Abstract
The reactions of coal impurity constituents in the flame are discussed in this paper with particular reference to the formation of corrosive deposits on the heat transfer surfaces in boilers. Consideration is given to the factors which make it difficult to give accurate predictions of metal wastage rates in these environments at high temperatures on the basis of laboratory experiments. These difficulties arise from variations in the operating conditions and are particularly problematic for the steam generating tubes which are located in the walls of the combustion chamber. Non-equilibrium reducing conditions can exist in this region and there is a large temperature gradient through the ash deposit and the corrosion scale on the tube surface. Molten sulphate deposits can be formed on the superheater tubes at the highest temperatures, and the temperature gradient again has an important influence on corrosion rates. The nature and concentrations of the coal impurities and also the influence of heat flux therefore have to be taken into account in the prediction of corrosion rates from laboratory data which may frequently have been obtained under isothermal conditions.
Published Version
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