170 years ago, people began to use vertical kilns to produce cement clinker, and the whole kiln uses a single variety containing Al2O330%-40% - clay bricks. 120 years ago, rotary kilns began to be used to produce cement clinker, and this experience is still followed on the shaft kiln. In the mid-1930s, a small number of rotary kilns began to use high-aluminum bricks in the firing belt, and a new concept was developed to select different refractory materials according to the clinker production process requirements. Since the 1940s, alkaline bricks have been used for the firing belt, with high aluminum bricks on both sides and clay bricks for the rest. In the 1950s, this basic pattern began to be laid down and has been followed ever since.

Cement kiln construction site

So far, refractory materials for rotary kiln have gone through the stages of clay brick, high aluminum brick, phosphate brick, phosphate wear-resistant brick, magnesium brick, polyphosphate bonded magnesia brick, ordinary magnesia chrome brick, direct bonded magnesia chrome brick, dolomite brick and now developing magnesia spinel brick. From the development trend, it can be summarized as the development of high aluminum products with low fire resistance to high fire resistance of magnesium products, from chromium materials that can bring environmental hazards to the development of environmentally friendly chromium-free refractories. For more than 10 years, the refractory industry at home and abroad has done a lot of work in finding alternative materials for magnesia-chromium bricks, and the chromium-free products studied are divided into five series of magnesia-aluminum, magnesia-aluminum iron, magnesia-aluminum manganese, magnesia-zirconium and magnesia-calcium.

In simple terms, the magnesia-alumina spinel material has good high temperature performance, thermal shock resistance, and is not sensitive to the change of REDOX atmosphere, but the resistance to CaO erosion and hanging kiln skin performance is poor. The ferro-aluminum composite spinel material has excellent thermal shock resistance and good performance of kiln skin in short and medium term, but poor high temperature resistance. Ferromagnesia aluminum-manganese composite spinel material is a substitute for ferromagnesia spinel material, but the thermal shock resistance is not as good as the latter. Magnesium zirconium materials are used in high temperature and ablative occasions, and can have good thermal shock resistance and kiln skin performance, but either the price is high or the thermal conductivity is high. Magnesium calcium material has good high temperature resistance, CaO corrosion resistance and kiln skin hanging performance, but it has poor hydration resistance, acid gas corrosion resistance and thermal shock resistance, and can only be used in areas where the kiln skin is stable.