Counter-current flame propagation in a cylindrical bed of activated carbon saturated with artificial volatile matter in an upward flow of O2/N2 mixture

Abstract

A counter-current flame propagation process, or traverse combustion, in a cylindrical bed packed with activated carbon (AC) saturated with artificial volatiles was studied experimentally to appreciate the effect of homogenous volatile oxidation in the combustion process of packed solid. The experiments were conducted with an upward flow of a 50/50 v/v O2/N2 mixture. Flame propagation velocity and total carbon consumption during traverse combustion period, from ignition to the time when the flame propagated to the bed bottom, were determined. Ethanol, isooctane and benzene, were used respectively as the artificial volatile. Results show that compared to the case of AC alone, the flame propagation velocity was reduced while the combustion duration extended in the presence of volatile. The visible gas phase flame due to homogeneous volatile combustion traversed in the opposite direction of the oxidizing gas stream, competing with heterogeneous carbon oxidation for available oxygen. The proportion of oxygen consumed by homogeneous oxidation was the highest for ethanol, up to 87–94%, while isooctane and benzene accounted for 30–65% and 27–63%, respectively. Despite the competing homogeneous volatile combustion, the total amount of carbon consumed in the heterogeneous carbon oxidation was even increased in the cases of isooctane and benzene due to the extended combustion durations and relatively higher proportions of O2 consumed by heterogeneous carbon oxidation than in the ethanol case.