Ignition behaviors of pulverized coal particles in O2/N2 and O2/H2O mixtures in a drop tube furnace using flame monitoring techniques

Oxy-steam combustion technology is regarded to be the next generation of oxy-fuel combustion technology. Because the physical and chemical properties of steam are very different from that of CO2 or N-2, especially its reactivity, the ignition characteristics of coal in oxy-steam combustion are expected to be different from those in conventional combustion or O-2/CO2 recycled combustion. This paper presents experimental investigations of the ignition behaviors of coal in O-2/N2 and O-2/H2O atmospheres using different oxygen fractions (21%, 30%, 35%, 40% and 50%). Ignition experiments were performed in a drop tube furnace. The ignition behaviors were recorded using a high-speed camera and a two-color pyrometer. According to the images of the ignition, the pulverized coals ignite homogeneously in all cases. The ignition of pulverized coal in the O-2/H2O atmospheres occurs sooner than in the O-2/N2 atmospheres at identical oxygen fractions. A high concentration of steam may enhance the steam gasification reaction (C + H2O -> CO + H-2) and the steam shift reaction (CO + H2O -> CO2+ H-2) in O-2/H2O atmospheres. These two reactions can form a large amount of H-2 and CO in O-2/H2O atmospheres in the gaseous mixture around the coal particle. This result is beneficial to reducing the ignition delay times of volatiles mixtures in O-2/H2O atmospheres. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.