LES of a swirl-stabilized 40 kW_th biomass flame and comparison to a coal flame

Recent advancements have introduced high-fidelity simulations in pulverized coal combustion, yet the shift toward renewable fuels like biomass raises questions about suitable modeling approaches to understand the influence of the new fuel. The current study aims to examine the variations between biomass and pulverized coal flames by employing extended high-fidelity modeling approaches integrated into a Large Eddy Simulation (LES) framework. A fully coupled solid fuel-gas phase model is developed to investigate pulverized biomass and coal flames. Models for particles that are treated in a Lagrangian manner include state-of-the-art devolatilization and char models calibrated with advanced conversion models for the conditions under investigation. Using five-dimensional tabulated flamelet manifolds, gas phase reactions are modeled by two chemical mechanisms tailored to the respective fuel properties. Radiation is considered by solving the radiative transfer equation employing the weighted sum of gray gas model. This high-fidelity simulation framework is applied to a self-sustained, swirl-stabilized 40 kW_th burner that is fired with walnut shells and Rhenish lignite, respectively. Both fuels are studied under the same flow conditions and thermal output to enable a thorough analysis of the fuel effects. The results are validated with experimental particle velocities. Using advanced post-processing for particle grouping, a close link between flame shape and differences in particle trajectories is established, indicating the high significance of particle size when transitioning between fuels.