EP0033812B1 - Apparatus for preparing coated bituminous products for road surfaces - Google Patents

Abstract

1. A device for the manufacture of bituminous coated products for road surfacings from liquid bituminous binders and from granular products consisting of recycled coated materials arising from worm road surfacings and of new aggregates, in which the proportion of recycled coated materials relative to the proportion of new aggregates can range from à to 100 %, consisting of a drum (1) of cylindrical shape mounted to rotate around its longitudinal axis on a platform, associated with means for driving in rotation and with means for supplying granular products to one of the ends of the drum (1), called the products entry end (2), and comprising a zone for introduction (10) for products brought by the means of supply (3), following the entry end (2), in which the drum (1) comprises helical fins (14) for the rapid introduction of the products into the drum (1), a burner (4) entering axially into the drum through the front face of the entry end (2), an isolation and drying zone (12) where the internal surface of the drum (1) is provided with uplifting devices (20-21) which make it possible to lift the granular materials up to the upper part of the drum (1) during its rotation and to form, through the downfall of these materials, a continuous screen of materials isolating the flame (5) of the burner (4) from the following zone of the drum which is a zone (13) for mixing in a hot atmosphere in which the drum comprises uplifting devices (26) for the uplifting of the products and their downfall in the entire straight section of the drum and at the entry of which issues an input device (6) for liquid bituminous binder, and finally a fixed chamber (16) for the discharge of the coated products and for the evacuation of gases (27) circulating in the drum (1), communicating with the exit end of the drum (1) this drum (1) being inclined from its entry end to its exit end to ensure the circulation of the products, characterized in that the drum (1) in addition comprises, between the introduction zone (10) and the isolation and drying zone (12) : a zone (11) for transfer and heating of the granular materials where the internal surface of the drum (1) is provided with sections of fins (17) wound in helices on the internal surface of the drum, projecting relative to this surface, and supporting by their edges which are distant from the internal surface of the drum, scree-sheets (18) arranged along the longitudinal direction over the entire length of the transfer and heating zone (11), the fins (17) functioning as guides for the granular materials circulating between the internal surfaces, and as webs for holding the screen-sheets (18) at a distance from the internal surface of the drum (1), the screen-sheets (18) overlapping along their adjacent lateral sides (19) providing an interstice between the adjacent sides (19), and in that the uplifting devices (20-21) of the isolation and drying zone (12) are arranged in several sets which are stagered angularly in the drum (1).

Description

The invention relates to a device for the preparation of bituminous coated products for road surfaces, from liquid bituminous binders and granular products constituted by recycled asphalts from used road surfaces and by new aggregates, the proportion of asphalt recycled by relative to the quantity of new aggregates which can range from 0 to 100%.

When repairing or maintaining pavements with an asphalt coating, it may be necessary to remove the used coating in order to deposit a new coating on the pavement. The purpose of this operation is to avoid going back to each leveling of the coating, the level of the roadway, by superposition of successive layers of coatings.

The used coating can be removed by milling or, if it has been removed by a plate, subjected to crushing: one thus obtains granules consisting of small aggregates such as pebbles coated and agglomerated together by the asphalt binder. The products resulting from these increases in pavement are generally eliminated, but it appeared desirable to reuse them in the coating plants, because this operation has the advantage of saving new products, aggregates or bituminous binders, and solving the problem of eliminating waste from lifting operations.

We have therefore imagined coating installations which make it possible to treat this waste by recycling it.

The most efficient coating installations which are now commonly used, include a large cylindrical drum inside which are carried out both the drying of the granular materials to be coated, the kneading of these granular products with the liquid bituminous binder and the coating in a hot atmosphere of the materials granulated with the bitumen. The materials are therefore brought into contact with very hot gases or with a flame during at least part of their journey in the cylindrical dryer-coating drum.

The materials are in fact dried and heated inside the drum by the flame of a burner penetrating by one of the faces of the drum and directed axially in this drum, generally by the inlet face of the products to be coated.

The drum is rotatably mounted around its longitudinal axis and slightly inclined so as to ensure the circulation of the products which are lifted inside the drum by fins arranged on the internal surface of this drum, so as to ensure contacting between the hot gases and the solid matter circulating in the drum.

Conventionally, the materials are generally introduced into the drum through the wet and cold inlet face and are heated and dried at least partially in the first zones of the drum before being kneaded with the liquid bituminous binder and coated in a hot atmosphere. in the last areas of the drum.

We know in particular such an installation which has been the subject of FR-A-2 327 048 filed by the applicant where the zone for drying and prior heating of the granulated materials, before kneading with the liquid bituminous binder, where the flame of the burner, is completely isolated, by a continuous curtain of materials raised in the drum by lifting devices, from the next zone where the introduction of the bitumen takes place. In this way, it avoids bringing the burner flame into contact with the bitumen, the destruction of which by combustion is thus avoided.

In the case of recycled material containing a high proportion of asphaltic materials and aggregates, such an installation cannot be used because the granulated products introduced at the inlet of the drum would be brought into contact with the burner flame throughout the drying and heating prior to mixing. In this zone, the asphaltic material would be altered by combustion upon contact with the burner flame and rendered unfit for road use. In addition, it is desirable to have means for creating an opaque continuous curtain in order to reduce the length of the zone necessary for the insulation of the flame.

On the other hand, it is practically essential to design installations which make it possible to treat materials as well including a more or less high proportion of recycled materials as new materials only. Indeed, recycled materials are generally not available in sufficient quantity to supply the coating installation for long periods of operation and it is very often necessary to supply the coating installation with a mixture of new materials and recycled materials or even with new materials only.

We have therefore imagined installations capable of handling both new materials and mixtures of new materials and recycled materials.

A coating installation is known, for example, comprising a conventional drying-mixing drum at the inlet end of which a combustion chamber of refractory steel has been adapted, so as to introduce the mixture of granulated products, which may include a certain proportion. of recycled products, after the burner flame to avoid destruction by combustion of the bitumen contained in the recycled materials. Indeed, thus the flame and the gases at very high temperature are produced in a separate chamber of the drum inside which the granulated materials are introduced and in which these materials are lifted throughout the section of the drum to bring them into contact with the hot gases coming from the combustion chamber, so that direct contact of the flame with the granulated materials containing bitumen is avoided and the use of recycled products, while avoiding their smoke-generating combustion, is made possible. In an installation of this type, it is also possible to process granulated products made from new materials only.

However, such installations have drawbacks since the length of the installation is increased by the presence of a combustion chamber, there are significant heat losses caused by the high temperature of the combustion chamber and there is a risk for personnel who have to work near a room with an extremely high external temperature. The heat losses of such an installation can be of the order of 5 to 10% of the combustion energy.

An installation is also known comprising a double drum constituted by an internal drum of small diameter and an external drum of large diameter mounted coaxially and in such a way that the drum of small diameter is projecting with respect to the drum of large diameter over a certain length corresponding to the entry area for new products which is introduced into the small internal drum inside which the burner flame penetrates. The recycled materials are introduced into the large-diameter external drum and run the length of this external drum until they are mixed with the new materials at the outlet of the small-diameter internal drum emerging inside the external drum. (Highway & Heavy Construction, November 1977, Page 92).

During their progression in the external drum, the recycled materials are isolated from the flame by the internal small diameter drum where the heating and drying of the new materials takes place by contact with very hot gases and with the flame. Mixing with bitumen and coating takes place in the large diameter drum after the zone of this drum where the outlet end of the small diameter internal drum opens.

This device has certain drawbacks since the production capacity is reduced, the small drum not leaving a sufficient free volume to allow the development of sufficient thermal power for a drum of the diameter of the outer drum, and that the separation between new materials and recycled materials at the time of their introduction into the installation requires two feeding devices with continuous weighing of materials. On the other hand, the length of the installation is considerably greater than the length of a conventional installation and the flexibility of use of this installation is not very great since it is not possible to manufacture coated materials from these installations. recycled materials only or from new materials only, in good conditions.

In fact, if only recycled asphalt were used, the small drum would be destroyed by the flame because it would no longer be protected during operation by new materials in contact with its internal wall. On the other hand, if one seeks to manufacture asphalt mixes from new materials only, the production capacity of the installation is reduced to that of a dryer-kneader drum whose diameter would be that of the small drum, c that is to say at a considerably lower level since production varies as the square of the diameter of the drum.

We have also thought of making holes in the wall of a conventional dryer-mixer drum and of adapting a device for introducing recycled materials therein, in order to introduce these materials into an area located after the burner flame (see for example EP-A-0 032 468).

However, this device has the drawback of requiring two different feeding devices with continuous weighing, one at the inlet of the drum for new materials and the other after the flame at the orifices provided in the drum for the introduction of recycled materials.

On the other hand, such a device cannot operate with recycled materials only because the burner flame would destroy the drum in its entry zone, the new materials no longer protecting the internal surface of the drum in this zone.

The object of the invention is therefore to propose a device of the type described in FR-A-2 327 048 for the preparation of bituminous coated products for road surfaces, from liquid bituminous binders and granular products constituted by recycled asphalt coming from used road surfaces and new aggregates the proportion of asphalt recycled compared to the proportion of new aggregates which can range from 0 to 100%, consisting of a cylindrical drum mounted to rotate around its longitudinal axis on a platform and comprising means for driving in rotation, means for feeding granulated products, at one end of the drum called the inlet end, an area for introducing the products brought in by the supply means following the inlet end, in which the drum has helical fins for the rapid introduction of the products into the drum, a burner penetrating axially into the drum from the cold side ntale of the entry end, an insulation and drying zone where the internal surface of the drum is lined with lifting devices allowing the lifting of the granulated materials up to the upper part of the drum during its rotation and the constitution by fallout of these materials, a continuous screen of materials insulating the flame from the next zone of the drum which is a zone of mixing in atmosphere hot in which the drum includes lifting devices with high holding capacity for lifting the products and their fallout in the entire straight section of the drum and at the entrance of which opens a device for supplying liquid bituminous binder and finally a chamber fixed discharge of coated products and evacuation of gases circulating in the drum, in communication with the outlet end of the drum, the drum being inclined from its inlet end to its outlet end to ensure circulation products, this device making it possible to avoid damaging the bituminous materials by exposing them to the flame of the burner and constituting an opaque flame insulation screen over a short length of the drum.

• - une zone de transfert et de chauffage des matériaux granulés où la surface interne du tambour est garnie de tronçons d'ailettes disposés en hélice sur la surface interne du tambour, en saillie par rapport à cette surface et supportant par leurs bords éloignés de la surface interne du tambour des tôles-écrans disposées suivant la direction longitudinale du tambour sur toute la longueur de la zone de transfert et de chauffage, les ailettes jouant le rôle de guides pour les matériaux granulés en circulation entre la surface interne du tambour et d'entretoises pour maintenir les tôles-écrans écartées de la surface interne du tambour, les tôles-écrans se recouvrant suivant leurs bords latéraux adjacents en ménageant un interstice entre les bords adjacents et les dispositifs releveurs de la zone d'isolation et de séchage sont disposés suivant plusieurs jeux décalés angulairement dans le tambour.

For this purpose and in accordance with the invention, the drum further comprises, between the introduction zone and the insulation and drying zone:

• - a transfer and heating zone for granulated materials where the internal surface of the drum is lined with sections of fins arranged helically on the internal surface of the drum, projecting from this surface and supporting by their edges distant from the surface internal of the drum of the sheet metal screens arranged in the longitudinal direction of the drum over the entire length of the transfer and heating zone, the fins acting as guides for the granular materials in circulation between the internal surface of the drum and spacers to keep the screen plates spaced from the internal surface of the drum, the screen plates overlapping along their adjacent lateral edges by leaving a gap between the adjacent edges and the lifting devices of the insulation and drying zone are arranged in several games offset angularly in the drum.

• La figure 1 représente une vue en coupe longitudinale d'un tambour sécheur-enrobeur suivant l'invention.
• La figure 2 représente une vue en coupe selon II-II de la figure 1.
• La figure 3 représente une vue en coupe suivant III-III de la figure 1.
• La figure 4 représente une vue suivant IV-IV de la figure 1.

In order to clearly understand the invention, we will now describe with reference to the attached figures, an embodiment of a device for the preparation of coated products allowing the use of new materials and recycled materials in any proportion .

• FIG. 1 represents a view in longitudinal section of a drying-coating drum according to the invention.
• FIG. 2 represents a sectional view along II-II of FIG. 1.
• FIG. 3 represents a sectional view along III-III of FIG. 1.
• FIG. 4 represents a view along IV-IV of FIG. 1.

In Figure 1, we see a drum 1 consisting of a cylindrical steel casing rotatably mounted about its longitudinal axis on a platform not shown.

Support and rotation devices also not shown make it possible to rotate this cylindrical casing continuously around its longitudinal axis during the operation of the installation.

The drum has an inlet face 2 through which a device for feeding granulated products 3 penetrates, which makes it possible to continuously feed into the drum, the granulated products constituted both by new materials and by recycled materials.

Through the inlet face 2 also penetrates a burner 4 whose flame 5 develops in the first zones of the drum.

The drum also includes a device 6 for supplying liquid bituminous binder making it possible to introduce this bituminous binder inside the drum and to spread it in divided form over the granulated materials.

The drum has an introduction zone 10 receiving the solid granulated products brought by the feed device 3 and causing them to arrive very quickly without contact with the flame 5 of the burner in the zone 11 of the drum.

For this, the internal surface of the drum in zone 10 is lined with helically wound fins 14 which allow, depending on the rotation of the drum, the extremely rapid introduction of products which have a practically negligible residence time in zone 10 and which remain during this short period of time retained against the wall of the drum by the fins 14.

The next zone 11 of the drum is a zone for transferring and heating the granulated materials coming from zone 10, inside which the flame 5 of the burner 4 develops.

In this zone 11 the drum is lined with fins arranged projecting from the internal surface of the drum, according to sections of short pitch propellers. On the end remote from the internal surface of the drum of these fins 17 are fixed screen sheets 18 in the longitudinal direction of the drum.

The internal surface of the drum in zone 11 is lined with several sets of fins on which screen sheets 18 are fixed, so that a large part of the internal surface of the drum in zone 11 is protected by these sheets. screens.

We see in Figure 2 the cross section of these screen plates 18 by a plane perpendicular to the axis of the drum. These sheets are practically flat and each have a straight edge and an edge 19 folded over a small width. This folded edge 19 makes it possible to slightly overlap the sheets so that the folded edge 19 of a sheet slightly covers the straight edge of the adjacent sheet. This makes it possible to cover the entire surface of the drum while leaving a possibility of expansion of the sheets undergoing the heating due to the flame of the burner.

When the granulated materials comprising a certain proportion of recycled materials are introduced into the zone 11 of the drum in contact with the wall of this drum, they are guided and entrained by the fins 17 in a movement advancing them towards the interior of the drum and isolated from the flame 5 by means of the screen plates 18 which make it possible to avoid direct contact with the flame 5. Only a very small quantity of material falls through the interstices between the sheets, in the flame zone. The granulated materials in zone 11, although isolated from direct contact with the flame, are in contact during the whole crossing of this zone with gases at very high temperature, passing through the interstices between the sheets and with the hot metallic surface of the sheets 18, which causes them to dry and heat, allowing the bitumen from recycled materials to melt while avoiding the destruction of this bitumen.

On the other hand, the materials kept in contact with the internal surface of the drum behind the screen sheets make it possible to limit the heat losses through the surface of the drum and thus to improve the efficiency of the installation. On the other hand, the fall of the materials in the flame and the direct contact between the flame and the recycled materials are avoided thanks to the sheet metal screens. Finally, the layer of materials retained between the screen sheets and the wall of the drum makes it possible to protect this wall against the flame.

The height of the fins arranged along sections of propellers is sufficient to allow the circulation of the products against the wall of the drum.

The length of this zone 11 is chosen so that the flame develops there normally.

Zone 12 of the drum which is a zone for insulating the heating and drying of the materials arranged after zone 11 is formed by a part of the drum where the internal surface of this drum is furnished with lifting devices whose cross section is visible in Figure 2. Two sets of identical lifting devices have been arranged along the length of the drum, the first set comprising lifting devices 20 the second set of lifting devices 21 angularly offset on the surface of the drum relative to the fins 20 and arranged following the fins 20 along the length of the drum.

It can be seen in FIG. 3 that these lifting devices allow a collection of the solid materials granulated at the bottom part of the drum and a lifting of these materials up to the highest part of the drum where the granulated materials fall in free fall through the entire section of the drum, during the rotation of this drum.

A screen is thus formed in the whole section of the drum, this screen making it possible to completely isolate the flame 5 from the zone 13 of the drum located beyond the zone 12 constituting an insulation zone.

On the other hand, in zone 12, the material previously heated by contact with the hot gases in zone 11 and traversed during its fall in rain into the drum by hot gases moving from the flame towards the outlet of the drum, undergoes intense drying which allows it to lose almost all of its moisture before it is introduced into zone 13. This addition of heat by the gases also makes it possible to complete the melting of the bitumen of the recycled materials.

The lifting devices 20 and 21, unlike the fins 14 and 17, do not produce a rapid advance of the product inside the drum so that zone 12 is an area where the product is slowed down and occupies the entire section of the drum for a relatively long time despite the short length of the zone 12.

On the other hand, the gases passing through the dense curtain of materials formed in zone 12 and causing the heating and drying of these materials, undergo a significant lowering of temperature, so that the gases penetrate into zone 13 at a much lower temperature. at the temperature prevailing in zone 11.

On the other hand, the mixing of the materials during their lifting and their fall back into the section of the drum causes a mixing and a homogenization of the different solid materials constituting the charge introduced into the drum whether they are new aggregates, powders or recycled materials. Thus these materials introduced simultaneously but not constituting a homogeneous mixture upon entering the drum are effectively mixed in zone 12.

Zone 12 is a zone of short length (10 to 15% of the length of the tube) so that, despite the intensive drying of the materials in this zone, it is possible to prevent elements from flying off in large quantities in the gases circulating in the drum which avoids rejection of a large amount of dust in the gases leaving the drum.

At the exit from zone 12, the materials are introduced into the next practically dry and heated zone, so that spreading of the binder on these granulated materials at the start of zone 13 is greatly facilitated. The binder spray tube 6 in fact opens roughly at the entrance to zone 13, that is to say at a place protected from the flame by the screen formed in zone 12 and where the gases circulating in the drum are at a moderate temperature.

In this way, the binder cannot be destroyed by the radiation of the flame and by the gases at too high a temperature.

In zone 13, which is a zone for mixing the solid granulated product and the bituminous binder in a hot atmosphere, the internal surface of the drum is provided with lifting devices 26 making it possible to lift the granulated materials up to the upper part of the drum and to make fall in all the section of this drum in order to ensure a good contact between these materials falling in rain and the gas crossing zone 13 of the drum to ensure the hot coating of the materials, that is to say a spreading and a bond between the surface of the granulated materials and the bitumen.

It can be seen that the lifting devices 26 are arranged in four successive sets offset angularly on the surface of the drum, along the length of the zone 13.

At the exit from zone 13 which constitutes the last zone of the drum, the coated materials fall into a discharge chamber 16 which allows on the one hand the collection of the coated materials and on the other hand, thanks to a chimney 27, the capture of gases as they exit the drum.

The area 13 is limited by two rings 28 and 29, the height of which is substantially the same as that of the lifting devices, these rings serving as a screen and helping to increase the thermal efficiency of the drum.

Inside zone 13, the circulating gases which entrain, in the zones where the granulated materials are dried, part of the pulverulent contained in these materials come into contact with coated particles which retain the pulverulent in suspension in the gases and thus dust this gas which leaves through the chimney 27 with a negligible proportion of dust. The coating quality and the dust removal efficiency of the gases in zone 13 are all the better the longer this zone is.

In all cases, the length of this zone is more than half the length of the drum.

One of the advantages of the device according to the invention is that it is possible to use granulated materials consisting of both new materials and recycled materials in any proportion. In particular, it is possible to use only new materials or only recycled materials or even any proportion of new materials with respect to recycled materials without, however, modifying the operation of the device according to the invention.

In the case where only recycled materials are used, it is possible to avoid the addition of binder, if the binder contained in the recovered materials has a composition in accordance with the desired final formula.

Generally, however, a certain quantity of virgin liquid binder is added as a function of the quantity of recycled material introduced into the drum, the weight of which is continuously measured by the conveyor belt supplying the introduction device.

Similarly, when using a mixture of recycled materials and new materials, it is possible to introduce bituminous binder in addition or to use only the bituminous binder of the recycled material.

In all cases, a weight detector which determines the flow rate of solid materials entering the drum allows continuous calculation, taking into account the water content of the materials measured by a humidity detector, and possibly the amount of recycled material. introduced with the new material, the content of filler binder necessary to carry out the coating.

The device according to the invention makes it possible to use the same drum for the coating of new materials and for the coating of recycled materials, the production capacity of the installation being the same in all cases and the combustion of the bitumen contained. in recycled materials being avoided through the use of sheet metal screens in the area where the flame develops.

Thus the screen sheets 18 can have a section, by a plane perpendicular to the axis of the drum said transverse plane, having an L-shape to ensure better retention of the product. It is also possible to have screen sheets having another profiled shape than the L shape, for example an inverted U shape whose branches are directed towards the wall of the drum.

Likewise, the shape of the lifting devices in zones 12 and 13 is not limited to the shapes which have been shown in FIGS. 3 and 4, these lifting devices being able to have an L-shape, a bucket shape as shown or a rounded shape in a more or less closed gutter.

Although it is preferable that the sheets occupy the entire surface of the drum with a slight overlap of their edges, the screen sheets can also occupy only part of the surface of the drum depending on the extreme conditions of use of this drum .

Finally, the device according to the invention can be used for the production of any bituminous mix usable for road surfaces.

Claims (5)

1. A device for the manufacture of bituminous coated products for road surfacings from liquid bituminous binders and from granular products consisting of recycled coated materials arising from worm road surfacings and of new aggregates, in which the proportion of recycled coated materials relative to the proportion of new aggregates can range from 0 to 100 %, consisting of a drum (1) of cylindrical shape mounted to rotate around its longitudinal axis on a platform, associated with means for driving in rotation and with means for supplying granular products to one of the ends of the drum (1), called the products entry end (2), and comprising a zone for introduction (10) for products brought by the means of supply (3), following the entry end (2), in which the drum (1) comprises helical fins (14) for the rapid introduction of the products into the drum (1), a burner (4) entering axially into the drum through the front face of the entry end (2), an isolation and drying zone (12) where the internal surface of the drum (1) is provided with uplifting devices (20-21) which make it possible to lift the granular materials up to the upper part of the drum (1) during its rotation and to form, through the downfall of these materials, a continuous screen of materials isolating the flame (5) of the burner (4) from the following zone of the drum which is a zone (13) for mixing in a hot atmosphere in which the drum comprises uplifting devices (26) for the uplifting of the products and their downfall in the entire straight section of the drum and at the entry of which issues an input device (6) for liquid bituminous binder, and finally a fixed chamber (16) for the discharge of the coated products and for the evacuation of gases (27) circulating in the drum (1), communicating with the exit end of the drum (1) this drum (1) being inclined from its entry end to its exit end to ensure the circulation of the products, characterised in that the drum (1) in addition comprises, between the introduction zone (10) and the isolation and drying zone (12) : a zone (11) for transfer and heating of the granular materials where the internal surface of the drum (1) is provided with sections of fins (17) wound in helices on the internal surface of the drum, projecting relative to this surface, and supporting by their edges which are distant from the internal surface of the drum, screen-sheets (18) arranged along the longitudinal direction over the entire length of the transfer and heating zone (11), the fins (17) functioning as guides for the granular materials circulating between the internal surfaces, and as webs for holding the screen-sheets (18) at a distance from the internal surface of the drum (1), the screen-sheets (18) overlapping along their adjacent lateral sides (19) providing an interstice between the adjacent sides (19), and in that the uplifting devices (20-21) of the isolation and drying zone (12) are arranged in several sets which are staggered angularly in the drum (1).

2. A device for the manufacture of coated products according to Claim 1, characterised in that the screen-sheets (18) are flat sheets, one edge (19) of which is folded towards the interior of the drum (1), and are arranged so that the folded edge (19) of a sheet (18) overlaps slightly the non-folded edge of the adjacent sheet.

3. A device for the manufacture of coated products according to Claim 1, characterised in that the screen-sheets (18) have a cross-section in a plane which is perpendicular to the axis of the drum, or a transversal cross-section, which is L-shaped.

4. A device for the manufacture of coated products according to Claim 1, characterised in that the screen-sheets (18) have a transversal cross-section which is U-shaped.

5. A device for the manufacture of coated products according to any one of Claims 1, 2, 3 and 4, characterised in that the means (3) for supplying granular products comprise a convoyer belt associated with means for weighing which receive both the new aggregates and the recycled materials.

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