The influence of Porous Media Heterogeneity on Smouldering Remediation

Jiahao Wanga, Gavin P. Grantb, Jason I. Gerharda

Dans les comptes rendus d’articles de la conférence: GeoNiagara 2021: 74th Canadian Geotechnical Conference; 14th joint with IAH-CNC

ABSTRACT: Self-sustaining Treatment for Active Remediation (STAR) is a thermal remediation technology that uses smouldering, a flameless form of combustion, for destroying nonaqueous phase liquids (NAPLs) in the subsurface soil. Heat is supplied to a relatively small ignition region, starting a self-sustained smouldering reaction that propagates outwards through the contaminated zone. Air injection into the treatment zone provides the oxidant (oxygen), supports the release of sufficient energy and the heat recycling central to the self-sustained process. However, the distribution and magnitude of air flux vectors can be complex in a heterogeneous environment as is common at contaminated sites. Thus understanding the factors that influence airflow in the subsurface is valuable to maximizing STAR's remedial performance. This research explores the influence of porous media heterogeneity on the airflow pattern and the subsequent impact on smouldering remediation, which applied the first laboratory investigation of smouldering remediation under varying degrees and patterns of permeability heterogeneity. Nine experiments examined smouldering remediation in contaminated layers in series, in parallel and in a complex pattern combining both. The results suggest that smouldering can successfully propagate through layers in series regardless of the layer permeability (at least down to 1x10-12 m2). However, extinction can occur in the finer layer when smouldering encountered layers in parallel with a permeability ratio equal or above 3:1. Numerical modelling of these cases with a published smouldering model revealed that this occurred due to insufficient airflow in the fine layers in some cases, or conductive heat transfer (thermal coupling) between parallel layers in other cases. However, for more complex heterogeneity patterns, where the coarse pathways are discontinuous, smouldering extinction may be eliminated, resulting in complete treatment. Overall, this research provides unique insights into understanding heterogeneous scenarios to ensure the successful application of smouldering remediation.

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