Abstract
The purpose of our work is to examine the characteristics of coal ash emissivitiy to better understand the heat transfer mechanism through ash deposits on tubes in coal-fired boilers. This paper presents a method for determining coal ash emissivity in high temperature atmospheres and the influence of the ash surface temperature on its emissivity. Emissivity was determined by comparing theoretical radiation intensities with measured value obtained by a shield tube emissometer. An ash sample was heated in an electric furnace during the measurement and the radiation intensity from the sample was measured with a digital pyrometer. Emissivity characteristics of Powder River Basin (PRB) coal ash and bituminous coal ash were examined. The results are as follows: (1) Emissivity of deposited ash increases with an increase in deposit surface temperature. (2) The emissivity of a sample having fused surface exceeds 0.9. (3) PRB deposits have lower emissivities compared with bituminous deposits in the range of the surface temperature from 600℃ to 1100℃.
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