LU88140A1 - Process and plant for granulating old tires - Google Patents

Description

PROCESS PHD SYSTEM FOR GRANULATING OLD TIRES

The invention relates to a method and a system for granulating old tires, using a subcooling which promotes brittleness.

It is known to cool old tires to temperatures of around minus 60 ° C or lower, so that the rubber becomes hard and brittle and can then be crushed in a suitable device and separated from the other components of the tire (steel wires, textile fabric).

Such a system has already been described in VDI News No. 39/1974, the used tires being cooled in a slightly inclined rotary drum and then crushed by impact mills. However, this system is characterized by a relatively high coolant consumption. Systems of this type can therefore hardly be used economically.

In a later known embodiment, the rotary drum is replaced by a cooling tunnel which consists of a closed screw conveyor which conveys upwards and into which the coolant is introduced via nozzles in the middle to upper region. A throw-in and discharge lock reduce the coolant loss when feeding the system. The connected shredding machine e.g. an impact mill is also included in this system in the largely sealed and insulated cold room, which has a favorable effect on the performance of the shredding machine.

To achieve economically justifiable operation of such systems, the coolant requirement would have to be reduced even further. Likewise, the energy requirement for shredding the used tires would have to be optimized and / or the added value of the end products obtained (rubber granulate, steel, textile fabric = plastics) would have to be increased by a qualitatively better shredding and sorting result. Especially the separation of the

Rubber from the tire reinforcements would have to be improved.

In this context, it must be mentioned that the industry today has a need for reused rubber in granular form for various applications. However, these granules must be characterized by a uniform particle size distribution in fineness ranges from a few millimeters to a few hundredths of a millimeter and largely free of foreign bodies. Such a result is not achieved by the existing plants, which are relatively simple in their structure, so that there is only a small supplement for the end product of these plants.

The present invention is based on the problem of simultaneously making better use of the coolant, substantially increasing the effectiveness of the comminution process (reducing the energy requirement and increasing the material throughput) and the quality, ie the fineness, uniformity, particle size and sorting sharpness of the end products obtained to improve.

This problem is solved with a method and a system according to claims 1 and 5. The invention is based on the following considerations.

An optimization of the energy consumption of the shredding and separation process can be achieved for the first time by dividing the shredding into several partial sections, so that shredding techniques that are matched to the particle size can be used. For the pre-crushing of approximately plate-sized tire pieces, for example, a type of roller crusher is suitable, which breaks the plate-sized, cold-brittle tire pieces into approximately palm-sized tire pieces between two counter-rotating rollers which are provided with cams. The latter, on the other hand, are optimally shredded in a brittle state in a vertical impact mill specially designed for this process. Fine grinding, on the other hand, is preferably carried out in one or more roller mills such as cylinder mills or bowl mills.

By coordinating the shredding technology (i.e. the fracture physics) with the respective particle size, the energy requirement for shredding is significantly reduced. This also means that the heating of the particles / parts to be shredded in the shredding machines is significantly reduced and the coolant requirement is also reduced.

Furthermore, the division of the comminution process into several sub-steps allows intermediate cooling of the particles / parts to be comminuted, which has a favorable effect on the fracture physics in the comminution process. Before each next comminution step, the particles / parts which have warmed up in the previous comminution step are subcooled again, so that they can be further comminuted in an ideal, cold-brittle state in the next comminution step. This will also make it a far better one

The rubber has been separated from the tire reinforcements.

With regard to the optimal use of the coolant, the following considerations are also fundamental

Importance. By gradually shredding a *

With every shredding step, the area of the global tire mass that is crucial for heat transfer increases. This also intensifies the heat transfer from coolant to the tire mass, i.e. that with the same temperature difference between the tire parts and the coolant, the cooling rate of the global tire mass increases, or that with the same cooling speed of the global comminuted tire mass, a low temperature difference (i.e. with a higher coolant temperature) can be used. In the present invention, this knowledge is used in that the vaporized and already slightly heated gaseous coolant, which of course has a lower cooling capacity than the liquid coolant, is used to cool the tire mass in the granular state. However, this is only possible if, as in the present invention, comminution and granulation in an integrated, closed, largely gas-tight and heat-insulated system have been successively slated.

It must also be taken into account that the best use of the coolant occurs when the evaporation of the coolant takes place directly on the surface of the body to be cooled and not on the walls or other parts of the system. For this reason, appropriate cooling tunnels were provided for the cooling of the even larger tire parts, on which these tire parts are sprayed with refrigerant via nozzles on a double chain enclosed on all sides of the conveyor conveyor, on the upper, conveying run. The liquid refrigerant is dosed so that accumulation of refrigerant in the liquid state in the system is largely avoided.

In the case of the granulate, on the other hand, it has been found that cooling with a vaporous coolant, without further spraying with a liquid coolant, gives good results, especially when the granulate is in suspension in the gaseous cooling medium and is subjected to a turbulent flow with it. With larger tire parts, however, this is not the case because a gaseous coolant would result in a much poorer heat transfer dynamics, which would result in the material in the cooling tunnels being too long, i.e. material flow for the system would be too low. It is therefore advantageous to recover the coolant evaporated during the cooling of the larger tire parts for the cooling of the granular tire parts, as is provided in the present invention.

In order to achieve an even better utilization of the coolant, the method of the present invention provides to use the residual cold from the granulate after the shredding process for the pre-cooling of the old tires to be shredded. In accordance with the present method, these used tires are pre-cooled in cold rooms (for example overnight) and then shredded into plate-sized pieces before the actual system is fitted. How this cold recovery works exactly is described in the embodiment of the invention.

It should also be pointed out that the fine crushing in the roller mills must be preceded by a metal separation in order to prevent larger metal parts (e.g. wire mesh) from damaging the rollers. A further metal separation should take place after the fine comminution in order to sort out all fine iron particles from the granulate.

Another advantage of the process is that the end products obtained are high-quality raw materials. For example, the size of the granulate can be adapted to industrial requirements in fine grinding. For example, it is possible to produce rubber powder for tire retreading etc. with this system. In order to separate the rubber granulate on the textile fabric, an electrostatic separator can also be installed downstream of the system.

All of the aforementioned advantages and features of the method advantageously complement one another through the combination and dynamic on which the invention is based

Sequence of the individual steps of the process.

Further advantages and features of the method result from the exemplary embodiment of a system according to the invention described below. This system is described in more detail with reference to the drawings according to structure and mode of action for illustration purposes.

FIG. 1 shows a block diagram which shows the construction of a system according to the invention; - Figure 2, a schematic cross section through the loading lock / the first cooling tunnel and the first coarse shredder; - Figure 3, a schematic cross section through an impact mill for a system according to the invention.

The block diagram of FIG. 1 represents the essential system components with their process engineering links. These system components are described below in accordance with the dynamic sequence of the individual sub-steps of the method. However, only those system components that represent the focal points of the present invention are dealt with in detail. Figures 2 and 3 show corresponding details of these system components in schematically executed cross sections.

First, the used tires are pre-cooled in one or more cold rooms 10. The volume of these cooling rooms should be designed according to the daily budget for the amount of used tires to be processed. The tires, which have been pre-cooled overnight, for example, are then pre-shredded into approximately plate-sized pieces of tire 15 in a shredder 20 before they are fed via a continuous conveyor 22 through a lock 30 into an insertion shaft 38 which opens into a first cooling tunnel 40 (see FIG. 2 ).

The lock 30 comprises an entrance flap 31 and an exit flap 32, which are arranged one above the other in the vertical insertion chute 38 and, in the closed state, delimit a sluice chamber 35 in the insertion chute 38, but in the open state free access from the

Allow continuous conveyor 32 to the cooling tunnel 40. The pre-shredded tire pieces 15 fall from the continuous conveyor 22 onto the closed entry flap 31. This entry flap 31 opens and the tire pieces 15 fall onto the closed exit flap 32. Then the entry flap 31 closes again and after it is closed, the exit flap 32 can open so that the tire parts 15 fall onto a continuous conveyor 41 in the first cooling tunnel 40. This assembly lock 30 serves the purpose of preventing loss of coolant when assembling the system. In addition, this lock can also be equipped with an overpressure / underpressure control (33 ', 34'), which will be described in more detail later.

The cooling tunnel 40 is an inclined, heat-insulated and gas-tight channel rising from the exit of the insertion shaft 38 to a second insertion shaft 72. The continuous conveyor 41 and a coolant distribution 50 are integrated in the cooling tunnel 40.

The continuous conveyor 41 is preferably a double chain driving conveyor, as is known from hard coal mining. The continuous conveyor 41 comprises a conveying strand 44 and a returning strand 43. In the conveying strand 44, plate-shaped carriers 45 are pulled by laterally arranged chains 43 over a trough rising in the conveying direction, so that the tire parts 15 are conveyed upwards into the second insertion shaft 72 . The coolant distribution 50, which has a plurality of nozzles 52, is installed above the conveying strand 44. Those nozzles 52 spray a liquid coolant, preferably liquid nitrogen, directly onto the tire parts 15 which are located on the conveying strand 44. The transport speed, i.e. The dwell time of the tire pieces in the cooling tunnel 40 and the coolant throughput are to be selected so that the tire pieces 15 have a temperature of approximately minus 60 ° C. at the entrance to the second insertion slot 72. This can be achieved by a temperature control which controls the coolant throughput and / or the conveyor speed as a function of actual temperature values measured at several system points. The temperature setpoints at these selected contact points are determined empirically.

The continuous conveyor 41 is the plant component which is most exposed to the liquid coolant. Therefore, all mechanically stressed parts should preferably be made of plastics, which are characterized by high tensile strength even at low temperatures (approx. Minus 100 ° C) (for example fiber materials or fiber-reinforced plastics that are not prone to brittleness).

The cold-brittle, plate-sized tire pieces 15 fall out of the continuous conveyor 41 into a first coarse shredder 70, which is integrated in the heat-insulated, gas-tight insertion shaft 72. The coarse shredder 70 is preferably a roll crusher. This means that the approximately plate-sized tire pieces 15, which are still cold-brittle after exiting the first cooling tunnel 40, are broken into two tire pieces 16, approximately the size of the palm of a hand, between two rollers rotating in opposite directions, which are provided with cams. This roller crusher is only shown schematically in FIG.

The tire pieces 16 then fall out of the roll crusher onto a continuous conveyor 81 into a second cooling tunnel 80. This second cooling tunnel 80 is basically identical to the first cooling tunnel 40 and is therefore not described further. This also applies to all of its components such as continuous conveyors, coolant distribution and regulation.

From the second tunnel 80, the tire pieces 16 pass from the continuous conveyor 81 into a second coarse shredder 100. This coarse shredder 100 is preferably an impact mill, which was specially developed for this plant. It is shown in a schematic cross section in FIG. 3. This impact mill consists of an elongated vertical hollow body with a cylindrical inner wall 101. The body of the impact mill naturally has, like all other parts of the system, a heat-insulated and gas-tight casing 25. At the upper base of the inner cylinder there is a filler neck 102 which is connected to the cooling tunnel 80 is connected, and in which the continuous conveyor 81 opens. Through these filler supports 102, the cold-brittle tire pieces enter a first grinding chamber 112, which is delimited by annular inlet and outlet baffles (116, 117) in the hollow body of the impact mill. In this grinding chamber 112, a rotor 105 rotates on a vertical shaft 103 which is in the vertical axis the impact mill 100 is arranged and equipped with appropriate drive means 119. On the cylindrical inner wall 101 of the grinding chamber 112, a plurality of baffle bars 114 are arranged in the axial direction, i.e. that the median planes of each baffle 114, extended in thought, each contain the shaft axis of the rotor 105. These baffle strips 114 delimit a cylindrical cavity in the grinding chamber, in which the rotor consisting of at least two diametrically arranged, same-sized flails 106, 107 rotates with a function-related play to the baffle strips. The annular inlet and outlet baffles (116, 117) narrow the inlet and outlet cross-sections of the grinding chamber 112 conically from the cylindrical inner wall in the direction of the material flow, thus defining a circular inlet and outlet opening 109 and 110 for the grinding chamber 112, the diameter of each is smaller than the diameter of the rotor 105.

This ensures that the tire pieces 16 falling through the entrance opening 109 are gripped by one of the two flails 106, 107 and are thrown against the bumper strips 114. The exit chicane 117 forms the entrance chicane of a next grinding chamber 112 '.

At least three such grinding chambers 112 are preferably arranged one above the other in the impact mill 100, the last grinding chamber opening into an outlet connection 104 of the impact mill 100 (FIG. 3 shows an impact mill with four grinding chambers).

The drive means 119 and the shaft 103 can be designed such that the rotors 105 rotate in opposite directions in two superimposed grinding chambers, which has a favorable effect on the fracture physics, i.e. the crushing result affects.

After the last grinding chamber, a scoop 108 rotating around the shaft 103 at a low speed can be arranged in front of the outlet opening 104, which blade facilitates the emptying of the material to be ground into the outlet nozzle 104. At the exit of the impact mill 100, the ground material then falls through a first metal separator 120 and is fed into a solid / fluid flow ring 130. The coarsest metal parts are separated out in the metal separator 120.

The solid / fluid flow ring 130 is a closed pipe system 131, 133 in which the tire particles are transported in suspension in a gaseous conveying medium. The pumped medium is the coolant evaporated in the two cooling tunnels 40, 80.

The solid / fluid flow ring comprises a conveying pipeline 131 (represented by a double line with blackened sections in FIG. 1), which in turn comprises a feed device 132 for the tire particles, at least one fine shredder 140, an additional metal separator 150 and opens into a cyclone separator 137, in which the tire particles are separated from the pumped medium (gaseous coolant). The ring 130 is connected via a second non-conveying line 133 (represented by a simple double line in FIG. 1), between the cyclone separator 137 and the

Feed device 132, closed for the pumped medium. This second line 133 conveys the conveyed medium (coolant) recovered in the cyclone separator 137 and contains at least one fan 135 which generates the solid / fluid flow. This fan 135, which, as mentioned, is located between the cyclone separator 137 and the feed point 132 in the line 133, is still on the pressure side via a line 34 and on the suction side via a line 33 to the lock chamber 39 of the lock 30.

The lines 33 and 34 each comprise a shut-off device 33 ', 34' which enable said overpressure / underpressure control for the lock chamber 31. As mentioned, this overpressure / underpressure control has the purpose of further reducing the coolant loss when feeding the system. This overpressure / underpressure control works as follows. If the flap 31 of the lock 30 is closed and the flap 32 is opened, the shut-off device 33 'in line 33 is open, but that in line 34 is closed. The blower 135 then sucks cold gaseous coolant from the cooling tunnel 40 and the cooling tunnel 80 into the lock space 39 and into the solid / fluid delivery ring 130 via the line 33. On the other hand, if one wants to open the lock flap 31, the lock flap 32 is first closed, then the valve 34 'is opened so that the closed lock chamber 39 is flushed with a delivery flow branched off from the line 133 via line 34 and line 33. This flushing of the lock chamber 39 avoids that when the flap 31 is opened, too much gaseous coolant is lost from the cooling tunnel 40, which has a much lower temperature (ie a larger cooling capacity) than the coolant in line 133 The lock valve 31 open closes the two locking devices 33 'and 34'.

As mentioned, the fine mill 140 is connected to the conveying pipeline 131 and is itself gas-tight and heat-insulated. It is, for example, a roller mill with two roller cylinders rotating in opposite directions, the distance between the roller cylinders, i.e. the fineness of the ground material is adjustable. With such a roller mill, tire particles can be crushed down to a granulate size of approx. 1 to 2 mm. At this point in time, however, the granulate still contains steel particles which would damage the roller cylinders if the roller spacing was less than 1-2 mm.

However, if a finer granulate (for example smaller than 1mm) is required, a second roller mill can be installed after another metal separation 150. Alternatively, the fine mill 140 can also consist of a roller bowl mill, which is less susceptible to steel particles contained in the granulate. In any case, a metal deposition 150 should still be carried out after the fine comminution.

The metal deposition 150, as well as the metal deposition 120, is preferably carried out in a device where the granulate falls between one or two rotating magnetic rollers, the shredded steel tire reinforcements sticking to the magnetic rollers and being ejected into a separate transport tunnel, where they are then compressed in a press. The metal waste can be exported from the plant via a lock similar to lock 30.

In the cyclone separator 137, the granulate, which still consists of rubber and textile particles, is separated from the conveying medium and passes through a closed conveying device 139 into a closed, thermally insulated intermediate container 161. This intermediate container 161 can be connected at the lower end via a cellular wheel lock 180 or the like Device, can be continuously emptied onto another transport device 181.

Conveyor 139 may be a simple down pipe, i.e. the cyclone separator 137 is located above the intermediate container 161. Alternatively, however, a closed continuous conveyor can also be implemented, or a second solid / fluid flow can be built up with a blower.

In the intermediate container 161, the filling level is kept quasi-constant via the cellular wheel sluice 180, so that there is always a quasi-constant granulate mass 169 in the intermediate container 161. Since this granulate mass 169 is still far colder than the ambient temperature, it makes sense to use this residual cold to precool the tire cold stores 10.

This is done by means of a device 160 which is described in more detail below and which, if desired, can supplement the system. This device 160 essentially consists of a supply air duct system 175 with a supply air fan 171 and an exhaust air duct system 165 with an exhaust air fan 163, which, via the intermediate container 161, represent a circulating air system with recooling for the cooling rooms 10. The fan 163 draws air from the cooling rooms 10 and blows this air into the granulate mass 169 via a corresponding device 167, for example a porous or perforated tube. This air cools in contact with the granulate mass 169 and is sucked off by the fan 171 via a device similar to device 167 in order to be blown back into the cooling rooms via the duct system 175.

It should also be mentioned that, of course, from the lock 30 to the cellular wheel lock 180, all system parts have a heat-insulated and gas-tight casing 25. This casing 25 is preferably of sandwich construction and consists of an insulating layer, for example made of plastic foam, between an outer and inner metal wall, for example made of corrosion-resistant or corrosion-resistant steels, bridging between the inner wall and outer wall should be largely avoided, and the inner wall forms the gas-tight envelope. From the cooling rooms to the lock, the system only needs to be heat-insulated but not gas-tight. All shaft exits are of course sealed accordingly, this can be done, for example, via a back pressure chamber.

At the exit of the cell lock 180, the granulate still consists of rubber and textile particles, the latter resulting from the shredded fabric base of the tire. If a sorting of these two components is still desired, the conveying device 181 should open into a textile particle separator 183, which separates the textile parts from the rubber granulate, for example by electrostatic means.

The method of the present invention brings about a substantial reduction in the comminution energy, better utilization of the coolant and better quality of the end product rubber granulate through an intelligent combination and linking of several individual steps.

The plant of the present invention is specially adapted to this method and has new ways of granulating used tires both in their composition and in essential parts of the plant. The use of nitrogen as a coolant means that it is completely environmentally friendly.

Claims (18)

1. Process for shredding old tires using undercooling which promotes brittleness, characterized in that the shredding of roughly pre-shredded tire pieces takes place in a continuous process in several shredding steps connected in series, adapted to the respective piece or particle size, that these shredding steps At least one coarse comminution and one fine comminution comprise that the tire pieces or particles to be comminuted are each intercooled before each comminution step, that this intermediate cooling takes place before the coarse comminution in that the tire pieces are sprayed in a metered manner with a liquid coolant which has an evaporation temperature below minus 100 ° C and, when evaporated, removes the heat of vaporization from the surface of the tire pieces and cools them down to approximately minus 60 ° C so that the vaporized gaseous cooling medium The medium used as a conveying medium in a solid / fluid flow for the tire particles after the last coarse comminution until after the last fine comminution is that after the fine comminution, the gaseous coolant is recovered in order to be used again as a conveying medium or to reduce coolant losses in system locks, before the first Fine crushing A first separation of the metallic reinforcements contained in the tire takes place such that this first separation of metal parts is at least supplemented by a second separation which takes place after or during the fine crushing. 2. The method according to claim 1, characterized in that said coolant is nitrogen. 3. The method according to claim 1 or 2, characterized in that the waste tires to be shredded are stored in cold rooms (10) in order to then be roughly shredded into approximately plate-sized pieces. 4. The method according to claim 1, 2 or 3, characterized in that the residual cold which is still contained in the granules after the fine comminution is recovered in an intermediate container (161) for cooling the cooling rooms (10). 5. Plant for the method described in claim 1 or 2, characterized by at least the following devices connected in series in the material flow direction, namely an assembly lock (30), a first closed cooling tunnel with an integrated continuous conveyor (41), a first coarse shredder (70) , a second closed cooling tunnel (80) with an integrated continuous conveyor (81), a second coarse shredder (100), a first metal separator (120), a blower (135) for the purpose of producing a solid / fluid flow after the second coarse shredder (100 ), a first fine mill (140), a second metal separator (150), a cyclone (137) for separating the conveying medium and the granulate, said devices being connected by a gas-tight duct system and being largely gas-tight even to the outside, so that the entire system works under a nitrogen pressure, and with all the jackets (25) of the An location are insulated. 6. Plant according to claim 5, characterized in that the cyclone (137) is connected via a closed conveyor (139) to a heat-insulated intermediate container (161), that suction and injection channels (167) are provided in the intermediate container, and that these suction and injection ducts are connected to the cooling rooms (10) via a closed air circuit (160). 7. Plant according to claim 5 or 6, characterized in that in the first and second cooling tunnels (40, 80) integrated continuous conveyors (41, 81) are double chain driver conveyors, in which, between two laterally arranged pull chains (46), plate-shaped Carriers (45) are fastened, which are arranged in the conveying section (44) such that they can be pulled over a channel (47) which rises in the conveying direction, wherein. Both the conveying strand (44) and the moving strand (43) are located within the cooling tunnel (40, 80). 8. Plant according to claim 7, characterized in that mechanically stressed, the cold exposed parts of the double chain driver conveyor (41, 81) are made of plastics which are characterized by high tensile strength even at low temperatures. 9. Plant according to claim 7 or 8, characterized in that the coolant spray nozzles (52) are arranged above the conveying strand (44). 10th System according to claim 9, characterized in that a coolant metering device is included as an actuator in a closed temperature control loop. 11. Plant according to one of claims 5 to 10, characterized in that the first coarse shredder (70) is a roller crusher with two rollers rotating in opposite directions, which are provided with cams. 12. Plant according to one of claims 5 to 11, characterized in that the second coarse shredder (100). is an impact mill. 13. Plant according to claim 12, characterized in that the impact mill (100) consists of a vertical, elongated hollow body with a cylindrical inner wall (101), that in this cylindrical hollow body there is a vertical shaft (103) with at least three rotors (105) is located, these rotors being arranged one above the other and consisting of at least two diametrically opposed flails (106, 107), the free cross section of the impact mill being conical from the cylindrical inner wall (101) in front of the first rotor (105) and after each further rotor is tapered, so that a cylindrical grinding chamber (112) is delimited for each rotor within the cylindrical body, with an outlet and inlet opening (109, 110) tapering conically in the direction of flow, so that a plurality of baffle strips (114 ) on the cylindrical inner wall (101) in the axial direction that the rotor (105) in the grinding chamber (112) in a v cylindrical cavity defined on the baffle bars (114) is rotatably arranged with a function-related play to the baffle bars (114), the diameter of the rotor (105) being larger than the smallest diameter of the conically tapered inlet opening (109) of the respective grinding chamber (112) . 14. Plant according to claim 13, characterized in that two successive rotors (105) are each driven in opposite directions. 15. Plant according to one of claims 5 to 14, characterized in that one or more magnetic rollers are rotatably arranged in said first and second metal separators (120, 150). 16. Plant according to one of claims 5 to 15, characterized in that the first fine mill (140) is a roller mill with two counter-driven roller cylinders, the distance between the roller cylinders i.e. the fineness of the ground material is adjustable. 17. Plant according to one of claims 5 to 15, characterized in that the first fine mill is a roller mill. 18. Plant according to one of claims 5 to 17, characterized in that the intermediate container (161) via a cellular wheel sluice (180) and a continuous conveyor (181) is connected to an electrostatic separator (183).