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Show Particle Size Distribution. Results of fly ash particle size analysis are shown in Figures 16, 17, and 18. The fly ash particles from micronized coals are finer than those obtained from pulverized coals. The fly ash particle size distribution from Indiana pulverized coal is finer than that of Ohio and West Virginia pulverized coals. This result may be due to the fine distribution of mineral matter in the Indiana coal. The particle size distribution results indicate that the amount of fire-side deposition may be less in the case of micronized coal as compared to pulverized coal; this is a result of lower target efficiency [8] of finer fly ash particles. (Target efficiency represents the fraction of particles in the combustion gases that will impinge on the boiler wall and tubes.) Scanning Electron Microscope Examination. The fly ash particles from micronized coals were finer than those from pulverized coals. One sample of each fly ash sample produced from micronized and pulverized coals was examined with the SEM. Figures 19, 20, and 21 show the comparison of micrographs of micronized coal fly ash and pulverized coal fly ash at 1000X magnification for Indiana, Ohio, and West Virginia coals, respectively. Figure 19 shows that the fly ash obtained from Indiana micronized coal is finer than that of Indiana pulverized coal. The fly ash particles are a combination of spherically coalesced ash particles, angular irregular fly ash, and quartz material. Note that the degree of agglomeration is less in the micronized coal fly ash. This is a consequence of the fine particle size of micronized coal. Similar results were obtained with Ohio and West Virginia coals; however, there are significant differences. The size of the agglomerates and the skeletal structures in the pulverized coal ashes (such as the white mass in the center of Figure 21, pulverized-coal fly ash) decreased from West Virginia to Ohio to Indiana coals. The difference in agglomerates could be due to the difference in ash fusion temperature, and skeletal structure results may be due to differences in combustion performance. 9-31 |