Effect of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in oxy-fuel condition

Abstract

Coal blending is an effective method to reduce the slagging tendency. The mineral transformation within blended coal ashes has an important influence on the slagging behaviors, which have been well studied under conventional air-fuel condition. Oxy-fuel combustion is recognized as one of the most promising CO2 reduction technologies. However, the mineral transformation within blended coal ashes in oxy-fuel condition has yet to be fully understood. This work is aimed to comprehensively study the influence of CO2 atmosphere on Ca-containing mineral transformation behaviors during a Ca dominated coal co-firing with a Si/Al dominated coal in O2/CO2 condition by TG-DSC, XRD and HSC simulation. These results show that the atmosphere significantly affects on the transformation of Ca-containing mineral and the final existing form of Ca in the blended coal ashes. When the high content Ca coal is blended with the high content Al/Si coal in the O2/CO2 atmosphere, the CO2 promotes the transformation of Ca into CaCO3 and Ca under low temperature mainly exists in the form of CaCO3 (little CaSO4) in the blended coal ashes. CaCO3 under high temperature is decomposed to produce highly active CaO, and CaO reacts with Al/Si to form the low melting point minerals, which may aggravate the slagging tendency. The present study can provide useful information to reduce the slagging behavior of the blended coals in the O2/CO2 atmosphere.