Design optimization of biogas digester for performance improvement and fault minimization

ABSTRACT The efficiency and fault tolerance of biogas plant depends on the proper mixing of the sludge in the digester. The quality of mixing can be numerically evaluated based on the velocity profile in the digester. Most of the earlier studies have been focused on improving these velocity patterns with the help of impellers, which requires extra energy to drive them. The current study explores a passive approach for improving velocity pattern by providing the static flaps of optimal sizes at optimal locations. The design optimization problem is formulated to maximize the surface and domain velocities in the digester by varying the geometries and locations of flaps. Sufficient surface velocity gives an advantage by preventing the process of scum formation whereas the improved domain velocity improves gas production rate by improving contact between biomass flocks and the substrate. This concept is demonstrated through the numerical results obtained using CFD and optimization tools of COMSOL Multiphysics software. GRAPHICAL ABSTRACT