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Show camera to give a general measure of size and devolatilization behavior, while the in situ particle counter provides detailed and quantitative information on the physical behavior of the spray. Two ignition criteria have been examined, including luminosity and devolatilization. Slurry and Flow Reactor Characterization A total of five different coal/water slurry mixtures (described in Tables IA and IB) have been characterized and studied in the laminar flow reactor.* The primary characteristics of each slurry are its chemical properties, extent of ash beneficiation, and particle size grind, with particlular emphasis on the top particle size in the slurry suspension. Table IA is organized to show the two coarse grind slurries at high and low ash content (#1,#2), followed by the fine grind slurries at high and low ash contents (#3,#4,#5). Ash beneficiation and finer particle grind are presumed desireable properties for fuel applications in gas turbines and diesel engines because of the need for fast combustion times and minimal ash deposition. Use of coal-water slurries in power plants may or may not require this additional fuel preparation. All slurries have been diluted to approximately 50% solids to provide steady feedrates in our small atomizer. We recognize that the solids concentration is an important property of the slurry in determining atomization properties. However, recent results (Kikkawa et al., 1984) have been obtained where solids content was varied from 50-75% and showed a small effect on combustion efficiency and NOx emissions. This result, coupled with a similar solids concentration for all fuels used here gives a uniform basis for a comparative study of the various fuel parameters described in Table I. Two particle size measurement techniques have been used to characterize the slurry solids (Leeds and Northrup Micro-Trac, and a Coulter counter) with good agreement in two cases and widely different results for two other slurries. The differences between the two techniques serve as a measure of the uncertainty with which the initial solids size distribution is known. All measurements in the following discussion were obtained for the laminar flow reactor conditions described in the section above. In addition, for most of the experiments discussed here (except as noted), the air atomizing flowrate was held constant to maintain uniform gas phase reactor conditions. Several experiments were performed with different air flowrates and different atomizer diameters to determine the sensitivity of results to various atomization conditions. Figure 7 shows a typical axial velocity profile as a function of axial reactor position for particles as they enter the flame and reach equilibrium with the hot gas flow. These measurements were obtained with the transit timing technique integrated with the particle counter (Holve, 1982) and are obtained from particles larger than 5 microns up to the maximum size. The particles do not reach equilibrium velocity with the gas flow until about 8 cm, so it is important to measure the velocity variation and determine the actual residence time history in the burner by integrating over the entire velocity history. Although the larger particles will lag behind the smaller particles due to Stokes drag, the ^Provided by Dan Gurney of the National Institute for Petroleum and Energy Research and Debbie Davis-Waltermire of the Morgantown Energy Technology Center. 8 |