WO2023242286A1

WO2023242286A1 - Method for industrial production of a hot mix

Info

Publication number: WO2023242286A1
Application number: PCT/EP2023/065994
Authority: WO
Inventors: Sébastien Langlois; Frédéric Vandenbussche
Original assignee: Colas
Priority date: 2022-06-17
Filing date: 2023-06-14
Publication date: 2023-12-21
Also published as: FR3136793A1

Abstract

The invention relates to a method for industrial production of a hot mix using a microwave furnace (2) provided with a heating body (4), at least one microwave generator (24a) and at least one waveguide extending in a longitudinal direction inside the heating body (4), the method comprising the following steps: • a) aggregates and/or mix aggregates are introduced into the heating body (4), • b) the aggregates and/or the mix aggregates introduced into the heating body (4) are exposed to the microwaves emitted by the microwave generator (24a) and fed into the heating body (4) by the waveguide, so as to produce heated aggregates and/or mix aggregates, the waveguide distributing the microwaves directly onto the aggregates and/or mix aggregates, • c) the heated aggregates and/or mix aggregates are extracted from the heating body (4), • d) the heated aggregates and/or mix aggregates are used to produce the hot mix, in which use is made of the at least one waveguide (22) which comprises a plurality of slots (32), and the slots are positioned facing the aggregates and/or mix aggregates.

Description

Title of the invention: Process for the industrial production of a hot mix

The present invention generally relates to the field of hot mix production.

It relates more particularly to a process for the industrial production of a hot mix using a microwave oven.

Hot mixes are composed of a mixture of aggregates, recycled mix aggregates, fines also called "fillers" generally limestone, possible additives and hydrocarbon binder such as bitumen.

The asphalt aggregates come from old milled or recrushed roadways. These are recycled materials.

The hot mix production processes currently used include the drying and heating of aggregates at temperatures between 80 and 200 °C then the mixing of the heated aggregates with hydrocarbon binder and filler in a mixing system and finally loading transport trucks 230.

These processes usually use a rotary kiln in which a flame is produced by combustion of fossil energy such as fuel, gas or lignite.

This type of oven has the disadvantage of comprising inhomogeneous heating zones. When passing near hotter zones of the oven, the bitumen of the asphalt aggregates undergoes thermal shock at temperatures well above the set temperature. In fact, to heat the asphalt aggregates to 160°C, they travel through hot air flows with a temperature above 250°C. These hot air flows cause the evaporation of part of the volatile fractions of the bitumen and induce inevitable oxidation.

This effect is well known to those skilled in the art since it is usually measured via the RTFOT test, which is intended to be characteristic of conventional aging obtained in a coating plant.

In addition, for a mix produced at an average temperature of 160°C, CO2 emissions are of the order of 16 to 55 kg of CO2 equivalent per tonne of mix produced.

In this field of ovens, the following documents are known: CN 113 152 212 A, US 4 276 093 A, FR 3070869 Al and EP 2 530059 Al. In order to limit the aforementioned drawbacks, the present invention proposes a process for the industrial production of a hot mix using a microwave oven provided with a heating body, at least one microwave generator and at least one waveguide extending in a longitudinal direction inside the heating body, the method comprising the following steps: a) aggregates and/or coated aggregates are introduced inside the body heating, b) the aggregates and/or coated aggregates introduced into the heating body are exposed to microwaves emitted by the microwave generator and conveyed into the heating body by the wave guide, so as to produce aggregates and/or heated asphalt aggregates, c) the aggregates and/or heated asphalt aggregates produced are extracted from the heating body d) the heated aggregates and/or asphalt aggregates are used to produce hot mix.

Thus, advantageously according to the invention, the hot mix is produced at least partially by an electrically powered microwave oven. Combustion gas emissions are reduced compared to a conventional process.

The method according to the invention also has the advantage of concentrating the microwaves on a bed of moving materials to homogenize the heating. The heating temperature of the aggregates and/or aggregates is particularly well controlled, which ensures satisfactory and uniform properties for the hot mix produced by this process.

The process is particularly advantageous for the heat treatment of asphalt aggregates. Indeed, the heat treatment according to the process of the invention allows less aging of the bitumen contained in the aggregates.

On the one hand, the material introduced into the heating body is at room temperature and remains so until receiving the microwaves, and, on the other hand, the dielectric effects caused by the microwaves gradually increase the internal temperature of the materials introduced into the heating body without exceeding the desired set temperature. There is therefore no excessive aging of the bitumen in the asphalt aggregates during heat treatment in the microwave oven.

Other non-limiting and advantageous characteristics of the process according to the invention, taken individually or in all technically possible combinations, are as follows: - the heating body of the microwave oven extending along a longitudinal axis between two opposite longitudinal ends, the aggregates and/or the coated aggregates are introduced, in step a), at a first of the two longitudinal ends of the heating body, in step b) the aggregates are advanced and/or the asphalt aggregates contained in the heating body according to a direction parallel to the longitudinal axis of the heating body, from the first longitudinal end towards a second longitudinal end, and the heated aggregates and/or asphalt aggregates are extracted, in step c), at the second longitudinal end of the heating body;

- the production of aggregates and/or coated aggregates is carried out continuously;

- said waveguide comprising a slotted waveguide mounted inside the heating body extending in a longitudinal direction parallel to the longitudinal axis (X-X) of the heating body (4) and connected to the one of its ends to said microwave generator; in step a), the aggregates and/or the coated aggregates are introduced into the heating body by a supply system opening into the heating body at the first of said two longitudinal ends thereof, at the step c), the heated aggregates and/or coated aggregates are extracted by an evacuation system opening into the heating body at the second longitudinal end thereof;

- the microwaves are trapped inside the oven using two fixed covers, each cover being mounted on one of the longitudinal ends of the heating body with the interposition of annular wave trapping seals;

- the heating body of the oven being cylindrical and rotary, during step b), said heating body is rotated around its longitudinal axis, the longitudinal axis of the heating body is inclined relative to the horizontal so as to regulate the speed of advance of the aggregates and/or coated aggregates in the heating body;

- the heating body is provided internally with stirring blades which extend in an inclined manner relative to the longitudinal axis of the heating body and are integral in rotation with it, and in step b), we put rotating the stirring blades with the heating body while tilting the longitudinal axis thereof to advance the aggregates and/or coated aggregates contained in the heating body;

- the heating body houses a belt conveyor, and during step b), the belt conveyor is activated to advance the aggregates and/or the coated aggregates contained in the heating body;

- in step b), the gases released during the heating of the aggregates and/or the coated aggregates are evacuated by an evacuation device ensuring a depression of the heating body of the oven and/or gases are injected inside the heating body;

- the oven comprising two microwave generators and two corresponding wave guides and the heating body of the oven comprising a first part in which extends a first of said two wave guides associated with a first of said two microwave generators -waves and a second part in which extends the second wave guide associated with the second microwave generator, in step b), the aggregates and/or the coated aggregates successively cross the first part then the second part of the heating body, said first and second parts of the heating body having different temperature profiles;

- the first microwave generator and the first wave guide being configured so as to produce a progressive increase in the temperature along the first part of the heating body and the second microwave generator and the second guide the waves being configured so as to maintain a constant target temperature along the second part of the heating body, in step b) the aggregates and/or the coated aggregates are subjected to the progressive increase in the temperature the along the first part of the heating body and maintained at the target temperature along the second part of the heating body;

- the aggregates and/or the asphalt aggregates introduced into the heating body comprise at least one of the following components: limestone aggregates, quartzite aggregates, asphalt millings;

- in step b), the aggregates and/or the coated aggregates are heated to a temperature between 80 and 200 degrees Celsius to dry and heat at least part of the aggregates and/or the coated aggregates;

- before their introduction into the heating body of the oven, the aggregates and/or the coated aggregates are preheated in a preheating device;

- the gases released during heating of the aggregates and/or asphalt aggregates in the oven are recirculated to the preheating device;

- after step c), the heated aggregates and/or asphalt aggregates are stored in hoppers then transported to a mixer;

- the heated aggregates and/or asphalt aggregates are mixed with a hydrocarbon binder;

- the aggregates and/or asphalt aggregates heated by the microwave oven are mixed with other aggregates and/or asphalt aggregates heated by a fossil energy heat treatment device;

- the aggregates and/or asphalt aggregates are heated without producing carbon dioxide.

The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

On the attached drawings:

[Fig. 1] is a schematic view of a first industrial assembly implementing a first embodiment of the method according to the invention,

[Fig. 2] is a schematic view of a second industrial assembly implementing a second embodiment of the method according to the invention, [Fig. 3] is a graph representing the variation of the temperature of a sample of material A as a function of time when heated in a microwave oven with a set temperature of 200°C for 17 minutes, material A comprising limestone aggregates and a mixture of grave bitumen type formula (GB) of granular class 0/14 mm with 3% water content,

[Fig. 4] is a graph representing the variation of the temperature of a sample of material C as a function of time when heated in a microwave oven with a set temperature of 160°C for 4.5 minutes, the material C comprising asphalt millings or asphalt aggregates (AE No. 1) of granular class 0/12 mm and 3.9% water content,

[Fig. 5] is a graph representing the variation of the temperature of a sample of material D as a function of time when heated in a microwave oven with a set temperature of 160°C for 10 minutes, material D comprising asphalt millings or asphalt aggregates (AE No. 1) of granular class 0/12 mm containing 50/70 bitumen with 0% water content,

[Fig. 6] is a graph representing the variation of the temperature of a sample of material B as a function of time when heated in a microwave oven with a set temperature of 200°C for 5 minutes, material B comprising quartzite aggregates and a mixture of grave bitumen type formula (GB) of granular class 0/14 mm with 4.3% water content,

[Fig. 7] is a schematic view in longitudinal section of a microwave oven provided with a rotating cylindrical heating body used for implementing the embodiments of the method shown in Figures 1 and 2,

[Fig. 8] is a sectional view along the plane ll-ll of Figure 7,

[Fig. 9] is a schematic view showing an example of a wave trapping joint of the microwave oven of Figure 7,

[Fig. 10] is a schematic view showing an example of a slotted waveguide of the microwave oven of Figure 7,

[Fig. 11] is a schematic cross-sectional view of a first example of a heating body of the microwave oven of Figure 7,

[Fig. 12] is a schematic cross-sectional view of a second example of the heating body of the microwave oven of Figure 7, [Fig. 13] is a schematic cross-sectional view of a third example of the heating body of the microwave oven of Figure 7.

In the description which follows, by convention, the terms "upstream" and "downstream" will be used with reference to the direction of the flow of the materials introduced into the microwave oven, and more generally with reference to the direction of the flow of the materials then products in the industrial assembly used for implementing the process according to the invention.

Preliminarily, it will be noted that, from one figure to another, the identical or similar elements of the different examples of implementation of the invention will be referenced by the same reference signs and will not be described each time.

The granular classes are indicated according to the formalism d/D where d is the smallest representative diameter, D the largest representative diameter of the grains of the material determined by particle size analysis. This analysis is carried out here by dry sieving according to standard NF EN 17892-4.

The invention relates to a process for the industrial production of a hot mix.

In Figures 1 and 2, two embodiments of an industrial assembly 300 are shown; 400; suitable for implementing the method according to the invention.

Each of these industrial units 300; 400 remarkably comprises a microwave oven 2 used according to the process of the invention to produce a hot mix according to this process.

This microwave oven 2 is provided with a heating body 4, at least one microwave generator 24a and at least one wave guide 22 extending inside the heating body 4 (see figures 1, 2 and 7).

According to the method of the invention, the following steps are carried out: a) aggregates and/or coated aggregates are introduced inside the heating body 4, b) the aggregates and/or aggregates are exposed coated introduced into the heating body 4 with microwaves emitted by the microwave generator 24a and conveyed into the heating body 4 by the wave guide 22, so as to produce aggregates and/or aggregates of heated asphalt, c) the heated aggregates and/or asphalt aggregates are extracted from the heating body; d) the heated aggregates and/or asphalt aggregates are used to produce the hot asphalt mixture.

Hot-mix asphalt is composed of a mixture of recycled aggregates and/or asphalt aggregates, generally limestone filler, possible additives and hydrocarbon binder, brought to temperatures between 80 and 200°C. Hot mix generally includes a mixture of aggregates or mix aggregates, fines also called “fillers” and hydrocarbon binder. The hydrocarbon binder may comprise, for example, bitumen, tar or a vegetable binder.

Additives can be added.

The aggregates are for example rock aggregates, for example limestone, diorite, gabbro, granite, basalt or quartzite.

Coated aggregates are recycled materials from old milled or recrushed roadways. They therefore contain one or more coatings, with aggregates, fillers and hydrocarbon binder such as bitumen.

Fillers contain, for example, sand and dust with a section of less than 63 micrometers. Fillers are naturally present in small quantities in the aggregates.

The hydrocarbon binder is generally composed of bitumen.

Finally, additives are chemical compounds modifying the mechanical or chemical properties of the hot mix.

Generally speaking, the heating body 4 of the microwave oven 2 extends along a longitudinal axis X-X between two opposite longitudinal ends.

Said waveguide 22 is mounted inside the heating body 4 of the oven 2. It extends in a longitudinal direction parallel to the longitudinal axis X-X of the heating body 4 and is connected to one of its ends F, F' to said microwave generator 24a, 24bThe heating body 4 comprises an internal cavity which accommodates the materials introduced into this heating body.

An example of a microwave oven suitable for implementing the method according to the invention will be described in more detail later with reference to Figures 7 to 13.

Step a)

In step a), the material comprising the aggregates and/or the coated aggregates introduced into the heating body 4 comprise at least one of the following components: limestone, dioritic, granitic, basaltic or quartzite aggregates, asphalt millings.

The material is introduced into the heating body 4 of the oven 2 preferably in divided form.

In practice, in step a), the aggregates and/or the coated aggregates are introduced into the oven 2 thanks to a supply system 34 opening into the heating body 4 at a first of said two longitudinal ends of that -this. An example of such a power system will be described later. The aggregates and/or coated aggregates are introduced at a first longitudinal end of the heating body.

Step b)

The material introduced into the heating body 4 of the oven 2 is heated by microwaves. This heating also makes it possible to dry the aggregates and/or coated aggregates.

Drying here corresponds to superficial dehydration of the material.

The aggregates and/or coated aggregates are preferably heated to a temperature between 80 and 200 degrees Celsius. Alternatively, the aggregates and/or coated aggregates are heated to a temperature for example equal to 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 degrees Celsius. The aggregates and/or the coated aggregates are preferably heated for a time of between 5 minutes and 20 minutes depending on the composition of the material and the set temperature of the oven.

These heat treatments can cause the release of gases, particularly water vapor.

During the heating of the aggregates and/or the coated aggregates, the gases released are evacuated by a gas evacuation device 42 (Figures 1 and 13) ensuring a depression of the heating body 4 of the oven 2.

The aggregates and/or coated aggregates are thus heat treated in oven 2 under a “closed” atmosphere.

It is also possible to inject gases inside the heating body 4. This injection can for example be carried out in line with the waveguide in order to avoid the entry of dust into the latter.

Step c)

In step c), the heated aggregates and/or asphalt aggregates produced in step b) are taken out of the heating body 4 of the oven 2, at the second longitudinal end of the heating body.

In practice, the heated aggregates and/or asphalt aggregates are removed from the oven 2 via an evacuation system 36 opening into the heating body 4 at a second longitudinal end thereof opposite the first longitudinal end . An example of such an evacuation system will be described later.

Step d) In step d), the heated asphalt aggregates and/or aggregates are used to produce the hot coating.

In practice, in step d) the aggregates and/or the heated mix aggregates extracted from the oven in step c) are mixed with hydrocarbon binder and/or with fillers in order to produce the hot mix.

The advantages of the process according to the invention are numerous. In particular, it allows microwaves to be concentrated on a bed of moving materials, which makes it possible to homogenize the heating. It also allows satisfactory control of the temperature of the material in the oven.

For the production of hot mix, the benefit of heating by a microwave oven is twofold:

- the material enters the oven cold and remains cold until it receives the microwaves,

- the dielectric effects caused by microwaves gradually increase the internal temperature of the material introduced into the oven without exceeding the desired set temperature. There is therefore no excessive aging of the bitumen contained in the asphalt aggregates during heating.

Finally, discharges of combustion gases and associated pollutants are reduced or even eliminated.

Note that one of the particularities of microwave heating is that it heats the core of the material, without directly heating the heating body. This is heated indirectly by raising the temperature of the material. As a result, the temperature of the heating body is lower than that observed in conventional fossil energy heat treatment devices. The lifespan of the oven is thus extended.

Generally speaking, the fossil energy used comes from the combustion of fossil fuels, such as gas, fuel oil, coal or coke.

The hot mix production process is preferably carried out continuously. In particular, steps a), b) and c) are preferably carried out continuously.

This means that the aggregates and/or asphalt aggregates are not heated in the microwave oven in successive separate batches. In other words, a first quantity of aggregates and/or coated aggregates is not introduced and heated in the microwave oven to produce the heated aggregates and/or coated aggregates, then completely extracted. of the oven before the introduction of a second quantity of aggregates and/or coated aggregates, as would be the case in a batch process.

After a transient regime corresponding to the initiation of the process, the aggregates and/or coated aggregates are introduced into the oven, heated and extracted from the oven continuously. In practice, it is then possible to carry out extraction step c) over a time range of more than 4 hours without interruption in the flow of heated aggregates and/or asphalt aggregates for more than 1 minute.

Thus, the heated aggregates and/or asphalt aggregates produced can for example be extracted either without interruption over a time period greater than 4 hours, or over short time intervals, separated for example from 0 to 1 minute, for example by 5, 10, 20, 30, 40 or 50 seconds, over this time range.

Preferably, when implementing such a continuous method, steps a), b) and c) can be carried out simultaneously. This is for example the case when the supply system of the microwave oven 2 used comprises a metal sluice valve type valve making it possible to regulate the flow rate of aggregates and/or coated aggregates introduced into the oven, such as this is described later. The supply of aggregates and/or coated aggregates to the oven and the extraction of heated aggregates and/or coated aggregates from the oven can then be carried out continuously, without interruption, over said time range.

Alternatively, steps a) and/or c) are carried out at time intervals. This is for example the case when the microwave oven supply system includes an inlet airlock which can be produced by two consecutive gate valves. Feeding is then carried out in jerky fashion. Similarly, the extraction of heated asphalt aggregates and/or aggregates can be carried out by jerking.

It is also possible to envisage as a variant that only the feeding or only the extraction is carried out by jerk.

In order to ensure this continuous operation, the aggregates and/or the coated aggregates are conveyed from one of the longitudinal ends of the heating body 4 to the other during its heating.

In step b), the aggregates and/or coated aggregates contained in the heating body are advanced in a direction parallel to the longitudinal axis X-X of the heating body 4, from the first longitudinal end towards the second longitudinal end. This advance of the materials contained in the heating body authorizes the continuous implementation of the method according to the invention.

Preferably, these materials are advanced continuously throughout the duration of the method. For this purpose, the oven has means of supply allowing the transport of the aggregates and/or coated aggregates from the first to the second longitudinal end of the heating body of the microwave oven.

According to a first embodiment of the microwave oven, a detailed example of which will be described later, the heating body 4 is rotary cylindrical and is rotated around its inclined longitudinal axis in order to advance the material contained in the furnace from the longitudinal end of the heating body to which the supply system introduces the aggregates and/or asphalt aggregates towards the longitudinal end of the heating body to which the evacuation system extracts the aggregates and/or aggregates of heated asphalt.

Thus, during step b), said heating body 4 is rotated around its longitudinal axis X-X, and the longitudinal axis X-X of the heating body 4 is inclined relative to the horizontal so as to regulate the speed of advance of the aggregates and/or coated aggregates in the heating body

The supply means therefore comprise a device for rotating the heating body and an inclined support for this heating body.

According to a second embodiment of the microwave oven, said supply means comprise a belt conveyor housed at least partially in the heating body. During step b), the belt conveyor is activated to advance the aggregates and/or the coated aggregates contained in the heating body. The belt conveyor extends for example at least from the first to the second longitudinal end of the heating body, in a direction parallel to the longitudinal axis X-X of the heating body 4. It allows the movement of the materials contained in the body heating in this direction parallel to the longitudinal axis X-X of the heating body 4.

In this second embodiment, the longitudinal axis of the heating body can be horizontal during the implementation of the method. The heating body is also fixed.

According to this second embodiment of the oven, the heating body may comprise a microwave tunnel and the conveyor belt may also constitute the supply system and the evacuation system of the microwave oven. The microwave oven can for example be arranged in a manner similar to the device described in document FR3070869. The belt conveyor is made of a material resistant to temperatures of up to 200°C. It includes a conveyor belt that runs through the microwave. The use of such a conveyor belt makes it possible to avoid the flight of dust linked to the mixing operation as it is carried out in the rotating tube. The use of the conveyor belt is preferred when mixing is not useful. Whatever the embodiment of the oven envisaged, the arrangement of the microwave oven 2, an example of which is detailed below, ensures airtightness as well as trapping microwaves inside. interior of the heating body.

These operations are carried out continuously in order to maintain all production equipment at a stable temperature.

The process according to the invention can also be carried out discontinuously: a batch of aggregates and/or coated aggregates is introduced into an oven. The introduction of the aggregates and/or the asphalt aggregates stops and the aggregates and/or the asphalt aggregates introduced are heated, then extracted from the oven during emptying before the introduction of another batch of aggregates and/or asphalt aggregates.

Furnace emptying operations lead to production stoppages during which temperatures drop sharply. This discontinuity induces excess energy consumption. In addition, during the production of a hot mix, controlling temperatures and heating times is essential to limit the aging of the bitumen present in the mix aggregates. Continuous heating therefore has a double advantage: on the one hand an improvement in the quality of the hot mix produced, and on the other hand the reduction in the energy consumption of the process. A discontinuous process can nevertheless be envisaged and implemented thanks to the industrial units described.

Particularly advantageously, in the microwave oven 2 used for implementing this method, said waveguide 22 comprises a slotted waveguide mounted inside the heating body 4 between the two longitudinal ends thereof and connected to one of these longitudinal ends to said microwave generator 24a. The waveguide preferably extends from one longitudinal end of the heating body to the other. The microwaves are therefore conveyed from one longitudinal end of the heating body to the other. Each microwave generator 24a, 24b is arranged outside the heating body 4, at one of the longitudinal ends of the heating body.

Each waveguide is preferably connected to a microwave generator. However, it is possible to consider connecting each waveguide to several microwave generators in order to increase the power delivered.

In addition, during steps a), b) and c), said heating body 4 is rotated around its longitudinal axis XX and the longitudinal axis XX of the heating body 4 is inclined relative to the horizontal so as to regulate the speed of advance of the aggregates and/or coated aggregates in the heating body 4 (see figures 1 and 2). This makes it possible to advance the aggregates and/or coated aggregates through the microwave oven 2.

As mentioned in the example detailed below, in the first embodiment of the microwave oven, the heating body can also be provided with stirring blades (not shown). The stirring blades extend inside the heating body. They extend parallel to the longitudinal axis or inclined relative to the longitudinal axis of the heating body. They are integral in rotation with it, and, in step b), the stirring blades are rotated with the heating body while tilting the longitudinal axis of the latter. The material contained in the heating body is then mixed during the rotation of the heating body. This makes it possible to homogenize the mixture of materials present in the heating body and to contribute, possibly, to controlling the advance of this mixture of materials in the heating body.

In addition, the microwaves are trapped inside the oven 2 using two fixed covers 14, each cover being mounted on one of the longitudinal ends of the heating body 4 with the interposition of annular seals 16 for trapping waves. (figures 7 and 9).

A detailed description of the first embodiment of the oven describing the means of implementing these characteristics of the process according to the invention is given below (with reference to Figures 7 to 13).

According to a particular embodiment of the method, which will be described in more detail later, the oven comprises two microwave generators 24a, 24b and two corresponding wave guides 22 and the heating body 4 of the oven 2 comprises a first part in which a first of said two waveguides associated with a first 24a of said two microwave generators extends and a second part in which the second waveguide associated with the second microwave generator 24b extends ( figure 7).

The two waveguides may comprise two independent waveguides each connected to one of the two microwave generators or two sections 22a, 22b of waveguide 22 connected to each other, each section 22a, 22b being connected at one end to one of the two microwave generators 24a, 24b. The two sections 22a, 22b then extend along the same axis parallel to the longitudinal axis X-X of the heating body as is the case in Figure 7. In this case, one of the two microwave generators 24a , 24b is arranged at a first of the two longitudinal ends of the heating body 4 and the other microwave generator is arranged at the second longitudinal end of the heating body.

Alternatively, two separate waveguides can be provided extending side by side, for example in two directions parallel to the longitudinal axis of the heating body. Of course, it is possible to envisage a number greater than two of wave guides extending in the heating body, each wave guide being connected to a separate microwave generator or to the same microwave generator.

Then, in step b), the aggregates and/or the coated aggregates successively pass through the first part then the second part of the heating body, said first and second parts of the heating body having different temperature profiles.

In a particularly advantageous manner, it can be provided that the first microwave generator and the first wave guide are configured so as to produce a progressive increase in the temperature along the first part of the heating body and the second microwave generator waves and the second wave guide being configured so as to maintain a constant target temperature along the second part of the heating body, in step b), the aggregates and/or the coated aggregates are subjected to the progressive increase in temperature along the first part of the heating body then are maintained at the target temperature along the second part of the heating body.

Said first part constitutes an upstream temperature rise zone, while the second part constitutes a downstream zone for maintaining a target temperature. The upstream temperature rise zone can bring the aggregates and/or asphalt aggregates to said target temperature.

Other temperature profiles can obviously be considered, with two or more than two waveguides defining two or more than two parts of the heating body having different temperature profiles.

In addition, it is possible to consider using two or more microwave ovens arranged in series to heat the aggregates and/or coated aggregates. For example, a first oven can be used to heat the aggregates and/or aggregates with a first temperature profile, for example a rise in temperature, and the second oven can be used to heat the aggregates and/or aggregates. 'coated with a second temperature profile, for example maintaining a heating temperature. The second oven is powered by the aggregates and/or asphalt aggregates heated in the first oven and extracted therefrom.

In practice, the hot mix production process includes other steps occurring before or after heating the aggregates and/or mix aggregates in the microwave oven 2.

Generally speaking, the method according to the invention may comprise one or more of the following additional steps: - before their introduction into the heating body 4 of the oven, the aggregates and/or the coated aggregates are preheated in a preheating device 180 (figure 1),

- after step c), the heated aggregates and/or asphalt aggregates are stored, for example in hoppers (figure 1),

- the heated aggregates and/or asphalt aggregates are transported to a mixer (figures 1 and 2),

- the heated aggregates and/or asphalt aggregates are mixed with hydrocarbon binder (figures 1 and 2),

- the heated aggregates and/or asphalt aggregates are mixed with fillers (figures 1 and 2),

- the heated aggregates and/or asphalt aggregates are mixed with additives (figures 1 and 2),

- the aggregates and/or asphalt aggregates heated by the microwave oven 2 are mixed with other aggregates and/or asphalt aggregates heated by a fossil energy heat treatment device 185 (figure 2),

- the temperature of the aggregates and/or the coated aggregates present inside the microwave oven 2 is measured, for example using an infrared pyrometer.

In general, it is expected, when the aggregates and/or coated aggregates are preheated, that the gases released during heating of the aggregates and/or coated aggregates in the oven 2 are recirculated towards the preheating device.

In the following, two embodiments of the method according to the invention are described with reference to Figures 1 and 2. In these figures, the transfers of material before and after heating are represented by arrows in solid lines. Hot gas transfers are represented by dotted lines. They use the first embodiment of the microwave oven described above.

According to the first embodiment of the method according to the invention shown in Figure 1, the material supplying the industrial assembly 300 is initially contained in a storage hopper 110. This hopper is preferably heated. It ensures preheating of the aggregates and/or asphalt aggregates. It thus plays the role of a preheating device.

As shown schematically in Figure 1, the gases heated in the hopper 110 during preheating are evacuated through a chimney 120 preferably comprising a filtration device (not shown).

The material preheated in the hopper 110 is introduced into the microwave oven 2. It is introduced into the heating body 4 through the supply system 34 and heated to a set temperature of between 80 and 200°C. The heating body 4 is movable in rotation around its longitudinal axis XX. It rotates continuously while heating the material.

The longitudinal axis a vertical axis, the material is gradually conveyed towards the evacuation system 36 located at the second longitudinal end of the heating body by the effect of gravity and the rotation of the heating body 4 around its longitudinal axis XX.

An example of a microwave oven 2 will be described in more detail later.

As schematically represented in Figure 1, the gases heated in the microwave oven 2 and evacuated by the gas evacuation device 42 are preferably recirculated towards the preheating hopper 110 in order to reduce its energy consumption.

At the exit from oven 2, the heated and dried material is conveyed to a storage device 210 such as a hopper. This hopper 210 is suitable for storing hot asphalt aggregates and/or aggregates.

The hot mix aggregates and/or aggregates stored in the hopper 210 are then conveyed to a mixer 220, in which they are mixed with bitumen and/or filler to produce the hot mix.

This hot mix is then stored, for example in a hopper 240 and/or loaded into transport trucks 230 to be taken to its place of use.

Depending on the desired flow rate of the hot mix, the electrical power required for heating the aggregates and/or mix aggregates can be very high. Consequently, taking into account the capacities available locally on the electrical distribution networks, the microwave oven 2 can be associated with a fossil energy heat treatment device, for example a continuously rotating kiln using a fossil fuel. In this case, the process according to the invention will be hybrid. An example of a hybrid process is shown in Figure 2 and described below.

According to the second embodiment of the method according to the invention shown in Figure 2, the material supplying the industrial assembly 400 is initially contained in a storage hopper 111. This hopper is without preheating device. The material stored in the hopper 111 is introduced into the microwave oven 2. It is introduced into the heating body 4 through the supply system 34 and heated to a set temperature of between 80 and 200°C.

Oven 2 is identical to that described in the first embodiment.

As is schematically represented in Figure 1, the gases heated in the microwave oven 2 and evacuated by the gas evacuation device 42 are evacuated by a chimney 2500 provided with a filtration device (not shown).

At the exit from oven 1, the heated and dried material is sent to a mixer 220, in which it is mixed with bitumen and fillers to produce hot mix.

In addition here, the heated and dried material is also mixed with other aggregates and/or coated aggregates heated by a fossil energy heat treatment device 185.

The fossil energy heat treatment device 185 can be any device known to those skilled in the art and adapted to heating the material, for example a fossil energy drying tube. It will not be described in further detail here.

It is supplied with other aggregates and/or asphalt aggregates initially stored in a hopper 310 without a preheating device. It heats the other aggregates and/or asphalt aggregates to a temperature between 80 and 200°C. The other heated asphalt aggregates and/or aggregates are extracted from the fossil energy heat treatment device 185 and conveyed to the mixer 220 in which they are mixed with the aggregates and/or asphalt aggregates heated in the oven 2.

As is schematically represented in Figure 2, the gases heated in the fossil energy heat treatment device 185 are evacuated by a gas evacuation device of this fossil energy heat treatment device 185. They pass through a filter with sleeves 320 which retains the particles of other aggregates and/or coated aggregates present. The gases are then evacuated from the bag filter 320 via a chimney 330 preferably provided with an additional filtration device. The particles of other aggregates and/or heated asphalt aggregates filtered by the bag filter 320 are conveyed to the mixer 220.

The hot mix produced in the mixer 220 is then stored, for example in a hopper 240 and/or loaded into transport trucks 230 to be taken to its place of use.

Feasibility tests of the hot mix production process using a microwave oven were carried out on a C400 type laboratory microwave oven, with a power of 6000 W and a frequency of 2450 MHz. This microwave oven includes a rotating cylindrical cavity diameter 400 millimeters (mm) and height 400 mm. This cavity is rotated by a variable speed motor. The temperature of the materials inside the oven is measured by an infrared pyrometer.

Such a microwave oven is for example described in document EP2530059.

Samples of four materials were tested in this laboratory microwave oven:

- material A includes limestone aggregates and a mixture of grave bitumen type formula (GB) of granular class 0/14 mm with 3% water content,

- material B includes quartzite aggregates and a mixture of grave bitumen type formula (GB) of granular class 0/14 mm with 4.6% water content,

- material C includes asphalt millings or asphalt aggregates (AE No. 1) of granular class 0/12 mm and 3.9% water content,

- material D includes asphalt millings or asphalt aggregates (AE No. 1) of granular class 0/12 mm containing 50/70 bitumen with 0% water content. The tests were carried out according to the experimental protocol summarized in the following table:

[Table 1]

The graphs represented in Figures 3 to 6 show the curves and levels of temperature rise measured as a function of time for each of the tests carried out. On each of the graphs the power in watts (w) is mentioned for information purposes only. Each graph shows the heating period as well as a cooling time for the different samples. It can be seen that the response to microwaves of the different materials A to D is very satisfactory. The set temperatures are never exceeded.

The quality of the heated asphalt aggregates obtained by heating materials C and D is excellent, the bitumen contained in these materials having not been overheated as in the current state of the art processes.

Visually, the heated asphalt aggregates have a shiny appearance, which is not the case for the heated asphalt aggregates according to the state of the art. These tests confirm that the aggregates and/or asphalt aggregates have been heated satisfactorily in the microwave oven.

In general, the bag filter, the storage devices, the preheating device, the mixer, the fossil energy heat treatment device and the other elements of the industrial assembly can be of any type known to man. profession and adapted to the implementation of the process described above. They will not be described in more detail here.

Thanks to the process according to the invention, the aggregates and/or coated aggregates are heated at least partially without producing carbon dioxide.

Provided that carbon-free electrical energy is used, the use of this oven technology will significantly reduce CO2 emissions from the heating of aggregates and/or asphalt aggregates. Depending on the process used (100% microwave or hybrid), CO2 emissions per tonne of dried and heated aggregates and/or asphalt aggregates will be between 4 and 12 kg per tonne depending on the heating temperature.

According to one embodiment of the method according to the invention, a microwave oven 2 is used as shown in Figures 13 to 19. This oven 2 can be used for example in one of the industrial assemblies 300; 400; described previously and shown in Figures 1 and 2.

The oven can make it possible to carry out continuous heat treatment of the materials introduced into this oven. During such continuous treatment, the heat-treated material is extracted from the oven over a time range of more than 4 hours, without interruption in the flow of aggregates and/or coated aggregates for more than 1 minute in this range. of time.

As shown in Figures 7 and 8, the oven 2 notably comprises the rotating cylindrical heating body 4 which is centered on the longitudinal axis X-X positioned so as to form an angle 6 of between 0.1 and 10° relative to the 'horizontal.

The heating body 4 is a tube made for example of refractory steel and which is open at each of its longitudinal ends. It is provided with an external thermal insulation layer 6 wrapped around its external diameter. Different design configurations of the heating body will be described later in conjunction with Figures 11 to 13.

At each of its longitudinal ends, the heating body 4 is provided with an annular disc 7 which extends from the external thermal insulation layer 6 and which makes it possible to create a controlled heating volume as a function of its height. Lifting blades 9 positioned inside the heating body ensure complete emptying of the heat-treated material by passing it over the annular disc 7 located at the outlet of the heating body 4. At its longitudinal ends, the heating body 4 further comprises rolling rings 8 which are mounted around the thermal insulation layer 6 and which rest on rotating rollers 10 so as to be able to rotate the heating body. heats 4 around its longitudinal axis XX at a speed typically between 0.1 and 40 revolutions per minute.

Of course, other mechanisms for rotating the heating body could be considered (gear motor, rack, etc.).

The rotating rollers 10 are mounted on a platform 12 adjustable in inclination relative to the horizontal of the angle 6 between 0.1 and 10° so as to regulate the speed of advance of aggregates and/or coated aggregates introduced into the heating body 4.

The heating body may also include stirring blades in order to promote and control the advance of the aggregates and/or coated aggregates in the heating body and to improve the homogenization of the temperature of the aggregates and/or aggregates. of coating contained in the heating body. The arrangement and geometry of these stirring blades can be very variable and depend on the material (powder, aggregate, dryness at the inlet, etc.). For example, the stirring blades can be arranged in sections in the direction of the longitudinal axis of the oven or be inclined relative to this axis. Lengths can be the same for all blades or variable. The profile of the blades can be triangular, straight, inclined or curved for example.

Thus, according to the method of the invention, the speed of advance of the aggregates and/or coated aggregates in the heating body is controlled. We also ensure temperature homogeneity in the aggregates and/or coated aggregates contained in the heating body.

The oven 2 also includes two fixed covers (or flanges) 14 which are mounted on each longitudinal end of the heating body with the interposition of annular wave trapping joints 16. These covers 14 are for example made of refractory steel.

More precisely, each cover 14 consists of a disc 14a which closes one of the longitudinal ends of the heating body and an annular collar 14b which partially covers the thermal insulation layer 6 of the heating body.

The wave trapping joints 16 are positioned between the flange 14b of each cover 14 and the thermal insulation layer 6 of the heating body. They ensure microwave tightness between the fixed covers and the rotating heating body despite thermal constraints and expansions. As shown in Figure 9, each wave trapping joint 16 comprises at least one pair of discs 18 centered on the longitudinal axis XX of the heating body and fixed on the flange 14b of the cover extending radially towards the layer thermal insulation 6 of the heating body.

The discs 18 are made of electrically conductive material and thermally resistant to high temperatures (of the order of 1000°C). For example, they can be made of refractory steel.

Furthermore, the discs 18 of the same pair are spaced longitudinally from each other so as to form an annular groove 20 having a depth p corresponding to a quarter of the wavelength of the microwaves emitted by the guide of waves to a multiple of the wavelength (that is to say: p = X/4 + k À with X for the wavelength and k an integer).

Preferably, each wave trapping joint 16 comprises several pairs of disks 18 (five pairs in number in the example of Figure 9) which are spaced longitudinally from each other by a distance d corresponding to a quarter of the wavelength of the microwaves emitted by the waveguide to a multiple of the wavelength (that is to say: d = X/4 + n À with X for the wavelength and n an integer).

This particular geometry of the wave trapping joints 16 makes it possible to largely cancel any wave which would pass between the flange 14b of the cover 14 and the thermal insulation layer 6 of the heating body. Indeed, part of the incident wave passes directly along the thermal insulation layer (in a longitudinal direction) and another part enters one of the pairs of discs 18. The length traveled (in a longitudinal direction) radial direction) by this wave part in the groove 20 is such that a round trip of the wave makes it possible to obtain a phase shift of X/2 relative to the incident wave, which has the effect of cancel this incident wave. The accumulation of several pairs of disks makes it possible to obtain zero leakage.

In addition, the longitudinal spacing d between the pairs of disks 18 represents a second type of wave trapping (in the longitudinal direction). Indeed, part of the incident wave escaping under the first pair of disks encountered is reflected by the disk of the next pair on its path and returns to the first pair of disks with a phase shift of X/2.

As shown in Figures 7 and 8, the oven 2 comprises the slotted waveguide 22 which is mounted inside the heating body 4 extending longitudinally between each end thereof.

The waveguide 22 is connected at one end to a microwave generator 24a, 24b (or to several microwave generators) and passes longitudinally through the heating body between its two longitudinal ends. It is designed to distribute microwaves in a regulated manner all along the heating body directly onto the aggregates and/or coated aggregates 26 to be treated.

Typically, the microwave generator 24a, 24b comprises a magnetron having a unit power which can vary between 1kW and 10MW, coupled to a frequency generator which can vary from 200MHz to 4000MHz. The waveguide 22 can be made in a single section or in several sections connected to each other, each section being connected at one end to a microwave generator. Thus, in the exemplary embodiment of Figure 7, the waveguide 22 comprises two sections 22a, 22b which are connected to each other and each connected to one of the two microwave generators 24a , 24b.

Likewise, it is possible to provide a plurality of wave guides which are mounted inside the heating body and which extend parallel to each other at each end of the heating body, each of these guides waves that can be produced in one or more sections.

Furthermore, the waveguide 22 is preferably enveloped in a thermal insulator 28 which is transparent to the microwaves generated by the wave generator. For example, this thermal insulator is made of silica and alumina or quartz fibers.

The waveguide 22 can also be isolated from dust by protective windows 30 (see Figure 8) which are transparent to microwaves generated by the wave generator and resistant to high temperatures. These protective windows are for example made of quartz or ceramic and have a thickness of between 5 and 20mm. They can be fixed to the waveguide using tabs or any other fixing system.

Alternatively, or in addition to the protective windows, the waveguide can be placed under slight overpressure (relative to the interior of the heating body) by injecting air into one of its longitudinal ends so as to limit dust entry.

Alternatively, a dust cleaning system may be provided comprising a perforated cylinder placed on an upper face of the waveguide. The cleaning phases are carried out by injection of pulsed air.

Furthermore, as shown in Figure 10, each waveguide 22 comprises a plurality of slots 32 which are positioned opposite the aggregates and/or coated aggregates 26 introduced into the heating body.

In the exemplary embodiment of Figure 10, the slots 32 of the waveguide have a substantially rectangular shape whose length is aligned with the longitudinal axis A of the waveguide. In addition, the slots 32 of this exemplary embodiment are arranged on either side of the longitudinal axis A of the waveguide.

Generally speaking, the arrangement and geometry of the slots 32 of the waveguide are designed on the one hand to be compatible with the frequency of microwaves used, and on the other hand so that the heating of the granulates and/or aggregates coating is carried out optimally with one or more specific heating zones depending on the desired temperature profile.

For example, it is possible to provide an upstream temperature rise zone and a downstream zone to maintain a target temperature. In this example, in the upstream temperature rise zone (see Figure 10), the slots 32 of the waveguide are for example spaced, on the one hand longitudinally from each other by a distance e corresponding to half of the wavelength of the microwaves emitted by the waveguide to a multiple of the wavelength (that is to say: e = X/2 + m À with X for the length d 'waves and m an integer), and on the other hand transversely of the longitudinal axis A of the waveguide by a distance h.

Still in this example with two specific heating zones, the slots of the waveguide corresponding to the downstream temperature maintenance zone (not shown in the figures) are spaced longitudinally from each other by a distance different from the distance e , and/or transversely of the longitudinal axis A of the waveguide by a distance different from the distance h.

Furthermore, the slot 32a which is the most downstream of the waveguide is located at a distance f from the downstream end F of the waveguide which is equal to a quarter of the wavelength of the microwaves emitted by the waveguide to a multiple of the wavelength (that is to say: f = X/4 + p À with X for the wavelength and p an integer).

Similarly, the slot 32b which is most upstream of the waveguide is located at a distance g from the upstream end F' of the waveguide which is equal to half the wavelength of the microphones. -waves emitted by the waveguide to a multiple of the wavelength (i.e.: g = X/2 + q X with X for the wavelength and q an integer) .

The oven 2 used in the process according to the invention also comprises the supply system 34 of aggregates and/or coated aggregates which passes through the upstream cover 14 and which opens into the heating body 4 at the first longitudinal end (or upstream end) of it.

Alternatively, the supply can be carried out by gravity using tubes whose diameter and length are determined so as not to present wave leaks. For products in the form of powders, we will choose a supply system using a metal sluice valve type valve making it possible to regulate the flow rate, avoid microwave leaks and prevent the body from being exposed to air. heated.

For granular products of larger particle size, we will preferably choose to feed the oven in jerks via an inlet airlock which can be created by two consecutive guillotine valves. This entrance airlock guarantees airtightness against waves and air.

Likewise, the oven comprises the evacuation system 36 of the heated aggregates and/or asphalt aggregates which passes through the downstream cover 14 and which opens into the heating body 4 at a second longitudinal end (or downstream end) of the latter opposite the first longitudinal end. This evacuation system 36 can be coupled to a flow control valve 38 and to a probe 40 for measuring the temperature inside the heating body.

The oven 2 also includes the gas evacuation device 42 which here includes a smoke evacuation tube. This tube can also be used for the injection of gas inside the heating body.

In conjunction with Figures 11 to 13, we will now describe different possible configurations for producing the heating body of the oven.

In the embodiment of Figure 11, the heating body 4-1 comprises in particular an internal tube 44 which is composed of a plurality of angular plates 46 made of refractory steel and distributed angularly around the longitudinal axis X-X of the body heating.

The plates 46 overlap two by two in the circumferential direction, each plate being able to slide tangentially on the two plates which are directly adjacent to it in order to allow the internal tube 44 to be able to absorb thermal expansions.

The heating body 4-1 also comprises an external tube 48 which is arranged around the internal tube 44 while being coaxial with it. Studs 50 extending in radial directions make it possible to connect the outer tube 48 to the plates of the inner tube 44.

Finally, a thermal insulator 52 is positioned in the annular space formed between the internal tube 44 and the external tube 48.

In the embodiment of Figure 12, the heating body 4-2 comprises an internal tube 54 which is made of refractory steel and which is in one piece, as well as an external tube 48 which is arranged around the internal tube being coaxial. In addition, a plurality of leaf springs 56 (or struts) extending in directions tangential to the internal tube connect the external tube 48 to the internal tube 54.

Finally, as for the previous embodiment, a thermal insulator 52 is positioned in the annular space formed between the internal tube 54 and the external tube 48. In the embodiment of Figure 13, the heating body 4-3 comprises an internal tube 58 which is made of refractory steel, one-piece and split longitudinally to allow it to expand in the circumferential direction. For this purpose, the internal tube 58 has a discontinuity 60, the two angular ends of the internal tube delimiting this discontinuity being connected to each other by a plate 62 screwed onto the internal tube. The heating body 4-3 also comprises an external tube 48 which is arranged around the internal tube 58 while being coaxial with it, and a thermal insulator 52 positioned in the annular space formed between the internal tube and the external tube.

Furthermore, in known manner, the rotary oven also includes devices (not shown in the figures) for gas tightness and for thermal insulation between the heating body and the fixed covers. Typically, these devices may be thermal fabric seals.

The present invention is not limited to the embodiments described and represented in the various figures.

Claims

Claims Process for the industrial production of a hot mix using a microwave oven (2) provided with a heating body (4), at least one microwave generator (24a, 24b) and at least one waveguide (22) extending in a longitudinal direction inside the heating body (4), the method comprising the following steps: a) aggregates and/or coated aggregates are introduced inside the heating body (4), b) the aggregates and/or coated aggregates introduced into the heating body (4) are exposed to the microwaves emitted by the microwave generator (24a, 24b) and conveyed into the heating body (4) by the waveguide (22), so as to produce heated aggregates and/or coated aggregates, the waveguide distributing the microwaves directly onto the aggregates and/or the coated aggregates, c) the heated aggregates and/or the coated aggregates are extracted from the heating body (4), d) the heated aggregates and/or the coated aggregates are used to produce the hot mix, in which said at least one waveguide (22) is used which comprises a plurality of slots (32) and the slots are positioned facing the aggregates and/or mix aggregates. Method according to claim 1, according to which, the heating body (4) of the microwave oven (2) extending along a longitudinal axis (X-X) between two opposite longitudinal ends,

- the aggregates and/or the coated aggregates are introduced, in step a), at a first of the two longitudinal ends of the heating body (4),

- in step b) the aggregates and/or coated aggregates contained in the heating body are advanced in a direction parallel to the longitudinal axis (X-X) of the heating body (4), from the first end longitudinal towards a second longitudinal end,

- the heated aggregates and/or asphalt aggregates are extracted, in step c), at the second longitudinal end of the heating body. Method according to claim 2, according to which the production of aggregates and/or its coated aggregates is carried out continuously. Method according to one of claims 2 and 3, according to which

- said slotted waveguide (32) being mounted inside the heating body (4) and extending in a longitudinal direction parallel to the longitudinal axis (X-X) of the heating body (4) and connected at one of these ends said microwave generator,

- in step a), the aggregates and/or the coated aggregates are introduced into the heating body (4) by a supply system (34) opening into the heating body (4) at the first of said two longitudinal ends thereof,

- in step c), the aggregates and/or coated aggregates heated by an evacuation system (36) opening into the heating body (4) at the second longitudinal end thereof are extracted . Method according to one of claims 1 to 4, according to which:

- the microwaves are trapped inside the oven (2) using two fixed covers (14), each cover (14) being mounted on one of the longitudinal ends of the heating body (4) with the interposition of joints annular wave trapping rings (16). Method according to one of claims 1 to 5, according to which, the heating body (4) of the oven (2) being cylindrical and rotary, during step b), said heating body (4) is rotated ) around its longitudinal axis (X-X), and the longitudinal axis (X-X) of the heating body (4) is inclined relative to the horizontal so as to regulate the speed of advance of the aggregates and/or aggregates d 'coated in the heating body (4). Method according to claim 6, according to which the heating body (4) is provided internally with stirring blades which extend in an inclined manner relative to the longitudinal axis of the heating body and are integral in rotation with it, and in step b), the stirring blades are rotated with the heating body (4) while tilting the longitudinal axis of the latter to advance the aggregates and/or coated aggregates contained in the heating body (4). Method according to one of claims 1 to 5, according to which the heating body houses a belt conveyor, and during step b), the belt conveyor is actuated to advance the aggregates and/or aggregates d coated contained in the heating body. Method according to one of claims 1 to 8, according to which, in step b), the gases released during the heating of the aggregates and/or coated aggregates are evacuated by an evacuation device (42) ensuring depression of the heating body (4) of the oven (2) and/or gases are injected inside the heating body (4). Method according to one of claims 1 to 9, according to which,

- the oven (2) comprising two microwave generators (24a, 24b) and two waveguides (22a, 22b) with corresponding slots and

- the heating body (4) of the oven (2) comprising a first part in which extends a first (22a) of said two slotted waveguides associated with a first (24a) of said two microwave generators and a second part in which extends the second (22b) of said two slotted waveguides associated with the second microwave generator (24b), in step b), the aggregates and/or the coated aggregates successively cross the first part then the second part of the heating body (4), said first and second parts of the heating body (4) having different temperature profiles. A method according to claim 10, wherein the first microwave generator (24a) and the first slotted waveguide (22a) are configured to produce a gradual increase in temperature along the first portion of the body heater (4) and the second microwave generator (24b) and the second slotted waveguide (22b) being configured so as to maintain a constant target temperature along the second part of the heating body (4 ), in step b) the aggregates and/or the coated aggregates are subjected to the progressive increase in temperature along the first part of the heating body (4) and maintained at the target temperature along the second part of the heating body (4). Method according to one of claims 1 to 11, according to which in step a), the aggregates and/or the coated aggregates introduced into the heating body (4) comprise at least one of the following components: limestone, dioritic, granitic, basaltic or quartzite aggregates, asphalt millings. Method according to one of claims 1 to 12, according to which, in step b), the aggregates and/or the coated aggregates are heated to a temperature between 80 and 200 degrees Celsius to dry and heat at least one part of the aggregates and/or asphalt aggregates Method according to one of claims 1 to 13, according to which, before their introduction into the heating body (4) of the oven (2), the aggregates and/or aggregates of coated are preheated in a preheating device (110). Method according to claim 14, according to which the gases released during the heating of the aggregates and/or asphalt aggregates in the oven (2) are recirculated towards the preheating device (110). Method according to one of claims 1 to 15, according to which, after step c), the heated aggregates and/or asphalt aggregates are stored in one or more hoppers (210) then transported to a mixer (220) . Method according to claim 16, according to which the heated asphalt aggregates and/or aggregates are mixed with a hydrocarbon binder. Method according to one of claims 1 to 17, according to which the aggregates and/or asphalt aggregates heated by the microwave oven (2) are mixed with other aggregates and/or asphalt aggregates heated by a fossil fuel heat treatment device (185). Method according to one of the preceding claims, according to which the aggregates and/or the coated aggregates are heated without producing carbon dioxide.