| OCR Text |
Show liquid phases of these compounds to the ideal solution model from which they are currently absent may result in their solid phases not precipitating out of the liquid solution until lower temperatures. This will have the effect of lowering to some extent the viscosities predicted by the extended viscosity method for slag A. This change would also affect the viscosity prediction for slag B. However, since the predicted behavior of this slag is mainly influenced by the precipitation of iron compounds from the slag solution, the addition of calcium and magnesium aluminosilicate compounds to the ideal solution model should not have a great effect. Other species, in addition to those mentioned above, should be considered for inclusion to the chemical equilibrium code. Ideally, the results of the code should be compared against experimental studies of slag composition as a function of temperature for the purpose of validating the ideal solution model. The ideal solution model used in this study has been compared against the results of a hot stage microscopy study of two British coals (9). Excellent agreement was found on the identification of the major species to precipitate out of the liquid slag solution. Further comparisons though may indicate the need for other compounds to be included in the ideal solution model. Besides improvements in the chemical equilibrium code, the extended viscosity method may also be optimized by the use of an improved viscosity prediction formula. The Watt-Fereday formula, upon which the extended method's predictions are based, was derived in the late 1960's and considered a range of coal compositions which were typical of British coals. A wider range of coals are in use today, of which many have ash compositions which lie outside the range of compositions considered by Watt and Fereday in deriving their formula. In addition, a coal ash whose liquid phase composition at high temperatures lies within the range of compositions studied by Watt and Fereday may have its liquid composition fall outside this range upon cooling. Thus, motivation exists for the development of a new viscosity prediction formula which is based on a broad range of ash compositions, and derived using state-of-the-art statistical techniques. In conclusion, the extended viscosity method is a promising approach for the improved prediction of the viscosity behavior of coal 3-9 |
