Modelling mass transfer during venting/soil vapour extraction: Non-aqueous phase liquid/gas mass transfer coefficient...

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Geotechnical Engineering

Background:

• Soil vapor extraction (SVE) is a key remediation technology for contaminated sites.
• Accurate simulation of SVE requires precise understanding of mass transfer processes.
• Existing models often neglect crucial factors like hydrodynamic dispersion.

Purpose of the Study:

• To investigate the influence of the mass transfer coefficient on SVE process simulation.
• To evaluate existing equations for estimating the non-aqueous phase liquid (NAPL)/gas initial mass transfer coefficient.
• To develop and validate a new model for SVE simulation.

Main Methods:

• A numerical model with five partial differential equations was developed.
• Five established equations for the NAPL/gas mass transfer coefficient were tested.
• Experiments were conducted in a sand column with varying saturation and flow rates.
• Model simulations were compared against experimental data.

Main Results:

• Hydrodynamic dispersion significantly affects mass transfer coefficient estimation, particularly at low velocities.
• Only the convection-dispersion equation and the proposed model accurately simulated experimental results.
• The developed model provided the best fit for experimental data and the tailing portion of the gas concentration curve.

Conclusions:

• The mass transfer coefficient is a critical parameter in SVE simulations.
• Hydrodynamic dispersion must be considered for accurate modeling of SVE.
• The newly developed model offers improved accuracy for simulating SVE processes and predicting contaminant removal.