Installation for producing asphalt

Abstract

The present invention relates to a plant for the production of asphalt, which, in addition to other assemblies such as mixers, loading silos, and bitumen tanks, comprises a recycled asphalt granulate heating drum (1) with a substantially hollow cylindrical base body rotatable about its longitudinal central axis and equipped with fire protection components (2) and deflector plates (4), and a first end wall (3) with a burner (6) arranged on the longitudinal central axis of the base body and a recycled asphalt discharge (7) at the end of the base body opposite the first end wall (3), wherein the discharge (7) has an extraction hood (7a) connected to an exhaust gas line (8), wherein the exhaust gas line (8) branches into a first line (8a) leading to an exhaust gas dust removal device (21) and a second line (8b) introducing a portion of the exhaust gases into the drum (1) tangentially in a spiral direction in the direction of rotation of the drum (1) at the first end wall (3).and wherein the exhaust gases are guided through a cross-sectional narrowing of the drum (1) into the center of the drum (1) in order to be burned there by the flame of the burner (6).

Description

[0001] The present invention relates to a plant for the production of asphalt in which the emission of air pollutants is minimized in order to protect air quality.

[0002] The TA-Luft (Technical Instructions on Air Quality Control) is an administrative regulation in Germany, issued under the Federal Immission Control Act (BImSchG). It establishes requirements and guidelines for the operation of facilities to minimize the emission of air pollutants and protect air quality.

[0003] Asphalt mixing plants are facilities that produce asphalt mixtures, primarily for road construction. These plants release various air pollutants during operation, which are regulated by the Technical Instructions on Air Quality Control (TA-Luft). The main emissions include dust, hydrocarbons, carbon monoxide, nitrogen oxides, and sulfur dioxide. Sulfur dioxide is generally not a problem, as fuels in Germany are very low in sulfur.

[0004] Sources of emissions and pollutants are: 1. Dust: This is mainly generated during the processing, drying, and transport of the mineral raw materials. 2. Hydrocarbons: These are released through the evaporation of bitumen and other organic components. 3. Sulfur dioxide: This can be produced during the combustion of sulfur-containing fuels used to heat the mixtures. 4. Carbon monoxide and nitrogen oxides can be produced during the combustion of the fuels.

[0005] The TA-Luft (Technical Instructions on Air Quality Control) requires various measures at asphalt mixing plants to control and minimize emissions: 1. Exhaust gas purification: Use of filter systems to reduce dust emissions. 2. Fuel selection: Use of low-sulfur fuels to minimize sulfur dioxide emissions. 3. Process optimization: Optimization of heating and mixing processes to increase efficiency and reduce emissions.

[0006] From DE 10 2017 212 046 A1, a plant for producing asphalt with the features of the preamble of claim 1 is known.

[0007] This asphalt production plant, in addition to other components such as mixers, loading silos, and bitumen tanks, includes a recycled asphalt granulate heating drum. The recycled asphalt granulate heating drum has a substantially hollow cylindrical base body, rotatable about its longitudinal axis and equipped with fire-resistant internals and deflectors. It features a first and a second end wall and a burner located on the longitudinal axis of the first end wall. A discharge chute with an extraction hood connected to an exhaust pipe is located on the second end wall.

[0008] In this plant, pollutant exhaust gases from the aforementioned additional components as well as the recycled asphalt granulate heating drum are co-combusted in a white mineral drying drum.

[0009] When using recycled asphalt granules, these are mixed with a specific proportion of white mineral granules. This proportion of the finished asphalt can be up to 90%.

[0010] When recycled asphalt granules are heated, the bitumen they contain releases pollutant emissions, particularly unburned hydrocarbons (Ctotal). To comply with the emission limits stipulated by the German Technical Instructions on Air Quality Control (TA-Luft), the proportion of recycled asphalt in the finished asphalt mixture would have to be drastically reduced, if this is even possible.

[0011] The present invention is based on the objective of further developing a plant for the production of asphalt with the features of the preamble of claim 1 in such a way that the emission of pollutant exhaust gases is minimized and appropriate proportions of recycled asphalt can still be used.

[0012] This problem is solved by the features of claim 1.

[0013] The dependent claims describe features of preferred embodiments of the present invention.

[0014] The principle of the present invention is that, when recycled asphalt granules are mixed with white mineral granules during the production of asphalt, the pollutant emissions generated in the recycled asphalt granule heating drum are co-combusted there to a certain extent, and are not co-combusted together with pollutant emissions from the other components in the white mineral drying drum.

[0015] This has the advantage that the burner output of the recycled asphalt granulate heating drum can be used for pollutant gas afterburning, and the amount of pollutant exhaust gas returned to the recycled asphalt granulate heating drum can be adjusted separately according to requirements in order to minimize pollutant emissions during asphalt production.

[0016] The present invention will now be explained in more detail with reference to exemplary embodiments and the drawings. These show: Fig. 1 a schematic representation of an embodiment of a recycling asphalt granulate heating drum according to the invention, and Fig. 2 a schematic representation of an embodiment of a white mineral drying drum according to the invention.

[0017] One embodiment of the asphalt production plant according to the invention comprises, in addition to other assemblies such as mixers, loading silos, bitumen tanks, scales and mixers, a recycled asphalt granulate heating drum 1, which is located in Fig. 1 is shown schematically.

[0018] The drum has a substantially hollow cylindrical base body lined with fire-resistant internals 2 and deflector plates 4. The drum is rotatable about its longitudinal center axis. The base body is bounded by a first end wall 3 and a second end wall 5, with a burner 6 arranged on the first end wall 3 on the longitudinal center axis of the base body. At the end of the base body opposite the first end wall 3, a recycled asphalt discharge chute 7 is arranged, which has a suction hood 8 connected to an exhaust gas line 8. This line branches into a first line 8a, which leads to an exhaust gas dust removal device (not shown). A second line 8b returns a portion of the exhaust gases to the drum 1. The exhaust gas is introduced tangentially along the inner wall of the drum 1 at the first end wall 3 in a spiral pattern and in the direction of rotation of the drum 1.The exhaust gas flow adheres to the drum wall and, due to the centrifugal force, does not come into contact with the flame of burner 6 for an initial distance. This prevents the burner flame from being cooled by the exhaust gas flow. On its spiral path into the drum 1, the exhaust gases are heated to ignition temperature solely by the heat radiation from the burner flame. A cross-sectional constriction approximately at the level of the tip of the burner flame deflects the exhaust gas flow towards the longitudinal axis of the drum 1 and causes it to strike the tip of the burner flame 6, where the exhaust gases are combusted.

[0019] The cross-sectional narrowing can take the form of an aperture consisting of at least one segment and made of high-temperature resistant steel, such as 16Mo3, Sicromal, or similar.

[0020] A fan 9 is arranged in the second exhaust duct 8b, through which a portion of the exhaust gases is extracted from the extraction hood 7a and blown into the drum 1. The speed of the fan 9 is adjustable and can be automatically or manually controlled depending on the burner output or on continuously measured exhaust gas values ​​based on pollutant content.

[0021] In the Fig. 1 In the illustrated embodiment, the recycled material is fed in from the first end wall 3 parallel to the direction of propagation of the flame of the burner 6, and the heated and dried recycled asphalt granules leave the drum on the side opposite the first end wall into the discharge 7, from where the recycled material is conveyed to a scale and then into the mixer.

[0022] In the mixer, recycled asphalt granules are mixed with so-called white mineral granules and liquid bitumen according to a requested formula to produce the final product.

[0023] Fig. 2 Figure 11 shows an embodiment of a white mineral drying drum according to the invention.

[0024] The general structure of the white mineral drying drum 11 according to the invention essentially corresponds to that of the one described in Fig. 1 The recycling asphalt granulate heating drum shown. The white mineral drying drum 11 also has an essentially hollow cylindrical base body rotatable about its longitudinal central axis, with fire protection components and deflector plates.

[0025] The in Fig. 2 The white mineral drying drum 11 shown is operated in countercurrent operation, i.e. the material input runs parallel to the propagation direction of the burner flame, but in the opposite direction.

[0026] Pollutants are extracted from at least one pollutant source, such as a mixer, loading silo, bitumen tanks, etc., and introduced into the white mineral drying drum 11 at the first end wall 13 via an exhaust pipe 20 containing an exhaust fan 19. This occurs, as with the recycled asphalt granulate heating drum, tangentially in the direction of rotation of the drying drum, spiraling along the inside of the drum. Here, too, the centrifugal forces guide the exhaust gases along the inner wall of the drum body, preventing them from cooling the burner flame. The circulating pollutant exhaust gases are heated to ignition temperature by the radiant heat generated by the burner flame. A cross-sectional constriction of the drum separates the combustion chamber, in which the burner flame spreads, from the drying zone of the drum.The cross-sectional narrowing directs the pollutant exhaust gases towards the longitudinal central axis of the base body at the level of the burner flame tip, where they are combusted. The exhaust gases exiting the drum on the side opposite the first end wall enter a dust collection system 21 and are then fed via an exhauster to a chimney 23.

[0027] The exhaust gas line 8a from the recycled asphalt granulate heating drum is also led into the dust extraction system 21.

[0028] The efficiency of pollutant afterburning in the asphalt production plant according to the invention is at least twice as high as in plants known in the prior art, since, according to the invention, two burners 6, 16 are used for pollutant co-combustion instead of just one. Furthermore, the operating temperatures in the two drums can be individually adjusted, which also increases the efficiency of the plant.

[0029] The above description of an embodiment of a plant according to the invention for the production of asphalt serves only to explain the invention claimed in the patent claims and is not to be understood as restrictive.

Claims

1. Plant for the production of asphalt, comprising, in addition to other assemblies such as mixers, loading silos, bitumen tanks, a recycled asphalt granulate heating drum (1) with a substantially hollow cylindrical base body rotatable about its longitudinal central axis, equipped with fire protection components (2) and deflector plates (4), and a first end wall (3) with a burner (6) arranged on the longitudinal central axis of the base body and a recycled asphalt discharge (7) at the end of the base body opposite the first end wall (3), wherein the discharge (7) has a suction hood (7a) connected to an exhaust gas line (8), characterized by the fact thatthe exhaust gas line (8) branches into a first line (8a) which leads to an exhaust gas dust removal device (21), and a second line (8b) which introduces a portion of the exhaust gases into the drum (1) at the first end wall (3) in a tangential spiral direction in the direction of rotation of the drum (1), and wherein the exhaust gases are guided through a cross-sectional narrowing of the drum (1) into the center of the drum (1) in order to be burned there by the flame of the burner (6).

2. System according to claim 1, characterized by the fact that The cross-sectional narrowing is achieved by an aperture and / or by deflector plates and / or by a reduction in the diameter of the hollow cylinder, which separates a combustion chamber (1a) from a drying and heating zone (1b).

3. System according to claim 1 or 2, characterized by the fact that in the second line (8b) a fan (9) with adjustable speed is arranged.

4. System according to claim 2, characterized by the fact thata pollutant measuring device is arranged in the extraction hood (7a) and the speed of the fan (9) is automatically or manually controlled depending on the continuously measured pollutant content.

5. System according to claim 3, characterized by the fact that The speed of the fan (9) is regulated depending on the burner output.

6. System according to at least one of the preceding claims, characterized bya white mineral drying drum (11) for heating white mineral granules, wherein the white mineral drying drum (11) has a substantially hollow cylindrical base body rotatable about its longitudinal central axis, equipped with fire protection components (11a) and deflector plates (11b), a first (13) and a second end wall (15) and a burner (16) arranged on the longitudinal central axis at the first end wall (13), wherein exhaust gases from at least one of the further assemblies are introduced tangentially in the direction of rotation of the drying drum (1) spirally on the inside of the drum (11) by means of an extraction line (20) via an extraction fan (19) and are guided through a cross-sectional narrowing of the drum (11) into the center of the drum (11).

7. System according to claim 6, characterized by the fact that The cross-sectional narrowing of the drying drum (11) is caused by an aperture made of a high-temperature resistant steel.

8. System according to claim 6, characterized by the fact that the cross-sectional narrowing is produced by an aperture and / or by the throwing plates (11b) and / or by a reduction in the diameter of the hollow cylinder.

9. System according to one of claims 6 to 8, characterized by the fact that the cross-sectional narrowing is located at the level of the tip of the burner flame and limits a combustion chamber in the drying drum (11).

10. Device according to one of the preceding claims, characterized by the fact that the white mineral drying drum (11) operates in countercurrent flow.

11. Device according to one of the preceding claims, characterized by the fact that the amount of exhaust gas introduced into the white mineral drying drum (11) is controlled via the speed of the extraction fan (19).

12. System according to claim 11, characterized by the fact that The amount of exhaust gas introduced is regulated depending on the burner output or via a continuous measurement of the pollutant content of the exhaust gases.

13. System according to claim 12, characterized by the fact that the regulation is automatic or manual.

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