Sulfur release and transformation during the pyrolysis of lignite with different particle sizes

•Experiments show that reducing the particle size of lignite promotes the release of sulfur-containing gas.•Reducing the particle size of lignite can promote the conversion of pyrite to pyrrhotite and troilite•At high temperatures stage, the formation of inorganic sulfides is enhanced in smaller particles.•Reducing the particle size effectively reduces the retention of sulfoxide sulfur and sulfone sulfur in char.