Effect of the coupling action between volatiles, char and steam on isothermal combustion of coal char

The effects of the coupling action between volatiles, char and the steam on combustion characteristics of coal char were studied in a customized isothermal thermogravimetric experimental system. The results showed that volatiles released during devolatilization played a key role in the combustion. Heat produced by volatiles combustion accelerated the burning rate of pulverized coal, at the same time, volatiles combustion depleted the oxygen surrounding the char particles. With the decrease of the furnace temperature, the acceleration effect on burning rate due to volatiles combustion improved while its impact to oxygen consuming reduced. The influence of volatiles on burning rate acceleration and oxygen depletion appeared to be inversely affected by the coal rank. When oxygen concentration decreased from 21% to 5% in the reactor, the burning process of volatiles and coal char displayed a tendency of separation. In addition, the presence of steam, which increased the burning rate and reduced the burning time noticeably, had a significant impact on the combustion of coal char.