Method and system for preparing plastic products, and dryer for such a system

Abstract

The invention relates to a method and a system for preparing plastic products, having the steps of: comminuting the plastic products in order to form small piece goods made of plastic, cleaning the small piece goods using a supply of liquid, and drying the wet small piece goods. According to the invention, the small piece goods made of plastic are dried in multiple stages in successive steps, wherein in a first stage, a mechanical draining process is carried out; in a second stage, a drying process is carried out using centrifugal force; and in a third stage, a drying process is carried out by thermally loading the small piece goods made of plastic. The invention also relates to a use of the method in a system for preparing plastic products.

Description

[0001] Process and plant for processing plastic products and dryer for such a plant

[0002] The invention relates to a method for processing plastic products, comprising the steps of: comminuting the plastic products into small plastic pieces, cleaning the small plastic pieces by means of a liquid supply, and drying the wet small plastic pieces. The invention further relates to a plant for processing plastic products, comprising a comminution device for comminution of the plastic products into small plastic pieces, a cleaning device for cleaning the small plastic pieces by means of a liquid supply, and a dryer for drying the cleaned small plastic pieces. The invention further relates to a dryer for a plant for processing plastic products, comprising a comminution device for comminution of the plastic products into small plastic pieces and a cleaning device for cleaning the small plastic pieces by means of a liquid supply.

[0003] Systems are used to process plastic products that include various cleaning, separating, sorting, and separation devices. The plastic products can be solid plastic products, such as plastic chairs, or plastic films. To process them, a large amount of liquid, particularly water, is added to the plastic products or further processed forms thereof (hereinafter also referred to as the material). This serves to clean, sort, and transport the material. At the end of the plastics processing process, the material is often in the form of plastic flakes. To achieve this, a residual moisture content of less than 5% is desired. For this purpose, conventional plastics processing processes include drying in several steps using mechanical and thermal drying processes.Drying is particularly complex for plastic films or plastic films shredded into flakes. These have a large surface area and a comparatively low weight. The flakes can clump together to form spheres or similar compact elements. This, combined with their high surface tension, causes a particularly large amount of liquid to adhere to the flakes.

[0004] Mechanical drying processes include liquid separation processes as well as agitation and pressing of the material. According to current technology, mechanical drying achieves a residual moisture content of the material of around 20%. Mechanical drying is followed by thermal drying, which reduces the residual moisture content to around 5%. Thermal drying requires a lot of energy compared to mechanical drying. In order to further dry the material after pressing in the subsequent thermal drying process, in which the material is dried with the addition of hot air, the material compacted by pressing must first be separated, i.e. broken up. The mixture of the separated, moist material and the hot air is passed through a drying tunnel where the moisture evaporates.In a downstream cyclone, the dried material is separated from the moist air, which is then released into the environment, preferably via a chimney.

[0005] The object of the invention is to provide a method, a system and a dryer of the type mentioned above which enable improved and more cost-effective drying of small plastic items compared to the prior art.

[0006] This task is solved for the process in that the plastic small goods are dried in several stages in directly successive process steps, whereby in a first stage a mechanical dripping takes place, in a second stage a drying by centripetal forces and in a third stage a drying by thermal exposure of the plastic small goods.

[0007] For the system and the dryer, the task is solved in that the dryer for drying the cleaned plastic small pieces is constructed in several stages, forming at least three different drying zones arranged directly one after the other, with a first drying zone designed as a mechanical drip zone, a second drying zone as a centrifuge zone, and a third drying zone as a thermal drying zone with a supply of thermally conditioned air. By combining the individual mechanical and thermal drying processes in a single dryer, some of the processing units can be eliminated, in particular a pressing unit for pressing the wet material and a dissolving unit for subsequently separating the pressed material. Furthermore, the conveying distances of the material to be dried during the drying process are reduced.The supply of thermally conditioned air in the third drying zone separates the moist material, increasing its surface area and promoting evaporation of the liquid. This accelerates the drying process and reduces the achievable residual moisture content.

[0008] In an embodiment of the invention, the drying zones each comprise a screening drum and at least one rotating paddle arranged parallel or at an acute angle to a central longitudinal axis of the screening drum. The respective screening drum and the associated rotating paddle are arranged for rotation relative to one another. The rotating paddle is preferably provided inside the respective screening drum, so that the screening drum surrounds the rotating paddle. The screening drums enable effective separation of the liquid from the material, which can flow through the screening structures of the screening drums and thus be separated from the material. While the liquid can flow through the screening structure of the screening drum, the material remains in the screening drum.In addition, additional liquid is removed from the material and thus separated from it when the moist material hits the rotating paddles, which rotate relative to the screen drum. The rotating paddles are advantageously oriented coaxially to the central longitudinal axis of the screen drums. This ensures that liquid is removed from the material evenly across the entire circumference of the screen drum.

[0009] The respective sieve drum and the associated rotating paddle can be arranged so that they can rotate relative to each other, with the draining zone having a significantly lower relative speed between the sieve drum and the rotating paddle than in the centrifuge zone. Due to the comparatively low relative speed between the sieve drum and the rotating paddle in the draining zone, a large portion of the liquid can drain away without requiring much energy. Due to the comparatively high relative speed in the centrifuge zone, the liquid, together with the material, is forced outward against a peripheral surface of the sieve drum.

[0010] The rotating paddles advantageously generate an airflow in the respective screening drum, which serves to advance the material and transport it through the screening drum. Instead or in addition, a device for generating an airflow, e.g., a fan, can be provided. The direction and speed of the relative rotation between the screening drum and the rotating paddle can be different or the same between the drying zones. The respective screening drum or the associated rotating paddle can be stationary, or both the screening drum and the rotating paddle can rotate in the same direction or in different directions.

[0011] In a further embodiment of the invention, the screening drums and the rotating paddles of the three drying zones are arranged coaxially in alignment one behind the other. This allows the material to be conveyed directly from one drying zone to the next. This saves time, and the material does not need to be transported between the drying zones by means of a transport device. In particular, an air stream can transport the material through all three drying zones. In addition, the dryer requires little installation space in this way and can therefore be set up particularly easily in a suitable location. Advantageously, the front sides of the screening drums are completely open, so that the small plastic items can be transferred directly from one zone to the next. In a further embodiment of the invention, at least two of the screening drums and / or at least two of the rotating paddles are rotationally coupled to one another. By coupling the rotation of, for example,By connecting two screening drums together, a rotary drive required for rotation of one of the screening drums can be eliminated. Advantageously, a gearbox is provided for coupling two of the screening drums or two of the rotary paddles, or the two screening drums or the two rotary paddles are connected to each other in a rotationally fixed manner. It is also conceivable for a screening drum to be rotationally coupled to a rotary paddle assigned to the screening drum, or for all three screening drums or rotary paddles to be coupled to each other. If the rotary paddles and the screening drums are arranged coaxially, one behind the other, the coupling of the screening drums or rotary paddles is particularly simple.

[0012] In a further embodiment of the invention, the rotating paddle and the screen drum of a first of the three drying zones and the rotating paddle and the screen drum of a second of the three drying zones have different relative rotational speeds. The different relative rotational speeds can promote the drying process in the respective drying zone.

[0013] In a further embodiment of the invention, the draining zone has a significantly lower relative speed between the screening drum and the rotating paddle than in the centrifuge zone. Advantageously, the relative speed in the draining zone is at most half that of the centrifuge zone. Due to the comparatively low relative speed between the screening drum and the rotating paddle in the draining zone, a large portion of the liquid can flow away without the need for much energy. Due to the comparatively high relative speed in the centrifuge zone, the liquid, together with the material, is forced outwards against a circumferential surface of the screening drum. In addition, the rotating paddle exerts a strong impulse on the material when the material hits the rotating paddle rotating at high speed, which allows a large amount of liquid to be knocked off the material.

[0014] In a further embodiment of the invention, a drive system for the screening drums and / or the rotating paddles is provided, which has at least two rotary drives for the screening drums and / or the rotating paddles, which can be controlled at different speeds. This allows different relative speeds to be generated between the screening drum and the rotating paddle in the respective drying zone as well as between the drying zones. Alternatively, the drive system comprises only a separate rotary drive for each screening drum and the associated rotating paddle. In this case, a screening drum or a rotating paddle can be stationary, or they can be rotationally coupled to one another. In this case, different speeds can be achieved by means of gears. In a further embodiment of the invention, a heat pump is provided for conditioning the air for the thermal drying zone.Thermal conditioning involves heating the air supplied to the third drying zone. The heat pump makes it possible to utilize the heat generated during the treatment process, particularly in exhaust air, and thus represents a cost-effective way to condition the air.

[0015] A heat pump is part of a heat pump system. This uses heat from the environment for heating with a comparatively low energy input. There are various types of heat pumps, the function of a compression heat pump of which is described below. The heat pump system consists of the heat source, the heat pump, and a heat distribution and storage system. The environment represents the heat source. In one variant, heat in groundwater, wastewater, or the earth is harnessed. For this purpose, a mixture of water and antifreeze (called brine) is circulated in the heat source. The brine absorbs heat from the heat source. In another variant, ambient air or exhaust air is sucked in. The brine or the sucked-in air then reaches the actual heat pump. In the heat pump, heat is transferred from the brine or air to a liquid refrigerant, which circulates in a refrigeration cycle of the heat pump.The absorbed heat causes the temperature of the refrigerant to rise, causing it to evaporate. Subsequent compression of the vaporous refrigerant increases both its pressure and its temperature. The hot, vaporous refrigerant is then brought into contact with a heating circuit in the heat distribution and storage system, to which it transfers heat. The vaporous refrigerant cools and condenses. The heat distribution and storage system allows the heat to be used or stored in any way, for example, to heat a room or another medium. Subsequent expansion of the refrigerant returns it to its initial state, where it can evaporate by absorbing heat from the heat source.With a heat pump, many times the energy used—for example, in the form of electrical power for pumping the brine, drawing in the air, and conveying and compressing the refrigerant—can be used as heat energy. The heat pump thus represents an energy-saving heating device.

[0016] In a further embodiment of the invention, the heat pump has a cooling register through which exhaust air from the thermal drying zone is passed. This allows heat contained in the exhaust air to be transferred to the coolant and from there to fresh air, which is fed to the third drying zone. This allows part of the heat in the air in the third drying zone to be reused. In a further embodiment of the invention, a condensate storage tank is assigned to the cooling register, which is connected to a fresh water supply of the system for processing plastic products in order to feed condensate produced in the cooling register to the fresh water supply of the plastics processing process. By extracting the heat from the exhaust air of the third drying zone, the air cools down. In the process, part of the moisture contained therein condenses and can be collected as liquid in the condensate storage tank.If this condensate is returned to the system and mixed with the fresh water for this purpose, a large portion of the liquid used in the system can be reused. This saves fresh water. If necessary, the condensate is first treated before being added to the fresh water.

[0017] Further advantages and features of the invention emerge from the claims and from the following description of preferred embodiments of the invention, which are illustrated with reference to the drawings.

[0018] Fig. 1 shows a schematic representation of a plant for processing plastic products according to the state of the art,

[0019] Fig. 2 shows a schematic representation of a section of an embodiment of a plant according to the invention for processing plastic products,

[0020] Fig. 3 shows a schematic representation of an embodiment of a method according to the invention for processing plastic products,

[0021] Fig. 4 shows a schematic representation of an embodiment of a dryer according to the invention.

[0022] The following describes a plant for processing plastic products according to the prior art, as shown in Fig. 1. Plastic parts to be processed, which have been created by comminuting the plastic products, are fed to the plant. This processing is also referred to as recycling. The plastic parts to be processed pass through a dosing device 1, a heavy-duty trap 2, also called a heavy-duty trap, in which stones, pieces of metal or similar solids are separated, and a cleaning device 3 for cleaning the plastic parts by adding liquid. This is also referred to as rinsing. The liquid fed to the plastic parts comprises, in particular, water, so that only water is referred to below. Other liquids or chemicals can of course be added to the water, or these liquids can be added to or removed from the plastic processing process without water.The water supplied to the cleaning device 3 can be fresh water or treated wastewater and is provided by a water treatment unit 4. The water supplied to the plastic parts advantageously serves not only to clean the plastic parts but also for their transport. From the cleaning device 3, the cleaned plastic parts reach a phase separation unit 5, in which a portion of the water supplied to the plastic parts is separated again. The separated water reaches the water treatment unit 4, where it is treated and fed back into the plastic processing process, in particular the cleaning device 3. After the phase separation unit 5, the plastic materials reach a comminution device 6, which comminutions the plastic parts into small plastic pieces. In another phase separation unit 5, further water is separated from the wet small plastic pieces.The water separated here is also treated by another water treatment unit 4 so that it can be fed back into the plastics processing process. In particular, the water can be fed to the comminution device 6, which can be configured as a wet mill. The plastics particles are cleaned again in another cleaning device 3. For this purpose, additional water can be added to the plastics particles. Water is separated again in a cyclone 7 and another phase separation unit 5.

[0023] The small plastic items are then fed to a mechanical drying device 8, which dries the wet plastic items by agitation. Agitation refers, among other things, to the removal of water from the small plastic items. This is achieved, for example, by the mechanical drying device 8 comprising a sieve basket and paddles rotating within the sieve basket. When a paddle hits the small plastic items, water is removed from them. In addition, the small plastic items are thrown against the sieve basket, through which the released water can flow and then be drained away separately from the small plastic items. Optionally, the paddles can be omitted, or the drying device 8 can have no sieve basket but a closed drum in which the paddles rotate.

[0024] After the mechanical drying device 8, the small plastic items are transported to a pressing unit 9, where they are compressed to press water out of them. However, agglomeration of the small plastic items also traps water in or between the small plastic items. To ensure that the pressed small plastic items can be effectively dried in the subsequent plastic processing process, they are separated again in a dissolving unit 10. A heater 11 heats air, which is then mixed with the separated small plastic items to be dried in a thermal drying device 12. The thermal drying device 12 comprises a drying tunnel through which the mixture of warm air and small plastic items is passed, allowing any water adhering to the small plastic items to evaporate. The warm, moist exhaust air is released into the environment via a chimney.The dried plastic small items pass through another cyclone 7 and a screening unit 13 into a silo 14, where they are stored for further processing.

[0025] Figs. 3 and 4 show schematic representations of embodiments of a method according to the invention for processing plastic products and of a dryer 30 according to the invention for use in such a method. The dryer 30 can be integrated into a plant for processing plastic products, as known from the prior art and described in connection with Fig. 1. For this purpose, the mechanical drying device 8 and the thermal drying device 12 are replaced by the dryer 30. The remaining structure of the plant can largely remain unchanged.

[0026] In step 101 of the method shown in Fig. 3, the wet plastic small items are fed to the dryer 30. In step 102, the plastic small items are dried in the dryer 30 in several drying stages. In a first drying stage 103, the wet plastic small items fed to the dryer 30 are dried by dripping. For this purpose, the plastic small items can, for example, rest against a sieve through which water can drain. In a second drying stage 104 following the first stage 103, the plastic small items are further dried by centripetal or centrifugal forces. This is advantageously carried out as already described in connection with the mechanical drying device 8 of the prior art system shown in Fig. 1. The water separated from the plastic small items in the first and second drying stages 103, 104 is collected in a step 106.Following the second stage 104, the small plastic items are dried in a third drying stage 105 by applying heat to the small plastic items. For this purpose, the small plastic items are advantageously mixed with thermally conditioned air so that any water adhering to the small plastic items evaporates. The dry material is then separated from the warm, moist air and discharged from the dryer 30 in step 108.

[0027] The moist air separated from the dried material is discharged from the dryer 30 as exhaust air in step 107. Liquid water contained in the exhaust air is removed from the exhaust air in step 109. This is advantageously done using a droplet separator. Cooling the exhaust air in step 110 condenses any water vapor it contains, and the exhaust air is then released into the environment in step 114. The resulting condensate is discharged together with the water collected in steps 106 and 109. The discharged water is then treated in step 111 and returned to the plastics processing process or permanently disposed of as wastewater.

[0028] Before the small plastic items are mixed with the fresh air supplied to the process in step 112 in the third stage 105 of the process, the air is heated to a higher temperature level in step 113. This allows the water adhering to the small plastic items to evaporate more quickly in the third drying stage 105, and the supplied fresh air to absorb more moisture. The heating of the fresh air and the cooling of the exhaust air are advantageously carried out using a heat pump, as described in detail below in connection with Fig. 4.

[0029] The embodiment of a dryer 30 shown in Fig. 4 comprises three screening drums 15 and three rotating paddles 16. The rotating paddle 16 comprises a shaft and a plurality of paddles held thereon. The rotating paddle 16 is aligned coaxially with a central longitudinal axis of the screening drum 15 and can rotate relative to the screening drum 15. The screening drums 15 are aligned coaxially with one another and connected directly one behind the other. One of the screening drums 15 and one of the rotating paddles 16 together form a first, second, and third drying zone 17-1, 17-2, 17-3. The first drying zone 17-1 serves as a mechanical draining zone, the second drying zone 17-2 as a centrifuge zone, and the third drying zone 17-3 as a thermal drying zone. The screening drum 15 and the rotating paddle 16 of the first and second drying zones 17-1, 17-2 rotate relative to each other, the relative rotational speed, ieThe rotational speed of the screening drum 15 relative to the rotating paddle 16 of the second drying zone 17-2 is greater than that of the first drying zone 17-1. This allows water to drip off the small plastic items in the first drying zone 17-1 with comparatively low energy expenditure. The greater relative rotational speed in the second drying zone 17-2, in contrast, enables water to be separated from the small plastic items by means of agitation and under the influence of centripetal forces. Advantageously, the screening drum 15 and the rotating paddle 16 of the third drying zone 17-3 rotate. This can promote air circulation and transport the material and the air in the axial direction through the third drying zone 17-3. Alternatively, the screening drum 15 and the rotating paddle 16 of the third drying zone 17-3 can be stationary and therefore do not need to have a relative rotational speed.

[0030] The dryer 30 has a drive system with several rotary drives 18, in the example shown six rotary drives 18, one of which is assigned to each of the three screening drums 15 and each of the three rotary paddles 16. Each of the rotary drives 18 has a rotary drive motor 19 and a sensor 20, as shown in Fig. 4 as an example for the rotary drive 18 assigned to the rotary paddle 16 of the first drying zone 17-1. The rotary drives 18 assigned to the screening drums 15 advantageously engage their circumference. By means of the sensor 20, a rotational speed or a rotational position can be measured, which enables a relatively precise adjustment of the rotational speed by means of a control unit of the drive system. The other rotary drives 18 are shown only in a simplified schematic. If one of the screening drums 15 or one of the rotary paddles 16 is stationary, the corresponding rotary drive 18 can of course be omitted.A rotary drive 18 can also be omitted if, for example, two of the screening drums 15 are coupled to one another, so that the rotation of one screening drum 15 forces the rotation of the other screening drum 15 and specifies the rotational speed depending on a transmission ratio.

[0031] As already mentioned, to generate the relative rotational speed between the screening drum 15 and the rotating paddle 16, either only the screening drum 15, only the rotating paddle 16, or both the screening drum 15 and the rotating paddle 16 can rotate. If both rotate, they can rotate in opposite directions or in the same direction, but at different rotational speeds. If one or more of the screening drums 15 or one or more of the rotating paddles 16 are stationary, the corresponding rotary drive 18 can, of course, be omitted. At least the following rotational configurations of the screening drums 15 and the rotating paddles 16 of the three drying zones 17-1, 17-2, and 17-3 are possible:

[0032] 1. The screening drums 15 are stationary and the rotating paddles 16 rotate.

[0033] 2. The screening drums 15 are stationary and the rotating paddles 16 rotate at different speeds.

[0034] 3. The screening drums 15 rotate at a first rotational speed and the rotating paddles 16 rotate at a second rotational speed in the opposite direction to the screening drums 15.

[0035] 4. The screening drums 15 rotate and the rotating paddles 16 are stationary.

[0036] 5. The screening drums 15 rotate at different speeds and the rotating paddles 16 are stationary.

[0037] 6. The screening drums 15 and the rotating paddles 16 rotate at different speeds and directions.

[0038] These are just a few examples of relative movements between the rotary paddles 16 and the screening drums 15 in the respective drying zones 17-1, 17-2, 17-3. Depending, for example, on the plastic products to be dried, one or the other constellation of relative rotary movements may be advantageous, or further constellations may be provided that are not described under 1. to 6. A rotary drive control unit 21 is assigned to the rotary drives 18. For this purpose, this is in communication with the rotary drives 18, which is indicated by the dashed line. The rotary drive control unit 21, also referred to as the control unit, controls the rotational speeds of the screening drums 15 and the rotary paddles 16 according to a user specification or according to a predetermined control program. The rotary drives 18 can be controlled independently of one another or together at the same or different speeds.

[0039] To supply thermally conditioned fresh air to the third drying zone 17-3, a plurality of fresh air nozzles 22 are provided. Fig. 4 shows four fresh air nozzles 22, which are arranged circumferentially on the screening drum 15 of the third drying zone 17-3 at an axial distance from one another. The fresh air is drawn in by a fan 23. Before the fresh air is supplied to the third drying zone 17-3, it is heated by a heat pump 24. The heat pump 24 comprises a heating register 25, in which heat from the refrigerant circulating in the heat pump 24 is transferred to the drawn-in fresh air. The heated fresh air is then supplied to the third drying zone 17-3 via the fresh air nozzles 22. Before the heat is transferred from the refrigerant to the fresh air, the refrigerant is in vapor form. During the heat transfer, the vaporous refrigerant cools and condenses.The liquid refrigerant is expanded via a throttle 26 and consequently cools further. In a cooling coil 29, heat is transferred from the moist, warm exhaust air of the third drying zone 17-3 to the liquid, cold refrigerant. As it heats up, the refrigerant evaporates, which is then compressed in a compressor 27 downstream of the cooling coil 29. Compression further increases the temperature of the vaporous refrigerant. The hot, vaporous refrigerant is fed to the heating coil 25, where it releases heat to the fresh air.

[0040] Before the exhaust air is fed to the cooling register 29, any water entrained in the exhaust air is separated by a droplet separator 28. The exhaust air is then fed to the cooling register 29. There, some of the moisture contained in the exhaust air condenses during cooling. This moisture is collected in a condensate storage tank 31 associated with the cooling register 29. The water from the droplet separator 28 and the water collected in the condensate storage tank 31 are treated and then fed back into the plastic processing process for the plastic products.

[0041] To dry the wet plastic small pieces, they are fed to the screening drum 15 of the first drying zone 17-1 in step 101. In step 108, the dried plastic small pieces are removed from the screening drum 15 of the third drying zone and can then be transported further. An air flow caused by the relative rotational speed between the screening drums 15 and the rotating paddles 16 can be designed to transport the plastic small pieces to be dried through the dryer 30 from one drying zone 17-1, 17-2, 17-3 to the next.

[0042] Fig. 2 shows a section of a plant according to the invention for processing plastic products with the dryer 30. Compared to the plant according to the prior art, as shown in Fig. 1, one of the phase separation units 5, the pressing unit 9 as well as the dissolving unit 10 and one of the cyclones 7 can be omitted. This is indicated schematically in Fig. 2 by striking out the corresponding processing units as provided in the plant according to the prior art. The other processing units can still be part of the plant. For example, the cleaning device 3 and the shredding device 6 continue to represent essential elements in the processing of the plastic products. The dryer 30 combines both mechanical and thermal drying processes, which is why it can also be referred to as a thermo-mechanical dryer.

[0043] As shown, the process, the system, and the dryer can eliminate the need for 30 different processing units in state-of-the-art plastic product processing plants and shorten transport routes between the remaining processing units. Furthermore, the use of a heat pump, among other things, makes the thermal drying of the small plastic products comparatively energy- and water-efficient.

Claims

Patent claims 1 . A process for processing plastic products comprising the steps: Comminuting the plastic products to small plastic items, cleaning the small plastic items by means of liquid supply and drying the wet small plastic items, characterized in that the small plastic items are dried in several stages in directly successive process steps, wherein in a first stage a mechanical dripping takes place, in a second stage a drying by centripetal forces and in a third stage a drying by thermal application of the small plastic items takes place.

2. Plant for processing plastic products with a comminution device (6) for comminuting the plastic products into small plastic pieces, with a cleaning device (3) for cleaning the small plastic pieces by means of a liquid supply and with a dryer (30) for drying the cleaned small plastic pieces, characterized in that the dryer (30) is constructed in several stages to form at least three different drying zones (17-1, 17-2, 17-3) which are arranged directly one after the other, wherein a first drying zone (17-1) is designed as a mechanical dripping zone, a second drying zone (17-2) as a centrifuge zone and a third drying zone (17-3) as a thermal drying zone with a supply of thermally conditioned air.

3. Dryer (30) for a plant for processing plastic products, with a comminution device (6) for comminuting the plastic products into small plastic pieces, and with a cleaning device (3) for cleaning the small plastic pieces by means of a liquid supply, characterized in that the dryer (30) for drying the cleaned small plastic pieces is constructed in several stages to form at least three different drying zones (17-1, 17-2, 17-3) which are arranged one after the other in time, wherein a first drying zone (17-1) is designed as a mechanical dripping zone, a second drying zone (17-2) as a centrifuge zone and a third drying zone (17-3) as a thermal drying zone with a supply of thermally conditioned air.

4. Dryer (30) according to claim 3, characterized in that the drying zones (17-1, 17-2, 17-3) each comprise a screening drum (15) and at least one parallel or pointed Have a rotary paddle (16) arranged at an angle of attack to a central longitudinal axis of the screening drum (15), which are arranged to be rotatable relative to one another.

5. Dryer (30) according to claim 4, characterized in that the screening drums (15) and the rotating paddles (15) of the three drying zones (17-1, 17-2, 17-3) are arranged coaxially aligned one behind the other.

6. Dryer (30) according to claim 4 or 5, characterized in that at least two of the screening drums (15) and / or at least two of the rotating paddles (16) are rotationally coupled to one another.

7. Dryer (30) according to one of claims 4 to 6, characterized in that the rotary paddle (16) and the screening drum (15) of a first of the drying zones (17-1, 17-2, 17-3) and the rotary paddle (16) and the screening drum (15) of a second of the drying zones (17-1, 17-2, 17-3) have a different relative speed.

8. Dryer (30) according to claim 7, characterized in that the dripping zone (17-1) has a significantly lower relative speed between the screening drum (15) and the rotating paddle (16) than the centrifuge zone (17-2).

9. Dryer (30) according to one of the preceding claims, characterized in that a drive system for the screening drums and / or the rotary paddles is provided, which has at least two rotary drives for the screening drums and / or the rotary paddles, which can be controlled at different speeds.

10. Dryer (30) according to claim 3, characterized in that a heat pump (24) is provided for thermally conditioning the air for the thermal drying zone (17-3).

11. Dryer (30) according to claim 9, characterized in that the heat pump (24) has a cooling register (29) through which an exhaust air of the thermal drying zone (17-3) is guided.

12. Dryer (30) according to claim 10, characterized in that the cooling register (29) is assigned a condensate storage (31) which is connected to a fresh water supply of the system for the processing of plastic products in order to feed condensate produced in the cooling register (29) to the fresh water supply.

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