EP0550834A1 - Process for the production of asphalt mixture - Google Patents

Abstract

The invention relates to a process for the production of asphalt mixtures using crude asphalt, in which the latter is mixed with mineral substances and, optionally after addition of hot bitumen, heated until a homogeneous mixture which is readily processable is formed. The object of the present invention is to prepare a mixture of this type in which the product from the heating has a minimised hydrocarbon content. This is achieved by classifying the starting material, comprising the crude asphalt and/or the mineral substances, before mixing into a coarse fraction and a fine fraction, and initially heating only the coarse fractions, while the fine fractions, optionally together with hot bitumen, are added at the end of the heating. An apparatus for carrying out the process provides for the arrangement of a classifier (2) before the feed into the warming device (5) for the crude asphalt, the connection for the fine fraction (3) of the crude asphalt being connected via a transport device (23) to a metering zone (13) in a mixing device (8) downstream of the warming device (5), while the connection for the coarse fraction (4) runs, optionally via a further transport device (16), into the warming device. <IMAGE>

Description

The invention relates to a process for the production of asphalt mix using expanded asphalt, the expanded asphalt being mixed with minerals and optionally after the addition of hot bitumen is thermally treated until a homogeneous, easily processable mix is formed.

The process of the type mentioned is usually carried out in forced mixers which are provided with internals for thorough mixing. Since the mix is extremely inhomogeneous and also of a sticky consistency, the dwell times and the temperatures during the thermal treatment must be selected accordingly in order to achieve a good processable asphalt mix.

With increasing demands on the quality of the mix, this leads to long treatment times at correspondingly high temperatures, as a result of which deposits from low-boiling fractions of the expansion asphalt, in particular in suction systems of the heating devices, have been observed to an increasing extent.

The object of the present invention is to produce a homogeneous, easily processable mixture, the waste gases from the thermal treatment being minimized with regard to their carbon-hydrogen content.

The object is achieved by the features specified in the patent claims.

The invention is explained in more detail below with the aid of several exemplary embodiments.

Figur 1

das Fließbild eines erfindungsgemäßen Paralleltrommel-Verfahrens,

Figur 2

das Fließbild eines Doppeltrommel-Verfahrens mit Abgasrückführung,

Figur 3

das Fließbild eines "Topdrum"-Verfahrens mit der erfindungsgemäßen Klassierung und

Figur 4

das Prinzipbild eines erfindungsgemäß ausgerüsteten Drummixers darstellt.

The exemplary embodiments relate to different variants of asphalt recycling plants, but all of them include the method according to the invention of dividing a coarse and fine fraction of the asphalt. They are shown in the form of four flow diagrams, whereby

Figure 1

the flow diagram of a parallel drum method according to the invention,

Figure 2

the flow diagram of a double drum process with exhaust gas recirculation,

Figure 3

the flow diagram of a "top drum" method with the classification according to the invention and

Figure 4

the basic diagram of a drum mixer equipped according to the invention.

In the explanation of the flow diagrams, the same reference numbers are used for matching method steps or device elements. It is also pointed out that the material flows of, for example, expansion asphalt 1, fine fraction 3, coarse fraction 4 and minerals 9 run in corresponding lines or transport devices, but in the description this was often only provided with the names of the respective substances to be transported.

Bituminous substances are standardized in DIN 55 946, the term "asphalt" being understood to mean a mixture of bitumen and minerals. The asphalts are mainly used for road construction purposes, whereby sand asphalt, asphalt concrete, mastic asphalt, etc. differs depending on their composition. Stone powder, sand, gravel-sand mixtures, gravel, broken gravel, broken natural rock or broken blast furnace or metal slag are used as mineral or aggregates. Stone flour and exhaust gate dust are suitable as fillers, but often only a fraction with grain sizes smaller than 0.09 mm is used as a filler. Stone flour is also referred to as "third-party filler" and Exhaustor dust as "own filler".

• Paralleltrommelverfahren, dargestellt in Figur 1
• Doppeltrommelverfahren mit Abgasrückführung, Figur 2
• Topdrum-Verfahren, dargestellt in Figur 3 und
• Drummixer, dargestellt in Figur 4.

The asphalt mix is produced in so-called "batch mixing plants", the main material used being asphalt granulate, broken from plaice or from the cold milling process when removing road surfaces as so-called "expansion asphalt". A distinction is made between the following processing methods:

• Parallel drum method, shown in Figure 1
• Double drum method with exhaust gas recirculation, Figure 2
• Topdrum process, shown in Figure 3 and
• Drum mixer, shown in Figure 4.

FIG. 1 shows a flow diagram of the parallel drum method, the asphalt being divided as material stream 1 after passing through a classification 2 into a fine fraction 3 and a coarse fraction 4, which is gently handled in a parallel drum 5 is heated by means of a burner 6 arranged in the material flow direction. At the end of the parallel drum 5 there is an outlet 7 which opens into the mixer 8.

At the same time, minerals are added to the heating drum 10 as material flow 9. They pass through the drum 10 in the opposite direction to the beam direction of the burner 11 and leave it via the outlet 12.

The outlets 7 and 12 from the heating drums 5 and 10 open into the mixer 8 on the inlet side. In the course of the mixing of the fractions entered from the outlets 7 and 12, the fine fraction 3 is added to the mixer 8. The exact location of the addition of the fine fraction is determined when the mixing of the coarse fraction has been completed to such an extent that the outer layer of the granules can absorb and bind the fine fraction. At the end of the mixer 8 there is accordingly a metering zone 13 within which the fines 3 can be added. The homogeneous asphalt mixture leaves the mixer 8 via the outlet 14.

In contrast to the parallel drum method according to FIG. 1, the exhaust gas from the parallel drum 5 is fed into the heating drum 10 via a line 15 in the double drum method according to FIG. The line 15 thus contains the "self-filling" or exhaust portion.

Similar to the parallel drum in FIG. 1, the material stream 1 representing the asphalt to be removed is divided into a fine and coarse fraction 3, 4 in the classifying device 2. The fine fraction reaches the mixer 8 at an earlier point in time than in the parallel drum method, so that the metering zone 13 is brought forward in comparison to FIG. This is made possible by the fact that the return of the self-filler via line 15 results in improved conditioning of the mineral substance mixture introduced into the heating drum 10 via the entry 9.

The heated starting materials enter the mixer 8 via the outlets 7 and 12 and their grain structure is coordinated with one another in such a way that they mix into a homogeneous asphalt-mineral granulate within a very short time. The exhaust gases discharged via the exhaust gas duct 15 do not contain any fine bitumen components, so that there is neither a risk of fine bitumen deposits nor the formation of blue smoke.

A parallel drum method (top drum) is also shown in FIG. 3, the input side being specially designed here. The expansion asphalt introduced via the material stream 1 is divided into a fine fraction 3 and a coarse fraction 4 in a classifier 2. The coarse fraction 4 is entered into the cold elevator 16 together with the minerals (entry 9). An entry belt 17 then provides for the cold addition to the parallel drum 5.

The combination of the cold addition with the parallel drum process is the "top drum principle". By dividing the grain fractions of the expansion asphalt it is prevented that the small parts of the starting mixture overheat when passing through the heating system (parallel drum 5). This would lead to the combustion or evaporation of hydrocarbon, which can result in deposits in the raw gas channel 18. This is prevented with the method according to the invention, at the same time avoiding the formation of higher-boiling hydrocarbons in the exhaust gas.

FIG. 4 shows a drum mixer with a drum 19, into which the asphalt on the input side is entered via entry 4 (coarse fraction). The coarse fraction usually consists of cubic parts up to 30 mm in diameter. The fine fraction is removed from the classifier 2 via a conveyor belt 3, with particle sizes of less than 1 mm usually reaching the metering zone 13.

The coarse fraction of the expansion asphalt and the minerals 9 are gently heated in the flame direction of the burner 6 and reach the area of the metering zone 13 in the flowable state. There, the fine fractions of the expansion asphalt can be incorporated directly into the mix without being caught by the flame front and be overheated. Usually 7 to 15% of the expansion asphalt is separated in the classifier 2 as a fine fraction. It has been shown that the remainder of about 80% of the asphalt can be easily heated using the parallel drum method, with the fine fraction also being added directly to the mixer as a cold addition. This creates a relatively clean, Gas-free heating process, whereby due to the small amount of cold addition no problems can arise with regard to the amount of water vapor.

A particular advantage of the method according to the invention is that the influence on the final recipe and the sieving line of the final recipe can be influenced by the separate handling of the fine fractions. This makes it possible to achieve a better quality of the end product even in the case of broken or milled asphalt with high fines, it being expedient that the fine fraction removed from the material flow can also be re-added asphalt pneumatically.

As a result of the method according to the invention, in addition to a substantial reduction in the environmental impact by avoiding harmful raw gas components, a better dosage and thus an improved mix quality is achieved.

In the plant area, savings can be achieved by simplifying the raw gas flow. Since the raw gas no longer contains low-boiling fractions, there is no longer any need for post-combustion of the exhaust gases. Furthermore, the cleaning steps previously required for the exhaust gas detection of recycling systems are no longer necessary, since the formation of unintentionally occurring fine bitumen is prevented. This is achieved by special control of the local addition of fine fractions (fine minerals and fine asphalt), whereby low-boiling combustion residues are avoided, which pollute the environment as toxic exhaust gas components.

In order to optimize the course of the mixture and to avoid low-boiling combustion residues, it is crucially important at which point the fine particles 3 are introduced into the mixer 8. In the illustration of the invention, the entry point was designated “metering zone” or “metering device” 13, 33, which expresses the fact that in the final phase of the mixer, the fines 3 at a location of the mixer 8 or 19 that is still to be precisely determined be added. The exact location is determined according to the consistency of the asphalt / mineral mixture, whereby in the final phase - also called compulsory mixer part 20 - a complete absorption and integration of the fine particles must take place. In order to ensure this, with a reduced absorption capacity, the metering should take place approximately in the middle of the total distance of the mixer 8 or drum mixer 19, the total distance being dimensioned in such a way that a quality which complies with DIN 55 946 is achieved.

Claims (13)

Process for the production of asphalt mix using expanded asphalt, wherein the expanded asphalt is mixed with minerals and, if necessary, after the addition of hot bitumen is thermally treated until a homogeneous, easily processable mix is formed, characterized in that
that the starting material, consisting of the expanded asphalt and / or the minerals, is classified into a coarse and a fine fraction before the mixing and initially only the coarse fractions are thermally treated, while the fine fractions, optionally together with hot bitumen, at the end of the thermal treatment be added. A method according to claim 1, characterized in
that the fine particles with a grain diameter smaller than 10 mm are removed by sieving from the asphalt or minerals. Method according to one of the preceding claims, characterized in that
that 5 to 20% fines are removed from the starting material before mixing. Method according to one of the preceding claims, characterized in that
that the expansion asphalt and the minerals are first mixed cold after classification, the coarse particles having an average grain diameter of 15 to 30 mm, then the mixture is subjected to a thermal treatment at temperatures of 200-900 ° C., after the coarse particles have melted on the surface the fine fractions from the previous classification, if necessary with the addition of hot bitumen, are introduced into the thermal treatment zone. Method according to one of the preceding claims, characterized in that
that the hot bitumen is first injected into the thermal treatment zone and the coarse fractions are wetted with it and then the fine fractions are mixed in, the spraying direction being countercurrent to the direction of blowing in the fine fractions. Method according to one of the preceding claims, characterized in that
that the separated fines are metered into the total batch. Method according to one of the preceding claims, characterized in that
that the starting material is granulated and heated in this form, the fine fractions of the granules being added in a final mixing phase following the heating. Device for carrying out the method according to one of the preceding claims, consisting of heating devices for asphalt and possibly for minerals, characterized in that
that before the entry into the heating device (5) for the asphalt a classifier (2) is arranged, the connection for the fine fraction (3) of the asphalt via a transport device (23) with a metering zone (13) in one of the heating device (5 ) downstream mixing device (8) is connected, while the connection for the coarse fraction (4), optionally via a further transport device (16) opens into the heating device (5). Device according to one of the preceding claims, characterized in that
that a heating drum (10) for the minerals is arranged parallel to the flow direction of the heating device (5) and both are connected to a mixing tower (8), the heating device (5) and the heating drum (10) each consist of a rotary tube with burners (6/11) arranged in the axis of the rotary tube and the entry for the coarse fraction (4) of the asphalt into the rotary tube end connected to the burner (6) and the entry for the minerals (9) open into the rotary tube end opposite the burner (11). Device according to one of the preceding claims, characterized in that
that an exhaust pipe (15) opens from the burner (6) of the heating device (5) opposite the end of the rotary tube into the burner (11) facing the rotary tube end of the heating drum (10), and after complete combustion of the low-boiling fractions a bitumen-free exhaust gas at the burner (11) opposite drum end is withdrawn from line (15). Device according to one of the preceding claims, characterized in that
that the connections for the coarse fraction 4 and the minerals (9) on the burner head side
a drum mixer (19) are arranged, and
that the transport line (23) of the classifier (2) for the fine fraction (3) is connected via a metering device (33) to the compulsory mixer part (20) into which a raw gas duct (18) opens on the discharge side of the drum mixer. Device according to one of the preceding claims, characterized in that
that the outlet of the classifier (2) for the coarse fraction (4) and the entry for the minerals (9) are connected to an elevator belt (16) in which the coarse fraction (4) and the minerals (9) in one common mixing chambers Heating device (5) are transported, an entry belt (17) being connected to the end of the heating device (5) on the burner side, while the fine fraction (3) is assigned to a post-mixer (8) via a transport and metering device (23, 33). Device according to one of the preceding claims, characterized in that
that all material flows are connected to weighing and dosing devices, the control being carried out centrally via a computer unit which characterizes the final state of the asphalt mixture.

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