Role of refractories in minimizing the shell corrosion phenomena in cement kilns

Continuous kiln availability for a period of one year or even higher is a prerequisite for achieving high production target in a cement plant. In the modern high capacity plants, it is neither affordable nor desirable to accommodate the kiln stoppages for any period and for any reason whatsoever. In the present scenario of utilizing non conventional raw materials and fuels, refractories have to not only play their dual role of conserving heat and withstanding very stringent service conditions with respect to thermo-mechanical stresses of highest order but also protect kiln shell from attack of detrimental elements even more effectively.
Corrosion of kiln shell is influenced by a number of factors such as composition of the metallic shell and its environment, temperature of the shell, cleanliness and roughness of the shell surface and its contact with other materials, etc. The corrosion phenomenon takes place mainly due to the presence of sulphates and chlorides of alkalies and calcium at high temperature in the cement kiln. Volatiles and decomposition products of these compounds present in the kiln atmosphere during the running of kiln reach the kiln shell causing its corrosion and gradually leading to reduced shell thickness. This may ultimately result in kiln stoppage of longer duration for shell replacement. Further, the effect of Corrosion is determined largely by the degree to which the scale formed under particular conditions blocks further action between the shell and environment. Each steel or alloy behaves more or less individually and forms its own characteristic type of scale whose composition and imperviousness are specific to the given alloy, atmosphere, temperature and duration of exposure.
Therefore, in order to avoid the occurrence of shell corrosion in cement kilns, it is necessary to prevent the passage of these volatiles through adequate refractory lining practice up to inner surface of kiln shell. The present paper highlights the mechanism of shell corrosion and role of refractories in reducing/minimizing the extent of shell corrosion based on the studies carried out by NCB in a few cement plants.
Author: S.K. Chaturvedi, M.M. Ali, A. Pahuja

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