THERMAL IN-SITU SUSTAINABLE REMEDIATION SYSTEM AND METHOD

Abstract

A closed-loop system and method for heating of target contaminant treatment zones (150) having environmental contaminants of concern present in the groundwater and the soil by thermal conduction, and subsequent enhancement of physical, biological and chemical processes to attenuate, remove and degrade contaminants in the target contaminant treatment zones, is disclosed. The system and method collects solar or other heat and transfers that heat via a closed-loop and a set of borehole exchangers (120) to subsurface soil in the proximity of and/or directly to the target contaminant treatment zones. The target contaminant treatment zone may comprise contaminated soil, contaminated groundwater in an aquifer, or industrial waste comprising water and/or solids. Solar collectors or heat exchangers capturing waste heat from industrial processes may be used as the heat source (110).

Claims

1. A system for heating a contaminated zone by thermal conduction comprising: a target zone in the subsurface of the ground containing contaminants to be treated by thermal heating; at least one heat source disposed on the surface of the ground in the proximity of the target zone; a plurality of borehole heat exchangers installed in the subsurface in proximity of the target zone; piping that connects the heat sources to the borehole heat exchangers; heat transfer fluid contained within the piping; and at least one pump for circulating the heat transfer fluid within the piping, wherein heat from the heat sources is transferred to the heat transfer fluid, wherein thereafter heat is transferred from the heat transfer fluid to the borehole heat exchangers, wherein thereafter heat is transferred from the borehole heat exchangers to the target zone, thereby increasing the temperature of the target zone and enhancing remediation of contaminants within the target zone.

2. The system of claim 1, wherein at least one heat source comprises solar collectors.

3. The system of claim 2, wherein the target zone further comprises a geothermal storage unit, wherein the geothermal storage unit stores some of the heat obtained from the solar collectors.

4. The system of claim 1, wherein at least one heat source comprises heat exchangers, wherein the heat transfer fluid comprises heated fluid from one or more industrial processes.

5. The system of claim 1, wherein at least one borehole heat exchanger is disposed within the target zone.

6. A method of thermal treatment of contaminants in a target treatment zone, comprising: circulating heated heat transfer fluid through borehole heat exchangers installed in the subsurface soil surrounding a target treatment zone, which target treatment zone comprises contaminants to be remediated; and thereafter heating the subsurface soil surrounding the target treatment zone, wherein the heat transfer fluid is heated by heat obtained from heat sources disposed on a ground surface substantially in the proximity of the target treatment zone and circulated from the heat sources to the borehole heat exchangers through piping by one or more pumps, wherein the heating of the target treatment zone increases reaction rates for contaminant degradation or enhances physical contaminant mass recovery rates, wherein the borehole heat exchangers are placed in the proximity of the target treatment zone.

7. The method of claim 6, wherein at least one heat source comprises solar collectors.

8. The method of claim 7, wherein the target zone further comprises a geothermal storage unit, wherein the geothermal storage unit stores some of the heat obtained from the solar collectors.

9. The method of claim 6, wherein at least one heat source comprises heat exchangers, wherein the heat exchangers capture waste heat from an industrial process.

10. The method of claim 6, wherein at least one borehole heat exchanger is disposed within the target treatment zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will be described with reference to the accompanying drawings, in which like elements are referenced with like numerals.

[0017] FIG. 1 depicts a schematic layout according to one embodiment of the system of the invention.

[0018] FIG. 2 depicts FlexPDE® 2D modelling results for TISR.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The system and method of the invention comprises a closed-loop system for the capture of solar heat and use of the captured solar heat to raise the temperature of subsurface soil and groundwater by thermal conduction in the proximity of a target contaminant treatment zone, which then heats the target contaminant treatment zone (“Thermal In situ Sustainable Remediation” (TISR)).

[0020] The TISR system comprises one or more solar collectors (or waste-heat sources) installed at the ground surface in the proximity of a target contaminant treatment zone; a network of borehole heat exchangers (BHEs) installed in a target heating interval in the subsurface in the proximity of the target contaminant treatment zone; tubing connecting the solar collectors and the BHEs; glycol, water, or other suitable heat-transfer fluid contained within the tubing; and one or more pumps circulating the heat-transfer fluid through the BHEs.

[0021] Each BHE comprises thermally conductive, high surface area tubing placed within a targeted heating interval to accomplish effective heat conductance to the soil in the subsurface and/or directly to the target contaminant zone.

[0022] Solar thermal energy collected by solar collectors are channeled to the subsurface and transferred to the soil and/or target contaminant zone via BHEs. Subsequently, the heat propagates radially outwards from the center of each BHE, heating the target contaminant treatment zone.

[0023] Vertical thickness of the target contaminant zone is a factor in determining the length of each BHE. Upper sections of the BHE may be insulated to minimize heat transfer to upper layers of soil in the subsurface and to focus delivery of thermal energy to the target contaminant zone.

[0024] Contaminant degradation and removal is a function of the temperature for physical, biological and chemical processes occurring in soils and groundwater. As the subsurface temperature rises, reaction rates increase concurrent with an increased rate of contaminant degradation/removal. Heating of the soil in the subsurface in the proximity of a target contaminant treatment zone and/or direct heating results in increasing physical, biological and abiotic reaction rates, resulting in increased contaminant attenuation and degradation within the target contaminant zone.

[0025] The closed-loop system operates in the absence of groundwater pumping or direct circulation of fluids through an aquifer. Energy delivery and heating of the subsurface is conducted via thermal conduction and the relatively uniform thermal conductivity of soils. The entire targeted treatment zone can be heated to the desired treatment temperature via a uniform and controlled process. Three to five times higher remediation rates are believed to occur due to increased reaction rates (both biological and abiotic) via the thermally conductive heating of the target contaminant in situ reactive zone.

[0026] In one embodiment, the heat source comprises a solar collector or a series thereof that harvest heat from the sun. In one embodiment, the target contaminant treatment zone comprises groundwater in an aquifer. In one embodiment, the target contaminant treatment zone comprises groundwater and soil in the subsurface. In one embodiment, the target contaminant treatment zone comprises soil in the subsurface. In one embodiment, the target contaminant treatment zone comprises waste water from industrial or municipal processes. In one embodiment, the target contaminant treatment zone comprises soil or solid waste from industrial or municipal processes. In one embodiment, the heat source comprises a heat exchanger that utilizes waste heat from an industrial process stream.

[0027] In TISR, the thermal properties of soil are utilized to increase the temperatures of contaminated treatment zones, thus increasing the micro-biological activity and physical and chemical reaction rates such as hydrolysis that helps to attenuate, recover, and remediate the contamination. Heat transport occurs through two processes: conduction through soil solids (soil particles) and water and advection through ambient groundwater flow. Heat transfer in soils and water depends on thermal conductivity and heat capacity of soil and groundwater, respectively. these thermal properties are a function of the soil mineral composition, soil density, porosity and saturation with water or air and can be determined by using well established field and laboratory methods or estimated from the existing scientific literature. Variability in soil properties, depth to groundwater below ground surface and nature of contaminants and clean-up goals are used to determine the design specifics for a given site as can be determined according to known techniques by those skilled in the art. The BHE surface area is adjusted to deliver optimal amount of heat required to provide treatment to the target contaminant treatment zone.

[0028] Globally, solar radiation varies based on the distance from the equator as well as seasonal and/or daily weather changes. The surface area of a solar collector for a given site is designed based on the geographical location to account for that variability. Additionally, geothermal heat storage allows for buffering low heat input days caused by low solar radiation on cloudy days and/or due to seasonal changes. After a four to six month period of time (including summer season at a site north of the Tropic of Cancer, in the US), elevated temperatures are believed to be sustained in the subsurface for several months without any solar heat input; the deeper the BHE is placed the longer will be the timeframe for which elevated temperatures should be able to be sustained without additional solar heat input. In one embodiment, the target contaminant zone comprises the geothermal heat storage facility.

[0029] Turning to the figures, FIG. 1 depicts a schematic layout according to one embodiment of the system of the invention. TISR system 100 comprises a heat source 110; a plurality of BHEs 120 comprising heat exchanger coils 125 that are shown placed in both vertical and horizontal boreholes; a pump 130; and conveyance piping 140. Further included are shut off/check valves 180 in conveyance piping 140; air traps and vents 185; and filling/drain valves 190. TISR system 100 further comprises flow meter 195; safety relief valve 197; and expansion tank 199. In the event of accidental abnormal high pressures, safety relief valve 197 will open and heat transfer fluids within conveyance piping 140 will directed to a containment tank 155 and thus avoid spills on the ground. Heat source 110 is installed at the ground surface 140 in the proximity of target contaminant treatment zones 150. The target contaminant treatment zones 150 comprise various contaminants. The BHEs 120 heat the surrounding subsurface of the target contaminant treatment zones 150 by thermal conduction, and/or are placed directly in and heat the target contaminant treatment zones 150.

[0030] Modelling Results.

[0031] FIG. 2 depicts FlexPDE® 2D modelling results for TISR showing contour plots in Row 1 of the vertical profile of heated boreholes with simulated heat transfer over 1 to 12 months. Row 2 shows the same information for the whole site from a plan view. X and Y axis are in meters and temperatures are in ° C. Simulations completed for two, five and ten years of operation (not shown) showed a sustained temperature similar to the 12 months of data. Based on FlexPDE® 2D modelling results as seen in FIG. 2, TISR is predicted to increase subsurface temperatures to 40-70° C. using a closed-loop (no groundwater pumping) heat storage system which in turn induces thermally-enhanced remediation within a target contaminant treatment zone 150. It is estimated that within six months of start-up, BHEs 120 spaced 8 m apart can heat the groundwater between them to 35-40° C. at a depth of 3 m below land surface. This data represented simulations run using a site data from northern Ohio. Geographical location of a subject site will affect these design parameters.

[0032] Heat transfer calculations were reviewed (and confirmed via multiple simulations) and revised to provide a basis for development of a conceptual design and approach for implementation.

[0033] In the foregoing description, the invention has been described with reference to specific exemplary embodiments thereof. It will be apparent to those skilled in the art that a person understanding this invention may conceive of changes or other embodiments or variations, which utilize the principles of this invention without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.