PREDICTING BED EXPANSION AND PHASE HOLDUPS FOR 3-PHASE FLUIDIZED-BED REACTORS WITH AND WITHOUT BIOFILM

A predictive model is developed for the hydraulic behavior, such as ba d height and overall gas, liquid, and solid holdups (volume fractions) , of three-phase fluidized-bed reactors. The model uses process parame ters, such as reactor dimensions, particle properties, and gas and liq uid flowrates, as input variables. A wake model is applied to predict the liquid holdup, while the solids holdup is obtained by iteration ba sed on material balance. Experimental results to evaluate the three-ph ase fluidization model are obtained from a laboratory-scale reactor us ing two sizes of clean glass beads under wide range of gas and liquid velocities. Modeling predictions and experimental results agree quanti tatively for two-phase and three-phase conditions. The model is furthe r applied to analyze fluidized beds with biofilm-coated media. Biofilm accumulation alters the drag coefficient (Go) and bed expansion index (n). Applying a modified correlation for Co to biofilm systems found in literature, the authors propose a new correlation for n which shows little dependence on the particle terminal Reynolds number. (C) 1997 Elsevier Science Ltd.