Effects of Water-Soluble Sodium Compounds on the Microstructure and Combustion Performance of Shengli Lignite.

Different water-soluble sodium compounds (NaCl, NaCO, and NaOH) were used to treat Shengli lignite, and the resulting effects on the microstructure and combustion performance of the coal were investigated. The results showed that NaCO and NaOH had a significant impact on combustion performance of lignite, while NaCl did not. The NaCO-treated lignite showed two distinct weight-loss temperature regions, and after NaOH treatment, the main combustion peak of the sample moved to the high temperature. This indicates that both NaCO and NaOH can inhibit the combustion of lignite, with the latter showing a greater effect. The FT-IR/XPS results revealed that Na interacted with the oxygen-containing functional groups in lignite to form a "-COONa" structure during the NaCO and NaOH treatments. It is deduced that the inhibitory effect on combustion of lignite may be attributed to the stability of the "-COONa" structure, and the relative amount is directly correlated with the inhibitory effect. The XRD/Raman analysis indicated that the stability of the aromatic structure containing "-COOH" increased with the number of "-COONa" structures formed. Additionally, experiments with carboxyl-containing compounds further demonstrated that the number of oxygen-containing functional groups combined with Na was the main reason for the differences in the combustion performance of treated lignite.