Microwave apparatus comprising a microwave cavity and a measuring system for determining an indicator of the symmetry of an electric field in the microwave cavity

Abstract

The invention relates to a microwave apparatus (1) for continuous treatment of a flowing fluid medium. It comprises an enclosure (2) made of a microwave-reflective material and internally defining a microwave cavity (3) in which the fluid medium flows along a flow axis (A1); an input waveguide (4) extending along a propagation axis (A2) orthogonal to the flow axis and coupled to an input window (41) provided in the enclosure for propagation of microwaves entering the microwave cavity. The invention is characterised in that it comprises a measurement system for determining a symmetry indicator representing a symmetry of an electric field relative to the flow axis inside the microwave cavity, thus representing a centring of the electric field in the fluid medium. Knowledge of this symmetry indicator advantageously allows the symmetry of the electric field in the fluid medium to be controlled.

Description

[0001] DESCRIPTION

[0002] TITLE: Microwave installation comprising a microwave cavity and a measuring system for determining a symmetry indicator of an electric field in the microwave cavity

[0003] [Technical field]

[0004] The invention relates to a microwave installation for continuous microwave treatment of a flowing fluidic medium, as well as to a microwave process implementing such a microwave installation.

[0005] The invention finds a favorite, but not limiting, application in a microwave plasma production installation, an installation for the removal by thermal oxidation of toxic or polluting gases contained in a flowing gas, and an installation for microwave heating of a flowing liquid or paste-like fluid.

[0006] [State of the art]

[0007] As is known, notably from FR3088797A1, DE102021104547A1 and EP1291076B1, a microwave installation may include:

[0008] - an enclosure made of a microwave-reflective material (usually a metallic enclosure) and internally delimiting a microwave cavity;

[0009] - a flow system connected to the enclosure to ensure flow of the fluidic medium through the microwave cavity along a flow axis; - an inlet waveguide extending along a propagation axis orthogonal to the flow axis and coupled to an inlet window provided on the enclosure for microwave propagation at the inlet of the microwave cavity;

[0010] - an output waveguide extending along the propagation axis and coupled to an output window provided on the enclosure, opposite to the input window with respect to the flow axis, for microwave propagation at the output of the microwave cavity; - a short-circuiting device, for example of piston type, mounted on the output waveguide.

[0011] For effective microwave treatment of a flowing fluid, the electric field must be relatively uniform, and therefore symmetrical, within the fluid (since electric field symmetry is characteristic of a traveling wave). Indeed, an asymmetry in this electric field, in terms of electrical power, would lead to asymmetrical treatment of the fluid, or even damage to the equipment. For example, in a plasma application, an asymmetry in the electric field would lead to an asymmetry of the plasma confined within a dielectric tube, potentially resulting in hot spots on the dielectric tube and leading to its melting.

[0012] A commonly implemented solution for modifying the distribution of the electric field in a microwave cavity, and therefore in a fluidic medium flowing through it, in order to obtain the desired uniformity, is to integrate a short-circuit device at the output, and at least one impedance matching element at the input, such as an iris or a piston impedance adapter (also called a stub adapter).

[0013] However, the short-circuit device and at least one impedance matching element are generally set at the start of the installation, whereas operating conditions may change during the treatment or between two treatments (e.g. the nature of the fluidic medium, the flow rate, the temperature and the pressure in the microwave cavity), so that the settings of the short-circuit device and at least one impedance matching element are no longer suitable or optimal to ensure uniformity / symmetry of the electric field in the fluidic medium.

[0014] There is therefore a need to better control the distribution of the electric field in the microwave cavity, and in particular to better understand a loss of uniformity or symmetry of the electric field in order to be able to take the necessary measures.

[0015] [Summary of the invention]

[0016] The invention positively addresses this need by proposing a means to evaluate a symmetry indicator representative of the symmetry of the electric field in the fluidic medium, and with respect to the flow axis, during a microwave process implemented by a microwave installation.

[0017] Thus, the invention relates to a microwave installation for the continuous microwave treatment of a flowing fluidic medium, said microwave installation comprising at least:

[0018] - an enclosure made of a microwave-reflective material and internally delimiting a microwave cavity;

[0019] - a flow system connected to the enclosure to ensure flow of the fluidic medium through the microwave cavity along a flow axis; - an inlet waveguide extending along a propagation axis orthogonal to the flow axis and coupled to an inlet window provided on the enclosure for microwave propagation at the inlet of the microwave cavity;

[0020] - an output waveguide extending along the propagation axis and coupled to an output window provided on the enclosure and positioned opposite the inlet window relative to the flow axis, for microwave propagation at the output of the microwave cavity; - a short-circuit device, for example of piston type, mounted on the output waveguide.

[0021] This microwave installation is remarkable in that it includes a measurement system to determine a symmetry indicator representative of the symmetry of an electric field with respect to the flow axis inside the microwave cavity (and therefore representative of the centering of the electric field in the fluidic medium), said measurement system comprising:

[0022] - a first connection port and a second connection port arranged on the enclosure on either side and equidistant from a first median plane which includes the flow axis and which is orthogonal to the propagation axis, in which the first connection port and the second connection port are arranged equidistant from a second median plane which includes the propagation axis and which is orthogonal to the flow axis, and in which the first connection port and the second connection port are arranged equidistant from or are contained in a third median plane which includes the propagation axis and the flow axis;

[0023] - at least one measuring probe suitable for connection to the first connection port and the second connection port in order to measure respectively a first physical parameter and a second physical parameter which are representative of the electric field inside the microwave cavity respectively at the level of the first connection port and the second connection port;

[0024] the symmetry indicator corresponding to the ratio between the first physical parameter and the second physical parameter.

[0025] The closer the ratio between the first and second physical parameters is to 1, the more the electric field tends to be symmetrical with respect to the flow axis inside the microwave cavity, and therefore centered within the fluidic medium. Centering of the electric field within the fluidic medium is achieved when the symmetry indicator is equal to 1.

[0026] Microwaves are for example generated by a microwave generator at a generation frequency within a frequency range of a microwave frequency range, which microwave generator is connected to the input waveguide.

[0027] In one variant, the first and second connection ports are equidistant from the second median plane, being on the same side of it. In another variant, the first and second connection ports are equidistant from and on opposite sides of the second median plane (in other words, the second connection port is symmetrical to the first connection port with respect to the second median plane).

[0028] As specified above, the invention advantageously allows a measurement of the first physical parameter and the second physical parameter (and therefore a determination of the symmetry indicator), which will advantageously allow a control of the centering / uniformity of the electric field in the fluidic medium, during a microwave process implemented by the microwave installation.

[0029] In one variant, the symmetry indicator can be determined in real time, i.e., continuously, throughout the entire microwave process. In another variant, this determination can be performed intermittently.

[0030] When the distribution of the electric field in the microwave cavity changes due to changes in the operating conditions of the microwave process (such as variations in temperature, pressure, flow rate in the microwave cavity), knowledge of the symmetry indicator during the microwave process makes it possible to control (i.e., modify / vary) the distribution of the electric field as needed so that the electric field is symmetrical in the fluidic medium; so that the treatment implemented by the microwave process remains as efficient as possible, and to limit or prevent any asymmetry (in other words, any decentering) of the electric field in the fluidic medium which risks damaging at least the enclosure of the microwave installation.

[0031] Furthermore, the method for determining whether the microwave installation is optimized or not (i.e. whether the electric field is symmetrical or not in the fluidic medium) is simple and practical to implement, since it is based on measuring the first physical parameter and the second physical parameter by at least one measuring probe, and then determining (for example, calculating) the ratio of the first physical parameter to the second physical parameter.

[0032] In one variant, the symmetry indicator can, for example, be displayed on a screen integrated into the microwave installation. When the symmetry indicator value shows an off-center electric field in the fluid medium, an operator viewing the screen can interact with the microwave installation to modify the electric field distribution and restore symmetry within the fluid medium. As described later, this interaction can involve modifying the short-circuit device when its position is adjustable along the propagation axis. In another variant, the measurement system is connected to, or in communication with, a control unit designed to control the operation of the microwave installation.The measurement system can, for example, transmit the symmetry indicator to the control unit which, depending on its value, controls or not a device (for example, the short-circuit device if it is adjustable in position) to modify the distribution of the electric field in the microwave cavity.

[0033] As further specified later, advantageously, the control and mastery of the centering / symmetry of the electric field in the fluidic medium can be achieved within the framework of different application contexts, i.e. different types of treatment implemented by distinct microwave processes.

[0034] According to a feature of the invention, the first connection port and the second connection port are arranged on the enclosure and have one of the following symmetries: - a symmetry with respect to the first median plane;

[0035] - a symmetry with respect to the flow axis;

[0036] - a symmetry with respect to a point of intersection between the flow axis and the propagation axis;

[0037] - a combination of symmetry with respect to the first median plane and symmetry with respect to the second median plane.

[0038] These different symmetries verify the characteristics / conditions of arrangement of the first connection port and the second connection port with respect to the first median plane, the second median plane, and the third median plane.

[0039] According to one embodiment of the invention, the enclosure has a lower wall and an upper wall which are flat and parallel to the second median plane, and in which:

[0040] - the first connection port and the second connection port are both located on the lower wall or on the upper wall; or

[0041] - One of the first connection ports and the second connection port is located on the lower wall, and the other of the first connection ports and the second connection port is located on the upper wall.

[0042] These arrangements of the first connection port and the second connection port on the lower and / or upper wall of the enclosure are made possible by the arrangement conditions of the two connection ports in relation to the three median planes listed previously.

[0043] In different embodiments:

[0044] - the first connection port and the second connection port are both located on the lower wall of the microwave cavity; or

[0045] - the first connection port and the second connection port are both located on the upper wall of the microwave cavity; or

[0046] - one of the first connection port and the second connection port is located on the lower wall of the microwave cavity, and the other of the first connection port and the second connection port is located on the upper wall of the microwave cavity.

[0047] According to one embodiment of the invention, at least one measuring probe comprises a single measuring probe adapted to be connected to the first connection port and to the second connection port in order to measure respectively the first physical parameter and the second physical parameter.

[0048] In other words, during the microwave process implemented by the microwave installation, the single measuring probe is connected to the first connection port to measure the first physical parameter (i.e., its value), then disconnected from the first connection port and connected to the second connection port to measure the second physical parameter (i.e., its value); or vice versa. The value of the symmetry indicator is determined based on these two measurements.

[0049] According to one embodiment of the invention, at least one measuring probe comprises:

[0050] - a first measuring probe adapted to be connected to the first connection port in order to measure the first physical parameter, and

[0051] - a second measuring probe adapted to be connected to the second connection port in order to measure the second physical parameter.

[0052] Using the first measuring probe and the second measuring probe to measure the value of the first physical parameter and the second physical parameter respectively allows, advantageously, compared to the previous method (use of a single measuring probe), a saving of time in determining the value of the symmetry indicator.

[0053] Furthermore, the use of the two measuring probes advantageously allows continuous measurement of the two physical parameters throughout the duration of the microwave process implemented by the microwave installation; and therefore a continuous determination of the symmetry indicator to ultimately control and continuously master the distribution of the electric field (and therefore its symmetry with respect to the flow axis) inside the microwave cavity and the fluidic medium.

[0054] According to one embodiment of the invention, the first measuring probe and the second measuring probe are pre-calibrated before their respective connections to the first connection port and the second connection port.

[0055] The calibration of the first and second measuring probes can, for example, be performed using a waveguide terminated by a load and through which a traveling wave propagates. The two measuring probes are connected separately to two connection ports on the waveguide and penetrate it identically. The two measuring probes are considered calibrated when they measure the same value of a physical parameter representative of this traveling wave. Ideally, this physical parameter is of the same nature as the first and second physical parameters.

[0056] According to one embodiment of the invention, the measurement system includes a third connection port disposed on the enclosure in the first median plane, at least one measurement probe being adapted to be connected to the third connection port in order to measure a third physical parameter representative of the electric field inside the microwave cavity at the level of the third connection port, and therefore of the first median plane.

[0057] As described below, the microwave installation of the invention can be used for the production of a microwave plasma. In this context, and advantageously, measuring the third physical parameter at the level of the first median plane (which contains the flow axis) makes it possible to determine the best ignition position of the microwave plasma, when the signal is at its maximum.

[0058] In the remainder of the description, and unless otherwise indicated, "plasma" means microwave plasma.

[0059] According to one embodiment of the invention, the short-circuit device is adjustable in position along the propagation axis, to allow adjustment according to the symmetry indicator; the short-circuit device being, for example, coupled, by means of a transmission mechanism, to an actuator.

[0060] In one example, the short-circuiting device is a piston mounted on the output waveguide and coupled to an actuator by means of a transmission mechanism. In other words, the actuator, through the transmission mechanism, moves the piston along the propagation axis (and thus adjusts its position).

[0061] Depending on the example, the actuator can be a motorized actuator, a hydraulic actuator, or a pneumatic actuator.

[0062] Changing the position of the short-circuit device, used as an impedance adapter, allows the distribution of the electric field to be modified in the microwave cavity and therefore in the fluidic medium.

[0063] As explained previously, when the value of the symmetry indicator shows an off-center electric field in the fluidic medium, the short-circuit device can advantageously be adjusted in position (manually or automatically) so that the electric field becomes symmetrical again in the fluidic medium.

[0064] According to one embodiment of the invention, the input waveguide includes an impedance matching element, for example, an iris or a piston adapter. The impedance matching element can, for example, be adjusted in position along the propagation axis to modify the distribution of the electric field in the microwave cavity, similarly to the short-circuiting device. Thus, advantageously, when the symmetry indicator shows an off-center electric field in the fluidic medium, the impedance matching element can advantageously be used to match the impedance so as to modify the distribution of the electric field in the fluidic medium so that it becomes symmetrical again.

[0065] Note that the mounting of an impedance matching element in the input guide may or may not be necessary to control the centering of the electric field in the fluidic medium, depending on the treatment applied to the fluidic medium and the experimental conditions of this treatment.

[0066] As an example, in order to be adjusted in position, the impedance matching element can be moved by sliding while being mounted on a guide rail provided on the upper wall of the input waveguide.

[0067] According to another example, in order to be adjusted into position automatically, the impedance matching element is moved along the guide rail by an actuator, which actuator is coupled to the impedance matching element by a transmission mechanism.

[0068] According to one embodiment of the invention, at least one measuring probe is a coaxial dipole, which includes a coaxial cable comprising a central core having a stripped termination forming an antenna having an antenna length and introduced inside the microwave cavity.

[0069] According to one embodiment of the invention, the first connection port and the second connection port both have an orifice passing through the enclosure along an orifice axis parallel to the flow axis, so that the antenna of at least one probe penetrates inside the microwave cavity and is parallel to the flow axis.

[0070] To accurately measure the first and second physical parameters, the antenna of at least one measuring probe must enter the microwave cavity through the openings of both connection ports in the same manner. In other words, the same length of antenna from the at least one measuring probe must penetrate the microwave cavity when the antenna passes through the opening of the first connection port and the opening of the second connection port.

[0071] Indeed, although the measured values ​​of the first physical parameter and the second physical parameter are characteristic of the electric field distribution at the level of the first connection port and the second connection port, they also depend on the antenna length of the antenna of at least one measuring probe, and the penetration of the antenna into the microwave cavity.

[0072] When at least one measuring probe includes the first measuring probe and the second measuring probe as previously described, the antenna of the first measuring probe and the antenna of the second measuring probe enter the interior of the microwave cavity through the openings presented by the first connection port and the second connection port for the same antenna length.

[0073] According to one embodiment of the invention, the first physical parameter and the second physical parameter correspond respectively to a first electric field intensity at the level of the first connection port and a second electric field intensity at the level of the second connection port, and wherein at least one measuring probe is coupled to a conversion device shaped to convert the first electric field intensity into a first electric voltage and the second electric field intensity into a second electric voltage; the conversion device being disposed outside the enclosure.

[0074] According to one example, the conversion device is included in the measurement system.

[0075] By "coupled", it is understood that at least one probe is electrically connected to the conversion device.

[0076] In other words, in this embodiment, the value of the symmetry indicator corresponds to the ratio of the first electrical voltage to the second electrical voltage.

[0077] The measured values ​​of the first electric field intensity and the second electric field intensity are characteristic of the electric field distribution.

[0078] According to one embodiment of the invention, the input waveguide and the output waveguide both have a rectangular cross-section with: two long sides defining a long dimension and two short sides defining a short dimension smaller than the long dimension such that:

[0079] - the long sides of the inlet waveguide and outlet waveguide are orthogonal to the flow axis, and the short sides are parallel to the flow axis; or - the long sides of the inlet waveguide and outlet waveguide are parallel to the flow axis, and the short sides are orthogonal to the flow axis.

[0080] When the long side of the inlet waveguide is parallel to the flow axis, the electric field, being perpendicular to the flow axis, advantageously does not experience a boundary or abrupt transition of dielectric losses. According to one embodiment of the invention, the microwave installation comprises a dielectric tube made of microwave-transparent material such that: - the dielectric tube extends longitudinally along the flow axis and passes completely through the enclosure and the microwave cavity;

[0081] - the dielectric tube has two ends, each connected to the flow system to ensure the flow of the fluidic medium through the microwave cavity, inside the dielectric tube, along the flow axis.

[0082] In one example, the dielectric tube has covers on each end, these covers being fitted with connecting sleeves to link the tube ends to the flow system so that the fluid can flow inside the dielectric tube, and thus into the microwave cavity. More precisely, the fluid to be treated enters the dielectric tube at one end and is discharged from the other end once treated.

[0083] In this embodiment, the symmetry indicator therefore makes it possible to control and master the symmetry of the electric field in the fluidic medium with respect to the flow axis, inside the dielectric tube.

[0084] Depending on the direction of microwave propagation (from the input waveguide to the output waveguide), the first connection port and the second connection port, which are arranged on the enclosure at an equal distance and on either side of the first median plane, are respectively arranged upstream of the dielectric tube and downstream of the dielectric tube.

[0085] The first connection port and the second connection port are positioned on the enclosure so that they are as close as possible to the dielectric tube.

[0086] According to one embodiment of the invention, a microwave plasma is generated in the dielectric tube inside the microwave cavity, the fluidic medium corresponding to a reaction gas for the ignition and maintenance of the plasma.

[0087] In other words, and advantageously, the microwave installation of the invention can be applied for the production of microwave plasma. The microwave installation can therefore, for example, correspond to a microwave plasma torch.

[0088] In order for a microwave plasma to be maintained in a dielectric tube when traversed by microwave waves generated for high microwave power, it is necessary that the microwave plasma be well centered and confined in the dielectric tube following its ignition.

[0089] As explained in the prior art, off-center placement of the microwave plasma can lead to the formation of hot spots on the dielectric tube wall, which can cause it to melt. Similarly, in microwave treatments where solid particles are created from the microwave plasma, off-center placement can lead to the formation of deposits on the inner wall of the dielectric tube, where the plasma is closest, necessitating subsequent cleaning of the dielectric tube's interior.

[0090] Once the microwave plasma is ignited, its impedance depends on numerous operating conditions, for example, but not limited to: the type of reaction gas used for its ignition and maintenance; the temperature and pressure inside the dielectric tube; the reaction gas flow rate; etc. Thus, the impedance of a microwave plasma can vary during the implementation of a microwave process; this variation in the impedance of the microwave plasma can therefore lead to its misalignment.

[0091] Advantageously, the symmetry indicator defined in the invention makes it possible to: - control and manage the centering of the electric field inside the reaction gas flowing in the dielectric tube during the ignition phase of the microwave plasma; then

[0092] - once the microwave plasma is generated, to control and master the centering of the electric field inside the reaction gas, and therefore of the microwave plasma, in order to significantly limit, or even prevent, the decentering of the plasma in the dielectric tube.

[0093] Centering the microwave plasma within the microwave cavity is achieved by centering the electric field within the microwave plasma. In practice, to ensure microwave plasma centering within the dielectric tube, the injection of the reaction gas must be optimized. More specifically, the reaction gas must be injected into the dielectric tube in the form of a vortex with high, uniform velocities near the inner wall of the dielectric tube and lower velocities at its center.

[0094] Control and mastery of electric field centering in this application context can for example be implemented for a microwave generation frequency equal, not exhaustively, to 433 MHz (when solid state technologies are used in the design / manufacture of the microwave installation), to 915 MHz, or to 2450 MHz.

[0095] In an application context, the plasma generated by the microwave system can be used to remove toxic or polluting gases from the gases being treated. It can therefore be used to remove volatile organic compounds (VOCs) from the gases being treated, or even to remove greenhouse gases (GHGs). As a reminder, VOCs are chemical compounds containing at least one carbon atom bonded to other atoms such as hydrogen, oxygen, nitrogen, sulfur, or phosphorus (with a few exceptions, such as carbon oxides).According to one embodiment of the invention, the microwave installation includes, inside the microwave cavity, a catalyst which is positioned opposite the inlet window and the outlet window, and centered on the flow axis; the catalyst being shaped to: confine through it the flow of a gas corresponding to the fluidic medium and comprising toxic or polluting gases; and thermally oxidize said toxic or polluting gases.

[0096] A known solution in the literature for removing VOCs from gases, and / or GSEs, is to thermally oxidize them using a catalyst heated to a temperature within a suitable thermal oxidation range for removal. Heating the catalyst by exposing it to microwaves is also described in the literature. For this purpose, the catalyst is placed in an enclosure, specifically the microwave cavity, of a microwave reactor, where it is exposed to radiation, and through which the gas containing the volatile organic compounds to be treated circulates.

[0097] The catalyst is centered on the flow axis. In other words, the catalyst: - extends along the flow axis;

[0098] - extends along the propagation axis, on either side of the first median and the third median plane, and symmetrically with respect to the first median plane and the third median plane.

[0099] In a first embodiment variant, the catalyst is placed in the microwave cavity.

[0100] The first and second connection ports are positioned on the enclosure so as to be as close as possible to the catalyst. Knowledge of the symmetry indicator.

[0101] Knowledge of the symmetry indicator allows control of the electric field distribution so that it is symmetrical with respect to the flow axis: both in the fluid medium (i.e., the gas to be treated or the GSE) and in the catalyst. Symmetry of the electric field in the catalyst ensures uniform heating.

[0102] Uniform heating of the catalyst allows its temperature to reach the thermal oxidation range more quickly. This uniform heating then enables more efficient thermal oxidation of VOCs and GHGs. In other words, controlling and managing the centering of the electric field allows for better microwave installation performance in reducing VOCs and GHGs contained in the flowing gas. The catalyst can, for example, be made from a macroporous ceramic material selected from at least the following: silicon carbide, zirconia, lanthanum chromite, and various metal oxides. Thus, the catalyst exhibits a macroporous structure throughout its entire volume.The macroporous ceramic catalyst can, for example, also have a so-called "honeycomb" geometry in order to have a very large exchange surface with the gases passing through it, in order to be able to heat and thermally oxidize them more quickly.

[0103] In a second embodiment, the microwave installation includes a dielectric tube as previously described; and the catalyst extends and is held in the dielectric tube, for example by means of retaining elements.

[0104] Controlling the symmetry of the electric field in the fluid medium with respect to the flow axis, inside the dielectric tube and in the catalyst allows:

[0105] - uniform heating of the catalyst; and

[0106] - to prevent the formation of hot spots on the wall of the dielectric tube which could eventually lead to the melting of the latter.

[0107] When the microwave installation is used for the treatment of VOCs and GSEs, the control and mastery of the centering of the electric field can, for example, be implemented for a microwave generation frequency within a microwave frequency range of 300 MHz to 30 GHz.

[0108] The invention also relates to a microwave process for the continuous microwave treatment of a flowing fluidic medium, the microwave process being implemented by a microwave installation as described above, the microwave process comprising:

[0109] - a generation step consisting of generating microwaves at a generation frequency within a frequency range of a microwave frequency range, the microwaves being guided to the input waveguide in order to propagate the microwaves into the input of the microwave cavity;

[0110] - a flow start step consisting of making the fluidic medium flow through the microwave cavity along the flow axis;

[0111] - a first measurement step in which at least one measuring probe, connected to the first connection port, measures the first physical parameter; - a second measurement step in which at least one measuring probe, connected to the second connection port, measures the second physical parameter; - a determination step in which the symmetry indicator corresponding to the ratio between the first and second physical parameters is determined. For example, when the at least one measuring probe comprises a first and a second measuring probe as described above, the first and second measurement steps can be implemented simultaneously.

[0112] According to one embodiment of the invention, the short-circuit device is adjustable in position along the propagation axis, for example by being coupled to an actuator via a transmission mechanism, and the microwave process includes an adjustment step in which the short-circuit device is adjusted in position according to the symmetry indicator.

[0113] According to one feature of the invention, the adjustment step consists of adjusting the short-circuit device in position so that the symmetry indicator is as close as possible to 1.

[0114] [Brief description of the figures]

[0115] Other features and advantages of the present invention will become apparent from the following detailed description, of a non-limiting example of implementation, made with reference to the accompanying figures in which:

[0116] [Fig 1] is a schematic profile view of the microwave installation of the invention according to a first embodiment;

[0117] [Fig 2] is a schematic top view of the microwave installation in Figure 1;

[0118] [Fig 3] is a schematic front view of the inlet and outlet waveguide sections comprising the microwave installation, for an embodiment in which they are rectangular and such that the long side of each is parallel to the flow axis along which the fluidic medium flows through the microwave cavity of the microwave installation;

[0119] [Fig 4] is a schematic view of a measuring probe used to measure a physical parameter representative of the electric field inside the microwave cavity;

[0120] [Fig 5] is a schematic top view of the microwave installation according to a second embodiment;

[0121] [Fig 6] is a schematic top view of the microwave installation according to a third embodiment;

[0122] [Fig 7] is a schematic profile view of the microwave installation of the invention according to a fourth embodiment;

[0123] [Fig 8] is a schematic top view of the microwave installation according to a fifth embodiment; [Fig 9] is a schematic profile view of a waveguide used for calibrating the measuring probe(s);

[0124] [Fig 10] is a graph illustrating three evolutions (curves Cl, C2 and C3) of the electric field in the microwave installation, in particular inside a dielectric tube which comprises the microwave installation when used in the context of the generation of a plasma; the microwave installation being simulated here from an electromagnetic model, and each of the evolutions corresponding to a given configuration of the electromagnetic model;

[0125] [Fig 11] is a figure related to Figure 10, and which illustrates the distribution of the electric field inside the simulated microwave installation associated with the evolution of the Cl curve;

[0126] [Fig 12] is a figure related to Figure 10, and which illustrates the distribution of the electric field inside the simulated microwave installation associated with the evolution of the C2 curve;

[0127] [Fig 13] is a figure related to Figure 10, and which illustrates the distribution of the electric field inside the simulated microwave installation associated with the evolution of the C3 curve.

[0128] [Detailed description of one or more embodiments of the invention] The microwave installation 1 of the invention, used for continuous microwave treatment of a flowing fluidic medium, is illustrated below with several figures. To enhance the readability of the figures, some elements of the invention are not shown, or are shown but not to scale.

[0129] Several embodiments of the microwave installation 1 are described below. These different embodiments are not exhaustive, are not mutually exclusive, and may be combined.

[0130] With reference to Figures 1 to 4, the microwave installation 1 comprises: - an enclosure 2 made of a microwave-reflective material and internally delimiting a microwave cavity 3;

[0131] - a flow system (not illustrated) connected to enclosure 2 to ensure flow of the fluidic medium through microwave cavity 3 along a flow axis Al;

[0132] - an inlet waveguide 4 extending along a propagation axis A2 orthogonal to the flow axis Al and coupled to an inlet window 41 provided on the enclosure 2 for microwave propagation into the microwave cavity 3;

[0133] - an output waveguide 5 extending along the propagation axis A2 and coupled to an output window 51 provided on the enclosure 2 and arranged opposite the inlet window 41 with respect to the flow axis Al, for microwave propagation at the output of the microwave cavity 3;

[0134] - a short-circuit device 52 mounted on the output waveguide 5.

[0135] Microwaves are generated by a microwave generator (not shown) which is connected to the input of the input waveguide 4, at a generation frequency within a frequency range of microwave frequencies.

[0136] Referring to Figure 3, the inlet waveguide 4 and the outlet waveguide 5 both have a rectangular cross-section with two long sides defining a larger dimension L4, L5 and two short sides defining a smaller dimension W4, W5, which is smaller than the larger dimension L4, L5, such that: the long sides of the inlet waveguide 4 and the outlet waveguide 5 are parallel to the flow axis Al; and the short sides are orthogonal to the flow axis (Al). Advantageously, since the long side of the inlet waveguide 4 is parallel to the flow axis Al, the electric field, which is perpendicular to the flow axis Al, advantageously does not experience a boundary or abrupt transition in the dielectric losses.

[0137] The short-circuiting device 52 is a piston whose position can be automatically adjusted along the propagation axis A2 by an actuator coupled to the piston via a transmission mechanism (the actuator and transmission mechanism are not shown). The actuator, through the transmission mechanism, pushes or pulls the piston inside the output waveguide 5.

[0138] The input waveguide includes an impedance matching element 7 designed to slide along a guide rail (not shown) integrated into the upper wall of the input waveguide 4, parallel to the propagation axis A2. Similar to the short-circuit device 52, the sliding of the impedance matching element 7 can be implemented automatically by an actuator coupled to the impedance matching element 7 via a transmission mechanism.

[0139] In the embodiments described below, the microwave installation 1 also includes a dielectric tube 6 made of microwave-transparent material such that the dielectric tube 6 extends longitudinally along the flow axis Al and passes through the enclosure 2 and the microwave cavity 3; and has two ends 61, 62 each connected to the flow system to ensure the flow of the fluidic medium through the microwave cavity 3, inside the dielectric tube 6, along the flow axis Al.

[0140] The first end 61 and the second end 62 have covers 611, 621, said covers 611, 621 being provided with connecting sleeves (not illustrated) to connect the ends of the tube 61, 62 to the flow system so that the fluid can flow inside the dielectric tube 6, and thus into the microwave cavity 3. For example, the fluid to be treated enters the dielectric tube 6 through the first end 61, and is discharged from the inside of the tube once treated through the second end 62.

[0141] The microwave installation 1 of the invention is remarkable in that it allows the distribution of the electric field within the fluid medium to be treated to be controlled and varied. In particular, the microwave installation 1 advantageously allows the centering of the electric field within the fluid medium inside the dielectric tube 6 (i.e., the symmetry of the electric field with respect to the flow axis Al). In other words, it allows a uniform electric field, characteristic of a traveling wave, to be maintained within the fluid medium.

[0142] To control the distribution of the fluidic medium within the fluidic medium and to determine whether the electric field is symmetrical / uniform or not, the microwave installation includes a measurement system to determine a symmetry indicator ESI representative of the symmetry of the electric field with respect to the flow axis Al inside the microwave cavity 3 (and therefore, in the described embodiments, inside the dielectric tube 6).

[0143] The measurement system includes a first connection port 81 and a second connection port 82 located on enclosure 2:

[0144] - on either side and equidistant from a first median plane PI which includes the flow axis Al and which is orthogonal to the propagation axis A2,

[0145] - equidistant from a second median plane P2 which includes the propagation axis A2 and which is orthogonal to the flow axis Al,

[0146] - equidistant from or contained in a third median plane P3 which includes the propagation axis A2 and the flow axis Al.

[0147] According to the trihedron given in Figure 1, the first median plane PI is formed by the x-axis and the y-axis; the second median plane 92 is formed by the x-axis and the z-axis, and finally the third median plane P3 is formed by the y-axis and the z-axis.

[0148] Thus, the first connection port 81 and the second connection port 82 can exhibit one of the following symmetries:

[0149] - a symmetry with respect to the first median plane PI;

[0150] - a symmetry with respect to the flow axis Al;

[0151] - a symmetry with respect to an intersection point IPI between the flow axis Al and the propagation axis A2;

[0152] - a combination of symmetry with respect to the first median plane PI and symmetry with respect to the second median plane P2. According to the direction of propagation of the microwaves (from the input waveguide 4 to the output waveguide 5), the first connection port 81 and the second connection port 82, which are arranged on the enclosure at an equal distance and on either side of the first median plane PI, are respectively arranged upstream of the dielectric tube 6 and downstream of the dielectric tube 6.

[0153] Also, the first connection port 81 and the second connection port 82 can be:

[0154] - both arranged on the upper wall 21 of enclosure 2; or

[0155] - both arranged on the lower wall 22 of enclosure 2; or

[0156] - arranged respectively and distinctly on the upper wall 21 and the lower wall 22 of the enclosure 2.

[0157] In the embodiment illustrated in Figures 1 and 2, the first connection port is 81 and the second connection port is 82:

[0158] - are two arranged on the upper wall 21 of enclosure 2;

[0159] - are arranged on either side and equidistant from a first distance dl of the median plane PI;

[0160] - are symmetrical both with respect to the first median plane PI and to the flow axis Al;

[0161] - are arranged equidistant from a second distance d2 from the second median plane P2 (and from the propagation axis A2); and

[0162] - are contained in the third median plane P3.

[0163] The first connection port 81 and the second connection port 82 are arranged so as to be as close as possible to the dielectric tube 6; which means that the first distance dl and the second distance d2 are defined as being as small as possible.

[0164] The ESI symmetry indicator is calculated based on the ratio of a first physical parameter SI to a second parameter S2, in other words ESI = S1 / S2.

[0165] The first physical parameter SI and the second physical parameter S2 are respectively representative of the electric field inside the microwave cavity 3 at the level of the first connection port 81 and the second connection port 82 respectively.

[0166] The measurement system includes a first measuring probe 91 adapted to be connected to the first connection 81 to measure a value of the first physical parameter SI; and a second measuring probe 92 adapted to be connected to the second connection port 82 to measure a value of the second physical parameter S2. With reference to Figure 4, the first measuring probe SI and the second measuring probe S2 are coaxial dipoles which each include a coaxial cable 911, 921 having a central core 912, 922 having a bare termination forming an antenna 913, 923 having an antenna length L91, L92.

[0167] The first connection port 81 and the second connection port 82 each include an orifice 811, 821 passing through the enclosure 2 along an orifice axis A811, A821 parallel to the flow axis Al, so that the antennas 913, 923 of the measurement seconds 91, 92, once connected to their respective connection port 81, 82, enter the interior of the microwave cavity 3 parallel to the flow axis Al.

[0168] In order to accurately measure the first physical parameter SI and the second physical parameter S2, the antennas 913, 923 of the two measuring probes 91, 92 must penetrate the microwave cavity by the same antenna length L91, L92. Indeed, although the measured values ​​of the first physical parameter SI and the second physical parameter S2 are characteristic of the electric field distribution at the first connection port 81 and the second connection port 82, they also depend on the antenna length L91, L92 of the antenna 913, 923 of the measuring probes 91, 92 penetrating the microwave cavity 3.

[0169] In the described embodiments, the first physical parameter SI and the second physical parameter S2 correspond respectively to a first electric field intensity at the level of the first connection port 81 and a second electric field intensity at the level of the second connection port 82. The two measuring probes 91, 92 are connected to a conversion device 100 (for example a crystal holder) which is included in the measuring system, outside the enclosure 2, and which is configured to convert the first electric field intensity into a first electric voltage and the second electric field intensity into a second electric voltage.

[0170] The ESI symmetry indicator therefore corresponds, in the described embodiments, to the ratio of the first electrical voltage to the second electrical voltage.

[0171] The two measuring probes 91, 92 advantageously allow continuous measurement of the values ​​of the first physical parameter SI and the second physical parameter S2 during a microwave process implemented by the microwave installation 1 for the treatment of a fluidic medium, and therefore a continuous determination of the value of the symmetry indicator ESI.

[0172] When the distribution of the electric field in the microwave cavity changes due to changes in the operating conditions of the microwave process (such as variations in temperature, pressure, flow rate in the microwave cavity), knowledge of the symmetry indicator during the microwave process makes it possible to control (i.e., modify / vary) the distribution of the electric field as needed so that the electric field is symmetrical in the fluidic medium with respect to the flow axis Al, and therefore that the electric field is centered in the fluidic medium; so that the treatment implemented by the microwave process remains as efficient as possible, and to limit or prevent any asymmetry of the electric field in the fluidic medium which risks damaging the enclosure of the microwave installation to a minimum.

[0173] The closer the ESI symmetry indicator is to 1, the more the electric field tends to be symmetrical with respect to the flow axis Al inside the microwave cavity 3 (here, dielectric tube 6), and therefore centered in the fluidic medium. Symmetry of the electric field in the fluidic medium is achieved when the ESI symmetry indicator is equal to 1.

[0174] The measuring system transmits the ESI symmetry indicator value to a control unit (not shown). In one variant, the measuring system is electrically / wired to the control unit. In another variant, the measuring system communicates with the control unit via a short-range communication protocol.

[0175] When the control unit receives a value of the symmetry indicator ESI that is far from 1 (whether this value is less than or greater than 1, for example ESI = 0.7 or ESI = 1.4), it is configured to control at least one of the actuator coupled to the short-circuit device 52 or the actuator coupled to the impedance matching element 7 so as to move the short-circuit device 52 and / or the impedance matching element 7 to change its / their position; so as to modify the distribution of the electric field so that it returns to symmetry in the fluidic medium.

[0176] Otherwise, when the control unit receives a symmetry indicator value ESI very close to 1 (e.g. ESI = 0.95 or ESI = 1.05) or equal to 1; it does not control the actuators.

[0177] The definition of the symmetry indicator threshold values ​​(ESI) that trigger the sending of a command by the control unit to the actuators, in order to move the short-circuit device 52 and / or the impedance matching element 7, depends on the application context. For example, for some application contexts, it will not be possible to obtain a symmetry indicator (ESI) equal to 1, at best a value close to 1 (for example, and not limited to: ESI = 0.95 or ESI = 1.05; or ESI = 0.9 or ESI = 1.1).

[0178] As an example, threshold values ​​can be determined such that the deviations from the mean for the first and second electric field intensities are less than or equal to 25%. This percentage can also be calculated using the ratio (lmax-lmin) / (lmax+lmin) where Imax (respectively Imin) corresponds to the higher (respectively lower) of the first and second electric field intensities.

[0179] When the symmetry indicator ESI is very close to 1 or equal to 1, the microwave installation is considered optimized. Therefore, and advantageously, determining whether a microwave installation is optimized or not is practical, easy, and quick to implement, since it relies on measuring the two parameters SI and S2, and then determining the value of the symmetry indicator ESI.

[0180] Other examples of the layout of connection ports 81, 82 are shown below on enclosure 2, by way of non-exhaustive list.

[0181] In the example illustrated in Figure 5, the first connection port 81 and the second connection port 82 are arranged on the upper wall of the enclosure 2, and such that:

[0182] - they are arranged on either side and equidistant from the first distance dl of the median plane PI;

[0183] - they are symmetrical with respect to the first median plane PI;

[0184] - are arranged equidistant from the second distance d2 of the second median plane P2 (and of the propagation axis A2); and

[0185] - are arranged at an equidistance of a third distance d3 from the third median plane P3.

[0186] In the example of Figure 6, the first connection port 81 and the second connection port 82 are arranged on the upper wall of the enclosure 2, and such that: - they are arranged on either side and equidistant from the first distance dl of the median plane PI;

[0187] - they are arranged symmetrically with respect to the flow axis Al;

[0188] - they are arranged equidistant from the second distance d2 of the second median plane P2 (and of the propagation axis A2); and

[0189] - they are arranged at an equidistance of the third distance d3 of the third median plane P3.

[0190] In a final example shown in Figure 7, the first connection port 81 and the second connection port 82 are respectively arranged on the upper wall 21 and the lower wall 22, and such that:

[0191] - they are arranged on either side and equidistant from the first distance dl of the median plane PI;

[0192] - they are arranged at an equidistance of the second distance d2 from the second median plane P2 (and from the propagation axis A2);

[0193] - they are symmetrical with respect to an intersection point IPI between the flow axis Al and the propagation axis A2). In one variant, the two connection ports 81, 82 are contained in the third median plane P3. In another variant, they are arranged on either side and equidistant from the third median plane P3.

[0194] In an embodiment illustrated in Figure 8, the measurement system includes a third connection port 83 disposed on the enclosure 2 in the first median plane PI, and a third measurement probe 93 adapted to be connected to the third connection port 83 in order to measure a third physical parameter S3 representative of the electric field inside the microwave cavity 3 at the level of the third connection port 93, and therefore of the first median plane PI.

[0195] The third measuring probe 93, like the other two measuring probes 91 and 92, is a coaxial dipole comprising a coaxial cable 931 with a central core 932 having a bare termination forming an antenna 933 with an antenna length L93. The third physical parameter S3 corresponds to a third electric field strength, at the level of the first PI plane. The third measuring probe 93 is also coupled to the conversion device 100 for converting the electric field strength into a third electrical voltage.

[0196] Similar to the first connection port 81 and the second connection port 82, the third connection port has an orifice 831 extending along an orifice axis A831 parallel to the flow axis Al so that the antenna 933 of the third measuring probe 93 can be introduced inside the enclosure 2, and thus into the microwave cavity 3.

[0197] Before being used for measurements of the first physical parameter SI and the second physical parameter S2, they are calibrated. With reference to Figure 9,

[0198] The calibration of the first measuring probe 91 and the second measuring probe 92 is performed using a waveguide 100 terminated by a load 101, in which a traveling wave propagates. One of the longitudinal walls of the waveguide 100 has two connection ports 110, 120 for connecting the two measuring probes. Each connection port 110, 120 has an opening 111, 121 extending along a vertical axis Alli, A121 so as to insert the antennas 913, 923 of the two measuring probes 91, 92 into the waveguide 100. The antennas 913, 923 penetrate the interior of the waveguide 100 by the same antenna length L91, L92. The two measuring probes 91, 92 are considered to be calibrated when they measure the same value of a physical parameter representative of this progressive wave, and which corresponds in the embodiments described to the intensity of the electric field in the waveguide 100.Advantageously, the microwave installation 1 of the invention can be used in various application contexts, and thus implement continuous microwave treatments of different kinds for fluids.

[0199] The microwave processes associated with each of these treatments include at least:

[0200] - a generation stage during which the microwave generator generates, within a frequency range of a microwave frequency range, the microwaves which are then guided to the input waveguide 4;

[0201] - a flow start step consisting of making the fluidic medium flow through the microwave cavity 3 along the flow axis Al;

[0202] - a first measurement step in which the first measuring probe 91 measures the first physical parameter SI;

[0203] - a second measurement step in which the second measuring probe 92 measures the second physical parameter S2;

[0204] - a determination step in which the ESI symmetry indicator is determined.

[0205] In an application context, the microwave installation 1 can be used for the production of a 200 microwave plasma in the dielectric tube 6 and inside the microwave cavity 3, with the fluidic medium corresponding to the reaction gas used for ignition and maintenance of the 200 plasma in the dielectric tube 6. According to one example, the microwave installation 1 can for example correspond to a microwave plasma torch.

[0206] For a 200-microwave plasma to be maintained within a dielectric tube 6 when traversed by microwaves generated at high microwave power, the 200-microwave plasma must be well-centered and confined within the dielectric tube 6 after ignition. Although the fluidic medium corresponds to the reaction gas, when the 200-microwave plasma is centered within the dielectric tube 6, the electric field is also symmetrical within the 200-microwave plasma with respect to the flow axis Al.

[0207] Once the plasma 200 is ignited, its impedance depends on numerous operating conditions, for example, but not limited to: the type of reaction gas used for its ignition and maintenance; the temperature, the pressure inside the dielectric tube 6; the reaction gas flow rate; etc. Thus, the impedance of a microwave plasma can vary during the implementation of a microwave plasma production process; this variation in the impedance of the plasma 200 can therefore lead to its misalignment.

[0208] As an illustration, the evolution and distribution of the electric field in microwave installation 1, when used for generating a plasma 200, are presented below, showing whether the electric field is centered or decentered in the fluidic medium, i.e., the reaction gas. These evolutions and distributions of the electric field are the result of electromagnetic simulations performed using an electromagnetic model of microwave installation 1.

[0209] Figure 10 illustrates three curves Cl, C2, C3. Each of the curves represents an example of the evolution of the electric field (given in volts per meter) for a similar configuration of the microwave installation (in other words, of the electromagnetic model of the microwave installation 1).

[0210] The evolutions of the electric field are given as a function of the z-axis of the trihedron, which is illustrated in Figure 1. In other words, the evolution of the electric field is shown / drawn along the propagation axis A2.

[0211] It is assumed that the flow axis Al passes vertically through the origin of the two axes of the graph. Thus, depending on the direction of microwave propagation in the microwave installation (from the input waveguide 4 to the output waveguide 5), the electric field is observed:

[0212] - upstream of the flow axis Al for negative z coordinates (for example in the inlet waveguide 4), and

[0213] - downstream of the flow axis Al for positive z coordinates (for example in the outlet waveguide 5).

[0214] The dielectric tube 6 and the plasma 200 are shown in profile in the graph, with the flow axis Al centered in each of them.

[0215] The electric field is simulated along an axis contained by the second median plane P2 and the third median plane P3 (in other words, it is simulated at the center of the two waveguides 4, 5 and the enclosure 2).

[0216] The simulations are carried out for a microwave generation frequency of 915 MHz, and for an incident power of 0.5 Watt.

[0217] Figures 11, 12, and 13 illustrate the distribution of the electric field inside the electromagnetic model of microwave installation 1, and are respectively associated with curves Cl, C2, and C3 in Figure 10.

[0218] In a first example, with reference to curve Cl in Figure 10 and Figure 11, the microwave installation 1 does not include an impedance matching element 7, and the short-circuiting device 52 is positioned in the output waveguide 5 in a P521 position. The impedance of the microwave installation is not matched, and the reflected power is -7 dB (for 20% of the incident power being reflected). In this example, the electric field is asymmetrical in the dielectric tube 6, dropping sharply from 240 V / m to 50 V / m, and in the plasma 200, dropping sharply from 175 V / m to 110 V / m.

[0219] In a second example, with reference to curve C2 in Figure 10 and Figure 12, microwave installation 1 includes an impedance matching element 7 positioned in the input waveguide 4 at position P7 and the short-circuit device 52 is positioned in the output waveguide 5 at position P521. The impedance of microwave installation 1 is matched and the reflected power is -31 dB (for 0.1% of the incident power being reflected). However, in this example, the wave is progressive only between the input of the waveguide 4 and the impedance matching element 7. The electric field is asymmetrical in the dielectric tube 6, dropping sharply from approximately 262 V / m to 50 V / m, and in the plasma 200, dropping sharply from 200 V / m to 120 V / m. The electric field strength is highest at position P7 of the impedance matching element (with an electric field of approximately 440 V / m).

[0220] In a third example, with reference to curve C3 and Figures 10 and 13, microwave installation 1 does not include an impedance matching element 7, and the short-circuiting device 52 is positioned in the output waveguide 5 at position P522 (instead of position P521, as in the first example). The impedance of microwave installation 1 is matched, and the reflected power is -Tl dB (for 0.5% of the incident power to be reflected). Furthermore, the wave propagating in the dielectric tube 6 and the plasma 200 is progressive until it enters the plasma, with the electric field decreasing slightly from 175 V / m to 150 V / m in the dielectric tube and remaining stable in the plasma 200 at approximately 160 V / m. In other words, in this third example, the electric field is centered in the dielectric tube 6, and in the plasma 200, with respect to the flow axis Al.

[0221] The first and third examples differ from each other only in the position of the short-circuit device 52 and the use of a stub impedance adapter. Both configurations show that adjusting the position of the short-circuit device 52, from position P521 to position P522, allows the distribution of the electric field to be varied; so that the field, initially asymmetrical in the dielectric tube 6 and the plasma 200 with respect to the flow axis Al, becomes symmetrical in said dielectric tube 6 and said plasma 200 with respect to said flow axis Al.

[0222] These simulation results also show that, depending on the type of treatment applied to the flowing fluidic medium and the experimental conditions, it is not necessary for the inlet waveguide 4 to include an impedance matching element 7 to control the uniformity / centering of the electric field in the fluidic medium; the short-circuit device 52 may suffice. In practice, inlet waveguides 4 generally include an impedance matching element 7. When a modification of the electric field distribution in the microwave cavity is implemented so that the symmetry indicator ESI is as close as possible to 1 or equal to 1, the impedance matching element 7 can be positioned in a neutral position, so that this modification depends only on a positional adjustment of the short-circuit device 52.When the positioning of the short-circuit device 52 is optimized and the symmetry indicator ESI is close to or equal to 1, the impedance matching element 7 can optionally be adjusted in position to match the impedance and decrease, if it is not considered negligible, the reflected power.

[0223] Advantageously, in this application context, the ESI symmetry indicator defined in the invention allows for:

[0224] - to control and manage the centering of the electric field inside the reaction gas flowing in the dielectric tube 6 during the 200-microwave plasma ignition phase; then

[0225] - once the plasma 200 is generated, to control and master the centering of the electric field inside the reaction gas, and therefore of the plasma 200, in order to significantly limit, or even prevent, the decentering of the plasma in the dielectric tube.

[0226] Thus, by preventing the decentering of the plasma 200, the microwave installation 1 of the invention makes it possible to avoid the formation on the wall of the tube of dielectric hot spots 6, where the plasma is closest, which can lead to its melting; and / or of chemical deposits in the context of microwave treatments where solid particles are created from the microwave plasma.

[0227] When the measurement system includes the third connection port 93 as illustrated in Figure 8, the measurement of the third physical parameter S3 at the level of the first median plane PI makes it possible to determine the best ignition position of the plasma 200, when the signal is at its maximum.

[0228] Note that in practice, the centering of the plasma 200 in the dielectric tube 6 is also favoured when the reaction gas is injected into the dielectric tube 6 in the form of a vortex with high velocities near the inner wall of the dielectric tube and lower velocities at the centre of the latter.

[0229] In this application context of plasma production 200, the control and mastery of the centering of the electric field can for example be implemented for a microwave generation frequency equal, not exhaustively, to 433 MHz (when solid state technologies are used in the design / manufacture of the microwave installation 1), to 915 MHz (as illustrated previously in Figures 10 to 13), or to 2450 MHz.

[0230] Plasma 200 can, for example, be used for the removal of VOCs contained in gases to be treated, and / or for the removal of GSEs. In another application context, the removal of VOCs contained in gases to be treated, and / or for the removal of GSEs, can be achieved by thermal oxidation using a catalyst contained within the microwave cavity 3 in the microwave installation 1. The catalyst is positioned in the microwave cavity so as to be opposite the inlet window 41 and the outlet window 51, and centered on the flow axis A1. The catalyst is designed to confine the flow of the gas to be treated (which corresponds to the fluidic medium) through it; and to thermally oxidize the VOCs and GSEs when its temperature is within a thermal oxidation temperature range.

[0231] In one embodiment, the catalyst can be contained and maintained inside the dielectric tube 6 as described so far. The gas to be treated therefore passes through the catalyst, propagating from the first end 61 of the dielectric tube 6 to its second end 62.

[0232] Since the catalyst is centered on the flow axis Al, controlling the symmetry / centering of the electric field, with respect to the flow axis Al, in the fluidic medium (i.e. the gas to be treated) also means controlling the symmetry / centering of the electric field in the catalyst and in the dielectric tube.

[0233] Centering the electric field in the catalyst and the gas to be treated with respect to the flow axis Al advantageously allows the catalyst to be heated uniformly, which allows its temperature to reach the thermal oxidation temperature range more quickly.

[0234] When the catalyst temperature is within the thermal oxidation temperature range, uniform heating of the catalyst allows for more efficient thermal oxidation of VOCs or GHGs. In other words, controlling and managing the centering of the electric field allows for better performance of the microwave installation 1 in removing VOCs or GHGs contained in the flowing gas.

[0235] Controlling and managing the centering of the electric field in the dielectric tube 6 also helps to prevent the formation of hot spots on the wall of the dielectric tube.

[0236] In this application context, the control and mastery of the centering of the electric field in the dielectric tube 6 can for example be implemented for a microwave generation frequency within a microwave frequency range of 300 MHz to 30 GHz.

[0237] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0238] It is also evident that all the characteristics described with reference to microwave installation 1 are transposable, alone or in combination, to the microwave process; and vice versa.

Claims

DEMANDS 1. Microwave installation (1) for continuous microwave treatment of a flowing fluidic medium, said microwave installation (1) comprising at least: - an enclosure (2) made of a microwave-reflective material and internally delimiting a microwave cavity (3); - a flow system connected to the enclosure to ensure flow of the fluidic medium through the microwave cavity (3) along a flow axis (Al); - an inlet waveguide (4) extending along a propagation axis (A2) orthogonal to the flow axis (Al) and coupled to an inlet window (41) provided on the enclosure (2) for microwave propagation into the inlet of the microwave cavity (3); - an output waveguide (5) extending along the propagation axis (A2) and coupled to an output window (51) provided on the enclosure (2) and arranged opposite the inlet window (41) with respect to the flow axis (Al), for microwave propagation at the output of the microwave cavity (3); - a short-circuit device (52) mounted on the output waveguide (5); said microwave installation (1) being characterized in that it comprises a measurement system for determining a symmetry indicator (SEI) representative of a symmetry of an electric field with respect to the flow axis (Al) inside the microwave cavity (3), said measurement system comprising: - a first connection port (81) and a second connection port (82) arranged on the enclosure (2) on either side and equidistant from a first median plane (PI) which includes the flow axis (Al) and which is orthogonal to the propagation axis (A2), in which the first connection port (81) and the second connection port (82) are arranged equidistant from a second median plane (P2) which includes the propagation axis (A2) and which is orthogonal to the flow axis (Al), and in which the first connection port (81) and the second connection port (82) are arranged equidistant from or are contained in a third median plane (P3) which includes the propagation axis (A2) and the flow axis (Al); - at least one measuring probe (91, 92, 93) adapted to be connected to the first connection port (81) and the second connection port (82) in order to measure respectively a first physical parameter (SI) and a second physical parameter (S2) which are representative of the electric field inside the microwave cavity (3) at the level of the first connection port (81) and the second connection port (82) respectively; the symmetry indicator (ESI) corresponding to the ratio between the first physical parameter (SI) and the second physical parameter (S2).

2. Microwave installation (1) according to claim 1, wherein the first connection port (81) and the second connection port (82) are arranged on the enclosure (2) and have one of the following symmetries: - a symmetry with respect to the first median plane (PI); - a symmetry with respect to the flow axis (Al); - a symmetry with respect to an intersection point (IPI) between the flow axis (Al) and the propagation axis (A2); - a combination of symmetry with respect to the first median plane (PI) and symmetry with respect to the second median plane (P2).

3. Microwave installation (1) according to any one of the preceding claims, wherein the enclosure (2) has a lower wall (22) and an upper wall (21) which are flat and parallel to the second median plane (P2), and wherein: - the first connection port (81) and the second connection port (82) are both disposed on the lower wall (22) or on the upper wall (21); or - one of the first connection port (81) and the second connection port (82) is located on the lower wall (22), and the other of the first connection port (81) and the second connection port (82) is located on the upper wall (21).

4. Microwave installation (1) according to any one of claims 1 to 3, wherein at least one measuring probe (91, 92, 93) comprises a single measuring probe adapted to be connected to the first connection port (81) and to the second connection port (82) in order to measure respectively the first physical parameter (SI) and the second physical parameter (S2).

5. Microwave installation (1) according to any one of claims 1 to 3, wherein at least one measuring probe (91, 92, 93) comprises: - a first measuring probe (91) adapted to be connected to the first connection port (81) in order to measure the first physical parameter (SI), and - a second measuring probe (92) adapted to be connected to the second connection port (82) in order to measure the second physical parameter (S2).

6. Microwave installation (1) according to claim 5, wherein the first measuring probe (91) and the second measuring probe (92) are pre-calibrated before their respective connections to the first connection port (81) and the second connection port (82).

7. Microwave installation (1) according to any one of the preceding claims, wherein the measuring system comprises a third connection port (83) disposed on the enclosure (2) in the first median plane (PI), at least one measuring probe (91, 92, 93) being adapted to be connected to the third connection port (83) in order to measure a third physical parameter (S3) representative of the electric field inside the microwave cavity (3) at the level of the third connection port (83), and therefore of the first median plane (PI).

8. Microwave installation (1) according to any one of the preceding claims, wherein the short-circuit device (52) is adjustable in position along the propagation axis (A2), to allow adjustment according to the symmetry indicator (ESI), the short-circuit device (52) being for example coupled, by means of a transmission mechanism, to an actuator.

9. Microwave installation (1) according to any one of the preceding claims, wherein the input waveguide (4) includes an impedance matching element (7), for example an iris or a piston adapter.

10. Microwave installation (1) according to any one of the preceding claims, wherein at least one measuring probe (91, 92, 93) is a coaxial dipole, which comprises a coaxial cable (911, 921, 931) comprising a central core (912, 922, 932) having a stripped termination forming an antenna (913, 923, 933) having an antenna length (L91, L92, L93) and introduced inside the microwave cavity (3).

11. Microwave installation (1) according to claim 10, wherein the first connection port (81) and the second connection port (82) both have an orifice passing through (811, 821) the enclosure along an orifice axis (A811, A821) parallel to the flow axis (Al), so that the antenna (913, 923, 933) of at least one probe (91, 92, 93) penetrates the interior of the microwave cavity (2) and is parallel to the flow axis (Al).

12. Microwave installation (1) according to any one of the preceding claims, wherein the first physical parameter (S1) and the second physical parameter (S2) correspond respectively to a first electric field intensity at the level of the first connection port (81) and a second electric field intensity at the level of the second connection port (82), and wherein at least one measuring probe (91, 92, 93) is coupled to a conversion device (10) configured to convert the first electric field intensity into a first electric voltage and the second electric field intensity into a second electric voltage; the conversion device (10) being disposed outside the enclosure (2).

13. Microwave installation (1) according to any one of the preceding claims, wherein the inlet waveguide (4) and the outlet waveguide (5) both have a rectangular cross-section with two long sides defining a large dimension (L4, L5) and two short sides defining a small dimension (W4, W5) smaller than the large dimension (L4, L5) such that: - the long sides of the inlet waveguide (4) and the outlet waveguide (5) are orthogonal to the flow axis (1), and the short sides are parallel to the flow axis (Al); or - the long sides of the inlet waveguide (4) and the outlet waveguide (5) are parallel to the flow axis (Al), and the short sides are orthogonal to the flow axis (Al).

14. Microwave installation (1) according to any one of the preceding claims, wherein the microwave installation (1) comprises a dielectric tube (6) made of microwave-transparent material such as: - the dielectric tube (6) extends longitudinally along the flow axis (Al) and passes completely through the enclosure (2) and the microwave cavity (3); - the dielectric tube (6) has two ends (61, 62) each connected to the flow system to ensure the flow of the fluidic medium through the microwave cavity (3), inside the dielectric tube (6), along the flow axis (Al).

15. Microwave installation (1) according to claim 14, wherein a microwave plasma (200) is generated in the dielectric tube (6) inside the microwave cavity (3), the fluidic medium corresponding to a reaction gas for the ignition and maintenance of the plasma (200).

16. Microwave installation (1) according to any one of claims 1 to 14, wherein the microwave installation (1) comprises, within the microwave cavity (3), a catalyst which is positioned opposite the inlet window (41) and the outlet window (51), and centered on the flow axis (Al); the catalyst being shaped to: confine through it the flow of a gas corresponding to the fluidic medium and comprising toxic or polluting gases; and thermally oxidize said toxic or polluting gases.

17. Microwave process for continuous microwave treatment of a flowing fluidic medium, the microwave process being implemented by a microwave installation (1) according to any one of the preceding claims, the microwave process comprising: - a generation step consisting of generating microwaves at a generation frequency within a frequency range of a microwave frequency range, the microwaves being guided to the input waveguide (4) in order to propagate the microwaves into the input of the microwave cavity (3); - a flow start step consisting of putting the fluidic medium into flow through the microwave cavity (3) along the flow axis (Al); - a first measurement step in which at least one measurement probe (91, 92, 93), which is connected to the first connection port (81), measures the first physical parameter (SI); - a second measurement step in which at least one measurement probe (91, 92, 93), which is connected to the second connection port (82), measures the second physical parameter (S2); - a determination step in which the symmetry indicator (ESI) is determined, which corresponds to the ratio between the first physical parameter (SI) and the second physical parameter (S2).

18. Microwave method according to claim 17, wherein the short-circuit device (52) is adjustable in position along the propagation axis, for example by being coupled to an actuator via a transmission mechanism, and the microwave method includes an adjustment step in which the short-circuit device (52) is adjusted in position according to the symmetry indicator (ESI).

19. Microwave method according to claim 18, wherein the adjustment step consists of adjusting the position of the short-circuit device (52) so that the symmetry indicator (ESI) is as close as possible to 1.

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