The kinetics of combustion of a size-graded fractions of petroleum coke (VM 0.9% db) of pulverised fuel size is determined by measuring the carbon burning rate in a CSIRO laminar flow reactor and using a critical ignition technique where a pulse of coke falls into a drop-tube furnace. At the temperatures where a visible flash is observed in the ignition technique little combustion is found to occur and the coke reactivities estimated assuming heterogeneous ignition exceed those from the burning rate by factors from 102 to 103 depending on assumptions made regarding the products of combustion and the definition of the critical ignition temperature. Ignition experiments with coke recycled through the furnace and coke doped with volatile materials indicate the temperature where flashing is detected decreases as volatiles are added and increases as volatiles are removed. The common assumption of heterogeneous ignition in such experiments may not be valid even for fuels of such low volatility.
