Three-dimensional numerical modeling and analysis of multiphase distribution in a UASB reactor with experimental validation of biogas volumetric flow rate

Research involving numerical simulations to model physical processes, such as the behavior of multiphase flow in upflow anaerobic sludge blanket (UASB) reactors, requires a validation step for the numerical data to ensure that the model accurately represents the physical dynamics of the studied process. In this context, the present study aimed to develop a mathematical model and perform numerical simulations to investigate the multiphase flow behavior in a UASB reactor, validating the numerical data regarding the biogas volumetric flow rate based on real data collected from the three-phase separator. Using Ansys® CFX software, three-phase, turbulent, transient, Eulerian-Eulerian simulations were conducted with different gas volume fractions (GVF of 0.026; 0.130; and 0.260) at the inlet of the model to examine their influence on phase distribution, velocity, and solid deformation rate. To validate the model, experimental biogas volumetric flow data at the liquid-gas interface were compared with the numerical results, showing a relative error of 4.2% for the case simulated with a GVF of 0.026. In the cases studied, the phase distribution behavior remained consistent. The velocities showed that the gas moved approximately 200 times faster than the liquid, while the solids reached speeds 10 to 30 times higher than the liquid, but in the opposite direction. It was also found that higher GVF led to increased solid deformation rates due to shear stresses. The validated model is suitable for future studies aiming to improve UASB reactor flow behavior.