Drying container and method for drying plastic granulate

Abstract

The invention relates to a drying container (1) for drying plastic granules, comprising a container wall (10) with a hollow cylindrical or hollow prism-shaped first section (11) transitioning into a funnel-shaped second section (12) having a dispensing opening (13) at its end and a gas inlet through the container wall (10) connected to a drying gas source, wherein the gas inlet opens into a gas guide channel (3, 4) arranged radially around the inner wall of the container, projecting towards the central axis of the container, which defines a closed, annular or partially annular space provided with at least one outlet opening (33, 44), at least one of which is directed towards the dispensing opening (13). The invention further relates to a method for drying plastic granules with such a device.

Description

[0001] The invention relates to a drying container for drying plastic granulate according to the preamble of patent claim 1. The invention further relates to a method for drying plastic granulate according to the preamble of patent claim 11.

[0002] Before processing, plastic granules must be dried. This is especially true for hygroscopic plastics such as PA or PBT, which retain water molecules like a sponge. Moisture in the plastic granules used results in inferior molded parts that do not meet the specified requirements. Typical defects range from moisture streaks to molecular chain degradation with a corresponding loss of strength.

[0003] Different drying processes are used to dry plastic granules. In dry air dryers, the dry air is generated in an air drying cartridge within the dryer. The air to be dehumidified flows past a so-called molecular sieve in the drying cartridge, which absorbs the water contained in the air. The molecular sieve consists of a porous granulate (e.g., a silicate gel) that has a high water absorption capacity. One such adsorption dryer is described, for example, in DE 20 2017 107 185 U1. A drying container containing the plastic granules to be dried is arranged. This container has an upper cylindrical section followed by a lower funnel-shaped section. The drying air is fed to the plastic granules via a diffuser cone arranged centrally in the drying container.This so-called adsorption process proves to be very energy-intensive, since heating to 250°C to 350°C is necessary for the required reactivation of the molecular sieve.

[0004] EP 0 041 941 A2 further describes a cooling bunker and a method for regulating the flow through a cooling bunker, wherein a further intended use is generally mentioned as use in drying plants, but not as use for drying plastic granulate.

[0005] Due to their simple design, compressed air dryers are also used for drying plastic granulate. A valve for pressure and flow rate reduction is connected to a regularly available compressed air connection. This valve is then connected to a process heater, which heats the air to drying temperature before it flows through the material container. The following effect is exploited: As pressure increases, the air's capacity to absorb water decreases. When air is compressed, a large portion of the water is already separated. If this compressed air is expanded to ambient pressure, the expanded air has a dew point of approximately -25°C. The dew point is the temperature at which the moisture bound in the air condenses on an object. The lower the dew point of the air, the higher its water absorption capacity.

[0006] The use of the above-mentioned devices for drying plastic granules has proven successful in practice. Given the considerable energy consumption of previously known drying devices, the invention is based on the object of increasing the efficiency of such drying devices. According to the invention, this object is achieved by a drying container having the features of patent claim 1.

[0007] The invention provides a drying container for drying plastic granulate whose efficiency is increased. Surprisingly, it has been shown that the discharge rate of the water contained in the plastic granulate is significantly increased by the drying gas introduced into the drying container if the drying gas is not introduced centrally via a diffuser cone, as is known in the prior art, but rather from the outside to the inside through a gas guide channel arranged at least partially radially circumferentially on the inner wall of the container, projecting towards the central axis of the container and delimiting a closed, annular or partially annular space provided with at least one outlet opening, which at least one outlet opening is directed towards the removal opening.By orienting the outlet openings toward the discharge opening, the drying gas, preferably preheated, expanded compressed air or air dried by an adsorption dryer, is introduced from the outside to the inside into the lower area of ​​the plastic granules in the container. From there, it slowly rises through the granules, absorbing moisture from the granule particles over an extended period of time as it flows around them. This achieves increased moisture removal from the granules. Furthermore, the outlet openings, which are directed downwards toward the discharge opening, prevent clogging of the outlet openings by penetrating granule particles.

[0008] All existing gas inlets are located on the vessel wall. In particular, there is no central internal body, such as a diffuser cone for introducing drying gas. This optimizes the drying process. It has been shown that such central internal bodies, known in the prior art, create shadow areas in which only a reduced flow of rising drying gas occurs.

[0009] A compressed inert gas such as nitrogen can also be used as the drying gas, as this gas also has a higher water absorption capacity after expansion. This also enables the drying of oxidizing plastic granules, which, when dried with compressed air according to the current state of the art, would react with oxygen and, in extreme cases, could even ignite.

[0010] Drying containers typically have a hollow cylindrical or hollow cuboid-shaped container wall that transitions into a funnel shape. Alternatively, the drying container can also be designed in a hollow prism shape. A hollow prism, in this case, is a geometric hollow body formed by the parallel displacement of a flat polygon along a straight line arranged orthogonally to it.

[0011] In a further development of the invention, the gas guide channel is arranged at least partially, preferably completely, on the second section of the container wall. This achieves maximum flow of drying gas through the plastic material. Preferably, the at least one outlet opening is oriented at an angle of between 10° and 100°, preferably between 30° and 70°, particularly preferably between 40° and 50°, to a plane extending orthogonally to the container's central axis.

[0012] In one embodiment of the invention, the at least one outlet opening is designed in the form of a slot or a gap. This creates a focused, narrow gas jet, which supports a uniform flow through the granulate material while avoiding turbulence.

[0013] In a further embodiment of the invention, the gas guide channel has a projection directed radially toward the center axis of the drying container, in which the outlet openings are located. This further counteracts the penetration of granulate particles.

[0014] Axially spaced from the gas guide channel on the side opposite the removal opening in the first section, a second gas inlet is arranged through the container wall and is connected to a second drying gas source comprising an arrangement with a heater and a fan. This enables the supply of preheated gas in an upper region of the container, through which heat energy is added to the drying gas cooled by the flow through the granules, thereby increasing the absorption capacity of the drying gas in the drying container for further flow through the plastic granules. In addition, the heated drying gas from the second drying air source converts water present in the plastic granules into the gas phase, whereby this water is better absorbed by the drying gas.This increases the degree of saturation of the introduced drying gas, thereby reducing the volume of drying gas required for the drying process.

[0015] The second drying gas source is preferably an ambient air source. The drying process is further supported by the supply of heated ambient air, which has an additional, albeit lower, absorption capacity than the drying gas. Alternatively, the second drying gas source can also be another drying air source, preferably formed by an adsorption dryer, to which either ambient air or largely saturated air taken from the drying vessel is supplied. Furthermore, the second drying gas source can also be an inert gas source, for example, a nitrogen source.

[0016] In a further development of the invention, the second gas inlet is arranged in the region of the lower half facing the removal opening, preferably in the region of the lower third of the first section of the container wall.

[0017] In an embodiment of the invention, the second gas inlet opens into a second gas guide channel which is arranged at least partially radially circumferentially on the inner wall of the container and projects towards the central axis of the container, said second gas guide channel having at least one outlet opening which is preferably designed in the form of an elongated hole or a gap and is directed towards the removal opening.

[0018] In an embodiment of the invention, at least one thermal sensor and / or at least one dew point sensor is arranged in the container, preferably on the container wall, which is connected to a control and regulating device via which the volume flow of at least one of the drying gas sources can be controlled, wherein the control and regulating device is connected to a valve and / or blower arranged in the supply line between the drying gas source and the drying container. This enables a demand-based supply of drying gas to the first and / or the second drying gas source, thereby increasing the energy efficiency of the drying process. In particular, the energy savings achieved by reducing the amount of expanded compressed gas, for example compressed air, introduced into the drying container are considerable.

[0019] The invention is further based on the object of providing a method for drying plastic granules that enables efficient removal of water from the plastic granules. According to the invention, this object is achieved by a method having the features of patent claim 11.

[0020] The invention provides a method for drying plastic granules which enables efficient removal of water from the plastic granules.By supplying a relaxed drying gas volume flow directed essentially in the direction of gravity to the plastic granulate via a first gas inlet arranged laterally on the container wall via at least one outlet opening of a gas guide channel arranged radially at least in some areas, wherein a further heated drying gas volume flow in the form of a heated ambient air flow introduced via a fan or a heated inert gas flow is supplied to the plastic granulate via a second gas inlet arranged on the container wall at a distance from the first gas inlet on the side thereof facing away from the removal opening of the drying container, the moisture absorption of the drying gas in the drying container is increased, thereby improving the efficiency of the drying process.By supplying heated drying gas, particularly ambient air, heat energy is added to the drying gas in the drying container, which has been cooled by flowing through the plastic granules, thereby increasing its moisture absorption capacity. Furthermore, the heated drying gas, particularly ambient air, converts water in the plastic granules into the gas phase, allowing it to be more effectively absorbed by the drying gas. This increases the saturation level of the drying gas introduced through the first gas inlet, reducing the volume of drying gas required for the drying process, such as cost-intensive compressed air or other compressed gas.

[0021] In a further development of the invention, the temperature and / or dew point in the drying container is detected by at least one sensor, and the first and / or second drying gas flow is controlled based on the detected measured values. This ensures that only a volume of drying gas tailored to the actual demand is supplied to the plastic granulate. The first drying gas flow is preferably formed from expanded compressed gas, such as compressed air, or from ambient air dried by an adsorption dryer.

[0022] Further developments and refinements of the invention are specified in the remaining subclaims. Embodiments of the invention are illustrated in the figures and described in detail below. They show: Figure 1 shows a schematic representation of a device for drying plastic granules; Figure 2 shows a schematic representation of a device for drying plastic granules in a further embodiment; and Figure 3 shows a schematic detailed representation of the gas guide channel of a drying container of a third embodiment.

[0023] The device chosen as an example for drying plastic granulate according to Figure 1essentially consists of a drying container 1 which is connected to a drying gas source 5. The drying container 1 comprises a hollow cylindrical first section 11, which is adjoined by a funnel-shaped second section 12 which has a removal opening 13 at its end. A first gas guide channel 2 is arranged in the cylindrical section 11 and is essentially delimited by a cylindrical inner wall 21 arranged parallel to the container wall 10 and two cover walls 22 arranged parallel to one another, which form a substantially rectangular cross-section with the container wall. The first gas guide channel 2 has a gas outlet 23 which is in the form of an annular gap and which is delimited by a gas guide plate 24. The gas guide plate 24 is angled such that the gas outlet 23 is directed in the direction of the removal opening.In the exemplary embodiment, the gas guide plate 24 is set at an angle of α = 45° to a plane E 1 running orthogonally to the container center axis.

[0024] A second gas guide channel 3 is arranged in the funnel-shaped second section 12 of the drying container 2. The gas guide channel 3 is essentially formed by a funnel-shaped inner wall 31 arranged parallel to the drying container wall, which is connected to the container wall via two cover walls 32 arranged parallel to one another, whereby a cross-section in the shape of a parallelogram is formed. The second gas guide channel 3 has a gas outlet 33 which is in the form of an annular gap and is delimited by a gas guide plate 34. The gas guide plate 34 is angled such that the gas outlet 33 is directed in the direction of the removal opening. In the exemplary embodiment, the gas guide plate 34 is angled at β = 45° to a plane E 2 running orthogonal to the container center axis. The gas outlets 23, 33 are each provided with a grid (not shown) to prevent blockages caused by penetrating granules.

[0025] The first gas duct 2 is connected to an ambient air source 5, which consists of a fan 51 and a heater 52 connected downstream of the fan. The second gas duct 3 is connected to a drying gas source 6, which comprises a compressed air source 61, which in turn is connected downstream of a heater 62, to which it is connected via an expansion valve 63.

[0026] A dew point sensor 14 and a thermal sensor 15 are arranged on the container wall 10. These sensors are connected to a control and regulating device 8 configured to adjust the temperature and dew point in the drying container to stored preset values ​​based on the measured values ​​determined by the sensors 14, 15. For this purpose, the control and regulating device 8 is connected to the fan 51 to control the volume flow of the ambient air source 5 and to the expansion valve 63 to control the volume flow of the compressed air source 6.

[0027] In the embodiment according to Figure 2 is in contrast to the execution according to Figure 1 The first gas duct 2 is connected to the outlet of an adsorption dryer 7. The adsorption dryer 7 essentially comprises a drying cartridge 71 containing a molecular sieve, which is connected via a first line 72 to a blower 73 and a downstream heater 74. Instead of heated ambient air, the expanded compressed air introduced into the drying container 1 is circulated through the drying cartridge 71 via the first line 72. Furthermore, a second line 75 is routed through the drying cartridge 71, through which ambient air heated by a blower 73 with a downstream heater 74 is passed for the regeneration of the drying cartridge 71.

[0028] In Figure 3a lower section of a further embodiment of a drying container 1 is shown in a detailed illustration. In this exemplary embodiment, the drying container 1 has a second gas guide channel 4, which is arranged in the transition between the cylindrical first section 11 and the funnel-shaped second section 12. A tubular cylindrical sheet 41 is introduced into the drying container 1 and rests on the container wall 10 in the region of the funnel-shaped second section 12 and is connected to the latter. The outer diameter of the cylindrical sheet 41 is smaller than the inner diameter of the container wall 10 of the cylindrical first section 11. Adjoining the cylindrical sheet 41 is a frustoconical funnel-shaped funnel sheet 42, which is connected to the cylindrical sheet 41 via an offset ring 43.The offset ring is provided with slot-shaped outlet openings 44 running radially around its circumference. The enlarged end of the funnel plate 42, opposite the offset ring 43, rests against the inner wall of the cylindrical first section 11 of the drying vessel 1 and is connected thereto. The gas guide channel 4 is delimited on the one hand by the vessel wall 10 and on the other hand by an inner wall formed by the cylindrical plate 41 and the funnel plate 42. To connect the gas guide channel 4 to a drying gas source, a connection 45 is attached to the drying vessel 1 and penetrates the inner wall 10 in the region of the gas guide channel 4.

[0029] If a drying container 1 of this design, filled with plastic granules, is supplied with drying gas, for example, with expanded and heated compressed air, via connection 45, the annular gas guide channel 4 is flooded with drying air. The drying air then flows through the outlet openings 44 of the offset ring 43 essentially in the direction of gravity, i.e., vertically downward toward the discharge opening 13, into the plastic granules, spreading radially inward through the plastic granules. Due to the buoyancy effect, the heated drying air then rises upward through the plastic granules.Via the flow path traveled by the plastic granulate after leaving the outlet openings 44 of the offset ring 43, a quantity of water is extracted from the plastic granulate by the drying air flowing around it, which quantity - as has surprisingly been shown - is significantly greater than in drying containers of the prior art with a central, central dry air supply.

[0030] As the drying gas flows through the plastic granulate, it releases heat into the granulate, causing the drying gas to cool down progressively. The drying gas is cooled by the gas duct located above the first gas duct. Figure 3 Heated ambient air is supplied to the plastic granules via the blower 51 through a second gas duct (not shown). This heated ambient air converts the water contained in the granules into the gas phase. At the same time, thermal energy is added to the drying gas, thereby increasing its water absorption capacity.

[0031] The temperature and dew point of the drying gas in the drying container, in this case drying air, are continuously recorded by a dew point sensor 14 and a thermal sensor 15, which are arranged on the inner wall of the container, and are reported to a control and regulating device 8, which regulates the temperature and dew point on the basis of stored default values ​​by controlling the fan 51 on the one hand and the expansion valve 63 on the other hand.

[0032] The drying container 1, as well as the cylindrical sheet metal 41, the funnel sheet metal 43, and the offset ring 42, are made of stainless steel in the illustrated embodiment. Of course, all components can also be made of other materials, particularly non-metallic ones. The term "sheet metal" refers exclusively to the "thin-walled" nature of the components, whose thickness is considerably less than their surface area, and not to the material itself.

[0033] The gas guide channel can be arranged at any position in the drying vessel. A position far down is preferred in order to maximize the flow path of the drying gas. Furthermore, as shown in Figures 1 and 2 As shown, several gas guide channels can also be arranged, in particular arranged parallel to one another, which can be fed via a common drying gas source or each via a separate drying gas source. By arranging several gas guide channels fed separately with drying gas, a different flow velocity and / or drying gas quantity can be set, whereby the flow of drying gas through the plastic granulate can be adjusted in more detail.

[0034] Although drying air is used as the drying gas throughout the above embodiments, the invention is not limited to the use of drying air. Of course, the use of all drying gases suitable for drying plastic granules is encompassed by the invention, in particular the use of inert gas such as nitrogen for drying oxidizable plastic granules.

Claims

1. Drying container (1) for drying plastic granulate, with a container wall (10) having a first section (11) of a hollow-cylindrical shape or the shape of a hollow prism, which first section merges into a funnel-shaped second section (12), which has a removal opening (13) at the end and a gas inlet guided through the container wall (10), which is connected to a drying gas source, wherein the gas inlet leads into a gas duct (3, 4), which is at least partially radially circumferentially arranged on the inner wall of the container and protrudes towards the central axis of the container, which gas duct delimits a closed annular or partially annular space, which is provided with at least one outlet opening (33, 44), which at least one outlet opening (33, 44) is directed towards the removal opening (13), characterised in that all existing gas inlets are arranged on the container wall (10) and there is no central inner body such as a diffusor cone for the introduction of dry gas, wherein a second gas inlet guided through the container wall (10) is arranged axially spaced apart from the gas duct (3, 4) on its side opposite the removal opening (13) in the first section (11), which second gas inlet is connected to a second drying gas source, which comprises an arrangement with a heater (52, 64) and a blower (51, 63).

2. Drying container according to claim 1, characterised in that the gas duct (3, 4) is arranged at least partially, preferably completely, at the second section (12) of the container wall (10).

3. Drying container according to claim 1 or 2, characterised in that the at least one outlet opening (33, 44) is oriented at an angle of between 10° and 100°, preferably between 30° and 70°, particularly preferably between 40° and 50° to a plane (E2), which runs orthogonally to the central axis of the container.

4. Drying container according to one of the previous claims, characterised in that the at least one outlet opening (33, 44) is in the form of an oblong hole or a slit.

5. Drying container according to one of the previous claims, characterised in that the gas duct (3, 4) has a projection directed radially towards the central axis of the drying container, in which projection the outlet openings (33, 44) are arranged.

6. Drying container according to one of the previous claims, characterised in that the drying gas source is formed by a compressed gas source, in particular a compressed air source (6) or by the drying gas outlet of an adsorption dryer (7).

7. Drying container according to one of the previous claims, characterised in that the second drying gas source is an ambient air source.

8. Drying container according to claim 7, characterised in that the second gas inlet is arranged in the area of the lower half facing the removal opening (13), preferably of the lower third of the first section (11) of the container wall (10).

9. Drying container according to claim 7 or 8, characterised in that the second gas inlet ends in a second gas duct (2), which has at least one outlet opening (23), which is preferably in the form of an oblong hole or a slit and is directed towards the removal opening (13).

10. Drying container according to one of the previous claims, characterised in that in the drying container (1), in particular at the container wall (10), at least one thermosensor (15) and / or at least one dew point sensor (14) is arranged, which is connected to a control and regulation device (8), via which the volume flow of at least one of the drying gas sources (5, 6) can be controlled, wherein the control and regulation device (8) is connected to a valve (63) and / or blower (51, 63) arranged in the feed line between drying gas source and drying container.

11. Method for drying plastic granulate in a drying container according to one of the previous claims, wherein a first drying gas volume flow substantially directed in the gravitational direction is supplied to the plastic granulate via a first gas inlet laterally arranged at the container wall (10) via at least one outlet opening (23, 33, 44) of a radially at least partially circumferentially arranged gas duct (2, 3, 4), wherein a further, second heated drying gas stream is supplied to the plastic granulate at a distance from the first gas inlet on its side facing away from the removal opening (13) of the drying container (1) via a second gas inlet arranged at the container wall (10), wherein the second drying gas volume flow is a heated ambient air stream or a heated inert gas stream introduced by means of a blower (51).

12. Method according to claim 11, characterised in that the temperature and / or the dew point in the drying container (1) is detected by at least one sensor (14, 15) and at least one drying gas volume flow is controlled on the basis of the detected measurement values.

13. Method according to claim 11 or 12, characterised in that the first drying gas volume flow is formed by expanded compressed gas, in particular expanded compressed air, or by ambient air dried by means of an adsorption dryer (7).

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