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Show Pa per No. 3 PSI-10241 SR-386 EXPERIMENTAL AND MODELING STUDY OF PYRITE TP~SFORMATIONS L~DER COAL COMBUSTION CONDITIONS Abstract Srivats Srinivasachar, Joseph J. Helble, Charles B. Katz, Joseph R. Morency, and Arthur A. Boni PSI Technology Company Research Park, P.O. Box 3100 Andover, MA 01810 Existing literature data on the decomposition and oxidation of pyrite was used to establish the basis for a kinetic model for describing the transformations of excluded pyrite (FeS2) particles in a combustion environment. The model follows the particle composition history, starting from the decomposition of pyrite to pyrrhotite (FeO.877S), followed by its oxidation successively to a molten sulfide-oxide mixture, magnetite (Fe304), and finally hematite (Fe203). Particle temperature is found to exceed the gas temperature during this process due to the exothermic oxidation of iron sulfide. A special feature of the model is that it predicts the existence and duration of the melt phase in the particle. The time spent in the molten state is found to constitute approximately 80 percent of the total time required for oxidation of the pyrite to solid magnetite. Experiments were carried out in a drop-tube furnace to determine the size evolution and particle deposition efficiencies as a function of residence time in the reactor. Fragmentation of pyrite particles during combustion is evident from a comparison of the size distribution of the feed with that of a partially oxidized sample. Particle sticking efficiencies remain at a high value at short residence times, then decrease abruptly at longer residence times where crystalline magnetite is predicted to dominate. Scanning electron micrographs of particles sampled at different residence times show the evolution of morphology as a function of particle conversion. 1 |
