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

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. ABSTRACT: 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, and fixed carbon, also called coke in the literature, without any oxidation, followed by (ii) an oxidation zone, where the fixed 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 CO 2 emissions are limited. Regardless of the front temperature, all of the fed oxygen is consumed and all of the fixed carbon is oxidized at the passage of the smoldering front.

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“…Smouldering combustion has been researched and/or applied in a variety of contexts including fire safety ( Bar-Ilan et al, 2002 ; Leppänen and Malaska, 2019 ; Rein et al, 2008 ; Santoso et al, 2019 ; Steen-Hansen et al, 2018 ; Torero and Fernandez-Pello, 1996 ; Yang and Chen, 2018 ), oil recovery/extraction ( Akkutlu and Yortsos, 2003 ; Castanier and Brigham, 2003 ; Garon et al, 1980 ; Martins et al., 2010 ; Sennoune et al, 2012 ; Xia et al., 2003 ) and sanitation ( Fabris et al, 2017 ; Saberi et al, 2020 ; Yermán et al, 2015 ). In addition, applied smouldering systems have also emerged as a viable thermal strategy for in situ and ex situ treatment of hydrocarbon-contaminated soils ( Ding et al, 2019 ; Gerhard et al, 2020 ; Grant et al, 2016 ; Scholes et al, 2015 ; Vidonish et al, 2016 ) as well as for disposal of waste organic liquids and sludges (e.g.…”

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