Determination of ignition and smoldering propagation of coal based industrial raw materials caused by embedding local hot spot

Abstract

Embedded local hot spot (EHP) poses a huge threat to the energy production of combustible coal-based industrial raw materials (CCIM), but it is also a source of good utilization of smoldering energy for waste removal. The characteristics of ignition and smoldering propagation of CCIMs by EHPs are studied based on two–step parallel reaction. The effects of temperature, buried depth (lp) and size of EHPs on the ignition characteristics of CCIMs are investigated. The temperature, chemical species and heat release evolution of the smoldering process of CCIMs are explained. The results show that the computational model is reliable. As the temperature and size of the EHPs increases, the ignition delay time (IDT) decreases. The IDT corresponding to the lp = 0 mm is greater than that of lp = 20 mm. Besides, the IDT is proportional to the reciprocal of the heat energy carried by EHPs. The critical temperature of EHPs increases with the increase of lp except in the case of lp = 0 mm. As the radius of the EHPs increases, the critical temperature decreases. The movement of hot spots shows four characteristics, namely, surface movement, movement to the surface, up–down–upward movement and decay.