Device and method for drying material and asphalt mixing plant with such a device

Abstract

Device for drying material for an asphalt mixing plant, the device (2, 3) comprising a rotary kiln (9) which can be driven to rotate about a rotational axis (19) and in which the material is dried, the rotary kiln (9) having a material inlet (10) and a material outlet (11), b. a heating unit coupled to the rotary kiln (9) for supplying heat to the rotary kiln (9), the heating unit being designed with a burner (12) having i. a burner housing (27) having a longitudinal axis (26), ii. an air line (16) arranged on the burner housing (27) for supplying air, wherein the air line (16) is arranged axially to the longitudinal axis (26) on the burner housing (27), iii. an air blower (29) arranged in the air line (16, 28), iv. a burner head (41) arranged on the burner housing (27) for generating a burner flame (13), v. a hydrogen gas line (14) connected to the burner (12) for supplying hydrogen gas into the burner (12), wherein a hydrogen gas nozzle (31) for discharging the hydrogen gas is connected to the hydrogen gas line (14), characterized in that c. the burner (12) is designed to be operated either exclusively by means of hydrogen gas or by means of hydrogen gas and secondary fuel, d. the burner (12) has a swirling element (35) for swirling the air in the burner (12) relative to the longitudinal axis (26), e. the swirling element (35) comprises a flow guide element in the burner housing (27), wherein the flow guide element is arranged immovably in the burner housing (27), f. the flow guide element is arranged concentrically to the longitudinal axis (26) and is designed as a baffle plate having a plurality of blades (53, 54) arranged in a circle with respect to the longitudinal axis (26) and oriented at an inclination, g. the heating unit comprises a hot gas generator (24) connected to the burner (12) which is connected to the rotary kiln (9) by means of a hot gas line (25).

Description

The invention relates to an apparatus and a method for drying material and to an asphalt mixing plant having such an apparatus.DE 10 2010 001 055 A1 discloses a system for heat recovery in a rotary kiln. EP 3 196 177 A1 discloses the use of hydrogen as fuel in cement production. DE 10 2018 108 802 B3 discloses a plant for the optional production of cement clinker for grey or white cement. DE 10 2013 224 910 A1 discloses an apparatus and a method for heating used asphalt granulate for producing asphalt. DE 195 30 164 A1 discloses a drying drum for processing asphalt granules. EP 1 785 202 A1 discloses an apparatus and a method for purifying contaminated materials. JP 2009-293 859 A discloses the warm air drying of inorganic powder and granulate material. DE 20 2010 002 774 U1 discloses a burner.In an asphalt mixing plant, various materials are processed, in particular dried and mixed with one another. During the drying of the material for asphalt mixing installations, a large part of the energy input takes place, which is necessary for the following mixing process of the asphalt. The material is thus also heated during drying. The temperature level is usually up to 450° C. depending on the type of asphalt to be mixed and the respective RC addition rate. Heat is supplied to the rotary kiln, which has been previously generated by means of a separate heating unit. Heat generation is usually based on the combustion of fossil energy carriers, such as natural gas, liquid petroleum gas, fuel oil and / or coal dust. Carbon dioxide is produced during the combustion of fossil energy carriers, which is problematic from the standpoint of climate control.It is the object of the present invention to make the drying of material for an asphalt mixing plant environmentally advantageous and in particular climate-friendly.This object is achieved according to the invention by an apparatus having the features specified in claim 1, by an asphalt mixing plant having the features specified in claim 5 and by a method having the features specified in claim 6.According to the invention, it has been recognized that material can be dried in an environmentally advantageous manner if heat, which is used in a rotary kiln for drying the material, is generated by means of a hydrogen gas burner. The hydrogen gas burner is a burner in which hydrogen gas is burned for heat generation. The device can also comprise a plurality of burners, which are in particular of identical design. The burners can also be designed differently, wherein at least one burner, in particular a plurality of burners and in particular all burners are designed as hydrogen gas burners. Hydrogen gas thus serves as fuel. According to the invention, the heat is generated at least partially and in particular exclusively by the combustion of hydrogen gas. The combustion of hydrogen gas is free of carbon dioxide, i.e. no carbon dioxide is generated. The combustion of hydrogen gas is climate-friendly. Exhaust gases and emissions are reduced. It is particularly advantageous if the hydrogen gas has been generated from regenerative energies, i.e. it is so-called green hydrogen.In the rotary kiln, in particular materials which can be used for an asphalt mixture are dried, such as used asphalt material, which is also referred to as recycling material or as RC material, and / or mineral rock, in particular white mineral. The rotary kiln is designed to be rotationally drivable about an axis of rotation and has in particular a cylindrical shape. The rotary kiln has a material inlet at which the material to be dried is fed to the rotary kiln and a material outlet at which the dried material is discharged from the rotary kiln. The material inlet and the material outlet are arranged spaced apart from one another with respect to the axis of rotation. In particular, the material inlet and the material outlet are each arranged in the region of the end faces of the rotary kiln and are in particular embodied opposite the end face of the rotary kiln.The material inlet can comprise a material chute, a conveyor belt, an insertion belt or other conveying techniques.The material outlet can have a material chute and / or a round elevator or other conveying techniques.In order to promote the transport of material in the rotary kiln, the rotary kiln is arranged with its axis of rotation inclined with respect to a horizontal direction, in particular towards the material outlet. The angle of inclination is in particular at most 8°, in particular at most 5°, in particular at most 4°, in particular at most 3° and in particular at least 1°. The residence time of the material within the rotary kiln is in particular at least one minute and in particular at most 10 minutes.The burner with which the hydrogen gas is burned for heat generation is part of a heating unit which is coupled to the rotary kiln for heat transmission. Coupled means within the meaning of the invention that the burner and rotary kiln are coupled in terms of process technology. A burner flame generated by the burner can burn directly in the rotary kiln. In this example of application, the burner and rotary kiln are also physically coupled. The burner is arranged directly on the rotary kiln.The burner flame can, however, also burn in a hot gas generator which conducts the heat via an air stream to the rotary kiln. The heat generated with the burner is supplied from the heating unit into the rotary kiln. Supplying heat to the rotary kiln includes generating the heat by the burner flame directly in the rotary kiln.The burner has a burner housing having a longitudinal axis and having an air line. Air line describes the supply of combustion air in the sense of this invention. In particular, this can be effected by a fan arranged in the burner housing, a fan connected via an air duct or another supply of air. In particular, a flange is arranged on the burner housing, in particular on the end face, with which flange a sound damper can be connected to the burner housing. By means of the air line, air, in particular ambient air, is supplied into the burner housing. In particular, the air line is connected to the burner housing axially with respect to the longitudinal axis. The supply of air into the burner housing is thereby simplified.A hydrogen gas line is connected to the burner, in particular to the burner housing, in order to supply hydrogen gas to the burner. A hydrogen gas nozzle is connected to the hydrogen gas line to selectively discharge the hydrogen gas in the burner housing. In the context of this invention, a hydrogen gas nozzle can be designed as an annular nozzle, annular gap, gas lance, needle nozzle or as an outlet in any other form. This promotes the generation of an air-hydrogen gas mixture and / or the generation of a burner flame. The hydrogen gas nozzle is arranged in particular inside the burner housing and is designed in particular as an annular nozzle with radial openings. It is also possible for a plurality of hydrogen gas nozzles to be present, which are designed identically or differently from one another. The hydrogen gas nozzles can be arranged at different positions with respect to the longitudinal axis, in particular in the radial, tangential and / or axial direction with respect to one another.The burner additionally has a swirling element which serves for swirling the combustion air, for mixing fuel and combustion air, as a flame holder, as a holder for fuel nozzles, for ignition burners or other burner components and / or for similar purposes. In particular, in the variant described, a swirling element is introduced in order to swirl the air in the burner housing relative to the longitudinal axis, in particular tangentially, radially and / or axially. The mixing of the air with the hydrogen gas is thereby improved, in particular the homogeneity of the air-hydrogen gas mixture. In particular, the hydrogen gas nozzle is arranged adjacent to the swirl element and opens in particular directly upstream of the swirl element. The swirling element serves to define the shape of the burner flame produced with the burner. In particular, the flame, in particular if it is arranged inside the rotary kiln, should not exceed a maximum length along the axis of rotation of the rotary kiln in order to prevent direct contact of the flame with the material in the rotary kiln. In addition, the maximum diameter of the flame should not exceed an upper limit value, i.e. the flame must not become too wide to subject the rotary kiln to too high a thermal stress. The drying drum is protected.The burner housing has a burner head which serves for generating the burner flame. The burner head is to be understood in the sense of this invention as an opening arranged on the end face of the burner housing, at which opening the flame forms. The burner head can be designed to be conically widening, in particular, at least in sections along the longitudinal axis.In particular, a hydrogen reservoir can be provided in which hydrogen, in particular hydrogen gas, is stored. The hydrogen reservoir is connected to the burner housing in particular by means of the hydrogen gas line. Along the hydrogen gas line, a gas safety and / or gas control section is provided in particular in order to ensure a reliable and safe supply of the hydrogen gas from the hydrogen reservoir into the burner housing. The gas safety and / or gas control section comprises, in particular along the gas flow direction, a shut-off cock, a gas filter, a gas pressure regulator, in particular with impulse lines, a pressure relief valve, in particular at least one pressure switch, in particular at least one safety shut-off valve, in particular further pressure switches, a gas control flap and / or an additional shut-off flap, and in particular at least one manometer. The hydrogen reservoir and / or the hydrogen gas line and in particular the hydrogen gas nozzle are in particular each produced from a material which is suitable for, and in particular permitted for, the storage, delivery and / or discharge of hydrogen gas. The components of the gas control section are in particular permitted for use with hydrogen.A swirling element with a flow guiding element ensures efficient air swirling. The flow guide element is arranged in the burner housing concentrically to the longitudinal axis. The flow guide element is arranged in the burner housing in a stationary, i.e. immovable manner. In particular, the flow guiding element does not have any movable parts. The flow guide element is low-maintenance and in particular maintenance-free. The flow guiding element is robust and reliable.In addition to the stationary flow guiding element, it is possible to feed the air line tangentially and / or radially with respect to the longitudinal axis of the burner housing, i.e. to connect the air line tangentially and / or radially to the burner housing. In this case, the swirling element is therefore formed by a tangential air feed.The axial arrangement of the air, by arranging the air line on the burner housing axially to the longitudinal axis, wherein an air blower is arranged in the air line, enables a simple and robust construction. The fan for generating the air flow in the air line can be designed in particular as an axial fan and can be arranged integrated in the air line. It is also possible to design the blower as a radial blower. In particular, a silencer is connected to the air line. The blower can also be arranged outside the burner housing, in particular upstream of the air line.A heating unit with a hot gas generator connected to the burner enables indirect heating of the rotary kiln and thus indirect drying of the material in the rotary kiln. The hot gas generator is connected to the rotary kiln by means of a hot gas line. The hydrogen burner serves for process heat generation in the hot gas generator.A baffle plate allows advantageous swirling of the air and advantageous generation of the air-hydrogen gas mixture. A plurality of blades which are arranged in a circular manner with respect to the longitudinal axis and are oriented at an inclination enable a specific deflection of the axial air flow radially and / or tangentially outwards in the direction of the inner wall of the burner housing. Specifically, the baffle plate includes a portion where the hydrogen gas nozzle opens and another region to which the air is supplied. In particular, the region for supplying the hydrogen gas is of annular design and oriented concentrically with respect to the longitudinal axis. The region for the supply of air to the diaphragm is arranged in particular centrally, that is to say centrally. In particular, the two regions of the hydrogen gas and air supply at the baffle plate are embodied separately from one another. At least one further region for the supply of a secondary fuel can additionally be provided on the baffle plate. This at least one additional region can be embodied separately from the other regions or connected thereto. This additional region can be arranged centrally or eccentrically on the diaphragm disk.The swirl element in the form of the baffle plate makes it easier to adjust the shape of the burner flame independently of the fuel used, in particular independently of whether the secondary fuel is used in addition to the hydrogen gas. It is possible in particular to adjust the shape of the burner flame as a function of the fuel used, in particular the fuels used, in such a way that the burner flame is suitable for drying the material in the rotary kiln, i.e. provides sufficient heat, and damage to the rotary kiln and / or the material to be heated is moreover ruled out. The shape of the burner flame is influenced in particular by the number, design and arrangement of the nozzles for the supply of the hydrogen gas and the at least one secondary fuel. The flame shape also depends in particular on the air curve.The arrangement and / or the size of the various regions of the baffle plate depends substantially on the fuels to be burned. It is additionally or alternatively possible to change the geometry of the blades, to change the arrangement of the blades in the baffle plate and / or to provide additional guide elements, such as cones and / or baffles.A cooling cone according to claim 2 enables air classification within the burner housing. During air classification, a plurality of combustion zones are created around the burner flame, which have different oxygen concentrations and increase in particular from the inside to the outside, i.e. in the radial direction. This increases the combustion range and thus also the residence time of the components in the burner flame. By means of the air classification, the formation of thermal nitrogen oxides (NO x) can be reduced and, in particular, complete combustion of the fuel, in particular of hydrogen gas, can be achieved. The cooling cone has an expanding cone section. The cooling cone is arranged in the burner housing at the transition to the burner head. Between the outer side of the cooling cone and the inner side of the burner housing, an annular gap is formed, in particular with a gap width that remains constant along the longitudinal axis. In addition, the cooling cone ensures an air flow through the said annular gap, as a result of which the axially flowing air is kept away from the burner flame, that is to say is guided around the burner flame and fed to the flame in the region of the burner head. This secondary air, which has been guided around the burner flame, cools the burner head, in particular in the region of the cooling cone. In particular, the flame temperature can thereby also be reduced in order to reduce the formation of nitrogen oxide.Additionally or alternatively, air gradation can also be ensured by means of an additional air connection, for example a secondary air connection. Secondary air may also be ambient air. In particular, a secondary air line can be a return line for returning emission-loaded air from the rotary kiln and for reburning and coburning.Additionally or alternatively, measures for reducing nitrogen oxide are possible, in particular local combustion at different air coefficients (λ), which defines the mass ratio of air and fuel in the combustion chamber. In particular, burns at λ>>1 or at λ<<1 are possible. Additionally or alternatively, it is conceivable to supply urea in a targeted manner in order to reduce the formation of nitrogen oxide. It is advantageous if the flame temperature is less than 1400° C., in particular less than 1350° C., in particular less than 1300° C., in particular less than 1250° C. and in particular less than 1200° C. It has been found that the formation of thermal NO x is reduced if the flame temperature does not exceed a predefined maximum value.A secondary fuel line according to claim 3 increases the variability of the burner usage. A plurality of secondary fuel lines can also be connected to the burner in order to supply in particular different types of secondary fuels. Natural gas, liquefied gas, fuel oil, wood dust, coal dust and / or synthetic fuels can be used as the secondary fuel for the purpose of example. Such synthetic fuels are typically produced from biomass by thermochemical conversion and are referred to as Biomass to Liquid (BtL). The secondary fuels can be supplied to the burner in particular in addition to the hydrogen gas, in particular if the hydrogen gas supply is restricted and / or interrupted. It is also conceivable in principle to control the secondary fuel supply in such a way that the burner is operated exclusively with secondary fuel, i.e. without hydrogen. However, it is essential that at least the hydrogen gas line and the hydrogen gas nozzle are provided.A secondary fuel nozzle is connected to the secondary fuel line for discharging the secondary fuel. A plurality of secondary fuel nozzles may also be connected to the secondary fuel line. The secondary fuel nozzle is disposed within the burner housing. The secondary fuel nozzle opens in particular at the baffle plate, in particular centrally.An exhaust gas line according to claim 4 enables the co-burning of exhaust gases, in particular in the burner. For the purposes of this invention, both exhaust gases from combustion processes and, in particular, exhaust gases from asphalt production, in particular by extraction in the mixing process and further handling of the asphalt, are referred to. These exhaust gases are supplied to the burner in particular as emission-loaded air. As a result, emissions can be additionally reduced, in particular odour emissions, carbon monoxide (CO), carbon dioxide (CO 2) and in particular hydrocarbons (C ges) overall. The exhaust gas line can additionally or alternatively supply exhaust gases to the heating unit as a whole and / or into the rotary kiln.An asphalt blending plant according to claim 5 and a method according to claim 7 substantially have the advantages of the apparatus according to claim 1, to which reference is hereby made. The asphalt mixing plant has a filter dust removal and / or a condensate separator. In the filter dust extraction, dust particles from the exhaust gas are filtered out of the rotary kiln.In the condenser separator, water contained in the exhaust gas stream can condense. This releases additional energy in the form of heat. This use of the calorific value in the condensate separation makes it possible in particular for undesired constituents, in particular acids, to be separated out of the exhaust gas. The exhaust gas is additionally purified by the condensate separator. The condensate separator is arranged in particular downstream of the filter dust extraction.The asphalt mixing plant in particular also has a blower and / or a chimney which are arranged downstream of the filter dust extraction and / or the condensate separator.The asphalt mixing plant may additionally comprise at least one mixing unit in which various materials required for an asphalt mixture are mixed with one another. These materials can originate, for example, from the rotary kiln. It is also conceivable for materials to be fed directly, in particular by means of a metering device, into a mixing unit.A method according to claim 7 enables a particularly efficient co-combustion of exhaust gases, so that the overall emissions are reduced.A method according to claim 8 enables the heat to be supplied directly to the rotary kiln. The burner flame is located, at least partially and in particular completely, within the rotary kiln, i.e. in a dust-laden environment.A method according to claim 9 or 10 ensures that the burner flame is reliably arranged within the burn-out zone of the rotary kiln and, in particular, fire protection installations of the rotary kiln are arranged, in particular radially spaced apart from the burner flame. Direct contact of the burner flame with the fire protection installations is prevented.Both features specified in the patent claims and features specified in the subsequent embodiment of the methods according to the invention are each suitable, per se, all or in combination with one another, for further developing the subject matter according to the invention. The respective combinations of features do not represent any restriction with respect to the developments of the subject matter of the invention, but essentially merely have an exemplary character.Additional features, advantageous embodiments and details of the invention are evident from the following description of an exemplary embodiment with reference to the drawing. The following are shown: FIG. 1 shows a schematic diagram of an asphalt mixing plant with an apparatus according to the invention, FIG. 2 is a schematic sectional view of a rotary kiln with burner according to FIG. 1, FIG. 3 is an enlarged sectional view along the section line III-III in FIG. 2, FIG. 4 is an enlarged sectional view along the section line IV--IV in FIG. 2, FIG. 5 shows an enlarged detail view of the detail V in FIG. 2, FIG. 6 shows a perspective view of the diaphragm in FIG. 5, and FIG. 7 shows a rear view of the diaphragm according to FIG. 5.An asphalt mixing plant shown as a whole as 1 in FIG. 1 is used for producing asphalt. The asphalt mixing plant 1 comprises a first device 2 and a second device 3, which are each connected to a filter dust extraction 5 by an emission line 4.The asphalt mixing plant 1 can also have only one device 2, 3 or more than two devices 2, 3. It is conceivable that the one or more devices 2, 3 are connected to the filter dust extraction 5 via a common emission line 4. In particular, the filter dust extraction 5 is a central filter dust extraction in the asphalt mixing installation, to which several and in particular all devices 2, 3 of the asphalt mixing installation 1 are connected. It is also conceivable that each device 2, 3 is respectively assigned to a separate filter dust extraction 5 and connected thereto.A condensate separator 6 is optionally connected to the filter dust extraction 5, which is connected to a chimney 8 via a blower 7. As shown in FIG. 1, the condensate separator 6 can be arranged behind the filter dust extraction 5 and additionally or alternatively also in front of the filter dust extraction 5. In particular, in addition to the condensate separator, a recuperation unit is present, which serves for recovering process heat, in particular process heat which arises in the condensate separator 6. It has been found that the condensate separator 6 can be used advantageously in the asphalt mixing plant 1 if the exhaust air of the devices 2, 3 is comparatively clean, i.e. has a reduced emission load and is in particular less emission loaded than the exhaust air of a burner which burns fossil fuels. It is also possible that the asphalt mixing plant 1 does not have a filter dust removal 5. In this case, the devices 2, 3 are connected directly to the condensate separator 6. It is also conceivable for a plurality of condensate separators 6, in particular one condensate separator 6 each, to be provided per device 2, 3.The first apparatus 2 comprises a rotary kiln 9 in which material is dried. The rotary kiln 9 has a material inlet 10 and a material outlet 11. According to the exemplary embodiment shown, the material inlet 10 and the material outlet 11 are each arranged on the end face, i.e. opposite, on the rotary kiln 9.To the rotary kiln 9 is coupled a heating unit having a burner 12. The burner 12 is designed to combust hydrogen gas and to generate a burner flame 13 which is arranged at least in regions in the rotary kiln 9. The burner 12 is a hydrogen burner. A hydrogen gas line 14 is connected to the burner 12, which is connected in particular to a hydrogen reservoir 15. The hydrogen reservoir 15 is in particular a storage container, in particular a storage tank, in which hydrogen, in particular gaseous, is stored. The hydrogen reservoir 15 can also be formed by a connection to a hydrogen supply network. The connection to the gas control system in the hydrogen gas line 14 is effected at a hydrogen gas distribution chamber 30 by means of a compensator 62. The compensator 62 serves to compensate movements of the hydrogen line 14, in particular as a result of thermal changes in length, vibrations, wall feedthroughs and / or in the event of settling phenomena. The compensator 62 is disposed at a flange joint 63 between the hydrogen distribution chamber 30 and the hydrogen gas line 14.An air line 16 is connected to the burner 12 in order to supply air, in particular ambient air.A material conveying direction 22 through the rotary kiln 9 is directed from the material inlet 10 to the material outlet 11 and oriented from right to left according to FIG. 1. A gas conveying direction 23 through the rotary kiln 9 is directed from the burner 12 to the emission line 4, i.e. from left to right according to FIG. 1. The material conveying direction 22 and the gas conveying direction 23 are oriented opposite to each other. The rotary kiln 9 is operated in a countercurrent process. The rotary kiln 9 can also be operated in the co-current process.Further, a first secondary fuel line 17 is connected to the burner for supplying a first secondary fuel. The secondary fuel used is, in particular, fossil energy carriers, such as, for example, natural gas, liquefied gas, fuel oil, coal, in particular pulverized coal, synthetic fuels (BtL) and / or pulverized wood. Natural gas is used as the first secondary fuel in the exemplary embodiment shown. The first secondary fuel line 17 is fed from a secondary fuel reservoir, not shown. The secondary fuel reservoir can be designed-similar to the hydrogen reservoir 15-as a storage container and / or as a supply network.The connection to the first secondary fuel line 17 and the gas control section there takes place at a secondary fuel distribution chamber 32 by means of a compensator 66. the compensator 66 is substantially identical to the compensator 62 and is arranged at a corresponding location between the first secondary fuel line 17 and the secondary fuel distribution chamber 32.It is understood that when using another first secondary fuel, for example a liquid secondary fuel such as liquefied gas and / or oil, the burner can have a different geometry, wherein this applies in particular to the burner head, the baffle plate, the combustion chamber, the arrangement, number and attachment of the nozzles used and the periphery such as, for example, an oil control section and / or a liquefied gas control section.The first device 2 further comprises an exhaust gas line 18 which is connected to the heating unit, in particular the burner 12, and / or to the rotary kiln 9. Exhaust gases and / or emissions can be supplied to the heating unit and / or the rotary kiln 9 by means of the exhaust gas line 18. The exhaust gas line 18 basically serves as a supply line for secondary air, wherein this can be in particular exhaust air from other emission sources, such as in particular a suction of a bucketway and / or a cargo. The secondary air is in particular emission-laden air. The exhaust line 18 may be connected, for example, to the emission line 4 of the first device 2 and / or to the emission line 4 of the second device 3 in order to recirculate exhaust gases. Additionally or alternatively, other exhaust gas sources of the asphalt mixing plant 1 may be connected to the exhaust gas line 18. A separate fan 48 is arranged in the exhaust gas line 18, which fan can supply additional combustion air. One or more flaps 49 can be arranged along the exhaust line 18 in order to control the air flow in a targeted manner and in particular to set the added air quantities in a targeted manner. Additionally or alternatively, an air flow rate control can also be effected with the fan 48 and in particular by means of a frequency converter closed thereon.According to the exemplary embodiment shown, the exhaust gas line 18 is of branched design, a first branch opening directly into the rotary kiln 9, in particular adjacent to the burner head 41. Another part of the exhaust line 18 opens directly into the burner housing 27, in particular in the region of an annular gap 50 and / or in the region of the burner head 41.The rotary kiln 9 is designed to be rotationally drivable about an axis of rotation 19. The drives required for this purpose, in particular rotary drives, are known per se and are not shown in the figures for reasons of clarity. Along the axis of rotation 19, the rotary kiln 9 has a burn-out zone 20 which extends along the axis of rotation 19 in the region of the burner flame 13.The rotary kiln 9 further comprises a heat transfer region 21 in which heat is transferred to the material by convection.The second device 3 is substantially identical to the first device 2, to which reference is hereby made. One difference is that the heating unit of the second device 3 comprises a hot gas generator 24 in addition to the burner 12. The hot gas generator 24 is connected to the rotary kiln 9 by means of a hot gas line 25. The hot gas generator 24 is arranged between the burner 12 and the rotary kiln 9. In the second apparatus 3, the burner 12 is constructed separately from the rotary kiln 9. In particular, the burner 12 is arranged completely outside the rotary kiln 9. Accordingly, the burner flame 13 is arranged in the hot gas generator 24. No burner flame is arranged in the rotary kiln 9 of the second apparatus 3. In the second device 3, air circulation fans and / or air exhaust fans, not shown in detail, can be used for guiding air, in particular in the rotary kiln 9 and / or in the hot gas generator 24. The fans are arranged in particular outside the rotary kiln 9 and / or outside the hot gas generator 24, in particular along connecting lines. Accordingly, a burning zone 20 in this rotary kiln 9 is not required. The rotary kiln 9 of the second apparatus 3 substantially exclusively comprises a heat transfer region 21.In the exemplary embodiment shown, each device 2, 3 has its own, separate hydrogen reservoir 15. It is also conceivable that a common, centrally arranged hydrogen reservoir 15 is available in an asphalt mixing plant 1, which reservoir is in fluid communication with several and at least with all burners 12 of the asphalt mixing plant 1.In the following, the structure and function of the first device 2, in particular of the burner 12, are explained in more detail with reference to FIG. 2.The burner 12 has a burner housing 27 having a longitudinal axis 26. The burner housing 27 has, at an end facing away from the rotary kiln 9, a suction chamber 28, via which air, in particular ambient air, is sucked into the burner housing 27. For this purpose, the air line 16 and / or a silencer can be connected to the suction chamber 28. Along the burner housing 27 there is arranged an air blower 29, which according to the exemplary embodiment shown is designed as an axial blower. It is understood that the air blower 29 can also be designed in the manner of another type of blower, in particular as a radial blower.The burner 12 has, in particular, a flame sensor 64, which serves for monitoring the burner flame 13. In particular, a plurality of flame sensors 64 can be embodied on the burner 12 and in particular arranged in the burner housing 27, in particular along the longitudinal axis 26, at a distance from one another. In the burner housing 27 there is also provided an ignition burner 65, which serves for igniting the burner flame 13.The hydrogen line 14 is connected to the burner housing 27 via a hydrogen gas distribution chamber 30 arranged annularly around the burner housing 27. At least one hydrogen gas nozzle 31 is connected to the hydrogen gas distribution chamber 30 to selectively supply the hydrogen gas into the burner housing 27. It is conceivable that no hydrogen gas distribution chamber 30 is provided. In this case, the hydrogen pipe 14 is directly connected to the hydrogen nozzle 31.The hydrogen gas nozzle 31 is designed in particular as an annular nozzle. It is also conceivable for the hydrogen gas nozzle 31 to have a geometry differing therefrom and in particular to be designed as a gas lance. It is also conceivable for a plurality of, in particular differently designed, hydrogen gas nozzles 31 to be provided, which are arranged in the burner housing 27 at different positions, in particular along the longitudinal axis 26 and / or at different positions in the circumferential direction and / or at different radial distances with respect to the longitudinal axis 26.Connected to the first secondary fuel line 17 is a secondary fuel distribution chamber 32, the function of which corresponds to the hydrogen gas distribution chamber 30, to which reference is hereby made. According to the embodiment shown, a plurality of secondary fuel nozzles 33 are arranged in the burner housing 27 and connected to the secondary fuel distribution chamber 32. The secondary fuel nozzles 33 are each designed as gas lances and are arranged adjacent to the hydrogen nozzle 31 in the burner housing 27. The first secondary fuel nozzles 33 are arranged in the burner housing at a distance in the radial direction with respect to the longitudinal axis 26.As shown in FIG. 2, a second secondary fuel nozzle 34 is arranged in the burner housing 27, which serves for supplying liquid fuels. The second secondary fuel nozzle 34 is arranged in particular centrally, i.e. centrally with respect to the longitudinal axis 26, in the burner housing 27. A second secondary fuel line is connected to the second secondary fuel nozzle 34, which is not shown in FIG. 2 for the sake of illustration. The second secondary fuel nozzle 34 serves in particular for the supply of oil, in particular light oil and / or heavy oil. The second secondary fuel nozzle 34 is designed, for example, as a compressed air or return nozzle. The second secondary fuel nozzle 34 can also be designed as an annular nozzle with a plurality of liquefied gas nozzles.The burner 12 is a combination burner, in particular a three-component burner, which can combust hydrogen gas, a first, in particular gaseous, secondary fuel, in particular natural gas, and a second, in particular liquid, secondary fuel, in particular light oil. In this case, the supply of the various fuels to the burner 12 can be effected independently by means of its suitable control, in particular in such a way that either only one of the three fuels, in particular hydrogen, two of the three fuels or all three fuels are supplied together to the burner 12 and are burned there.In the region of the nozzles 31, 33 and 34, a swirling element 35 is arranged in the burner housing 27. The swirling element 35 serves for tangentially swirling the air. The swirling element 35 is designed in particular as a baffle plate, which has in particular a guide wheel. Depending on the fuel combination used, the baffle plate 35 can be designed differently in diameter, shape and structural details.In the exemplary embodiment shown, the nozzles 31, 33, 34 are each arranged upstream of the swirling element 35. It is possible that individual nozzles 31, 33, 34, several of the nozzles or all of the nozzles are arranged downstream of the swirling element 35 in the burner housing 27. The geometry of the burner flame 13 also depends on the number and / or the position of the nozzles 31, 33 and 34.By using the different nozzles 31, 33 and 34, a separate addition of the different fuels is possible. In particular, a time-controlled addition of the different fuels and in particular a locally separate addition of the fuels is possible. The regulation of the addition quantity and / or the addition time is effected by a burner control, not shown in detail. The burner control can be carried out in a controlled manner by means of temperature monitoring by means of temperature sensors, not shown in detail, and / or as a function of a signal generated by the flame sensor 64.It is possible in particular to use a staged addition for the hydrogen gas, for example by the hydrogen gas nozzles being designed as gas lances of different lengths and / or with a radially arranged gas outlet.The swirling element 35 is arranged in a cooling cone 36. According to the exemplary embodiment shown, the cooling cone 36 has a cylindrical section, the outer diameter of which is at least 80% of the inner diameter of the burner housing 27 at this point. In particular, the outer diameter of the cooling cone 36 is at least 85%, in particular at least 90%, in particular at least 95% and in particular at most 99% of the inner diameter of the burner housing 27 at this point. The cooling cone 36 is arranged in particular in a region of the burner housing 27 in which the burner housing widens conically. The burner housing 27 has an expansion section 39 which merges into a terminating section 40. The end section 40 and the widening section 39 form a burner head 41; a circumferential annular gap 50 is formed between an outer wall of the cooling cone 36 and an inner wall of the burner head 41. The air flowing through this annular gap is referred to as secondary air. The secondary air thus flows past the cooling cone 36. The air flowing through the cooling cone 36 is referred to as primary air. Because at least a portion of the air is guided past the cooling cone 36 as secondary air, air classification is possible.In the embodiment shown, the burner head 41 improves the mixing of the fuels, in particular of hydrogen with air. The burner flame 13 forms after the burner head 41, wherein the shape of the burner flame 13 is influenced by the geometry of the burner head 41. This means that by a suitable selection of the burner head geometry, the shape of the burner flame 13 can be adjusted in a targeted manner. In particular, the larger the diameter at the outlet of the burner head 41, the larger the diameter D F of the burner flame 13 is.The burner 12 is fixed to an end wall 42 of the rotary kiln 9. The end wall 42 is referred to as the outlet end wall, since the material outlet 11 is arranged in this region. The fastening of the burner 12, in particular of the burner housing 27, to the end wall 42 is effected by means of fastening elements which are not shown in more detail.As indicated in FIG. 2, the end wall 42 is arranged on the rotary kiln 9 in an overlapping manner, in particular in the axial direction and / or in the radial direction with respect to the axis of rotation 19. In particular, the rotary kiln 9 is not hermetically sealed by the end wall 22. A circumferential gap 46 remains between the end wall 42 and the rotary kiln 9.The burner 12 is arranged on the rotary kiln 9 in particular in such a way that the longitudinal axis 26 of the burner housing 27 and the axis of rotation 19 of the rotary kiln 9 coincide, i.e. are identical. The burner 12 is arranged concentrically with respect to the rotary kiln 9.The burner 12 is fastened directly to the rotary kiln 9 and is integrated therein at least in regions. In particular, the burner head 41 and the burner flame 13 generated by the burner 12 are arranged, in particular, completely within the rotary kiln 9.The burner 12 has a burner frame 47, with which the burner 12 is placed on a base. According to the exemplary embodiment shown, the burner frame 47 is designed to be static, i.e. immovable, in particular fixed. It is also conceivable for the burner frame to have rollers on its underside, which rollers can be rolled in particular on rails suitable for this purpose. In particular, it is conceivable for the burner 12 to be axially displaced along the rails by means of an axial drive, in particular by means of a pneumatic drive.Along the longitudinal axis 26 or the axis of rotation 19, the burner flame 13 has a length L F and a diameter D F oriented perpendicular thereto.The rotary kiln 9 has an inner diameter D i. In the burning-out zone 20, fire protection installations 43 are provided which are fastened to the inner wall of the rotary kiln 9. As a result of the fire protection installations 43, a reduced internal diameter D red. results in the burn-out zone 20. In the axial direction, the fire protection installations 43 extend along a length L A, which corresponds to the length of the burn-out zone 20. It is essential that the length L A of the burn-out zone 20 is greater than the length L F of the burner flame 13, and that the burner 12 is arranged on the rotary kiln 9 in such a way that the burner flame 13 is arranged completely within the burn-out zone 20, in particular in the axial direction with respect to the axis of rotation 19. It is also essential that the diameter D F of the burner flame 13 is smaller than the reduced diameter D red. Direct flame contact of the fire protection installations 43 is avoided.In the heat transfer region 21, throwing plates 44 are arranged and fastened in particular to the inner side of the rotary kiln 9. The sheets 44 are open and serve to produce a veil 45 of material. It is possible to quantify the density of the material veil 45 indirectly, in particular by means of a measurement of the exhaust gas temperature. The lower the exhaust gas temperature, the greater the heat transfer to the material that had previously taken place. This means that the lower the exhaust gas temperature will be, the more dense the material mist 45 will be, and vice versa. The exhaust gas temperature results from the burner output, the predispensing output, i.e. the mass flow of the supplied material into the rotary kiln 9, and the material temperature. The material temperature serves in particular as an input variable for the regulation of the burner output. It has been found that it is advantageous if the exhaust gas temperature is at least 100° C. in the exemplary embodiment shown. It is understood that, depending on the material used, the burner 12 or the fuels used, the exhaust gas temperature for monitoring the material mist 45 can assume other values.The geometry of the throw plates 44 is explained in more detail below with reference to FIG. 3. It is possible that different geometries of throwing plates are used. According to the illustration shown, two different sheet metal geometries are arranged alternately and at a distance from one another along the circumferential direction. The individual throw plates 44 are fastened to the inside of the rotary kiln 9 by means of a holding element, in particular a holding angle. The throw plates 44 are so-called open installations and in particular are designed in the manner of blades. The throw plates 44 are multiply edged, i.e. have at least two edges 51. During operation of the rotary kiln 9, the throw plates 44 pick up the material to be dried and release it again in an upper region when the rotary kiln 9 rotates. The throwing plates 44 are designed in such a way that a continuous and homogeneous material veil 45 is formed which is as dense as possible. The material screen 45 has a particularly large surface area, whereby the heat transfer by convection is improved.The specific geometry of the throwing plates 44 and in particular their arrangement on the inner side of the rotary kiln 9 can vary with different materials, different material humidities and / or drying powers in order to produce a material veil 45 that is as dense as possible. For example, when drying recycled asphalt, rake-like internals, radially oriented half shells or other geometries may be advantageous for producing the material veil. The background is that the discharge characteristic from the sheets 44 can vary depending on the material used, its moisture content and / or the drying performance of the rotary kiln 9.The geometry and function of the fire protection installations 43 are explained in more detail below with reference to FIG. 4. The fire protection installations 43 are closed installations, i.e. as shown in FIG. 4, form a substantially C-shaped frame which is arranged with its open side on the rotary kiln 9 and is thereby closed. Each fire protection installation 43 and the corresponding section of the rotary kiln 9 form a closed chamber 67 which is open only in the axial direction, i.e. perpendicular to the plane of the drawing of FIG. 4.The fire protection installations 43 are each held by means of a retaining clip 52.The material disposed in the chamber 67 is protected. Direct contact with the burner flame 13 in the burn-out zone is thereby avoided. The material is transferred indirectly into the material by thermal radiation from the surface of the fire protection installations 43. The fire protection installations 43, the throw plates 44 and the rotary kiln 9 as a whole are produced from heat-resistant and wear-resistant material.In the following, the structure and the function of the swirling element 35 are explained in more detail by means of FIGS. 5 to 7. The swirling element 35 is designed as a baffle plate. The essential function of the baffle plate 35 is to swirl the air arriving along the longitudinal axis 26, i.e. the primary air, tangentially. The baffle plate 35 is arranged concentrically to the longitudinal axis 26 in the burner housing 27. The baffle plate 35 has a plurality of blades 53, 54. The inner vanes 53 are arranged overlapping one another in a circular manner in the circumferential direction about the longitudinal axis 26. In the embodiment shown, sixteen blades 53 are arranged. A central through opening 55 remains in a central region surrounded by the inner blades 53. The transverse web 56 is connected integrally via the edge 57 to a diagonal web 58. The transverse web 56 and the diagonal web 58 enclose an opening angle that is greater than 90° and less than 180°, in particular between 120° and 150°.The inner vanes 53 are held in an inner ring 59. The inner ring 59 is surrounded by outer blades 54 which are held on their outer side on an outer ring 60. The outer ring 60 protrudes in both directions in the axial direction with respect to the longitudinal axis 26 on the inner ring 59. The outer blades 54 are in particular configured without a chamfer, i.e. have a planar, planar geometry. On the outer blades 54, a middle ring 61 is axially fitted in relation to the radical direction between the inner ring 59 and the outer ring 60. In the direction of the longitudinal axis 26, the baffle plate 35 has an inflow surface which is divided into three. The upstream surface comprises the inner central region formed by the passage 55 and the inner blades 53 and closed by the inner ring 59. In this region, in particular, the second secondary fuel nozzle 34 for oil is arranged. A second section results in the radial direction between the inner ring 59 and the middle ring 61, in which region the first secondary fuel nozzles 33 for gas, in particular natural gas, are arranged.The outer blades 54 are oriented inclined with respect to the longitudinal axis 26 and are arranged in particular in a plane which substantially corresponds to the plane of the corresponding diagonal webs 58 of the inner blades 53.An outer, in particular annular, section between the middle ring 61 and the outer ring 60 can be acted upon by the hydrogen nozzle 31 designed as an annular nozzle.In the following, a method for drying material in the asphalt mixing plant 1 is explained in more detail with reference to FIGS. 1 to 7.In the first device 2, material can be supplied to the rotary kiln 9 via the material inlet 10. The material is conveyed along the material conveying direction 22 at the material inlet 10 by means of the conveying elements, which are not shown in detail and are in particular designed as inlet screw segments and are fastened to the inner wall of the rotary kiln. In this case, in the heat transition region 21, a dense, continuous and homogeneous material veil 45 is produced on account of the special configuration of the thrower plates 44, with the result that the material is arranged with a very large surface within the rotary kiln 9. Heating of the material can be effected by means of the burner flame 13 by convection, which is arranged directly in the rotary kiln 9.The burner flame 13 is generated by the burner 12 which is designed as a combination burner and which burns hydrogen gas as primary fuel. Natural gas and light oil are used in particular as secondary fuels. It is understood that secondary fuels differing therefrom can also be used, in particular only one secondary fuel or more than two secondary fuels. The burner 12 can also be operated without secondary fuels and / or exclusively by means of secondary fuels. By using hydrogen gas as primary fuel, exhaust gases and / or emissions are reduced and in particular avoided. Because exhaust gases and / or emission-laden air are supplied via the exhaust line 18 and burned as well, an overall reduction of the exhaust gases results.Because closed fire protection installations 43 are arranged in the burn-out zone 20 in the rotary kiln 9 in which the burner flame 13 is arranged, direct material contact with the burner flame 13 is avoided. It is essential that the burner flame 13, due to the geometry of the burner head 41 and / or the baffle plate 35, of the number, arrangement and design of the fuel nozzles 31, 33 and / or 34, can be adjusted in a targeted manner such that it is arranged completely within the combustion zone 20 in the rotary kiln 9. In particular, the cooling cone 36 and the annular gap 50 formed between the cooling cone 36 and the burner housing 27 cause the prerequisite for air classification. Secondary air is guided past the baffle plate 35 and around the burner flame 13.In particular, it is possible to keep the flame temperature as low as possible, in particular at less than 1400° C., with the result that the formation of nitrogen oxides (NO x) is minimized and in particular avoided.In order to be able to set the desired shape of the burner flame 13 depending on the fuels used, it may be advantageous to change the number, configuration and / or position of the fuel nozzles 31, 33 and / or 34 relative to the baffle plate 35. In particular, it is possible to arrange individual and / or all nozzles 31, 33 and 34 behind the baffle plate 35 with respect to the gas conveying direction 23. The inner diameter D I of the rotary kiln 9 is selected in particular such that, in the exhaust gas volume flows of the various fuels which are produced, the flow velocity thereof is so low that only filler, i.e. rock dust having a particle size of at most 200 μm, is discharged from the rotary kiln 9. In particular, the flow speed is less than 20 m / s and in particular between 15 m / s and 20 m / s. It is advantageous if the flow speed and / or the volume flow of the exhaust gas is kept low. As a result, wear in raw gas channels and / or in an exhaust line can be reduced and in particular minimized.

Claims

A device for drying material for an asphalt mixing plant, wherein the device (2, 3) comprises a. a rotary kiln (9) which can be driven in rotation about a rotation axis (19) and in which the material is dried, wherein the rotary kiln (9) has a material inlet (10) and a material outlet (11), b. a heating unit coupled to the rotary kiln (9) for supplying heat into the rotary kiln (9), wherein the heating unit is designed with a burner (12) which has i. a burner housing (27) having a longitudinal axis (26), ii. an air line (16) arranged on the burner housing (27) for supplying air, wherein the air line (16) is arranged on the burner housing (27) axially to the longitudinal axis (26), iii. an air blower (29) arranged in the air line (16, 28), . a burner head (41) arranged on the burner housing (27) for generating a burner flame (13), v. a hydrogen gas line (14) connected to the burner (12) for supplying hydrogen gas into the burner (12), wherein a hydrogen gas nozzle (31) for discharging the hydrogen gas is connected to the hydrogen gas line (14), characterized in that c. the burner (12) is configured to be operated both exclusively by means of hydrogen gas and by means of hydrogen gas and secondary fuel, d. the burner (12) has a swirling element (35) for swirling the air in the burner (12) relative to the longitudinal axis (26), e. the swirling element (35) comprises a flow guide element in the burner housing (27), wherein the flow guide element is arranged immovably in the burner housing (27), iv, The flow-guiding element is arranged concentrically to the longitudinal axis (26) and is designed as a baffle plate which has a plurality of blades (53, 54) which are arranged in a circle and oriented at an angle with respect to the longitudinal axis (26), g. the heating unit comprises a hot gas generator (24) which is connected to the burner (12) and is connected to the rotary kiln (9) by means of a hot gas line (25).Device according to claim 1, characterised bya cooling cone (36) arranged in the burner housing (27), which is arranged along the longitudinal axis (26) between the swirling element (35) and the burner head (41).Apparatus according to any preceding claim, characterised bya secondary fuel line (17) connected to the burner (12) for supplying secondary fuel, the secondary fuel line (17) having a secondary fuel nozzle (33, 34) connected thereto for discharging the secondary fuel.Apparatus according to any of the preceding claims, characterized byan exhaust gas conduit (18) for supplying exhaust gases to the burner (12) and / or to the rotary kiln (9).Asphalt mixing plant with a device (2, 3) according to one of the preceding claims and with a filter dust extraction (5) and / or with a condensate separator (6) which are fluidically connected to the rotary kiln (9).Method for drying material comprising the method steps - providing an asphalt mixing plant according to claim 5, - feeding the material into the rotary kiln (9) which can be driven in rotation about the axis of rotation (19), - generating heat with the burner (12) of the heating unit by burning hydrogen gas, - feeding the heat into the rotary kiln (9) and drying the material.Method according to claim 6, characterised byfeeding exhaust gases to the burner (12) and / or to the rotary kiln (9) by means of an exhaust pipe (18).Method according to claim 6 or 7, characterised in that the supply of the heat is effected by a burner flame (13) within the rotary kiln (9), so that the burner flame (13) is arranged in a dust-laden environment.Method according to claim 8, characterised in that the burner flame (13) in the rotary kiln (9) has a length (L F) oriented along the axis of rotation (19) which is less than or equal to a length (L A) of a burn-out zone (20) of the rotary kiln (9) oriented along the axis of rotation (19).Method according to claim 8 or 9, characterised in that the burner flame (13) has a diameter (D F) oriented perpendicularly to the axis of rotation (19), which is smaller than an inner diameter (D red) of the burning zone (20) of the rotary kiln (9) reduced by fire protection installations (43).

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