Hydrodynamic performance evaluation of continuous stirred-tank anaerobic reactor model using CFD

Abstract : In this paper, a computational fluid dynamics (CFD) model that evaluates recirculating mixing in a laboratory scale flat bottom anaerobic reactor was developed. Rheological properties of fluid were included in this model to investigate their influence on performance in steady state. The digest fluid was rheologically characterized. A non-Newtonian behavior was observed, which can be adjusted according to power law model. In this case a single phase model of Newtonian fluid was used as reference to illustrate the non-Newtonian impact on flow patterns. In the comparison, the flow rates and effective viscosity were used in different planes and heights of digester. Dead zones were determined according to the effective viscosity because it depends on shear rate. It was found that using non-Newtonian fluid, velocity recirculations are greater than those generated by Newtonian fluid and have different directions. Furthermore, effective viscosity reduces through digester when non-Newtonian fluid is used. Analyzing different flow rates for input and using CFD model with rheological properties of fluid, made it possible to reduce dead zones.