Comprehensive numerical modeling of ignition of coal dust layers in different configurations

Abstract

Ignition of coal dusts deposited over sufficiently hot surfaces represents a common industrial hazard. If these surfaces are above a minimum threshold temperature, then the heat transfer from them and the associated chemical heat release can cause spontaneous ignition. This ignition front can be an ignition site for nearby combustibles as well, which depends on the location of ignition and the corresponding surface temperature attained by the coal dust. A comprehensive numerical study of ignition process of coal dust layers in different configurations, by solving the coupled Navier–Stokes and energy equations, provides a clear insight of the thermal field in the coal layer as well as the flow field over the coal surface. Such study will also provide quantitative information about the convective heat transfer coefficient, which varies for different cases. In this study, ignition phenomena of coal dusts deposited over a flat plate, wedges of different angles and a 3D corner, have been analyzed using a comprehensive numerical model. The governing equations are solved using Ansys FLUENT and user defined functions. The model has been validated using experimental results and is used to study the effect of wedge angles and the direction of gravity vector on the ignition process.