Na&Ca removal from Zhundong coal by a novel CO2-water leaching method and the ashing behavior of the leached coal

Zhundong coalfield in China is the largest intact coalfield in the world. However, serious fouling and slagging issues occurred when the Zhundong coal combustion, because of its high Na and Ca contents. In this study, a novel CO2-water leaching method was proposed to remove Na and Ca in Zhundong coal. The removal efficiencies of Na and Ca and the ash characteristics of the leached coal were investigated in detail. The results show that the CO2-water leaching can be easily achieved at room temperature under atmospheric pressure. The removal efficiencies of Na and Ca by the CO2-water leaching were significantly higher than those of water leaching. It is attributed to the effective removal of the organic Na and Ca in the coal. In addition, the CaCO3 in the coal was also effectively removed by CO2-water leaching. The volatility of Na from CO2-water leached coal is only 25% of that of raw coal during the combustion at 900 °C. The alkali-acid ratio (B/A) of the CO2-water leached coal ash was significantly lower than those of the raw coal and the water leached coal ashes. The fusion temperature of the CO2-water leached coal ash significantly increased, compared with those of the raw coal and the water leached coal ashes. The deformation temperature of the CO2-water leached coal ash was as high as 1202 °C, much higher than those of the raw coal and water leached coal ashes, which were 1098 °C and 1142 °C, respectively. Besides, the agglomeration and sintering phenomena of coal ash was also inhibited significantly by the CO2-water leaching. Therefore, the CO2-water leaching method was found to be an effective and promising method for AAEM removal from Zhundong coal, and can markedly mitigate the fouling and slagging during Zhundong coal combustion.