CERIUM-ADDED ALUMINA AND CERIUM-ADDED ZIRCON AS HIGH EMISSIVITY COATINGS FOR CEMENT ROTARY KILNS

摘要

86% of the energy used in cement production is consumed in the rotary kiln . Refractories are used to protect the kiln structure, which reduce heat losses but about 40-60% of this energy is still lost during the process. One approach to reduce heat loss is to apply a coating layer inside the kiln, which will re-emit the heat from the coating back to the kiln.It has been reported that rare earth (RE) materials could be used as main material for a coating or added as additive to various materials such as zirconia, zircon, alumina and alumina silicate, silicon carbide and ZrB_2/SiC to improve emissivity. Hoicombe Jr and Chapman3 claimed in 1997 that a RE coating gave high emissivity and can be used in the interior of a furnace. Cerium oxide is a potential RE candidate because it possesses a high melting point (2477°C), high emissivity (0.9 from 1000-2000°C) and good base and acid chemical resistance. It has been suggested that a higher cerium oxide content will lead to a higher emissivity. Terbium oxide is another RE with similar behaviors but which is rarer than cerium oxide. Moreover, RE additions in coatings have also enhanced toughness and reduced the work of fracture for intergranular failure of alumina ceramics.