Relationship between pyrolytic sulfur migration behavior and structural composition of high-sulfur fat coal

•Lengquan high-sulfur fat coal was separated into LQE and LQR via ultrasonic extraction.•LQE acts as hydrogen/oxygen radical donor and mass transfer promoter for sulfur migration.•LQR with loose structure serves as assistor for release of gaseous sulfurs.•Both LQE and LQR can enhance the sulfur migration in LQ-LQE/LQR co-pyrolysis. The migration behavior of organic/inorganic sulfurs is vital for producing high-quality metallurgical coke via pyrolysis. Herein, Lengquan (LQ) fat coal was separated into extract (LQE) and residue (LQR) via ultrasonic extraction, and migration behavior of extracted and residual sulfur as well as effects of LQE and LQR on sulfur removal from coke were further explored in pyrolysis process. The results indicate that LQE has higher volatiles, hydrogen and oxygen contents, while more ash and organic aromatic matrix were remained in LQR. The predominance of difficultly eliminated organic sulfurs in LQE and higher content of easily pyrolyzable inorganic sulfurs in LQR result in weaker and stronger desulfurization effect in pyrolysis, respectively. Sulfides, pyrites, and sulfates are relatively easy to be removed from coke, while sulfones, thiophenes, and sulfoxides are more thermally stable. In co-pyrolysis of LQ with LQE/LQR, the migration of various sulfurs, particularly thiophenes, from coke was significantly enhanced, and the maximum sulfur removal ratio of ca. 56% was achieved in LQ and LQE co-pyrolytic coke. LQE acts as hydrogen/oxygen radical donor and mass transfer promoter, while LQR serves as assistor for gaseous sulfur release, resulting in synergistic desulfurization in LQ with LQE/LQR co-pyrolysis.