Use of equilibrium calculations to predict the behavior of coal ash in combustion systems

Abstract

This paper examines the use of computer calculations to estimate the phase and species composition of silica-based systems which are important in slagging and high-temperature fouling deposits that form in pc-fired utility boilers. Advanced numerical techniques were used to minimize the free energy of the system in order to determine the equilibrium composition and phase distribution while avoiding the numerical problems often associated with such calculations. The equilibrium model, which assumed ideal solutions of complex species, adequately approximated the behavior of a variety of systems for which experimental phase diagrams were available. The model, however, performed poorly for certain silica-rich systems due to an inadequate representation of the silica activity