Evaluation of Combustion Characteristics of Chinese High-Ash Coals

The combustion characteristics of four Chinese high-ash coals were evaluated by thermogravimetric and surface analysis. Changes in surface area and porosity during combustion were investigated with original (as-received) coals, coal samples before ignition, and chars after burnout. To understand the roles of various ash components, comparative experiments were carried out with as-received, de-ashed, and impregnated coals. SiO2, Al2O3, CaCO3, MgO, Na2CO3, TiO2, K2CO3, Fe2O3, FeS2, FeSO4(NH4)SO4·6H2O, and NH4Fe(SO4)2·12H2O at different concentrations were used as chemical additives impregnated into the de-ashed coals to investigate their influence on coal combustion. Most of these minerals inhibited coal ignitability; only K and Ca were found to promote coal ignition. Fe, Al, Na, and Ca were found to hinder both ignition and burnout of coal. Other ash components demonstrated variable effects on coal ignition and burnout with changing concentrations and species. A full understanding of the different effects of mineral matter is essential to achieve improved performance with high-ash coal applications.