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Licensed Unlicensed Requires Authentication Published by De Gruyter June 10, 2015

Effect of Scale on Hydrodynamics of Internal Gas-Lift Loop Reactor-Type Anaerobic Digester Using CFD

Mehul S. Vesvikar ORCID logo and Muthanna Al-Dahhan

Abstract

This work evaluates the ability of computational fluid dynamics (CFD) to simulate the flow and predict the hydrodynamics of internal gas-lift loop reactor (IGLR)-type anaerobic digester. In addition, it also analyzes if CFD can account for the effects of operating conditions, geometry as well as scale of the reactor. For this purpose, three-dimensional two-phase CFD simulations were performed using CFX for laboratory-scale and pilot-scale IGLR. The CFD predictions were evaluated against experimental data obtained from computer automated radioactive particle tracking (CARPT). The CFD predictions provided good qualitative but only reasonable quantitative comparison. After validation of CFD model, effect of gas flow rate, draft tube diameter, sparger geometry and reactor scale on flow pattern, liquid velocity and dead volume was investigated. Higher gas flow rates did not offer any significant advantage in increasing liquid circulation in the downcomer or decreasing the dead volume. Configuration with draft tube diameter half of tank diameter, equipped with cross sparger showed comparatively better liquid circulation than other configurations. For same superficial gas velocity, increasing the scale increases the magnitude of liquid velocity but fails to match the mixing intensity observed in laboratory scale. Different interphase forces, turbulence models and closures are also evaluated to improve the predictability of CFD models.

Acknowledgments

The authors would like to thank the United States Department of Energy for sponsoring the research project (Identification Number: DE-FC36-01GO11054), ANSYS for providing the CFX software and the Oak Ridge National Laboratory group for their support.

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Published Online: 2015-6-10
Published in Print: 2015-9-1

©2015 by De Gruyter