Three-Dimensional Numerical Model for Soil Vapour Extraction
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Abstract
Mass transfer limitations impact the effectiveness of soil vapour extraction (SVE) and cause tailing. In order to identify the governing mass transfer processes, a three-dimensional SVE numerical model was developed. The developed model was based on Comsol Multiphysics® a finite element method and incorporates multi-phase flow, multi-component transport and non-equilibrium transient mass transfer. Model calibration was done against experimental data from previous lab-scale reactor experiments and a previously remediated site. The developed model, 3D-SVE, nicely simulates laboratory findings and allows for changes in the important governing mass transfer relationships. It was seen that a single averaged mass transfer value is a poor representation of the entire SVE operation and that a transient mass transfer coefficient is required to understanding SVE tailing. The laboratory results did not transfer well to the field, showing the presence of scale-up factors that are related to the increased mass transfer resistant taking place. Further research is required to elaborate on this scale-up factor. However, both lab and field scale calibration showed that the most important mass transfer is between NAPL and vapour phase, with the mass transfer coefficient values for aqueous to solid phase, and NAPL to aqueous phase being identical in both scenarios.