Numerical investigation of multiphase contaminant removal from NAPL-impacted soils: A comparative study of thermal...

In-situ thermal desorption is widely applied to remediate vadose-zone soils impacted by non-aqueous phase liquids (NAPLs), yet the role of adsorbed-phase desorption kinetics in thermal processes has received little attention. Moreover, although several thermal technologies have been studied separately, there is still a lack of quantitative comparison of their remediation performance and energy efficiency within a unified modelling framework. Here, we extend a non-isothermal compositional multiphase-flow model by explicitly coupling a kinetic description of contaminant desorption from the adsorbed phase, and apply it to simulate the removal of n-dodecane (C₁₂) from unsaturated soil using three representative thermal approaches: saturated steam-enhanced extraction (Sat-SEE), superheated steam-enhanced extraction (SSEE), and thermal conductive heating (TCH). The model is used to compare multiphase removal efficiencies and specific energy consumption, and to perform a sensitivity analysis of the kinetic parameters. Simulation results show that, with increasing injection rate, SSEE achieves substantially higher removal of C₁₂ than TCH at comparable or lower specific energy consumption. Both the injection rate and the temperature of the injected steam enhance remediation performance by enlarging the superheated zone that controls adsorbed-phase desorption. The sensitivity analysis identifies activation energy as the dominant kinetic parameter, exerting a stronger control on desorption behavior and required heating temperature than the pre-exponential factor or reaction model. The extended model thus provides a mechanistic basis for designing thermal remediation strategies and selecting appropriate thermal technologies for NAPL-contaminated sites.