S. Degterov

Thermodynamic modelling of the system Al2O3SiO2CaOFeOFe2O3 to predict the flux requirements for coal ash slags

Slags are formed during coal combustion processes as a result of the melting and reaction of the mineral matter. Predicting the outcome of these complex chemical reactions has long been a problem. Improvements in chemical thermodynamic models of oxide systems and computational methods now make these predictions possible. In this paper a model of the system Al2O3---SiO2---CaO---FeO---Fe2O3, developed using the F*A*C*T computer system, is presented. Examples are given of the use of the model to predict the phases formed as a function of ash composition, temperature and oxygen partial pressure of the system. These examples show how results can be presented in forms which can be readily used by practising combustion engineers, and coal production and marketing personnel.

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr2O3, CrO-Cr2O2-Al2O3, and CrO-Cr2O2-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toPO2 = 10−3 atm for the CrO-Cr2O3-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr2O3-SiO2 and CrO-Cr2O3-SiO2-Al2O3 systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasi-chemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.