Time-temperature histories of bituminous coal particles in a drop-tube reactor

A device often used to simulate pulverized coal combustion conditions is the drop-tube reactor. It can adequately simulate residence times, heating rates, temperatures and flow conditions. Nevertheless, derived Arrhenius pre-exponential factors for devolatilization studies can span several orders of magnitude (1), probable due to difficulties in repeating time-temperature histories for different coals (2). CFD modeling of a simple drop-tube reactor incorporating coal particles as a second phase permitted time-temperature histories to be obtained for narrow size cuts for two bituminous vitrinites. Despite a narrow particle size distribution and the rank of the vitrinites being the same, significant differences were obtained in the time-temperature histories, among the size cut and between the vitrinite samples. Furthermore, the common and simplifying assumption of spherical particles for coal was found to underestimate the characteristic heating time by 22%, in comparison to the more reasonable "house brick" particle shape obtained from microscopic observations with video capture and computational analysis.