GASIFICATION SLAG RHEOLOGY AND CRYSTALLIZATION IN TITANIUM-RICH, IRON-CALCIUM-ALUMINOSILICATE GLASSES

The Texaco Gasification Process employs a high temperature, high press ure slagging gasifier, in which the viscosity of the slag plays a key role in determining operating conditions. Empirical slag viscosity mod els available in the literature, as well as prior laboratory testing h ave generally concentrated on low titanium slags/ashes. During the gas ification of waste materials, titanium dioxide is an important compoun d with respect to ash and slag behavior. In the present study, slag vi scosity was measured under reducing conditions between 1150 and 1500 d egrees C on FeO-CaOAl2O3-SiO2 based slags containing up to 30 wt.% add ed TiO2. Most of the titanium-rich slags exhibited viscosity behavior characteristic of crystalline slags, with critical viscosities ranging from similar to 1230 to similar to 1380 degrees C. Crystalline phase analysis of the slag samples reveals that titanium dioxide (as well as other phases) readily nucleate, and that the residual glass phase gen erally consists of CaO +/- TiO2 +/- Al2O3 +/- FeO silicate glasses hav ing low melting points. Thermochemical modeling of the titania bearing slags using fractional crystallization theory shows some promise for predicting the observed crystalline phases and residual melt compositi onal evolution. Accurate activity coefficients of high temperature sla g components, nucleation and growth kinetics information of crystallin e phases, and thermodynamic data for several unusual species discovere d by electron microprobe analysis are needed, however, before computer modeling can be expected to accurately predict slag behavior. (C) 199 8 Elsevier Science B.V. All rights reserved.