Indian Journal of Chemical Technology, Vol.1, No.1, 20-26, 1994
COMBUSTION OF COAL CHAR IN A FLUIDIZED-BED - MASS-TRANSFER EFFECTS
The burning rates of lignite char particles in a fluidised bed combustor have been studied by injecting batch mass of particles into the bed. The burn out times of lignite char are found to decrease with larger inert size, higher fluidising velocity and higher bed temperature, but increase with larger char size and batch mass charge. The combustion process is shown to be both kinetic and mass transfer controlled. The rate of combustion when limited by mass transfer has been derived delineating the effect of chemical reaction rate. Sherwood number around burning lignite char particles is found to increase with Reynolds number and the modified Frossling's equation appeared to well fit the measured data. Further, a correlation to predict N-SH for all the range of particle size and operating conditions has been proposed. The suitability of the equations proposed is verified by predicting batch burn out times and comparing with the measured values.