The measurement and interpretation of radiation from fly ash particles in large pulverized coal flames

Abstract

Narrow wave-band measurements have been used to determine the absorption coefficient of combustion chamber gases in large utility boilers with an accuracy of about ±25%. Effective absorption efficiencies and refractive indices for, the fly ash have been deduced where dust burden details could be measured. Modifications to instrument design would improve the accuracy. The absorption characteristics were shown to be influenced by the chemical composition of the ash. For a brown and a sub-bituminous coal of high alkali ash the measurements indicated a very high specific surface in the furnace, incompatible with sizing of collected fly ash samples, and a very high wavelength dependence of absorption. Small molten particles in the furnace gases could account for the high apparent surface area and the wavelength dependence. Results for two bituminous coals with high ash fusion temperatures indicate that an absorption coefficient K ¯ a of 0.4 to 0.5 would be adequate for eingineering purposes. However this value appears to be strongly influenced by chemical composition of ash; the cloud surface area may be more dependent on inherent ash and combustion characteristics than on the total ash or the coal grind.