| Understanding coal-water slurry atomization is a key step in governing, predicting and modeling the combustion of this fuel. Photographic and laser diffraction techniques were used to characterize the atomization of 70 weight % coal-water slurry by a commercially-sized, external mix atomizer in the region relevant to combustion (0 - 250 mm downstream). The use of two complemen- tary analytical techniques has provided much information about the nature of the spray as well as the strengths and limitations of each technique. The mechanism of slurry breakup and atomization is similar to that of water except that much higher atomization energy is required. At very high air/fuel mass ratios (m(,a)/m(,f) = 1.2) the size distribution profile of slurry sprays resembles that of other liquids rather than that of the solid particles composing the slurry. The appropriate model choice for the Malvern analysis is critical in obtaining accurate and meaningful results. The Rosin Rammler model is shown to severely underestimate the contribution of large particles in slurry sprays. Obscuration, size distributions and mean diameters all vary with axial and radial position in slurry and water sprays. Comparison of slurry spray and raw coal size distributions shows that use of only the mean spray diameter can be misleading. Reporting only the mean diameter determined by the Malvern at a particular axial location in the spray does not adequately charac- terize the nature of the spray. A more meaningful quantitative description would be a size distribution based on a radial traverse of the spray at the particular axial location. Also, since the Malvern has a limited size range, it is inappropriate to use only this technique as a check for large drops or ligaments (>500 (mu)m). Photographs or other imaging techniques should be used to monitor large drops in the spray. |
