Generally, the working zones of a rotary kiln system (including the preheating zone at the kiln tail and the cooling zone at the kiln head) are divided into the following categories based on the temperature of the materials in the cement kiln: drying zone, preheating zone, decomposition zone, exothermic reaction zone, firing zone, and cooling zone. So, how should I choose refractory bricks for these working zones?
① Requirements for the rotary kiln discharge port and cooling zone: The refractory linings in these zones are subject to severe mechanical wear and chemical corrosion due to the combined effects of high-temperature clinker, secondary air, and high-temperature flames. Therefore, they must possess excellent wear resistance, slag resistance, and thermal shock resistance. Selection criteria: For the cooling zone, Grade I high-alumina bricks (with an Al₂O₃ content of 65%-75%), thermal shock-resistant high alumina bricks, spinel bricks, chrome-magnesia bricks, and phosphate bricks are commonly used. For the discharge port, high alumina refractory bricks, refractory concrete (with corundum as the aggregate), and silicon carbide bricks are commonly used.
② Requirements for the Rotary Kiln Firing Zone: The refractory lining in the rotary kiln firing zone is primarily subject to high-temperature shock and chemical corrosion (alkaline corrosion). Therefore, refractory materials with sufficient refractoriness and resistance to high-temperature lining are required. Magnesia bricks and chrome-magnesia bricks are recommended.
③ Requirements for the Rotary Kiln Transition Zone (Exothermic Reaction Zone): The kiln lining in this zone experiences intermittent lining, frequent temperature fluctuations, high drum temperatures, and severe chemical corrosion. Therefore, refractory materials that can withstand high-temperature shock, possess high high-temperature flexural strength, and a low elastic modulus are required. Recommended materials include high-alumina bricks made from corundum (50%-80% Al₂O₃ content) and bauxite, directly bonded chrome magnesia refractory bricks, ordinary chrome-magnesia bricks, and spinel bricks.
④ Requirements for the Preheater and Calciner: Refractory materials with high-temperature resistance and thermal insulation performance are recommended. The cyclones in the upper stages, where temperatures are lower, can be directly cast using castables (refractory concrete). The lower stages of the preheater, calciner, and connecting pipes can be constructed with alkali-resistant and wear-resistant clay bricks, with a composite insulation layer. The roof should be constructed with refractory bricks, backed by slag wool. Castables can also be used. Elbows should be cast with castables. Dense semi-silica clay bricks can be used in areas such as the kiln tail riser to prevent alkali corrosion.
⑤ Cement clinker cooler system. The refractory linings used in grate coolers include refractory firebricks, lightweight castable bricks, insulating bricks, and insulating panels. Conventional chrome-magnesia bricks or high-purity high-alumina bricks can be used in the high-temperature areas and the discharge throat. Clay bricks can be used in the medium- and low-temperature areas.
