Combustion of single walnut shell particles in a laminar flow reactor under oxy-fuel conditions: Optical measurements and particle sampling

Despite the extensive literature on single-particle biomass combustion measurement, there is a significant gap between the abundance of conducted experimental investigations and the inadequacy of the resulting database for calibrating predictive burnout models. This research aims to address this gap by providing an experimental database for single-particle combustion of walnut shells, chosen as a representative lignocellulosic biomass, in a laminar flow reactor for oxy-fuel combustion. Eight different oxy-fuel atmospheres were examined. A stereoscopic imaging system, utilizing four intensified CCD cameras, enables in-situ measurements of temperature, size, shape, velocity and residence time of solid fuel particles. The system's optical resolution is approximately 10 µm and its temporal resolution is 1 μs. In addition to the optical measurements, partially converted solid samples were extracted from the reactor with a sampling probe. The elemental composition, the proximate analysis, pore evolution during the burnout and the morphology of particles were analyzed using samples collected at different residence times. Notably, walnut shells always ignite heterogeneously in oxy-fuel atmospheres and the volatile flame is of low luminosity. With increasing burnout, spheroidization of particles occurs. The novel dataset is presented, compared, and discussed alongside results from current literature.