Temperature estimation using optical reflectance

As described earlier, the optical reflectance of vitrinite depends on its degree of aromatization and, hence, the loss of volatile matter. This natural process can be substituted by artificial heating without oxidant (pyrolysis) in a laboratory furnace. Because of evolving anisotropic reflectance character during such coking processes, the maximum reflectance of vitrinite is reported to be used for temperature tracing [3], but Bunt et al. [8] also demonstrated the applicability of the mean reflectance. 

Usually the thermal decay starts at temperatures around 300 °C where the first increase of reflectance of vitrinite occurs. Between 400 and 900 °C, a nearly linear increase up to i max 8.0% can be observed, whereas at higher temperatures, as soon as all volatile matter is released, the reflectance stabilizes at a constant final value even decreasing slightly. 

Technical gasification systems must fulfill two conditions for using optical reflectance for temperature estimation  

A coal bed inventory for investigation must be available (fluid-bed or moving-bed gasifiers, coking plants). 

The operating temperatures should be at least partly between 400 and 900 °C, where the linear relationship between reflectance and temperature occurs. 

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Bunt, J., Joubert, J., and Waanders, F. (2008) Coal char temperature profile estimation using optical reflectance for a commercial-scale Sasol-Lurgi FBDB gasifier. Fuel, 87, 2849-2855. 

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