CFD Analysis on the Impact of Biogas Generation and Bubble Size on the Hydrodynamics of a UASB Reactor

The influence of biogas flow rate and bubble size on the hydrodynamic behaviour of an Upflow Anaerobic Sludge Blanket (UASB) reactor producing biogas was studied using Computational Fluid Dynamics (CFD). The study encompassed biogas flow rates ranging from 4.15x10(-2) to 1.65x10(-1) m(3)/h along with the investigation of three distinct bubble sizes between 1 to 3 mm. The simulations were performed assuming a Eulerian-Eulerian, transient framework. A three-dimensional approach was adopted for the simulations. The outcomes revealed that higher gas flow rates resulted in increased biogas upflow velocities and elevated gas volumetric fractions. Concurrently, liquid upflow velocities and magnitudes were augmented due to the heightened gas flow rates, establishing a direct relationship between gas and liquid velocities. Regarding variations in bubble size, the findings indicated that bubble size influenced gas velocity. When bubble size increased at constant gas flow rates, a reduction in gas volumetric fraction inside the reactor was observed. These results highlight the significance of considering the gas phase when employing CFD for the simulation of UASB reactors.