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Show INTRODUCTION Atomization, whe-< it precedes combustion, is the preparation of a liquid fuel for combustion. A good atomizer breaks up a liquid fuel into the smallest droplets that are both technically possible and economically feasible. By transforming the bulk liquid into a large number oi* small droplets, the fuel's surface area is greatly increased and interaction between the fuel and combustion environment is promoted. Thus, ignition by radiation or direct contact with hot combustion products is faster and more probable. With slurries, the atomization technology must additionally subdivide the bulk fuel to roughly the size of the coal particles suspended in the slurry, since this would allow the ignition process to begin immediately upon atomization for at least some fraction of the coal. If this does not occur, a longer residence time within the combustor will be necessary to evaporate the water encasing the particles which shields them from radiation heat transfer and quicker ignition. Currently, several gToups of researchers [2,3] are investigating the application of pressure-type or two fluid atomizers to coal-water slurry combustion systems. Several problem areas have been identified with the use of the abrasive slurry in nozzle atomizers [4-6]. The strategy has often been to modify nozzle atomizers which have been designed for heavy fuel oil by increasing the orifice diameter and straightening the tortuous fuel passages. However, these measures, especially increasing the atomizer orifice, decrease the quality of the ensuing atomization [7] since larger droplets of fuel are produced. Nozzle clogging can still occur when large particles of the fuel solid or particle agglomerates become wedged in the critical flow passages. The result is furnace shutdown. Aside from this degradation in performance which is inherent to nozzle atomizers, the other major problem area associated with their use in coal-water slurry atomization is nozzle life time and durability. Several materials have failed to withstand the erosive environment of this application. Erosion resulting from coal-water slurry operation under conventional circumstances reduces nozzle life to hours or days, which is unacceptable for large scale continuous operation. E X P E R I M E N T A L E Q U I P M E NT Spray Test Facility and Nozzle Types Two types of nozzles have been tested under the same conditions for water and coal-watter slurry at 65 percent of coal loading by weight. The spray was generated in an optical accessible spray chamber which was operated under lower than atmospheric 2 |