Investigation of ignition and volatile combustion of single coal particles within oxygen-enriched atmospheres using high-speed OH-PLIF

To study devolatilization, ignition, and volatile combustion processes of single coal particles at a fundamental level, a flat flame burner was designed to provide oxygen-enriched exhaust gas environments at elevated temperatures and varying gas compositions. In one set of experiments coal particles were carried by a central jet using a gas mixture of the same composition as the flat flame. By this means a homogenous and connected flame was generated. At the instant when single coal particles transited this stationary flame, start of particle heat-up was well defined. This allows studying start of ignition more accurately compared to the other set of experiments where an inert carrier gas jet was used for transportation of coal particles. Heat-up and ignition were retarded temporally due to precedent mixing between inert gas and ambient flue gases. Coal particles with a high percentage of volatiles (36 wt%) and a particle distribution ranging from 90 to 125 µm were used. Coherent anti-Stokes Raman spectroscopy (CARS) measurements were performed to characterize ambient gas phase temperatures. By high-speed laser-induced fluorescence, imaging of OH-radicals ignition and volatile combustion was visualized for individual coal particles. Reaction zones surrounding each coal particle and the corresponding distances to coal particles were identified. This distance depended strongly on oxygen concentration of the ambient flue gas atmosphere. In addition to an improved phenomenological understanding the data may serve for model validation.