EP0203856A1 - Method and apparatus for making bitumen-coated products with aggregates containing a large quantity of fines - Google Patents

Abstract

A mixing drum dryer having an envelope (1) internally lined with fins is used, some of which perform a complete lifting of the aggregates, in a drying zone (7, 8). Liquid bitumen is incorporated into the aggregates at the end of the drying zone (7, 8) with raising of the aggregates. The aggregates and the bitumen are kneaded hot in a zone (9) where the aggregates remain in contact with the wall of the drum. The excess fines are recovered in the hot gases at the outlet (3) of the drum. The process also applies in the case where recycled materials are used to prepare asphalt.

Description

The invention relates to a method and a device for manufacturing bituminous coated products in a mixing dryer drum, from aggregates containing an amount of fines in excess of the amount required in the coated materials.

It is well known to carry out the hot manufacture of bituminous mixes, from aggregates and molten bitumen, in a cylindrical-shaped mixer drum dryer rotatably mounted around its axis which is slightly inclined relative to the horizontal plane to allow the circulation of products in the drum.

The aggregates are introduced continuously by one end of the drum through which the flame of a burner penetrates, so that the drum is traversed by the aggregates and hot gases circulating in the same direction. The blades arranged inside the drum make it possible to lift the aggregates and then to let them fall so that they occupy practically the entire cross section of the drum, over at least part of its length. The molten bitumen is introduced into the drum so as to be mixed with the aggregates, the drum ensuring the drying of the aggregates and their coating with the bitumen. At the exit of the drum, ready-mix mixes and the hot gases which have passed through the drum are recovered.

Bituminous mixes must contain, in addition to aggregates and bitumen, a certain proportion of fines, that is to say materials having a particle size less than 80 microns. If the starting aggregates contain a small quantity of fines, it may be necessary to add them, as independent constituents, to the inlet of the drum. On the other hand, during the drying of the aggregates, the hot gases circulating in the drum tend to separate the fines from the aggregates and to entrain them towards the exit of the drum where these fines are found in the hot gases escaping. at the fireplace. It is therefore necessary to provide on the coating installations, filters allowing the trapping of fines before letting escape the gases recovered in the drum, by the chimney of the coating station. The fines recovered by the filters can be reintroduced into the drum to maintain the level of fines in the asphalt at its necessary value.

Methods have been proposed for manufacturing coated products in which the bitumen is introduced onto the aggregates while the latter still contain practically all of their starting moisture. The subsequent drying of the aggregate takes place during the mixing of the aggregates and the bitumen which are exposed to the hot gases by lifting in the section of the drum. In such processes, the separation of the fines and their entrainment by hot gases are avoided, these pulverulent substances being fixed on the aggregates, first by the remaining moisture and then by the bitumen.

A device has also been proposed, described in French patent application No. 2,327,048 of October 8, 1975, which makes it possible to carry out a practically complete drying of the aggregates, prior to the introduction of the bitumen and, despite everything, to avoid the emission of dust in the gases discharged at the outlet of the drum. For this, the preliminary drying is carried out in an area of the drum where a very dense curtain of materials is formed throughout the section of the drum. The introduction of the bitumen is carried out just behind the curtain, the mixing then being carried out by lifting and falling of the materials throughout the section of the drum. The bituminous coated materials occupying the entire section of the drum make it possible to trap the fines entrained by the hot gases in the drying zone. There are therefore gases leaving the drum containing a small proportion of fines and it is thus possible to guarantee a minimum content of fines in the mix.

However, in some cases, the starting content of fines in the aggregates is extremely high and this content exceeds the desirable final content in mixes.

The methods and devices of the prior art described above cannot make it possible to reduce the content of fines in the aggregates so as to maintain the composition of the mixes at an optimum.

There are also known methods and devices making it possible to reuse asphalt recovered from repaired roads after crushing. Such devices may include an introduction ring for recycled materials obtained by crushing or milling in the vicinity of the central part of the drum. It has been proposed to extract the excess fines at the level of the recycling ring by taking a portion of the gases in circulation. However, such a method has the drawback of reducing the efficiency of the installation and preventing it from operating in recycling, when the device for extracting the gases in the recycling ring is put into operation.

The object of the invention is therefore to propose a process for the production of bituminous coated products in a mixing drum dryer, from aggregates containing an amount of fines in excess of the quantity required in the coated materials, the aggregates being introduced in continuous at one end of the drum through which the flame of a burner enters then transported inside the drum whose axis is slightly inclined with respect to the horizontal, so as to be brought into contact with the hot gases of the burner crossing the drum in the same direction as the aggregates and finally, mixed with a liquid bituminous substance and kneaded to achieve their coating by this substance, the aggregates being lifted and falling in the drum to occupy a large part of its cross section during a part of their journey inside the drum corresponding to an aggregate drying zone, a process which makes it possible to easily obtain an optimal final content e n fines in aggregates.

• -on incorpore la substance bitumineuse liquide aux agrégats à la fin de la zone de séchage par soulèvement des agrégats, de façon que les fines excédentaires qui sont séparées des agrégats pendant leur mise en contact avec les gaz chauds restent en suspension dans ces gaz chauds en circulation dans ce tambour,
• - on effectue le malaxage à chaud des agrégats et de la substance bitumineuse sans soulèvement des agrégats dans le tambour, au contact de la paroi interne de ce tambour,
• -et on effectue le captage des gaz chauds à la sortie du tambour de façon à entrainer hors du tambour les fines excédentaires.

For this reason :

• the liquid bituminous substance is incorporated into the aggregates at the end of the drying zone by raising the aggregates, so that the excess fines which are separated from the aggregates during their contact with the hot gases remain in suspension in these hot gases in circulation in this drum,
• the hot mixing of the aggregates and the bituminous substance is carried out without lifting the aggregates in the drum, in contact with the internal wall of this drum,
• -and the hot gases are captured at the outlet of the drum so as to entrain excess fines from the drum.

The invention also relates to a device for manufacturing bituminous coated products from aggregates containing a large amount of fines.

• La Fig. 1 est une vue schématique en coupe longitudinale d'un tambour sécheur malaxeur selon l'invention permettant la fabrication d'enrobés bitumineux à partir de matériaux neufs.
• Les Fig. 2, 3, 4 et 5 sont des vues en coupe suivant II-II, III-III, IV-IV et V-V de la Fig. 1 ou de la Fig. 6, respectivement.
• La Fig. 6 est une vue schématique en coupe longitudinale d'un tambour sécheur malaxeur comportant un anneau d'introduction de matériau recyclé.
• La Fig. 7 est une vue en coupe suivant VII-VII de la Fig. 6.
• La Fig. 8 est une vue schématique en élévation d'un poste d'enrobage permettant de limiter la teneur en fines des enrobés.

In order to clearly understand the invention, a description will now be given, by way of nonlimiting examples, of two embodiments of a device according to the invention, in the case of the manufacture of mixes from new materials and in the case of the manufacture of aggregates partially from recycled materials.

• Fig. 1 is a schematic view in longitudinal section of a mixing drum dryer according to the invention allowing the production of bituminous mixes from new materials.
• Figs. 2, 3, 4 and 5 are sectional views along II-II, III-III, IV-IV and VV of FIG. 1 or of FIG. 6, respectively.
• Fig. 6 is a schematic view in longitudinal section of a mixing dryer drum comprising a ring for introducing recycled material.
• Fig. 7 is a sectional view along VII-VII of FIG. 6.
• Fig. 8 is a schematic view in elevation of a coating station making it possible to limit the content of fines in the coated materials.

In Fig. 1, we see a kneading dryer drum constituted by a cylindrical casing 1 of great length having a longitudinal axis whose direction is close to the horizontal. This drum is rotatably mounted around its axis by means of devices not shown and this axis is slightly inclined relative to the horizontal so that the end of the inlet 2 of the drum is at a level slightly higher than the end outlet 3. The flame 4 of a burner (not shown) penetrates through the inlet end 2 of the drum, through which the aggregates also penetrate. These aggregates are constituted by a material with a large particle size such as pebbles and / or sand containing a proportion of fines with a particle size less than 80 microns relatively large and for example greater than 8%, that is to say greater than the maximum proportion of fines generally accepted to obtain a good quality asphalt.

The drum has successive zones 5, 6, 7, 8 and 9 which are distinguished from each other by the shape of the blades lining the surface of the drum over the length of the corresponding zones.

In the entry area 5, the interior surface of the drum is lined with helical fins which ensure rapid introduction of the aggregates into the drum, so that these aggregates remain in contact with the interior wall of the drum cover 1. In zone 6, as can be seen in FIG. 2, the inner surface of the drum is lined with screen vanes 10 which allow the material to be transported to the periphery of the drum and protect it from the flame 4. Such screen vanes are described in French patent application 80-00570 of January 11, 1980. The aggregates 12 are thus protected in the entry zones 5 and 6 against a direct action of flame 4 and undergo only limited preheating. The flame develops in the free central zone of the drum, the envelope 1 of which is protected by the aggregates 12 retained by the screen vanes 10. The use of screen vanes also makes it possible to avoid the bursting of the aggregates by direct contact. with the flame and therefore the formation of fines in addition to those introduced with the aggregates.

In zone 7, the internal surface of the casing 1 is lined with several sets of blades 14, the cross section of which is in the form of hooks. These hook blades 14 make it possible to raise the aggregates 12 to the highest point of the drum and to allow them to fall over the entire cross section of the drum to form an extremely dense curtain of aggregates stopping the radiation of the flame and allowing drying. intense aggregates 12.

In zone 8, the casing 1 of the drum is lined with blades 15 in the form of gutters placed less closely together than the hook blades 14 and making it possible to pour the aggregates 12 practically dry, over a large part of the section of the drum. . The aggregates 12 are thus in contact with the hot gases circulating in the drum between the inlet face 2 and the outlet face 3, so that these gases entrain the fines provided by the aggregates 12. During the drying of the aggregates, the fines which are no longer bound by the humidity of the aggregates can detach from them, so that they are entrained by hot gases.

At the end of the zone 8, is disposed the end of the cane 17 for introducing liquid bitumen which allows watering of the aggregates circulating in the drum by the bitumen.

In zone 9 which is the kneading zone of the drum, the casing 1 is provided with angles 18 of low height which make it possible to knead the aggregates mixed with the bitumen in contact with the internal surface of the casing 1, in the lower part of the drum. The bitumen-coated aggregates 12 are not lifted in the drum section, so that the hot gases loaded with fines do not come into contact with these coated aggregates. The fines are therefore not trapped and are found in the hot gases at the outlet of the drum which are sent to the dedusting installation allowing their separation.

By adjusting the position of the end of the rod 17 (displacement x in Fig. 1), that is to say the point of introduction of the bitumen, relative to the exit from zone 8, it is possible to obtain very easily an adjustment of the quantity of fines extracted and therefore of the quantity of fines remaining in the mixes.

Indeed, if the bitumen cane opens into the drum before the end of zone 8, there is a zone of length D in which the aggregates mixed with the bitumen are raised throughout the drum section and constitute a curtain of materials covered with liquid bitumen that the gases containing fines must pass through before entering zone 9. This curtain formed of materials with high adhesiveness makes it possible to retain part of the fines suspended in the gases and thus constitutes a filter for hot gases. The quantity of fines retained obviously depends on the length D and it is possible to adjust the position of the point of introduction of the bitumen to maintain exactly the quantity of excess fines in the hot gases. These excess fines are then entrained by the gases up to the exit of the drum and retained in the dust collectors of the coating station. The rod 17 can also be placed just at the exit from the zone 8 and in this way the length D of the hot gas filtering zone is zero. A large quantity of fines is thus entrained with the hot gases towards the outlet of the drum.

The length of the zone 9 is determined so as to obtain sufficient mixing and therefore a good quality asphalt.

An adjustment is therefore obtained for the content of fines in the mix, however accepting an increase in the total length of the drum due to the presence of a mixing zone without lifting the materials in the drum.

In Fig. 6, we see a mixer dryer drum modified with respect to the drum shown in FIG. 1, to allow the introduction and processing of recycled materials. The zones and equivalent elements in Figs. 1 and 6 have been designated by the same references.

The only difference between the drums depicted in Figs. 1 and 6 relates to the design of the zone 20 interposed between the zones 7 and 8 of the drum, at the level of the recycling ring visible in FIG. 7.

In this intermediate zone for introducing recycled material 20 which has been described in French patent application 80-00570, the casing 1 of the drum has openings 22 separated by introduction troughs 23 having inclined surfaces. The recycling ring 24 surrounding the casing 1 of the drum in the area 20 includes a hopper 25 for introducing recycled materials 26. Inside the casing 1 is fixed a second coaxial casing of smaller diameter 27 on which are attached externally hético'tciates fins 28 and internally hook blades 29. The recycled material 26 enters through the openings 22 in the casing 1 where these materials are supported by the inner casing 27 and the helical fins 28 which drive this material into the zone 8 of the drum.

The recycled materials are then dried and heated in zone 8, by direct contact with the hot gases circulating in the drum.

At the exit from zone 8, the heat input to the recycled materials is such that the bitumen contained in these materials begins to melt.

Simultaneously with the introduction of recycled materials into the drum, an introduction of new aggregates is carried out in the manner already described by the inlet end 2 of the drum. The new materials and the recycled materials are thus mixed and additional bitumen is introduced by the cane 17, the sprinkling end of which is disposed in the vicinity of the end of the zone 8.

As previously, the fines entrained by the gases are not stopped by the materials in the kneading zone 9, kneading taking place without lifting the materials in contact with the internal surface of the casing 1.

In zone 8, the recycled materials raised in the drum also do not allow significant trapping of the fines entrained by the gases since the melting of the bitumen contained by the recycled materials does not really start until the exit from zone 8.

As before, it is therefore very easy to adjust the content of fines in the coated materials, these fines coming both from the new starting aggregate and from recycled materials.

In Fig. 8, we see a coating station which includes a drum 30 whose casing 1 is inclined relative to the horizontal plane fixed on a platform 31. A burner 32 penetrates through the inlet end of the drum and a chamber evacuation 33 collects at the outlet of the drum the prepared mixes and communicates at its upper part with a sheath 36 allowing the hot gases containing the fines to pass through a dedusting installation 37. The dedusting installation 37 contains either multicyclones and scrubbers or bag filters. The purified gases are discharged into the atmosphere through a chimney 38 and the recovered fines are evacuated (arrow 40) by a screw handling device 39.

The method and the device according to the invention have the main advantages of making it possible to reduce the content of fines in an aggregate and to carry out the coating of this aggregate in the same device comprising a simple means of adjusting the residual content of fines. . This adjustment means can advantageously consist of a bitumen introduction lance opening into the drum at an adjustable introduction point in the vicinity of the end of the drying zone with lifting of the materials in the drum.

The device can also be designed to be able to process recycled materials obtained by milling or by crushing bituminous road surfaces and containing a relatively large quantity of fines produced during milling or crushing. In this case also, the content of fines in the mixes coming either from recycled materials or from new aggregates introduced at the inlet of the drum can be lowered using the process according to the invention, by entraining the excess fines in the hot gases passing through the drum. In this case, the extraction of the fines with the gases leaving the drum and not at the level of the recycling ring makes it possible to simultaneously remove the fines and the recycling.

The process and the device according to the invention therefore make it possible to develop bituminous products from aggregates containing large proportions of fines.

The invention is not limited to the embodiments which have been described; on the contrary, it includes all variants.

This is how it is possible to design mixing dryer drums of a different type from those which have been described for implementing the method according to the invention: The blades for lifting the materials in the different zones of these drums can have different shapes from those that have been described and shown. The kneading devices for the end region of the drum can be of any shape and size and, in some cases, it is even possible to design a kneading zone where the interior surface of the drum casing does not have any mixing device is completely smooth.

The bitumen introduction device can be constituted by a device different from a cane whose outlet end has an adjustable position in the vicinity of the end of the drying zone with lifting of the materials. This device can be fixed and arranged, for example, exactly at the exit from the drying zone with lifting, that is to say at the entry to the mixing zone without lifting. This provision will generally be adopted in the case of extremely dusty aggregates.

Finally, the method and the device according to the invention apply to the hot production of any bituminous mix, from aggregates containing large amounts of fines, with or without introduction of recycled materials.

Claims (8)

1.-Process for manufacturing bituminous coated products in a mixing dryer drum, from aggregates containing an amount of fines in excess of the amount required in the coated materials, the aggregates being introduced continuously at one end (2) of the drum through which the flame (4) of a burner enters, then transported inside the drum (1) whose axis is slightly inclined relative to the horizontal, so as to be brought into contact with the hot gases of the burner passing through the drum in the same direction as the aggregates and finally, mixed with a liquid bituminous substance and kneaded to coat them with this substance, the aggregates being lifted and falling in the drum to occupy a large part of its cross section, during part of their journey inside the drum corresponding to a zone (7, 8) for drying the aggregates, characterized by the fact: -that the liquid bituminous substance is incorporated into the aggregates at the end of the drying zone by lifting up the aggregates (7, 8), so that the excess fines which are separated from the aggregates (12) during their contact with the hot gases remain in suspension in these hot gases circulating in the drum (1), that the aggregates (12) and the bituminous substance are hot mixed without lifting the aggregates in the drum, in contact with the internal wall of this drum, -and that the hot gases are captured at the outlet of the drum so as to entrain excess fines from the drum. 2. -Process of manufacturing coated products according to claim 1, characterized in that the liquid bituminous substance is incorporated into the aggregates at an adjustable position along the length of the drum, near the end of the zone (7, 8 ) drying by lifting the aggregates. 3. -Process of manufacturing coated products according to claim 1, characterized in that the liquid bituminous substance is incorporated into the aggregates at the outlet of the drying zone (7, 8) by lifting the aggregates, that is ie at the entrance to the mixing zone (9) without lifting the aggregates. 4. -Process of manufacturing coated products according to any one of claims 1, 2 and 3, characterized in that one incorporates in addition to the aggregates (12) a recycled bituminous material, obtained by milling or crushing and containing excess fines, in the drying area (7, 8) by lifting the aggregates (12). 5.-Device for manufacturing bituminous coated products comprising a mixer-drying drum (1) having an inlet end (2) through which the flame (4) of a burner penetrates and also receiving the aggregates (12), a set successive zones (5, 6, 7, 8, 9) between its inlet end (2) and its outlet end - (3) which is in communication with a device for recovering asphalt and hot gases having passed through the drum, the different successive zones (5, 6, 7, 8, 9) comprising on the internal surface of the casing (1) of the drum different fins from one zone to another, at least one of the zones ( 7, 8) comprising fins ensuring the complete lifting of the material and its fallout throughout the section of the drum, characterized in that it comprises a means (17) for introducing bituminous substance at the outlet of the zone (7 , 8) ensuring complete lifting of the aggregates (12) and a mixing zone (9) according to the drying zone (7, 8) with re lifting and comprising devices (18) for kneading on the internal surface of the casing (1) of the drum, ensuring mixing without lifting the aggregates (12) and the bituminous substance. 6. -A device for manufacturing bituminous coated products according to claim 5, characterized in that the fins (18) in the mixing zone (9) are formed by angles of small height in the radial direction of the envelope ( 1) of the drum arranged with a slight inclination relative to the axis of the casing (1) of the drum. 7. - Device according to any one of claims 5 and 6, characterized in that the device (17) for introducing the bituminous substance consists of a rod whose outlet end has an adjustable position in the direction axial of the drum. 8. -Device according to any one of claims 5, 6 and 7, characterized in that it comprises an area (20) for introducing recycled materials comprising inside a recycling ring (24) successively in the radial direction, the casing (1) of the drum comprising openings (22) for introducing recycled materials (26) and a second envelope (27) along the length of the zone (20) only, integral with the envelope (1) of the drum and carrying helical fins on its external surface (28) and on its internal surface of the lifting fins (29).

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