Investigation on the ignition, thermal acceleration and characteristic temperatures of coal char combustion

•A new thermal model and measuring method for the ignition temperature are proposed.•Ignition occurs in a region but not a point with ambient conditions changing.•Ignition region is measured from the minimum to maximum ignition temperature.•Tig,max of coal char in TG-DSC is in line with the ignition temperature of EFR. Through using a new thermal analysis model and a method of coal/char combustion, the minimum ignition temperature and minimum ignition heat of three different ranks of pulverized coal char were measured by simultaneous Thermogravimetry and Differential Scanning Calorimetry (TG-DSC) experiments. The results show that the ignition of coal char occurs in the range between the minimum ignition temperature and the inflection-point temperature. The thermal acceleration and its gradient GT increase with increasing heating rate and decrease with increasing coal char rank. The higher the GT of the coal char, the more easily the ignition occurs and more rapidly the burning and burnout occur. The data show that the GT of coal char of SLH lignite is 1.6 times more than that of coal char of ZCY bituminous and JWY anthracite in ignition zone, and 3.4 times in burning zone. The characteristic temperatures increase with increasing temperature of prepared char, heating rate and char rank. Moreover, the Tig,max calculated in DSC experiment is approximately in line with the ignition temperature obtained in the entrained flow reactor, which demonstrates the feasibility of the proposed theory.