The influence of included minerals on the intrinsic reactivity of chars prepared at 900 °C in a drop tube furnace and a muffle furnace

Two fractions, representing organic-rich particles and organic particles with included minerals, were separated from each of four Chinese coals of different rank. They were then devolatilized at 900 °C in a drop tube furnace (DTF) and a muffle furnace, respectively. The chars were subjected to thermogravimetric analysis, SEM observation and a nitrogen adsorption study. It was found that when three conditions were all met, high mineral content, high volatile content and high heating rate, the included minerals show inhibition on combustion. Otherwise, the included minerals show promotion. Mechanism analysis shows that this is the result of an interaction between the liquid phase and mineral matter during devolatilization. In cases when there is no, or little, liquid phase the included minerals act as pore producer in the coal matrix. Otherwise, the included minerals dilute and absorb the liquid phase, leading to the formation of a char structure with fewer voids and more ordered structure, thus, lower reactivity.