Device and method for characterizing a soil heat treatment process

Abstract

This disclosure relates to a device (1) for characterizing a soil heat treatment process, which comprises: A cylindrical lysimeter (10) having watertight side walls, open at its upper base, and whose lower base forms a watertight wall inclined with respect to the horizontal and having an opening equipped with a valve; A water pump (16) configured to inject and / or drain water into the lysimeter through the valve; A removable heating device (18) configured to be inserted vertically into the lysimeter through its open upper base, in a central area relative to the side walls; A three-dimensional array of temperature sensors (191-192) comprising at least one fiber optic sensor, the sensors being placed at different heights, radial distances, and angular positions within the lysimeter; Means for recording the temperatures measured by the sensors. Abstract figure: Figure 2.

Description

Title of the invention: Device and method for characterizing a soil heat treatment process. Technical field

[0001] This disclosure falls within the field of soil remediation, and more specifically, the thermal treatment of soils for remediation purposes. This disclosure relates in particular, but not exclusively, to a technique for characterizing a soil thermal treatment process, in order, for example, to evaluate its effectiveness, energy consumption efficiency, or to determine its optimal parameters. 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 causing The method involves raising the temperature of the contaminated soil, with or without excavation, to vaporize 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 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 very 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 microwave heating technique [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; 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 quickly and more homogeneously than conventional techniques: for many years they have been a means of rapid and energy-efficient heating.

[0011] Microwaves can be generally defined as all electromagnetic radiation with a frequency between 300 MHz and 300 GHz. However, not all materials can be heated by microwaves. Depending on their behavior with respect to electromagnetic waves, there are three groups of materials: (i) conductors, which reflect waves; (ii) insulators, which allow waves to pass through them; and (iii) absorbers, also called dielectric materials, which absorb waves.

[0012] This has led the scientific community to undertake numerous experiments in recent years 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 absorbents, etc.). The results are numerous and varied, reflecting the complexity of adapting a thermal desorption remediation technique to the specific conditions encountered in the field, related to the cocktail of pollutants present on site and the very composition of the soil in which they are dispersed, as well as its water content.

[0013] Thus, while microwaves are known and described in the literature as an effective technique for treating various types of pollutants, 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.

[0014] 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 remediation [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], all three of which have shortcomings in terms of experimental data regarding the evolution of temperature in the soil (absence of measurements or incomplete measurements, too small an excursion range, etc.).

[0015] In conclusion, despite the promising nature of microwave treatment, current industrial soil heating techniques for remediation rely primarily on the use of heating needles. At the laboratory or pilot scale, tests have been carried out with microwave ovens (laboratory scale) or waveguides (pilot site scale). However, it remains very difficult to accurately and reliably evaluate these different soil heating techniques and to compare them with one another.

[0016] There is therefore a need for a technique that allows for the precise characterization of the capabilities of a soil thermal treatment method under pilot-scale conditions. In particular, there is a need for such a technique that allows for the introduction of full-scale thermal desorption antennas to determine energy consumption and technical efficiency of a thermal antenna (scattering radii, temperature profiles, temperature rise, maxima obtained, heating over time, etc.) or to perform a comparison of methods under identical conditions (e.g., conventional heating element vs. microwave antenna).

[0017] There is still a need for such a technique which allows comparison of different operating conditions (e.g. dry soils, wet soils, ...) or different soil compositions (sands, clays, mixtures with absorbents, ...), or which allows determination, at scale 1, of the depollution capacities of a soil artificially polluted with a compound of interest or a cocktail of pollutants.

[0018] Finally, there is a need for such a technique that allows for the sizing of a pollution treatment operation before its implementation in the field (choice of microwave frequencies / powers to be used, laboratory pre-tests, heating time, ...). Summary

[0019] The present disclosure addresses these needs by proposing a device for characterizing a soil thermal treatment process, which includes: a. A cylindrical lysimeter comprising watertight side walls, open at its upper base, and whose lower base forms a watertight wall, inclined with respect to the horizontal and having an opening equipped with a valve; b. A water pump configured to inject and / or drain water into the lysimeter through the valve; c. a removable heating device configured to be inserted vertically into the lysimeter through its open upper base, in a central area relative to the side walls; d. a three-dimensional array of temperature sensors comprising at least one optical fiber temperature sensor, the sensors being placed at different heights, radial distances and angular positions within the lysimeter; e. means of recording the temperatures measured by the sensors of the three-dimensional network.

[0020] According to another aspect, a method for characterizing a soil heat treatment process is proposed using a device described above, which comprises the following steps: i. Insertion of the removable heating device through the open upper base of the lysimeter and positioning of the heating device on a central support; ii. Filling a lower portion of the lysimeter with a drainage material; iii. Provision of a membrane layer covering the drainage material; iv. Until the lysimeter is completely filled, alternate the following steps: a. Filling the lysimeter with a layer of material constituting the soil to be treated up to a determined height and, optionally, injecting water into the lysimeter; b. Placement, at the determined height, of temperature sensors of the sensor network in a set of determined radial positions; v. Optional gravity drainage of residual water contained in the lysimeter via the valve; vi. Heating of the heating device for a determined heating time and continuous recording at determined time intervals of the temperatures measured by the temperature sensors of the three-dimensional sensor network; vii. Establishment of a temperature map within the lysimeter as a function of time from the recorded temperatures, the temperature map characterizing the soil treatment process by thermal desorption.

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

[0022] The three-dimensional sensor network comprises a first set of optical fiber temperature sensors arranged near the heating device and a second set of thermocouple temperature sensors arranged at a distance from the heating device.

[0023] The three-dimensional sensor network is structured as a set of superimposed sensor layers located at different heights within the lysimeter. A sensor layer has a star-shaped structure comprising at least three angularly spaced branches extending from the central area of ​​the lysimeter to the lateral walls, each branch comprising a plurality of sensors spaced from each other in a radial direction.

[0024] Within a layer, a surface density of sensors decreases from the central area of ​​the lysimeter towards the lateral walls.

[0025] The branches of the star structure are spaced angularly so as to cover an angular sector of the lysimeter substantially equal to 90°.

[0026] The walls of the lysimeter are formed from a microwave-proof material.

[0027] The device also includes a microwave leak detector.

[0028] The removable heating device belongs to the group comprising: • A conduction heating device (including, for example, a heating needle); • A heating device using hot fluid injection; • A microwave heating device (including, in particular, a microwave antenna).

[0029] The device also includes means for measuring soil moisture by time-domain reflectometry.

[0030] The device also includes a buffer tank connected to the water pump and means for powering the water pump (for example a 24V battery with adjustable voltage).

[0031] The device also includes a central support within the lysimeter intended to receive the removable heating device.

[0032] The device also includes, when the removable heating device is a microwave heating device, air injection means connected to the upper part of the microwave heating device. Brief description of the drawings

[0033] Other features, details and advantages will become apparent from reading the detailed description below and from analyzing the accompanying drawings, in which: Fig. 1

[0034] [Fig-1] presents a perspective view of the device for characterizing a soil thermal treatment process, according to one embodiment. Fig. 2

[0035] [Fig.2] illustrates a synoptic diagram of the device for characterizing the [Fig.1], according to a particular embodiment. Fig. 3

[0036] [Fig.3] presents a view of the device of [Fig.2], according to a main section. Fig. 4

[0037] [Fig.4] presents a cross-sectional view of the device of [Fig.2], in a horizontal plane. Fig. 5

[0038] [Fig.5] presents an example of the removable heating device and associated equipment, according to a particular embodiment. Fig. 6

[0039] [Fig.6] illustrates a view of the upper part of the device of [Fig.1] in which the removable heating device is a microwave antenna, according to one embodiment. Fig. 7

[0040] [Fig.7] illustrates a view of the upper part of the device of [Fig.1] in in which the removable heating device is a heated needle, according to one embodiment. Fig. 8

[0041] [Fig.8] presents in flowchart form the different stages of the process of characterization implementing the device of figures 1 to 7, according to one embodiment. Fig. 9

[0042] [Fig.9] illustrates the temperature curves obtained after antenna heating microwave within the device of [Fig.1], according to one embodiment. Fig. 10

[0043] [Fig. 10] presents the temperature maps within the device of [Fig.1] established to compare a soil treatment process based on a microwave antenna and a soil treatment process using a heating needle, according to one embodiment. Description of the implementation methods

[0044] The general principle of the present disclosure lies in the design of an experimental device of the instrumented lysimeter type, allowing to characterize, at scale 1, different processes of thermal treatment of soil, thanks to a continuous recording of temperatures in the whole volume of the lysimeter.

[0045] An example of the realization of such an experimental device is now presented in relation to the figures.

[0046] Figure 1 shows a perspective view of such a device 1, which includes a cylindrical lysimeter 10. A lysimeter is a device used to study and measure the evolution of water in soil, most often in the form of a cylinder open at the surface and filled with the soil to be tested. In one embodiment, this cylinder is a cylinder of revolution, having an internal diameter of 1 m and a height of 2 m. These dimensions allow for a full-scale characterization of soil thermal treatment processes.

[0047] In one embodiment, the lysimeter 10 is made of a microwave-proof material, for example stainless steel, to secure the environment of the device 1 when it is used to test a microwave soil treatment process, by preventing microwaves from passing through the side walls of the lysimeter 10. It is indeed important to avoid exposing operators to waves that are potentially harmful to their health.

[0048] Although not visible in [Fig. 1], the upper base 11 of the lysimeter 10 is open to ambient air; its lower base is solid and forms a watertight wall, which has a slight slope relative to the horizontal, for example on the order of 2%, to allow fluids to drain by gravity. At the end of this slope, an opening in the bottom of the lysimeter is closed by a double valve 12 located at the end of a branch 13 in the side wall of the lysimeter 10. This double valve 12 serves as an inlet / outlet for water, in order to vary the water saturation in the soil.

[0049] Indeed, the moisture content in the soil is an important parameter influencing the effectiveness of thermal desorption techniques. Thus, while soil moisture negatively impacts conventional thermal desorption by conduction or convection, conversely, the soil decontamination efficiency of microwaves increases with the moisture content. It is therefore important to be able to vary the moisture content of the soil contained in the lysimeter 10 for a complete characterization of the soil treatment process under study.

[0050] In one embodiment, a 60L tank serves as a buffer reservoir 14 allowing the controlled injection and drainage of water into the lysimeter 10. The water is, for example, injected by a water pump 16, powered by electrical supply means 17, which may take the form of an adjustable voltage battery, or even a generator, for example (illustrated in the block diagram of [Fig.2]).

[0051] Several ports referenced 15i to 155 are distributed on the side walls of the lysimeter 10, to allow the passage of the connectors associated with the various sensors, which will be described in more detail with figures 2 and following.

[0052] The lower part of the lysimeter 10 is preferably filled with a drainage material, for example coarse gravel, forming, for example, a layer approximately 10 cm high at the bottom of the column. This drainage material advantageously homogenizes the water inlet / outlet conditions in the column 10.

[0053] In one embodiment, this drainage material is covered with a membrane layer allowing it to be isolated and prevented from mixing with the soil to be treated which fills the upper part of the column of the lysimeter 10. It is thus easy to remove the soil sample studied, and replace it with another soil composition, without needing to replace the layer of drainage material, from which it remains isolated.

[0054] In one embodiment, the same porous medium, namely 99% quartz sand (0.7-1.3 mm), with a permeability of 285 ± 37 darcy units (measured) and a porosity of 35.5 ± 0.5% (measured), is used to test and characterize different soil heat treatment processes. This sand fills the lysimeter from the membrane layer separating it from the drainage material to a maximum column height. The composition of the medium (soil) can, of course, be modified depending on the experiment, particularly to compare the effect of the same heat treatment process on different soil compositions, such as those with varying sand or clay content.

[0055] In one embodiment, the imbibition of this sand is carried out with tap water, injected into the lysimeter 10 by the water pump, and the volume of water required to reach 100% saturation is approximately 500 liters.

[0056] The internal structure of device 1 will be better understood by reading the synoptic diagram in [Fig.2] and the section and cross-section views in Figures 3 and 4, and the associated description.

[0057] The interior of the lysimeter 10 is equipped with a three-dimensional array of temperature sensors. In the example of [Fig. 2], this 3D sensor array comprises a first set 19i of optical fiber temperature sensors, arranged in a central area of ​​the lysimeter 10, near the removable heating device, and a second set 192 of temperature sensors in the form of thermocouples. Alternatively, it is possible to use only optical fiber temperature sensors.

[0058] Unlike thermocouples, optical fiber sensors have the advantage of not generating interference when using microwaves, and therefore allow continuous temperature measurement, even during microwave emission, which allows for better accuracy and characterization of the soil treatment technique under study.

[0059] In one embodiment, the lysimeter 10 is equipped with a three-dimensional array of temperature sensors comprising thirty-seven type thermocouples The K-type probe from TC® SA and twenty-five WEIDMANN® optical fibers, which consist of a PTFE (polytetrafluoroethylene) coated glass fiber with a GaAs (gallium arsenide) crystal at the tip, are all non-metallic and therefore completely non-conductive. They offer complete immunity to radio frequency and microwave radiation, high-temperature operation, intrinsic safety, and non-invasive use. They are also designed to withstand harsh and corrosive environments. GaAs becomes optically translucent at a light wavelength of 850 nm. Since the band gap position is temperature-dependent, it shifts by approximately 0.4 nm / Kelvin. The measuring device includes a light source and a spectral band gap detection device. This ensures fast and repeatable measurements.

[0060] The manufacturer's stated accuracy is + / - 2.2 °C for thermocouples and + / - 0.2 °C for optical fibers. All temperature data are recorded every minute, for example, by a Campbell® temperature measurement system (associated with the 192 thermocouple sensors) and an Optocon® system (associated with the 19i optical fiber sensors). Two different software programs can be used to record the sensor temperature data: Fotemp Assistent 2® for the 19i optical fiber sensors and LoggerNet® for the 192 thermocouple sensors.

[0061] The organization and structure of this 3D network of temperature sensors will be better understood by reading Figures 3 and 4. Figure 3 illustrates the main section of device 1, the block diagram of which is given in Figure 2. Figure 4 is a horizontal cross-sectional view of this same device 1.

[0062] As can be seen, the temperature sensors are placed at different heights, radial distances from the axis of revolution of the lysimeter 10, and angular positions.

[0063] In an advantageous embodiment illustrated in [Fig. 4], all the sensors are placed in a single quarter of the column of the lysimeter 10, in order to reduce the number of sensors used, and therefore the costs of the device. Given the rotational structure of the lysimeter 10, and the fact that the removable heating device is placed in a central area coinciding substantially with the axis of rotation of the column, and allows heat to radiate in all radial directions from this axis of rotation, it is indeed possible to record temperature measurements only within an angular sector of approximately 90° from this axis of rotation. By extrapolation, it is then possible to reconstruct a temperature map over the entire volume of the lysimeter 10.

[0064] As illustrated in [Fig. 3], the removable heating device 18 is immersed in the column of the lysimeter 10 to a depth of approximately 150 cm from its upper base open. A layer of approximately 10cm of gravel is placed at the bottom of column 10, then completed with sand until reaching a height of 200cm of the column.

[0065] The three-dimensional sensor network is structured as a set of superimposed sensor layers located at different heights within the lysimeter 10. For example, a deep sensor layer is located 150 cm from the surface level and comprises three optical fiber sensors referenced F00, F01 and F02, and four thermocouples referenced T00, T01, T02 and T03. In the example of [Fig. 3], nine main temperature sensor layers are thus shown, each located at a distinct height within the column 10, and comprising a variable number of sensors, but at least one optical fiber sensor located in the immediate vicinity of the heating device 18 facing the slits.These nine main sensor layers are complemented by a layer of thermocouples labeled TB0 to TB3, located at the bottom of the lysimeter, and by a layer of thermocouples labeled TT0 to TT3, located near the top surface of the lysimeter. The latter allows for measuring the impact of the heating technique used on the ambient air temperature. These two upper and lower thermocouple layers thus enable the collection of temperature measurements throughout the entire volume of the column.

[0066] Preferably, in the nine main layers, the density of sensors per unit area is higher in the central zone of the lysimeter, near its axis of revolution and the removable heating device 18, for greater accuracy in analyzing the temperature rise capacity of the process under study. This density decreases as one moves away from the central zone towards the lateral walls of the column 10. On at least some layers, at least one temperature sensor, for example a thermocouple, is preferably placed in the immediate vicinity of the lateral wall of the lysimeter 10, in order to measure the temperature evolution at any point within the column's internal volume, up to its periphery.

[0067] The cross-sectional view of [Fig. 4] provides a better understanding of the structure of one of these sensor layers. It has a star-shaped structure comprising three angularly spaced branches extending from the central area of ​​the lysimeter 10 (near the heating device 18 and the axis of revolution of the column) to the side walls. A first branch comprises the fiber optic sensors referenced F30 to F33 and the thermocouples referenced T30 to T33; a second branch comprises the fiber optic sensors referenced F30' to F33' and the thermocouples referenced T30' to T33'; a third branch comprises the fiber optic sensors referenced F30" to F33" and the thermocouples referenced T30” to T33”. Thus, each branch comprises a plurality of sensors spaced from each other in a radial direction from the central area of ​​the lysimeter 10.

[0068] The sensors are connected to each other by a wired network providing them with the necessary power supply, and ensuring the transmission of measurement data to the recording means located outside the lysimeter 10. The lengths of cables interconnecting the sensors determine their relative distances, which facilitates their positioning within the lysimeter 10.

[0069] A different number of branches can of course be provided, for example four or five, depending on the desired compromise between the cost of the device and the accuracy of the measurement. Preferably, the two outermost branches are spaced at an angle of approximately 90°, as indicated above.

[0070] The experimental device 1 also includes a removable heating device 18, as well as the equipment associated with its operation. Such a removable heating device can take various forms. The following section describes an example of an embodiment in which the experimental device 1 is used to compare the efficiency and characteristics of a first soil treatment process based on a heating element (such as a heating resistor or a heating needle) and a second soil treatment process based on a microwave antenna.

[0071] The first soil treatment method uses a vertical heating element 18 in the form of a conventional Jeannot® electric heating rod made of stainless steel, 51 mm in diameter and 1.5 m long, with a power rating of 1000 W and a voltage of 230 V three-phase. This heating rod is equipped with a stainless steel outlet tube 13.5 mm in diameter and 120 mm long, and its sealing is ensured by a heat-shrink sleeve with resin. It can be fitted with a handling hook to facilitate its use. Insulation is provided by a 100 m roll of Superwool® mineral wool, and the high-voltage cable is a 3x2.5 mm MC-ECS cable, 5 meters long.

[0072] The second soil treatment method uses as a heating device 18, a round coaxial microwave antenna in the form of a 2 m long, 5 cm diameter slotted aluminum dip tube 18i and a concentric inner rod 182 with a diameter of 0.9 cm, as illustrated in more detail in [Fig. 5] (part (a) for an exploded view and part (b) for an assembled view ready for use). The tube 18i has slots on its lower part, over a length of approximately 1 m. In one embodiment, glass wool is used to cover the slots of the antenna to prevent sand from entering the tube 18i, while allowing microwaves to pass from the inside to the outside of the tube, the glass wool being sandproof but permeable to microwaves. In another embodiment, small holes The diameters are drilled at the bottom of the tube 18i to allow water to drain during the soaking / draining phase. The dip tube 181 terminates, at its upper part, with a flange referenced 186. This example of a heating device 18 is shown as an example in the block diagram of [Fig.2].

[0073] As can be seen in [Fig.5], the dip tube 18i terminates at its lower end with a conical tip 184 covered with a disc 185. The plate referenced 183, preferably made of stainless steel, and the metal seals referenced 187, in the shape of a sponge, are configured to prevent microwaves from rising to the surface, and thus preserve a safe environment around the experimental device 1.

[0074] In one embodiment, the microwave unit associated with the antenna consists of a power supply (generator 20) and a magnetron 21, illustrated in the block diagram of [Fig. 2]. The generator 20 can deliver a maximum power of 2 kW (modulatable power between 0.25 and 2 kW) and is connected to a magnetron 21 capable of emitting microwaves at a frequency of 2.45 GHz. The antenna 18 is, for example, connected to the magnetron 21 after a waveguide bend (90° angle), thus allowing it to be fixed in a vertical position.

[0075] In one embodiment, the experimental setup 1 also includes a 30 cm long TDR 22 probe (for Time Domain Reflectometry) (e.g., Campbell® Scientific CS650 model) which allows for real-time measurement of the soil water content during the imbibition / drainage phase at the sand surface. The water content data are recorded using the software used for thermocouple sensors (LoggerNet®). The manufacturer states the accuracy of the probe 22 to be + / - 3% of the measured value. The TDR 22 probe is, for example, placed at the top of the column and measures the average water content over a depth of 30 cm. Preferably, this probe 22 is used only during sand imbibition and drainage for microwave experiments due to the potential for wave interference.

[0076] Finally, a microwave leak detector is used during heating around column 10 and magnetron 21 to ensure that there are no leaks exceeding safety levels (5 W / m2).

[0077] In an optional embodiment, the upper part of the dip tube 18i is connected to an air injection device 23, for example, for hot air, by means of air injection valves allowing connection to a compressed air supply. Air is injected from the inside of the tube 18i to the outside, through slots located in its lower part. By coupling microwave heating and air injection, the transfer and diffusion of accumulated heat from the area adjacent to the antenna to more distant areas, at the periphery of the lysimeter 10, is optimized.

[0078] We now turn to describe, in relation to Figures 6 and following, an example of results obtained with the instrumented lysimeter 1, intended to compare the effectiveness of a soil treatment process using an electrical resistance type heating element 18 and using a round coaxial microwave antenna as illustrated in [Fig.5].

[0079] As illustrated in the flowchart of [Fig. 8], initially (step E1), the 18r 182 microwave coaxial antenna of [Fig. 5] was inserted inside the empty column 10, for example, onto a central support which could be in the form of a central brick pillar built into the lower part of the lysimeter 10. In a step E2, the column 10 was filled with gravel to a height of approximately 10 cm. The gravel layer was covered with a membrane layer to isolate it from the soil sample.

[0080] Steps E3 to E5 were repeated until the column 10 was completely filled, namely by alternating the deposit of a soil layer (e.g., sand, step E3) and the positioning of sensor layers (step E5). During this sand filling, water can optionally be added simultaneously (step E4) to obtain the most homogeneous filling possible. The sensors are placed (E5) as the column is filled, at predetermined radial positions.

[0081] When the column is full of sand (test E6), the water can be removed (E7) by gravity to reach saturation of the residual water in the sand.

[0082] Figure 6 illustrates a view of the upper base of the experimental device 1, into which a coaxial microwave antenna 18r 182 was inserted during step EL

[0083] Microwave heating is carried out during a step E8, during which the temperatures measured by the three-dimensional sensor network are continuously recorded, for example at predetermined time intervals on the order of minutes or tens of minutes.

[0084] After the microwave heating experiment, the microwave antenna 18r182 was carefully removed from the wet sand, and the heating element 18 was placed in the same position, as illustrated in [Fig. 7]. The experiments were carried out for at least 15 days to achieve a stable heating state.

[0085] Figure 9 illustrates the temperature curves obtained (step E9) over time during heating by microwave antenna 18i-182 at a depth of 105.3 cm from the top of the lysimeter 10. The curves are obtained from data measured by fiber optic sensors (F30 to F33) or thermocouples (T30 to T33) installed in a horizontal line around the antenna at various radial distances. Experimental results using this device 1 showed that the maximum temperature reached was 112.5°C, near the slots of antenna 18i-182. The temperature of 100°C was only achieved within a 6 cm radius around the 18 r182 antenna, during an experiment that lasted 9 days (of continuous heating).

[0086] For example, it can be observed that, thanks to this instrumented lysimeter device 1, it is possible to access the different temperature profiles generated over time and at different distances from the central heating element 18, all along the same horizontal radial line. The acquisition allows us to: • Know the temperature reached at each point of the lysimeter 10, as a function of the distance to the heating element 18, the diffusion being variable depending on the soils and the heating technology used; • Observe the heat diffusion and the maximum temperature reached: diffusion profiles, time required to reach the maximum temperature; • Evaluate the necessary treatment time, size a treatment operation: T° / duration / distance / pollutant(s).

[0087] As mentioned previously, this device 1 also allows for the comparison of two different underfloor heating techniques. Figure 10 shows the temperature maps generated during step E9 (Fig. 8) for the two heating techniques being compared: the heating element 18 (Fig. 7 and Fig. 10(a)) and the microwave antenna 18r 182 (Fig. 6 and Fig. 10(b)) after 16 days of heating. The temperature maps are interpolated from the temperature sensors in column 10, with distances normalized by the column radius (1 m).

[0088] From these temperature profiles, it can be observed, for example, that the electric heating method allows a high temperature to be reached near the heating element 18, but that this temperature decreases more rapidly with radial distance. The temperature isotherms obtained with the microwave method clearly show better horizontal heat diffusion. The temperature maps also show that the vertical temperature distribution is more homogeneous for the microwave method. This device has thus made it possible to validate the feasibility of microwave heating via a vertical antenna for treating polluted soils. Industrial application

[0089] The object of this description may find applications in the field of soil remediation, but also in other in-situ soil heating applications. For example, it could be used to evaluate soil heating techniques for oil recovery in underground reservoirs or for controlled cracking of concrete in the construction industry. These broad applications highlight the versatility and relevance of this technology in various industrial and environmental fields. List of documents cited Patent documents

[0090] For the sake of clarity, the following patent documents are cited: -patcitl: US 10137486; - patcit2: CN203343163; - patcit3: US5076727; -patcit4:CNl 11360055. Non-patent literature

[0091] A toute fin utile, les éléments non-brevets suivants sont cités : - nplcitl : 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; - 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 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 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. Device (1) for characterizing a soil heat treatment process, characterized in that it comprises: a. A cylindrical lysimeter (10) comprising watertight side walls, open at its upper base (11), and whose lower base forms a watertight wall, inclined with respect to the horizontal and having an opening equipped with a valve (12); b. A water pump (16) configured to inject and / or drain water into said lysimeter through said valve; c. a removable heating device (18) configured to be inserted vertically into said lysimeter through its open upper base, in a central area relative to said side walls; d. a three-dimensional network of temperature sensors (19i -192) comprising at least one optical fiber temperature sensor, said sensors being placed at different heights, radial distances and angular positions within said lysimeter; e. means for recording the temperatures measured by said sensors of said three-dimensional network.

2. Device according to claim 1, characterized in that said three-dimensional sensor network comprises a first set (19J) of optical fiber temperature sensors disposed near said heating device (18) and a second set (192) of thermocouple temperature sensors disposed at a distance from said heating device.

3. A device according to any one of claims 1 and 2, characterized in that said three-dimensional sensor network is structured as a set of superimposed sensor layers located at different heights within said lysimeter, in that a sensor layer has a star structure comprising at least three angularly spaced branches, extending from said central zone of said lysimeter to said lateral walls, a branch comprising a plurality of sensors spaced from each other in a radial direction, and in that within a layer, a surface density of sensors decreases from said central zone of said lysimeter towards said lateral walls.

4. Device according to any one of claims 1 to 3, characterized in that said branches of said star structure are angularly spaced so as to cover an angular sector of said lysimeter substantially equal to 90°.

5. Device according to any one of claims 1 to 4, characterized in that said walls of said lysimeter (10) are formed in a microwave-proof material, and in that said device also comprises a microwave leak detector.

6. Device according to any one of claims 1 to 5, characterized in that said removable heating device (18) belongs to the group comprising: • A conduction heating device; • A hot fluid injection heating device; • A microwave heating device.

7. Device according to any one of claims 1 to 6, characterized in that it also comprises means (22) for measuring soil moisture by time-domain reflectometry.

8. Device according to any one of claims 1 to 7, characterized in that it also comprises a buffer tank (14) connected to said water pump (16) and power supply means (17) supplying said water pump.

9. Device according to any one of claims 1 to 8, characterized in that it also comprises a central support within said lysimeter (10) intended to receive said removable heating device (18).

10. Device according to claim 6, characterized in that, where said removable heating device is a microwave heating device, said characterization device also includes air injection means (23) connected to the upper part of said microwave heating device.

11. A method for characterizing a soil heat treatment process using a device according to any one of claims 1 to 9, characterized in that it comprises the steps of: i. Insertion (El) of said removable heating device through the open upper base of said lysimeter and positioning of said heating device on a central support; ii. Filling (E2) of a lower portion of said lysimeter with a drainage material; iii. Provision of a membrane layer covering said drainage material; iv. Until the lysimeter is completely filled, alternate the following steps: a. Filling (E3) of said lysimeter with a layer of constituent material of said soil to be treated up to a determined height and, optionally, injection (E4) of water into said lysimeter; b. Placement (E5), at said determined height, of temperature sensors of said sensor network in a set of determined radial positions; v. Optional gravity drainage (E7) of residual water contained in said lysimeter through said valve; vi. Heating (E8) of said heating device for a determined heating time and continuous recording at determined time intervals of the temperatures measured by said temperature sensors of said three-dimensional sensor network; vii. Establishment (E9) of a temperature map within said lysimeter as a function of time from said recorded temperatures, said temperature map characterizing said soil treatment process by thermal desorption.

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