Abstract
This study proposes a simplified methodology to determine coal ash emissivity for the thermal design of coal-fired boilers. For this purpose, the Konopelko equation expressing spectral emissivities in relation to the wavelength and iron content in ash was modified. Spectral emissivity of coal ash is known to have a positive wavelength dependence; it is low at short wavelengths and increases with a rise in wavelengths which then remains constant (εmax) over a certain wavelength (λmax). In the modified equation, input parameters are εmax, λmax and spectral emissivity in the shorter wavelength:1.6μm(ε1.6(T)). Based on spectral emissivity data from early studies, we determined εmax, λmax as 0.85 and 8μm, respectively. To verify our modification, we compared total emissivities obtained by calculated spectral emissivities with those obtained by measured spectral emissivity for several literature. The modified equation predicts 90% of data records with an error of 15%. Additionally, to obtain ε1.6(T) without measurements, we investigated dependences of iron content in ash and temperature on ε1.6(T) using a shield tube emissometer. With reflecting these results, our equation requires only iron content in ash to obtain spectral emissivity of coal ashes. This simplified equation determines total emissivities obtained in different studies with an error of almost 20%.
Published Version
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