Investigation on thermal radiation spectra of pulverized coal ash deposits in boiler furnaces

We deal with thermal radiation characteristics of coal ash layers. Normal emittance spectra in the 2.5 - 25 mum wavelength region and total normal emittance are measured on four kinds of ash layers of a mm order thickness and at 600 - 1100 K. It is found that the ash powder layers are opaque for the infrared radiation. The emittance increases with an increase of wavelength of radiation and temperature of the ashes. The emittance spectrum does not depend sensitively on chemical composition of the ashes. The total emittance decreases with an increase of temperature. For the safety design of thermal engineering systems including ash layers whose chemical/ physical state are not defined well, it is recommended to use the emittance spectra evaluated by a simple curve fit.