1 Development of shaped refractories
1.1 Development of chromium-free alkaline brick technology
Based on the consideration of environmental protection, in order to create chromium-free green refractory materials, through the active exploration and research of domestic manufacturers, the development process of chromium-free cement kiln refractories has been effectively promoted, and some products have been obtained in practical applications. A good result.
1.1.1 Magnesium-iron-aluminum spinel brick (MgO-FeO · Al2O3)
Magnesium-iron-aluminum spinel bricks not only have good thermal shock resistance and kiln skin resistance, but also are relatively inexpensive, and have low thermal expansion and thermal conductivity. They will not cause the shell to deform due to overheating, which will lead to energy loss. Therefore, It has been widely used in the burning zone of cement rotary kiln with stable atmosphere in modern kilns. In addition, magnesium-iron-aluminum spinel bricks should also have excellent structural flexibility to effectively extend the service life of the material. It can react with cement clinker to form CaO-Al2O3-Fe2O3 series compounds, and the diffusion of Fe2O3 components makes the reaction The parts have been further enlarged, which promotes better stability of the kiln skin. At the same time, the bonding structure of bricks tends to be developed due to the effect of Fe2O3, which in turn significantly improves the adhesion and peeling resistance of the kiln skin. However, the disadvantage is that the oxidation-reduction, corrosion resistance and high temperature resistance of magnesium-iron-aluminum spinel bricks are poor, which restricts its application and development to a certain extent.
1.1.2 Magnesium calcium zirconium brick (MgO-CaO-ZrO2)
The so-called magnesia-calcium-zirconium brick is a magnesia-calcium-zirconium brick product formed by adding a certain amount of pre-synthesized calcium zirconate to the original ingredients. It not only has good thermal shock resistance and kiln skin resistance, but also has high high-temperature strength and can It resists the erosion effect of Portland cement and solves the shortcomings of easy hydration of magnesia-calcium bricks. In an environment of 1500°C, calcium zirconate (CaO · ZrO2) exists on the interface as an inactive compound. It does not chemically react with the spinel, but affects the refractory materials in the cement clinker. The penetration of chemical components plays a role in hindering the chemical corrosion resistance of magnesia-calcium-zirconium bricks; in an environment of 1200°C, zirconia (ZrO2) reacts with the compounds in the cement clinker very easily to produce a higher melting point Monocalcium zirconate (CaO·ZrO2), magnesia motelite (Ca3MgSi2O8) and wonotite (CaO·ZrO2, CaSi2O5), so the magnesia-calcium zirconium bricks have excellent corrosion resistance and kiln-hanging properties, and they are also effective It resists the change of the atmosphere in the kiln, and has a good application effect in the burning zone of the new dry-process cement kiln at present, and it has great promotion prospects.
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1.2 The development of silicon-mo brick technology
As a kind of firing conversion, the main mineral composition of silicon carbide brick is silicon carbide (SiC) and mullite (3Al2O3, 2SiO2), which is based on the application of traditional high alumina brick technology and improved by impregnating silicon carbide technology. Therefore, compared with high alumina bricks, it not only has higher strength, but also has the wear resistance and corrosion resistance of silicon carbide and the high temperature resistance of mullite. Adding silicon carbide to brick products can form a protective film on the surface, so that the alkali resistance of the product is improved, and the further oxidation of silicon carbide is effectively prevented; in high temperature environments, silicon carbide can be matured with high alumina bauxite The material reacts to form mullite, which can increase the strength and density of the product, and then effectively improve the product in terms of corrosion resistance, abrasion resistance and thermal shock stability. In the transition zone and decomposition zone of the cement rotary kiln, the traditionally configured anti-stripping high alumina bricks and phosphate bonded high alumina bricks have been replaced by silica bricks to achieve good application effects.
Based on the improvement of the performance of silica bricks, after adding kyanite, sillimanite and andalusite, researchers have obtained the high-temperature strength, creep resistance and thermal shock resistance of the product through the use of its high-temperature expansion. Significantly improved. After adding andalusite to the silica-modified silica bricks, the silica-modified red bricks have superior thermal shock resistance and abrasion resistance, and have achieved good application effects in cement kilns.
2 Development status of monolithic refractories technology
2.1 The development status of refractory castable technology
Based on the application and development of traditional high-aluminum high-strength castables, kiln-mouth castables have changed greatly in the formulation system. It is a high-performance low-cement castable with the addition of superplasticizer and ultrafine powder as the main features. On the basis of the traditional high-alumina castable formulations, corundum-silicon carbide castables, andalusite-based low-expansion castables, and corundum-mullite high-strength low-cement castables using composite aggregates have been gradually evolved. The reduction of the expansion coefficient of the castable can effectively suppress the internal stress of the material under high temperature environment, thereby improving its volume stability and thermal shock resistance; after adding ultra-fine powder and additives to the new formula of the castable, the whole of the castable can be improved. The performance has been significantly improved, and its service life has been extended from the previous 4 to 6 months to 10 months or even more than 1 year.
For a long time, the use of coal injection pipe castables has been difficult due to harsh operating conditions, which has made it difficult to achieve the expected use effect, which has formed a certain degree of restriction on the normal operation of cement kilns to a certain extent. At present, the castables for coal injection pipes are mainly aluminum-silicon carbide castables and corundum-spinel castables. The former adds ultra-fine powder and silicon carbide to high-alumina raw materials. The addition of silicon carbide improves the thermal shock resistance of the material , And form a liquid phase layer on the surface of the material at high temperature, which improves the alkali resistance of the material and greatly increases the service life of the material; the corundum-spinel castable is added -Al2O3 powder and aluminum-rich spinel to the material Fine powder, with high high temperature flexural strength, spinel itself has certain alkali resistance, and it has also achieved a certain effect on coal injection pipes. The development and application of these new products and technologies has increased the service life of the coal injection pipe from 3 to 4 months before to the current 6 to 8 months.
2.2 Progress in prefabrication of refractory castables
Prefabrication is another main direction for the development of monolithic refractories. In the production workshop, various special-shaped parts are poured into shape and dried and then transported to the site for installation. This method is easy to appear in the baking process when low-cement castables are poured on site. The bursting disease can be effectively avoided, greatly reducing the quality problems caused by irregular construction, and increasing the service life of refractory materials while effectively shortening the construction period. At present, some cement plants have selected precast parts to replace traditional castables in the grate cooler throat, tertiary air duct gate valve, and grate cooler low wall, and have achieved ideal results. Based on the analysis of its own advantages such as easy maintenance of preforms, avoidance of baking, and good use effects, it is bound to be widely promoted and applied as a unique solution in the future development.
2.3 Development of construction technology of unshaped refractories
Compared with traditional techniques, spraying construction (including wet spraying and dry spraying) has significantly improved the construction efficiency due to its higher degree of mechanization, which in turn provides cement manufacturers with economic benefits and social benefits through the compression of the production cycle. Benefits have been significantly improved. The spraying process is used for construction, and the process can effectively avoid the influence of human factors on the construction quality, and the product quality is stable, so that the service life of refractory materials is improved.
3 Conclusion
To sum up, the research of refractory materials for cement kilns is a systematic and complex task. In the course of its research and application, only the standardized control of production technology can realize its diversified development direction.
