Device and method for in situ heating of soil by microwaves

Abstract

The invention relates to a soil thermal-treatment device comprising: a. a microwave energy source (11, 12) configured to generate microwaves; b. a cylindrical microwave antenna (101, 102) connected to the microwave energy source and inserted substantially vertically into soil to be treated, the antenna comprising a plurality of openings for emitting the generated microwaves into the soil to be treated; c. fluid injection means (13) connected at the upper part of the antenna in order to the fluid into the soil to be treated through the openings, at the same time as the microwaves are emitted; d. at least one optical fibre temperature sensor inserted into the antenna; e. adjustable means for at least partially sealing at least a lower part of the antenna.

Description

Description Title: Device and method for in-situ floor heating using microwaves technical field

[0001] This disclosure relates to the field of thermal soil treatment, particularly, but not exclusively, for remediation purposes. This disclosure concerns, in particular, but not exclusively, a technique for the simultaneous treatment of soil and groundwater by heating, which can, for example, be used in the disinfection of water wells. Previous technique

[0002] Soil remediation is a growing issue, driven by a policy in favor of environmental protection and the fight against soil artificialization, and framed, at least in France and Europe, by numerous regulatory constraints, notably making soil remediation mandatory at the end of a site's occupation.

[0003] There are several types of soil pollution: - hydrocarbon pollution (petroleum derivatives, microplastics, etc.), - pollution from agricultural fertilizers (pesticides, etc.), - pollution linked to industrial activities (chemicals, heavy metals, ...) and construction companies (asbestos, lead, ...).

[0004] In practice, soil is rarely contaminated by a single pollutant. This means that diagnosed pollution is generally complex, combining a "cocktail of pollutants" whose behavior in mixture differs significantly from that of each component individually during a remediation operation. Furthermore, industrial and technological advancements have led to the identification of "emerging pollutants" whose treatment is not yet fully understood. This complexity of mixtures and pollution highlights the difficulty of finding an effective soil remediation method that offers general, rather than specific, efficacy.

[0005] The most advantageous soil remediation techniques are those that can be implemented on-site to treat pollutants directly and without excavation. This avoids transportation costs and the need for disposal at treatment or storage facilities.

[0006] Today, one of the effective in-situ methods for treating soil pollution is thermal desorption. The principle of this method is to raise the temperature of the polluted soil, with or without excavation, in order to vaporize / destroy the pollutant. This method is suitable for treating many organic pollutants (volatile, semi-volatile, and even slightly volatile) such as petroleum hydrocarbons (gasoline, diesel, kerosene, etc.), heavier hydrocarbon fractions, chlorinated solvents, oils, PCBs (Polychlorinated Biphenyls), pesticides, dioxins / furans, PAHs (Polycyclic Aromatic Hydrocarbons), etc. Other remediation methods also require heating the soil to decontamination, for example to reduce the viscosity of pollutants and thus facilitate their extraction by pumping, or to increase bacterial activity conducive to the elimination of pollutants present in the soil.

[0007] Several methods exist for heating the ground in situ: - Conduction heating uses vertical or horizontal metal rods (heating needles) placed in the ground and / or in extraction shafts, and heated by a heating element. The ground heats up by conduction, and especially by radiation near the metal rods; - Steam or hot air injection heating, or convection heating, uses the injection of water vapor or hot air via vertical or horizontal injection points; - Electric resistance heating uses electrodes placed in the soil on either side of the area to be treated. An electric current passes between the electrodes through the soil matrix. The resistance of the soil causes a rise in temperature and therefore the volatilization of pollutants.

[0008] These methods, despite their effectiveness, have several drawbacks. First, the heating and treatment times can be very long. Second, the heating is generally not uniform throughout the soil and may have a very limited range. Finally, depending on the method chosen, the heating can create new pollution (for example, in the event of reactions between water vapor and the pollutant).

[0009] Conduction heating, in particular, has the main drawback that the rise to high temperature of the heating needles is very energy-intensive and the necessary treatment time is long, which leads to significant pollution control costs and a bad environmental impact, due to a poor carbon footprint.

[0010] Pour pallier cet inconvénient, il a été proposé d’utiliser une technique de chauffage in situ par micro-ondes [Chien, Yi-Chi, 2012, « Field study of in situ remediation of petroleum hydrocarbon contaminated soil on site using microwave energy », Journal of Hazardous Materials 199: 457-61 ; Pauli, M, T Kayser, et W Wiesbeck, 2016, « A novel antenna design for soil decontamination with microwaves », In Proceedings of the GeMiC, German Microwave Conference, Karlsruhe, Germany ; Falciglia, PP, Scandura P., Vagliasindi FGA, 2018, « Modelling and preliminary technical, energy and economic considerations for full-scale in situ remediation of low-dielectric hydrocarbon-polluted soils by microwave heating (MWH) technique», J Soils Sediments 18: 2350-2360].Microwaves have the advantage of increasing temperature very quickly and more evenly than conventional methods: for many years they have been a fast and energy-efficient heating solution. Microwaves can be generally defined as all electromagnetic radiation with a frequency between 300 MHz and 300 GHz.

[0011] Numerous experiments have been conducted in recent years by the scientific community to evaluate the effectiveness of microwave thermal desorption on various types of pollutants in different soil compositions. These experiments have varied the experimental conditions in terms of microwave frequency, applied power, treatment time, soil moisture content, microwave-generating antenna design and structure, and have tested mixtures (soils with added microwave absorbers, etc.). However, most laboratory studies have been carried out with small-volume soil samples placed as close as possible to the microwave source (near the waveguides, and therefore the irradiation source). This means that the samples received the maximum amount of radiation without accounting for losses, which is far from the conditions of in-situ treatment.

[0012] Indeed, to the Applicant's knowledge, only three studies using a microwave antenna directly implanted in the soil have been conducted to analyze in situ soil decontamination [Kawala, Zdzislaw, and Tomasz Atamahczuk, 1998, “Microwave-enhanced thermal decontamination of soil”, Environmental science & technology 32 (17): 2602-7; Chien, Yi-Chi, 2012, “Field study of in situ remediation of petroleum hydrocarbon contaminated soil on site using microwave energy”, Journal of Hazardous Materials 199: 457-61; Pauli, M, T Kayser, and W Wiesbeck, 2016, “A novel antenna design for soil decontamination with microwaves”, In Proceedings of the GeMiC, German Microwave Conference, Karlsruhe, Germany].

[0013] However, it would be advantageous to have an effective microwave soil heat treatment technique that can be used in situ.

[0014] US patent document 10,137,486 B1 describes a technique for the thermal treatment of a contaminated soil sample, consisting of subjecting the soil sample to microwave irradiation to heat it to a temperature between 150°C and 1200°C. In one embodiment, a waveguide, connected to a microwave power source, is inserted into the soil sample to be treated. It has a plurality of apertures allowing microwaves, with a frequency between 0.1 and 10 GHz, to be directed through the soil sample. When slow combustion is initiated in the sample, the microwave irradiation is stopped, and a flow of oxidizing gas is then injected to sustain and propagate this combustion within the sample.

[0015] This interesting technique, however, is only suitable for treating porous media, which can consist of natural soil, mud, drilling debris, sediments, and / or industrial waste. Some soils requiring decontamination or disinfection consist of a low, water-saturated zone, such as a water table, and an unsaturated upper zone. This is particularly true, for example, of light refined petroleum hydrocarbons (LNAPL: gasoline, diesel, motor oil, etc.) which, at high concentrations, accumulate on the top of the water table and form a pure-phase product called a supernatant. Furthermore, water wells can contain ubiquitous microorganisms (viruses, bacteria, etc.) capable of developing at depth. Some of these organisms may be pathogenic, while others can develop into biofilms that provide support and protection for other colonies or species of microorganisms. Depending on the development In the presence of biological materials, boreholes may require disinfection, often more difficult in the presence of biofilms, before being exploited.

[0016] This disinfection is generally carried out using biocidal products (chlorination, etc.). However, it would be advantageous to offer an alternative, more environmentally friendly solution, such as thermal disinfection, which would not require the use of chemicals. This solution would be particularly beneficial for treating thermal water wells (hot springs, etc.) and water intended for bottling, which is often prohibited from being chemically treated under current regulations. Summary

[0017] This disclosure improves the situation.

[0018] A soil thermal treatment device is proposed comprising: a. a microwave energy source configured to generate microwaves; b. at least one cylindrical microwave antenna connected to the microwave energy source and configured to be inserted substantially vertically into the soil to be treated, the cylindrical microwave antenna(s) having a plurality of openings for the emission of the generated microwaves into the soil to be treated; c. fluid injection means configured to be connected to the upper part of the cylindrical antenna(s) and to inject the fluid into the soil to be treated through the plurality of openings concomitantly with the emission of microwaves; d. at least one optical fiber temperature sensor configured to be inserted into the cylindrical antenna(s); e. adjustable means for at least partially sealing at least a lower part of the antenna(s).

[0019] Throughout this document, a cylinder is defined as a ruled surface whose generatrices are parallel, that is, a surface in space made up of parallel lines. A cylindrical antenna therefore refers to an antenna in the shape of a right cylinder, regardless of the cross-section of that cylinder (circular, rectangular, elliptical, etc.).

[0020] According to another aspect, a method for thermally treating soil comprising a water-saturated lower zone and an unsaturated upper zone is proposed, using a soil thermal treatment device as described above, the method comprising the steps of: a. drilling the soil from a soil surface down to at least the lower zone; b. inserting the cylindrical microwave antenna(s) into the borehole; c. adjusting the adjustable sealing means to seal at least a lower part of the antenna intended to be immersed in the upper saturated lower zone; d. generation of microwaves by the microwave energy source and emission of the generated microwaves through the openings of the antenna in the upper and lower zones of the soil to be treated; e. concomitant injection of fluid into the soil to be treated through the openings of an upper part of the antenna positioned in the upper unsaturated zone; f. temperature measurement in the lower and upper parts of the antenna by means of the device's fiber optic temperature sensor(s); g. interruption of microwave emission when the temperature measured in the lower and / or upper parts reaches a predetermined treatment temperature setpoint for a predetermined duration.

[0021] The features described in the following paragraphs may optionally be implemented, independently of each other or in combination with each other:

[0022] Adjustable sealing methods include: - a sheath configured to slide over an outer wall of at least one lower portion of the antenna; and - a heat-resistant sealing gasket configured to be interposed between an upper end of the sheath and the outer wall of the antenna.

[0023] The cylindrical microwave antenna comprises a first cylindrical tube of circular cross-section having the plurality of openings and a core coaxial to the first tube, and the adjustable sealing means comprise a second tube forming a sheath for at least a lower part of the first tube.

[0024] Adjustable sealing means include means for pushing the second tube on the first tube to close all or part of the plurality of openings.

[0025] The second tube has a plurality of openings corresponding to the plurality of openings of the first tube, and the adjustable sealing means include means for rotating the second tube on the first tube to pass from an open position in which the openings of the first and second tubes are opposite each other to a closed position in which a solid wall of the second tube closes the openings of the first tube, and vice versa.

[0026] Adjustable sealing methods include: - a sheath covering an outer wall of at least one lower part of the antenna; and - at least one inflatable shutter configured to be secured between the lower and upper parts of the antenna.

[0027] The adjustable sealing means also include at the base of the inflatable plug(s) a flexible mesh disc of diameter adapted to the diameter of a borehole into which the soil thermal treatment device is inserted.

[0028] The sheath and / or an external wall of the second tube is made of Teflon®.

[0029] The cylindrical microwave antenna has a rectangular cross-section and the openings are positioned on two faces opposite the cylindrical antenna with a rectangular cross-section for bidirectional emission of microwaves generated in the soil to be treated.

[0030] The device also includes an envelope made of refractory material and / or microwave-absorbing material, configured to surround at least part of the cylindrical microwave antenna.

[0031] The fluid injection means are connected to a hot air exhaust from the microwave energy source (magnetron) to inject the hot air through the antenna into the soil to be treated.

[0032] The cylindrical microwave antenna comprises a plurality of antenna sections mounted in series.

[0033] The device also includes a sealing cap configured to seal one lower end of the cylindrical antenna. Brief description of the drawings

[0034] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which: Fig. 1

[0035] [Fig. 1] shows an example of the use of a heat treatment device according to one embodiment. Fig. 2

[0036] [Fig. 2] illustrates a first example of the realization of a cylindrical microwave antenna with a circular cross-section according to one embodiment. Fig. 3

[0037] [Fig. 3] shows a first embodiment of adjustable means for sealing a microwave antenna. Fig. 4

[0038] [Fig. 4] shows a second embodiment of adjustable means for sealing a microwave antenna.

[0039] Fig. 5

[0040] [Fig. 5] shows a third embodiment of adjustable means for sealing a microwave antenna.

[0041] [Fig. 6] presents examples of inflatable shutters that can be used in the embodiment of Figure 5. Fig. 7

[0042] [Fig. 7] shows an example of the use of the device in Figure 5 in a water well according to one embodiment. Fig. 8

[0043] [Fig. 8] presents in the form of a flowchart an example of the implementation of a soil thermal treatment process according to one embodiment. Fig. 9

[0044] [Fig. 9] shows temperature profiles obtained by implementing the process of figure 8 according to one embodiment. Fig. 10

[0045] [Fig. 10] illustrates the impact of adding to the device an envelope made of microwave-absorbing material (slate powder) according to one embodiment. Description of the implementation methods

[0046] The general principle of the invention is based on a microwave soil thermal treatment device that is particularly suitable for treating soils comprising a water-saturated zone and an unsaturated zone, for example, a water well. Such a device is illustrated schematically in Figure 1.

[0047] Figure 1 illustrates an in-situ application of such a device for the thermal treatment of soil comprising an upper zone Z1 unsaturated with water, for example, soil constituting a porous medium (earth, sand, gravel, etc.), and a lower zone Z2 saturated with water, for example, a water table. All or part of zones Z1 and Z2 may be polluted or require disinfection by thermal treatment, for example, to induce the evaporation of organic pollutants present in the soil or the water table, or to destroy ubiquitous microorganisms (viruses, bacteria, etc.) that may be present as biofilms in the water table Z2.

[0048] To carry out this thermal treatment, a cylindrical microwave antenna is inserted almost vertically into the soil to be treated, more or less deeply, depending on whether one wishes to treat only the upper zone Z1 or the upper zone Z1 and lower zone Z2.

[0049] Such an antenna, various embodiments of which will be described in more detail with reference to Figures 2 and following, is preferably cylindrical, with a circular or rectangular cross-section. It may, for example, be in the form of a stainless steel or aluminum tube, the upper portion 10i of which is solid, and the lower portion 102 (the woven part of the antenna in Figure 1) of which has a plurality of openings, for example, a plurality of slots.

[0050] In its upper part, outside the soil to be treated, the antenna is connected to a microwave energy source, comprising, for example, a generator 11 and a magnetron 12. The Generator 1, capable of delivering a maximum power of 8 kW (modulatable between 0.25 and 8 kW), provides the necessary electrical power to magnetron 12 to generate microwaves at a frequency of 2.45 GHz, for example. The antenna is connected to magnetron 12 via a waveguide bend (90° angle), allowing it to be mounted in a vertical position.

[0051] The microwaves generated by the magnetron 12 are emitted through the openings of the lower part 102 of the antenna towards the ground to be treated.

[0052] Such a device also includes means 13 for injecting fluid through the antenna cylinder, for example, air, possibly preheated. This fluid is emitted into the soil to be treated, simultaneously with the microwaves generated by the magnetron 12, through the openings in the lower portion 1 Ü2 of the antenna. Such fluid injection, for example of hot air or gas, allows for more efficient propagation of the heat generated by the microwaves in the soil to be treated.

[0053] The coupling of air injection 13 and microwave heating thus advantageously increases the heating range. Indeed, the injection of air from inside the antenna to the outside via the slots located in the lower portion 1 Ü2 of the antenna optimizes the transfer and diffusion of accumulated heat from the area adjacent to the antenna to more distant, and therefore cooler, areas.

[0054] In one example, two air injection valves are installed on top of the antenna to allow connection to a compressed air supply. A ball flow meter measures the injected air flow rate, which is adjustable between 4 and 50 L / min via a valve.

[0055] In one embodiment, the fluid injection means 13 are coupled to the microwave energy source to use the heat generated and dissipated by this source to preheat the air or gas injected into the antenna. For example, the fluid injection means 13 recover the air exhausted by the fans of the magnetron 12 to inject preheated air into the ground via the antenna at a lower cost.

[0056] In one embodiment, such a device also includes a casing 14 made of refractory material or microwave-absorbing material (e.g., slate powder) configured to surround the heating element of the microwave antenna cylinder. Such a casing 14 may be in the form of a reusable cylinder made of refractory or absorbent material, the inner diameter of which coincides with the outer diameter of the antenna, and which can, as required, be slid around the antenna. Such a casing 14 may be made from absorbent and / or refractory material (slate, activated carbon, refractory cement, etc.) that has been previously ground and sieved, and advantageously allows for an increase in the heating temperature.

[0057] The enclosure material can be absorbent (high emissivity) and / or refractory (high thermal inertia) depending on the application and the desired temperature. Both types of materials have the capacity to either absorb microwave energy (absorbent material) or retain and diffuse it. the heat generated by microwaves (refractory material). One can imagine, in particular, designing an envelope comprising an inner layer of absorbent material and an outer layer of refractory material.

[0058] In the case where the antenna is inserted into a borehole drilled in the ground, the envelope 14 can take the form of absorbent elements (slate powder, activated carbon ...) added in the form of sieved powder in the borehole, which is positioned so as to surround the antenna on the heating part.

[0059] The presence of this type of compound accelerates the temperature rise at the start of heat treatment, increases the heating temperature, and absorbs heat to extend the heating time. Furthermore, the use of natural microwave-absorbing materials such as slate is advantageous because it has a low environmental impact; these materials can be left in the ground after heat treatment without generating additional pollution or disturbing the environment. Of course, using a reusable casing, for example, in the form of a removable cylinder, is preferable in terms of sustainability.

[0060] In the example in Figure 1, we have shown the envelope 14 which covers only the lower portion 102 of the antenna located in the upper zone Z1: this envelope can be of variable height according to the needs and cover all or part of the heating part 2 of the antenna.

[0061] Figure 2 illustrates a first example of such a cylindrical microwave antenna with a circular cross-section. This coaxial microwave antenna consists of a 2 m long, 5 cm diameter, slotted aluminum dip tube 15i and a concentric inner rod 152 with a diameter of 0.9 cm, as shown in more detail in Figure 2 (part (a) for an exploded view and part (b) for an assembled, ready-to-use view). The tube 15i has slots along its lower part, over a length of approximately 1 m. In one embodiment, glass wool is used to cover the antenna slots to prevent porous material from zone Z1 (e.g., sand) from entering the tube 15i, while allowing microwaves and air to pass from the inside to the outside of the tube, the glass wool being impermeable to sand but permeable to microwaves and air.The 15i dip tube terminates, at its upper part, with a flange referenced 15e.

[0062] As can be seen in Figure 2, the dip tube 15i terminates at its lower end with a conical tip 154 ​​covered by a disc 15s. These elements can form a sealing plug at the bottom of the antenna. The plate referenced 15s, preferably made of stainless steel or aluminum, and the sponge-shaped metal gaskets referenced 15?, are configured to prevent microwaves from rising to the surface, thus preserving a safe environment around the device for a potential operator.

[0063] In another example (illustrated, for instance, in Figure 3), the cylindrical microwave antenna has a rectangular cross-section, is made of stainless steel or aluminum, and has slots on two of its opposite faces. This forms a bidirectional rectangular antenna: Indeed, with the slots positioned on two opposite faces of the antenna, the wave propagation is bidirectional. This bidirectional rectangular antenna design advantageously reduces energy losses by approximately 25% compared to the coaxial antenna design shown in Figure 2.

[0064] Indeed, initial tests conducted by the inventors on the waves emitted and reflected by the coaxial antenna in Figure 2 demonstrated a significant energy loss of 25%, likely due to the change in cross-section between the waveguide at the magnetron output (rectangular) and the coaxial antenna (circular). Using a rectangular antenna advantageously avoids this change in cross-section between the magnetron output and the antenna, thus optimizing the emitted-to-reflected power ratio.

[0065] It is clear from Figures 1 and 2 and the associated description above that such an antenna structure, whether circular or rectangular in cross-section, is unsuitable when immersed in a water-saturated zone Z2. Water can indeed enter the antenna cylinder through the slots.

[0066] We now present below, in relation to Figures 3 to 7, various embodiments of such a soil thermal treatment device, which also includes adjustable means for sealing the lower part of the antenna intended to be immersed in the water-saturated zone Z2. The adjustable nature of these sealing means is indeed necessary to allow the device to be adapted to different depths of zones Z1 and Z2.

[0067] A first embodiment of such adjustable sealing means is illustrated in Figure 3, for an antenna with a rectangular cross-section. Such an embodiment could of course also be suitable for an antenna with a circular cross-section, such as the antenna in Figure 2.

[0068] Figure 3 shows, for illustrative purposes only, the lower portion 102 of the antenna in a perspective view. Slots 19 are provided on one of the two visible faces of this lower portion 1 Ü2 of the antenna, but it is understood that other corresponding slots are also provided on the opposite face.

[0069] A sheath (or sleeve) 17, for example made of Teflon®, covers the antenna 1 Ü2 and seals the lower part of the stainless steel (or aluminum) antenna, which is intended to be immersed in the water-saturated zone Z2. This sheath 17 can be shaped like a sock that can be pulled to a greater or lesser height, depending on the respective depths of zones Z1 and Z2, so as to completely or partially cover the stainless steel (or aluminum) antenna, but above all, to prevent the liquid contained in zone Z2 from entering through the slots 19 of the antenna. The sheath 17 should therefore preferably cover the entire part of the antenna immersed in zone Z2.

[0070] A heat-resistant sealing gasket 18 is also planned at the junction between the sheath 17 and the portion 102 of the antenna.

[0071] Figure 3 also shows a sheath 16, preferably also made of Teflon®, protecting the optical fiber that forms the temperature sensor. Such an optical fiber is inserted into the hollow body of the antenna and allows for temperature monitoring. The use of such a fiber sensor Optical technology advantageously allows continuous temperature measurements, even during the microwave emission phase.

[0072] Figure 4 illustrates a second embodiment of the adjustable sealing means, for an antenna with a circular cross-section, such as the antenna in Figure 2.

[0073] In this second embodiment, the lower portion 102 of the antenna (Le, the lower part of the dip tube 15i) cooperates with a second tube 20, the inner diameter of which corresponds to the outer diameter of the dip tube 15i. The outer part of this second tube 20 is preferably coated with Teflon®. As in the first embodiment of Figure 3, a heat-resistant seal 18 is also provided at the junction between the second tube 20 and the dip tube 15i of the antenna. Although, for the sake of simplicity, it is not shown in Figure 4, a fiber optic sensor is also provided, inserted into the body of the antenna, which can be protected by a Teflon® sheath 16.

[0074] In a first variant, the adjustable sealing means include means for pushing the second tube 20, illustrated by arrow 21. The wall of the second tube 20 is, for example, solid and closes the slots 19 over a greater or lesser height, depending on the force exerted. It is thus possible to slide the second tube 20 along the dip tube 15i, to close all the openings 19 submerged in the water-saturated zone Z2.

[0075] In a second variant, the adjustable sealing means include means for rotating the second tube 20, illustrated by arrow 22. The wall of the second tube 20 has, for example, a plurality of openings corresponding to the slots 19 of the dip tube 15i. In an open position, the slots of the second tube 20 overlap the slots 19 of the dip tube 15i. The rotation means 22 allow, for example, the second tube 20 to be rotated a quarter turn, placing it in a closed position, in which a solid wall of the second tube 20 closes the slots 19 of the dip tube 15i, the slots of the second tube 20 and the dip tube 15i no longer being directly opposite each other. Thus, by simple rotation, the slots 19 of the antenna can be opened or closed, depending on whether they are located in zone Z1 or zone Z2 of the soil to be treated.

[0076] In the second embodiment of figure 4, the plugging of the slots 19 of the antenna is therefore carried out either by pushing one tube on the other (first variant), or by rotating one tube on the other (second variant).

[0077] We could of course also consider combining the thrust movements 21 and rotation movements 22 to simultaneously adjust, on the one hand, the height of the antenna on which it is necessary to close the slots 19, and on the other hand, the open or closed position of the slots 19, according to the use cases, and the profile (Z1 / Z2) of the ground to be treated.

[0078] We now present, in relation to figures 5 to 7, a third embodiment of adjustable means for sealing the lower part of the antenna.

[0079] Figure 5 shows an exploded view of the antenna, for example the circular cross-section coaxial microwave antenna of Figure 2.

[0080] In this embodiment, the antenna is formed from a plurality of antenna sections connected in series, which is advantageous for adapting the antenna length to the depth of the borehole to be thermally treated. For example, four antenna sections, labeled 23i to 234, are shown: two initial antenna sections, 23i-232, which, after assembly, form an upper antenna section 24 intended for placement in the upper zone Z1 of the soil to be treated, and two antenna sections, 233-234, which, after assembly, form a lower antenna section 25 intended for placement in the lower zone Z2 of the soil to be treated. A different number of sections can, of course, be considered. In particular, it is not necessary to provide the same number of sections in the upper zone Z1 and the lower zone Z2, but rather the number of sections should be adapted according to the depth of each of the saturated zone Z2 and unsaturated zone Z1.It should be noted that such an antenna structure from antenna sections mounted in series is not limited to this third embodiment of adjustable sealing means but can also be considered for the first embodiment of Figure 3 or the second embodiment of Figure 4.

[0081] The upper antenna portion 24, like the lower antenna portion 25, is, for example, made of stainless steel and equipped with slots, as in the example of Figure 2 (the upper 24 and lower 25 portions of the antenna form the lower section, referenced as 102, of the antenna in Figure 1). Furthermore, the antenna sections 233-234 of the lower antenna portion 25 are preferably coated with Teflon®. This Teflon® coating may be fixed or achieved using the embodiment shown in Figure 3, i.e., by positioning a sliding Teflon® sleeve over the antenna sections 233-234.

[0082] A sealing plug 26 is secured, for example by screwing, to the lower part of the lower part of the antenna 25.

[0083] An inflatable packer 27, also called an inflatable packer, is interposed between the lower part of the antenna 25 and the upper part 24 of the antenna. It can be inflated by means of a hose, shown schematically, and designated 28. This hose 28 is, for example, connected to a compressor, and the pressure is controlled by a pressure gauge.

[0084] Inflatable plugs 27i, 272 of different lengths and diameters can be used, as illustrated for example in figure 6. It is in particular possible to provide an inflatable plug 272 in two sections.

[0085] In one embodiment, a flexible mesh stainless steel disc 29 is also provided, the diameter of which is chosen according to the diameter of the borehole 31 into which the antenna of the soil thermal treatment device is inserted (see Figure 7). Such a disc 29 prevents microwaves from traveling back up through the borehole 31.

[0086] Figure 5 also shows two sheaths, referenced 161 and 162, each containing an optical fiber for temperature control. Sheath referenced 161 is inserted into the hollow body of the first section 23i of the upper part 24 of the antenna; sheath referenced 162 is crimped into the hollow body of the first section 23s of the lower part 25 of the antenna, into which it is inserted via the inflatable shutter 27.

[0087] Microwave injection is done through the upper part of the antenna (arrow referenced 30).

[0088] Elements 24, 25, and 27 have the same inner diameter. The various elements are preferably screwed together using an external watertight sleeve to maintain consistent tube diameters throughout the antenna.

[0089] Figure 7 illustrates the device of Figure 5 when installed in a borehole 31. In this antenna installation position, the inflatable shutter 27 is inflated. This isolates the upper part 24 from the lower part 25 of the antenna. It is positioned in an intermediate zone Z3 between the upper, unsaturated soil zone Z1 and the lower, water-saturated zone Z2. This isolation allows for the simultaneous treatment of soil (upper part, unsaturated zone Z1) and groundwater (lower part, water-saturated zone Z2).

[0090] The shutter 27 thus allows: - on the one hand, to separate the saturated zone Z2 from the unsaturated zone Z1; - on the other hand, an increase in pressure on the lower part located under the shutter 27. This has the effect of improving the efficiency of the treatment by increasing the temperature.

[0091] The inflatable shutter 27 also prevents water vapor generated by heating the saturated zone Z2 from escaping towards the upper part 24 of the antenna. In a variant, the use of two inflatable shutters (instead of one) can also ensure a seal over a segment between the upper part 24 and the lower part 25.

[0092] The thermal device, as described above in relation to Figures 1 to 7, can be used for the thermal treatment of soil, such as a water well for example, according to the process described below in relation to Figure 8.

[0093] In the first step, referenced as E1, a borehole is drilled into the soil to be treated. This borehole may be drilled for the purpose of carrying out the thermal treatment of the soil, or it may be a borehole drilled upstream of this treatment, for the exploitation of resources contained in the soil (for example, for the exploitation of water contained in an underground aquifer).

[0094] The heat treatment device described above is installed on the ground surface, at the level of the borehole), and in particular the microwave antenna is inserted into the borehole, during a step referenced E2. Depending on the configuration of the ground, and in particular the respective depths of the unsaturated zone Z1 and the saturated zone Z2 at the top, the adjustable sealing means of the antenna are adjusted during a step E3, so as to seal the lower part of the antenna which will be immersed in the lower zone Z2.To do this, depending on the implementation of these adjustable sealing means, a Teflon sleeve is slid onto the lower part of the antenna to seal the slots (figure 3), or the position (height and / or orientation) of a second tube surrounding the lower part of the antenna is adjusted (figure 4), or an inflatable shutter is inflated and positioned at an intermediate zone Z3 between the high unsaturated zone Z1 and the low water-saturated zone Z2 (figures 5 to 7).

[0095] When the position of the antenna and the adjustable sealing means are adjusted, microwave emission (step E4A) is carried out simultaneously through the slots of The antenna and fluid injection (step E4B), preferably hot air, are involved. Microwaves are emitted through the antenna slots, whether or not they are sealed by a Teflon® sheath or sleeve, thus emitting both the upper unsaturated zone Z1 and the lower water-saturated zone Z2. The hot air escapes only through the slots in the upper part of the antenna, located in the upper unsaturated zone Z1, the slots in the lower part being sealed by a sheath or the second tube.

[0096] Thanks to fiber optic temperature sensors, the temperature is monitored at different parts of the antenna during a step referred to as E5. When the temperature reaches a predetermined threshold value (depending on the type of heat treatment to be carried out, the nature of the disinfection desired, for example), for a predetermined heating time, the treatment is stopped (step referred to as E6), by stopping the emission of microwaves and / or the injection of fluid.

[0097] The air injection carried out during step E4B, concomitant with the microwave injection, allows for better distribution of microwave heating in the ground via an airflow emitted by the antenna, as illustrated by figures 9(a) (without air injection) and 9(b) (with air injection).

[0098] In the example shown in Figure 9(b), a flow of (dry) air maintained at a temperature of approximately 16 °C enters through one of the air injection valves located above the antenna and then exits through the slots along the antenna, thus ensuring air propagation through the ground (flow rate of 40 L / min). Temperature contours plotted on a horizontal section of the device were measured using temperature sensors. The notable difference between the results in Figures 9(a) and 9(b) lies in the observation of a weaker temperature gradient during air injection. Indeed, the temperature contours are more spread out, with slightly smaller value intervals, compared to the case without air injection. The use of air injection during microwave heating is therefore advantageous for extending the area of ​​effect and thus covering a larger volume for thermal desorption.In this study, the injected air was at room temperature (16°C). However, using preheated air, such as the air exhausted by the fans of the microwave device, could lead to even more promising results.

[0099] In addition, the addition of an absorbent material (slate, activated carbon, etc.), previously crushed and sieved, makes it possible to increase the heating temperature, not only in terms of speed of start-up of treatment but also over the duration of the treatment.

[0100] Figure 10 illustrates the impact of this addition. Figures 10(a) and (b) illustrate the experimental protocol, in which a microwave antenna was inserted vertically into a column of moistened sand. Part of the antenna was wrapped with a layer of slate powder, to a height of approximately 0.5 m, and a portion of the antenna of the same height was left without any added absorbing material. This layer of slate powder was approximately 4 cm thick. Figures 10(c) and (d) illustrate the temperature evolution over time, as a function of the distance r from the antenna, for the area with slate (Figure 10(c)) and for the area without slate (Figure 10(d)). As can be seen, the addition of slate resulted in a considerable increase in temperature, which roughly doubled. These promising results led to the idea of ​​designing the envelope 14 in refractory and / or absorbent material around the antenna. Industrial application

[0101] These technical solutions can be applied in various fields, including soil remediation, particularly the disinfection of water wells, as well as other in-situ soil heating applications. For example, they could be used for oil recovery in underground reservoirs. These broad applications highlight the versatility and relevance of this technology in diverse industrial and environmental sectors. List of reference signs

[0102] - 10i: upper portion of antenna; - 2: lower portion of antenna - 1 1: generator; - 12: magnetron; - 13: means of fluid injection; - 14: refractory material casing; - Z1: high unsaturated zone; - Z2: lower zone saturated at the top; - Z3: intermediate zone; - 15i: split plunger tube; - 152: stem; - 153: platinum; - 154: conical tip; - 155: lozenge; - 15th: bridle; - 15? : metal joint; - 16, 161, 162: optical fiber sheath; - 17: sheath or sleeve; - 18: heat-resistant seal; - 19: slots; - 20: second tube; - 21: means of propulsion; - 22: means of rotation; - 23I-234: antenna sections; - 24: upper part of antenna; - 25: lower part of antenna; - 26: sealing plug; - 27, 27i, 272: inflatable shutter; - 28: pipe; - 29: wire mesh disc; - 30: direction of microwave injection; - 31: drilling; - E1: drilling; - E2: antenna insertion; - E3: adjustment; - E4A: microwave emission; - E4B: fluid injection; - E5: temperature monitoring; - E6: end of processing. List of documents cited Patent documents

[0103] For the record, the following patent documents are cited: - patcitt: US10137486; - patcit2: CN203343163; - patcit3: US5076727; - patcit4 : CN111360055. Non-patent literature

[0104] For the record, the following non-patent elements are cited: - nplcitl: Dog, Yi-Chi. 2012. “Field study of in situ remediation of petroleum hydrocarbon contaminated soil on site using microwave energy”. Journal of Hazardous Materials 199: 457-61; - nplcit2: Davarzani, H., Cochennec, M., Djigo, OA, Menard, Y. and S. Colombano. 2022. « Influence of water saturation and soil properties on the removal of organic pollutants using microwave heating », Journal of Contaminant Hydrology 251 : 104095; - nplcit3 : Dawei, Li, Yaobin Zhang, Quan Xie, et Zhao Yazhi. 2009. « Microwave thermal remediation of crude oil contaminated soil enhanced by carbon fiber ». Journal of Environmental Sciences 21 (9): 1290-95; - nplcit4 : Falciglia, Pietro P, Guido De Guidi, Alfio Catalfo, et Federico GA Vagliasindi. 2016. « Remediation of soils contaminated with PAHs and nitro-PAHs using microwave irradiation ». Chemical Engineering Journal 296: 162-72; - nplcit5 : Falciglia, Pietro P, Giuseppe Urso, et Federico GA Vagliasindi. 2013. « Microwave heating remediation of soils contaminated with diesel fuel ». Journal of Soils and Sediments 13 (8): 1396-1407; - nplcit6 : Falciglia, PP, Scandura P., Vagliasindi FGA. 2018. « Modelling and preliminary technical, energy and economic considerations for full-scale in situ remediation of low-dielectric hydrocarbon- polluted soils by microwave heating (MWH) technique». J Soils Sediments 18: 2350-2360; - nplcit7 : Horikoshi, Satoshi, Masaru Muratani, Kouta Miyabe, Keisuke Ohmura, Tomoaki Hirowatari, Nick Serpone, et Masahiko Abe. 2011 . « Influence of humidity and of the electric and magnetic microwave radiation fields on the remediation of TCE-contaminated natural sandy soils ». Journal of oleo science 60 (7): 375-83; - npIcitS : Kawala, Zdzislaw, et Tomasz Atamahczuk. 1998. « Microwave-enhanced thermal decontamination of soil ». Environmental science & technology 32 (17): 2602-7; - nplcit9 : Kingston, Jennifer T, Paul R Dahlen, Paul C Johnson, Eric Foote, et Shane Williams. 2010. « Critical evaluation of state-of-the-art in situ thermal treatment technologies for DNAPL source zone treatment ». ENVIRONMENTAL SECURITY TECHNOLOGY CERTIFICATION PROGRAM OFFICE; - nplcitl 0 : Liu, Xitao, Qing Zhang, Guixiang Zhang, et Ran Wang. 2008. « Application of microwave irradiation in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil ». Chemosphere 72 (11 ): 1655-58; - nplcitl 1 : Pauli, M, T Kayser, et W Wiesbeck. 2006. « A novel antenna design for soil decontamination with microwaves ». In Proceedings of the GeMiC, German Microwave Conference, Karlsruhe, Germany; - nplcitl 2 : Regan, AH, WT Roybal, R Ortega, M Palomares, DE Rees, et D Tischler. 1996. « In situ RF / microwave remediation of soil experiment overview ». Los Alamos National Lab.(LANL), Los Alamos, NM (United States); - nplcitl 3 : Robinson, John, Eleanor Dinner, Abdul Saeid, Mohammed Al-Harahsheh, et Sam Kingman. 2014. « Microwave processing of oil sands and contribution of clay minerals ». Fuel 135: 153-61 ; - nplcitl 4 : Sayakhov, F. 1980. « Particular properties of filtration and fluid flow under the influence of high-frequency electromagnetic field ». Joint University Scientific Book; - nplcitl 5 : Spencer, HL. 1987. « Electromagnetic Oil Recovery Ltd ». Calgary, Canada; - nplcitl 6 : Yuan, Songhu, Meng Tian, et Xiaohua Lu. 2006. « Microwave remediation of soil contaminated with hexachlorobenzene ». Journal of hazardous materials 137 (2): 878-85.

Claims

Demands

1. Soil thermal treatment device comprising: a. a microwave energy source (11, 12) configured to generate microwaves; b. at least one cylindrical microwave antenna (10i, 2) connected to the microwave energy source and configured to be inserted substantially vertically into a soil to be treated, said at least one cylindrical microwave antenna having a plurality of openings (19) for the emission of said microwaves generated in said soil to be treated; c. fluid injection means (13) configured to be connected to the upper part of said at least one cylindrical antenna and to inject said fluid into said soil to be treated through said plurality of openings (19) concomitantly with said emission of said microwaves; d. at least one fiber optic temperature sensor configured to be inserted in said at least one cylindrical antenna; e.adjustable means for sealing at least partially of at least a lower part (25) of said at least one antenna.

2. A soil heat treatment device according to claim 1, characterized in that said adjustable sealing means comprise: - a sheath (17) configured to slide over an outer wall of at least one lower portion (25) of said at least one antenna; and - a heat-resistant sealing gasket (18) configured to be interposed between an upper end of said sheath and said outer wall of the antenna.

3. Soil heat treatment device according to claim 1, characterized in that said at least one cylindrical microwave antenna comprises a first cylindrical tube (15i) of circular cross-section having said plurality of openings and a coaxial core (152) to said first tube, and in that said adjustable sealing means comprise a second tube (20) forming a sheath for at least a lower part of said first tube.

4. Soil heat treatment device according to claim 3, characterized in that said adjustable sealing means comprise means for pushing said second tube on said first tube to close all or part of said plurality of openings.

5. Soil heat treatment device according to claim 3 or 4, characterized in that said second tube (20) has a plurality of openings corresponding to said plurality of openings of said first tube, and in that said adjustable sealing means comprise means for rotating said second tube on said first tube to pass from an open position in which said openings of said first and second tubes are opposite each other to a closed position in which a solid wall of said second tube closes said openings of said first tube, and vice versa.

6. A soil heat treatment device according to claim 1, characterized in that said adjustable sealing means comprise: - a sheath covering an outer wall of at least a lower portion (25) of said at least one antenna; and - at least one inflatable shutter (27) configured to be secured between said lower part (25) and said upper part (24) of said at least one antenna.

7. Soil heat treatment device according to claim 6, characterized in that said adjustable sealing means also include at the base of said at least one inflatable plug a flexible mesh disc (29) of diameter adapted to the diameter of a borehole (31) into which said soil heat treatment device is inserted.

8. Soil thermal treatment device according to any one of claims 1, 2, 6 and 7, characterized in that said at least one cylindrical microwave antenna has a rectangular cross-section and in that said openings (19) are positioned on two faces opposite said cylindrical antenna of rectangular cross-section for bidirectional emission of said microwaves generated in said soil to be treated.

9. Soil heat treatment device according to any one of claims 1 to 8, characterized in that it also comprises a refractory material casing (14) configured to surround at least a portion of said cylindrical microwave antenna.

10. Soil thermal treatment device according to any one of claims 1 to 9, characterized in that said fluid injection means (13) are connected to a hot air outlet from said microwave energy source (11, 12) to inject said hot air into said soil to be treated.

11. A method for thermally treating soil comprising a water-saturated lower zone (Z2) and an unsaturated upper zone (Z1) by means of a soil thermal treatment device according to any one of claims 1 to 13, said method comprising the steps of: a. drilling (E1) said soil from a soil surface to at least said lower zone; b. inserting (E2) into said drilling of said at least one cylindrical microwave antenna; c. adjusting (E3) said adjustable sealing means to seal at least a lower portion of said at least one antenna intended to be immersed in said upper saturated lower zone; d. generating microwaves by said microwave energy source and emitting (E4A) said generated microwaves through said openings of said antenna into said upper and lower zones of said soil to be treated; e.concomitant injection (E4B) of fluid into said soil to be treated through said openings of an upper part of said at least one antenna positioned in said unsaturated upper zone; f. measurement (E5) of temperature in said lower and upper parts of said at least one antenna by means of said at least one fiber optic temperature sensor of said device; g. interruption (E6) of microwave emission when the temperature measured in said lower and / or upper parts reaches a determined processing temperature setpoint for a determined time.

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