EP3344816B1 - Method for producing asphalt - Google Patents

Description

Technical field

The invention relates to a method for producing asphalt from a bulk material and bitumen having residual moisture.

State of the art

Asphalt generally refers to a mixture of bitumen and minerals such as sand, grit and the like. Asphalt naturally occurs on the one hand, for example in the Val de Travers, Neuchâtel (Switzerland) or on the island of Trinidad. On the other hand, asphalt is also manufactured artificially. Bitumen is obtained, for example, by distilling petroleum as a volatile, high-molecular residue. Bitumen can be modified to achieve different properties. For example, polymers such as atactic polypropylene (APP), styrene-butadiene-styrene (SBS), ethylene propylene diene terpolymer (EPDM), ethylene vinyl acetate copolymer (EVA) or rubber powder, waxes, paraffins, zeolites etc. can be added. With these or other additives, properties such as viscosity, application temperature, strength, abrasion resistance, fatigue resistance, weather resistance etc. can be influenced. These properties can also be influenced by mixing several different bitumen.

The majority of the installed asphalt is produced in asphalt mixing plants. The individual components of the asphalt mix are specifically put together and mixed. For this purpose, the aggregates are added to a drying drum in a pre-metered amount in order to evaporate the moisture contained in the rock and generate the required temperature of the asphalt. The amount of fine dust (also called filler) in the mixing plant, especially in the drying drum, is typically separated with the help of a downstream dedusting plant. The pre-dosed mixture of minerals leaves the drying drum and reaches a mixing tower. There the exact dosage of the warm minerals takes place, usually after prior screening in different grain sizes. The hot bitumen is then injected into the mixing container and mixed with the minerals. The asphalt typically has a temperature of about 160 to 180C at this point. Finally, the finished asphalt is loaded hot via loading silos or directly onto the loading areas of trucks in order to be used in road and path construction.

The drying drum, also called rotary kiln, is an oven for the continuous drying of fabrics. In addition to their use in the drying of minerals for asphalt production, such furnaces are also known in the manufacture of cement.

The drying drum is heated either directly, inside the oven, for example by a burner. There are also indirect heaters in which the heat is transferred via the rotary tube wall. These have the advantage that the temperature of the interior of the drying drum is easier to control. However, these heaters have an extremely poor efficiency.

Next is from the WO 92/01751 A1 (AHO ) heating the mineral material or the mixture of mineral material and crushed asphalt with superheated steam at a temperature between 250 ° C. and 350 ° C., the gas leaving the mixture at a temperature of approximately 20 ° C. to 30 ° C. so that the entire amount of heat can be given off to the mixture.

The FR 2 265 914 A1 (Taiyou ) discloses a method for storing and heating asphalt mixtures, the asphalt mixture being introduced into a double-walled cylinder, subjected to superheated steam at a temperature of approx. 150 ° C. and then the container being sealed.

• Doppelwandig: Im Aussenmantel wird das Schüttgut getrocknet, am Ende der Trommel wird das getrocknete Schüttgut in den Innenmantel überführt. In den Innenmantel ragt eine Lanze, über welche das Bitumen eingespritzt wird. Über geeignete Schaufelgeometrien wird der Asphalt gemischt und zurückbefördert. Solche Anlagen zeichnen sich durch den kompakten Aufbau aus und sind typischerweise mobil.
• Einwandig: Die Trommel weist eine grössere Länge auf, wobei im ersten Abschnitt der Trommel die Trocknung und im zweiten, sich anschliessenden Abschnitt der Trommel die Mischung erfolgt. Eine Lanze zum Eintragen des Bitumens ragt typischerweise über den Endbereich in die Trommel hinein.

The drying drum can also be used in combination to dry the bulk material and to mix the asphalt from bitumen and bulk material. In principle, two devices are known for this:

• Double-walled: The bulk material is dried in the outer jacket, at the end of the drum the dried bulk material is transferred into the inner jacket. A lance protrudes into the inner jacket, through which the bitumen is injected. The asphalt is mixed and transported back using suitable bucket geometries. Such systems are characterized by their compact structure and are typically mobile.
• Single-walled: the drum has a longer length, with drying taking place in the first section of the drum and mixing in the second, subsequent section of the drum. A lance for introducing the bitumen typically projects into the drum through the end region.

• Trockentrommeln sind konstruktiv sehr aufwändig. So müssen die Rohre drehbar gelagert und motorisch angetrieben sein.
• Aufgrund der aufwändigen Konstruktion sind solche Vorrichtungen teuer in der Herstellung.

Overall, the drying drums have the following disadvantages:

• Drying drums are very complex to construct. For example, the pipes must be rotatably mounted and driven by a motor.
• Due to the complex construction, such devices are expensive to manufacture.

• Drehrohröfen, die in voller Beladung mit heissen Materialien plötzlich stehenbleiben, erleiden oft aussergewöhnlich teure Schäden durch die einseitige Hitzeeinwirkung des stehengebliebenen Gutes: Dabei kann eine irreversible Krümmung des Drehrohres bis zu dessen Unbrauchbarkeit erfolgen.
• Die Trommel ist schwierig zu isolieren, so dass das Verfahren energetisch äusserst aufwändig und damit teuer ist.
• Die direkte Beheizung der Trockentrommel hat den Nachteil, dass die Wärmeverteilung nicht optimal ist, so kann zum Beispiel das Produkt örtlich überhitzt werden. Weiter steht das Produkt in direktem Kontakt mit dem Brenner und dessen Abgasen, womit das Produkt kontaminiert werden kann.
• Die indirekte Beheizung der Trockentrommel weist typischerweise einen schlechten Wirkungsgrad auf.
• Die Rückgewinnung von Wärme ist in der Regel unwirtschaftlich, da das Abgas eine relativ niedrige Temperatur aufweist.
• In der Trockentrommel wird Staub aufgewirbelt, welcher aufwändig aus den Abgasen filtriert werden muss.
• Die Abgase müssen auch nachbehandelt werden, um Emissionen von VOC's (volatil organic compounds) aus den Verbrennungsabgasen des Brenners zu verhindern. Solche Verfahren (Filtern, katalytische Nachverbrennung) sind kostenintensiv und aufwändig.
• Aufgrund des hohen Anteils an Luftsauerstoff und brennbaren Stoffen, wie zum Beispiel Stäube, besteht latente Feuer- und Explosionsgefahr.
• Weiter darf bei den Abgasen der Taupunkt nicht vor dem Kamineintritt unterschritten werden. Um die Temperatur solange über dem Taupunkt zu halten, muss viel Energie eingesetzt werden.

The motor drive and the storage of the drum are expensive to maintain. In particular, if the drive fails during operation, ie loaded drum may be difficult to rotate the drum again without having to discharge the product.

• Rotary tube furnaces that suddenly stop when fully loaded with hot materials often suffer exceptionally expensive damage from the one-sided heat exposure of the goods that have been left standing: This can result in an irreversible curvature of the rotary tube until it becomes unusable.
• The drum is difficult to isolate, so the process is extremely energy-intensive and therefore expensive.
• The direct heating of the drying drum has the disadvantage that the heat distribution is not optimal, for example the product can be overheated locally. The product is also in direct contact with the burner and its flue gases, which can contaminate the product.
• Indirect heating of the drying drum typically has poor efficiency.
• The recovery of heat is usually uneconomical because the exhaust gas has a relatively low temperature.
• Dust is whirled up in the drying drum, which has to be filtered out of the exhaust gases.
• The exhaust gases must also be post-treated in order to prevent emissions of VOCs (volatile organic compounds) from the combustion exhaust gases of the burner. Such processes (filtering, catalytic afterburning) are costly and complex.
• Due to the high proportion of atmospheric oxygen and combustible substances, such as dusts, there is a latent risk of fire and explosion.
• Furthermore, the exhaust gas must not fall below the dew point before the chimney enters. A lot of energy has to be used to keep the temperature above the dew point.

The industry has been researching the optimization of the production of asphalt for decades, especially since it is a product that is produced in enormous quantities worldwide. So far, only minor successes have been achieved through modifications to the burners and in heat recovery.

The use of recycled asphalt is also becoming increasingly important. At present, small amounts of undried recycled asphalt can be added when mixing asphalt (in the range of 5%). It is also known to dry the recycled asphalt beforehand so that larger quantities of the asphalt production can be added. Due to the large angle of repose (approximately 60 °), the recycled asphalt can hardly be added to the bulk material before drying. The poorer flow properties of the recycled asphalt negatively affect transport in the rotary kiln, i.e. the angle of the rotary kiln would have to be adjusted to the amount of asphalt added. There is also the danger in the rotary kiln that the bitumen present in the recycled asphalt can ignite. Furthermore, exhaust gases are increasingly generated. The entire drying plant and conveyor systems are also contaminated by the use of recycled asphalt. Various efforts have been made so far to be able to efficiently dry the recycled asphalt. On the one hand, two drying systems are operated in parallel (so-called "black" and "white" drying systems) and on the other hand, the drying systems are arranged directly above the silo or the mixing system (raised). With the latter measure, a transport device, in particular a warm transport device, between the drying drum and the silo can be dispensed with.

However, both measures have major disadvantages. Obviously, the use of a separate drying plant for the recycled asphalt increases the costs massively, because not only does a second drying plant have to be built, but also used, maintained and, if necessary, repaired. The arrangement above the mixing device also has the disadvantage that it is technically very complex.

Presentation of the invention

The object of the invention is to provide a process for the production of asphalt belonging to the technical field mentioned at the outset which can be carried out in an energy and cost-efficient manner and is in particular also suitable for the use of recycled asphalt.

The solution to the problem is defined by the features of claim 1. According to the invention, for the production of asphalt, the bulk material is subjected to superheated steam in order to reduce the residual moisture in the bulk material and the bulk material with the reduced residual moisture is mixed with bitumen in order to obtain asphalt.

According to the invention, superheated steam is used in the production of asphalt to reduce residual moisture in a bulk material.

A corresponding device for reducing a residual moisture content of a bulk material comprises a drying room for reducing the residual moisture content of the bulk material, the drying room being followed by a mixer for mixing the bulk material with bitumen and thus for producing asphalt. The device further comprises a generating device for generating superheated steam, with which superheated steam can be introduced into the drying room.

In the following, a percentage, for example 10% residual moisture, is understood to mean a percentage in percent by weight, unless stated otherwise.

Superheated water vapor is water vapor with a temperature above the boiling point. For example, water vapor is considered overheated at atmospheric pressure if the temperature is above 100 ° C. Such superheated steam is dry, which means that it does not contain any water drops. The superheated steam is therefore also called dry steam.

Surprisingly, experiments have shown that in the production of asphalt, the use of superheated steam allows bulk goods to be dried efficiently for the production of asphalt, which means that asphalt production can be carried out more cheaply and easily. While in conventional drum dryers the bulk material is first heated and only then dries, tests have shown that the heat transfer from superheated steam to the residual moisture in the bulk material is so optimal that the residual moisture already begins to evaporate before the actual or final heating of the bulk material. Accordingly, the heat transfer between the overheated water vapor and the residual moisture appears to be significantly better than between the overheated water vapor and the bulk material.

This effect could be observed to a particularly large extent in the case of mineral bulk goods such as sand. A major advantage that results from this effect is particularly energy-efficient drying, since a substantial part of the heat can be transferred directly to the residual moisture. Furthermore, not only the residual moisture on the surface but also capillary water can be removed particularly efficiently. The tests have also shown that the residual moisture can not only be reduced using relatively little energy, but that the residual moisture itself can also be reduced particularly strongly in a short time and with little energy expenditure.

When using superheated steam for drying bulk goods, not only the absorption capacity for the residual moisture is relevant, but the formation of "new" superheated steam from the residual moisture. This is done by transferring the thermal energy of the superheated steam to the residual moisture in the bulk material. The higher the temperature of the superheated steam, the more residual moisture can be transferred to the vapor phase, causing the bulk material to lose this residual moisture.

1. 1. Überhitzter Wasserdampf weist eine wesentlich bessere Wärmeübertragung auf das Schüttgut und damit auf die Restfeucht im Schüttgut auf. Damit erfolgt eine schnelle Verdampfung der Restfeuchte im Schüttgut.
2. 2. Überhitzter Wasserdampf kann so lange Restfeuchte aufnehmen, bis der Taupunkt des Wasserdampfs erreicht ist (100°C bei Atmosphärendruck).
3. 3. Überhitzter Wasserdampf weist gegenüber Luft eine wesentlich höhere, in etwa die doppelte spezifische Wärmekapazität auf. Damit wird ein schneller Wärmeübergang erreicht.
4. 4. Überhitzter Wasserdampf weist gegenüber Luft eine wesentlich geringere, rund 40 % geringere, Viskosität auf. Damit wird das Eindringen des überhitzten Wasserdampfs in Poren des Schüttgutes und damit der effektive Wärmetransport verbessert.
5. 5. Da die Atmosphäre über dem Schüttgut aus Wasserdampf besteht, ist der Sauerstoffgehalt entsprechend klein, womit kaum Oxidationsprozesse einsetzen und eine Brand- und Explosionsgefahr gering gehalten werden kann.
6. 6. Da kein Diffusionswiderstand zwischen verdampfter Feuchte und dem überhitzten Wasserdampf besteht, ergibt sich ein effizienterer Massentransport von innen nach aussen (auch aufgrund der geringen Viskosität unter Punkt 4).
7. 7. Die Fördertechnik ist damit nicht auf die Trockentrommel beschränkt, sondern kann weitgehend beliebig gewählt werden. Mit einem Verzicht auf die Trockentrommel können insbesondere einfachere und kostengünstigere Fördertechniken eingesetzt werden, welche unter Umständen auch eine geringere Staubentwicklung verursachen, womit wiederum auf eine Abluftfiltrierung verzichtet oder auf eine einfachere und kostengünstigere Abluftfiltrierung zurückgegriffen werden kann.
8. 8. Da bei der Erzeugung des Wasserdampfs typischerweise eine indirekte Heizung eingesetzt wird, ist der überhitzte Wasserdampf frei von Abgasen, womit wiederum auf aufwändige Filter verzichtet werden kann.
9. 9. Es sind keine Schleusen oder Absperrungen notwendig.
10. 10. Der Energiebedarf kann im Vergleich zur Heisslufttrocknung um bis zu 50% verringert werden.
11. 11. Bis zu 90 % der Energie sind rückführbar.
12. 12. Die Trocknungszeit kann um bis zu 80 % reduziert werden.
13. 13. Die Trocknungsanlage kann kompakter und kostengünstiger ausgebildet werden, woraus auch geringere Investitionskosten resultieren.
14. 14. Es entstehen kaum gesundheitsschädliche oder geruchsbelästigende Emissionen.

The use of superheated steam when drying the bulk material in the production of asphalt has the following advantages over the usual use of hot air in the drying drum:

1. 1. Superheated steam has a much better heat transfer to the bulk material and thus to the residual moisture in the bulk material. This quickly evaporates the residual moisture in the bulk material.
2. 2. Overheated water vapor can absorb residual moisture until the dew point of the water vapor is reached (100 ° C at atmospheric pressure).
3. 3. Superheated water vapor has a much higher, approximately twice the specific heat capacity compared to air. Thereby a quick heat transfer is achieved.
4. 4. Superheated water vapor has a much lower, around 40% lower, viscosity than air. This improves the penetration of the superheated steam into the pores of the bulk material and thus the effective heat transfer.
5. 5. Since the atmosphere above the bulk material consists of water vapor, the oxygen content is correspondingly low, which means that hardly any oxidation processes are used and the risk of fire and explosion can be kept low.
6. 6. Since there is no diffusion resistance between evaporated moisture and the overheated water vapor, there is a more efficient mass transfer from the inside to the outside (also due to the low viscosity under point 4).
7. 7. The conveyor technology is therefore not limited to the drying drum, but can largely be chosen as desired. By dispensing with the drying drum, in particular simpler and less expensive conveying techniques can be used, which under certain circumstances also cause less dust, which in turn means that there is no exhaust air filtration or simpler and less expensive exhaust air filtration.
8. 8. Since indirect heating is typically used to generate the water vapor, the superheated water vapor is free of exhaust gases, which in turn means that expensive filters can be dispensed with.
9. 9. No locks or barriers are necessary.
10. 10. The energy requirement can be reduced by up to 50% compared to hot air drying.
11. 11. Up to 90% of the energy can be traced.
12. 12. The drying time can be reduced by up to 80%.
13. 13. The drying system can be made more compact and less expensive, which also results in lower investment costs.
14. 14. There are hardly any harmful or odor-causing emissions.

The bulk material is preferably a mineral bulk material, in particular gravel or sand, the residual moisture of which is reduced. This is advantageous because mineral bulk goods are typically available as components for asphalt production which have a residual moisture to be reduced.

Alternatively, residual moisture in other starting materials in asphalt production can be reduced with this process. For example, residual moisture from recycled asphalt can also be reduced so that it can then be mixed with the bitumen and the mineral bulk material in the mixing device.

The residual moisture to be reduced is preferably less than 10%, preferably less than 7%, particularly preferably less than 5%. Because a starting material to be dried with a relatively low residual moisture is selected for the process, the asphalt production can be carried out in a particularly energy-efficient manner. In particular, it has surprisingly been found that even with a small proportion of residual moisture, efficient heat transfer can be achieved through the superheated steam, so that even relatively dry substances can be dried efficiently with superheated steam.

Bulk goods with residual moisture greater than 10% can also be dried with superheated steam.

A reduced residual moisture is preferably less than 2%, preferably less than 1%, particularly preferably less than 0.5%. For asphalt production, it is particularly advantageous if the bulk material used, which is typically mixed with bitumen after the drying process, has a low residual moisture - however, it is not absolutely necessary that the residual moisture is as low as desired. It has been shown that, in particular, a residual moisture of approximately 0.5% is particularly ideal with regard to the economy in the production process and with regard to the requirements for the asphalt quality.

In principle, it is not excluded that even bulk goods with a residual moisture content of greater than 2% can already be mixed with bitumen to asphalt. This can be sufficient if the asphalt has to meet lower requirements or if the asphalt is still being treated. For example, hygroscopic substances that reduce the free residual moisture in the asphalt can be added to the asphalt or to the bulk material.

Method according to one of claims 1 to 4, characterized in that the method takes place at a pressure of 900 to 1100 mbar. The process is particularly preferably carried out at local normal pressure. A complex construction of a drying room as a pressure vessel can thus be dispensed with. The term “drying room” is to be understood below to mean a room in which the bulk material is dried. The installation and maintenance of the same are therefore particularly cost-effective.

Variants can also use superheated steam at a different pressure.

The superheated steam is preferably introduced into a drying room through which the bulk material is continuously transported in a transport direction. This ensures continuous drying of the bulk material. Continuous processes have the advantage that apart from the maintenance times or for repairs, no interruption of the process is necessary. In the present case, the continuous procedure is of particular advantage since the superheated steam creates an atmosphere in the drying room which can be kept constant, especially if the material throughput and the bulk properties remain essentially constant. A particularly easy-to-control method for drying a bulk material can thus be created, in which continuous fine adjustments of the process parameters such as steam throughput, steam temperature, material throughput etc. can be carried out. Apart from starting the process, the desired process conditions (typically the residual moisture achieved after drying) can thus be kept constant.

In principle, the method can also be carried out discontinuously, so that the residual moisture in the bulk material would change in the manner of a sawtooth pattern (or tilting oscillation, sawtooth oscillation). The residual moisture would increase abruptly each time the batch was changed, and then decrease continuously.

The superheated steam is preferably introduced into the drying room in counterflow, counter to the direction of transport. So a temperature gradient continuously increase while the bulk material is being fed into the drying room, thus achieving monotonous heating of the bulk material. When entering the drying room, surface water (if available) and then coarse capillary water are transferred to the vapor phase. The greatest amount of energy is needed to remove the fine capillary water. However, since the fine capillary water is only removed towards the end of the drying process, it is advantageous if the bulk material is subjected to the superheated steam in countercurrent. The countercurrent process also has the advantage that increased convection is achieved, which results in improved contact between superheated steam and bulk material and thus more efficient evaporation of the residual moisture in the bulk material.

In variants, the superheated steam can also be transported through the drying room in cocurrent with the bulk material. This has the advantage that the bulk material itself, which exits the drying room at a lower temperature, dissipates less energy from the system.

The device preferably comprises a conveying device, by means of which the bulk material can be conveyed through the drying space into the mixing unit. The bulk material is thus preferably conveyed through the drying room via a conveyor belt. This conveyor technology is particularly easy to install and inexpensive to purchase and maintain. The bulk material can be transported with conveyor belts, in particular during a large part of the manufacturing process. A supply to the drying room can also already take place via conveyor belts. This means that the bulk material does not have to be reloaded onto another conveying device, such as a drum or a screw, during the process. The already dried bulk material can also be transported further using the same conveying device, for example to a mixing device in which bitumen is added to the bulk material. A conveyor belt can also be used to adjust the fabric turnover particularly easily by changing the loading (for example, quantity of bulk material per linear meter) or by adjusting the feed speed of the conveyor belt. In this context, the use of superheated steam has the advantage that the bulk material during the Drying process is not necessarily mixed, because the superheated steam ensures very good heat transfer.

In variants, a drying drum can also be used, i.e. H. the drying room can itself be designed as a funding. This has the advantage that existing plants for the production of asphalt, in particular the drying plant, can be retrofitted relatively easily with a generating device for generating superheated steam. The bulk material can also be conveyed by means of a screw conveyor or other conveying means for solids known to the person skilled in the art. In particular, drying can also be carried out batchwise, i.e. H. done discontinuously.

In a further variant, a largely arbitrary conveying device, for example a conveying device for conveying the bulk material after drying to a silo, in particular a hot silo or a mixing plant, can also be used. When conveying into a silo, this conveying device can comprise, for example, a vertically aligned blade conveyor belt which can be retrofitted to a drying room. This means that the asphalt production plant can be upgraded and made compact in a particularly cost-effective manner.

The conveyor device can also be designed as a chain conveyor, vibration conveyor, tube conveyor, rail conveyor with transport carriage, screw conveyor, shaking chute, vibrating conveyor and the like.

In a preferred variant, however, the typical drum dryer in the asphalt production plant is replaced by a drying room which particularly preferably contains a conveyor belt as the conveying device.

According to the invention, the superheated steam is cooled by absorbing residual moisture in the bulk material and discharged from the drying room at a temperature of at least 100 ° C., preferably at least 105 ° C.

Superheated steam is preferably introduced into the drying room at a temperature between 100 ° C. and 350 ° C., preferably between 170 ° C. and 270 ° C., particularly preferably between 200 ° C. and 240 ° C. Experiments have shown that the process can be carried out well at 220 ° C, for example. The temperature of the superheated steam above 100 ° C. is particularly preferred. In principle, the temperature with a constant material throughput of superheated steam is proportional to the quantity of bulk material converted. The goal when choosing the entry temperature of the superheated steam in the drying room is that the water vapor emerging from the drying room - although at a lower temperature - is still overheated. If the temperature of the water vapor would drop below the boiling point, the steam would condense and the bulk material would be moistened. On the other hand, the temperature of the superheated steam should only be so high for economic reasons when it is introduced into the drying room that the temperature of the water steam emerging from the drying room is not far above the boiling point. The superheated steam is preferably circulated, the amount of steam supplied to the superheated steam through the drying process being separated off, for example, via a heat exchanger.

The drying process can be regulated, for example, via the steam temperature at the point of entry, via the steam quantity or via the bulk material flow. The control is preferably carried out continuously on the basis of current measurement data of these parameters. The regulation can also be carried out sporadically, on the basis of periodic analyzes of the water content in the dried bulk material or at other intervals.

It is clear to the person skilled in the art that the superheated steam can also have a temperature above 350 ° C. Such high temperatures can be beneficial, for example, in the production of mastic asphalt.

The outlet temperature of the bulk material with reduced residual moisture preferably has a temperature of above 100 ° C., particularly preferably above 150 ° C., in particular of more than 160 °. This temperature has proven to be particularly advantageous for the further processing of the bulk material to asphalt.

In variants, the discharge temperature can also be higher than 160 ° C or lower than 100 ° C.

In a particularly preferred method, the superheated steam is introduced into the drying room at a temperature of 220 ° C. and the volume flow of the superheated steam is controlled in such a way that the temperature of the superheated steam inside the drying room does not fall below 200 ° C., preferably not below 210 ° C falls. These parameters are of particular advantage since the discharged bulk material is not only sufficiently dry, but can also be heated to a sufficiently high processing temperature, in particular to over 160 ° C., even with a relatively short residence time in the drying room.

However, it is clear to the person skilled in the art that the parameter control can be varied as desired in order to achieve the same result. For this purpose, the inlet temperature and the volume flow of the superheated steam as well as the material throughput of the bulk material can be varied.

Tests have shown that typically the residual moisture in the bulk material can be reduced so efficiently that the desired discharge temperature of the bulk material has typically not yet been reached, while the residual moisture is already sufficiently reduced. In this case, the dwell time in the drying room is artificially extended to reach the desired discharge temperature.

In variants, the bulk material can be brought to the desired temperature in an additional heating device in a separate process step. This may make it possible to provide a more cost-effective drying process, since a lower power of the generating device is used for the superheated steam and a smaller drying device can also be used.

The bulk material is preferably heated with the superheated steam to a temperature of preferably above 140 ° C., particularly preferably from 150 ° C. to 170 ° C., in particular to 155 ° C. to 165 ° C. This achieves an ideal processing temperature for the production of the asphalt.

In variants, a different temperature, for example above 165 ° C., can also be provided. For example, a temperature of 260 ° C can be provided for the production of mastic asphalt.

The bulk material of reduced residual moisture is preferably dedusted, in particular by shaking or suction. Because there is no need for a drum dryer in the drying process, the dusts contained in the bulk material, which are not desirable in asphalt production, are not whirled up (whirling takes place on the one hand due to the rotation in the drum, but on the other hand also due to the burner gas stream). This means that there is no need for complex filtration of the exhaust air. In order to be able to remove these dusts efficiently and inexpensively, a vibrating screen or a suction device can be provided, for example, as a particularly simple and inexpensive variant. However, other variants for dedusting the bulk material after the drying process are known to the person skilled in the art. In principle, the bulk material could also be dedusted before the drying process.

The drying room preferably forms a closed system, in particular a closed circuit. The system preferably includes the generating device for generating the superheated steam. This means that after passing through the drying room, the water vapor can either be directly heated up and returned, or the residual energy of the water vapor can be recovered via a heat exchanger integrated in the system, while the remaining condensate can be disposed of. The closed system has the advantage that the process can be carried out in a particularly energy-efficient manner. The closed system also has the advantage that no exhaust gases, dusts or other emissions can escape, which ensures particularly safe operation.

In variants, the device can also be kept open. In this case, too, energy can be recovered - if not with the same efficiency.

If the system is operated in a cycle, the water vapor can be used again directly for the production of superheated steam, since after the use of the Water vapor is still present - the difference lies essentially in the lower temperature and in the higher amount, which increases during the drying process due to the evaporated residual moisture. Since the water vapor was not exposed to the flue gas of a burner, it is only contaminated by volatile parts of the bulk material. If only gravel or sand is used as bulk material, the water vapor can still be relatively clean even after the drying process, since apart from water there are hardly any volatile substances in the gravel or sand.

In contrast, dry air is used in hot air drying, which has moisture after use and is therefore not reusable. In contrast to the present method, the principle of hot air drying is based on the fact that dry air can absorb a certain amount of water until it is saturated. Then the moist air must be cleaned of the pollutants of the burner and, if necessary, the heat can be recovered via a heat exchanger.

Further advantageous embodiments and combinations of features of the invention result from the following detailed description and the entirety of the claims.

Brief description of the drawings

Fig. 1

eine schematische Darstellung einer Vorrichtung zur Herstellung von Asphalt gemäss dem Stand der Technik;

Fig. 2

eine schematische Darstellung einer Vorrichtung zur Herstellung von Asphalt unter Verwendung von überhitztem Wasserdampf in einer Trockentrommel, die nicht unter den Schutzumfang des Anspruchs 1 fällt;

Fig. 3

eine schematische Darstellung einer zweiten Ausführungsform einer Vorrichtung zur Herstellung von Asphalt unter Verwendung von überhitztem Wasserdampf in einem Trocknungsraum mit einem Förderband bei über dem Silo angeordnetem Trocknungsraum;

Fig. 4

eine schematische Darstellung einer dritten Ausführungsform einer Vorrichtung zur Herstellung von Asphalt unter Verwendung von überhitztem Wasserdampf in einem Trocknungsraum mit einem Förderband und einem Trommelmischer;

Fig. 5

eine schematische Darstellung einer vierten Ausführungsform eines Teils der Vorrichtung zur Herstellung von Asphalt unter Verwendung von überhitztem Wasserdampf, welcher innerhalb eines Trocknungsraums erzeugt wird;

Fig. 6

eine schematische Darstellung einer fünften Ausführungsform eines Teils der Vorrichtung zur Herstellung von Asphalt unter Verwendung von überhitztem Wasserdampf, welcher in einen Rührkessel eingeleitet wird.

The drawings used to explain the exemplary embodiment show:

Fig. 1

a schematic representation of a device for the production of asphalt according to the prior art;

Fig. 2

a schematic representation of an apparatus for the production of asphalt using superheated steam in a drying drum, which does not fall within the scope of claim 1;

Fig. 3

is a schematic representation of a second embodiment of an apparatus for producing asphalt using superheated Water vapor in a drying room with a conveyor belt with the drying room arranged above the silo;

Fig. 4

a schematic representation of a third embodiment of an apparatus for producing asphalt using superheated steam in a drying room with a conveyor belt and a drum mixer;

Fig. 5

a schematic representation of a fourth embodiment of part of the device for the production of asphalt using superheated steam, which is generated within a drying room;

Fig. 6

is a schematic representation of a fifth embodiment of part of the device for the production of asphalt using superheated steam, which is introduced into a stirred tank.

In principle, the same parts are provided with the same reference symbols in the figures.

Ways of Carrying Out the Invention

The Figure 1 shows a schematic representation of a device 100 for producing asphalt 104 according to the prior art. In such a device essentially a moist bulk material 101 is dried in a drum dryer 120 to a bulk material with reduced residual moisture 102 and then mixed with bitumen 103 and possibly other additives to form asphalt. The method is explained in more detail below in an exemplary embodiment.

In a first step, the moist bulk material 101, for example moist sand 101, is conveyed on a conveyor belt 110 into a drum dryer 120. The drum dryer 120 is also known by the term rotary kiln, drying drum, etc. It has a cylinder jacket or a drum which is rotatably driven. At one opening, the entry 121 of the drum dryer, the bulk material 101 to be dried, in the present case with a conveyor belt 110, is entered. Transporting the bulk goods in the drying drum is reached by a slight inclination of the drum in the conveying direction, from the entry 121 to the discharge 122, so that the bulk material 101 can be discharged continuously in the direction of the discharge 122 when the drum is rotating. In the area of the discharge 122 of the drum there is a burner 130, with which the interior of the drum is heated in order to dry the bulk material 101. The waste gases are removed on the entry side of the drum and processed with filters (not shown).

The dried bulk material 102 discharged from the drum dryer 120 is transported via a further conveyor belt 140 into an entry of a heat-insulated scoop conveyor 150. The dried bulk material 102 is thus introduced into a silo 160. Another silo 170 arranged peripherally to the silo 160 contains bitumen 103. The bitumen 103 is mixed in a mixing device 180 with the dried bulk material 102 to form asphalt 104, which can be transported to its destination by a transporter 190 for further use.

Variants of the method described above are known. For example, the use of indirect heating of the drum dryer is also known. Methods are also known in which the bitumen is fed directly into the drying drum and the asphalt is mixed there. In a further embodiment, the bulk material is dried in a double jacket and then mixed with bitumen during recycling in the inner jacket.

The Figure 2 shows a schematic representation of a first embodiment of an apparatus 200 for producing asphalt 204 using superheated steam in a drying drum 201.

The present device 200 shows one possibility of how a device 100 according to the prior art (see Figure 1 ) can be upgraded so that it can be operated with superheated steam (SHS, Super Heated Steam) instead of a burner 130. The aim is to convert an existing device for the production of asphalt as simply and inexpensively as possible.

The device 200 essentially comprises the parts according to FIG Figure 1 , but in the present case the drum dryer 220 has no burner 130. Instead, the drum dryer 220 has a device for generating SHS 230. In the area of the discharge 222, this comprises a supply line 231 for SHS and in the area of the entry 221 a supply line 232 for removing the moisture and / or the SHS. In the process, the moist bulk material 201 is continuously transported by means of the conveyor belt 110 into the entry 221 of the drum dryer 220. The rotation of the drum dryer 220 continuously transports the bulk material through the drum dryer. SHS is generated with the SHS generating device 230 and introduced via the feed line 231 into the discharge 222 of the drum dryer 220, that is to say against current or against the conveying direction of the bulk material 201 in the drum dryer 220. The SHS heats the moist bulk material 201 and thereby allows at least some of the moisture in the bulk material to evaporate. At the same time, the temperature of the SHS drops because its heat is used to evaporate the moisture in the bulk material 201. The mass flow and the temperature of the SHS entered are regulated in such a way that the SHS does not condense or that the SHS does not fall below a temperature of 100 ° C. at a normal pressure of 1 bar. The mass transport in the drum dryer 220 is set such that the residual moisture can be reduced to the desired extent (for example 1% or 0.5%). The SHS is returned at the inlet 221 of the drum dryer 220 via a discharge 232 of the SHS generating device 230.

Due to the drying process, the SHS mass flow at the inlet 221 is larger than at the outlet 222. Therefore, a part of the mass flow is branched off at the SHS generating device 230. This partial flow is condensed and disposed of. The condensation is preferably carried out via a heat exchanger, with which at least part of the thermal energy can be recovered. If necessary, a cleaning step with filter, activated carbon, via sedimentation or the like takes place before or after the condensation. The partial stream which has not been disposed of is processed so that it can be fed back to the drum dryer 220 as SHS. The preparation can include cleaning the SHS. For example, the SHS can be passed over filters, cyclones or other systems known to the person skilled in the art in order to separate contaminants. The preparation also includes heating the SHS or, depending on the temperature of the Water vapor / water (the SHS should not reach the condensation temperature in the drum dryer, but the SHS could cool down to the point of reprocessing). The SHS can also be cleaned before it is divided into the partial streams.

The SHS is thus largely used in the cycle, only the amount of water generated by the drying is taken from the cycle. After the initiation of the process, no fresh water is required for SHS generation, which means that the system can be operated ecologically. Since only SHS comes into contact with the bulk material, contamination of the bulk material can also be avoided. Contamination can be caught directly with the SHS and transferred to the water phase by condensation. The use of a cyclone, for example, can be an advantage here, since it can be used to concentrate the water to be separated with the impurities.

In a variant not shown, the SHS generating device 230 can also be dispensed with. In this case, the SHS is generated from the moisture in the moist bulk material 201 by heating the interior, preferably indirectly. However, this procedure has the disadvantage that it can take a relatively long time to start up before the SHS atmosphere is established. In a further variant, the SHS atmosphere 230 is used to generate the SHS atmosphere and then switch it off when the SHS atmosphere can be maintained with the residual moisture of the bulk material.

The dried bulk material 202 discharged from the drum dryer 220 is fed into an entry of a paddle conveyor 150 via a further conveyor belt 140. The dried bulk material 202 is thus introduced into a silo 160. Another silo 170 arranged peripherally to the silo 160 contains bitumen 203. The bitumen 203 is mixed in a mixing device 180 with the dried bulk material 202 to form asphalt 204, which can be transported to its destination by a transporter 190 for further use.

It is clear to the person skilled in the art that the silo 160 can also be dispensed with. In this case, the bulk material can be continuously processed into asphalt. This has the Advantage that the thermal energy contained in the freshly dried bulk material 202 can be used for the asphalt mixture.

It is also clear to the person skilled in the art that the transport devices, in particular the conveyor belts and the scoop conveyor, are also replaced by other transport devices or, depending on the arrangement of the parts, for example if the discharge of the drum dryer 220 lies directly above the entry of the scoop conveyor 150, completely dispenses with the transport device can be. The blade conveyor can be replaced, for example, by a screw conveyor.

The Figure 3 shows a schematic representation of a second embodiment 300 of an apparatus for producing asphalt 304 using superheated steam. The essential difference from embodiment 200 according to FIG Figure 2 is that the drying process does not take place in a drum dryer, but in a drying room 320. In addition, the drying device is not at ground level, but is arranged above the silo 160 for receiving the dried bulk material 302. In the present case, the drying chamber 320 is essentially cuboid and in each case comprises an entry opening 321 and an opposite discharge opening 323 in a bottom region, between which a conveyor belt 322 for conveying the moist bulk material 301 is provided within the drying chamber. The drying room can also be configured otherwise, in particular cylindrical. In the present case, the moist bulk material 301 is continuously transported from below through the entry 321 onto the conveyor belt 322 by means of a scoop conveyor 150. The entry can also take place with a screw conveyor, a conveyor belt or other conveying means instead of with a blade conveyor 150.

The drying room 320 is connected to an SHS generating device 330, analogous to the SHS generating device 230. This is connected to the drying chamber 320 via a feed line 331 in the area of the discharge 323 in the bottom area, so that SHS can be led into the drying room 320. Also in the bottom area, but in the area of the entry 321, a derivative 332 is provided for the SHS stream, with which the cooled SHS stream of the SHS generating device 330 for processing can be traced back. The preparation can be provided analogously to the preparation of the generating device 230.

The inlet 321 and outlet 322 are preferably arranged in the bottom region of the drying chamber 320. This creates a largely inert atmosphere made of SHS. SHS with a higher temperature thus remains within the drying chamber 320, while SHS with a lower temperature is returned via the discharge line 332 of the SHS generating device due to the higher density in the base region.

In the present case, the drying room 320 is arranged such that the discharge 323 comes to lie vertically above the silo 160. The dried bulk material 302 or the bulk material 302 with reduced residual moisture thus passes from the conveyor belt 322 in the interior of the drying room through the discharge 323, in the present case directly into the silo 160. This method is of particular advantage when using bituminous bulk material, such as, for example, a Addition of recycled asphalt to the bulk material. Due to the heating of the bitumen in the bulk material, the mixture can have a sticky, poorly flowing consistency. Because the drying device is now arranged above the silo, the hot bituminous bulk material can be dropped directly into the silo. Because no conveying means is provided between the drying device and the silo, the temperature of the dried material can be kept simpler, in particular no blade conveyor which is difficult to isolate is necessary.

It is clear that instead of the drying room with the conveyor belt, a drying room comprising a drying drum with an SHS production device can also be arranged above the silo. The drying devices explained below can also be arranged either at ground level or above the silo.

In variants, a transport means, for example a conveyor belt, can also be provided between the discharge 323 and the silo 160.

Another silo 170 arranged peripherally to the silo 160 contains bitumen 303. The bitumen 303 is mixed with the dried bulk material 302 in a mixing device 180 Asphalt 304 mixed, which can be transported to its destination with a transporter 190 for further use.

The Figure 4 shows a schematic representation of a third embodiment of an apparatus for producing asphalt using superheated steam in a drying room 320 with a conveyor belt 301 and a drum mixer 340.

The drying room 320 corresponds to that from that described above Figure 3 , that is, the drying room 320 of the second embodiment. In contrast to the second embodiment, in the present case the bulk material 301 to be dried is fed into the drying chamber 320 via a screw conveyor 310 via the entry 321. In the area of the discharge 323, the drying space 320 protrudes into an entry 341 of a drum mixer 340, so that the dried bulk material from the conveyor belt 322 can be fed directly into the drum mixer 340. In addition to the drying room 320, a lance of the bitumen silo 170 also projects into the drum mixer 340 in the area of the entry 341. For this purpose, at least the last section of the drying room 320 has smaller outside dimensions than the drum mixer 340 has inside dimensions at the entry 341. In the present case, the lance of the bitumen silo 170 protrudes only slightly into the drum mixer 340, but in order to create better mixing ratios, the lance can also distribute the bitumen over further distances within the drum mixer 340.

In the present case, the drum mixer 340 itself has essentially the same structure as the drum dryer 120, but no burner is provided in the present case. The drum mixer 340 is thermally insulated on the outside. In principle, however, the drum mixer can also be heated, for example indirectly via the outer casing or also via a burner analogous to the drum dryer 120. This means that the drying of the bulk material takes place exclusively in the drying room 320, while the temperature control of the bulk material takes place together with the Bitumen can be done in the drum dryer. For this purpose, the lance can also be designed such that the bitumen is only added deeper in the drum mixer 340, where the dried bulk material 301 has the desired temperature. Due to the inclination of the tumble dryer 340, the asphalt 304 in Conveyed in the direction of discharge 342 and can then be collected, for example, by a transporter 190, another transport device or also by a container or a silo.

The Figure 5 shows a schematic representation of a fourth embodiment of a part 400 of the device for producing asphalt using superheated steam, which is generated within a drying room 410;
The drying room 410 comprises similar to the embodiment of FIG Figure 3 an entry 412 in the bottom area of a first end face and an exit 414 in the bottom area of a second end face opposite the first. The entry of the moist bulk material 401 takes place by means of a scoop conveyor 411 through the entry 412 onto a conveyor belt 413 in the interior of the drying room 410. The conveyor belt 413 transports the bulk material 401 during the drying process through the drying chamber to the discharge 414, where the dried bulk material 402 a further conveyor belt 430 lying outside the drying room 410 is conveyed for further processing to asphalt.

In the present case, the drying device comprises a heating coil 422 within the drying room 410, by means of which the drying room 410 is heated. In the present case, the heating coil is heated by means of a burner 421, which is located outside the drying room 410. The hot exhaust gases from the burner 421 are cleaned after passing through the heating coil 422 and, before or after, passed through a heat exchanger 423 to recover at least part of the heat.

In the present case, a circulation blower 415 is located within the drying room 410 in order to be able to circulate the SHS (in the embodiment according to FIG Figure 2 or 3 The circulation is preferably carried out directly by the SHS supply lines, although other fans can also be provided to support the circulation).

In the area of the entry, a condenser 440 is connected in such a way that cooled SHS (still above the condensate point) is condensed and can be cleaned if necessary.

In the operation of the present embodiment, heating is initiated to initiate the process until an SHS atmosphere is formed in the drying room 410. The bulk material that has been converted until an equilibrium has been reached can be too moist. In this case, the bulk material that has already been converted can be returned to the drying process after the equilibrium has been set.

After equilibrium has been established, the discharged, dried bulk material 402 is processed to asphalt with the addition of bitumen and possibly other additives.

The Figure 6 shows a schematic representation of a fifth embodiment of a part 500 of the device for producing asphalt using superheated steam, which is introduced into a drying tank 510 or a stirred tank. In contrast to the above embodiments, this is a discontinuous drying process in which individual batches are dried one after the other.

The device comprises a drying container 510 with a stirrer 512 which is driven by a drive motor 511. The device 500 further comprises an SHS generation device 520 analogous to that of the embodiment 200 of FIG Figure 2 respectively 300 of Figure 3 , The drying container 510 is connected in an upper region via a feed line 521 and a discharge line 522 to the SHS generating device 520 in such a way that the SHS can be circulated and can be processed after it has left the drying container 510. The moist bulk material 501 is circulated in the drying container 510 and SHS is applied until the required residual moisture is reached. The bulk material is then processed into asphalt together with bitumen and possibly other additives.

In summary, it can be stated that, according to the invention, a production method for the production of asphalt is created which is particularly easy to set up and can be operated cost-effectively.

Claims (10)

1. Process for producing asphalt (304) from a bulk solid (301) having a residual moisture and bitumen (303) comprising the steps of:

   a. treating the bulk solid (301) with superheated steam in a drying space to reduce the residual moisture in the bulk solid (301);

   b. mixing the bulk solid (302) having reduced residual moisture with bitumen (303) to obtain asphalt (304),

   wherein the superheated steam is cooled by absorption of residual moisture in the bulk solid (301) and discharged from the drying space at a temperature of at least 100°C, preferably at least 105°C, thus reducing the residual moisture in the bulk solid (301).
2. Process according to Claim 1, characterized in that the bulk solid (301) is a mineral bulk solid (301) whose residual moisture is reduced.
3. Process according to Claim 1 or 2, characterized in that the residual moisture to be reduced is less than 10%, preferably less than 7%, particularly preferably less than 5%.
4. Process according to any of Claims 1 to 3, characterized in that a reduced residual moisture is less than 2%, preferably less than 1%, particularly preferably less than 0.5%.
5. Process according to any of Claims 1 to 4, characterized in that the process is carried out at a pressure of 900 to 1100 mbar.
6. Process according to any of Claims 1 to 5, characterized in that the superheated steam is introduced into a drying space (320) through which the bulk solid (301) is continuously transported in a transport direction.
7. Process according to Claim 6, characterized in that the superheated steam is introduced into the drying space (320) in countercurrent, counter to the transport direction.
8. Process according to any of Claims 1 to 7, characterized in that superheated steam is introduced into the drying space (320) at a temperature between 100°C and 350°C, preferably between 170°C and 270°C, particularly preferably between 200°C and 240°C.
9. Process according to any of Claims 1 to 8, characterized in that the bulk solid is heated with the superheated steam to a temperature of preferably above 140°C, particularly preferably to 150°C to 170°C, in particular to 155°C to 165°C.
10. Process according to any of Claims 1 to 9, characterized in that the bulk solid having reduced residual moisture is dedusted by shaking or aspiration in particular.

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