EXPERIMENTAL AND NUMERICAL CHARACTERIZATION OF LIQUID FLUIDIZED-BEDS OF COAL PARTICLES

Liquid fluidized-bed reactors are being investigated for the biologica l conversion of coal to clean-burning liquid fuels. The efficient desi gn, operation, and scaleup of such reactors require accurate, predicti ve mathematical models which describe their performance. A fully predi ctive model is proposed to describe both the bed height and the partic le size distribution obtained in such liquid fluidized beds of coal pa rticles. This model is validated on both the macroscopic and microscop ic scales. First, using well-characterized charges of Illinois #6 bitu minous coal having a particle size of 10-250 mu m, the bed was studied macroscopically by observing the bed height as a function of Flow rat e and coal charge. Secondly, to characterize the bed on a microscopic level, a novel, noninvasive fluorescence technique was used. This tech nique allowed direct observation of particle size distributions as a f unction of axial position and flow rate. Use of this experimental tech nique revealed patterns in bed segregation and elutriation that will b e paramount to the operation of a bioreactor for coal solubilization. Over a wide range of particle sizes, liquid velocities, and coal loadi ngs, the predicted bed heights agree very well with the experimental r esults. In addition, agreement is demonstrated between the predicted a nd measured particle number distributions as a function of flow rate a nd axial position. The mathematical model proposed here will have an i mpact on many low-Reynolds-number fluidized-bed applications, includin g other bioprocesses such as ethanol production and fermentation of or ganic acids.