Low thermal conductivity multi-layer composite mullite brick (Figure 1) adopts a multi-layer composite structure design of working layer, insulation layer, and thermal insulation layer. Using bauxite based sintered mullite as the main raw material instead of natural bauxite clinker used in traditional silica bricks, with mullite as the main phase, the overall thermal conductivity of mullite bricks is reduced, and the high-temperature structural strength is effectively improved. Based on the poor slag erosion resistance of mullite, the alkali erosion resistance of refractory bricks was improved by adding some composite additives and increasing the content of alumina in the matrix to optimize the matrix. To further reduce the thermal conductivity of the working layer of the product, 97 # silicon carbide fine powder with well-developed crystals was used, and red columnar fine powder was added to enhance the matrix. This not only reduces the thermal conductivity, but also improves the high-temperature structural strength and thermal shock stability of the refractory brick.
(1) Working layer: M70 alumina based sintered mullite is used as the main raw material, homogenized alumina is used as the aggregate and powder, and multiple additives such as red pillar stone and carbonized cinnamon are added to extend the service life. The performance indicators of its working layer are: Al2O3 ≥ 67%, apparent porosity ≤ 20%, bulk density 2.70 g/cm3, cold compression strength 90-100 MPa, load softening temperature more than 1650 ℃, thermal shock stability (1100 ℃ water cooling) ≥ 30 times, comprehensive thermal conductivity ≤ 1.65 W/(m · K).
(2) Insulation layer: mainly composed of mullite phase, using M60 alumina based sintered mullite as the main raw material, and adding some composite additives to adjust the expansion coefficient, making it close to the working layer, to avoid cracks from occurring at the connection during sintering or use. Improve the insulation effect while meeting the strength requirements.
(3) Thermal insulation layer: Thermal conductivity is an indicator of a substance's thermal conductivity, and the thermal conductivity of different substances varies greatly. By adding materials with lower composite thermal conductivity to the insulation layer, the overall thermal conductivity can be reduced. Improve the thermal insulation effect of refractory bricks while meeting the strength requirements.
In the area where this product is used on the rotary kiln, the temperature of the cylinder can be reduced by 50-80 ℃. The average temperature in the transition zone before the rotary kiln is 250 ℃, and the insulation effect is significant. Especially suitable for the front transition zone of large and medium-sized cement rotary kilns. The service life shall not be less than that of spinel brick, silica brick or silica brick. In addition to being applied to the transition zone in front of the rotary kiln, it can also achieve satisfactory results when used in areas such as the tertiary air duct and the side wall of the grate cooler.
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