The effect of strengthening thermal fragmentation by rotary kiln on sulfur distribution of fragmentation char with low-rank coal

[Display omitted] •Plastic layer hindered the effect of desulfurization by thermal fragmentation.•Destruction of conjoined structure reduced the sulfur content of the large-size char.•Thermo-mechanical action inhibited adhesion of the fine particles with high-sulfur.•Thermo-mechanical action promoted the fragmentation of sulfones into small-size char. Thermal fragmentation of low-rank coal was generally viewed as a negative effect. Actually, the thermal fragmentation had a positive effect on the pyrolysis desulfurization of low-rank coals, and it is expected to be a new way to realize the desulfurization of large-size char. A fixed bed pyrolysis device and rotary kiln pyrolysis device were used to investigate the effect of pure thermal action and thermo-mechanical action on the sulfur distribution in thermal fragmentation char of lignite and sub-bituminous coal at 300–900 °C. The intervention mechanism of thermo-mechanical strengthen thermal fragmentation on low-rank coal with different coalification degrees was obtained. For lignite, the non-sulfur components were more fragmented than the high-sulfur components due to thermo-mechanical action at the low-temperature stage. Fragmentation of high sulfur components dominated thermal fragmentation at the high-temperature stage. For sub-bituminous coal, conjoined structures and plastic layer hindered the fragmentation of sulfur-containing components by pure thermal action. The thermo-mechanical action under rotary kiln pyrolysis was helpful for the fragmentation of the conjoined structure and the separation of the char and plastic layer, thereby reducing the Fe-S minerals and organic sulfur content of the large-size char. The difference in organic sulfur caused by thermo-mechanical action is mainly due to the fragmentation of sulfone components.