The ignition characteristics and combustion processes of the single coal slime particle under different hot-coflow conditions in N2/O2 atmosphere

The ignition characteristics and combustion processes of single coal slime particle in a vertical heating tube furnace in N2/O2 oxidant atmosphere were investigated under different hot-coflow conditions, including variations in coflow temperature (Tc = 923, 1073, and 1173 K), gas flow rate (V = 0–30 L/min), and oxygen concentration (O2% = 5%–100%). All investigated hot-coflow conditions exhibited three ignition behaviors, homogeneous ignition of volatiles, heterogeneous ignition of char, and heterogeneous ignition of coal. Additionally, three corresponding ignition regimes were observed in the oxygen concentration-coflow temperature plane. Critical conditions for the transitions of the three ignition mechanisms varied as flow was increased from 0 to 30 L/min. Various ignition mechanisms resulted in various combustion processes. Under medium-to-low oxygen concentration and low coflow temperature, the heterogeneous ignition of char resulted in flameless combustion. The ignition temperature and ignition delay decreased as coflow temperature and oxygen concentration were increased. The trends became more obvious when test conditions progressed in medium-to-low oxygen concentrations. As the flow rate increased, ignition temperature and delay became increasingly sensitive to oxygen concentration. Experimental results are then discussed in conjunction with the various observed trends influencing mechanisms of different hot-coflow conditions.