Aplicação de modelagem multifásica para estudo de biorreatores anaeróbios

Abstract

Aiming to understand the hydrodynamics of a Upflow Anaerobic Sludge Blanket (UASB) reactor, this work aimed to apply multiphase modeling through computational fluid dynamics (CFD) to assess the behavior of the three phase flow (liquid, gas and solid) in a UASB reactor, which is used in the biogas production using vinasse as substrate and the to validate the results using Particle Image Velocimetry (PIV) techniques. Therefore, the UASB reactor was designed and then the geometry and mesh were developed. The simulations were performed using the software Fluent and a mesh with 528.000 control volumes. Initially, monophasic simulations of the liquid phase were carried out. Next, two phase simulations were performed considering the pairs of phases gas/liquid and solid/liquid. An Eulerian-Eulerian approach was adopted, together with isothermal, transient and tridimensional conditions. After validated, the two-phase models (solid/liquid and gas/liquid) were combined into a three-phase model. PIV was used for the experimental validation of the two and three-phase models. The numerical model validation showed maximum differences lower than 4% between experimental and computational results for the three cases (gas/liquid, solid/liquid and liquid/gas/solid). Numerical results showed that the drag force plays the major role on the gas/liquid flow profile. Regarding the solid/liquid flow, Gidaspow model was chosen to estimate the drag force coefficient after comparisons between numerical and experimental results. Three-phase simulations showed that the gas was the main responsible for the mixing quality within the reactor. Dead zones were reduced from 44% in the solid/liquid simulations to 0,02% in the three-phase simulations and the liquid and solid velocity magnitude increased in about eight times. The configuration of the gas distribution system played a major role on the overall flow profile and drove liquid recirculation along the axial position. Understanding the multiphase flow within this reactor will allow optimizations on the process as well as on the reactor, in order to seek an increase on the efficiency both in the treatment and biogas in the production.