Emissivity of burning bituminous coal char particles - Burnout effects

The investigation of burnout effects on the char particle emissivity in the spectral range from 1.25 to 5.5 µm is presented. Single coal particles of a bituminous coal were combusted in a flat flame burner under oxy-fuel conditions (20.1 mol%). The emissivity was determined using a test-rig, which also measures particle temperature and diameter, both being necessary input parameters for single particle emissivity, in the visual spectral range. The infrared radiation was measured spectrally resolved with a fiber spectrometer (1.25-2.25 µm) and integrated with an InSb detector (2.4-5.5 µm). The emissivity decreases clearly with progressing burnout: E.g. at 1255 nm the emissivity decreases from 0.49 to 0.38. The effect is larger in the spectral range from 1.25 to 2.25 µm, but still visible in the longer wave length range.