Methods for processing bitumen- and / or tar-containing solids

Abstract

Method for processing bitumen- and / or tar-containing solids (1), comprising the steps: a) Provision of the bitumen and / or tar-containing solids to be processed (1); b) Feeding the bitumen and / or tar-containing solids to be processed (1) into a plant (2) in which the bitumen and / or tar-containing solids are heated until solid and gaseous products are obtained; c) Making the remaining solids (3) available for further use, carrying out the following steps after step a) and before step b): A) Breaking up (4) the bitumen and / or tar-containing solids (1) so that particles (5, 6, 7, 8) of different sizes are present; B) Seven of the particles (5, 6, 7, 8) in at least two size classes; C) Mixing the particles (5, 6, 7, 8) of at least two size classes in a specified ratio; D) Feeding the mixture of particles (5, 6, 7, 8) into the system (2), characterized in that the heating of the bitumen and / or tar-containing solids to be processed in the system (2) takes place to a temperature between 600 °C and 800 °C.

Description

[0001] The invention relates to a method for processing bitumen- and / or tar-containing solids, in particular road demolition material consisting of chippings and bitumen and / or tar, comprising the steps: (a) provision of the bitumen and / or tar-containing solids to be processed; b) feeding the bitumen- and / or tar-containing solids to be processed to a plant, in particular a rotary kiln, in which the bitumen- and / or tar-containing solids are heated until solid and gaseous products are obtained; c) Provision of the remaining solids, in particular the chippings, for further recycling.

[0002] A generic method is known from DE 10 2009 025 361 A1.

[0003] For the recycling of bitumen- and / or tar-containing solids, it is crucial to determine whether they are also contaminated with polycyclic aromatic hydrocarbons (PAHs). For example, the particular focus in the case of reclaimed asphalt is on maximizing the reuse of old asphalt. This reuse is significantly influenced by the PAH content. The contamination determines whether the material is used or recycled.

[0004] Currently, reclaimed asphalt with low or no PAH contamination may be added to new asphalt. Mixing ratios must be observed to ensure that the old bitumen only accounts for a small proportion of the new mix to avoid negatively impacting the quality of the new road surface.

[0005] The key advantage, the recycling of chippings, which can account for 90 to 97% of the total mass depending on the asphalt, is uncontrolled. The individual chipping classes are not taken into account during reuse. This means that targeted composition is only possible to a limited extent with the use of recycled asphalt.

[0006] In cases of existing PAH contamination, the legislator predominantly promotes thermal recycling. During thermal recycling, the bitumen is separated from the chippings. In conventional incineration plants, the combustion temperature is in a range where outgassing can occur from the carbonate rock, making it unusable. Co-incineration results in a high ash content. In mono-incineration, sand is formed primarily through temperature-induced rock decomposition. Therefore, a solution is required that, on the one hand, removes the bitumen and / or tar and, on the other hand, delivers a usable product - in the case of reclaimed asphalt, chippings with primary material properties. The product must be completely free of PAH contamination and have an organic carbon content of less than one percent.

[0007] The topic of asphalt processing has already been studied several times. Since every asphalt plant uses a rotary kiln, it stands to reason that rotary kilns would also be used in asphalt recycling. One such solution is described in DE 10 2014 001 257 A1. While DE 29 31 367 A1, DE 34 47 079 A1, and DE 35 31 647 A1 describe the removal of pollutants from a product, they do not address the reusability of the raw material.

[0008] The above-mentioned DE 10 2009 025 361 A1 describes a plant for processing road demolition material that does not require specific material preparation and whose maximum operating temperature of 600 °C cannot guarantee that the organic carbon content will be significantly reduced. Similarly, DE 10 2012 016 882 B4 describes a plant for processing road demolition material. Again, specific material preparation is omitted, which is also not possible in this case due to the material selection and is therefore inefficient. This plant is described as mobile and is therefore limited to a pilot plant-scale throughput.

[0009] The basis for sensible material preparation is outlined in EP 0 810 276 A1. Here, the material is pre-sorted and treated according to its size. However, the planning is based on fixed ratios which, while technically desirable, represent an ideal, unattainable state in practice. The resulting fractions are then combined using a binder. Depending on the area of ​​application, a maximum bitumen and / or cement content is then defined. This, as well as the fixed distributions of the fractions, represents a practically ideal state. However, this concept is not practical, as it cannot capture the material properties and the ranges of variation in reclaimed asphalt. The use of a binder then aims at the direct use of this mixture and not at its removal, for example, of contaminants containing PAHs.

[0010] US Pat. No. 4,189,238 A follows a similar approach to EP 0 810 276 A1. In the latter document, the reclaimed asphalt is also fractionated by size and then treated at different gas temperatures according to size. The maximum gas temperature of the largest fraction is 1,000 °F, or approximately 540 °C. All fractions are finally combined for a further thermal treatment step. A material temperature of 225 °F is targeted, which corresponds to approximately 110 °C. The inventor is aware of the relationship between particle size and heating time; he deliberately strives for low temperatures in order to be able to reuse as much asphalt, including bitumen, as possible. The partial escape of volatile hydrocarbons is seen as a positive effect in terms of energy savings. This step does not yet occur in a targeted manner at these temperatures. Contamination containing PAHs remains unaffected.The multi-stage thermal process is not practical.

[0011] The invention is based on the object of further developing a generic method in such a way that it is possible to provide a further improved and more efficient recycling of bitumen- and tar-containing solids, in particular road demolition material, whereby high-quality chippings are to be obtained which can be reused.

[0012] Furthermore, the process is to be optimized from an energy perspective.

[0013] The solution to this problem by the invention provides that after step a) above and before step b) above, the following steps are carried out: A) breaking up the bitumen- and / or tar-containing solids, in particular in a roller crusher or impact mill, so that particles of different sizes are present; B) sieving the particles into at least two size classes; C) mixing the particles of at least two size classes in a predetermined ratio; D) feeding the mixture of particles into the plant, in particular into the rotary kiln, whereby according to the invention the bitumen- and / or tar-containing solids to be processed are heated in the plant to a temperature between 600 °C and 800 °C.

[0014] Sieving according to step B) above is preferably carried out into at least three, particularly preferably four, size classes. Sieving is preferably carried out into a first size class for a particle size between 0 mm and 4 mm, into a second size class for a particle size between 4 mm and 10 mm, into a third size class for a particle size between 10 mm and 20 mm, and optionally into a fourth size class for a particle size between 20 mm and 40 mm.

[0015] The mixing according to step C) above is preferably carried out in such a way that the mixture has a predetermined calorific value.

[0016] The mixing according to step C) above can also alternatively be carried out in such a way that all size classes obtained are combined according to their quantitative proportion.

[0017] A further alternative provides that the mixing according to step C) above is carried out in such a way that a predetermined ratio between the size classes obtained is maintained.

[0018] This proposed approach ensures that a defined degree of heterogeneity is always achieved, thus generally optimizing the recycling process of the material, especially the chippings. At the same time, it can be used to optimize energy efficiency, ensuring that the combustion process takes place in the best possible range.

[0019] A defined residence time within the plant, especially the rotary kiln, ensures that the chippings are not overheated but are nevertheless freed from their organic load.

[0020] By crushing and sieving, and subsequently combining the fractions, the material for combustion can be optimally selected and its properties defined. The material is always heterogeneous, which is due on the one hand to its lumpiness and on the other hand to the respective proportions of bitumen within the individual grain sizes. This problem is solved with the procedure described above, which involves first fractionating the crushed material and then re-mixing it in a defined manner. While this does not eliminate the heterogeneity and does not lead to homogeneity of the material, it does ensure that the distribution of the heterogeneity remains largely constant. This allows the combustion conditions to be better controlled and the process to be carried out more gently for the chippings.

[0021] Finally, the resulting chippings are screened into individual screening classes, allowing the primary material to be reused directly.

[0022] The provision of the remaining solids according to step c) above preferably also includes sieving the solids into different size classes.

[0023] The heat generated during heating of the bitumen and / or tar-containing solids to be processed in the plant, particularly in the rotary kiln, can be dissipated via a heat exchanger and used separately.

[0024] In this case, a particularly preferred embodiment of the proposed method provides that the heat generated is used at least partially to preheat the bitumen- and / or tar-containing solids to be processed before being fed in according to step b) above.

[0025] A rotary kiln is the preferred system for this purpose.

[0026] The proposed method enables efficient utilization of bitumen- and tar-containing solids, especially those containing PAHs. The proposed process thermally treats the solids, resulting in maximum material utilization of the raw material, allowing primary and / or secondary raw materials to be extracted from the input material. Heat is generated as a byproduct, some of which can be used internally and some of which can be discharged.

[0027] It is possible to use the heat of at least part of the gaseous product produced during heating.

[0028] During heating or combustion in the plant (i.e. in particular in the rotary kiln), the aim is to ensure that the organic carbon content in the carbon-containing solid raw material used is below 1%.

[0029] The proposed process is advantageously combined with other measures that are advantageous from an energy and ecological point of view.

[0030] In this way, the medium intended for heat utilization can be post-combusted to produce exhaust gas.

[0031] The exhaust gas can be subjected to dust removal.

[0032] Heat can be extracted from the exhaust gas via a heat exchanger and used for other purposes.

[0033] The cooled exhaust gas can be subjected to exhaust aftertreatment. Gas scrubbers or a gas scrubber column are preferred for this purpose.

[0034] After the material, in particular the chippings, has been extracted, it can be sieved so that material of different size classes or fractions can be obtained.

[0035] The process can be visually monitored to ensure smooth operation.

[0036] It is also possible that the extracted material, especially the chippings, is crushed to obtain further size classes.

[0037] The excess heat from the process can be used to preheat the bitumen and / or tar-containing solid and / or the air or oxygen demand.

[0038] During the preparation of the material (i.e. during the breaking up of the bitumen- and / or tar-containing solids), the particle size can be adjusted by means of a (roller) crusher, an (impact) mill, a grinder and / or a shredder, whereby a particle size of up to 200 mm, preferably up to 100 mm and particularly preferably up to 40 mm, is aimed for.

[0039] The bitumen- and / or tar-containing solids are preferably screened using a drum screen, a vibrating screen, a screening machine, and / or a filter into at least three fractions. One of these fractions may have a grain diameter of 0 mm to 10 mm, preferably 0 mm to 5 mm.

[0040] The mixing of the particles (at least two size classes) has the advantage of achieving a constant heterogeneity of the material, which then enters the rotary kiln.

[0041] Preferably, the material, and if necessary also the air and the natural gas used for firing, are preheated by means of a heat exchanger before the actual combustion takes place.

[0042] The rotary kiln is preferably directly heated and preferably operated in direct current direction.

[0043] The following has proven particularly effective for the combustion of the material compiled according to the invention: The combustion temperature is preferably between 180 °C and 900 °C, particularly preferably between 500 °C and 850 °C and most preferably between 600 °C and 800 °C.

[0044] The residence time in the plant (ie in particular in the rotary kiln) is preferably between 0.01 and 10.0 hours, particularly preferably between 0.05 and 5.0 hours and most preferably between 0.25 and 0.5 hours.

[0045] The particle size of the material when introduced into the plant (i.e. in particular into the rotary kiln) is preferably less than 200 mm, particularly preferably less than 80 mm and most preferably less than 40 mm.

[0046] The proportion of organic carbon in the material entering the plant (i.e. in particular in the rotary kiln) is preferably below 20% by mass, particularly preferably below 10% by mass and most particularly preferably below 6% by mass.

[0047] The heat can be utilized by an afterburner chamber downstream of the plant (i.e. in particular the rotary kiln), where afterburning of the exhaust gases takes place, preferably at a temperature of 800 °C to 1,200 °C, particularly preferably at 850 °C to 900 °C.

[0048] The recycling of the extracted material represents a provision of primary raw materials and / or secondary raw materials.

[0049] Furthermore, the exhaust gas can be dedusted using a cyclone or a filter.

[0050] Furthermore, the cooling of the exhaust gas can be provided by means of a heat exchanger, preferably in the form of a waste heat boiler, to cool the exhaust gas after dedusting; the waste heat can be used to generate steam or to heat water, thermal oil, heat transfer salt or air.

[0051] When treating exhaust gases to comply with legal requirements, nitrogen oxide and sulfur oxide limits are met; scrubbers, filters, or catalytic processes can be used for this purpose.

[0052] The cooling of the solid product can be carried out by means of a rotary tube cooler, whereby a product temperature in the range between 20 °C and 80 °C is aimed for, preferably between 30 °C and 50 °C.

[0053] The screening of the solid, cooled product (grit) into at least two screening fractions can be carried out using a drum screen, a screening machine, a vibrating screen and / or a filter.

[0054] Optical monitoring of the solid product and / or the product fractions can be carried out by optical sensors, whereby color deviations and / or geometric deviations can be detected.

[0055] The crushing of the solid product and / or the product fractions is preferably carried out by means of a mill, grinder, shredder and / or crusher.

[0056] The resulting heat can be used to preheat the bitumen- and / or tar-containing solid and / or the air provided for combustion and / or the natural gas required for combustion.

[0057] The proposed process is particularly used for the treatment of reclaimed asphalt containing PAHs.

[0058] The combustion preferably takes place in a plant in the form of a combustion reactor, wherein the combustion reactor preferably comprises a directly heated rotary kiln system (rotary kiln).

[0059] In the proposed process, the proportion of bitumen and / or tar in the bitumen- and tar-containing solid is preferably reduced to below 0.5% by combustion.

[0060] The drawing illustrates an embodiment of the invention. The sole figure schematically shows an arrangement for recycling road demolition material, whereby the chippings contained therein are recovered.

[0061] The figure initially shows a container 9 in which bitumen- and / or tar-containing solid 1 is stored. This solid originates from a road whose surface has been milled. The solid 1 is to be processed to extract the chippings contained within it; this chippings are to be recycled. In this regard, explicit reference is made to the above-mentioned DE 10 2009 025 361 A1, where this process is generally described.

[0062] Accordingly, the solid 1 is provided in the form of road demolition material from the container 9 and then transferred to a facility 2 in the form of a rotary kiln. The solid 1 is combusted in the rotary kiln 2, producing solid and gaseous products. The chippings 3 thus obtained, freed from bitumen or tar, are then provided for recycling.

[0063] It is essential that the following steps are carried out between the provision of the solid 1 from the container 9 and the introduction of the material into the rotary kiln 2: First, the bitumen- and / or tar-containing solids 1 are broken up using a crusher 4. This is typically a roller crusher or an impact mill. The crushing of solid 1 results in particles 5, 6, 7, and 8 of varying sizes.

[0064] These particles are then sieved, for which a screening machine 10 is used. In this case, the screening machine 10 separates the broken particles into four size classes: The first size class provides a particle size between 0 mm and 4 mm, the second size class a particle size between 4 mm and 10 mm, the third size class a particle size between 10 mm and 20 mm, and the fourth size class a particle size between 20 mm and 40 mm. The sieved particles are transferred to the respective silos 11.

[0065] Subsequently, the particles 5, 6, 7, and 8 of the four different size classes are mixed in a predetermined ratio. For this purpose, dosing units 12 are provided, which are assigned to each silo 11 and can be used to discharge a defined amount of particles (per unit of time), whereby the particles 5, 6, 7, and 8 are then mixed (this is not shown in detail). The mixture is fed to the rotary kiln 2 and processed there in the manner described.

[0066] The proposed concept therefore envisages that the solid 1 is first crushed. The crushed material then enters a screening machine, where the four aforementioned fractions are screened. The aforementioned screenings are based on the chippings classes of the asphalt or concrete specifications. The fractions are placed in their respective silos 11. From there, they are transported via the dosing units 12 to a common conveyor belt. This then transports the defined mixture either directly to the rotary kiln; however, it can also be initially transferred to an interim storage facility (not shown).

[0067] As explained above, the composition of the mixture can in principle be done in different ways: First, the calorific value of the individual fractions is assessed, thus defining the calorific value for the rotary kiln. The underlying idea here is that the bitumen content, and thus the calorific value, is higher in the finer fractions. The rotary kiln then operates optimally in terms of energy input, but not necessarily in terms of overall throughput.

[0068] Alternatively, a mixture based on the proportions of the resulting fractions is possible. In this case, the dosing units 12 independently control the mixture so that the individual fractions are always added according to their respective proportions. This means that there is no difference compared to the classic and previously known quantity distribution, but the mixture on the conveyor belt is significantly more homogeneous due to the aforementioned process and can therefore be processed more easily.

[0069] Alternatively, it is also possible to mix the fractions in a fixed ratio. The most common fraction is the decisive factor. For larger fractions with very large particle sizes, the material can be broken down again.

[0070] The result is always advantageous in that a certain limitation of the calorific value is always achieved while at the same time ensuring the throughput.

[0071] Experiments on this topic have shown that the proposed approach leads to better results than those achievable with previously known methods. By fractionating the crushed material and subsequently mixing it in the manner described, negative effects resulting from a highly heterogeneous material distribution could be avoided.

[0072] Without the proposed approach, the auxiliary firing partially reaches its limits and the thermodynamics within the reactor (rotary kiln) are more difficult to control.

[0073] Behind the rotary kiln 2, which is not further shown, the remaining solids can be prepared in such a way that different size classes are provided by sieving the solids obtained.

[0074] Preferably, the rotary kiln combustion is coupled with the utilization of the products, i.e. in particular the utilization of heat and the material utilization.

[0075] During combustion in plant 2 (i.e. in the rotary kiln), it is preferred that combustion takes place at a low temperature, at which the bitumen or tars are burned, but the outgassing or deacidification from the rock is prevented.

[0076] Preference is given to the content of organic carbon (C org ) of the material used in Plant 2. The organic carbon content of the material used in the rotary kiln is preferably between 1% and 50%, particularly preferably between 2% and 6%. Combustion oxidizes the organic carbon to gases. The solid is thereby separated from its organic load.

[0077] Another relevant property of the bitumen- and / or tar-containing solid is its grain size and grain size distribution. During the extraction of the bitumen- and / or tar-containing solids, a heterogeneous grain size arises. Transportation, intermediate storage, and / or further transport naturally result in a separation of finer and coarser fractions. Crushing the material and selectively screening it into at least two fractions, as well as the subsequent defined adjustment of the fraction proportions, allows for optimal, constant heterogeneity to be achieved for the process. This allows the combustion process in the plant (i.e., particularly in the rotary kiln) to run more consistently, increasing combustion efficiency compared to an undefined material composition.

[0078] The aforementioned adjustment of the grain size may also be advantageous if the grain size of the bitumen- and / or tar-containing solids provided is already sufficiently small for combustion in Plant 2.

[0079] Preheating of the material, the air, and, if applicable, the natural gas used for combustion can be achieved using any suitable heat exchange process. Preheating is preferably carried out using a gas-to-solid heat exchanger, a liquid-to-solid heat exchanger, or a combination thereof.

[0080] In this respect, it is possible to supply heat using a heat transfer medium, whereby the heat transfer medium is thermal oil, air or a heat transfer salt.

[0081] Preheating can be carried out at temperatures between 50 °C and 250 °C, preferably between 65 °C and 100 °C, and particularly preferably between 70 °C and 80 °C. To avoid undesirable side reactions, it may be advantageous to carry out preheating indirectly.

[0082] In Plant 2, specifically in the rotary kiln, the material is burned. This term refers to oxidation achieved exclusively at high temperatures, which is carried out in Plant 2. Preferably, the rotary kiln is heated directly for this purpose, and preferably operated using the cocurrent principle, meaning that the material feed and combustion take place on one side. The material discharge takes place on the opposite side.

[0083] It may be sufficient and advantageous to use only a portion of the provided bitumen- and / or tar-containing solid and, after the described treatment, to mix a portion of this with the remaining portion of the provided solid. It may also be advantageous to use only a portion of the provided bitumen- and / or tar-containing solid for preheating and to mix the heated portion thus obtained with additional provided bitumen- and / or tar-containing solid.

[0084] It is advantageous that the combustion takes place depending on the product mixture formed, wherein at least one further recorded property of the bitumen- and / or tea-containing solid is adapted, ie one or more combustion conditions are adapted to the product mixture provided before it reaches plant 2.

[0085] The relevant properties of the product mixture are therefore recorded before the combustion step and can be adapted as desired depending on the process.

[0086] The bitumen and / or tea-containing solid provided contains partly carbonaceous substances and partly inorganic substances which are in solid form under standard conditions (25 °C; 101.325 kPa).

[0087] The control of plant 2, in particular of the rotary kiln, i.e. the selection of the conditions for combustion, is carried out depending on the above-mentioned recorded properties of the bitumen- and / or tar-containing solid.

[0088] In principle, any device known to the person skilled in the art that is suitable for combustion and allows a choice of combustion conditions can be used to carry out the combustion.

[0089] Depending on the selected combustion conditions, the combination of the measured properties of the bitumen- and / or tar-containing solid can be advantageous for the overall process, particularly with regard to overall energy efficiency and heat yield. For example, measuring the organic carbon content and particle size of the bitumen- and / or tar-containing solid and selecting the appropriate combustion temperature and residence time can be advantageous for overall energy efficiency and, where appropriate, heat yield. List of reference symbols: 1 bitumen and / or tar-containing solid 2 Combustion plant (rotary kiln) 3 gravel 4 crushers 5 first size class particles 6 second size class particles 7 particles of the third size class 8 particles of the fourth size class 9 containers 10 screening machine 11 Silo 12 Dosing unit

Claims

[1] Process for processing bitumen and / or tar-containing solids (1), comprising the steps: (a) providing the bitumen- and / or tar-containing solids to be processed (1); b) feeding the bitumen- and / or tar-containing solids (1) to be processed to a plant (2) in which the bitumen- and / or tar-containing solids are heated until solid and gaseous products are present; c) providing the remaining solids (3) for further recycling, whereby after step a) and before step b) the following steps are carried out: A) breaking up (4) the bitumen- and / or tar-containing solids (1) so that particles (5, 6, 7, 8) of different sizes are present; B) sieving the particles (5, 6, 7, 8) into at least two size classes; C) mixing the particles (5, 6, 7, 8) of at least two size classes in a predetermined ratio; D) feeding the mixture of particles (5, 6, 7, 8) into the system (2), characterized by that the heating of the bitumen- and / or tar-containing solids to be processed takes place in the plant (2) to a temperature between 600 °C and 800 °C. [2] Method according to claim 1, characterized by that the screening according to step B) according to claim 1 is carried out in at least three, preferably four size classes. [3] Method according to claim 2, characterized by that the sieving is carried out into a first size class for a particle size between 0 mm and 4 mm, into a second size class for a particle size between 4 mm and 10 mm and into a third size class for a particle size between 10 mm and 20 mm and preferably into a fourth size class for a particle size between 20 mm and 40 mm. [4] Method according to one of claims 1 to 3, characterized bythat the mixing according to step C) of claim 1 is carried out such that the mixture has a predetermined calorific value. [5] Method according to one of claims 1 to 3, characterized by that the mixing according to step C) of claim 1 is carried out in such a way that all size classes obtained are combined according to their quantitative proportion. [6] Method according to one of claims 1 to 3, characterized by that the mixing according to step C) of claim 1 is carried out in such a way that a predetermined quantitative ratio between the size classes obtained is maintained. [7] Method according to one of claims 1 to 6, characterized by that providing the remaining solids according to step c) of claim 1 comprises sieving the solids into different size classes. [8] Method according to one of claims 1 to 7, characterized bythat the heat generated during heating of the bitumen- and / or tar-containing solids to be processed in the plant (2) is dissipated via a heat exchanger and fed into a separate utilisation facility. [9] Method according to claim 8, characterized by that the resulting heat is used at least partially to preheat the bitumen- and / or tar-containing solids to be processed before feeding according to step b) of claim 1. [10] Method according to one of claims 1 to 9, characterized by that a rotary kiln is used as plant (2).

Images