Measurements of surface temperature distributions on coal dust particles

Abstract

The rate of thermochemical conversion of solid fuel depends strongly on temperature. However, temperature can vary significantly across a single particle's surface and can locally change reactivity for combustion. To account for this phenomenon in numerical models, we carried out an experimental investigation of the temperature profiles for particles obtained from two chars prepared from hard coal and lignite. We used a custom-built, two-color pyrometer to measure surface temperature distributions for particles with an approximate diameter of 100 μm. We used CCD cameras as detectors what allowed for measure temperature with high resolution. The applied research method allowed for the analysis of thousands of individual particles in different conditions. We carried out experiments under O2/N2 and O2/CO2 atmospheres with the oxidizer concentration between 10 and 30% (vol%). We observed highly non-uniform temperature distributions on the surface of the reacting particles with differences greater than 100 K. The standard deviation of the surface temperatures increased with the mean temperature of the particles. The observed variations could be due to inherent particle heterogeneity for ash content, porosity, and shape. Non-uniform temperature profiles and reactivities may alter the Stefan flow at the outer surface of the particles, affecting the mass and heat transfer balance and changing the trajectory of the particles as they move through the combustion chamber. Therefore, the correction factors determined in this study may be applied to existing numerical models of solid fuel combustion.