cement kiln
In the modern cement production process, cement rotary kilns are still the main high-energy-consuming equipment, especially the front and rear transition zones without kiln skin protection. Due to direct contact with cement materials, the thermal conductivity of the original refractory materials is too high, making the rotary kiln The surface temperature of the cylinder increases, which increases heat dissipation loss and fuel consumption per ton of clinker. The multi-layer (i.e. working layer, insulation layer and insulation layer) composite design method can reduce heat dissipation, and the high-performance working layer is directly related to the life of the cement kiln. The refractory material of the working layer is easily damaged due to erosion by cement materials, mechanical impact, etc. Therefore, it is required to have high strength, low thermal conductivity, high softening temperature under load, good high temperature wear resistance, corrosion resistance and heat resistance. Only with good shock resistance and other characteristics can stable and long-term use be achieved. The working layer of multi-layer composite bricks still uses silica-molybdenum bricks, which are commonly used as working linings in cement kiln transition zones.
Traditional silica molybdenum bricks generally use natural bauxite clinker with w (Al2O3) of 80% to 88% as the main raw material, and are prepared by adding some silicon carbide and andalusite fine powder. Since natural bauxite clinker is a heterogeneous material, the performance of the raw material itself varies greatly from place to place, and is more obvious between blocks, resulting in uneven physical and chemical indicators of finished bricks; in addition, w (Al2O3) = 85% to 88% The main crystal phase of natural bauxite clinker is corundum phase, and the crystal form of corundum is barrel-shaped, short columnar or plate-shaped. Its thermal conductivity is high at 1000℃ (35W·m-1·K-1), 20~1000℃ The thermal expansion coefficient is large ((7～10)×10-6℃-1), which also affects the high-temperature performance of the product. The physical and chemical indicators of alumina-based synthetic mullite are also relatively stable. Its main crystal phase is mullite phase. The crystal form of mullite is needle-like or long columnar and intertwined into a network. Its thermal conductivity at 1000°C is low. (3.83W·m-1·K-1), and the thermal expansion coefficient is small (5.3×10-6℃-1) from 20 to 1000℃. Therefore, using alumina-based sintered mullite as the main raw material is expected to solve the shortcomings of high thermal conductivity and unstable high-temperature performance caused by using natural bauxite clinker as raw material.
01 test
01Raw materials
The test raw materials include M60 and M70 alumina-based mullite with particle sizes of 5 to 3, 3 to 1 and <1mm, M60 and M70 mullite with particle sizes of <0.074mm, 80 homogenized material, 85 homogenized material, carbonized Silica powder and andalusite powder, Guangxi white mud with particle size <0.044mm.
02Sample preparation process
After mixing the dry materials evenly, add calcium lignosulfonate mixed with water as a binding agent. After stirring in a mixer for 15 minutes, use a universal press to press the evenly mixed mud into a 50mm × 50mm cylindrical sample at a pressure of 30MPa. , while using a 630t friction press to make standard bricks of 65mm×114mm×230mm. After the green body sample is air-dried, it is dried in a drying oven at (110±5)°C for 24 hours, and then calcined in an electric furnace at 1490°C for 3 hours. Allow to cool naturally for later use.