Mathematical Model for Multiphase Extraction Simulation

In this work, a model was built to simulate the multiphase extraction (MPE) applied to soil polluted by toluene. The model is composed of three differential partial equations simulating the multiphase flow of the three present phases using the capillarity equations and four equations to simulate the transport and the transfer between the three phases. The model was applied to a hypothetical pollution at field scale. A first step was applied to simulate the toluene propagation in the soil in saturated and unsaturated zones during a period of 2 months and its distribution in different phases. Results show a decrease of nonaqueous-phase liquid (NAPL) residual saturation under the effect of mass transfers between phases. It was observed that the propagation by gas-phase diffusion was greater than liquid-phase diffusion. The MPE application shows the important effect of the strainer location and the applied vacuum on the velocity fields. The proposed model shows the limitation of the MPE method in the capillary zone, which could not be remediated after 1 year of treatment. This observation confirms the necessity to ameliorate the process by lowering or deepening the groundwater or by using several extraction wells. The mass transfer coefficients were estimated from the literature. This work also highlighted the importance of a good identification of parameters.