Effects of Water Content and Particle Size on Yield and Reactivity of Lignite Chars Derived from Pyrolysis and Gasification

Water inside coal particles could potentially enhance the interior char⁻steam reactions during pyrolysis and gasification. This study aims to examine the effects of water contents on the char conversion during the pyrolysis and gasification of Shengli lignite. The ex-situ reactivities of chars were further analyzed by a thermo gravimetric analyzer (TGA). Under the pyrolysis condition, the increase in water contents has monotonically decreased the char yields only when the coal particles were small (<75 µm). In contrast, the water in only large coal particles (0.9⁻2.0 mm) has clearly favored the increase in char conversion during the gasification condition where 50% steam in argon was used as external reaction atmosphere. The waved reactivity curves for the subsequent char⁻air reactions were resulted from the nature of heterogeneity of char structure. Compared to the large particles, the less interior char⁻steam reactions for the small particles have created more differential char structure which showed two different stages when reacting with air at the low temperature in TGA.