Two-Phase CFD Simulation Coupled with Chemical Reactions in a Plug-Flow Reactor

In order to design and exploit a process successfully, it's necessary to understand how it works. Anaerobic digestion is a sequential complex biochemical process that involves a series of reactions that are mediated by several different groups of anaerobic microorganisms. This research describes a simulation-based on three-dimensional Computational Fluid Dynamics (CFD) coupled with reactions in a semi-continuous Plug Flow Reactor (PFR). The commercial software FLUENT 6.3 was employed to solve the governing equations. The gas-liquid flow was modeled using a Eulerian multiphase and k-e turbulence (RNG) model. Hydrodynamics and anaerobic digestion reactions investigated the mixing regime using the Multiple Reference Frame (MRF) model within the whole multiphase bioreactor. Simulation results indicate that flow pattern within the reactor was highly influenced by the substrate density and viscosity, and stirring intensity. A comparison of three impellers mixing speed in the reactor demonstrates that mixing intensity has affected the gas phase above the fluid surface. Such a mixing intensity may create a turbulent region with a homogenous mixture of gas and liquid, which is not suitable for this anaerobic digestion. Concentration profiles of CH4 and CO2 in the anaerobic system displayed a plug flow pattern.