CFD Analysis for Anaerobic Digestion Inside a Batch Digester Augmented With Extended Surfaces

Abstract

The household batch reactor using cow manure as the substrate generates methane gas used as fuel. This paper presents two-dimensional (3D) axisymmetric using commercial COMSOL 5.5 Multiphysics software. This is a computational fluid dynamics (CFD) model based on conservation equations with the chemical reaction model of anaerobic digestion (AD) processes to investigate the influence of different horizontal circular extended surfaces augmented to the inside digesters on the performance of the anaerobic digestion. Using four batch digesters, D1 with no extended surfaces and D2, D3, and D4 have augmented with four horizontal circular extended surfaces of width 2,4 and 6 cm, respectively. The numerical results showed that the cow manure's velocity distribution depends on the chemical reaction's heat, which produces natural convection currents. Furthermore, the temperature and species profiles of the anaerobic digestion process depended on the extended surface area. The D4 has a maximum methane molar concentration, augmented with a higher extended surface area than other digesters. Simulation results agreed with the experimental literature results of various anaerobic digestion processes: for all cases, the mean absolute present error (MAPE) was less than 10%, which is acceptable.