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_{{\mathrm{O}}_2}<21%) was conducted using a tube furnace. The surface temperature (T_s) and the center temperature (T_c) 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_{{\mathrm{O}}_2} values and furnace temperatures T_w. Compared with literature experimental data obtained at a high X_{{\mathrm{O}}_2} value, the ignition delay time t_i decreases more rapidly as X_{{\mathrm{O}}_2} increases at the low X_{{\mathrm{O}}_2} region. The responses of T_s and T_c to the variation of X_{{\mathrm{O}}_2} are different: T_s decreases while T_c remains nearly constant with increasing X_{{\mathrm{O}}_2} at a low X_{{\mathrm{O}}_2} value. In addition, t_i is less sensitive to T_w while the ignition temperature T_i is more sensitive to T_w at a low X_{{\mathrm{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_{{\mathrm{O}}_2} decreases. At a low X_{{\mathrm{O}}_2} value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.

Key words： coal particles; low oxygen concentration; ignition; ignition temperature; ignition modes

Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant No. 11872231).

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