Combustion fume structure and dynamics. Period of performance: 8/16/91--2/15/92

During pulverized coal combustion, a fume of submicron particles is formed when minerals that have volatilized from the parent coal nucleate to form new particles. The particles thus generated are extremely small, but they grow rapidly due to Brownian coagulation. Much has been learned about these fine particles in experimental studies of the particles formed in coal combustion. Measurements of the variation of chemical composition with particle size clearly demonstrate that the particles smaller than about 0.1 {mu}m in diameter are formed from vapors while larger particles are dominated by residues from the mineral matter in the coal. Theoretical predictions of the evolution of the particle size distribution suggest that the nuclei should produce a sharp peak which may approach 0.1 {mu}m, but they are unlikely to grow much beyond that size in the limited time available in practical combustors. The focus of this research program is on elucidating the fundamental processes that determine the particle size distribution, composition, and agglomerate structures of coal ash fumes. The ultimate objective of this work is the development and validation of a model for the dynamics of combustion fumes, describing both the evolution of the particle size distribution and the particle morphology. The study employs model systems to address the fundamental questions and to provide rigorous validation of the models to be developed. This first phase of the project has been devoted to the development of a detailed experimental strategy that will allow agglomerates with a broad range of fractal dimensions to be studied in the laboratory