Fast devolatilization of biomass : An experimental study using high-speed imaging, relevant for suspension firing technologies

Sammanfattning: We have performed experiments using imaging techniques in a flame-assisted, drop-tube reactor with optical access, to extract information relevant to the improvement of multi-particle devolatilization models. These models could be of interest for different suspension firing techniques, such as entrained flow biomass gasification, (EFBG) and oxyfuel combustion.Reactor-scale CFD simulations usually disregard the implications of the elongated shape of biomass particles, (high aspect ratio: AR) and their morphological changes during devolatilization for their heat-transfer and fluid-dynamics behavior. In addition, solid-fluid interactions are prone to take place in highly seeded flows, potentially causing heat and mass transfer limitations during thermochemical conversion. Although there is sufficient experimental evidence supporting that particle morphology affects the devolatilization rate and the motion of the individual particles in a particle-laden flow, there is a lack of experimental data documenting the morphological transformations during biomass devolatilization and the heat and mass transfer limitations due to solid-fluid interactions. In this work, we have documented the morphological transformations and fluid dynamics behavior during biomass devolatilization in relation to the initial particle shape and operation conditions relevant to suspension firing technologies. In addition, we have observed an interesting phenomenon related to the fast release of volatile matter during pyrolysis that affected significantly the particle fluid dynamics. We have also performed CFD simulations to observe whether taking into account the phenomenon described in this work can help to reproduce better the experimental results. Future work should aim to provide a better model for this phenomenon, and to complement the current results with thermometric and spectroscopic measurements, which can draw a better insight on the transformations taking place during devolatilization.