded SiC, mullite-bonded SiC and SiO2-bonded SiC.
② Nitride-bonded SiC
The bonding phase is covalently bonded compounds such as Si3N4, Si2N2O and Sialon. Silicon nitride-bonded silicon carbide products are hard in texture and have a Mohs hardness of about 9. They are hard materials among non-metallic materials, second only to diamond.
Silicon nitride-bonded silicon carbide products have high strength at room temperature. At high temperatures of 1200~1400℃, they can maintain their strength and hardness for almost the same time as at room temperature. Depending on the use atmosphere, the maximum safe use temperature can reach 1650~1750℃.
It has a small thermal expansion coefficient and a high thermal conductivity compared to silicon carbide and other products. It is not easy to generate thermal stress, has good thermal shock stability and a long service life. It has strong high-temperature creep resistance, corrosion resistance, extreme cold and heat resistance, and oxidation resistance. It is easy to make products with high dimensional accuracy and meet the requirements.
The products are widely used in various industries such as steel, nonferrous metals, chemical building materials, etc., which are energy-saving, environmentally friendly and cost-reducing.
In addition, refractory products with a SiC content of less than 50% are usually called semi-SiC products. Semi-SiC products include clinker SiC products, high-aluminum SiC products, zircon SiC products, mullite SiC products and corundum SiC products.
(4) Dense clay bricks
Including low-porosity clay bricks and ultra-low-porosity clay bricks, which have low porosity, low Fe2O3 content, high compressive strength, and strong erosion resistance; small volume shrinkage under high-temperature and long-term operation, reducing the precipitation of carbon in the pores, avoiding the expansion and loosening of bricks during use and damage, and less formation of low-melting-point materials.
(5) Casting material
The use of casting material in the dry quenching furnace: light and heavy high-aluminum casting materials are used from the dry quenching furnace outlet to the boiler inlet; high-aluminum casting materials are used for the primary dust collector ash discharge device; high-strength wear-resistant casting materials are used after the cooling chamber is worn.
(6) Refractory Clay
Different refractory clay is used in different parts of the CDQ oven. The high and low temperature performance of refractory clay is an important factor in ensuring the tightness and strength of the masonry. The damage of the annular airway and the corbel part mostly starts from the peeling of the brick joints. It is necessary to study the improvement of the post-burning strength of the refractory clay, the thermal expansion of the refractory clay during the heating process, the change of the reburning line and the matching requirements of the shaped bricks to ensure the firmness of the overall structure of the refractory clay and the bricks.
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