Effect of combustion heat on release and transformation of the sodium during Zhundong coal ash-forming process

As a typical Zhundong coal, Wucaiwan coal was chosen as the object of the investigation. The combustion ash with coal sample and the reheated ash with ashing sample at 400℃ were prepared in a muffle furnace. K-type thermocouple was used to measure the temperature, XRF and XRD were used to investigate the composition of ash, and the sequential chemical extraction was used to examine the modes of occurrence of Sodium. The results show that the combustion ash and the reheated ash have marked differences in composition and melting points, sodium content in the reheated ash is higher than that in the combustion ash and the melting temperature of the reheated ash is lower than that in the combustion ash. With the increase of temperature, the total content of sodium decreases obviously, the water-soluble and ammonia-soluble sodium decreases rapidly, while the HCl soluble sodium increases first and then decreases and the insoluble sodium increases. The sodium released is mainly soluble. Heating temperature and time have an influence on the releasing of sodium, and the combustion reaction leads to the temperature on particle surface higher than surrounding temperature by 200℃, which is the main cause of releasing more sodium.