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Show of unburned material. Given that the coal has a 7% mineral matter content, this result is quite reasonable if all the pulverized coal is assumed to be burned. For these experiments we did not have the capability of measuring the extent of combustion, but for the small coal particles transported by the fluidized bed feeder, complete combustion in 150 msec is a reasonable assumption. The distribution shape of the burned pulverized coal also changes from that of the raw pulverized coal giving a fourfold decrease in particle size for particles above 10 microns with less than a 30% change in particle sizes below 0.5 microns. This result is consistent with previous observations that the percentage of mineral matter in pulverized coal increases with decreasing particle size and that fragmentation should decrease with increasing mineral matter.' Thus larger particles would show a greater change in particle size than small particles. Hot Flow C shows the results for a factor of 4.4 increase in the pulverized coal feedrate over that of Hot Flow B, with a corresponding similar increase in the number and mass frequency distributions of the measured unburned material. For Hot Flow C it is clear that the burned pulverized coal distributions are nearly identical to the disbursed flyash. Hot Flow D shows the results of an intermediate mass feedrate between Hot Flows C and B, resulting in a number distribution that is appropriately between the measured distributions of Hot Flows C and D. 4.0 CONCLUSIONS A variety of independent measurements have been conducted in parallel with the Sandia single particle counter to validate the measurement capabilities of this instrument. An in situ alignment system provides flexible and reliable capability for obtaining accurate measurements in a variety of experimental conditions. Independent calibrations and total mass comparisons give confidence that the instrument provides correct number and mass frequency distributions in the size range 0.25-100 microns. As an example of the utility of this instrument we have obtained the first in situ measurements of flyash and burning pulverized coal in the size range below 5 microns. These results show that the raw input pulverized coal contains a large number of fine particles, similar to the flyash produced after combustion. This result suggests another source for much of the submicron flyash formed in pulverized coal combustion. Potential control methods for fine particles clearly depend on a quantitatively correct understanding of the chemical and physical methods of formation. If most of the fine particles arise directly from the input pulverized coal, then this suggests that pre-combustion separation of the fines might be a more efficient particle emissions control strategy. Other results for homogeneous materials suggest that particle fragmentation throughout the combustion process would provide a large source of fine particles, which would negate any pre-combustion control strategy.^ In addition, other studies show that vaporization-condensation is an important source of fine particles and is 11 |