Electrical Resistance Heating of Clay Layers in Water‐Saturated Sand

Abstract

Electrical resistance heating (ERH) experiments were performed in a two‐dimensional water‐saturated porous medium comprising an electrically conductive, low‐permeability clay lens embedded within a less electrically conductive, higher permeability silica sand. These were compared to experiments performed in homogeneous silica sand. All experiments were performed in the absence of a non‐aqueous phase liquid (NAPL) or dissolved volatile organic compound (VOC). Temperature monitoring showed preferential heating in the clay lens and higher overall heating rates throughout the test cell compared to the homogeneous case. Gas production was localized around the sand–clay interface due to high temperature and low capillary displacement pressure. Above the clay lens, unexpected temperature plateaus were observed, similar to those observed in previous experiments during NAPL–water co‐boiling. A conceptual model based on the consumption of thermal energy as latent heat of vaporization in the highly localized heating and gas production region adjacent to the clay lens is proposed to explain the temperature plateaus. Supporting data is drawn from images of the gas phase and electric current measurements. These results show that the use of co‐boiling plateaus as an indicator of NAPL–water co‐boiling could be misleading during applications of ERH at sites containing electrically conductive, low‐permeability clay lenses embedded within less electrically conductive, higher‐permeability sands.

The transformation and migration of contaminants during the remediation process of heterogeneous strata by the in-situ thermal conductive heating (TCH) technology: A literature review

“…The heat transfer effects of ERH technology on soils differs significantly, due to the fact that electrical conductivity of different soil types vary by 0-200 times. In general, clay has higher electrical conductivity than sand and heats up faster (Martin et al 2016). SEE technology is inappropriate for the treatment of low permeability media or heterogeneous sites since the soil permeability varies by 10 2 -10 4 times (Suthersan et al 2016).…”

“…on the surface of the soil particles, and the gas nucleates here first due to the geometry of the gas cavities, local wetting characteristics, capillary pressure and priority contact angles. Experimental results have shown that when the sites are heterogeneous, the generation of bubble begins with nucleation in the gas cavities on the surface of soil particles at the high-low permeability interface and then extends outward (Martin et al 2017, Martin et al 2016. Contaminants are preferentially removed in areas with high permeability, whereas the areas with low permeability may maintain high pollutant concentrations (Martin et al 2017, Kevin et al 2021.…”

“…When treating TCE contaminated soil with ERH, Martin et al (2016) found that under the fine-grained capillary barrier, high capillary entry pressure prevents upward migration of gases and forms gas accumulation. Jonah et al (2016) found that during DNAPLs-water co-boiling process, gases generated at the DNAPLs pool interface accumulate in the coarse sand layer, due to higher entry pressure in the upper part of the coarse sand layer, and the lower part of the soils with low-permeability.…”

“…Limited studies focusing on lowpermeability materials are conducted in homogeneous systems Kueper 2011, Munholland et al 2016), and the removal of pollutants in heterogeneous media is less studied. Laboratory studies by some international scholars have confirmed that pollutants-carrying gases accumulate under low-permeability soil layers and migrate horizontally when using ERH technology remediation heterogeneous soil (Martin et al 2016, Martin et al 2017. However, to date, no reasonable solution has been proposed for this phenomenon.…”

Removal of TCE from Clay Lenses by Multi-Phase Diffusion during Electrical Resistance Heating

“…A promising technique for clay geologies is electrical resistance heating (ERH) and related technologies such as ET-DSP TM . Laboratory experiments have demonstrated preferential heating in clay materials and preferential phase change at interfaces with soils with lower displacement pressures [1]. Other experiments have quantified gas production in the interior of clay lenses, which may exist as an unconnected phase within the low permeability clay [2].…”