Correlating the sodium release with coal compositions during combustion of sodium-rich coals

Sodium release (SR) has caused a series of severe problems during combustion of the special sodium-rich coals. An enhanced understanding of SR is crucial for designing the appropriate control measures. Thus, with a special focus on the sodium-rich coals, the correlations between compositions and SR, including the underlying mechanisms, are investigated on an atmospheric lab-scale tube furnace at 1000 °C. Some properties of coal compositions, such as the occurrence modes of Na, the mass ratios of Na/Cl, Na/S, Na/Ash and Na/(Si + Al), were quantitatively correlated with SR, respectively. The results show that the inhibiting effect of Si-Al minerals played a dominant role on the SR compared with the promoting effect of Cl. A strongly positive correlation was observed between Na/(Si + Al) and SR. Besides, the high content of calcite in the ash could obviously promote the SR, whereas the formation of thenardite in the residue markedly inhibited it. The comparison between combustion and gasification has been conducted, and it indicates that the SR also has a strongly positive correlation with the Na/(Si + Al) during steam gasification. In addition, the promoting effect of calcite on the SR could be mitigated by SO3 due to the formation of anhydrite.