Oxy-fuel combustion of a single fuel particle in a fluidized bed: Char combustion characteristics, an experimental study

• Combustion of single char in a fluidized bed in O2/CO2 and O2/N2 was studied.
• Four ranks of coal from lignite to anthracite and one wood were accessed.
• Microstructure, combustion rate, burnout time, and maximum temperature reached of the char particle were analyzed.
• Microstructure of the generated char particle after the devolatilization is independent on the atmosphere.

The effect of an oxy-fuel atmosphere on char conversion in a fluidized bed (FB) was examined by comparing measurements of single fuel particles exposed to O2/N2 and O2/CO2 atmospheres. The experiments were carried out in a transparent and electrically heated FB at 1088 K and five O2 inlet concentrations (ranging from 0 up to 40%vol) using four ranks of coal (from anthracite to lignite) and one type of wood, all with 6 mm (spherical) diameter. The evolution of temperature with time of the various fuels at different gas atmospheres and the microstructure of the char resulting after devolatilization are presented, from which the effect of the oxy-fuel atmosphere (changing CO2 by N2 at different fixed O2 concentrations) on char combustion characteristics is determined and analyzed. Results show that the apparent average combustion rate of a fuel particle decreases (and consequently the burnout time increases) when changing O2/N2 by O2/CO2. This effect was more significant at high O2 concentrations and most notable for anthracite. Consistently, the time to reach the peak temperature was longer when shifting from O2/N2 to O2/CO2. However, the char specific surface area, pore volume, and average pore diameter of char were not significantly modified by replacing N2 with CO2.