Microwave reactor for the reduction of toxic or polluting gases by thermal oxidation

Abstract

The invention relates to a microwave reactor (1) designed to reduce by thermal oxidation toxic or polluting gases contained in a gas flowing in an enclosure (3) which comprises said microwave reactor, which enclosure contains at least one macroporous ceramic element (7) through which the flowing gas passes. The treatment by thermal oxidation of the toxic or polluting gases is made possible when the flowing gas passes through the at least one macroporous ceramic element while the latter is at a temperature within a thermal oxidation temperature range. To reach such a temperature, the at least one macroporous ceramic element is heated by microwaves which come from at least one input waveguide (4); which is coupled to the enclosure. Abstract figure: Figure 1

Description

Title of the invention: Microwave reactor for the reduction of toxic or polluting gases by thermal oxidation Technical field

[0001] The invention relates to a microwave reactor for the reduction by thermal oxidation of toxic or polluting gases contained in gases.

[0002] The invention also relates to a microwave installation comprising the microwave reactor, as well as to a microwave treatment method implemented by the microwave installation for the reduction by thermal oxidation of toxic or polluting gases contained in gases.

[0003] The invention finds a preferred, and non-limiting, application in the industrial environment for treating, more precisely incinerating, volatile organic compounds resulting from the implementation of industrial processes, and thus enabling industry players to comply with regulations relating to Health and the Environment. It is also extendable to the treatment of toxic or polluting gases, such as greenhouse gases. Prior art

[0004] It is known that, in the context of their use and / or their activity, numerous industrial applications and infrastructures release toxic or polluting gases into the atmosphere which are harmful both to the environment (being partly responsible for pollution, global warming, etc.) and / or to human health (being, for example, mutagenic or carcinogenic).

[0005] It is also known that volatile organic compounds (abbreviated VOC in French) are chemical compounds containing at least one carbon atom associated with other atoms such as hydrogen, oxygen, nitrogen, sulfur, or phosphorus (with a few exceptions, such as carbon oxides). Emissions of volatile organic compounds come from many biological phenomena but also from combustion reactions or evaporation of organic compounds such as solvents present in paints, glues or cosmetics.

[0006] Emissions of volatile organic compounds produced by many industrial sectors are subject to very strict regulations at national and international level, which regulations also evolve over time.

[0007] Also, the treatment of volatile organic compounds constitutes an environmental and financial imperative for many industrial sites.

[0008] One of the best known solutions for the treatment of volatile organic compounds is thermal oxidation, also called incineration, which consists of destroying the volatile organic compounds using a heated catalyst. Thermal oxidation is carried out using incinerators. When incinerated (or thermally oxidized), volatile organic compounds are then transformed at least in part into carbon dioxide (CO2) and water (H2O). However, a disadvantage of incinerators is that they require natural gas to burn volatile organic compounds, which results in the generation of significant quantities of carbon dioxide, a gas known to contribute negatively to global warming. As a result, incinerators may potentially no longer meet environmental regulations such as those limiting carbon dioxide emissions. Furthermore, incinerators can generate significant investment and operating costs depending on the size of their infrastructure.

[0009] To treat volatile organic compounds by thermal oxidation in a more flexible and less cumbersome manner, while being more energy-efficient, it is known from the literature, for example in documents CN113209918 A and KR20180107584 A, to heat the catalyst by exposing it to microwaves. The catalyst is for this purpose placed in an enclosure of a microwave reactor inside which it is exposed to radiation, and in which circulates the gas which contains volatile organic compounds to be treated. Summary of the invention

[0010] The invention proposes a microwave reactor which advantageously makes it possible to heat in a homogeneous / uniform manner the catalyst contained in the reactor enclosure, here a macroporous ceramic element, with a view to reducing as effectively as possible by thermal oxidation the toxic or polluting gases contained in gases.

[0011] In particular, one aim of the invention is to achieve the objectives set by the environmental standards currently in force for the treatment and elimination of volatile organic compounds, while doing so without the use of combustible gases.

[0012] Thus, the invention provides a microwave reactor for the reduction by thermal oxidation of toxic or polluting gases contained in a flowing gas, said microwave reactor comprising:

[0013] - an enclosure made of a microwave-reflecting material and extending longitudinally along a flow axis for a flow of gas inside said enclosure;

[0014] - at least one input waveguide coupled to the enclosure and extending along an axis propagation orthogonal to the flow axis for microwave propagation along said propagation axis, said at least one input waveguide having a rectangular section with two long sides defining a large dimension and two short sides defining a small dimension less than the large dimension, such that the long sides of the input waveguide are parallel to the flow axis, while the short sides of the at least one input waveguide are orthogonal to the flow axis;

[0015] in which the enclosure has:

[0016] - an external diameter, said external diameter being greater than the small dimension of the at least one input waveguide which is fixed transversely on the enclosure,

[0017] - an internal diameter less than the external diameter, and

[0018] - an enclosure length measured along the flow axis between a first end and a second opposite end, said enclosure length being strictly greater than the large dimension of the input waveguide;

[0019] wherein at least one input window is provided on the enclosure surrounded by the at least one input waveguide for propagation of microwaves through the at least one input window inside the enclosure,

[0020] and wherein said microwave reactor comprises, within the enclosure, at least one macroporous ceramic element positioned at least opposite the at least one inlet window, which has an element diameter of between 0.25 and 0.8 times the internal diameter of the enclosure, and which confines the flow of gas through the at least one macroporous ceramic element within the enclosure.

[0021] It is thus quite clear, within the meaning of the invention, that when the gas reaches the or each macroporous ceramic element, the gas passes through this or each macroporous ceramic element, without bypassing it. Also, there is no need to resort to any dielectric tube, transparent to microwaves to confine the flow of gas.

[0022] In other words, the microwave reactor does not comprise a dielectric tube, made of a material transparent to microwaves, arranged inside the enclosure of the microwave reactor and internally receiving the at least one macroporous ceramic element.

[0023] In other words, the microwave reactor, in order to treat by thermal oxidation the toxic or polluting gases which are injected and propagate along a flow axis inside it, comprises an enclosure inside which is contained at least one macroporous ceramic element of the particle filter type. During their flow in the enclosure, the toxic or polluting gases, such as for example volatile organic compounds, pass through the at least one macroporous ceramic element.

[0024] The at least one macroporous ceramic element has properties di electrical elements allowing it to rapidly increase its temperature by absorbing electromagnetic radiation. When it rises in temperature, the at least one macroporous ceramic element heats the gases passing through it, and when this temperature, called the heating temperature, reaches a temperature range called the thermal oxidation temperature range, it thermally oxidizes the toxic or polluting gases. These temperatures reached by the at least one macroporous ceramic element to thermally oxidize the toxic or polluting gases are advantageously competitive with the operating temperatures of current gas incinerators which are used for this type of treatment, and which are of the order of 900°C.

[0025] When completely treated (i.e. thermally oxidized), the gases purified of any toxic or polluting gases can be released into the atmosphere without impacting the environment.

[0026] For volatile organic compounds, the microwave reactor advantageously offers a conversion rate (also called heat treatment efficiency) of approximately 99%. This conversion rate concerns a plurality of volatile organic compounds, for example and not exhaustively: xylene, isopropanol (IPA), methyl ethyl ketone (MEK, butanone), methyl tert-butyl ether (MTBE).

[0027] Furthermore, in the case where the treatment by thermal oxidation of a volatile organic compound generates emissions of harmful gases, these emissions remain lower than the emission limit values (ELV) specified in Article 27.7 of the Order in France of February 2, 1998 relating to the withdrawal and consumption of water as well as to emissions of all kinds from installations classified for the protection of the environment subject to authorization, which is applicable to atmospheric discharges at the outlet of a thermal oxidation treatment installation, namely: - an emission limit value for total volatile organic compounds equal to 20 mg eq.C / Nm3 (milligram equivalent Carbon per normal cubic meters),

[0028] - an emission limit value for carbon monoxide (CO) equal to 100 mg eq.CO / Nm3 (milligram equivalent CO per normal cubic meters), - an emission limit value for nitrogen oxides (NOx) equal to 100 mg eq.NO2 / Nm3 (milligram equivalent NO2 per normal cubic meters,

[0029] - an emission limit value for methane (CH4) equal to 50 mg eq.CHVNm3 (milligram equivalent CH4 per normal cubic meters).

[0030] Advantageously, the microwave reactor of the invention can process gas injection flow rates containing volatile organic compounds of the order of 30 m3 / h (i.e. approximately 500 L / min) for minimum concentrations of total volatile organic compounds of the order of 15,000 mg eq. C / Nm3 in an atmosphere containing at least 6% oxygen (vol%), without the formation of harmful co-products or at least the formation of these co-products at concentrations lower than their ELV. The time required for the gas to pass through and for 99% conversion of the toxic or polluting gases it contains for such gas injection rates and concentrations is of the order of one to two seconds.

[0031] In order to heat it quickly, the at least one macroporous ceramic element is positioned at least opposite the at least one inlet window through which the microwaves penetrate inside the enclosure.

[0032] The application of an electric field perpendicular to the flow axis, with the large side of the at least one input waveguide which is parallel to the propagation of the gases, advantageously means that said electric field will not see any boundary or abrupt transition of the dielectric losses.

[0033] The at least one macroporous ceramic element also has a honeycomb geometry in order to have a very large exchange surface with the gases passing through it, in order to be able to heat them and thermally oxidize them more quickly.

[0034] Geometrically, the at least one macroporous ceramic element has an element height extending into the enclosure along the flow axis, as well as an element diameter. The larger the element diameter, the more the thermal oxidation of toxic or polluting gases is accelerated.

[0035] In one embodiment of the invention, the at least one macroporous ceramic element is made of silicon carbide which is advantageous for rapidly heating up when exposed to microwaves.

[0036] The thermal oxidation temperature range depends on the nature of the toxic or polluting gases to be treated, and the flow rates at which they are injected into the microwave reactor.

[0037] For a macroporous silicon carbide ceramic element, the thermal oxidation temperature range for thermally oxidizing volatile organic compounds is between 800°C and 1000°C.

[0038] In other embodiments, the at least one macroporous ceramic element is chosen from: zirconia, lanthanum chromite, metal oxides.

[0039] In one embodiment of the invention, the enclosure is of circular section with a diameter corresponding to the lateral dimension. The at least one macroporous ceramic element is then in the form of a cylinder of macroporous structure (since the interior of the cylinder has a macroporous structure over its entire height).

[0040] According to another characteristic, the flow axis is a vertical axis so that the enclosure extends vertically, and the propagation axis is a horizontal axis so that the input waveguide extends horizontally.

[0041] Advantageously, the enclosure rests high on a support base, such as a support base provided with several support feet, so that the enclosure is raised off the ground thanks to the support base.

[0042] According to a characteristic of the invention, the at least one macroporous ceramic element has two opposite ends along the flow axis and, when the element diameter is strictly less than the internal diameter of the enclosure, the at least one macroporous ceramic element is held in the enclosure by means of holding elements fixed around the two respective ends.

[0043] According to different embodiments of the invention, the holding elements correspond to crowns or spacers. These holding elements also participate in the confinement of the gas so that it flows through the or each macroporous ceramic element.

[0044] According to a characteristic of the invention, the at least one macroporous ceramic element and the at least one inlet window respectively have an element height and a window height measured along the flow axis, said element height being greater than or equal to the window height.

[0045] Advantageously, when the at least one macroporous ceramic element has, in the direction of the flow axis, the same height as the at least one inlet window, it is heated quickly, but also uniformly, increasing the conversion rate of toxic or polluting gases.

[0046] According to one possibility, the at least one input window is delimited by two longitudinal edges parallel to the long sides of the at least one input waveguide and by two lateral edges parallel to the short sides of the at least one input waveguide, where the longitudinal edges have a length less than or equal to the long dimension and the lateral edges have a length less than or equal to the short dimension.

[0047] Thus, the at least one input window has a rectangular section equivalent to or smaller than the rectangular section of the input waveguide.

[0048] Advantageously, the longitudinal edges of the input window, by means of which the at least one input waveguide is fixed to the enclosure, have a length less than the major dimension and the lateral edges of the input window have a length equal to the minor dimension, so that the input window forms an input iris. Such an input iris optimizes the heating of the at least one macroporous ceramic element, by improving the penetration of microwaves therein. The size of the iris can be adapted so that the at least one macroporous ceramic element: rises to a heating temperature within the thermal oxidation temperature range and which is ideal for oxidizing ther- only a toxic or polluting gas of a given nature; and can be maintained at this said temperature.

[0049] According to a characteristic of the invention, the microwave reactor comprises at least one output waveguide fixed transversely to the enclosure in a manner diametrically opposite to the at least one input waveguide, where: - said at least one output waveguide extends along the propagation axis and has a rectangular section with two long sides defining a long dimension and two short sides defining a short dimension less than the long dimension, the long sides of the at least one output waveguide being parallel to the flow axis, while the short sides of the at least one output waveguide are orthogonal to the flow axis, the long dimension of the at least one output waveguide being equivalent to the long dimension of the at least one input waveguide and the short dimension of the at least one output waveguide being equivalent to the short dimension of the at least one input waveguide;

[0050] - said enclosure has at least one outlet window diametrically opposite to the at least one input window and surrounded by the at least one output waveguide for propagation of microwaves through the at least one output window.

[0051] According to a characteristic of the invention, the microwave reactor further comprises at least one short-circuit device fixed to the at least one output waveguide, said at least one short-circuit device being either of the short-circuit piston type adjustable along the propagation axis, or of the fixed short-circuit type.

[0052] Advantageously, the at least one short-circuit device serves as an impedance adapter to optimize / maximize the transmission of microwave radiation to the at least one macroporous ceramic element, so that it is heated homogeneously.

[0053] According to a characteristic of the invention, the enclosure length is between 1.5 times and 6 times greater than the large dimension of the at least one input waveguide.

[0054] Advantageously, this size ratio makes it possible to ensure progressive absorption of the microwaves by the at least one macroporous ceramic element, and to avoid the appearance of a resonance phenomenon inside the enclosure: if this enclosure had an enclosure length less than or equal to the large dimension of the input waveguide, the absorption of the microwaves would not be progressive along the flow axis, leading to heterogeneous heating of the at least one macroporous ceramic element.

[0055] According to one possibility, the at least one input waveguide is fixed transversely on the enclosure:

[0056] - either at a distance from the first end of between 0.4 and 0.6 times the enclosure length (therefore substantially in the middle of the enclosure);

[0057] - either at a distance from the first end of between 0.1 and 0.4 times the enclosure length (therefore substantially closer to one end of the enclosure).

[0058] According to a characteristic of the invention, the enclosure comprises covers provided on the first end and the second end, said covers being provided with connection sleeves for connecting the first end and the second end of the enclosure respectively to a pipe of a gas injection system and to a pipe of a gas exhaust system for setting the gas into flow.

[0059] In one embodiment of the invention, wherein the connecting sleeves (34, 36) each have a sleeve internal diameter (D34, D36) such that the element diameter (D7) is greater than or equal to said sleeve internal diameter (D34, D36).

[0060] According to one embodiment of the invention, the microwave reactor is such that:

[0061] - the at least one input waveguide comprises a first input waveguide and a second input waveguide which are offset from each other in a direction parallel to the flow axis, - the at least one input window comprises a first input window and a second input window which are also offset from each other in a direction parallel to the flow axis, the first input window being surrounded by the first input waveguide and the second input window being surrounded by the second input waveguide; and wherein the at least one macroporous ceramic element is positioned at least opposite the first inlet window and the second inlet window.

[0062] In other words, in this embodiment, the microwave reactor comprises two input waveguides, called respectively first and second input waveguides, which are arranged in parallel and which have similar structural and geometric characteristics.

[0063] Each input waveguide is coupled to its own input window for introducing microwaves into the enclosure. The two input windows are offset from each other along the flow axis.

[0064] Advantageously, the first input waveguide and the second input waveguide have in particular the same large dimension and the same small dimension. It is also advantageous for the second input waveguide to be made of the same material as the first input waveguide, so that the propagation kinematics of the microwaves in the two input waveguides are the same.

[0065] According to one embodiment of the invention, the at least one ceramic element ma croporeuse extends at least from the first inlet window to the second inlet window.

[0066] In other words, in one embodiment, the at least one macroporous ceramic element: - has an element height at least equal to the heights of the two inlet windows added to the distance separating them both in the direction of the flow axis, and - is located in the enclosure opposite the two entrance windows.

[0067] Advantageously, in this configuration, the at least one macroporous ceramic element is heated more quickly than in the case where, for the same element height, the enclosure would have only one inlet window. Given that the two inlet waveguides and the two inlet windows are structurally identical, the positioning as indicated of the at least one macroporous ceramic element in the enclosure also makes it possible to heat it uniformly.

[0068] The greater the element height of the at least one macroporous ceramic element, the longer the contact time of the gas with the at least one macroporous ceramic element. If the at least one macroporous ceramic element is furthermore uniformly heated, then the thermal oxidation is more efficient and the conversion rate of toxic or polluting gases is higher.

[0069] According to one embodiment of the invention, the at least one macroporous ceramic element comprises a first macroporous ceramic element positioned at least opposite the first inlet window, and a second macroporous ceramic element distinct from the first macroporous ceramic element and positioned at least opposite the second inlet window.

[0070] In this configuration, the enclosure comprises two macroporous ceramic elements such that each of them is at least positioned facing one of the two input windows. Since the two input waveguides and the two input windows are structurally identical, the two macroporous ceramic elements, in the case where they have the same geometry and are identically arranged at least facing their respective input window, are advantageously similarly heated. In other words, the heating time required to reach a heating temperature within the thermal oxidation temperature range is the same for the two macroporous ceramic elements.

[0071] Thermal oxidation of toxic or polluting gases therefore consists of the gas passing through the two macroporous ceramic elements. Some, or possibly all, of the toxic or polluting gases can be converted when the gas comes into contact with the first of the two macroporous ceramic elements that it encounters in the direction of flow. The role of the second macroporous ceramic element is therefore to thermally oxidize toxic or polluting gases which would not have been converted following the passage of the gas in the first macroporous ceramic element.

[0072] According to a characteristic of the invention, the first input waveguide and the second input waveguide are connected to the same upstream waveguide provided for the introduction of microwaves inside each of said first input waveguide and second input waveguide, said upstream waveguide having at least one rectilinear portion having a rectangular section with two large sides defining a large dimension and two small sides defining a small dimension smaller than the large dimension, the large sides of said upstream waveguide being parallel to the flow axis, while the small sides of said upstream waveguide are orthogonal to the flow axis.

[0073] It is thus possible, by means of the upstream waveguide, to carry out propagation of microwaves simultaneously in the first input waveguide and in the second input waveguide, parallel to the propagation axis. The upstream waveguide therefore has the function of transmitting the microwaves propagating within it to each of the two input waveguides.

[0074] It is also advantageous that the large dimension and the small dimension of the upstream waveguide are respectively equivalent to the large dimension and the small dimension of the first and second input waveguides. In this way, the propagation of microwaves in the upstream waveguide is identical to that in the first and second input waveguides.

[0075] According to one characteristic, the at least one output waveguide comprises a first output waveguide and a second output waveguide which are respectively fixed transversely on the enclosure in a manner diametrically opposite to the first input waveguide and to the second input waveguide, where:

[0076] - said second output waveguide extends parallel to the propagation axis and has a rectangular section with two long sides defining a long dimension and two short sides defining a short dimension less than the long dimension, the long sides of the second output waveguide being parallel to the flow axis, while the short sides of the second output waveguide are orthogonal to the flow axis, the long dimension of the second output waveguide being equivalent to the long dimension of the second input waveguide and the short dimension of the second output waveguide being equivalent to the short dimension of the second input waveguide;

[0077] - said enclosure has a second outlet window diametrically opposite the second input window and surrounded by the second output waveguide for microwave propagation through the second output window.

[0078] In other words, the microwave reactor comprises a second output waveguide associated with the second input waveguide, this second output waveguide having similar structural and geometric characteristics and the same function as the first output waveguide associated with the first input waveguide.

[0079] In particular, this second output waveguide may have the same large dimension and the same small dimension as the first output waveguide and the first input waveguide.

[0080] This second output waveguide can also, in the same way as the first output waveguide, be provided with a short-circuit device, for example of the short-circuit piston type adjustable parallel to the propagation axis or of the fixed short-circuit type.

[0081] According to a characteristic of the invention, the at least one macroporous ceramic element is a single piece or is formed from a stack of at least two macroporous ceramic blocks in the direction of the flow axis.

[0082] In one embodiment of the invention, the at least one macroporous ceramic element comprises at least two or more macroporous ceramic elements stacked and pressed against each other in the direction of the flow axis, and such that an addition of their respective element heights is equal to at least 90% of the enclosure length.

[0083] In a particular embodiment of the invention, the addition of the element heights of the macroporous ceramic elements stacked on top of each other is equal to the enclosure length.

[0084] The invention also relates to a microwave installation for reducing by thermal oxidation toxic or polluting gases contained in a flowing gas, said microwave installation comprising at least: - a microwave reactor as described above, - at least one microwave generator, connected to the at least one input waveguide of the microwave reactor

[0085] In other words, in the installation, the microwaves used to heat the at least one macroporous ceramic element, so that they thermally oxidize the toxic or polluting gases contained in the gases flowing in the enclosure of the microwave reactor, come from at least one microwave generator connected to the at least one input waveguide.

[0086] The higher the microwave power delivered by the at least one microwave generator, the more quickly the at least one macroporous ceramic element heats up.

[0087] Advantageously, the installation makes it possible to treat toxic or polluting gases by thermal oxidation over a microwave frequency range from 300 MHz to 30 GHz. Note that the dimensions of the microwave reactor vary proportionally with the inverse of the frequency considered for the treatment.

[0088] Previously, it was indicated that the microwave reactor makes it possible to advantageously treat, when the internal diameter of the enclosure is equal to 150 mm, gas injection flow rates containing volatile organic compounds of the order of 30 m3 / h (i.e. approximately 500 L / min) for minimum concentrations of volatile organic compounds in the air of the order of 15,000 mg eq.C / Nm3. To treat such gas injection flow rates and such concentrations, the at least one microwave generator must advantageously provide a maximum microwave power of between 13 kW and 15 kW.

[0089] According to a characteristic of the invention, the microwave installation comprises a control unit connected to the at least one microwave generator and configured to control a microwave power at the output of the at least one microwave generator and thus to regulate a temperature of the at least one macroporous ceramic element in a thermal oxidation temperature range.

[0090] According to a characteristic of the invention, the microwave installation comprises a temperature measuring device shaped to measure the temperature of the at least one macroporous ceramic element, the control unit being at least in communication with said temperature measuring device and configured to control the microwave power as a function of the measurement of the temperature of the at least one macroporous ceramic element.

[0091] According to one embodiment of the invention, the temperature measuring device is an infrared sensor, for example a camera or a pyrometer, placed on a skylight flange arranged on the enclosure of the microwave reactor.

[0092] Advantageously, the infrared sensor is a temperature measuring device compatible with a microwave installation used for the thermal oxidation of toxic or polluting gases included in gases. Indeed, the insertion of thermocouple type sensors inside the at least one macroporous ceramic element is impossible due to the interactions between this type of metal sensor and the microwave radiation, which can distort the measurements and generate electric arcs. The insertion of fiber optic sensors is also not possible due to the thermal degradation of the polymer sheath of this type of sensor at the heating temperatures to which the at least one macroporous ceramic element must rise (above 800°C).

[0093] According to a characteristic of the invention, the microwave installation comprises: - an injection system for injecting the gas with a given injection flow rate inside the enclosure of the microwave reactor, said injection system comprising an injection pipe connected to the first end of the enclosure for injecting the gas at said first end; - an exhaust system for exhausting gas from the microwave reactor enclosure, said exhaust system comprising an exhaust pipe connected to the second end of the enclosure for exhausting gas at said second end after treatment through the at least one macroporous ceramic element.

[0094] The injection flow rate of gas injected into the enclosure of the microwave reactor influences the efficiency of the thermal oxidation treatment of the toxic or polluting gases, and therefore the conversion rate. Indeed, the higher the injection flow rate, the more quickly the gas spreads in the enclosure, and the more the contact time between the toxic or polluting gases and the at least one macroporous ceramic element is reduced.

[0095] In other words, in order to completely convert the toxic or polluting gases, and so that the treatment is not partial and therefore does not give rise to the generation of harmful products, the heating temperature of the at least one macroporous ceramic element must be adapted within the thermal oxidation temperature range as a function of the gas injection flow rate. Increasing the gas injection flow rate involves increasing the heating temperature of the at least one macroporous ceramic element, which means that the at least one microwave generator must then provide more microwave power. Conversely, by reducing the gas injection flow rate, the contact time between the gas and the at least one macroporous ceramic element is longer.The oxidation reactions can then be completed for lower heating temperatures of the thermal oxidation temperature range, and therefore lower microwave powers delivered by the at least one microwave generator.

[0096] According to a characteristic of the invention, the installation comprises a flow meter for measuring the gas injection flow rate, and in which the control unit is at least in communication with the flow meter and is configured to control the microwave power as a function of the gas injection flow rate.

[0097] The invention finally relates to a microwave treatment method for the reduction by thermal oxidation of toxic or polluting gases contained in a flowing gas, said microwave treatment method being implemented by a microwave installation as described above and comprising at least the following steps: - a preliminary heating step during which the at least one microwave generator generates microwaves until the at least one macroporous ceramic element reaches a heating temperature within a thermal oxidation temperature range; - an injection step, taking place after the preliminary heating step, during which is continuously injected into the enclosure the gas with a given injection flow rate.

[0098] According to a characteristic of the invention, the microwave treatment method comprises a power control step during which a microwave power at the output of the at least one microwave generator is controlled to regulate a temperature of the at least one macroporous ceramic element in the thermal oxidation temperature range.

[0099] According to a characteristic of the invention, the power control step implements the control of the microwave power as a function of the gas injection flow rate. Brief description of the drawings

[0100] Other characteristics and advantages of the present invention will appear on reading the detailed description below, of a non-limiting example of implementation, made with reference to the appended figures in which:

[0101] [Fig-1] is a schematic sectional view of the microwave reactor of the invention according to a first embodiment of the invention for which three macroporous ceramic blocks are stacked in the enclosure, in the direction of flow of the gas injected into the enclosure and comprising toxic or polluting gases, forming at least one macroporous ceramic element, which is heated by microwaves coming from an input waveguide;

[0102] [Fig.2] is a schematic perspective view of the microwave reactor of [Fig.l];

[0103] [Fig.3] is a schematic sectional view of the microwave reactor of the invention according to a second embodiment of the invention for which are stacked in the enclosure, in the direction of flow of the gas injected into the enclosure and comprising toxic or polluting gases, four macroporous ceramic blocks forming the at least one macroporous ceramic element, which is heated by microwaves coming from two input waveguides connected, via a "Y"-shaped junction portion to an upstream waveguide provided for the introduction and propagation of said microwaves;

[0104] [Fig.4] is a close-up schematic sectional view of one of the two input waveguides, called the first input waveguide, of the microwave reactor of [Fig.3];

[0105] [Fig.5] is a perspective view of the microwave reactor illustrated [Fig.3] and [Fig.4];

[0106] [Fig.6] is a schematic perspective view (a), and from above and below (b) of a macroporous ceramic element.

[0107] [Detailed description of one or more embodiments of the invention]

[0108] The invention relates to a microwave reactor 1, 1' for the reduction by thermal oxidation of toxic or polluting gases contained in a gas in flow.

[0109] In the remainder of the description, it is considered that the microwave reactor 1, 1' is used in an application context of thermal oxidation of volatile organic compounds. However, the microwave reactor 1, 1' can be used in any other application context for which toxic or polluting gases are transformed by thermal oxidation. In addition, it can be used for the reduction of greenhouse gases.

[0110] A first embodiment of the microwave reactor 1 is illustrated in Figures 1 and 2. A second embodiment of the microwave reactor 1 is illustrated in Figures 3 to 5. The invention is not limited to these two embodiments described and illustrated.

[0111] With reference to Figures 1 and 2, the microwave reactor 1 comprises:

[0112] - an enclosure 3 made of a microwave-reflecting material and extending longitudinally along a flow axis 20 for a flow, inside said enclosure 3, of the gas containing volatile organic compounds;

[0113] - an input waveguide 4 coupled to the enclosure 3 and extending along a pro axis pagation 40 orthogonal to the flow axis 20 for microwave propagation along this propagation axis 40.

[0114] The microwave reactor 1 rests on a support base 90 provided with several support feet 91, possibly vertically adjustable support feet 91, so that the enclosure 3 is raised from the ground thanks to the support base 90.

[0115] The input waveguide 4 is defined by a rectangular section having: two large sides 41 defining a large dimension GD, and two small sides 42 defining a small dimension PD less than the large dimension GD. The large sides 41 of the input waveguide 4 are parallel to the flow axis 20, while the small sides 42 of the input waveguide 4 are orthogonal to the flow axis.

[0116] The flow axis 20 is a vertical axis so that the enclosure 3 extends vertically, and the propagation axis 40 is a horizontal axis so that the input waveguide 4 extends horizontally.

[0117] Enclosure 3 presents:

[0118] - an external diameter DE measured parallel to the short sides 42 of the waveguide input, and which is greater than the small dimension PD of the input waveguide which is fixed transversely on the enclosure 3;

[0119] - an internal diameter DI less than the external diameter DE;

[0120] - an enclosure length LE measured along the flow axis 20 between a first end 31 and a second opposite end 32, and which is strictly greater than the large dimension GD of the input waveguide 4.

[0121] It is conceivable that the input waveguide 4 is fixed transversely on the enclosure 3:

[0122] - at a distance from the first end 31 of between 0.4 and 0.6 times the length LE speaker (therefore substantially in the middle of speaker 3), or

[0123] - at a distance from the first end 31 of between 0.1 and 0.4 times the length of enclosure LE (therefore substantially closer to one end 31, 32 of enclosure 3).

[0124] The microwave reactor also comprises an output waveguide 5 fixed transversely to the enclosure 3 in a manner diametrically opposed to the input waveguide 4. The output waveguide 5 extends along the propagation axis 40 and has a rectangular section with: - two large sides 51 equal to the large dimension GD and parallel to the flow axis 20, and - two small sides 52 equal to my small dimension PD and orthogonal to the flow axis 20.

[0125] Enclosure 3 comprises: - an input window 37 which is surrounded by the input waveguide 4 in order to couple the enclosure 3 to the input waveguide 4, and thus propagate the microwaves inside the enclosure 3, and - an output window 38 which is surrounded by the output waveguide 5 in order to couple the enclosure 3 to the output waveguide 5, and thus propagate the microwaves from inside the enclosure 3 to the output waveguide 5.

[0126] The enclosure 3 comprises covers 33, 35 provided on the first end 31 and the second end 32. Each of the two covers 33, 35 is provided with a connecting sleeve 34, 36 for connecting respectively the first end 31 and the second end 32 of the enclosure 3 to a pipe 61 used to inject the gas to be treated into the enclosure 3 and to a pipe 62 for flowing the gas once treated. The two pipes 61, 62 are illustrated [Fig. 3] and [Fig. 5].

[0127] With reference to [Fig.l], 2 and 6, the treatment by thermal oxidation of the volatile organic compounds is carried out by means of at least one macroporous ceramic element 7 which is contained in the enclosure 3, which has an element diameter D7 of between 0.25 and 0.8 times the internal diameter DI of the enclosure 3.

[0128] Within the meaning of the invention, when the gas reaches the at least one macroporous ceramic element 7, the gas passes through this or each macroporous ceramic element 7, without bypassing it. Also, there is no need to use any dielectric tube transparent to microwaves to confine the flow of gas.

[0129] In other words, whatever the embodiment of the invention, the reactor microwave 1, 1' does not include a dielectric tube, made of a material transparent to microwaves, arranged inside the enclosure 3 of the microwave reactor 1, 1' and internally receiving the at least one macroporous ceramic element 7.

[0130] The at least one macroporous ceramic element 7 has dielectric properties allowing it to rapidly increase its temperature by absorbing electromagnetic radiation. When it rises in temperature, the at least one macroporous ceramic element 7 heats the gases passing through it. When this temperature, called the heating temperature, reaches a temperature range called the thermal oxidation temperature range, it thermally oxidizes the volatile organic compounds. When they are completely treated (i.e. thermally oxidized), the volatile organic compounds transform (or are converted) into water (H2O) and carbon dioxide (CO2). The temperature in this range required to thermally oxidize a quantity of volatile organic compounds contained in a gas depends partly on the nature / type of said volatile organic compounds.Non-limitingly, volatile organic compounds can correspond to xylene, isopropanol, methyl ethyl ketone (also called butanone).

[0131] Geometrically, the at least one macroporous ceramic element 7 has an element height H7 extending into the enclosure 3 along the flow axis 20, as well as an element diameter D7. The larger the element diameter D7, the more the thermal oxidation of the volatile organic compounds is accelerated. Also, the larger the element height H7 of the at least one macroporous ceramic element 7, the longer the contact time of the gas with the at least one macroporous ceramic element 7. If the at least one macroporous ceramic element 7 is furthermore heated uniformly, then the thermal oxidation is more efficient and the conversion rate of the volatile organic compounds higher.

[0132] As illustrated [Fig.6], the at least one macroporous ceramic element 7 also has a so-called “honeycomb” geometry in order to have a very large exchange surface with the gases passing through it, to be able to heat them and oxidize them thermally more quickly. When the enclosure 3 is of circular section with an external diameter DE corresponding to the lateral dimension, as is the case for the two embodiments presented, the at least one macroporous ceramic element 7 is then in the form of a cylinder with a macroporous structure (the interior of the cylinder has a macroporous structure over the entire height of the element H7).

[0133] In one embodiment of the invention, the at least one macroporous ceramic element 7 is made of silicon carbide which is advantageous for rapidly heating up when exposed to microwaves. The oxidation temperature range The thermal temperature of silicon carbide is between 800°C and 1000°C.

[0134] In other embodiments of the invention, the at least one macroporous ceramic element 7 is chosen from: zirconia, lanthanum chromite, metal oxides

[0135] In one embodiment of the invention, the at least one macroporous ceramic element 7 is monobloc, that is to say that it is formed from a single piece.

[0136] In other embodiments of the invention, such as those illustrated in this description, the at least one macroporous ceramic element 7 is formed by stacking in the direction of the flow axis 20 several macroporous ceramic blocks (each having the structure illustrated [Fig. 6]). In the first embodiment presented, the at least one macroporous ceramic element 7 is by stacking three macroporous ceramic blocks.

[0137] The at least one macroporous ceramic element 7, or each macroporous ceramic block composing it, has two ends 71, 72 opposite along the flow axis. When the element diameter D7 of the at least one macroporous ceramic element 7, or of the macroporous ceramic blocks, is strictly less than the internal diameter DI of the enclosure 3, the at least one macroporous ceramic element 7 or each macroporous ceramic block is held in the enclosure 3 by means of holding elements 73, for example crowns or spacers, fixed around the two ends 71, 72. The holding elements 71, 72 also participate in the confinement of the gas so that it flows through the macroporous ceramic element 7 or each macroporous ceramic block forming it.

[0138] Whatever the embodiment of the microwave reactor, it is provided that the at least one macroporous ceramic element is positioned at least opposite the at least one inlet window 37, 37' through which the microwaves penetrate inside the enclosure 3.

[0139] The advantage of this positioning and this height ratio is to be able to gradually heat the at least one macroporous ceramic element 7 so that ultimately, its temperature rise is uniform throughout its volume. In the given embodiment example [Fig.l] and [Fig.2], the central macroporous ceramic block of the stack forming the macroporous ceramic element 7 is positioned opposite the inlet window 37. When the microwaves begin to propagate in the enclosure 3, this central block will begin to rise in temperature compared to the other blocks. As the microwaves propagate, the other blocks of the stack will also rise in temperature. Ultimately, the temperature rise will be uniform throughout the stack / macroporous ceramic element 7.

[0140] In order to gradually heat the at least one macroporous ceramic element, it is also conceivable, whatever the embodiment of the invention, that:

[0141] - the element height H7 of the at least one macroporous ceramic element 7 is greater than the window height H37 of the at least one entrance window 37, 37'; and / or

[0142] - that the enclosure length LE can be between 1.5 times and 6 times su larger than the large dimension GD of the input waveguide 4. This dimension ratio makes it possible to avoid the appearance of a resonance phenomenon inside the enclosure, and to ensure progressive absorption of the microwaves by the at least one macroporous ceramic element 7 which, ultimately, will be heated homogeneously throughout its volume.

[0143] Concerning the first point, the at least one macroporous ceramic element, whether it is a single piece or formed by stacking several blocks, may have an element height H7 equal to at least 90% of the enclosure length LE.

[0144] In the first embodiment shown in Figures 1 and 2, the three stacked macroporous ceramic blocks constitute a macroporous ceramic element 7 whose element height H7, which corresponds to the combined heights of the three blocks, is equal to the enclosure length LE.

[0145] The connecting sleeves 34, 36 each have a sleeve diameter D34, D36 smaller than the element diameter D7 of the three macroporous ceramic blocks.

[0146] The outlet of the connecting sleeve 34 is in sealed connection with one of the ends of the macroporous ceramic element 7, and the inlet of the connecting sleeve 36 is in sealed connection with the other end of said macroporous ceramic element 7. In such a configuration, the risks that the gas to be treated and once treated can propagate in the enclosure 3 elsewhere than in the macroporous ceramic element 7 are eliminated.

[0147] It is also conceivable, as illustrated, to fix a short-circuit device on the output waveguide 5 used as an impedance adapter to optimize / maximize the transmission of microwave radiation to the macroporous ceramic element 7 and thus heat it uniformly.

[0148] To improve the penetration of microwaves into the macroporous ceramic element 7, it is also possible to delimit the input window 37 by two longitudinal edges parallel to the large sides GD of the input waveguide 4 and by two lateral edges parallel to the small sides PD of the input waveguide, where the longitudinal edges have a length less than or equal to the large dimension GD and the lateral edges have a length less than or equal to the small PD dimension.

[0149] Thus, the input window 37, which is of rectangular section equivalent to or smaller than the rectangular section of the input waveguide 4, forms an input iris 377. The size of the iris 377 can be adapted so that the macroporous ceramic element 7: rises to a heating temperature included in the thermal oxidation temperature range and which is ideal for thermally oxidizing a volatile organic compound of a given nature, and can be maintained at this said temperature.

[0150] Finally, the input waveguide 4 is connected to an upstream waveguide 8 from which the microwaves originate and whose role will be specified later in the description. Just like the input waveguide 4, the microwaves propagate inside the upstream waveguide 8 along the propagation axis 40. The upstream waveguide 8 has a rectilinear portion having a rectangular section with two large sides 81 equal to a large dimension, and two small sides 82 equal to a small dimension smaller than the large dimension, the large sides 81 being parallel to the flow axis 20, while the small sides 82 are orthogonal to it. In the first embodiment, the large dimension of the upstream waveguide 8 is equal to the large dimension GD of the input waveguide 4, and its small dimension is equal to the small dimension GD of the input waveguide 4.

[0151] Overall, a microwave reactor 1, 1' within the meaning of the invention may comprise one or more input waveguides, with each of the input waveguides opening via an input window into the enclosure 3 to propagate microwaves therein.

[0152] With reference to [Fig.3] to [Fig.5], in the second embodiment described, the microwave reactor 1' comprises, in addition to the input waveguide 4, called the first input waveguide, a second input waveguide 4' offset from the first waveguide 4 in a direction parallel to the flow axis 20. The second input waveguide surrounds a second input window 37' which is offset in a direction parallel to the flow axis 20 relative to the input window 37, called in this embodiment the first input window.

[0153] The first input waveguide 4 and the second input waveguide 4' are made of the same material and are geometrically identical (i.e. they both have the same large dimension GD and the same small dimension PD), so that the propagation kinematics of the microwaves in the two input waveguides 4, 4' are the same.

[0154] The microwave reactor 1' comprises a macroporous ceramic element 7 formed by stacking four macroporous ceramic blocks.

[0155] In different embodiments, it is provided that the ceramic element ma croporeuse can extend at least from the first inlet window 37 to the second inlet window 37', meaning that it:

[0156] - has an element height H7 at least equal to the heights of the two windows inlet H37, H37' to which is added the distance separating them both in the direction of the flow axis 20, said two inlet windows, and

[0157] - is arranged in enclosure 3 facing the two entrance windows 37, 37'.

[0158] This is the case of the second embodiment presented where the element height H7 of the macroporous ceramic element 7 is equal to the enclosure length LE. More precisely, the first inlet window 37 faces the two macroporous ceramic blocks closest to the first end 31, while the second inlet window 37' faces the two macroporous ceramic blocks closest to the second end 32.

[0159] As illustrated, each of the two input windows forms an input iris 377, 377'. The two input irises 377, 377' are geometrically identical.

[0160] In this second embodiment, the macroporous ceramic element 7, as positioned in the enclosure 3, is heated more quickly compared to the first embodiment for which the microwave reactor 1 has only one input waveguide 4. Since the two input waveguides 4, 4' and the two input windows 37, 37' are structurally and geometrically identical, the positioning of the macroporous ceramic element 7 in the enclosure 3 also allows it to be heated uniformly.

[0161] The microwave reactor 1' also comprises, in addition to the output waveguide 5, called the first output waveguide, another output waveguide, called the second output waveguide 5'. The first output waveguide 5 (respectively the second output waveguide) is fixed transversely to the enclosure 3 in a manner diametrically opposite to the first input waveguide 4 (respectively to the second input waveguide 4').

[0162] The second output waveguide 5': - extends parallel to the propagation axis 40; - is made of the same material as the first output guide 5; - has the same geometry as the first output guide 5.

[0163] The enclosure 3 then has, in addition to the outlet window 38, called the first outlet window, a second outlet window 38' which is surrounded by the second outlet guide 5'. The two outlet windows 3 may have an identical geometry. In this second embodiment, the longitudinal edges of the two outlet windows 38, 38' are equal to the large dimension GD, and the lateral edges of the two outlet windows 38, 38' are equal to the small dimension PD.

[0164] The second output waveguide 5' can also, in the same way as the first output waveguide 5, and as shown, be provided with a short-circuit device.

[0165] The first input waveguide 4 and the second input waveguide 4' are connected, by means of a "Y" junction portion 83', to the same upstream waveguide 8' provided to introduce the microwaves inside each of them.

[0166] The upstream waveguide 8' has a rectilinear portion having a rectangular section with two large sides 81' equal to a large dimension, and two small sides 82' equal to a small dimension less than the large dimension, the large sides 81' being parallel to the flow axis 20, while the small sides 82' are orthogonal to it. In the second embodiment, the large dimension of the upstream waveguide 8' is equal to the large dimension GD of the two input waveguides 4, 4', and its small dimension is equal to the small dimension GD of the two input waveguides 4, 4'.

[0167] The upstream waveguide 8' has at least one rectilinear portion having a rectangular section with two large sides 81' equal to the large dimension GD, and two small sides 82' equal to the small dimension PD, the large sides 81' being parallel to the flow axis 20, while the small sides 82' are orthogonal to it.

[0168] It is thus possible, by means of the upstream waveguide 8', to carry out microwave propagation simultaneously in the first input waveguide 4 and in the second input waveguide 4', parallel to the propagation axis 40.

[0169] It is also advantageous that the large sides 81' and the small sides 82' of the upstream waveguide are respectively equal to the large dimension GD and the small dimension PD of the input waveguides 4, 4' because the propagation of the microwaves in the upstream waveguide 8' is identical to that in the first and second input waveguides 4, 4'.

[0170] Finally, compared to the first embodiment, the microwave reactor 1' is here arranged on a support base 90', the geometry of which is in particular adapted to that of the input waveguides 4, 4' and the upstream waveguide 8'.

[0171] In order to carry out thermal oxidation of the volatile organic compounds that gases may contain, the microwave reactor 1, 1' is integrated into a microwave installation (not illustrated) which also comprises: - at least one microwave generator configured to generate microwaves for frequencies within a microwave frequency range of 300 MHz to 30 GHz. The at least one microwave generator is connected to the input waveguides 4, 4' of the microwave reactors 1, 1' via the upstream waveguides 8, 8'. In other words, the microwaves propagating inside the input waveguides 4, 4' and entering the enclosure 3 of the microwave reactors 1, 1' come from the at least one microwave generator. In both embodiments presented, the upstream waveguide 8, 8' has a rectilinear section. However, in other embodiment variants, the upstream waveguide 8, 8' may be vertical and / or be horizontal and / or have bends and / or be formed of several waveguide sections depending on the arrangement and location of the at least one microwave generator relative to the microwave reactor 1, 1' and according to inclinations of the flow axis 20 and the propagation axis 40; - an injection system used to inject the gas to be treated into the enclosure 3 of the microwave reactor 1, 1'. The injection system is connected to the first end 31 of the enclosure 3 by means of the pipe 61; - an exhaust system for exhausting the treated gas, water (H2 O) and carbon dioxide (CO2) produced following the thermal oxidation of the volatile organic compounds, from the enclosure 3 of the microwave reactor 1, 1'. The exhaust system is connected to the second end 32 of the enclosure 3 by means of the pipe 62; - a control unit connected at least to the at least one microwave generator and configured to control a microwave power output from the at least one microwave generator; and thus control the temperature of the at least one macroporous ceramic element 7. Such a control unit is for example of the type comprising an automaton, a processor, a microcontroller, an electronic card or any other equivalent calculation and processing means.

[0172] The higher the power delivered by the at least one microwave generator, the more quickly the at least one macroporous ceramic element 7 rises in temperature.

[0173] The microwave installation implements a microwave treatment method starting with a preliminary heating step during which the at least one microwave generator generates microwaves until the at least one macroporous ceramic element 7 reaches a heating temperature within the thermal oxidation temperature range. As previously indicated, this temperature range, for a macroporous ceramic element 7 made of silicon carbide, is between 800° and 1000°C.

[0174] Once the heating temperature of the at least one macroporous ceramic element is in the thermal oxidation range, the control unit implements a power control step during which it controls the microwave power output from the at least one microwave generator in order to maintain the heating temperature in the thermal oxidation temperature range. In other words, depending on the heating temperature of the at least one macroporous ceramic element 7, the control unit sends power setpoints in the form of signals to the at least one microwave generator to lower or increase or possibly actually maintain the power it delivers.

[0175] The heating temperature of the at least one macroporous ceramic element 7 is measured by a temperature measuring device which can be in communication with the control unit, by means of a radiofrequency communication protocol, or else connected to it. The temperature measuring device therefore communicates to the control unit a temperature datum relating to the at least one macroporous ceramic element, which upon receipt of this temperature datum transmits appropriate power instructions. The temperature measuring device is an infrared sensor, for example a camera or a pyrometer, placed on a skylight flange 92 arranged on the enclosure 3 of the microwave reactor 1, 1' (see [Fig.5]).

[0176] Following the preliminary heating step, and in parallel with the control step, the microwave installation implements an injection step during which the gas containing volatile organic compounds is continuously injected into the enclosure 3 according to a given injection rate. The gas injection rate is measured by means of a flow meter included in the installation and which can be in communication with the control unit, by means of a radiofrequency communication protocol, or connected to it. The flow meter transmits the measured gas injection rate to the control unit, which upon receipt of said gas injection rate can transmit, according to it and also to the heating temperature of the at least one macroporous ceramic element 7, power setpoints to the at least one microwave generator to increase, or decrease, or maintain the power that it delivers.

[0177] As previously stated, when fully processed / converted, volatile organic compounds in a gas are converted into water and carbon dioxide. However, if only partially processed, they may generate emissions of harmful products such as carbon monoxide (CO), nitrogen oxide (NOx), or aldehyde-type compounds.

[0178] The injection flow rate of the gas injected into the enclosure 3 of the microwave reactor 1, 1' influences the efficiency of the thermal oxidation treatment of the volatile organic compounds, and therefore the conversion rate. Indeed, the higher the injection flow rate of the gas, the more quickly the latter propagates in the enclosure, and the more the contact time between the volatile organic compounds and the at least one macroporous ceramic element 7 is reduced.

[0179] In other words, in order to completely convert the volatile organic compounds, and for the heat treatment not to be partial, the heating temperature of the at least one macroporous ceramic element 7 must be adapted within the thermal oxidation temperature range depending on the gas injection flow rate. Increasing the gas injection flow rate involves increasing the heating temperature of the at least one macroporous ceramic element 7. at least one macroporous ceramic element 7, which means that the at least one microwave generator must then provide more power. Conversely, by reducing the gas injection rate, the contact time between the gas and the at least one macroporous ceramic element 7 is longer. The oxidation reactions can then be completed for lower heating temperatures in the thermal oxidation temperature range, and therefore lower microwave powers delivered by the at least one microwave generator. This is why, during the power control step, the control unit sends power setpoints to the at least one microwave generator as a function of the gas injection rate and the heating temperature of the at least one macroporous ceramic element when the thermal oxidation of the volatile organic compounds begins.

[0180] The microwave reactor 1, 1' of the invention is capable of treating, when its internal diameter is equal to 150 mm, gases containing volatile organic compounds for gas injection flow rates of the order of 30 m3 / h (i.e. approximately 500 L / min) for minimum concentrations of total volatile organic compounds of the order of 15,000 mg eq. C / Nm3 in an oxygen-depleted atmosphere, i.e. an atmosphere containing at least 6% oxygen (vol%) under nitrogen inerting, without the formation of harmful co-products or at least the formation of these co-products at concentrations lower than their ELV. To treat such gas injection flow rates and such concentrations, the at least one microwave generator must advantageously provide a maximum microwave power of between 13 kW and 15 kW.The time required for the gas to pass through and for 99% conversion of the toxic or polluting gases it contains for such gas injection rates and concentrations is of the order of one to two seconds.

Claims

Claims

1. Microwave reactor (1, 1') for abatement by thermal oxidation of toxic or polluting gases contained in a flowing gas, said microwave reactor (1, 1') comprising: - an enclosure (3) made of a microwave-reflecting material and extending longitudinally along a flow axis (20) for a flow of the gas inside said enclosure (3); - at least one input waveguide (4, 4') coupled to the enclosure (3) and extending along a propagation axis (40) orthogonal to the flow axis (20) for microwave propagation along said propagation axis (40), said at least one input waveguide (4, 4') having a rectangular section with two long sides (41) defining a large dimension (GD) and two short sides (42) defining a small dimension (PD) smaller than the large dimension (GD), such that the long sides (41) of the input waveguide (4, 4') are parallel to the flow axis (20), while the short sides (42) of the at least one input waveguide (4, 4') are orthogonal to the flow axis (20); in which the enclosure (3) has: - an external diameter (DE), said external diameter (DE) being greater than the small dimension (PD) of the at least one input waveguide (4, 4') which is fixed transversely on the enclosure (3), - an internal diameter (ID) less than the external diameter (OD), and - an enclosure length (LE) measured along the flow axis (20) between a first end (31) and an opposite second end (32), said enclosure length (LE) being strictly greater than the large dimension (GD) of the input waveguide (4, 4'); wherein there is provided on the enclosure (3) at least one inlet window (37) surrounded by the at least one inlet waveguide (4, 4') for propagation of microwaves through the at least one inlet window (37) inside the enclosure (3), and wherein said microwave reactor (1) comprises, inside the enclosure (3), at least one macroporous ceramic element (7) positioned at least opposite the at least one inlet window (37), which has an element diameter (D7) of between 0.25 and 0.8 times the internal diameter (DI) of the enclosure (3), and which confines the flow of gas through the at least one macroporous ceramic element (7) inside the enclosure (3).

2. Microwave reactor (1, 1') according to claim 1, wherein the at least one macroporous ceramic element (7) has two ends (71, 72) opposite along the flow axis (20) and, when the element diameter (D7) is strictly less than the internal diameter (DI) of the enclosure (3), the at least one macroporous ceramic element (7) is held in the enclosure (3) by means of holding elements (73) fixed around the two respective ends (71, 72).

3. Microwave reactor (1, 1') according to claim 1 or 2, wherein the at least one macroporous ceramic element (7) and the at least one inlet window (37) respectively have an element height (H7) and a window height (H37) measured along the flow axis (20), said element height (H7) being greater than or equal to the window height (H37).

4. Microwave reactor (1, 1') according to any one of the preceding claims, comprising at least one output waveguide (5) fixed transversely to the enclosure (3) in a manner diametrically opposite to the at least one input waveguide (4, 4'), wherein: - said at least one output waveguide (5) extends along the propagation axis (40) and has a rectangular section with two long sides (51) defining a long dimension (GD) and two short sides (52) defining a short dimension (PD) smaller than the long dimension (GD), the long sides (51) of the at least one output waveguide (5) being parallel to the flow axis (20), while the short sides (52) of the at least one output waveguide (5) are orthogonal to the flow axis (20), the long dimension (GD) of the at least one output waveguide (5) being parallel to the flow axis (20), the long dimension (GD) of the at least one output waveguide (5) being orthogonal to the flow axis (20), the long dimension (GD) of the at least one output waveguide (5) being parallel to the flow axis (20), while the short sides (52) of the at least one output waveguide (5) are orthogonal to the flow axis (20), the long dimension (GD) of the at least one output waveguide (5) being parallel ... output waveguide (5) being equivalent to the large dimension (GD) of the at least one input waveguide (4,4') and the small dimension (PD) of the at least one output waveguide (5) being equivalent to the small dimension (PD) of the at least one input waveguide (4, 4'); - said enclosure (3) has at least one output window (38) diametrically opposite the at least one input window (37) and surrounded by the at least one output waveguide (5) for propagation of microwaves through the at least one output window (38).,

5. Microwave reactor (1,1') according to claim 4, further comprising at least one short-circuit device (55) fixed on the at least one output waveguide (5), said at least one short-circuit device being either of the short-circuit piston type (55) adjustable along the propagation axis (40), or of the fixed short-circuit type.

6. Microwave reactor (1, 1') according to any one of the preceding claims, wherein the enclosure length (LE) is between 1.5 times and 6 times greater than the major dimension (GD) of the at least one input waveguide (4, 4').

7. Microwave reactor (1,1') according to any one of the preceding claims, wherein the enclosure (3) comprises covers (33, 35) provided on the first end (31) and the second end (32), said covers (33, 35) being provided with connecting sleeves (34, 36) for connecting the first end (31) and the second end (32) of the enclosure (3) respectively to a pipe (61) of a gas injection system and to a pipe (62) of a gas exhaust system for gas flow.

8. Microwave reactor (1,1') according to claim 8, wherein the connecting sleeves (34, 36) each have a sleeve internal diameter (D34, D36) such that the element diameter (D7) is greater than or equal to said sleeve internal diameter (D34, D36).

9. Microwave reactor (1') according to any one of the preceding claims, wherein: - the at least one input waveguide (4, 4') comprises a first input waveguide (4) and a second input waveguide (4') which are offset from each other in a direction parallel to the flow axis (20), - the at least one input window (37) comprises a first input window (37) and a second input window (37') which are also offset from each other in a direction parallel to the flow axis (20), the first input window (37) being surrounded by the first input waveguide (4) and the second input window (37') being surrounded by the second input waveguide (4'); and wherein the at least one macroporous ceramic element (7) is positioned at least opposite the first inlet window (37) and the second inlet window (37').

10. A microwave reactor (1') according to claim 9, wherein the at least one macroporous ceramic element (7) extends at least from the first inlet window (37) to the second inlet window (37').

11. A microwave reactor (1') according to claim 9, wherein the at least one macroporous ceramic element (7) comprises a first macroporous ceramic element positioned at least opposite the first inlet window (37), and a second macroporous ceramic element distinct from the first macroporous ceramic element and positioned at least opposite the second inlet window (37').

12. Microwave reactor (1') according to any one of claims 9 to 11, wherein the first input waveguide (4) and the second input waveguide (4') are connected to a same upstream waveguide (8') provided for the introduction of microwaves inside each of said first input waveguide (4) and second input waveguide (4'), said upstream waveguide (8') having at least one rectilinear portion having a rectangular section with two long sides (81') defining a long dimension (GD) and two short sides (82') defining a short dimension (PD) less than the long dimension (GD), the long sides (81') of said upstream waveguide (8') being parallel to the flow axis (20), while the short sides (82') of said upstream waveguide (8') are orthogonal to the flow axis (20).

13. Microwave reactor (1, 1') according to any one of the preceding claims, wherein the at least one macroporous ceramic element (7) is in one piece or is formed from a stack of at least two macroporous ceramic blocks in the direction of the flow axis (20).

14. Microwave installation for abatement by thermal oxidation of toxic or polluting gases contained in a flowing gas, said microwave installation comprising at least: - a microwave reactor (1, 1') according to any one of claims 1 to 13, - at least one microwave generator, connected to the at least one input waveguide (4, 4') of the microwave reactor (1, 1').

15. Microwave installation according to claim 14, comprising a control unit connected to the at least one microwave generator and configured to control a microwave power output from the at least one microwave generator and thus to regulate a temperature of the at least one macroporous ceramic element (7) in a thermal oxidation temperature range.

16. Microwave installation according to claim 15, comprising a temperature measuring device shaped to measure the temperature of the at least one macroporous ceramic element (7), the control unit being at least in communication with said temperature measuring device and configured to control the microwave power as a function of the measurement of the temperature of the at least one macroporous ceramic element (7).

17. Microwave installation according to any one of claims 14 to 16, comprising: - an injection system for injecting the gas with a given injection flow rate inside the enclosure (3) of the microwave reactor (1, 1'), said injection system comprising an injection pipe (61) connected to the first end (31) of the enclosure (3) to inject the gas at said first end (31); - an exhaust system for exhausting the gas from the enclosure (3) of the microwave reactor (1, 1'), said exhaust system comprising an exhaust pipe (62) connected to the second end (32) of the enclosure (3) to evacuate the gas at said second end (32) after treatment through the at least one macroporous ceramic element (7).

18. Microwave installation according to claims 15 and 17, comprising a flow meter for measuring the injection flow rate of the gas, and in which the control unit is at least in communication with the flow meter and is configured to control the microwave power as a function of the injection flow rate of the gas.

19. Microwave treatment method for abatement by thermal oxidation of toxic or polluting gases contained in a flowing gas, said microwave treatment method being implemented by a microwave installation according to any one of claims 14 to 18 and comprising at least the following steps: - a preliminary heating step during which the at least one microwave generator generates microwaves until the at least one macroporous ceramic element (7) reaches a heating temperature included in a thermal oxidation temperature range; - an injection step, taking place after the preliminary heating step, during which the gas is continuously injected into the enclosure (3) with a given injection flow rate.

20. A microwave treatment method according to claim 19, comprising a power control step during which a microwave power at the output of the at least one microwave generator is controlled to regulate a temperature of the at least one macroporous ceramic element (7) in the thermal oxidation temperature range.

21. A microwave treatment method according to claim 20, wherein the power control step implements controlling the microwave power as a function of the gas injection flow rate.

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