Electrical heating for the removal of recalcitrant organic compounds

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ABSTRACT

This paper presents a remediation technology that combines electrical heating of the soil with extraction to achieve removal of vapour pressure sensitive compounds, such as chlorinated solvents, volatile and semi-volatile organic compounds, and heavier hydrocarbons. This technology is commercially known as the Electro-Thermal Dynamic Stripping Process (ET-DSP). As well the results of a Shell operated field test (the CFB Pilot) are presented to demonstrate the feasibility and effectiveness of the technology in a commercial environment.

Electrical heating technology has been used in the past (Buettner and Daily, 1995, U.S. DOE, 1995, McGee et. al., 1994). In a typical application of the ET-DSP process, electrodes are strategically placed into the contaminated zone. The pattern of electrodes is designed so that conventional three-phase power can be used to heat the soil. Also, the distance between electrodes and their location is determined from the heat transfer mechanisms associated with vapour extraction, electrical heating and fluid movement in the contaminated zone. Without consideration of all the heat transfer mechanisms, a less effective heating process will result. To determine the ideal pattern of electrode and extraction wells, a multiphase, multi-component, three-dimensional thermal model is used to simulate the process.

Operational data were monitored and compared to the numerical simulation of the process. Excellent agreement between field temperature, electrical operating, and energy consumption data and the numerical simulation predictions was observed. Additionally numerical modeling was used to design the power delivery system, the power requirements from the utility, and the project capital requirements.

Several sites have been remediated using this technology. At all locations removal of contaminates was achieved, typically in less than four months of heating. This is a direct result of a substantial temperature increase in the contaminated soil and concurrent increase in the vapour pressure. The increase in vapour pressure of the contaminants makes it easier to extract them from the soil. Although the data from site to site vary, the typical cost for three phase electrical power is a minor component of the overall cleanup costs for the project. Greater cost reductions are further realized as a result of the significant decrease in time required to complete the remediation for a recalcitrant site.

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