An Experimental Study of Coal Dust Ignition in Wedge Shaped Hot Plate Configurations

Ignition behavior of bituminous coal dust deposited between two hot surfaces forming wedges of 60º, and 90º is experimentally studied. Three thermocouples placed along the symmetry plane of the wedge cross-section at various heights from the apex (lowermost, middle and top) are used to record the transient temperature data. Results show that the ignition always occurs around the region surrounding the top thermocouple in the case of 60º wedge and both the top and the middle regions in the case of 90º wedge. The trends are explained by investigating three parameters affecting the ignition behavior, namely, the heat transfer from the hot plate to the coal dust, the subsequent chemical heat release, and the heat transfer between different regions within the coal dust. Furthermore, an experimental setup, similar to the standard ASTM E 2021 test, is used to determine the minimum ignition temperatures of coal layers of various thicknesses and to assess the ignition scenario in the wedge configuration using an effective length scale. Measured quantities such as minimum hot plate temperature that causes ignition and the ignition time, as well as the transient heat release rate and heat conducted between various zones, calculated based on the temperature data are used to quantify the three parameters and their effects on ignition behavior. Nomenclature α Angle between two hot surfaces ρ Bulk density (kg/m 3) A Pre-exponential constant (1/s) A c Area of cross section (m 2) c Heat capacity of coal dust (J/kgK) E Activation energy (J/mol) k Bulk thermal conductivity (W/m-K) n dimensional θ-coordinate (m) Q Heat of reaction (J/kg) r radial coordinate (m) R u Universal gas constant (J/mol-K) t ig Time of ignition (minutes) T Instantaneous temperature (ºC or K) T p Hot plate temperature (ºC or K) θ angular coordinate (radians)