The order with respect to oxygen and the activation energy for the burning of an anthracitic char in O2 in a fluidised bed, as measured using a rapid analyser for CO and CO2

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 (similar to 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 vas similar to 8 s and comparable to the time for combustion at 900 degrees 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 degrees C; at 900 degrees 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. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.