Ignition characteristics and alkali metal release behaviors of single-particle coal in O2/CO2 or O2/N2 atmospheres using optical diagnostic technology

In this study, the ignition characteristics of and alkali metal release behaviors of single-particle coal were investigated using single-particle coal combustion system coupled with optical diagnostic technology. Furthermore, the effects of coal types (Yangchangwan bituminous coal (YCW), and Naomaohu lignite (NMH)) and oxygen concentration in different atmospheres (i.e., O2/CO2 and O2/N2) were analyzed. The results show that since the specific heat capacity of CO2 is higher than that of N2, the flame temperature in the O2/CO2 atmosphere is lower in the combustion process of coal particles, resulting in a longer ignition delay and combustion time for both coals than in the O2/N2 atmosphere. The maximum flame area of the YCW is twice as long as that of the NMH coal in the different atmospheres. The Na* and K* radiation intensity of coal particles in the O2/N2 atmosphere is stronger than in the O2/CO2 atmosphere, and due to the influence of the volatile matter content of NMH. However, the Na* radiation intensity in the O2/N2 atmosphere is more likely to show a bimodal distribution with increasing oxygen concentration, i.e. the boundary between the volatile reaction phase and the coke combustion phase is clearer.