DK3296462T3

DK3296462T3 - Plant and method for making asphalt

Info

Publication number: DK3296462T3
Application number: DK17181252.2T
Authority: DK
Inventors: Frank Wagner
Original assignee: Benninghoven Gmbh & Co Kg Muelheim
Priority date: 2016-09-16
Filing date: 2017-07-13
Publication date: 2019-01-07
Also published as: ES2693606T3; EP3296462A1; DE102017212046A1; PL3296462T3; EP3296462B1

Description

The invention relates to an installation and a method for the manufacture of asphalt.

For manufacturing asphalt, drying drums are used for heating old asphalt material, the drying drums being operated in a co-current process. A drying drum of this type is known from DE 36 24 735 A1. Further installations for the manufacture of asphalt are known from US 5,174,650, from US 5,538,340 and from DE 41 40 964 A1. Co-current operation means that the material to be heated and the heat are supplied along the rotational axis of the drying drum in equal directions. When exiting the drying drum, the old asphalt material has a temperature of approximately 130°C. Exhaust gas, which is generated by a burner serving as a heat source and then supplied to the drying drum, has a temperature of approximately 150°C. Typically a target temperature of the old asphalt material of approximately 160°C is aimed for. An increase of the temperature level reduces the efficiency of performing the heating of the old asphalt material. As the temperature rises, heat losses increase as a result of the radiation in the fourth power of the temperature. The efficiency of the method at increased temperature is reduced significantly. An increase of the temperatures also results in an additional increase of the amount of pollutants, in particular the amount of unburnt hydrocarbons (Cges), in particular carbon monoxide (CO) and carbon dioxide (CO2) in the exhaust gas. Furthermore, increased exhaust gas temperatures may lead to a self-ignition of the fine particles in a dedusting device.

The invention is based on the object of improving the manufacture of asphalt in such a way that in particular the amount of pollutants in the exhaust gas is reduced and the manufacture is possible in an uncomplicated manner.

This object is achieved by the features set out in claims 1 and 12. The gist of the invention is that exhaust gas is supplied to a white mineral drying drum for heating white mineral and is burnt there. By means of a flow guide unit, the exhaust gas is supplied to the white mineral drying drum in a guided manner. The combustion of pollutants in the exhaust gas in the white mineral drying drum is effective. The amount of pollutants in the exhaust gas is reduced. In particular the amount of hydrocarbons Cges is reduced as they are burnt in the white mineral drying drum.

The installation includes a flow guide unit with a plate-fin recuperator and improves the targeted combustion of the pollutants in the exhaust gas and/or byproduct exhaust gas. The plate-fin recuperator has fin-like guide plates, which form an outer casing for the helical flow movement of the exhaust gases and/or by-product exhaust gases. The plate-fin recuperator prevents pollutants in the exhaust gas and/or in the by-product exhaust gas from being expelled in an uncontrolled manner due to the centrifugal force of the helical flow.

An installation as claimed in claim 2 allows old asphalt material to be heated in a co-current drying drum, wherein exhaust gas is extracted from the co-current drying drum by means of an extraction device, is supplied to the white mineral drying drum for heating the white material and is burnt there. The combustion of pollutants in the exhaust gas from the co-current drying drum in the white mineral drying drum is effective. Surprisingly, it was found that a prior-art installation for the manufacture of asphalt can be retrofitted with a co-current drying drum in an uncomplicated manner by connecting the extraction device for extracting the exhaust gas from the co-current drying drum to the white mineral drying drum. It is possible to convert installations with high pollutant emissions into an installation according to the invention by retrofitting, said installation having reduced pollutant emissions.

An extraction hood as claimed in claim 3 ensures an improved extraction of the exhaust gases from the co-current drying drum. An exhaust fan of the extraction device improves the extraction of the exhaust gases from the co-current drying drum and in particular from the extraction hood into the white mineral drying drum. The exhaust fan is arranged in particular along an exhaust gas line, in particular between the extraction hood and the white mineral drying drum. A by-product exhaust gas line as claimed in claim 4 allows the supply of by-product exhaust gases, which may be produced in the installation, for example by extracting a mixer or from a loading silo, in particular a mixture loading silo. The total amount of pollutants in the exhaust gas is reduced additionally. A burner as claimed in claim 5 ensures an uncomplicated and direct heating of the white mineral. The combustion of the exhaust gases in the white mineral drying drum is improved. A swirl chamber as claimed in claim 6 allows the exhaust gases and/or the byproduct exhaust gases to be supplied to the white mineral drying drum in a swirling manner. Supplying in a swirling manner means that the exhaust gases and/or by-product exhaust gases are supplied eccentrically to the longitudinal axis of the white mineral drying drum. The exhaust gases and/or by-product exhaust gases are supplied to the burner flame in particular not directly. The swirling supply ensures that the exhaust gases and/or the by-product exhaust gases are introduced substantially along a helical line about the longitudinal axis of the white mineral drying drum. The exhaust gases and/or the by-product exhaust gases flow around the burner flame along a helical flow path.

The embodiment of the plate-fin recuperator as claimed in claim 7 ensures controlled combustion of the pollutants in the exhaust gas and/or in the by-product exhaust gas. The helical flow of the exhaust gas and of the by-product exhaust gas may widen around the burner flame in particular along a widening portion. A direct combustion of the pollutants after being fed to the white mineral drying drum is thus prevented. This prevents cooling of the flame core. This prevents an incomplete combustion of the pollutants. The pollutants in the exhaust gas and/or in the by-product exhaust gas are heated in the widening portion, in particular owing to the radiant heat of the plate-fin recuperator, which in particular causes them to become ignitable. In a tapering portion arranged in particular downstream of the widening portion, the ignitable pollutants are supplied to the tip of the burner flame where they are burnt. A cylinder portion arranged along a longitudinal axis of the white mineral drying drum between the widening portion and the tapering portion allows a targeted heating of the pollutants in the exhaust gas and/or in the by-product exhaust gas. In particular, the pollutants can be evaporated, which improves combustion thereof.

An embodiment of the plate-fin recuperator as claimed in claim 8 ensures a reliable discharge of rock material, in particular of old asphalt material, from the combustion chamber. In particular, a plurality of tapering portions are provided, which are in particular arranged in succession and concentrically to the longitudinal axis. The plate-fin recuperator is in particular configured in the shape of a funnel. In particular, the tapering portions arranged in succession are spaced from each other along the longitudinal axis such that a substantially annular front face gap is formed, which faces the burner flame. The rock material is able to exit the combustion chamber via said annular front face gap.

Afire tube as claimed in claim 9 is arranged in particular in the front region of the burner flame such as to protect the flame from an undesirable cooling. The combustion process is thus secured. Another positive effect thereof is that the fire tube is heated by the radiant heat of the burner flame and has a very high surface temperature. This heat can be transferred to the recuperator air. This causes the recuperator air to be heated such that pollutants contained therein are evaporated and/or become ignitable. A heat/protection element as claimed in claim 10 protects the lifter plate area arranged in the white mineral drying drum along the longitudinal axis behind the flow guide unit against a flame propagation. The heat/protection element is in particular configured as a cylindrical plate, in particular in the manner of an impact wall. The impact wall is oriented in particular perpendicular to the longitudinal axis. The impact wall ensures that the heat is transferred to the white mineral drying drum evenly, and in particular over a large surface area. Along the longitudinal axis, an accumulation pressure is generated in the region of the surface of the heat/protection element facing the flow guide unit, said accumulation pressure resulting in a forced flow of the recuperator air through the burner flame at least in regions. Consequently, a greater amount of pollutants in the recuperator air are burnt in this process. As a result, pollutant emissions are reduced and the heat yield is increased. A dedusting unit as claimed in claim 11 allows the residual amounts of pollutants in the exhaust gas to be reduced.

The method as claimed in claims 12 and 13 substantially has the same advantages as the installation, which have already been explained above and to which reference is herewith made.

The subject matter according to the invention can be further developed on the basis of the features set out in the patent claims and on the basis of the features set out in the following exemplary embodiment of the installation according to the invention, taken either individually or in combination with each other. The respective feature combinations are not to be considered as limitations of the further developments of the subject matter of the invention but are included substantially as examples only.

Further advantageous embodiments, additional features and details of the invention will be apparent from the ensuing description of exemplary embodiments, taken in conjunction with the drawing, in which

Fig. 1 shows a schematic view of an installation according to the invention;

Fig. 2 shows a sectional view along section line ll-ll in Fig. 1;

Fig. 3 shows a schematic view, corresponding to Fig. 1, of a white mineral drying drum according to another embodiment.

An installation 1 shown in a schematic view in Figs. 1 and 2 is used for the manufacture of asphalt by admixing old asphalt material, which is referred to as recycling material.

The installation 1 comprises a co-current drying drum 2 for heating the old asphalt material. The co-current drying drum 2 is rotatable about a first rotational axis 3. At a front end 4, shown on the right-hand side of Fig. 1, of the co-current drying drum 2, a material inlet 5 is provided for feeding old asphalt material. The old asphalt material passes through the co-current drying drum 2 along a material conveying direction 6, which is directed from the front end 4 towards the interior of the co-current drying drum 2, and is oriented in particular parallel to the first rotational axis 3. A first heat source configured as a burner 7 is arranged at the front end 4. The burner 7 is used to supply heat directly to the co-current drying drum 2. The heat is guided through the co-current drying drum 2 along a heat transfer direction 8. The heat transfer direction 8 is oriented parallel to and in the same direction as the material conveying direction 6. The co-current drying drum 2 is operated in a co-current process.

An extraction hood 9 is connected to the co-current drying drum 2 at a front end arranged opposite the front end 4. An extraction hood 9 of this type the details and mode of operation of which are known from German Patent Application No. DE 10 2015 217 845.5 to which reference is herewith made. A key element of the extraction hood 9 is an integrated particle separator unit to separate dust particles having a particle size of at most 100 pm, in particular of at most 63 pm, and in particular of at most 20 pm. For this purpose, a collecting vessel 10 for collecting fine particles is arranged in particular below the extraction hood 9.

The extraction hood 9 has a substantially cylindrical housing 29, a housing longitudinal axis 30 being oriented substantially perpendicular to the rotational axis 3 of the co-current drying drum 2. The housing longitudinal axis 30 is oriented substantially vertically. A collecting vessel 10 forfine particles is arranged in a lower region of the extraction hood 9. In a lower region remote from the housing 29, the collecting vessel 10 has a conical design to improve a collecting effect and in particular a discharge of the fine particles from the collecting vessel 10. A conveyor device with a screw conveyor can be arranged at a lower side of the collecting vessel 10 remote from the housing 29.The conveyor device is used to discharge material collected in the collecting vessel 18. The conveyor device may further include a conveyor belt, which is loaded with the material from the collecting vessel 10 by means of the screw conveyor. As an alternative or in addition to the conveyor belt, the conveyor device may include a trough screw conveyor.

The housing 29 of the extraction hood 9 has an inflow opening. Via the inflow opening, particle-containing gas is able to flow from the co-current drying drum 2 into the housing 29. The inflow opening is arranged in the outer cylindrical wall of the housing 29. The inflow opening is oriented substantially perpendicular to the rotational axis 3. The inflow opening is oriented substantially vertically.

The housing 29 has an outflow opening to which an extraction line 11 is connected.

Seen along the housing longitudinal axis 30, the outflow opening is arranged above the inflow opening. The inflow opening connects the outflow opening via a flow conduit, which is formed by the housing 29 of the extraction hood 9. The housing 29 has an internal diameter Da, which defines a flow cross-sectional surface of the flow conduit.

The flow conduit is part of a flow influencing unit, which is configured passively. The flow influencing unit is a particle separator unit. The flow influencing unit comprises a flow guide member, which is not shown in more detail. The flow guide member is arranged in particular in the region of the inflow opening and is configured as a flap, which is pivotable about a pivot axis 30. The flow influencing unit may include a stop member for the flow guide member to bear against when there is no or an insufficient exhaust gas flow from the co-current drying drum 2 into the extraction hood 9. The stop member is arranged in particular vertically below the rotational axis in such a way that the flow guide member is oriented in a vertically suspended manner when it is not actuated. The flap is arranged such that a projection of the flap in a direction perpendicular to the inflow opening is arranged in the inflow opening. Figuratively speaking, the flap protrudes into the inflow cross-section formed by the inflow opening.

An extraction line 11 is connected to the extraction hood 9, which connects the extraction hood 9 to a white mineral drying drum 12. An extraction fan 13 is arranged along the extraction line 11 to extract exhaust gas from the extraction hood 9. A by-product exhaust gas line 14 by means of which a by-product exhaust gas generator 15, in particular in the mixture loading silo and/or a mixer, are connected to the extraction line 11, opens into the extraction line 11.

The extraction hood 9, the extraction line 11 and the extraction fan 13 form an extraction device, which may optionally also comprise the by-product exhaust gas line.

The white mineral drying drum 12 is rotatable about a second rotational axis 16. A second heat source configured as a second burner 17 is arranged concentrically to the second rotational axis 16 at the front end 18 of the white mineral drying drum 12. At a front end arranged opposite the front ends 18, a white mineral inlet 19 is provided for feeding white mineral into the white mineral drying drum 12. The white mineral drying drum 12 is operated in a counter-current process, wherein a white mineral conveying direction is directed parallel but counter to the heat conveying direction along the second rotational axis 16. At the front end 18, a material outlet 31 is provided for the heated white material.

In the region of the second burner 18, a flow guide unit 20 is arranged on the white mineral drying drum 12, the flow guide unit 20 comprising a swirl chamber 21 and a plate-fin recuperator 22.

By means of the swirl chamber 21, the flow of exhaust gases from the extraction hood 9 and of by-product exhaust gases from the by-product exhaust gas generators 15 can be fed to the white mineral drying drum 12 and introduced into the white mineral drying drum 12 at a position, which is eccentric in relation to the second rotational axis 16. The exhaust gases and by-product exhaust gases describe a helical flow path about the second rotational axis and, therefore, about the flame of the second burner 17. The plate-fin recuperator 22 serves to guide the exhaust gas flow inside the white mineral drying drum 12.

The plate-fin recuperator 22 has a length along the second rotational axis 16, which substantially corresponds to a length of the burner flame 26 of the second burner 17.

Along the second rotational axis 16, the plate-fin recuperator 22 has a widening portion 23, a cylinder portion 24 and a tapering portion 25. The widening portion 23 is connected directly to the swirl chamber 21. The tapering portion 25 is arranged such as to be remote from the swirl chamber 21. The cylinder portion 24 is arranged along the rotational axis 16 between the widening portion 23 and the tapering portion 25. The widening portion 23, the cylinder portion 24 and the tapering portion 25 are arranged concentrically in relation to the second rotational axis 16.

The widening portion 23, the cylinder portion 24 and the tapering portion 25 each have a plurality of, in particular eight, individual plate fins 32 which are arranged such as to overlap each other at least partly in the circumferential direction of the second rotational axis 16. As a result, a radial overlap region 33 is obtained between in each case two adjacent plate fins 32. Each overlap region 33 comprises an overlap opening 34, which has a surface normal oriented tangentially to a circular line about the rotational axis 3. Along the second rotational axis 16, the overlap region 33 extends in each case along the respective length of the widening portion 23, the cylinder portion 24 and the tapering portion 25. Seen in the circumferential direction 35 about the second rotational axis 16, the overlap region 33 extends over approximately 5% to 10% of a circumferential length 33 of an individual plate fin.

The overlap opening 34 is oriented such that in the operation of the white mineral drying drum 12, material, which has inadvertently entered the inside of the plate-fin recuperator 22, is discharged from the plate-fin recuperator 22 via the overlap opening 34 automatically, in particular due to gravity.

Each plate fin 32 is rigidly connected to the rotary kiln 2 via two mounts 36. The mounts 36 are designed substantially identically. The mounts 36 are spaced from each other along the second rotational axis 16. The mounts 36 ensure that each individual plate fin 32 is connected to the white mineral drying drum 12 in such a way as to be non-rotatable in relation to the second rotational axis 16. In particular, the plate fins 32 are not connected to each other directly. The plate fins 32 are mounted to the white mineral drying drum 12 only by means of the mounts 36. The mounts 36 are configured such that an arrangement of the plate fins 32 in relation to the white mineral drying drum 12 is variable. In particular, the mounts 36 serve to change the opening angle of the funnel. The mounts 36 are height-adjustable.

The individual plate fins 32 may have a curvature, which is not visible in the illustrations of Figs. 1 and 2. Along an outer circumferential line of the plate-fin recuperator 22, the plate fin 32 extends linearly such that the funnel of the plate-fin recuperator 22 has a conical, in particular a frustoconical, shape.

In the widening portion 23, the plate fins are arranged in a conically widening manner, in other words in the shape of a frustrum of a cone, in relation to the rotational axis 16. Along the rotational axis 16, the cross-sectional surface in the widening portion 23 is configured such as to widen conically. A widening angle at which the plate fins in the widening portion 23 are arranged such as to widen conically in relation to the second rotational axis 16 is approximately 15° in the exemplary embodiment shown. The widening angle may in particular amount to between 5° and 45°.

In the cylinder portion 24, the plate fins are arranged substantially parallel to the second rotational axis 16. The cross-sectional surface of the plate-fin recuperator 22 is substantially constant along the cylinder portion 24.

The plate fins of the plate-fin recuperator 22 are arranged in a concially tapering manner along the tapering portion 25. The cross-sectional surface of the plate-fin recuperator 22 tapers along the second rotational axis 16. A tapering angle at which the plate fins are inclined in relation to the second rotational axis is approximately -15° in the exemplary embodiment shown. The tapering angle may amount to between -5° and -45°, for example. In particular the widening angle and the tapering angle are substantially identical in terms of their absolute values.

The design, in particular the dimensioning of the widening portion 23, the cylinder portion 24 and the tapering portion 25 are substantially dependent on the geometry of the open burner flame 26 of the second burner 17. A key factor is that the exhaust gases supplied via the swirl chamber 21 are able to move around the burner flame 26 when following their helical flow path such that the exhaust gases are supplied to the burner flame 26, in particular to the tip of the burner flame, when exiting the plate-fin recuperator 22. A dedusting unit 27 comprising a chimney 28 is arranged downstream of the white mineral drying drum 12. Via the chimney 28, purified exhaust gases are released to the environment.

The mode of functioning of the installation 1 will be explained below. In the co-current drying drum 2, old asphalt material supplied via the material inlet 5 is heated and dried. In the extraction hood 9, particles, in particular dust, are separated and collected in the collecting vessel 10. Particle-containing gas from the co-current drying drum 2 enters the extraction hood 9 via the inlet opening. The flow cross-sectional surface of the extraction hood 9 is dimensioned such that a flow velocity of the inflowing gas is obtained, which is smaller than 2 m/s in the exemplary embodiment shown. Owing to the reduced flow velocity and in particular the fact that the gas flows from the inlet opening at least to the outlet opening, particles in the gas are separated from the gas flow automatically due to gravity and collected in the collecting vessel 10. The air discharged from the extraction hood 9 is pre-purified.

The flow guide element ensures an even more improved a particle separation. The flow guide element prevents an exhaust gas flow from the co-current drying drum 2 from entering the extraction hood 9 via the inlet opening in an unimpeded manner. The exhaust gas flowing in from a substantially horizontal direction must flow around the flow guide element, causing it to be accelerated at least partly in a downward direction towards the collecting vessel 10. Because of this downward acceleration, the exhaust gas flow velocity may amount to approximately 6 m/s in this region. The exhaust gas flow then changes its direction towards the outflow opening. The comparatively high acceleration in the region of the flow guide element and the deflection of the flow cause in particular heavy particles to be separated from the material flow. The exhaust gas flow then rises to the outflow opening at the reduced flow velocity of approximately 2 m/s.

By means of the extraction fan 13, exhaust gas from the extraction hood 9 is extracted, together with by-product exhaust gas from an exhaust gas generator 15, via the extraction line 11, and is then fed to the swirl chamber 21 of the flow guide unit 20. The swirl chamber 21 causes the exhaust gases and by-product exhaust gases to move around the burner flame 26 in a helical flow pattern. The centrifugal force of the helical flow of the exhaust gases causes pollutants to be thrown radially outwardly and away from the rotational axis 16 and the burner flame 26. This prevents the exhaust gases, and in particular the pollutants contained therein from being fed directly to the burner flame 26, which would cause the flame core to cool, thus resulting in an incomplete combustion. The plate-fins of the plate-fin recuperator 22 prevent the exhaust gases, and in particular the pollutants contained therein, from being inadvertently thrown outwardly, in other words radially in relation to the second rotational axis 16, too far. In particular, the plate fins of the plate-fin recuperator 22 prevent the exhaust gases with the pollutants to be heated from contacting the white mineral, which is heated in the white mineral drying drum 12.

After a widening of the helical flow of the exhaust gases and by-product exhaust gases in the widening portion 23, exhaust gases and by-product exhaust gases are guided around the burner flame 26 in the cylinder portion 24. Inside the cylinder portion 24, the exhaust gases, and in particular the pollutants contained therein, in particular hydrocarbons Cges, are heated by the radiant heat of the plate-fin recuperator. In the adjoining tapering portion 25, the exhaust gases and by-product exhaust gases are fed closer to the second rotational axis 16 and the burner flame 26 in a conically tapering manner. The exhaust gases and pollutants are heated even more. This causes the pollutants in the exhaust gas to evaporate so as to become ignitable. The pollutants can be fed to the tip of the burner flame where they are burnt substantially without producing harmful emissions. The purified exhaust gases from the white mineral drying drum 12 are fed to the dedusting unit 27 where they are filtered and released, via the chimney 28, to the environment.

The installation 1 according to the invention provides the necessary conditions for burning the entire amount of pollutants contained in the exhaust gas. The pollutant emissions are reduced. Another, particular advantage of the installation 1 is that a hot gas generator can be arranged directly in front of the white mineral drying drum 12.

Surprisingly, it was found that an already existing installation for producing asphalt can be converted into an installation according to the invention in a simple manner. For this purpose, substantially all that is necessary is to connect existing co-current drying drums to the swirl chamber 21 and the plate-fin recuperator 22 of the white mineral drying drum 12 via the exhaust gas line 11 and the extraction fan 13. A second exemplary embodiment of the invention will hereinafter be described with reference to Fig. 3. Identically designed parts carry the same reference numerals as in the first embodiment to the description of which reference is made. Differently designed parts having the same function carry the same reference numerals followed by an “a”.

An essential difference with respect to the first exemplary embodiment is that the plate-fin recuperator 22a of the white mineral drying drum 12a has a plurality of tapering portions 25 arranged in succession along the second rotational axis 16. The tapering portions 25 are designed substantially identically, wherein the smaller outlet opening of the tapering portion 25 shown on the left-hand side of Fig. 3 leads, in particular protrudes, into the larger inlet opening of the tapering portion 25 shown on the right-hand side of Fig. 3. As a result, an axial overlap region 40 is obtained, which is directed in the axial direction of the second rotational axis 16, said axial overlap region 40 having an annular front face via which material can exit the plate-fin recuperator 22a in a direction, which is substantially parallel to the second rotational axis 16. This ensures that a sufficient amount of rock material, in particular old asphalt material, can be discharged from the plate-fin recuperator 22a.

It is also conceivable to arrange only one tapering portion 25 or more than two tapering portions 25 along the second rotational axis 16.

In the region of the burner flame 26, a fire tube 41 is arranged. Said fire tube 41 is configured as a cylinder tube, which is arranged in a front flame region of the second burner 17. The fire tube 41 is made of a high-temperature resistant material, in particular of a heat-resistant metal material, in particular of a heat resistant stainless steel alloy, which is available under the trade name Sicromal. These are high-alloy chromium steels with the material numbers 1.4713, 1.4724 1.4742, 1.4749, 1.4762, 1.4878, 1.4828, 1.4821, 1.4841 or 1.4864, for example.

The fire tube 41 protects the burner flame 26 from an undesirable cooling. The surface of the fire tube 41 is heated by the burner flame 26 such that recuperator air, which is fed, via the swirl chamber 21, to the front end of the white mineral drying drum 12a, is heated. This causes pollutants in the recuperator air to evaporate and become ignitable. The fire tube 41 is mounted to a retaining tube 43 via a retaining device comprising a plurality of retaining members 42. The retaining tube 43 and the fire tube 41 are arranged in particular concentrically to the rotational axis 16. The retaining tube 43 has a larger diameter than the fire tube 41. The retaining members 42 are in particular arranged along the rotational axis 16 in such a way as to be spaced from each other. The retaining members 42 are in particular arranged parallel to each other. The retaining members 42 are configured as annular disks, for example. The retaining members 42 may also be configured as radial webs and/or circular-segment shaped disks, which are spaced from each other along the circumferential direction about the rotational axis 16 but are arranged in a plane, which is perpendicular to a rotational axis 16.

The recuperator air flows, via the swirl chamber 21, into an annular conduit 44, which, in a radial direction relative to the rotational axis 16, is bounded on an inner side by the outer surface of the fire tube 41, and on an outer side by the inner surface of the retaining tube 43.

Along the second rotational axis 16, a heat/protection element 45 configured as an impact wall is arranged at an end of the plate-fin recuperator 22a opposite the second burner 17. The impact wall is mounted to an inner side of the white mineral drying drum 12a by means of fasteners not shown. The impact wall 45 is configured as a disk member or plate member and is arranged perpendicular to the second rotational axis 16 in the white mineral drying drum 12a. Recuperator air exiting the plate-fin recuperator 22a via the outlet opening 46 impinges the impact wall 45. This prevents flames of the burner flame 26 from propagating into the lifter plate area 47 arranged behind the impact wall 45. In the region of the discharge opening 46, the flow direction of the recuperator air is deflected and/or decelerated. In particular, the original flow direction, which is oriented substantially parallel to the second rotational axis 16, is deflected by up to 90° in a direction perpendicular to the second rotational axis 16. This causes an accumulation pressure to develop, which acts on the recuperator air in such a way that the combustion of remaining pollutants in the recuperator air is improved.

The impact wall 45 further ensures an improved heat distribution in the white mineral drying drum 12a. In particular, the heat of the burner flame 26 is distributed to the recuperator air in a more homogeneous manner and over a larger surface area thereof. Heating the white mineral drying drum 12 is more efficient and uniform. The heating of the material is thus improved.

Claims

An asphalt preparation plant, comprising a. A white mineral dryer (12; 12a) for heating white mineral, b. A flow guide unit (20) in the white mineral dryer (12; 12a), of flue gas to the white mineral drying drum (12; 12a), characterized in that the flow guide unit (20) has a slat lamellar recuperator (22; 22a) having an outer casing for the helical flow movement of the flue gases and / or by-product tubes. for the purpose of combustion of pollutants in flue gas and / or by-product flue gas.

Installation according to claim 1, characterized by a direct-current dryer (2) for heating old asphalt material and a direct-current dryer (2) connected to a flue gas extraction device and the white mineral dryer (12; 12a) is connected to the suction device.

System according to claim 2, characterized in that the suction device comprises a suction cap (9) directly connected to the DC dryer (2) and / or that the suction device is a suction fan (13).

Installation according to claim 2 or 3, characterized in that the suction device has a by-product flue gas line (14) which is connected to the white mineral drying drum (12; 12a) for supplying the by-product flue gas.

Installation according to one of the preceding claims, characterized in that the white mineral dryer (12; 12a) has a burner.

System according to one of the preceding claims, characterized in that the flow guide unit (20) has a swirl chamber (21) for swirling supply of the flue gas and / or by-product flue gas in the white mineral drying drum (12; 12a).

Installation according to one of the preceding claims, characterized in that the slat recuperator (22; 22a) has a narrowing section (25) and, in particular, along a longitudinal axis (17) in the white mineral drying drum (12) between an expansion section ( 23) and a narrowing section (25) is provided with a cylindrical section (24).

Installation according to claim 7, characterized in that the slat recuperator (22a) has several narrowing sections (25) arranged one behind the other along the longitudinal axis (17).

Installation according to one of the preceding claims, characterized in that the flow guide unit (20) has a flame pipe for wrapping a burner flame (26).

Installation according to one of the preceding claims, characterized by a heat / protection means which, as seen from the longitudinal axis (17) of the white metal dryer (12), is arranged behind the flow guide unit (20).

System according to one of the preceding claims, characterized by a device (27) for removing dust and which is arranged particularly downstream of the white mineral dryer (12; 12a).

12. A process for making asphalt, comprising the steps of - heating old asphalt material by a DC method by means of a DC dryer (2), - extracting flue gas from the DC dryer (2) by means of a suction device - heating the white mineral by means of a white mineral dryer (12; 12a); - first passing the flue gas into the white mineral dryer (12; 12a) by means of a flow guide unit (20); particulate matter in flue gas and / or by-product flue gas by means of a slat-like lamellar recuperator (22; 22a) which forms an outer casing for the helical flow movement of the flue gases and / or by-product gases in the white mineral drying chamber (12); ).

Process according to claim 12, characterized in that the by-product flue gases are fed into the white mineral drying drum (12; 12a) by means of a by-product flue gas pipe (14).