Electro Thermal Dynamic Stripping Process
Electro Thermal Dynamic Stripping Process (ET-DSP) is a patented in situ thermal environmental remediation technology, created by McMillan-McGee Corporation, for cleaning contaminated sites.
ET-DSP uses readily available three phase electric power to heat the subsurface with electrodes.
Electric current to each electrode is controlled continuously by computer to uniformly heat the target contamination zone.
The governing equation for Electro Thermal Dynamic Stripping Process (ET-DSP) is given by,
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.
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.
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.
TDC and IPS controls the electrical sine wave of three-phase power to the millisecond such that each phase can be individually manipulated.
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 power delivery system (PDS) is a computer controlled three-phase current transformer.
The PDS can come in a range of KVA (kilovolt amp) ratings and are fully modular for plug and play applications.
ET-DSP can heat soil matrixes that range from tight clays to sands and rock.
Electrodes for ET-DSP can be made in diameters up to 12”, lengths up to 10 feet long and are rated for up to 180 °C (356 °F) at more than 50 kW.
Using three phase power synchronization means that electrode patterns are not geometrically limited.
Electrodes are fabricated from high temperature resistant materials and are connected to the PDS.
The majority of the electrode’s energy is concentrated at the ends due to the current density.
This process dynamically strips more slightly volatile organic compounds (SVOCs) and other non-volatile contaminants such as creosote.
The rest re-enters the electrode through upper slots and is then re-circulated back to the water holding tank.
The amount of water that is directed into the formation is dependent on the permeability of the subsurface soils.
Typical injection rates into the formation are usually on the order of 0.1 to 0.2 gpm (gallon per minute) per electrode.
Contaminant vapors can be discharged into the ambient air or combusted, dependent on local regulatory requirements.
Extraction wells are placed within the electrode array in order to maximize the recovery of the volatilizing hydrocarbons and are designed to control the groundwater to minimize the potential for offsite migration of the mobilized contaminant.
Depending on the contaminant of concern either steel or an approved thermoplastic can be used in the header system.
The treatment system typically consists of a sedimentation tank and an air stripper or granular activated carbon.
The clean effluent water is then discharged or removed by an approved method.
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.
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.
