Evaluation of Steam Flushing for Removal of A Mixture of Volatile and Non-Volatile Compounds from Layered Porous Media
Abstract
In this study, two-dimensional numerical simulations were performed to evaluate the potential to remove a mixture of volatile and non-volatile compounds, present as denser-than-water non-aqueous phase liquids (DNAPL), from porous media. A multiphase flow and transport model (a nonisothermal compositional simulator) was used to simulate an experiment of steam flushing for the remediation of a fully water saturated layered sandbox contaminated with a mixture of Dichlorodiphenyltrichloroethane (DDT) and monochlorobenzene (MCB). The model accounted for changes in DNAPL properties (vapor pressures, viscosities, densities) as a function of DNAPL composition and temperature. The sandbox contained two high-permeability silica sand layers separated by a layer of lower permeability silica sand acting as a capillary barrier. A single DNAPL pool perched above the continuous capillary barrier was subjected to steam flushing, heating the soil layers to a temperature exceeding the DDT melting point of 108.5°C. In the experiment and model results, a condensation bank of DNAPL, primarily composed of MCB, was displaced to the extraction well. As over 99% of MCB was preferentially removed from the system, the composition of the remaining NAPL mixture shifted to non-volatile DDT. The results showed that steam flushing may not be an effective technique to remove DDT by hydraulic displacement as over 90% of the DDT remained in the system after flushing 5.8 volumes of steam (measured as condensate produced). Based on the experimental observations and model predictions, partial desaturation of the capillary barrier occurred during steam flushing, reducing the effectiveness of this layer as a capillary barrier against the downward migration of DNAPL. Consequently, significant redistributions of MCB and DDT occurred during steam flushing including migration into and below the capillary barrier. Additional simulations were performed with different steam injection scenarios to address the problem of downward mobilization of low volatility compounds.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H11E..07S
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1831 Groundwater quality;
- HYDROLOGY;
- 1832 Groundwater transport;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY