Direct and two-step gasification behaviour of Victorian brown coals in an entrained flow reactor

This study assesses the gasification behaviour of three Victorian brown coals in CO₂ using a bench – scale entrained flow reactor in terms of gas quality and carbon conversion. Two gasification processes were investigated: a) gasification of coal in a single step, b)pyrolysis of coal followed by gasification of the char in two steps. The effect of temperature (1000–1400 °C)and input CO₂ (10–40 vol%) concentration on two gasification process was investigated. It was found that higher temperature and input CO₂ concentration increased CO concentration and carbon conversion. The gasification process (direct and two-step gasification) had little effect on the overall carbon conversion but had a significant effect on the gas composition of the product gases. During two-step gasification, coal pyrolysis contributed to around 65% carbon conversion, almost all H₂ and 22–30% CO. Char gasification contributed to around 35% carbon conversion and 70–78% CO. By contrast, direct gasification generated little H₂ and more CO in the product gases than two-step gasification. It was estimated that the CO was generated from coal pyrolysis (18.8–24.2%), Boudouard reaction (55.1–66.5%), and the reverse water-gas shift reaction (13.1–19.3%). Regardless of direct or two-step gasification, it was found that entrained flow gasification achieved very high carbon conversion (∼98%)for Victorian brown coals at 1200 °C with around 7 s residence time for the particle size of 90–106 µm.