Influence of internal biogas production on hydrodynamic behavior of anaerobic fluidized-bed reactors

Predictive models for describing the hydrodynamic behavior (bed-expansion and bed-pressure gradient) of a three-phase anaerobic fluidized bed reactor (AFBR) was developed according to wake theory together with more realistic dynamic bed-expansion experiments (with and without internal biogas production). A reliable correlation equation for the parameter k (mean volume ratio of wakes to bubbles) was also established, which is of help in estimating liquid hold up of fluidized beds. The experimental expansion ratio of three-phase fluidized beds (EGLS) was approximately 18% higher than that of two-phase fluidized beds (ELS); whereas the experimental bed-pressure gradient of the former [(−ΔP/H)GLS] was approximately 9.3% lower than that of the latter [(−ΔP/H)LS]. Both the experimental and modeling results indicated that a higher superficial gas velocity (ug) gave a higher EGLS and a higher EGLS to ELS ratio as well as a lower (−ΔP/H)GLS and a lower (−ΔP/H)GLS to (−ΔP/H)LS ratio. As for the operation stability of the AFBR, the sensitivity of ug to expansion height (HGLS) and (−ΔP/H)GLS is between the sensitivity of superficial liquid velocity and biofilm thickness. The model predictions of EGLS, (−ΔP)GLS, and (−ΔP/H)GLS agreed well the experimental measurements. Accordingly, the predictive models accounting for internal biogas production described fairly well the hydrodynamic behavior of the AFBR.