Toward the Control of the Smoldering Front in the Reaction-Trailing Mode in Oil Shale Semicoke Porous Media

Results of an experimental investigation on the feasibility of propagating a smoldering front in reaction-trailing mode throughout an oil shale semicoke porous medium are reported. For oil recovery applications, this mode is particularly interesting to avoid low-temperature oxidation reactions, which appear simultaneously with organic matter devolatilization in the reaction-leading mode and are responsible for oxidation of part of the heavy oil. The particularity of this mode is that, contrary to the reaction-leading mode largely studied in the literature, the heat-transfer layer precedes the combustion layer. This leads to two separated high-temperature zones: (i) a devolatilization zone (free of oxygen), where the organic matter is thermally decomposed to incondensable gases, heavy oil, andfixed carbon, also called coke in the literature, without any oxidation, followed by (ii) an oxidation zone, where thefixed carbon left by devolatilization is oxidized. The transition from reaction-leading to reaction-trailing mode was obtained using low oxygen contents in the fed air. It is shown that two distinct layers, the heat-transfer layer and the combustion layer, propagate in a stable and repeatable way. The decrease of the oxygen fraction leads to a decrease of the smoldering temperature and to strongly limit the decarbonation of the mineral matrix. The CO2 emissions are limited. Regardless of the front temperature, all of the fed oxygen is consumed and all of thefixed carbon is oxidized at the passage of the smoldering front

Scaling the transport of firebrands by wind-blown plumes

International audienceThe possibility of using a reduced-scale model based on the Froude-scaling technique to study the transport of spherical, cylindrical and disk-shaped firebrands by a wind-blown plume was investigated theoretically. The cases of hot particles produced by arcing copper power lines and burning sparks produced by arcing aluminium power lines were also considered. In each case, scaling relationships were derived for mass, linear-momentum, angular momentum and energy transport equations of the firebrands, using well-established models. The analysis shows that, in the case of cylindrical firebrands, incompatible conditions on brand diameter are obtained to scale both the linear-momentum equation and the mass and energy equations. It also shows that all physical processes scale correctly for hot copper particles as well as spherical and disk-shaped burning embers with the exception of the conservation of angular momentum in the case of disks. Despite this drawback, numerical results, obtained using an integral model representing a wind-blown plume, show that the mass and spatial distributions for both types of firebrands can be satisfactorily reproduced down to a scale of 1:5. (C) 2010 Elsevier Ltd. All rights reserved

Simulation of ignition of unburnt gases in the extraction vent of a room fire

International audienc