A Model of the Enhancement of Coal Combustion Using High-Intensity Acoustic Fields

A model for the enhancement of coal combustion in the presence of high-intensity acoustic fields has been developed. A high-intensity acoustic field induces an oscillating velocity over pulverized coal particles otherwise entrained in the main gas stream, resulting in increased heat and mass transfer. The augmented heat and mass transfer coefficients, expressed as space and time-averaged Nusselt and Sherwood numbers for the oscillating flow, were implemented in an existing computer code (PCGC-2) capable of predicting various aspects of pulverized coal combustion and gasification. Increases in the Nusselt and Sherwood numbers about 45, 60 and 82.5 percent at sound pressure levels of 160, 165 and 170 dB for 100-μm coal particles were obtained due to increase in the acoustic slip velocity associated with the increased sound pressure levels. The main effect of the acoustic field was observed during the char combustion phase in a diffusionally controlled situation. A decrease in the char burn-out length (time) of 15.7 percent at 160 dB and 30.2 percent at 170 dB was obtained compared to the case with no sound for the 100-μm coal particles.