Smouldering Combustion for Soil Remediation: Two-dimensional Experiments and Modelling

Smouldering combustion is an innovative approach that has significant potential for the remediation of soils contaminated with Non-Aqueous Phase liquids (NAPLs). Sustaining Treatment for Active Remediation (STAR) is a novel technology which is based upon the concept of liquid smouldering, in which NAPLs embedded in a porous medium are progressively destroyed via an exothermic oxidation reaction which propagates in a self-sustaining manner through the contaminated material. The In Situ Smouldering Model (ISSM), developed to simulate the propagation of STAR as a function of NAPL content and local air velocity, was calibrated for a suite of one-dimensional experiments (MacPhee et al., 2010). However, STAR application at field sites involves propagation of a smouldering front in multiple directions simultaneously. This study presents the further development and validation of the model against experiments for two-dimensional (2D) smouldering propagation. 2D STAR experiments were conducted to explore the simultaneous vertical (upwards), lateral (horizontal) and opposed (downwards) front propagation rates and final extent of remediation as a function of air injection rate in coal tar-contaminated sand. The model was then calibrated to the base case experiment and predictive simulations demonstrated strong agreement with the remaining experiments. This work provides some of the first evidence of multidimensional smouldering under forced, complex air flow fields and provides confidence in a tool that will be useful for designing STAR soil remediation schemes at the field scale.