A new technique for the measurement of the product CO/CO2 ratio at the surface of char particles burning in a fluidized bed

A new experimental technique is proposed to measure the product CO/CO2 ratio at the surface of spherical char particles during fluidized bed combustion. It is based on the measurement of the burning rate of a single char particle under low oxygen concentration conditions and on the use of an accurate prediction of the particle Sherwood number. This technique was applied to spherical char particles obtained from a bituminous coal which is characterized by a low attrition and fragmentation propensity. The product CO/CO2 ratio was measured at a bed temperature of 850 °C and at a fluidization velocity of 0.3 m/s in a lab-scale apparatus operated with a bed of 0.5–0.6 mm sand. The char particle size was varied between 2 and 7 mm and the inlet oxygen concentration between 0.1% and 2.0%. Results showed that under the experimental conditions investigated carbon was mostly oxidized to CO2 within the particle boundary layer, with a maximum fraction of carbon escaping as CO of 10–20% at the lowest oxygen concentrations and largest particle sizes.