Solar skimming: mixed system for pollutant removal from groundwater by skimming using solar energy

Abstract

The present innovation focuses on a method for cleaning up groundwater containing polluting substances having a density of less than 1 g / cm3, such as hydrocarbons. This proposition presents a novel method for removing the layer of floating contaminants based on skimming technology. The method consists in heating the contaminated saturated area until the required temperature is reached, for a time sufficient to reduce the viscosity of the contaminants constituting the floating layer. Skimming technology focuses on the accurate extraction of this floating layer. The present invention aims to combine the use of solar energy for heating the contaminants present in the floating layer of the saturated area, with the skimming method. This aims to optimize the treatment time of the saturated area by heating the contaminants, thus increasing their mobility in order to facilitate their extraction by skimming.

Description

[0001] SOLAR SKIMKING: A MIXED SYSTEM FOR GROUNDWATER POLLUTION CONTROL BY

[0002] SOLAR-POWERED SKIMMERING

[0003] FIELD OF INVENTION

[0004] The innovation described in the present invention is based on the synergy between groundwater remediation technologies and methods of heating and generating electricity from solar energy, thus offering a sustainable solution. More specifically, the invention focuses on an innovative process combining skimming techniques and the heating of light non-aqueous phase liquids (LNAPLs), such as petroleum hydrocarbons, using solar energy for this heating.

[0005] A key aspect of the innovation concerns the cleaning of a floating layer within the saturated zone. The use of solar heating accelerates the movement of this layer towards the skimming devices, significantly reducing the viscosity of the pollutant.

[0006] This ingenious combination of technologies offers an innovative approach to solving groundwater remediation problems. By harnessing solar energy at two distinct levels—powering skimming equipment and heating pollutants—this invention demonstrates considerable potential for improving the efficiency of the remediation process and contributing to environmental protection and the promotion of sustainability.

[0007] CONTEXT

[0008] The issue of groundwater contamination is of paramount importance in a world where environmental protection and sustainable development are increasingly paramount. This often insidious concern can stem from a wide range of contaminants, whether chemical, biological, or even radioactive, and caused by an equally diverse array of pollution sources. If no action is taken, this contamination risks spreading, leading to irreversible consequences for the surrounding flora and fauna. It is therefore imperative, both for public health and environmental preservation, to address this situation by eliminating these pollutants before they produce devastating effects. Groundwater remediation methods are varied and generally fall into three main categories: thermal, biological, and physicochemical.The choice of method will depend on the specific characteristics of the site, the nature of the pollutants, and the available resources. A thorough assessment of the site and environmental conditions is essential to determine the best approach for rehabilitating the contaminated area. Current innovation combines two technologies: heating the floating layer using solar energy and cleaning the floating layer using a skimming process.

[0009] Removal of pollutants from groundwater

[0010] One technique for removing the floating layer in the saturated zone is skimming. The aim of the present invention is to provide a device for skimming LNAPL pollution, particularly petroleum hydrocarbons above groundwater, that is capable of precisely positioning itself at the hydrocarbon-water interface based on buoyancy in water.

[0011] The device of the present invention, installed in a well previously drilled to reach the level of the water table, must allow skimming of the upper part of the groundwater and thus ensure total recovery of the supernatant liquid, even if the thickness is small and regardless of the variation in the level of the water table.

[0012] In particular, it aims to provide a method capable of skimming floating hydrocarbon layers less than 1 mm thick in an industrial environment, such as oil ports or petrochemical complexes where the extent of the floating hydrocarbon layer can reach areas of several hectares. These areas are generally located near large rivers or near the sea, where the water table can vary significantly due to tides or locks, and the invention, in a preferred embodiment, aims to take this characteristic into account.

[0013] EP1334780A2 and EP1518614A1 are recognized as prior art to the invention.

[0014] The present invention discloses a device for skimming pollutants such as a floating layer of hydrocarbons on a water table comprising at least one float and at least one pollutant suction pipe, characterized in that the latter also comprises at least one collection orifice and at least one groove in its upper part, allowing access of said pollutants to said collection orifice and in that said float has an intermediate density between the density of the water and the density of the pollutants to be recovered allowing it to be positioned at the interface between the water and the pollutants floating therein.

[0015] According to the invention, the device further comprises at least one water suction pipe to form a deflecting cone.

[0016] According to an essential feature of the present invention, the pollutant suction pipes and water suction pipes simultaneously serve as a slide for said float.

[0017] The invention also discloses a method for cleaning up bodies of water characterized in that a hydrocarbon floating on a body of water is sucked towards a central collection unit via a pipe connected to a device comprising a float having a groove and a collection orifice, the upper part of said float hooking onto the hydrocarbon / water interface by being guided on the slides and conveying said hydrocarbons via a collection pipe connected to a suction pipe through a transfer channel in an assembly profile.

[0018] The collection unit typically consists of a compressor, a vacuum pump, and a programmable logic controller (PLC), powered either by traditional electrical energy or by solar energy when the conditions for using the latter are met.

[0019] Limits of skimming

[0020] The effectiveness of the skimming method for groundwater treatment depends on how pollutants are moved to the skimming wells, which is closely related to the viscosity of the compound present in the floating layer. Consequently, as the viscosity of the pollutant increases, the duration of the pumping process lengthens.

[0021] Heating polluted groundwater

[0022] According to the present invention, the floating layer is first heated to a temperature below the evaporation temperature of the pollutants it contains. Once the desired temperature is reached, the viscosity of the pollutants decreases and their flow towards the skimming wells is accelerated. The heating system for the floating layer consists of a set of solar thermal collectors, which convert the energy from solar radiation into heat for a heat transfer fluid. This fluid, other than air, preferably water to which, in a preferred embodiment, one or more additives are added to increase its heat capacity, is then injected into the system to heat the floating layer.

[0023] There are several groundwater heating techniques, often used in the remediation of sites where the soil and groundwater are contaminated:

[0024] Resistive electric heating is a method that involves passing an electric current through resistive elements installed in the ground. The electrical energy generates heat, which is transferred to the soil and to the groundwater.

[0025] Steam injection heating involves injecting steam directly into the ground to raise the temperature and facilitate the volatilization of contaminating compounds. This method is primarily used for hydrocarbons and other volatile substances.

[0026] Radiofrequency heating involves emitting radiofrequency waves into the ground, which heats water particles and contaminants. The generated heat helps accelerate the desorption and volatilization of contaminants.

[0027] Microwave heating, which is used to heat the ground and groundwater. Adsorbed contaminants can be released and vaporized at high temperatures.

[0028] Geothermal heating, this method harnesses the natural heat of the subsoil by pumping groundwater, heating it at the surface, and then reinjecting it into the ground. It is primarily used for applications such as in-situ decontamination.

[0029] Assisted solar heating, where solar energy is captured by solar thermal collectors on the surface and transferred to the ground via a heat transfer fluid. This heat can be used to increase the temperature of the soil and groundwater for contaminant degradation, desorption, vaporization, improved permeability by reducing groundwater viscosity, and stimulation of biodegradation.

[0030] Vacuum steam heating (VSE) is a method that combines steam injection heating with vacuum extraction of the generated vapors. It is used to eliminate volatile and semi-volatile compounds.

[0031] Hot liquid injection heating involves injecting heated liquids (often water) into the ground to raise the temperature of the soil and contaminants. Underground heating systems are quite complex to design, install, and operate. Managing heat distribution, precisely controlling temperatures, and continuously monitoring the process require specialized expertise.

[0032] While heating methods have proven effective in soil remediation, they are less effective for groundwater treatment. These methods are associated with substantial energy consumption and require specific facilities to manage the vapors produced during heating.

[0033] SUMMARY OF THE INVENTION

[0034] The present invention and its implementations serve to provide a solution to one or more of the drawbacks mentioned above. To this end, the present invention relates to solar skimming, which reduces the viscosity of pollutants composing the floating layer to be treated by heating the saturated zone.

[0035] Solar heating can be used in both saturated and unsaturated soil layers. Skimming is used to treat floating layers. Combining these two techniques accelerates the removal of the floating layer from the saturated zone.

[0036] BE2022 / 5382 is identified as a prior reference and describes a system in which the skimming of the floating layer is improved by introducing heating elements into the soil, thereby promoting the mobility of pollutants. In this scheme, both the vadose zone and the saturated zone are heated using a network of tubes supplied by a burner. The present invention aims to improve this prior technology by introducing a sustainability dimension, using solar energy to heat the soil.

[0037] Similarly, WO2022-122555A1 is recognized as prior art, describing a soil heating system for soil remediation by thermal desorption, using solar energy as the power source. This system focuses primarily on cleaning the contaminated vadose zone. The innovation presented here consists of merging and improving these two prior approaches, thereby creating a more comprehensive and sustainable solution for groundwater remediation. The invention is further described by the following non-limiting examples, which further illustrate the invention and are not intended to, nor should be construed as, limit the scope of the invention.

[0038] The present invention discloses a pollutant skimming device combined with a heating system. The pollutant skimming device, such as for a floating layer of hydrocarbons on a water table, comprises at least one float and at least one hydrocarbon suction pipe, characterized in that the latter further comprises at least one collection orifice and at least one groove on its upper part, allowing access of said hydrocarbon to said collection orifice, and in that said float has a density intermediate between the density of water and the density of the hydrocarbons to be recovered, enabling it to be positioned at the interface between the water and the floating hydrocarbons.

[0039] According to the invention, the device further comprises at least one water suction pipe to form a deflecting cone.

[0040] According to an essential feature of the present invention, the hydrocarbon suction pipes and water suction pipes simultaneously serve as a slide for said float.

[0041] Also, according to the invention, the float is made essentially of high-density polyethylene (HDPE) whose density can vary in the range of 0.94 to 0.97 g / cm3.

[0042] Advantageously, the suction pipe communicates via a lower connecting piece with a collection pipe communicating with the collection port and constitutes an assembly for the suction of hydrocarbons.

[0043] Another feature of the invention is that the float is made up of modular elements.

[0044] The invention also discloses a method for cleaning bodies of water characterized in that a pollutant floating on a body of water is drawn to a central collection unit via a pipe connected to a device comprising a float having a groove and a collection orifice, the upper part of said float gripping the hydrocarbon / water interface while being guided on slides and conveying said hydrocarbons through a collection pipe connected to a suction pipe through a transfer channel in an assembly profile. In a particular embodiment of the invention, water is drawn through a water suction pipe to form a deflecting cone to facilitate the collection of hydrocarbons.

[0045] Finally, the invention describes the use of the skimming device for the recovery of hydrocarbons that have infiltrated into groundwater.

[0046] The present invention also provides a method for heating the floating layer and promoting the flow of pollutants towards the pollutant recovery points by the skimmers. Thus, in a preferred embodiment, the system comprises

[0047] - at least one heating element to be inserted into the ground, said heating element comprises an unperforated outer tube having an open end and a closed end and an unperforated inner tube having both ends open, the inner tube is inserted into the outer tube thus forming an internal space between the two tubes, the open ends of the tubes and the internal space where a heat transfer fluid circulates are connectable to a solar thermal collector to heat the floating layer thus reducing the viscosity of the components of the floating layer;

[0048] - at least one solar-powered heating element (solar thermal collector), the power of which is adjustable;

[0049] - at least one liquid heat transfer fluid circulating in the inner and outer tubes, and heated in a thermal collector;

[0050] - at least one heat transfer fluid circulation element (circulator or pump) connecting the outlet of the solar thermal collector to the inlet of the tube whose flow rate is adjustable;

[0051] - at least one element for measuring the temperature of the heat transfer fluid placed between the upper open end of the inner tube and the outlet of the solar thermal collector and connected to the control box;

[0052] - at least one element for measuring the temperature of the heat transfer fluid placed between the open end of the outer tube and the inlet of the solar thermal collector and connected to the control box;

[0053] - at least two remote-controlled electric valves placed at the inlet and outlet of the solar thermal collector, said box;

[0054] - at least one means for measuring the temperature of the floating layer, said means is inserted into the ground up to the floating touch;

[0055] - at least one control box connects the three temperature measurement elements, the two remote-controlled electric valves and the circulator described above, regulating the flow of the heat transfer fluid according to the measured temperatures;

[0056] DESCRIPTION OF THE FIGURES

[0057] The following description of specific embodiments of the invention is purely exemplary and is not intended to limit the teachings, their application, or their uses. In all drawings, the corresponding reference numbers indicate similar or corresponding parts and features.

[0058] Figure 1 shows a perspective view of the device of the invention.

[0059] Figure 2 represents a schematic view of the operation of a pollution control process using the device according to Figure 1 installed in a borehole.

[0060] Figure 3 illustrates solar heating by the action of heating tubes equipped with solar thermal collector and the heat transfer fluid circulation system, temperature measurement elements and control box.

[0061] Figure 4 is an illustration of the first configuration combining solar heating and skimming technologies for the treatment of the floating layer.

[0062] DETAILED DESCRIPTION OF THE INVENTION

[0063] Definitions

[0064] Heat transfer by conduction occurs when two materials or objects are in direct contact and the temperature of one is higher than that of the other. Thermal conduction is the transfer of kinetic energy from the warmer medium to the cooler medium. The term "conduction," as used here, is therefore intended to refer to all types of heat transfer in which heat is moved from one (warmer) object to another (cooler) by direct contact. It should be understood that in the present invention, when heat transfer by conduction is mentioned, a very small amount of heat is also generally transferred to the ground by radiation.

[0065] The term "groundwater" (or water table) refers to the water-saturated zone of contaminated soil. The term "floating layer" refers to a certain amount of liquid pollutants, which are very poorly soluble in water and lighter than water (LNAPL), that have reached the water table. In such a context, the liquid accumulates in the capillary fringe, just above the water table. The floating (or supernatant) layer forms when this accumulation reaches a critical level.

[0066] Throughout this specification, a reference to "an embodiment" or "a particular feature, structure, or element" means that a particular feature, structure, or element described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, the expressions "in an embodiment" or "in a particular feature" appearing in various places in this specification do not necessarily refer to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.Furthermore, although some embodiments described in this document include certain features, but not others, that are included in other embodiments, combinations of features from different embodiments are intended to fall within the scope of the invention and form different embodiments, as a person skilled in the art would understand them. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0067] The invention

[0068] The present invention is based on the principle that the specific weights of pollutants such as hydrocarbons are generally less than 1 g / cm³ 3and that they therefore float on the surface of the water. It also relies on the principle that the viscosity of pollutants decreases with temperature according to the relationship p~e ((l / T)), thus allowing for more mobile pollutants. Furthermore, the present invention is based on the fact that the density of pollutants decreases with temperature, causing the heaviest fraction to rise above groundwater. It is also based on the fact that heat reduces the interfacial tension between the water and the pollutant, thus making the water-pollutant bonds easily broken. The groundwater skimmer is used to recover a layer of supernatants, pollutants in general and hydrocarbons in particular, from a groundwater aquifer or subsurface, this floating layer being previously observed by a monitoring piezometer in a drilled well equipped with a perforated tube (20).

[0069] The device of the present invention, shown in Figures 1 and 2, comprises a cylindrical profile made of high-density polyethylene, called a "float" (5), the specific gravity of which is such that its upper part will be positioned at the interface between the layer of water-insoluble hydrocarbons (15) and the water table. Generally, the specific gravity of the high-density polyethylene used varies, depending on the catalysts used, from 0.94 to 0.97 g / cm³. 3 but is preferably around 0.96 g / cm³ 3 that of hydrocarbons of approximately 0.8 g / cm³ 3 and that of water, approximately 1 g / cm³ 3 Another resin with a similar specific gravity and good strength properties may also be suitable.

[0070] The float (5) is provided with two external guide grooves (10) and a collection hole (3) passing through the float across its diameter. The dimensions of the float (5) must be smaller than the diameter of the receiving well (20), which may be, for example, a well of 4 inches (114 mm) (Figures 2 and 3).

[0071] Two guides formed by the water (9) and oil (2) suction pipes, or equivalent means, guide the float (5), which can then follow local variations in the water level in the well (20). High-density polyethylene is the ideal material for this type of float because, in addition to its density being intermediate between that of pollutants and water, it is highly resistant to the effects (dissolution, softening, swelling) of most hydrocarbons; this is why it is used, like polypropylene, in the manufacture of automotive fuel tanks.

[0072] The float (5) is preferably constructed in a modular fashion, so that the length of the device can be considerably modified by stacking modules. The same applies to the length of the guides formed by the water (9) and oil (2) suction pipes, as the device must be able to automatically adapt to extreme fluctuations in the groundwater level for months without any monitoring. As mentioned above, the groundwater level can vary considerably from place to place and from time to time, for example, due to rainfall caused by tides or nearby locks.The two tubes, which also serve as guides (2) and (9), are connected to the head and base respectively by means of an upper (1) and lower (7) connecting profile, with a suction tube (6) in the center of the lower connecting piece (7), the length of which corresponds approximately to half the sliding height on the guides. The head piece (1) is provided with a suitable means, such as an opening (11), for attaching the skimmer to a chain in order to maintain it in the well at a midpoint between the maximum and minimum groundwater levels, thus allowing for the integration of variations in the groundwater level over time.

[0073] Initially, a skimmer with a diameter slightly smaller than the diameter of the drilled well (20) should be selected. One of the two slides of the shape shown serves as a transfer tube (2), drawing the product through the collection port (3) of the float. This product is then conveyed via the collection tube (6) and the channel (8) to the suction tube (2), which is connected by a flexible tube (12) to a central collection unit (16). The entire device is then lowered into the well by a positioning chain (13) until it reaches the water level. The required distance is usually measured beforehand. Thanks to its float (5), the device follows the variations in the water-pollutant interface level and thus the level of the local water table. The float (5) is perfectly capable of adapting to this level because it is held and guided by the two slides (2) and (9).It is also possible to drill several wells with an inter-distance of 1.0 to 10 m and to install a device according to the invention in each of them.

[0074] In the presence of a floating layer of hydrocarbons (15), the float (5) of the device of the invention stabilizes at the water-hydrocarbon interface due to its density and profile.

[0075] By means of a suitable pumping unit (16), the product will thus be drawn through the device of the invention.

[0076] In a preferred embodiment, a separate set of photovoltaic panels is installed to provide electricity to certain essential components of the pumping unit (16).

[0077] The present invention also relates to a network of vertical heating wells (21) installed in ground with a floating layer of hydrocarbons present in the groundwater, with spacing of 1.0 to 10 m, and at a variable depth to accommodate variations in the depth of the floating hydrocarbon layer (15). Each vertical heating element (21) is constructed from two coaxial metal tubes, each consisting of an inner tube (22) and an outer tube (23), where the hot fluid enters the inner tube and rises through the annular space between the inner and outer tubes. The outer tubes have a variable diameter ranging from 20 to 250 mm, and preferably from 30 to 100 mm, depending on the depth of the heating element and the calorific value of the heating fluid.A remote-controlled electric valve (24) is placed on the inner tube and / or at the outlet of the outer tube (25) and serves to regulate the flow rate of the heating fluid, heated by the solar thermal collector (26); the circulation of the heating fluid between the heating element and the solar thermal collector is ensured by the circulator (27). The network consists of a set of solar thermal collectors (26), which convert the energy of solar radiation (28) into heat for a heat transfer fluid. This fluid, other than air, preferably water to which, in a preferred embodiment, one or more products are added to increase its heat capacity, is then injected into the network (29) to heat the saturated zone (19) and the floating layer (15).

[0078] The network of heating elements (21) and the network of solar thermal collectors (26) is woven in such a way that the heating of the saturated zone is as efficient as possible.

[0079] The temperature of the heat transfer fluid is controlled by the temperature measuring elements (30) placed at the inlet of the heating element (21) and the element (31) placed at the outlet of the heating element (21). The temperature of the floating layer is controlled by the temperature measuring element (32) placed in a measuring well.

[0080] In a preferred embodiment, the heat transfer fluid heated in a solar thermal collector (26) can be directed to one or more heating elements (21) so that heating of the saturated zone and the floating layer is as efficient as possible. In a preferred embodiment, a separate set of photovoltaic panels is installed to supply electricity to certain elements essential for the circulation of the heat transfer fluid. In a preferred embodiment, remote-controlled automatic valves (24 and 25) allow the heat transfer fluid to be directed to specific zones based on the temperature of the floating layer measured by the element (32) and the amount of energy available. In a preferred embodiment, the remote-controlled automatic valves (24 and 25) are closed to prevent circulation of the heat transfer fluid when the solar thermal collectors are not producing heat.

[0081] In a preferred embodiment, the remote-controlled automatic valves (24, and 25) are partially and / or completely closed in order to decrease and / or stop the circulation of the heat transfer fluid as a function of the temperature of the floating layer.

[0082] LEGEND

[0083] 1. Top assembly profile

[0084] 2. Suction tube for the floating layer, which also serves as a guide for the float.

[0085] 3. Float orifice for oil recovery

[0086] 4. Connection groove on top of the float positioned at the oil / water interface.

[0087] 5. Float

[0088] 6. Floating layer collection tube

[0089] 7. Lower assembly profile including the transfer channel to the floating layer collector tube.

[0090] 8. Transfer channel to the central suction tube

[0091] 9. Water suction tube to create an additional drop also serving as a slide for the float.

[0092] 10. Diameter slot for guiding the float

[0093] 11. Hole for attaching the device to a chain

[0094] 12. Flexible suction tube

[0095] 13. Chain to maintain position in the well

[0096] 14. Water level

[0097] 15. Floating layer of hydrocarbons

[0098] 16. Central collection unit with vacuum tank

[0099] 17. Ground level

[0100] 18. Unsaturated zone

[0101] 19. Saturated zone

[0102] 20. Pipe installed in a borehole

[0103] 21. Heating element

[0104] 22. Inner tube of the heating element

[0105] 23. Outer tube of the heating element

[0106] 24. Remote-controlled electric valve at the inlet of the heating element

[0107] 25. Remote-controlled electric valve at the outlet of the heating element

[0108] 26. Solar thermal collector

[0109] 27. Heat transfer fluid circulator

[0110] 28. Solar radiation

[0111] 29. Heat transfer fluid circulation network

[0112] 30. Temperature measurement sensor at the inlet of the heating element

[0113] 31. Temperature measurement sensor at the output of the heating element

[0114] 32. Floating layer temperature measurement sensor.

[0115] 33. Control Unit

Claims

DEMANDS 1. A groundwater treatment process comprising heating the saturated zone and pumping the floating layer, including: an assembly of at least one heating well (21) in the floating layer and in a portion of the saturated zone combined with a pumping well (20) in which the skimming system is installed; at least one solar heating system, consisting of at least one solar thermal collector (26), heating a heat transfer fluid to a temperature above 100°C; at least one system for managing the circulation of the heat transfer fluid based on the solar energy produced 2. A method according to claim 1, said heating element comprising: at least one system of internal and external tubes connected to a heat source for heating the saturated zone and thus reducing the viscosity of the pollutant that makes up the floating layer (15); at least one control unit (33) controlling the remote-controlled automatic valves (24 and 25) and the circulator (27), said control unit being able to be connected to or removed from the end of the heating element.

3. A method according to claim 1, wherein a groundwater hydrocarbon skimming device installed in a pumping well comprises a float (5) having the following characteristics: a density between the density of water (1 g / cm³ at 20°C) and the density of the hydrocarbons (<1 g / cm³) to be recovered; and a high-density polyethylene (HDPE) material with a density that can vary in the range of 0.94 to 0.97 g / cm³.

4. Method according to claims 1 to 3 wherein the distance between the heating wells (21) is between 1m and 20m, preferably between 2 and 8m and even more preferably between 2.5 and 5m.

5. Method according to claims 1-4 wherein the distance between the pumping wells (20) is between 1m and 20m, preferably between 2 and 8m and even more preferably between 2.5 and 5m.

6. Method according to claims 1-5 wherein the heating zone can be limited to the floating layer or to the entire saturated zone by moving the heat source in the inner and outer tube to the desired depth.

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