Electro Thermal Dynamic Stripping Process

Electrical Resistance Heating (ERH) curve showing the temperature as a function of radial distance away from the electrode.

ET-DSP curve showing the temperature as a function of radial distance away from the electrode.

The difference between Electrical Resistance Heating (ERH) and ET-DSP is heat transfer due to convection. Water injected around the ET-DSP electrodes is heated and flows radially toward the vacuum extraction wells heating the formation in the process. The difference between ERH and ET-DSP is shown in the governing equations.

The governing equation for electrical resistance heating (ERH) is given by,

${\displaystyle {\bar {\rho \,\!c}}\left({\frac {\partial T}{\partial t}}\right)\ ={\bar {\lambda }}\left({\frac {\partial ^{2}T}{\partial t^{2}}}+{\frac {1}{r}}{\frac {\partial T}{\partial r}}\right)+{\frac {1}{\bar {\sigma }}}\left({\frac {I}{2{\pi }Lr}}\right)^{2}}$

where ${\displaystyle {\bar {\rho \,\!c}}}$ is the bulk heat capacity of the formation, T is the temperature, t is the time, ${\displaystyle {\bar {\lambda \,\!}}}$ is the thermal conductivity, ${\displaystyle {\bar {\sigma \,\!}}}$ is the electrical conductivity, I is the electric current and L is the electrode length.

The governing equation for Electro Thermal Dynamic Stripping Process (ET-DSP) is given by,

${\displaystyle {\bar {\rho \,\!c}}\left({\frac {\partial T}{\partial t}}\right)\ ={\bar {\lambda }}\left({\frac {\partial ^{2}T}{\partial t^{2}}}+{\frac {1}{r}}{\frac {\partial T}{\partial r}}\right)+{\frac {1}{\bar {\sigma }}}\left({\frac {I}{2{\pi }Lr}}\right)^{2}-\underbrace {\rho _{w}\,\!c_{w}{\frac {Q}{2{\pi }Lr}}{\frac {1}{r}}{\frac {\partial T}{\partial r}}} _{Convection}}$

where ${\displaystyle \rho _{w}}$ is the density of water, ${\displaystyle \!c_{w}}$ is the specific heat of water and Q is the water injection rate.

The effects of heat on vapor pressure.[1]

ET-DSP electrodes are placed into the contaminated zone and are designed so that conventional three-phase power can be used to heat the soil. The distance between electrodes and their location is determined from the heat transfer mechanisms associated with vapor extraction, electrical heating, and fluid movement in the contaminated zone.

To determine the ideal pattern of electrode and extraction wells, a multi-phase, multi-component, 3-D thermal model is used to simulate the process. Numerical modeling is also used to design the power delivery system (PDS), the power requirements from the utility and the project capital requirements.

Electrical heating increases the temperature of the soil and groundwater by conducting current through the resistive connate water that fills the porosity of the soil. The increase in temperature raises the vapor pressure of volatile and semi-volatile contaminants, increasing their ability to volatilize and be recovered through conventional techniques such as soil vapor extraction.

ET-DSP utilizes a system of Time-Distributed Control (TDC) and Inter-Phase Synchronization (IPS) to control the power to the electrodes. This process controls the amount and timing of power sent to individual electrodes. If electrodes are in electrically resistive zones resulting in cold spots, the power to the electrodes can be increased in these areas to uniformly heat the formation. TDC and IPS controls the electrical sine wave of three-phase power to the millisecond such that each phase can be individually manipulated.

3-D numerical simulation of an ET-DSP temperature distribution.[1]

Prior to the implementation of the ET-DSP, site information such as surface infrastructure, surrounding land uses, short term site usage during remediation, subsurface lithology, depth to groundwater, plume characterization, type of contaminant, distribution of the contaminant and required time to attain target temperatures is collected. Numerical modeling and analysis simulation software combined with bench-scale experiments are used to determine the optimal thermal remediation strategy for the site.

Numerical modeling is important to determine optimum electrode configuration in terms of pattern type, shape, and separation; power supply requirements; power synchronization; optimal target temperature; and estimated time to attain the targeted temperature.

The Electro Thermal Dynamic Stripping Process (ET-DSP) is currently being used in the Athabasca Oil Sands to thermally recover bitumen and heavy oil by E-T Energy Limited. This electrothermal process converts electromagnetic energy into thermal energy by inducing current through the formation using excitor electrodes. Considerable control can be effected over the path taken by the currents and over the temperature profiles that will develop in the deposit by varying the operating frequency and excitor spacing.[3] Electrothermal processes are virtually free of problems related to very low initial formation injectivity, poor heat transfer and the near impossibility of adequately controlling the movement of injected fluids and gases.[3]

• McMillan-Mcgee Corporation Website
• E-T Energy Limited Website