A Simulation Model to Predict Slag Composition in a Coal-Fired Boiler

Abstract

A major problem in the operation of coal-fired boilers is the formation of slag and fouling of the boiler tubes. The slagging problem may become detrimental to the operation of the boiler, especially when different coals are blended. The objective of this project was to develop a model to predict the composition of slag or fouling at different locations of a boiler. A simple computer model was developed to predict the rate of deposition and the composition of deposits formed at different locations in the boiler. A multicell, lumped parameter approach was used, assuming that the cells are well mixed and deposition occurs only by condensation of the stable minerals on the boiler walls. An energy balance was used to calculate the coal flame temperature, which was then used to estimate the temperature distribution in the boiler. Chemical equilibrium constants were evaluated to define the stable compounds at different temperatures. The amount of each compound deposited at various locations was determined from the vapor pressure of that compound. Predictions of this model are in general agreement with the power plant data, suggesting that the dominant compounds in the high temperature zone are the aluminosilicates, whereas the major compounds in the low temperature zone are the alkali sulfates.

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