EP0347271A1 - Drum apparatus for preparing coated bituminous products - Google Patents

Abstract

Means (18, 18') for lifting solid materials circulating in the drum are arranged between a zone (22) in which the flame of the burner (12) develops and a kneading zone (30). These lifting means (18, 18') form a dense curtain of materials, isolating the kneading zone (30) from the flame zone (22) by means of the solid materials being lifted and falling back during rotation of the drum (2). The device may comprise means (32, 34, 37) for introducing recycled materials into the zone (23) where the dense curtain is formed. …<IMAGE>…

Description

The invention relates to a device for preparing bituminous coated products from new aggregates and liquid bitumen and optionally recycled bituminous mixes.

Devices are known for preparing bituminous mixes for road surfaces, from new aggregates, liquid bitumen and powders in which recycled used bituminous mixes are optionally incorporated. These devices generally consist of a large cylindrical drum rotatably mounted on a platform around its axis and slightly inclined relative to the horizontal plane. New aggregates and powders are introduced into the drum at one of its ends. Asphalt recycled in granular form is introduced by a recycling ring surrounding the drum in an intermediate zone between its two ends.

A burner penetrates into the drum at one of its ends and allows hot gases to circulate which ensure the drying and heating of the materials circulating in the drum.

Such a drum performs both the drying and heating of the cold and wet aggregates entering the drum, the reheating of recycled asphalt and the mixing of new aggregates and recycled asphalt, in contact with liquid bitumen brought into the drum by a injection rod.

The internal wall of the drum is lined with blades of different shapes depending on the zones of the drum to ensure, thanks to the rotation of the drum, transport, mixing and / or lifting of the materials circulating in the drum.

Compared to the older process where the drying and heating of the aggregates were carried out in a rotary dryer and the mixing with liquid bitumen in an independent mixer with a fixed envelope, the integration of the drying, heating and mixing functions in the same drum has brought a certain simplification of the procedures and materials involved. However, the drum-dryers-mixers have the disadvantage of bringing together in a single enclosure, a flame, very hot gases and liquid bitumen. This results in a entrainment of bitumen vapor by the hot gases circulating in the drum, which results in a rapid clogging of the bag filters used for the dedusting of the gases leaving the drum and in a rejection of harmful vapors to the atmosphere. These drawbacks are particularly marked in the case of drum-dryer-mixers with parallel currents, that is to say drum-dryer-mixers where the hot gases circulate inside the drum in the same direction as the solid materials. .

We therefore proposed counter-current drum-dryer-mixers, that is to say drum-dryer-mixers where the hot gases circulate inside the drum in the direction opposite to the direction of circulation of the solid materials. , in which it is sought to avoid contacting hot gases from the burner with material containing bitumen as much as possible, such as recycled materials or aggregates being coated with liquid bitumen. For this purpose, a burner is used comprising a very elongated body which penetrates into the drum by its lower outlet end, so that the end of the burner from which the flame develops located relatively distant from the drum outlet. The zone for mixing solid materials with liquid bitumen and possibly the introduction zone. to reheat and mix the recycled asphalts are placed between the drum area where the flame develops and the drum outlet, around the burner body.

Such devices make it possible to largely avoid the formation of bitumen vapor since the hot gases coming from the burner and circulating against the current with respect to the new aggregates introduced by the inlet end of the drum are directed towards this end. inlet, that is to say opposite to the area or areas receiving bituminous materials.

However, these zones located downstream from the flame remain exposed to the radiation of the flame, which can produce heating and vaporization of the bituminous products. In addition, the development of the flame towards the outlet of the drum is not perfectly controlled, so that this flame or hot gases can come into contact with bituminous products, when the kneading zone is immediately downstream of the flame area.

To overcome these drawbacks, it has been proposed to have in the section of the drum, around the body of the burner, a metal screen in the form of a disc ensuring material separation between the flame zone and the kneading zone. The need to provide a screen complicates the structure of the drum and reduces the passage section of solid materials. In addition, the screen undergoes degradation and accelerated wear by the fact that it is located in a very hot area.

The object of the invention is therefore to propose a device for preparing bituminous coated products from new aggregates and liquid bitumen and optionally recycled bituminous coated materials comprising a cylindrical drum mounted to rotate around its axis and slightly inclined relative to in the horizontal plane, a device for feeding cold and wet aggregates through the upper inlet end of the drum and a burner penetrating into the drum through its lower outlet end and opening into a flame zone remote from the ends of the drum , so that hot gases from the burner flame and the new aggregates circulate in opposite directions, the drum comprising, on its internal wall, in a mixing zone situated between the flame zone and the outlet end of the drum, blades for mixing solid materials circulating in the drum and liquid bitumen introduced at the entrance to the mixing zone, this device making it possible to perfectly separate the flame zone from the zones of the drum receiving bituminous materials, without complicating the structure of the drum and without disturbing its operation.

For this purpose, means for lifting the solid materials in circulation, integral with the internal wall of the drum, are arranged between the flame zone and the mixing zone to constitute a dense curtain of materials insulating the mixing zone from the zone of flame, by lifting followed by a fall of solid materials throughout the drum section during rotation of the drum.

• La figure 1 est une vue en coupe longitudi­nale et en élévation du dispositif suivant l'inven­tion.
• La figure 2 est une section suivant 2-2 de la figure 1.
• La figure 3 est la section suivant 3-3 de la figure 1.
• La figure 4 est la section suivant 4-4 de la figure 1.
• La figure 5 est la section suivant 5-5 de la figure 1.
• La figure 6 est la section suivant 6-6 de la figure 1.

In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, with reference to the appended figures, an embodiment of a device for preparing coated products according to the invention.

• Figure 1 is a longitudinal sectional view in elevation of the device according to the invention.
• Figure 2 is a section along 2-2 of Figure 1.
• Figure 3 is the next section 3-3 of Figure 1.
• Figure 4 is the next section 4-4 of Figure 1.
• Figure 5 is the next section 5-5 of Figure 1.
• Figure 6 is the next section 6-6 of Figure 1.

In Figure 1, we see the installation which includes a platform 1 for supporting the cylindrical drum 2 which is rotatably mounted on the platform about its axis XX ′. The platform 1 comprises support devices on the ground of the site not shown and means for adjusting its inclination relative to the horizontal plane making it possible to adjust the inclination of the axis XX ′ of the drum 2.

In the case of a mobile station, the platform 1 can be constituted by the platform of a road trailer comprising extensible and retractable support crutches for the installation of the device on the site.

The cylindrical envelope of the drum 2 is rotatably mounted on the platform 1 around its axis XX ′, by means of four rolling rollers 4 and two rolling rings 5.

The drum 2 has a first end 2a or inlet end through which the outlet end of a belt conveyor 6 penetrates, enabling cold and wet aggregates 7 to be supplied to the drum.

The inlet end 2a of the drum is engaged inside a suction box 8 for the gases circulating in the drum.

The outlet end 2b of the drum opposite its inlet end 2a is engaged inside a box 10, the lower part 11 of which forms a discharge chute for bituminous coated products leaving the drum through its end 2b. The box 10 is fixed to the platform 1 and comprises a rear closing plate 10a which is crossed by the elongated cylindrical body 12 of a burner 13 comprising a fan 14 carried by the platform.

The body of the burner 12 disposed along the axis XX ′ of the drum 2 opens at its end 12a inside the drum 2, at a certain distance from its outlet end 2b engaged in the box 10.

The flame 16 of the burner develops inside the drum, starting from the end 12a of the body 12 of the burner in an area remote from both the inlet end 2a and the outlet end 2b of the drum .

The drum 2 comprises, along its length, several successive zones which are differentiated by the shape of the elements lining the internal surface of the drum in the zone considered and by the function provided by this zone, when the device is in service. From the end 2a of the drum to the outlet end 2b, the latter comprises an introduction zone 20, a drying zone 21, a flame zone 22, a zone for introducing recycled asphalt 23 , a reheating and mixing zone 24 and a kneading zone 30. As will be explained below, a dense curtain of solid materials falling in cascade in the section of the drum is formed, in the recycling zone 23, by the solid materials circulating in the drum, so that the zone 23 achieves a complete separation between the zone 22 and the zones 24 and 30.

Zone 20 ensures rapid introduction of the aggregates 7 brought to the drum by the conveyor 6 into the drying zone 21. In this zone, the internal wall of the drum 2 is lined with fins 19 projecting radially from the internal surface of the drum and arranged along helices having as axis the axis XX ′ of the drum.

As can be seen in FIGS. 1 and 2, in zone 21, the interior surface of the drum is provided with lifting vanes 25, the cross section of which can be, for example, in the form of a hook, makes it possible to raise the aggregates 7 up to the upper part of the drum and constitute a continuous curtain of aggregates falling in cascade in the section of the drum during its rotation. The continuous curtain of aggregates is traversed by the hot gases coming from the flame 16 of the burner located in the zone 22 and circulating in the axial direction of the drum (arrow 51). The drum is inclined so that its inlet end 2a is at a level higher than its outlet end 2b. Solid materials and in particular aggregates 7 therefore circulate in the drum in the opposite direction to the direction of circulation 51 of the hot gases. The cold and wet aggregates 7, on entering the drum, are dried and heated by a circulation of hot gases against the current. When they exit through the suction box 8 (arrows 52), the gases are loaded with dust released by the aggregates 7 during their drying.

In the flame zone 22 (see FIG. 3), the internal wall of the drum 2 is furnished with blades 26 making it possible to retain the aggregates 7 dried and heated in the zone 21 against the internal wall of the drum 2. The blades 26 formed by folded sheet metal strips have a concave section directed towards the wall of the drum and a substantially planar external surface directed towards the flame 16.

The vanes 26, of a form known in the art of drying drums and wrappers, make it possible to provide a free zone at the central part of the drum in which the flame 16 can develop.

In zone 23, the drum 2 is surrounded by the recycling ring 32 which comprises an annular fixed part 33 constituting at its upper part a hopper 34 for introducing recycled materials 27 and an annular movable part 35 secured to the external wall drum comprising chutes and passage openings towards the interior of the drum, so as to pass the recycled materials poured into the hopper 34 inside the zone 23 of the drum.

In known manner, a small internal drum 37 is fixed inside the drum 2 coaxially and ensures the passage of the recycled materials introduced into the drum, in the part of the zone 23 located downstream of the recycling ring 32 .

In the part of the zone 23 situated upstream of the recycling ring 32, the internal surface of the wall of the drum 2 is lined with hook blades 18 which ensure the lifting and the fall in the whole section of the drum 2 of the aggregates 7 dried and heated from the flame zone 22 and transported by the vanes 26. Similarly, the surface in of the small drum 37 is lined with hooked vanes 18 ′ ensuring the lifting of the aggregates throughout the section of the drum 37.

It is obvious that zone 23 thus ensures complete separation between zone 22 where the flame 16 develops and zones 24 and 30 located downstream. The separation is ensured on the one hand by the dense curtain of solid materials formed by the vanes 18 throughout the section of the drum 2 and on the other hand by the rotating part of the recycling ring secured to the casing of the drum 2 and the dense curtain of solid aggregates formed throughout the section of the small drum 37 by the vanes 18 ′, during the rotation of the drum.

Helical fins 17 are fixed on the outer surface of the drum 37 and transport the recycled asphalt 27 introduced by the hopper 34 to the zone 24.

The aggregates 7 arrive in zone 24 through the internal part of the drum 37 while the recycled coated products 27 arrive in this zone 24 through the external part of the drum 37.

In the zone 24 located downstream of the zone 23 for introducing recycled asphalt (see FIG. 5), the internal surface of the drum 2 is provided with flat vanes 28. The recycled materials 27 introduced into the drum are mixed by the action of the vanes 28 during the rotation of the drum with the aggregates 7 coming from the drying zone 21 via the flame zone 22 and the drum 37.

The vanes 28 perform a mixing of the bed of granular materials constituted by the aggregates 7 and the bituminous mixes 27. The mixing is carried out without significant lifting of the bed of materials which remains in contact with the wall of the drum.

The aggregates entering zone 24 have been dried and heated in zone 21 and in zone 22 and are therefore at a high temperature when they come into contact with the recycled coated materials 27. The recycled coated materials are therefore heated by contact with the aggregates, which produces a softening and a fusion of the bitumen layer covering the recycled asphalt. The molten bitumen at least partially covers the aggregates during mixing, so that at the outlet 2b of the drum, the products pouring into the kneading zone 30 consist partly of recycled materials covered with molten bitumen and partly with pre-coated aggregates.

The recycled asphalt is heated and mixed with the aggregates are carried out in a calm zone which is not subjected to the circulation of hot gases originating in zone 22, at the outlet 12a of the burner 13.

In the kneading zone 30 which extends from the outlet of the mixing zone 24 to the end 2b of the drum, the internal surface of the wall of the drum 2 is furnished by L-shaped vanes 31 which are visible in Figure 6. A bitumen injection pipe 42 passing through the rear wall 10a of the box 10 enters the drum at its end 2b and opens at the entrance to the mixing zone 30. In addition, a transport device powder 40 consisting of a tube in which a conveying screw rotates also passes through the plate 10a so as to penetrate longitudinally into the drum and to lead to the entry of the mixing zone 30 slightly downstream from the end of the cane 42. In this way, solid materials in Troducts in the mixing zone are first coated with bitumen and then added with a certain quantity of pulverulent making it possible to adjust the composition of the bituminous material being produced in the drum.

The hot pre-coated materials leaving the reheating and mixing zone 24 are therefore sprinkled with bitumen when they enter the kneading zone 30. A pulverulent material is optionally added to the pre-coated material sprayed with bitumen, the pulverulent material thus being retained by adhesion, by bitumen. This prevents any flight of fine materials into the outlet part of the drum, which avoids the outlet of dusty gases and ensures perfect dosing of the quantity of powder in the mixes produced in the mixing zone.

As can be seen in FIG. 6, the blades 31 ensure a lifting of the materials being kneaded with the bitumen in the zone 30, to the highest point of the drum, then a fall in rain of these materials practically in all the drum section. This produces intense agitation of the mixture consisting of the hot pre-coated aggregates and the liquid bitumen. This intense agitation produces an effective mixing throughout the zone 30. In addition, the pre-coated aggregates arriving at the entrance to the zone 30 are at a high temperature, the aggregates 7 having been strongly overheated in the zones 21 and 22. Mixing with recycled asphalts in a proportion which can be, for example, of the order of 80%, produces only limited cooling of these aggregates, so that these pre-coated aggregates resulting from the mixing of new aggregates 7 and recycled coated materials 27 are, at the entrance to zone 30, at a temperature favoring good coating.

On leaving the zone 30, the bituminous coated products 50 poured into the chute 11 therefore have very good quality.

The dense curtain of materials constituted by the aggregates falling in the section of the drum, inside the zone 23, makes it possible to considerably improve the operation and the performances of the drum-drier and kneader, in particular with regard to the points which will be shown below.

As indicated above, the curtain of materials constitutes a screen protecting the reheating and mixing zone 24 and a fortiori the kneading zone 30 of the flame 16 of the burner. The bitumen or bituminous products introduced into these zones 24 and 30 therefore do not undergo excessive heating and its vaporization rate is very low. In addition, the small amount of bitumen vapor formed in zones 24 and 30 is sucked through the curtain of materials in zone 23 which makes it possible to condense and retain part of the bitumen vapors. In this, the curtain plays the role of an active filter. The very small amount of steam reaching zone 22 is burned by flame 16 of the burner. The gas flow 51 circulating in the zone 21 in the direction of the suction box 8 therefore no longer contains bitumen vapor. It should be noted that the vapor flow passing through the curtain of zone 23 is finely divided, which facilitates its combustion in zone 22.

The dense curtain of materials in zone 23 also has the advantage of allowing efficient recovery of the thermal energy released by the burner flame towards the outlet of the drum. This thermal energy is transmitted to the aggregates, mainly by radiation. We increase thus the thermal efficiency of the drum-dryer-mixer.

Compared to the prior art installations comprising a drum dryer and a separate fixed-jacket mixer, the device according to the invention has the advantage of greater simplicity and lower cost since it consists of a simple rotating drum with continuous operation. The presence of the curtain of materials also makes it possible to virtually eliminate the discharges of bitumen vapor. In the case of installations according to the prior art comprising a mixer separate from the dryer drum, these discharges were very small but not zero; this was achieved with a more complex installation in terms of its structure and operation.

Compared to the counter-current gas circulation dryer-mixer-mixer comprising a metal screen separating the flame zone from the zones receiving bituminous products, the device according to the invention has the advantage of using a screen consisting of a curtain of materials, that is to say an indestructible element and whose filtration and gas distribution functions cannot be obtained using a metal screen. In addition, the circulation of aggregates in the drum is absolutely not disturbed.

It should be noted that in the reheating and mixing zone 24, the superheated aggregates 7 are brought into intimate contact with the recycled asphalt 27 thanks to the flat vanes 28 which ensure gentle mixing of the mixture and which slow down the speed of advance in the drum 2. However, the solid materials remain in mass against the wall of the drum and the possible release of bitumen vapors in this area is very reduced.

The pulverulent or filler product which is introduced by the device 40 is immediately picked up by the pre-coated products or the liquid bitumen at the entrance to the zone 30. This therefore prevents a flight of filler and if this flight occurs despite everything in a limited way, the filler is captured by the coated materials which rain in the drum and which constitute a filter for the very weak gas current circulating in the terminal part of the drum.

The filler introduced into the mixes can consist of all or part of the fines recovered in the gases leaving through the suction box 8 or by a powdery material with fine particle size such as cement.

The invention is not limited to the embodiment which has been described.

In particular, the invention can be applied very advantageously to a drum-drier-mixer in which there is no recycling of mixtures. In this case, the dense curtain of material is formed in an area located downstream of the flame area and upstream of the terminal kneading area of the drum. In the area where the curtain is made up, the drum has lifting vanes, for example of the hook vane type having a high capacity for retaining materials. Several sets of successive offset blades can be used to make the curtain more dense. This zone where the curtain is made up can replace both zone 23 and zone 24 of the drum described in the exemplary embodiment.

In the case of a drum allowing the recycling of bituminous mixes and comprising an area such as the area 23 in which a small drum such as the drum 37 ensures the introduction of the recycled mixes into a reheating and mixing area, this small drum can be arranged over the entire length of the recycled introduction zone or, on the contrary, only over a part of the length of this zone as in the case of the device which has been described.

This second arrangement is advantageous since it facilitates the passage of the dry aggregates from the large diameter part to the small diameter part of the zone for introducing the recycled material. In addition, this arrangement makes it possible to create a dense curtain in the entire section of the drum immediately after the flame zone.

Ultimately, the device according to the invention can be used for the manufacture of any bituminous coated product, as well from new aggregates and liquid bitumen only as from new aggregates, liquid bitumen and coated materials bituminous recycled.

Claims (8)

1.- Device for preparing bituminous coated products from new aggregates and liquid bitumen and possibly recycled bituminous mixes comprising a cylindrical drum (2) rotatably mounted around its axis (XX ′) and slightly inclined relative to the horizontal plane, a device for feeding cold and wet aggregates (6) through the upper inlet end (2a) of the drum and a burner (12) penetrating into the drum through its lower outlet end (2b) and opening into a flame zone (22) remote from the ends of the drum, so that hot gases from the flame (16) of the burner and the new aggregates (7) circulate in opposite directions, the drum having, on its wall internal, in a mixing zone (30) situated between the flame zone (22) and the outlet end (2b) of the drum, mixing vanes (31) of the solid materials circulating in the drum and of liquid bitumen introduced at the entrance to the mixing zone (30), character laughed at by the fact that lifting means (18, 18 ′) of the solid materials in circulation, integral with the internal wall of the drum (2) are arranged between the flame zone (22) and the kneading zone (30) to constitute a dense curtain of materials isolating the kneading zone (30) from the flame zone (22), by lifting followed by a fall of solid materials throughout the section of the drum during rotation of the drum. 2.- Device according to claim 1 comprising a zone (23) for introducing bituminous mixes recycled into the drum (2) characterized in that the lifting vanes (18, 18 ′) are arranged in the zone (23 ). 3.- Device according to claim 2, in the case where a drum (37) of smaller diameter than the drum (2) is arranged inside thereof and coaxially in the introduction region of recycled coated materials (23), characterized in that the lifting vanes (18 ′) are fixed to the inner wall of the smaller diameter drum (37). 4.- Device according to claim 3, characterized in that the lifting vanes (18, 18 ′) are fixed on the one hand on the inner wall of the drum (2) and on the other hand on the inner wall of the drum with a smaller diameter (37). 5.- Device according to claim 1, characterized in that the lifting vanes (18) are fixed on the internal wall of the drum (2) over the entire length of an area between the flame area (22) and the mixing zone (30). 6.- Device according to any one of claims 1 to 5, characterized in that the lifting vanes (18, 18 ′) have the shape of hooks in a cross section plane of the drum. 7.- Device according to claim 1, characterized in that it comprises, inside the drum, from its inlet end (2a) to its outlet end (2b):
- an introduction zone (20) where the inner surface of the drum is lined with projecting vanes (24) arranged along helices having the axis (XX ′) of the drum as their axis,
- a drying zone (21) in which the inner surface of the drum is lined with lifting vanes (25),
- a flame zone (22) in which the inner surface of the drum is lined with retaining vanes (26) materials against the inner surface of the drum,
- a zone (23) in which lifting vanes (18, 18 ′) are fixed on the internal surface of the drum (2), to constitute a dense curtain in the whole section of the drum with the materials circulating in the drum during the rotation of this drum,
- And a mixing zone (30) in which the inner surface of the drum is provided with material lifting vanes and in which opens a bitumen introduction device (42). 8.- Device according to claim 7, characterized in that it comprises, in the zone (23) of constitution of the dense curtain of materials, a device (32, 34, 37) for introducing recycled coated materials and that a heating and mixing zone (24) in which the internal surface of the drum is furnished with flat vanes is interposed between the zone (23) of constitution of the dense curtain of materials and the mixing zone (30).

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