Fluidized bed combustion characteristics of high-ash coal char under O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si127.svg" display="inline" id="d1e1408"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:m

The combustion characteristics of a batch of in-situ prepared high-ash coal char have been investigated under different fluidized bed operating conditions (i.e. O2 concentration, balance gas, bed temperature, particle size) in an optically accessible fluidized bed. A fast Universal Exhaust Gas Oxygen (UEGO) sensor measured the oxygen partial pressure at the exhaust to determine the reaction rate and burnout time of char particles, which demonstrates a novel application of this type of sensor in high H2O (wet) environments. A pre-calibrated two-colour pyrometry technique was employed to measure the temperature of char particles. The effect of the oxyfuel atmosphere on the burnout time of char particles was found to be prominent at higher bed temperatures, lower O2 concentrations, and larger particle sizes. The sensitivity of combustion behaviour to variations in the combustion environment was higher for larger particle size. Results show that the burnout time was the lowest in O2/H2O for both 1.2 mm and 3 mm particle sizes. This was attributed to the higher diffusivity of O2 in H2O and the H2O gasification reaction. The addition of H2O to O2/CO2 environment enhanced the diffusivity of O2, making it comparable to that in N2. In 10% O2/45% CO2/45% H2O environment, competitive interactions among O2, CO2 and H2O were more pronounced for smaller particles. The reactivity of char in 10% O2/90% H2O at higher bed temperatures became comparable to that in 20% O2/80% N2 environment making oxy steam combustion a potential advancement to oxyfuel combustion.