COMBUSTION OF COAL CHAR IN A FLUIDIZED-BED - MASS-TRANSFER EFFECTS

The burning rates of lignite char particles in a fluidised bed combust or 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, bu t 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 del ineating the effect of chemical reaction rate. Sherwood number around burning lignite char particles is found to increase with Reynolds numb er and the modified Frossling's equation appeared to well fit the meas ured data. Further, a correlation to predict N-SH for all the range of particle size and operating conditions has been proposed. The suitabi lity of the equations proposed is verified by predicting batch burn ou t times and comparing with the measured values.