Attenuation of Thermal Radiation by Pulverized Coal and Char

The absorption and scattering of thermal radiation within a dilute cloud of pulverized coal and char is investigated. Results are presented of monochromatic absorptivity measurements on particles 50–150 μm in diameter under conditions representative of the early pyrolysis zone of a combustion chamber. No dependence of absorptivity on coal composition could be discerned for the three lignite and bituminous coals selected. A slight increase in monochromatic absorptivity with temperature and extent of char was observed. For the spectral region investigated, 1.2–5.3 μm, an empirical equation of the form α_λ = 0.78 + 0.18/λ^1/2 was found to represent the data for all coals and chars within 5 percent. A single total hemispherical absorptivity of 0.89 is recommended for heat-transfer calculations in pulverized coal and char clouds if the particles can be assumed to act as Mie scatters, and if the volume fraction of ash and soot particles is small.