Thermochemical and combustion behaviors of coals of different ranks and their blends for pulverized-coal combustion

In this research, a laboratory-scale slit burner, which accurately represents the conditions of a practical flame with a high heating rate and jet velocity, was used to study the combustion characteristics using thermal analysis. Results of thermogravimetric and differential thermal analyses (TGA and DTA) showed that low-rank coals influenced the ignition temperatures of blends whereas high-rank coals influenced their burnout temperatures. The first-order differential method was used to determine the kinetic parameters for coals of different ranks and their blends. Additionally, in pulverized-coal flames with CH∗ chemiluminescence band intensity, three reaction regions (Zone I: preheating, Zone II: volatile matter reaction, and Zone III: char reaction) were identified. The length of the reaction region and the mean flame temperature were found to be close to those for coal with a higher fuel ratio in Zone I. In Zone II, the fuel ratio influenced the length of the reaction region, but the mean flame temperature was closer to that for the low-rank coal and the maximum combustion reactivity shifted to a lower position. Moreover, the correlation between TGA and pulverized-coal flame was investigated. Based on the correlation, it was expected that prediction of the practical flame structure would be possible to some degree.

► A laboratory-scale slit burner was used to study combustion characteristics via thermal analytical results.
► The coal rank could affect the characteristic temperature such as the ignition and burnout temperature.
► The fuel ratio influenced the flame lengths and mean flame temperatures of the blended coals.
► The blending showed non-additive behaviors between the parent coals and their blends.
► There were some correlations between the characteristic parameters from TGA and the combustion region.