Technical level and development trend of refractory materials

In order to adapt to the increasing development of environmental protection industry and meet the needs of incinerators, various high-quality refractory materials have been developed and used in various countries in the world, and remarkable results have been achieved. It has become urgent to continue to research and develop refractory materials with excellent performance.

A silicon carbide material

SiC refractories are often used in domestic waste incinerators because of their good properties. Their excellent properties mainly include strong anti-erosion and anti-scour ability, good thermal shock resistance and high anti-wear. Usually used SiC block or brick is combined with silicate or nitrous compounds, the content of SiC is different, under the influence of temperature and different atmosphere, SiC is more than 800℃ when easy to decomposition, which is extremely adverse to the development of volatile SiC products, and the formation of silicon oxide layer on the surface of SiC can protect SiC grains from further erosion. The formation of silicon oxide by oxygen chemistry is also promoted by water vapor, SiC is greater than 1000℃, due to the crystallization and formation of squamous quartz and quartzite its surface has many cracks, so that its erosion resistance weakened, reduce the service life. At present, it is commonly used to cool the combustion chamber lining so that the surface temperature of the combustion chamber is below 1000 ° C to suppress the adverse effects mentioned above. In the incinerator temperature up to 1100℃ area, the advantage of special SiC products bonded by silicon binder is that they form a closed glassy silicate layer locally to prevent erosion. When the temperature is higher than 1200℃, the SiC bricks combined with nitride compounds have good corrosion resistance. In contrast, in the range of 550~1050℃, the life of SiC materials bound by siliceous binders is longer than that of nitrogen-bound materials due to their optimized stable layer. The results show that when the surface temperature reaches 850℃, the content of SiC ranges from 50% to 70. In the range of 850~1100℃, SiC content of 90% is more suitable. However, under the melting erosion condition (1250~1350℃), the high-alumina products of chromium corundum are superior to those of SiC. Some national experiments of Al₂O₃-SiC gravity flow low cement castable incinerator lining, not only simple and conducive to the protection of reactor anchorage parts from erosion; The heat conduction of the multifunctional double-layer protection system can be adjusted freely, but it is still under discussion.

B High aluminum material

The materials with higher alumina content are mainly used in special waste incinerators. Different stresses require different alumina content. The experimental results show that the brick with alumina content greater than 60% has good corrosion resistance, but to make the alumina content high, the matrix bonding needs special conditions, and a large amount of corundum mullite crystal matrix bonding is inevitable. Usually, containing 5% CR ₂O₃ chrome corundum products can be achieved by adding chromium oxide or application of pre-reaction chrome corundum particles. The use of corundum, the main raw material without silica, and the high chromium oxide section formed in the matrix can make the product have higher corrosion resistance. ₄ by adding oblique zircon (commonly ZRSIO ₄) to improve thermal shock resistance, containing less than 5% chromium.

High aluminum material (chromium corundum products) is the development direction of the Cr ₂ O ₃ content increased to 10% and 30%, put the SiO ₂ content is reduced to less than 2% of erosion resistance to improve products, but with the increase of the content of Cr ₂ O ₃ large amounts of chromium in the high temperature region of stability for 3 price and slag of CaO, Na, K ₂ O ₂ O base classes should be contrary, such as 6 chromium harmful to human body. Therefore, from the point of view of environmental protection, want to develop the use of non-chrome refractory, generally in the oxidation atmosphere can choose Al₂O₃ (melting point 2050 C), ZRO ₂ (melting point 2950 C), MgO (melting point 2800 C) and other oxide refractory; In the reducing atmosphere can choose C, SiC and other non-oxide refractory materials. An additive containing zirconia can be used instead of chromite to improve its corrosion resistance at high temperatures.

At present, some western countries are developing the equipment that makes the waste form glass to make the polluted waste produce inertia. The lining material is required to have good combination elasticity and low resistance to temperature change. Research shows that: choose polycrystalline ZRO ₂ can produce inhibition matrix crack structure, so the structure of the elastic properties of the products have better anti cracking and good anti temperature change. In conclusion, when the combustion temperature of the incinerator is less than 1250℃, the materials with different SiC contents are all suitable for its lining, and the SiC products combined with siliceous binder are the optimal choice because of the formation of dense permanent inert layer surrounding SiC grains in the application. When the combustion temperature is greater than 1250℃, in the higher stress area, the performance of SiC products combined with nitride compounds is good, but also can choose high aluminum products, chrome corundum products. Therefore, the development of high quality SiC products, high alumina products, chromium corundum products and high alumina products containing zirconium matrix is called the main trend of future development.

With the development of waste incinerator in China, the key to popularize waste incineration technology is to develop efficient and economical refractory materials for incinerator. Refractory kiln tries to prolong its life, reduce its cost and increase its economic benefit. In addition, from the consideration of environmental protection, it is expected to develop a new type of chromium-free refractory.