Mechanisms of inorganic element transfer during zhundong coal combustion in drop tube furnace

The recently discovered Zhundong coal field is one of the main energy bases in China for the huge prototyped coal reserve. However, the Zhundong coal causes seriously fouling and slagging problems during combustion for the high content of Na and Ca. In this study, the Zhundong coal combustion experiments were carried out in drop tube furnace and the ashes sampled at different temperature were analyzed by SEM–EDS (scanning electron microscope–energy dispersive spectrometer) to obtain the microstructure and composition of ashes. The results show that a lot of Na-based compounds and a part of CaO could be vaporized during the early stage of Zhundong coal combustion. With the fume temperature decreasing, the gaseous Na and Ca compounds react with SO to form NaSO and CaSO which are divided into three parts. A part condensates on the ash particle surface, and the remainder forms to aerosol. A fraction of aerosol united to form flocculent particles and adhered ash particles and the others released to air as fine particles.