Résumé
An experimental study is performed on a pilot-scale combustion facility to evaluate the structure and characteristics of pulverized biomass flames. The design of the 20kW burner and the combustion chamber is made in a way to allow analyzing the different involved phenomena using OH* chemiluminescence imaging and in-flame measurements of gas concentrations. The characterization of the flames of pine, moderately torrefied pine and pyrolyzed pine, was completed by a CFD simulation, which predicted the aerodynamics, trajectory of the particles, and their degradation process. The chemiluminescence signal of OH* marks the reaction zone of volatiles. The intensity of the signal is strongly dependent on the volatile content. However, the position and size of the reaction zone is rather affected by the particle size distribution than by the biomass thermal treatment. The wide particle size distribution of pine produces a two-stage devolatilization, promoting the reduction of NOx fraction in the second devolatilization region. Higher and earlier devolatilization, oxygen consumption and temperature rise are detected for the treated pine compared to their raw counterpart. The added heat in the recirculation zone helps heating the injected air and biomass which increases flame stability of the finer torrefied and pyrolyzed fuels.