Abstract:
A plant and a method for the recycling of plastics, preferably PET, including a switching device for switching between a first process line for a first production process for the production of a first recycling product, in particular pellets, and a second process line for a production process for the production of a second recycling product, in particular flakes, so as to render the recycling process more flexible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of priority of German Application No. 102011005568.1, filed Mar. 15, 2011. The entire text of the priority application is incorporated herein by reference in its entirety. 
       FIELD OF THE DISCLOSURE 
       [0002]    The disclosure relates to a plant and a method for the recycling of plastics, preferably PET. 
       BACKGROUND 
       [0003]    PET is used on a large scale for containers in the food industry, especially for beverage bottles. In consequence, large quantities of spent waste containers are produced, which can no longer be returned to the filling process. Methods and plants for recycling these waste containers and process them to obtain again a PET source material suited for use with food, for the production of new containers are already known. Such a recycling plant may be provided directly upstream of a production line for the production of new PET containers, where the recycled product coming from the recycling plant can directly be introduced, for example, into an injection molding machine for the production of preforms as starting product for new PET bottles. 
         [0004]    There are recycling plants for PET, which are each designed for a specific type of recycling product. For example, the recycling plant may be designed for the production of so-called flakes or the production of pellets. In principle, flakes are the products from a grinder, which have been cleaned, sorted and decontaminated for use in foodstuffs. Pellets are products from an extruder, where they were homogenized by thermal influence. Both production methods have advantages and disadvantages. The advantages of the flake process lie, for example, in a small energy input, in the fact that no acetaldehyde is formed, that the intrinsic viscosity is not reduced, that possibly contained foreign plastics cannot coalesce, and that drying is possible at low temperatures. Disadvantages of the flake process are that flakes are less suitable for being admixed to newly produced PET (virgin PET) and that foreign plastics can oxidize. The advantages of the pellet process lie in a simple and unproblematic admixture to virgin material, and in the use of a melt filter filtration technique for removing finest particles. The disadvantages of the pellet process lie in a considerably greater energy input, in the risk that acetaldehyde is formed, and that foreign plastics may coalesce, so that no homogenous PET is obtained. 
         [0005]    Due to this fact both processes are in use and are employed, depending on the interests of the manufacturer. However, once a recycling plant is installed the user is committed to this process, at least for the service life of the plant. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    One aspect of the disclosure is obtaining more flexibility for the recycling of PET. 
         [0007]    The embodiment according to the disclosure allows the user to switch from one process to the other, according to requirements and preconditions. 
         [0008]    Preferably, both processes are not strictly carried out in parallel, but are interconnected with each other, and a changeover from one process line to another process line can be realized by material flow switches. The interconnection is preferably accomplished to allow the use of as many of the present plant components as possible in both process lines. The interconnection may also be realized with bypass transport routes, allowing that specific plant components in the different process lines are started in different orders, with the controller being configured in such a way that shared plant components can be operated subject to different programs and with different parameters, if necessary. 
         [0009]    A shared plant component can be, for example, a vacuum reactor, in which a material flow switch can be provided particularly easily, in which, for example, two alternately operable outlet paths are provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    An embodiment of the disclosure will be explained in more detail below by means of the drawings: 
           [0011]      FIG. 1  shows a block diagram of the plant according to the disclosure for carrying out the method according to the disclosure, and 
           [0012]      FIG. 2  shows a schematic perspective view of a material flow switch associated with a reactor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]      FIG. 1  shows a block diagram of a plant  1  according to the disclosure for the recycling of PET, to obtain a recycled product which is suited for the production of containers usable in the food industry. However, the disclosure can also be used for those plants that provide recycled PET for a non-sterile application, or it may be employed for the recycling of other plastics. 
         [0014]    Plant  1  according to the disclosure comprises a conventional grinder, not illustrated in  FIG. 1 , in which PET products are ground to material shred or so-called flakes. A washing plant for removing label residues or dirt is not shown in  FIG. 1  either. Plant  1  according to  FIG. 1  first comprises, for example, a sifter  2  of the washing device, by means of which visible impurities are removed. At the outlet of the sifter  2  a switching device is located, e.g. in the form of a first material flow switch  3  conducting the material flow into a first process line A, which is shown by a dashed line, and into a second process line B, which is shown by a continuous line. In the exemplary embodiment shown, the first process line A comprises the plant components for the production of a first recycling product, preferably pellets. The plant components of process line A, which are passed through in the order specified below, are a sifter  4  for fines, a sieve  5  for removing the fines, a color sorter  6  for sorting out discolored or false color flakes, and a silo  7  for collecting the cleaned and washed flakes, followed, for example via another material flow switch  18 , by a decontamination stage  8 . In the exemplary embodiment shown, the decontamination stage  8  is formed of a first heating screw  9 , a second heating screw  10  and a vacuum reactor  11 . The flakes are heated in the heating screws. Next, residual contents are extracted in the vacuum reactor  11 . 
         [0015]    The vacuum reactor  11  is associated with a switching device, e.g. in the form of another material switch  12  explained in more detail below, leading into an extruder  13  for the production of pellets. In the extruder  13  the flakes are plasticized by the supply of heat and brought into a shape from which pellets may be formed. These pellets subsequently run through a cooler  14 , and are transported by another material flow switch  15  either into packaging containers  16 , or as bulk cargo into transport containers  17 , or are directly introduced into a further processing machine (not illustrated in  FIG. 1 ), e.g. an injection molding machine for the production of preforms for beverage bottles. 
         [0016]    The second process line B comprises the plant components for the production of a second recycling product, preferably flakes, and employs the plurality of the plant components of process line A, however, with some of the plant components being run through in a different order. The non-illustrated grinder and the sifter/washing device  2  are run through in the same order as in process line A. The material flow switch  3  is set in such a way that the flakes leaving the sifter  2  are immediately transported into the silo  7 , and from there into the decontamination device  8  comprising the first heating screw  9 , the second heating screw  10  and the vacuum reactor  11 . The decontamination process is carried out analogously to the pellet production process in process line A. Then, the material flow switch  12  is set to make the flakes run through the sifter  4 , the sieve  5 , and the color sorter  6  so that flakes that were possibly discolored during the heating can be sorted out. From the color sorter  6  the flakes are transported via a bypass route  12   a , bypassing extruder  13  and cooler  14 , directly to the material switch  15 , which distributes the flakes to the containers  16 ,  17  or to the injection molding machine. 
         [0017]      FIG. 2  schematically shows the material switch  12  associated with the vacuum reactor  11 . The vacuum container  11  comprises a vacuum bottom  11   a , which has two outlet openings  18  and  19  spaced away from each other. Both outlets  18 ,  19  are designed as bulk material feeders and can be locked, for example, by a slide or a blind cover accessible through an access opening. The outlet  18  leads into process line A, i.e. to the extruder  13 , for example through a conduit  20 . The outlet  19  leads into process line B for flakes, and is connected, e.g. by a chute  21 , to the sifter  4  for fines. 
         [0018]    The controller of the plant  1  is configured such that the user merely has to preselect a specific process line A or B so as to start the desired process. Where necessary, a manual switching may be required, e.g. at material flow switch  12 , for opening and closing special access openings and for inserting and removing blind covers. Moreover, the controller ensures that plant components such as the sifter  4 , the sieve  5 , the color sorter  6  and the decontamination device  8  are operated in accordance with the production process for the first recycling product (pellets) or the second recycling product (flakes) with different parameters, adapted to the selected process. Such parameters are, for example, the conveying speed in a continuous or discontinuous operation, holding times, temperatures such as drying temperatures or temperatures of conveyor members, parameters of sorters or the like. 
         [0019]    The switching operations will be explained in more detail below by means of examples. 
       Example 1 
       [0020]    The plant is operated in the flake process and is to be switched to the pellet process. The following operations take place: 
         [0021]    1. The user selects the switching to the pellet process. 
         [0022]    2. The vacuum reactor  11  no longer delivers flakes and breaks the vacuum. 
         [0023]    3. The sifter/washing device  2  interrupts the transport to the decontamination device  8 . 
         [0024]    4. After the vacuum in the vacuum reactor  11  was broken (which is signaled to the user), the material flow switch  12  is switched over. To this end, the access opening at the pellet process outlet has to be opened and the blind cover for the material flow has to be removed. After that, process line A is open, and this access opening is closed again. Next, the access opening at the flake process outlet is opened, and the outlet is closed with the blind cover. Thus, product line B is locked. The access opening of the flake process is now closed again. 
         [0025]    5. The sifter  4  for fines, the sieve  5  for fines and the color sorter  6  continue to operate until they are empty. 
         [0026]    6. The other material switches  3  and  15  are switched over. 
         [0027]    7. After the sifter  4 , the sieve  5  and the color sorter  6  have been emptied, the parameter sets for the operating state of the first process line A for pellets are automatically loaded into the plant components used for both product lines. 
         [0028]    8. The controller is being signaled as soon as all manual alterations are concluded. 
         [0029]    9. The sifter/washing device continues the transport to the decontamination module  8 . 
         [0030]    10. The production process for pellets is now initiated, and the alteration is concluded. 
         [0031]    The controller detects which one of the production processes is in operation, and it is capable without any further intervention to automatically switch the relevant parameter set required therefor and change over the switch position for the different product lines. 
       Example 2 
       [0032]    The plant is operated in the pellet production process and is to be switched to the flake production process. The following operations are necessary: 
         [0033]    1. The user selects the desired production process (flake process). 
         [0034]    2. The vacuum reactor  11  no longer delivers pellets and breaks the vacuum. 
         [0035]    3. The sifter/washing device interrupts the transport to the decontamination module  8 . 
         [0036]    4. After the vacuum in the vacuum reactor  11  was broken (which is signaled to the user), the vacuum bottom  11  is converted. To this end, the access opening at the flake process outlet has to be opened and the blind cover for the material flow has to be removed. After that, product line B is open, and this access opening is closed again. Next, the access opening at the pellet process outlet is opened, and the outlet is closed with the blind cover. Thus, process line A is locked. The access opening of the pellet process is now closed again. 
         [0037]    5. The sifter  4  for fines, the sieve  5  for fines and the color sorter  6  continue to operate until they are empty. 
         [0038]    6. The material switches  3  and  15  are switched over. 
         [0039]    7. After the sifter  4 , the sieve  5  and the color sorter  6  have been emptied, the parameter sets for the production process for flakes are automatically loaded into the plant components used for both product lines A and B. 
         [0040]    8. The controller is being signaled as soon as all manual alterations are concluded. 
         [0041]    9. The sifter/washing device continues the transport to the decontamination module  8 . 
         [0042]    10. The production process for flakes is now initiated, and the alteration is concluded. 
         [0043]    The controller detects the currently used production process, and it is capable without any further intervention to automatically switch the relevant parameter set and change over the switch position for the different product lines A, B. 
         [0044]    According to a modification of the exemplary embodiments described and illustrated above, the product lines may, on the one hand, be provided with different plant components according to requirements and, on the other hand, also be designed for the production of other recycling products. Further, the switching can be accomplished fully automatically by the process controller, also in the region of the material switch at the vacuum reactor, with two controllable outlets of the vacuum reactor being optionally provided.