A Numerical Study of Turbulent Combustion of a Lignocellulosic Gas Mixture in an Updraft Fixed Bed Reactor

Lignocellulosic biomass is an established source of energy with various applications. Yet, its diversity renders the proper combustion of its thermochemical degradation vapors challenging. In this work, the combustion of syngas obtained from biomass thermochemical conversion was numerically investigated to limit pollutant emission. The Computational Fluid Dynamics (CFD) simulation was performed using the open-source OpenFOAM. The reactor was considered in an axisymmetric configuration. The gas mixture resulting from the pyro-gasification devolatilization was composed of seven species: CO, CO2, H2O, N-2, O-2, light, and heavy hydrocarbon, represented by methane (CH4) and benzene (C6H6), respectively. The evolutions of mass, momentum, energy, and species' concentrations were tracked. The flow was modeled using the RANS formulation. For the chemistry, reduced kinetic schemes of three and four steps were tested. Moreover, the Eddy Dissipation Concept (EDC) model was used to account for the turbulence-chemistry interaction. The numerical prediction enabled us to describe the temperature and the species. Results show that all transported variables were closely dependent on the mass flow rate of the inflow gas, the primary and the secondary air injections. Finally, from a process perspective, the importance of the secondary air inlet to limit pollutants emissions can be concluded.