EP1713977B1 - Method and device for heating worn road coating materials - Google Patents

Description

The present invention relates to a method and a device for heating road asphalt, in particular used asphalt for recycling.

It is known from the patent application European No 98 925705 ( EP-A-994922 ) in the name of the same depositor, a process for the continuous manufacture of modified bitumens requiring, for example, a temperature control of the mixes.

The manufacture of road asphalt has several successive stages, which require warming up and / or maintaining temperature, steps that generate constraints that should be provided solutions.

In addition, we are aware of the constraints imposed by the new environmental legislation, which explains the search for new processes for the achievement of certain stages, especially those of warming up. Two situations are to be studied separately, the method and the device according to the invention finding an application indistinctly in one case as in the other, without modification.

Currently, schematically, the manufacture of asphalt mix includes a first step of processing aggregates.

These aggregates are of different particle sizes and mixed in suitable proportions to obtain a base of aggregates studied according to the coating to be produced.

These aggregates must be mixed with bitumen, itself prepared elsewhere. In order for the bitumen to adhere to aggregates in the best possible way, it is necessary that the bitumen, before mixing, be raised in temperature but that the aggregates are also heated.

In addition, the aggregates must be free of water and facilities take advantage of the rise in temperature required for this coating to dry the aggregates in a preliminary step.

One of the means for heating these aggregates is to use a rotary drum type oven, inclined, with a burner that emits a flame, this preferably against the flow of aggregates flow, the displacement of the aggregates being obtained by a suitable inclination of the drum . A suitable rotation and fins and other stirring means disposed on the internal walls of said drum to obtain the proper speed of movement and the desired brewing.

The burner is fed with liquid or gaseous petroleum fuel and the flame generated is in profile adapted for propagation along the longitudinal axis of the drum.

The aggregates are thus subjected to heating by the various transmission means: convection, conduction and radiation.

Most of the heat transfer comes from the convection generated by the hot gas flow of the flame. An air stream is even associated with the combustion gases to suitably advance this hot gas stream.

The other modes of transfer are minor, the conduction being limited to the contacts with the walls and the metallic stirring elements. As for radiation, this transfer is significant only near the walls and / or the flame.

The different parameters: aggregate flow rate, direction of passage of the aggregates with respect to that of the flame, stirring energy and circulation velocities, drum length, burner output, air flow rate, type of fuel and calorific value, are adapted to achieve the desired result.

It is found that during this heating step, there is an emission of combustion gases which are discharged into the atmosphere as the evaporation water.

On the other hand, when mixing aggregates, two antinomic constraints have to be met: as soon as the aggregates are stirred, they generate dust and since the gas flow is necessarily important, it is necessary to be able to treat the gases and to collect all the fine particles, the quantity that can reach values of the order of 200 g / m ³ of evacuated gas.

It is thus possible to work on the temperature of the input aggregates, to dry them and to take into account environmental constraints for discharges.

These hot aggregates are then optionally sieved and stored and then metered and stirred in kneaders in the presence of hot new bitumen otherwise preserved in order to coat them and obtain a mix ready to be used. In some cases, the coating operation is carried out in the final part of the heating drum, before leaving.

To these mixes, addition fines are added in addition to recovery fines after filtration of the heating gases at the time of coating so as to obtain more compact asphalt layers.

The mix thus prepared is then deposited on a prepared surface to receive it and it is compacted energetically before cooling. During this cooling step, the bitumen acts as a cohesion and bonding agent.

The original formulation of the asphalt mix, nature and composition of the aggregate mix, quantity and evolutionary nature of the bitumen, the compactness of the layers, the intensity of the traffic and the climatology of the place of use of the asphalt, then the Granulometry changes produced by grinding operations for its recovery have important implications for asphalt recycling.

In fact, the hot recycling of asphalt mixes consists in using for a part or even all road costs. These recovered mixes consist of isolated aggregates but also agglomerates whose elements are strongly bound by bitumen. The analysis of the asphalt to be recycled indicates the granulometry of the mixture, the nature and the content of the bitumen present. The knowledge of these parameters will allow complementary bitumen supply operations and / or specific additives as well as additional new aggregates and / or correctors.

On the other hand, the problem is the treatment of recycled asphalt because it is necessary to bring to temperature aggregates that are already coated with bitumen and which are in the form of small or large particles isolated or in the form of agglomerates with bitumen contained within even of these agglomerates.

The known installations which reprocess these mixes are identical to those for new aggregates. The rotary kiln equipped with a burner is used but arrangements avoid contacting the asphalt directly in contact with the flame.

However, it is known that the flame, which is of the order of 1100 ° C. at the burner outlet, propagates while maintaining 900 ° C. at its end. The gases then pass 700 ° C outside the flame zone to fall to about 200 ° C, that is to say 50 ° C above the temperature to be reached within the same asphalt.

There are then various harmful phenomena within the bitumen.

Firstly, given the maximum temperatures reached in certain areas of the furnace, well beyond the refining temperatures of the bitumen refinery, degradation phenomena by cracking and pyrolysis in particular. These phenomena cause an aging of bitumen recycled. The combustion gases carry with them volatile organic compounds, in quantities much higher than the authorized standards.

In addition, parallel to the aging phenomenon, the gas stream from combustion, which are added very large amounts of air for its diffusion into the chamber, causes oxidation and additional evaporation adding to its degradation.

As in the case of new aggregates, the fines present are entrained with the gaseous effluents. The small size and their limited mass induce a very rapid temperature rise compared to other aggregates and thus a quick and easy detachment of the support.

Unlike new aggregates, these fines entrained are impregnated with bitumen therefore strongly adhesive.

During mechanical reprocessing by filtration, whatever the mode chosen, clogging of the circulation ducts occurs.

As for filters, they clog quickly and permanently prohibiting their proper operation.

Recycling must be able to be applied as well from production units established in a fixed place, from dismountable and mobile installations as for units operating directly on the roadway to be treated. For the latter operating by continuous reprocessing on costs also produced continuously, the problems mentioned above are intensified, especially the rejections. Similarly with the devices heating the surface of the roadway to be recycled, it is difficult to achieve diffusion in the thickness of the asphalt layer due to poor heat transfer and degradation consequences of the bitumen.

A document DE-B-2916187 aims to solve some problems including the transfer of used asphalt through conveyors stacked superimposed into each other successively. Nevertheless, the The method does not provide heating at two temperatures in two modules in order to treat the different compounds of bitumens according to their degree of volatility.

This device provides either a heating with heating conveyor soles or a flame heating but no radiant heating on top of used road asphalt is provided to refine the heating temperature of each sole or part of hearth.

The present invention proposes solutions to overcome the problems mentioned in the preamble and uses heating means by radiant panels with a particular arrangement for illustrating the method and provide a solution in terms of device, satisfactory but not limiting.

• figure 1 : une vue schématique en élévation latérale d'un premier module de traitement selon la présente invention permettant la mise en oeuvre du procédé
• figure 2 : une vue schématique en élévation latérale d'un second module de traitement selon la présente invention, et
• figure 3, une vue d'une variante de réalisation d'une enceinte du module de traitement.

In order to better explain this device, the method and the device are now described in detail, according to one embodiment, with reference to the appended drawings in which the various figures represent:

• figure 1 : a schematic view in side elevation of a first processing module according to the present invention for carrying out the method
• figure 2 a schematic side elevational view of a second processing module according to the present invention, and
• figure 3 , a view of an alternative embodiment of an enclosure of the treatment module.

The method according to the present invention consists in treating asphalt mixes in a device equipped with radiant heating means by panels.

For the remainder of the description, the milled mixes are used for the description of the description, but also the mixes resulting from mechanical block and crushed shrinkage.

Similarly, the term "radiant heating panels" used cover any surface arrangement capable of emitting radiation leading to radiant heating.

This makes it possible to treat the charges without causing the movements of violent air currents imposed by the heating modes of the prior art, by combustion.

In addition, it is impossible to achieve different temperatures within the same module since it is sufficient to adjust the heat emission according to the load.

It is therefore noted that, thanks to this mode of heating, even in the event of a fall in heating power, it remains perfectly distributed, thanks to the panels which emit calories in a homogeneous way. In the case of a flame, when the power is decreased, the distribution is also significantly modified.

In fact, the maximum point temperature reached can not exceed the deterioration temperature of the bitumens as will be indicated below. These characteristics lead to immediate benefits that solve the first important problems that were mentioned in the preamble. Nevertheless, it is then necessary to obtain the final result sought namely to warm up the aggregates already coated with bitumen.

However, to give an idea, it is known that the aggregate mixture aggregate has a specific surface area of 15 to 20 m ² per kilogram with about 50 grams of bitumen, which leads to thicknesses of bitumen films of a few microns.

The majority of these films are trapped in agglomerates constituting the costs and it should maintain this structure during warm-up to reduce the creation of new surfaces venting the bitumen.

Between the large elements composing the agglomerates are fractions of mineral elements small fine and very fine. These fractions concentrate a greater quantity of bitumen due to differences in specific surface area.

These agglomerates must remain cohesive preferentially. Therefore, a mechanically flexible treatment process is required.

The method also consists of mechanical conveying preferentially by gravity but also by forced conveying and with vibrations. These vibrations, in their emission, will have at least one vertical component, preferably with a high amplitude, so as to allow a regular reversal of the grains. This change of orientation allows a homogeneity of presentation of the entire surface of each grain in front of the infrared radiation of the radiant heating means.

It is noted on this occasion that the bitumen is not exposed in an extreme way to the air and therefore to the oxygen it contains, which can cause accelerated oxidation and aging.

The associated device is represented on the figure 1 . It comprises a first enclosure 10 in which conveyors or transfer belts 12 are arranged. This enclosure is of substantially parallelepipedal shape in this embodiment to be the simplest.

In the case of mobile machines, the device is necessarily the road gauge to allow movement and positioning in the immediate vicinity of construction sites. This same limitation to the road gauge is applicable to mobile machines moving continuously along the site to work the costs as and when continuous. The limitation of the size of the device and the need for a sufficient residence time of the mixes generate constraints.

Also, there is provided several transfer mats arranged one below the other, these mats being inclined or horizontal and vibrated by any means 14 adapted to vibration and for example unbalance motors. Above these mats, there are provided heating means of radiant type, in the form of panels 18. The power, the distribution and the power supply means must be adapted to the processing capacity.

Indeed, it must be taken into account that the materials to be treated contain a certain amount of water that must be removed and the residence time, the heating power are parameters to be taken into account also when sizing the installation.

In the process chosen, the temperature of the asphalt to be reached at the outlet is of the order of 105 to 130 ° C. so as to bring the bitumen into the viscous state and cause complete evaporation of the water and completely dry the introduced materials.

The gases generated during heating, water vapor and the most volatile organic products, derived from bitumen, are discharged to the atmosphere, but it is found that the gaseous effluents contain very small proportions of organic substances at these temperatures.

The method then provides a second step which consists of bringing the mix to the final working temperature, ie 160 to 220 ° C, into a second module. Beforehand, the grains and agglomerates derived from the first module are preferably continuously introduced into means for agglutinating fine elements, grains and agglomerates. The fines ensure cohesion.

It is a hot and completely dry material, at about 105 to 130 ° C, consisting of agglomerates of cohesive elements, which is then carried according to the process of the invention at a temperature of 160 to 220 ° C.

In fact, there are emissions of organic products because the temperatures are higher and these emissions must be treated before their release to the atmosphere. It is noted, however, that the air currents being removed and the elements having been agglutinated, the entrainment of fines is extremely reduced or even eliminated.

In the second module substantially identical to the first, the heat output is modified to fill the heat sink and reach the desired temperature.

Another problem that may arise is the treatment of gaseous effluents. These can be effectively treated by passage through decomposition catalysts which, for many of them, are sensitive to moisture. In fact the elimination of water in the first module is of great importance also to solve this problem.

The second module presented in figure 2 is substantially identical in design to the first module and the identical elements bear the same references with a "".

By cons, not shown but using known devices, it is necessary to provide scraper means to remove the portion of bituminous mortar that is deposited on conveyors or carpets.

The mixes resulting from this second module can be composed of 100% of materials to be recycled. It is necessary to add regeneration additives of the old bitumen, this operation to be carried out in a kneader, in a known manner. These additives are preheated and dosed in an amount related to the mass flow rate of recycled mixes in a continuous production unit or a mass of previously weighed mixes before introduction into the mixer for a discontinuous unit.

The importance of water removal in the first module is again found.

The mixes from this second module can be recycled with a supply of virgin aggregates which are introduced together with the asphalt used in the first module. This virgin material is also prepared in a known manner.

In addition to the bitumen supplied by the used asphalt, it is added regeneration additives and new bitumen as well as filler.

At the end of the mixer, the mix including all or part of the recycled mix is ready for use.

According to a variant of the device of the invention it is possible to use the radiating surface differently. In this case, see figure 3 two coaxial, rotating and inclined cylinders 100, 100 'are provided.

The central cylinder 100 receives heating means 124, for example a burner 126 using liquid fuel. The flue gases are evacuated in known manner at the upper end 128 of the central cylinder, the burner being arranged at the bottom.

The mixes are introduced into the space between the two cylinders, in the upper part and flow by gravity downwards.

The rotation ensures the presentation of all the faces of the grains to the infrared radiation emitted by the outer wall of the central cylinder.

It is therefore noted that the grains and the bitumen which is bound to them, are never in contact with the combustion gases, which eliminates any problem of flight of the coated fines. At the outlet, the effluents are treated as before before returning to the atmosphere.

In this variant, the radiating surfaces are curved and can be equipped with any suitable mixing means.

The methods and devices according to the present invention make it possible to solve the problems posed by the recycling of old mixes while respecting the environmental constraints.

Claims (9)

1. A method for heating a material comprising at least partly old coated road materials to be recycled, in particular issuing from milled road surface or crushed conglomerates, which comprises heating these old coated road materials to be recycled by exposing the various faces of these aggregates and/or coated road materials to the heating, characterised in that:

   - heating is carried out, in a first chamber (10) of a first module, at a first temperature by means of first radiant heating means (16) disposed close to the old coated road materials to be recycled so as to make the bitumen viscous and to cause evaporation of the water and to completely dry the materials, that is to say from 105° to 130°C,

   - these coated road materials heated to a temperature of 105° to 130°C are heated in a second chamber (10') of a second module to a second temperature by means of second radiant heating means (16') disposed close to the old coated road materials to be recycled so as to raise the coated road materials to a working temperature, that is to say 160° to 220°C.
2. A method according to claim 1, characterised in that, between the two heating steps, the old coated road materials to be recycled are caked.
3. A method according to claim 1 or 2, characterised in that at least additives are added at the discharge from the second heating step so as to regenerate the bitumen or reconstitute a novel type of bitumen, by mixing.
4. A method according to claim 3, characterised in that at least a proportion of untreated aggregates prepared elsewhere is added.
5. A device for implementing the method according to any one of the preceding claims, characterised in that it comprises at least one first chamber (10) of a first module provided with mechanical transfer means (12) and heating means (16) of the radiant type making it possible to expose all the faces of the old coated road materials to be recycled and to reach a first temperature of between 105° and 130°C, means for discharging the gaseous effluent and a second chamber (10') of a second module provided with mechanical transfer means (12') and heating means (16') of the radiant type, enabling the old coated road materials to be recycled to reach a second temperature of between 160° and 220°C and means for discharging the gaseous effluent.
6. A device according to claim 5, characterised in that it comprises means for caking the old coated road materials to be recycled disposed at the discharge from the first chamber (10).
7. A device according to claim 5 or 6, characterised in that it comprises a substantially parallelepipidal chamber (10, 10') and in that the mechanical means comprise inclined and/or horizontal conveyors (12, 12') equipped with vibration means (14, 14') and heating means (16, 16') of the radiant type in the form of panels (18, 18').
8. A device according to claim 5 or 6, characterised in that each chamber (10, 10') comprises first and second chambers (100, 100'), cylindrical, coaxial, rotary and inclined, and heating means (124), the old coated road materials to be recycled flowing in the space between the two chambers, by gravity from top to bottom.
9. A device according to one of claims 5 to 7, characterised in that it comprises means for treating the gaseous effluent emitted in the second chamber, including decomposition catalysts.

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