Effect of H2O on the combustion characteristics of pulverized coal in O2/CO2 atmosphere

•Three types of Chinese coals were investigated in O2/CO2/H2O atmosphere.•Effect of H2O and CO2 on coal combustion characteristics was distinguished.•H2O will lead to a larger ignition delay, faster burnout in oxy-fuel atmosphere.•H2O will lead to a higher comprehensive reactivity in oxy-fuel atmosphere.•Coal reactivity in O2/CO2/H2O atmosphere is related to the heating rate. The H2O concentration in real oxy-fuel combustion atmospheres is significantly higher than that in conventional air combustion, which strongly affects the combustion characteristics of pulverized coal. This study studies the effect of H2O on pulverized coal combustion behaviour in O2/CO2 atmosphere. The ignition temperature, burnout temperature and comprehensive reactivity of three types of Chinese coal at different H2O and O2 concentrations in O2/CO2/H2O atmosphere were investigated. The effect of particle size and heating rate on the pulverized coal combustion was also studied under high-H2O-concentration oxy-fuel atmosphere. The results showed that the presence of H2O strongly affects the combustion characteristics of coal and coal char in O2/CO2 atmosphere, leading to a greater ignition delay, faster burnout and higher comprehensive reactivity. These changes are more obvious for brown coal. Under O2/CO2/H2O atmosphere, H2O can improve the diffusivity and heat capacity of the combustion atmosphere and therefore has a positive effect on pulverized coal combustion. In addition, based on a comparison of the combustion reactivity between O2/CO2 atmosphere with and without H2O, the mechanism of coal combustion reactivity in H2O-containing atmosphere is significantly related to the heating rate.