Transformation characteristics of sodium during high-sodium coal combustion process

The high sodium content of high-sodium coal results in severe ash-related problems during its combustion. In the paper, the occurrence modes of the sodium contained in Zhundong coal (ZD) and Hami coal (HM) were determined by sequential extraction with ultrapure water, 0.1 mol/L CH3COONH4 solution and 0.1 mol/L HCl solution. The sodium content of the sample was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and the minerals contained in the ashes were determined by X-ray diffraction (XRD) to investigate the sodium transformation characteristics during the high-sodium coal combustion process. The results indicate that the main occurrence modes of the sodium contained in ZD and HM were water-soluble species and NH4Ac-soluble sodium. During the combustion process, due to the volatilization of the water-soluble species and NH4Ac-soluble sodium, most of the sodium released from the coal before 815 degrees C. However, not all the water-soluble species and NH4Ac-soluble sodium released during 815 degrees C combustion. The sodium content of the residues from the high-sodium coals decreased with the combustion temperature increasing. During ZD combustion process, the soluble sodium contained in the coal reacted with other minerals contained in the coal to form the insoluble sodium. At the same time, the insoluble sodium contained in the coal transformed into the volatilize sodium. And the HCl-soluble sodium promoted the insoluble sodium transformed into the volatilize sodium.