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Show concentrations are larger than the uncertainty in the data. However, the data in both figures are in reasonable agreement and, for the most part, show consistent trends. CONCLUSIONS The deposition of mineral matter during coal combustion can be described as a process involving four general mechanisms, each with two time scales. The mechanisms include inertial deposition, thermophoresis, condensation, and chemical reaction. Both particle residence time and clock time are important in each of the processes. Coal mineralogy, as opposed to the elemental composition of the ASTM coal ash, determines many important deposition mechanisms and deposit properties. Other important variables determining deposit properties include operating conditions, and boiler geometry. Means of incorporating all of these variables in a tractable engineering model for ash deposition have been demonstrated. Deposit properties can be anticipated with reasonable accuracy based on their elemental composition and the predicted rates of various deposition mechanisms. Deposit composition, morphology, removability, and emissivity have been reasonably well anticipated based on the mechanistic details of the engineering model. While not all properties currently are predicted or anticipated within our ability to measure them, the results of this approach to anticipating deposit properties are encouraging. ACKNOWLEDGMENTS This research is supported in part by the U.S. Department of Energy through the Pittsburgh Energy Technology Center's Direct Utilization Advanced Research and Technology Development Program. Major contributions are also made by Consolidation Coal Company and Central lliinois Public Service Co. Several visitors at the Sandia Combustion Research Facility (CRF) and the MFC laboratory have contributed to this work. The contributions of Krishnan Padmanabhan in performing some of the initial impaction and thermophoresis predictions is gratefully acknowledged. Krishnan Padmanabhan recently completed his undergraduate degree at Princeton University and worked as a summer employee at Sandia before initiating his graduate studies at Stanford. The assistance of Eric Harwood, Joe Stieve, and James Brandt in performing experiments and maintenance of the MFC during this quarter are gratefully acknowledged. Eric Harwood is a student at the University of California at Davis. Joe Stieve teaches at the Spring Valley High School, Aiken, SC. James Brandt is a student at Livermore High School. The assistance of Alan Salmi and Ephraim Arquitola, both from Sandia, in maintaining the MFC is also gratefully acknowledged. LITERATURE CITED 1. Raask, E., "Mineral Impurities in Coal Combustion," Hemisphere, New York, (1985). 2. Chow, O.K., and G.F. Lexa, "Combustion Characterization of the Kentucky No.9 Cleaned Coals," EPRI Final Report, CS-4994, Research Project 2425-1, (1987). 3. Griffith, B.F., G.F. Lexa, and B.C. Teigen, "Pilot-Scale Combustion Characterization of Two lllinois Coals," EPRI Final Report, CS-6009, Research Project 2425-1, (1988). 13 |