Effect of H_2O on the combustion characteristics of pulverized coal in O_2/CO_2 atmosphere

摘要

The H_2O 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 H_2O on pulverized coal combustion behaviour in O_2/CO_2 atmosphere. The ignition temperature, burnout temperature and comprehensive reactivity of three types of Chinese coal at different H_2O and O_2 concentrations in O_2/CO_2/H_2O atmosphere were investigated. The effect of particle size and heating rate on the pulverized coal combustion was also studied under high-H_2O-concentration oxy-fuel atmosphere. The results showed that the presence of H_2O strongly affects the combustion characteristics of coal and coal char in O_2/CO_2 atmosphere, leading to a greater ignition delay, faster burnout and higher comprehensive reactivity. These changes are more obvious for brown coal. Under O_2/CO_2/H_2O atmosphere, H_2O 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 O_2/CO_2 atmosphere with and without H_2O, the mechanism of coal combustion reactivity in H_2O-containing atmosphere is significantly related to the heating rate.