An experimental study on ignition of single coal particles at low oxygen concentrations

Abstract

An experimental study on the ignition of single coal particles at low oxygen concentrations ( $${X_{{{\rm{O}}_2}}} < 21\% $$ ) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different $${X_{{{\rm{O}}_2}}}$$ values and furnace temperatures Tw. Compared with literature experimental data obtained at a high $${X_{{{\rm{O}}_2}}}$$ value, the ignition delay time τi decreases more rapidly as $${X_{{{\rm{O}}_2}}}$$ increases at the low $${X_{{{\rm{O}}_2}}}$$ region. The responses of Ts and Tc to the variation of $${X_{{{\rm{O}}_2}}}$$ are different: Ts decreases while Tc remains nearly constant with increasing $${X_{{{\rm{O}}_2}}}$$ at a low $${X_{{{\rm{O}}_2}}}$$ value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low $${X_{{{\rm{O}}_2}}}$$ value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as $${X_{{{\rm{O}}_2}}}$$ decreases. At a low $${X_{{{\rm{O}}_2}}}$$ value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.