Experimental study on ignition delay and reaction characteristics of zhundong coal particles in o₂/co₂/h₂o atmosphere

Abundant Zhundong coal has the advantages of easy mining and high stability of combustion. However, its high alkali-metal content may cause problems, including furnace slagging and heating surface contamination, which affect the safety of boiler operation and limit the application of Zhundong coal. Oxy-fuel combustion is a promising technology that may fundamentally alleviate the fouling and slagging problems during the combustion of Zhundong coal, since the combustion temperature could be controlled by flue-gas recirculation. Moreover, lower particle temperature and alkali release could be achieved because of the endothermic reaction of carbon with carbon dioxide and water vapor. In this study, a one-dimensional entrained flow reactor was specifically designed with nonintrusive optical measurement technology to investigate the effects of the flue-gas temperature and composition on particle temperature and ignition delay of combustion in O2/CO2/H2O/N2 atmosphere. The experimental results showed that the ignition was advanced and the particle temperature increased as the flue gas temperature and oxygen concentration increased. Higher carbon dioxide concentrations would delay the ignition and cause a lower particle temperature. When the water vapor concentration increased within the range of 20%-30%, the ignition delay distance first increased and then decreased, while the particle temperature showed an opposite trend simultaneously. When water vapor concentration was 26%, the ignition delay distance reached the maximum value and the particle obtained the lowest surface temperature. Those results may be helpful for efficient combustion and safe application of high-alkali coal.