Release characteristic of different classes of sodium during combustion of Zhun-Dong coal investigated by laser-induced breakdown spectroscopy

Serious fouling and slagging problems are associated with the combustion of Chinese Zhun-Dong coal due to its high content of sodium (Na). Understanding the release characteristic of Na during the combustion is essential to viable utilization of this coal. In this work, coal samples were treated with a sequence of solvents: water (H2O), ammonium acetate (NH4Ac), hydrochloric acid (HCl), and the release characteristics of various classes of Na during coal combustion were investigated using the technique of laser-induced breakdown spectroscopy. The relative contribution of various Na classes to the Na release during each combustion stage was found to be similar, in the order of H2O-soluble Na > NH4Ac-soluble Na > HCl-soluble Na > insoluble Na. Sodium released during the devolatilization stage can be attributed to each of the sodium classes. After the devolatilization stage, H2O-soluble Na and NH4Ac-soluble Na dominated the Na release during both char and ash stages. Over 64 % of the total Na released during combustion comes from the H2O-soluble Na, which suggests that the Na release during the combustion of Zhun-Dong coal can be reduced effectively after treatment by H2O washing.