Device and method for in-situ floor heating using microwaves

Abstract

The invention relates to a soil thermal treatment device comprising: a microwave energy source (11, 12) configured to generate microwaves; a cylindrical microwave antenna (101, 102) connected to the microwave energy source and inserted substantially vertically into the soil to be treated, the antenna having a plurality of openings for the emission of the generated microwaves into the soil to be treated; fluid injection means (13) connected to the upper part of the antenna for injecting the fluid into the soil to be treated through the openings concurrently with the emission of microwaves; at least one fiber optic temperature sensor inserted in the antenna; and adjustable means for at least partially sealing at least a lower portion of the antenna. Abstract figure: Figure 1

Description

Title of the invention: 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 relates in particular, but not exclusively, to 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 favour of environmental protection and the fight against soil artificialization, and framed, at least in France and Europe, by numerous regulatory constraints, making soil remediation mandatory at the end of the occupation of a site.

[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 the behavior of each component individually during a remediation operation. Furthermore, industrial and technological developments 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 a good soil remediation method that offers general, rather than specific, effectiveness.

[0005] The most advantageous soil remediation techniques are those that can be implemented in situ to treat pollutants directly and without excavation. This avoids the costs of transport and 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 consists of raising the temperature of the polluted soil, with or without excavation, in order to obtain Vaporization / destruction of the pollutant. This method is suitable for treating many organic pollutants (volatile, semi-volatile, or 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 be treated, 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 time can be very long. Second, the heating is generally not uniform in 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 possible reactions between water vapor and the pollutant, etc.).

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

[0010] To overcome this drawback, it has been proposed to use an in situ heating technique using microwaves [Chien, Yi-Chi, 2012, “Field study of in situ remediation of petroleum hydrocarbon contaminated soil on site using micro wave 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; Falciglia, PP, Scandura P., Vagliasindi FGA, 2018, “Modeling 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 rapidly and more homogeneously than conventional techniques: for many years, they have been a means of rapid and energy-efficient heating. Microwaves can be defined generally 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 different types of pollutants in various soil compositions, by varying the experimental conditions in terms of microwave frequency, applied power, treatment time, soil water content, design and structure of the microwave-generating antenna, or by testing mixtures (soils with added microwave absorbers, etc.). However, most laboratory studies have been conducted 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 they received the maximum amount of radiation without taking losses into account, 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 efficient microwave soil heat treatment technique that can be used in situ.

[0014] US patent document 10,137,486 B1 describes a technique for heat-treating 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 for directing microwaves, with a frequency between 0.1 and 10 GHz, through the soil sample to be treated. When the Slow combustion is initiated in the sample, microwave irradiation is stopped, and a flow of oxidizing gas is then injected to maintain and propagate this combustion in the sample.

[0015] This interesting technique, however, is only suitable for treating porous media, which may consist of natural soil, mud, drilling cuttings, 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 surface 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 may be able to develop into biofilms that provide support and protection for other colonies or species of microorganisms.Depending on the biological growth present, boreholes may require disinfection, often more difficult in the presence of biofilms, before they can be 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 advantageous for treating thermal water wells (thermal springs, etc.) and water intended for bottling, which is generally not permitted to be 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 a soil to be treated, the cylindrical microwave antenna(s) having a plurality of openings for the emission of microwaves generated in 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 fiber optic temperature sensor configured to be inserted into the cylindrical antenna(s); e. adjustable means for at least partial sealing of 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 this 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 of the soil from a soil surface down to at least the lowest zone; a. insertion into the borehole of the cylindrical microwave antenna(s); b. adjustment of the adjustable sealing means to seal at least a lower part of the antenna intended to be immersed in the lower area saturated at the top; c. 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 areas of the ground to be treated; d. 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; e. temperature measurement in the lower and upper parts of the antenna using the optical fiber temperature sensor(s) of the device; f. interruption of microwave emission when the temperature measured in the lower and / or upper parts reaches a setpoint value of processing temperature for a specified 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 means 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] The 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 means 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 heat 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 enclosure 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 outlet 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 a lower end of the cylindrical antenna. Brief description of the drawings

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

[0035] [Fig-1] shows an example of the use of a heat treatment device according to a method of implementation. Fig. 2

[0036] [Fig.2] illustrates a first example of the realization of a cylindrical microwave antenna with a circular cross-section according to an 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. Fig. 6

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

[0042] [Fig.7] shows an example of use of the device of [Fig.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 an embodiment. Fig. 9

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

[0045] [Fig. 10] illustrates the impact of adding a microwave-absorbing material (slate powder) casing to the device according to one embodiment. Description of embodiments

[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 borehole. Such a device is illustrated schematically in [Fig.1].

[0047] Figure 1 illustrates an in situ application of such a device for the thermal treatment of soil comprising an upper zone Z1 not saturated 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 the zones Z1 and Z2 may be polluted, or may require disinfection by thermal treatment, for example, to induce the evaporation of organic pollutants present in the soil or in the water table, or to destroy ubiquitous microorganisms (viruses, bacteria, etc.) that may be present as a biofilm in the water table Z2.

[0048] To carry out this thermal treatment, a cylindrical microwave antenna is inserted substantially vertically into the soil to be treated, more or less deeply, depending on whether it is desired to treat only the high zone ZI or the high zone ZI and low 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 is, for example, 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 [Fig. 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 power source, comprising, for example, a generator 11 and a magnetron 12. The generator 11, which can, for example, deliver a maximum power of 8 kW (modulatable between 0.25 and 8 kW), provides the necessary electrical power to the magnetron 12 to generate microwaves, at a frequency of, for example, 2.45 GHz. The antenna is, for example, connected to the magnetron 12 after a waveguide bend (90° angle), thus allowing it to be fixed 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, concurrently with the microwaves generated by the magnetron 12, through the openings in the lower portion 102 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] Coupling the air injection 13 and microwave heating thus advantageously increases the heating radius. Indeed, injecting air from inside the antenna to the outside via the slots located in the lower portion 102 of the antenna optimizes the transfer and diffusion of the heat accumulated from the area adjacent to the antenna to more distant, and therefore cooler, areas.

[0054] In one embodiment, two air injection valves are installed on top of the antenna to allow connection of a compressed air supply. A ball flow meter measures the injected air flow rate, which is between 4 and 50 L / min and adjustable 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 (for example, slate powder) configured to surround the heating portion 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 an 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 envelope material can be absorbent (high emissivity) and / or refractory (high thermal inertia) depending on the application and the desired temperature. These two types of materials have the capacity either to absorb microwave energy (absorbent material) or to retain and diffuse the heat generated by microwaves (refractory material). One can, in particular, imagine 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 made 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 makes it possible to accelerate temperature increases at the start of heat treatment, to increase the heating temperature, and to absorb heat in order to extend the heating time. Furthermore, the use of Natural microwave-absorbing materials such as slate are advantageous because they have 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 of [Fig.1], the envelope 14 is shown which covers only the lower portion 102 of the antenna located in the upper zone ZI: this envelope can be of variable height according to the needs and cover all or part of the heating part 102 of the antenna.

[0061] Figure 2 illustrates a first example of the realization of such a microwave antenna. A cylindrical, circular-section coaxial microwave antenna is formed by a 2-meter-long, 5-cm-diameter aluminum immersion tube 15i and a concentric inner rod 152 with a diameter of 0.9 cm, as illustrated in more detail in [Fig. 2] (part (a) for an exploded view and part (b) for an assembled, ready-to-use view). The tube 151 has slots along its lower portion, extending for a length of approximately 1 m. In one embodiment, glass wool is used to cover the antenna slots to prevent porous material from zone ZI (e.g., sand) from entering the tube 15b, while allowing microwaves and air to pass from the inside to the outside of the tube. The glass wool is impermeable to sand but permeable to microwaves and air. The 15i dip tube terminates, at its upper part, with a flange referenced 156.

[0062] As can be seen in [Fig. 2], the dip tube 15i terminates at its lower end with a conical tip 154 ​​covered by a disc 155. These elements can form a sealing plug at the bottom of the antenna. The plate referenced 153, preferably made of stainless steel or aluminum, and the sponge-shaped metal gaskets referenced 157, 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 embodiment (illustrated, for example, in [Fig. 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: since the slots are positioned on two opposite faces of the antenna, the wave propagation is bidirectional. Such a bidirectional rectangular antenna design advantageously reduces energy losses by approximately 25% compared to the coaxial antenna design of [Fig. 2].

[0064] Indeed, initial tests carried out by the inventors on the waves emitted and reflected by the coaxial antenna of [Fig. 2] demonstrate a significant energy loss of 25%, probably due to the change in cross-section between the waveguide at the magnetron output (rectangular) and the coaxial antenna (circular). The use of a rectangular antenna advantageously avoids this change in cross-section between the magnetron output 12 and the antenna and optimizes the emitted-to-reflected power ratio.

[0065] It is clear from reading 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] Various embodiments of such a soil thermal treatment device are therefore presented below, in relation to Figures 3 to 7. These devices also include 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 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 [Fig. 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 [Fig. 2].

[0068] In [Fig. 3], only the lower portion 102 of the antenna is shown in a perspective view for illustrative purposes. Slots 19 are provided on one of the two visible faces of this lower portion 102 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 102 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 provided 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 forming 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 optic sensor advantageously enables continuous temperature measurements, even during the microwave emission phase.

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

[0073] In this second embodiment, the lower portion 102 of the antenna (i.e., 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 [Fig. 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 [Fig. 4], a fiber optic sensor inserted into the antenna body is also provided, which can be protected by a Teflon® sheath 16.

[0074] In a first embodiment, 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 15b to close all the openings 19 submerged in the water-saturated zone Z2.

[0075] In a second embodiment, 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 plunger tube 15i. In an open position, the slots of the second tube 20 overlap the slots 19 of the plunger tube 15i. The rotation means 22 allow, for example, the second tube 20 to be rotated a quarter turn, to place it in a sealing position, in which a solid wall of the second tube 20 seals the slots 19 of the plunger tube 15i, the slots of the second tube 20 and the plunger tube 15i no longer being 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 ZI or in zone Z2 of the soil to be treated.

[0076] In the second embodiment of [Fig.4], the sealing 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] It would of course also be possible to 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 soil to be treated.

[0078] A third embodiment of adjustable means for sealing the lower part of the antenna is now presented in relation to Figures 5 to 7.

[0079] Fig. 5 shows an exploded view of the antenna, for example the circular cross-section coaxial microwave antenna of Fig. 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, referenced 231 to 234, are shown: two initial antenna sections 231-232, which, after assembly, form an upper antenna portion 24 intended to be placed in the upper zone Z1 of the soil to be treated, and two antenna sections 233-234, which, after assembly, form a lower antenna portion 25 intended to be placed 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 in the lower zone Z2, but 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 the adjustable sealing means but can also be considered for the first embodiment of [Fig.3] or the second embodiment of [Fig.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 [Fig. 2] (the upper 24 and lower 25 portions of the antenna form the lower portion, referenced as 102, of the antenna in [Fig. 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 of [Fig. 3], i.e., by positioning a sliding Teflon "sock" 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 antenna portion 25 and the upper antenna portion 24. It can be inflated by means of a hose, shown schematically, and bearing the reference numeral 28. This hose 28 is, for example, connected to a compressor and the pressure is controlled by a pressure gauge.

[0084] Inflatable plugs 27b 272 of different lengths and diameters can be used, as illustrated for example in [Fig.6]. In particular, it is 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 [Fig. 7]). Such a disc 29 prevents microwaves from traveling back up through the borehole 31.

[0086] In [Fig. 5], two sheaths, referenced 16i and 162, containing are also shown Each has an optical fiber for temperature control. The sheath referenced 16i is inserted into the hollow body of the first section 231 of the upper part 24 of the antenna; the sheath referenced 162 is crimped into the hollow body of the first section 233 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] The elements referenced 24, 25 and 27 have the same inner diameter. The different elements are preferably screwed together via an external sealed sleeve to maintain the same 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 zone Z1 of the soil 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 ZI; - 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 one embodiment, 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 borehole for example, according to the process described below in relation to [Fig.8].

[0093] In a first step referred to as El, 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 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 soil configuration, and in particular the respective depths of the unsaturated Z1 and saturated Z2 zones at the top, the adjustable sealing means for 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 embodiment of these adjustable sealing means, a Teflon sleeve is slid onto the lower part of the antenna to close the slots ([Fig.3]), or the position (height and / or orientation) of a second tube surrounding the lower part of the antenna is adjusted ([Fig.4]), or an inflatable plug is inflated and positioned at an intermediate zone Z3 between the high unsaturated zone ZI 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 antenna slots and fluid injection (step E4B), preferably hot air, is performed. The microwaves are emitted through the antenna slots, whether or not they are sealed by a Teflon® sheath or sleeve, thus both in the upper unsaturated zone Z1 and in 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 by the second tube.

[0096] Thanks to fiber optic temperature sensors, the temperature is monitored, during a step referenced E5, at the level of the different portions of the antenna. 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 terminated (step referenced 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 the 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 of [Fig. 9](b), a (dry) airflow 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 ​​action and thus covering a larger volume for thermal desorption.In this study, the injected air was at room temperature (16°C). However, the use of 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, ...), 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 covered 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 (Fig. 10(c)) and for the area without slate (Fig. 10(d)). As can be seen, the addition of slate resulted in a considerable increase in temperature, which approximately 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 particularly in the field of soil remediation, and especially the disinfection of water wells, but also for other in-situ soil heating applications. For example, they could be used for oil recovery in underground reservoirs. These wide-ranging applications highlight the potential versatile and the relevance of this technology in different industrial and environmental fields. List of reference signs

[0102] - High portion of antenna; - 102: lower portion of antenna - 11: generator; - 12: magnetron; - 13: means of fluid injection; - 14: refractory material casing; - ZI: 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; - 156: bridle; - 157: metal joint; - 16, 16i, 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; - 23r234: 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; - El: 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 avoidance of doubt, the following patent documents are cited: -patcitl: US 10137486; - patcit2: CN203343163; - patcit3: US5076727; -patcit4:CNl 11360055. Non-patent literature

[0104] For the avoidance of doubt, 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, O. A., Ménard, Y. et 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 Sédiments 13 (8): 1396-1407; - nplcitô : Falciglia, PP, Scandura P., Vagliasindi FGA. 2018. « Modelling and preliminary technical, energy and économie considérations for full-scale in situ remediation of low-dielectric hydrocarbon-polluted soils by microwave heating (MWH) technique». J Soils Sédiments 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 micro wave radiation fields on the remediation of TCE-contaminated natural sandy soils ». Journal of oleo science 60 (7): 375-83; - nplcit8 : Kawala, Zdzislaw, et Tomasz Atamanczuk. 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 évaluation of state-of-the-art in situ thermal treatment technologies for DNAPL source zone treatment ». ENVIRONMENTAL SECURITY TECHNOLOGY CERTIFICATION PROGRAM OFFICE; - nplcitlO : 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 Micro wave Conférence, Karlsruhe, Germany; - nplcitl2 : 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); - nplcitl3 : Robinson, John, Eleanor Binner, Abdul Saeid, Mohammed Al-Harahsheh, et Sam Kingman. 2014. « Microwave processing of oil sands and contribution of clay minerais ». Fuel 135: 153-61; - nplcitl4 : Sayakhov, F. 1980. « Particular properties of filtration and fluid flow under the influence of high-frequency electromagnetic field ». Joint University Scientific Book; - nplcitl5 : Spencer, HL. 1987. « Electromagnetic Oil Recovery Ltd ». Calgary, Canada; - nplcitlô : 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 heat treatment device comprising: a. a microwave energy source (11, 12) configured to generate microwaves; b. at least one cylindrical microwave antenna (10i, 102) 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. means (13) for injecting fluid configured to be connected in 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 into said at least one cylindrical antenna; e. adjustable means for sealing at least partially at least one lower part (25) of said at least one antenna.

2. 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 a lower part (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. 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 one lower part (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 (El) of said soil from a surface of the soil down to at least said low zone; b. insertion (E2) in said borehole of said at least one cylindrical microwave antenna; c. adjustment (E3) of said adjustable sealing means to seal at least a lower part of said at least one antenna intended to be immersed in said lower zone saturated at the top; d. generation of microwaves by said microwave energy source and emission (E4A) of said microwaves generated through said openings of said antenna in said upper and lower areas 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 the said lower and upper parts of said at least one antenna by means of said at least one optical fiber temperature sensor of said device; g. interruption (E6) of microwave emission when the temperature measured in said lower and / or upper parts reaches a setpoint value of processing temperature determined for a determined time. 23