Metal Corrosion has been a subject of growing important in cement furnaces during the past few years. This development is mainly a result of the tendency to use alternative fuels with high concentrations in sulphur, chlorine and other elements (such as fluorine, zinc or lead) forming corrosive constituents in the flue gases. Examples of such fuels are tires, plastics and solid municipal or industrial waste. The condensation of corrosive gaseous components together with water vapour on the relatively cool metal surfaces can produce extremely corrosive conditions, depending on metal surface temperature as well as water and pollutant concentration in the gas phase.
Inside the refractory lining, at higher temperatures, molten salts can also deposit on the material surface. The special conditions in a cement furnace can result in very high concentrations of sulphates and especially chlorides due to the fact that these compounds are captured in a cycle in the region between the central part of the kiln and the adjacent parts in the preheater. This circulation is caused by the evaporation of sulphates and chlorides in the hot zones of the furnace and the re-condensation of the gaseous components as liquid salts when the flue gases reach the cooler parts of the system.