The order with respect to oxygen and the activation energy for the burning of an anthracitic char in O 2 in a fluidised bed, as measured using a rapid analyser for CO and CO 2

Abstract

Measurements of the oxidation of a coal char in a fluidised bed have the advantages that the rates of heat and mass transfer to and from a reacting particle are large and characterised well. However, problems have arisen from a combination of the slow, but typical, response–time (∼4 s) of the analysers for CO and CO 2 and the slow mixing of gases when filling a fairly large fluidised bed. The resulting time constant for the sampling system was ∼8 s and comparable to the time for combustion at 900 °C or above. The purpose of this work was to measure the kinetics of oxidation of a char in a smaller fluidised bed (with a shorter mixing time) using an analyser for CO and CO 2 with a response time as low as 0.1 s. The result is that the oxidation of an anthracitic char is now found to be first order in O 2 between 700 and 900 °C; at 900 °C the order previously measured was almost zero. The activation energy is now measured here to be 145 ± 25 kJ/mol, in agreement with some early work.