Modeling Reactive Heat and Mass Transfer in Biogas Production Unit

Biogas production is one of the existing ways to produce renewable energy from wastes. This is mainly governed by multiphase transport processes and biological reactions without oxygen. Consequently, a fine description of those phenomena at the production unit scale is required in order to characterize the biogas production. It is necessary to take into account the various heterogeneities (phase distribution, gas composition, temperature) inside the production unit to accurately predict the installation efficiency.

The goal of this work is the development and the validation of a CFD software solving the complete set of equations constituting the model. The code is developed using the OpenFOAM® platform, an open-source CFD toolbox highly programmable, which enables parallel computation and disposes powerful pre- and post-processing tools.

The set of equations is solved sequentially, decoupling the hydrodynamics part from component transport and heat transfer. First, gas and liquid flows in the porous medium are solved using the IMPES method (Implicit Pressure and Explicit Saturation) with, for each equation, an adaptive independent time-step. Then, the reactive mass transfer is solved decoupling the purely reactive part from the transport part. Finally, heat transfer is computed using the fields previously updated.

Results on the hydrodynamic part are first validated on the Buckley-Leverett case by comparison with the analytical results. Then, results of the complete model are compared with experimental data obtained on a pilot unit.