Conveying system and method for pneumatically conveying plastic granulate

Abstract

A conveying system for pneumatically conveying plastic granulate comprises a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location, in conveying connection with the feed location, for moisture contained in the conveying gas, and a condensation tempering unit, which is arranged along a section or sections of the conveying line, for making the conveying line such temperature to at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line.

Claims

1. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, wherein the condensation tempering unit is arranged along the conveying line along a conveying direction between the feed location and the target location.

2. The conveying system according to claim 1, wherein the condensation tempering unit has at least one passive element.

3. The conveying system according to claim 2, wherein the at least one passive element is embodied as at least one of a shading element, as a passive cooling element and as a thermal insulating element.

4. The conveying system according to claim 1, wherein the condensation tempering unit has at least one active element.

5. The conveying system according to claim 4, wherein the at least one active element is embodied as at least one of an active heating element and as an active cooling element.

6. The conveying system according to claim 1, comprising a control unit for controlling the temperature at the internal wall of the conveying line for the formation of a sliding film.

7. The conveying system according to claim 6, wherein the control unit is in signal communication with the condensation tempering unit and with at least one of at least one temperature sensor and with a sensor for humidity measurement at least one of in the conveying line and in a pressurized gas line.

8. The conveying system according to claim 1, comprising a distribution unit for the selective distribution of the sliding film formed on the internal wall of the conveying line.

9. The conveying system according to claim 8, wherein the distribution unit is arranged in the region of the condensation tempering unit.

10. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, a distribution unit for the selective distribution of the sliding film formed on the internal wall of the conveying line, wherein the distribution unit has at least one swirl vane for generating swirl in the conveying flow.

11. The conveying system according to claim 10, wherein the at least one swirl vane is arranged within the conveying line along a rectilinear section of the conveying line.

12. The conveying system according to claim 8, wherein the distribution unit has at least one deflection element for deflecting a fluid flow in the conveying line.

13. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, a distribution unit for the selective distribution of the sliding film formed on the internal wall of the conveying line, wherein the distribution unit has at least one deflection element for deflecting a fluid flow in the conveying line, wherein the at least one deflection element is embodied as a baffle which is secured on the internal wall of the conveying line.

14. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, a distribution unit for the selective distribution of the sliding film formed on the internal wall of the conveying line, wherein the distribution unit has at least one deflection element for deflecting a fluid flow in the conveying line, wherein the at least one deflection element is embodied as a guide groove, which is embodied in a manner integrated on the internal wall of the conveying line.

15. The conveying system according to claim 8, wherein the distribution unit has at least one gas injection element, which is connected to the conveying line for the additional injection of a gas for the distribution of the sliding film.

16. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, wherein the internal wall of the conveying line is embodied with a hydrophilic wetting surface.

17. The conveying system according to claim 1, comprising a humidification unit for humidifying at least one of the conveying gas and the plastic granulate by adding liquid.

18. The conveying system according to claim 17, wherein the liquid is added by means of a separate liquid connection.

19. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, a humidification unit to humidify at least one of the conveying gas and the plastic granulate.

20. A conveying system for pneumatically conveying plastic granulate by means of humid conveying gas, having a feed location, at which the plastic granulate is fed into a conveying line by pressurized conveying gas, a target location in conveying connection with the feed location, comprising a condensation tempering unit, which is arranged along one of a section and sections of the conveying line, for making the conveying line such temperature for the at least partial condensation of moisture contained in the conveying gas to form a sliding film on an internal wall of the conveying line, wherein the condensation tempering unit extends along the conveying line over at least 20% of the total length of the conveying line.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic illustration of a conveying system according to the invention having a condensation tempering unit with passive elements,

(2) FIG. 2 shows a schematic cross-sectional illustration according to section line II-II in FIG. 1,

(3) FIG. 3 shows a perspective, partially sectioned view of the pneumatic conveyance of plastic granulate in the conveying line,

(4) FIG. 4 shows an illustration, corresponding to FIG. 1, of a conveying system according to another embodiment having passive elements in the form of thermal insulating elements,

(5) FIG. 5 shows a schematic cross-sectional illustration according to section line V-V in FIG. 4,

(6) FIG. 6 shows an illustration, corresponding to FIG. 1, of a conveying system according to another embodiment having passive elements,

(7) FIG. 7 shows an illustration, corresponding to FIG. 1, of a conveying system according to another embodiment having active cooling elements for the condensation tempering unit and having an evaporation tempering unit,

(8) FIG. 8 shows a schematic perspective view of the conveying line with a distribution unit in the form of swirl vanes,

(9) FIG. 9 shows a section according to section line IX-IX in FIG. 8,

(10) FIG. 10 shows an illustration corresponding to FIG. 8, wherein the distribution unit has a deflection element in the form of a guide groove, and

(11) FIG. 11 shows an illustration corresponding to FIG. 8 with the distribution unit as a gas injection element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) A conveying system denoted overall by 1 in FIGS. 1 to 3 is used for pneumatic conveying, in particular for suspended conveyance or conveyance in strands, of plastic granulate, which is stored in a receptacle 2. The receptacle 2 is arranged at a storage location 3.

(13) By means of a feed metering unit 5, which, according to the illustrative embodiment shown, is embodied as a rotary feeder, the plastic granulate is fed in a metered fashion from the receptacle 2 to a conveying line 6 at a feed location 7.

(14) It is also possible to provide a plurality of receptacles 2, which are each connected to the conveying line 6 by means of a separate feed metering unit 5. However, it is also possible for the plastic granulate to arrive in pre-metered form from an upstream process, in particular in a granulation device after an extruder.

(15) At the feed location 7, the plastic granulate fed to the conveying line 6 is supplied with pressurized conveying gas. The conveying gas is air. The conveying air is supplied from a compressed air source 8 through a filter 9 and a pressure generator 10, e.g. in the form of a compressor or of a blower.

(16) According to the illustrative embodiment shown, a humidification unit 11 is connected to a compressed air line 12 upstream of the feed location 7.

(17) The compressed air line 12 connects the compressed air source 8 to the feed location 7 and opens into the conveying line 6. Compressed air is transported along the compressed air line 12 as far as the liquid feed by the humidification unit 11. The compressed air is humidified by the addition of liquid and is conveyed to the feed location 7 as humid conveying gas.

(18) The mixture of plastic granulate 13 and the humid conveying gas 14 flows along the conveying line 6. The flow direction of the mixture is characterized by the flow arrow 14a. Along the conveying line 6, the flow direction of the conveying gas 14 corresponds to the flow direction of the plastic granulate 13.

(19) In addition or as an alternative to the humidification unit 11, at least one further humidification unit can be arranged downstream of the feed location 7, in particular along the conveying line 6. It is possible to dispense with humidification by an additional liquid feed if, for example, moist plastic granulate is conveyed, the moisture in which is used to humidify the conveying gas. In this case, the moist plastic granulate, which releases the liquid to the conveying gas, is interpreted as the humidification unit.

(20) A condensation tempering unit 15 is arranged in a section of the conveying line 6. The condensation tempering unit 15 is arranged between the feed location 7 and a target location 16 along the conveying line 6. The target location 16 is connected to the feed location 7 in terms of conveying by means of the conveying line 6. According to the illustrative embodiment shown, three target receptacles 17 are arranged at the target location 16. Each target receptacle 17 has an exhaust air filter 18 and a feed member 19 for feeding the plastic granulate in from the conveying line 6.

(21) According to the illustrative embodiment shown, the condensation tempering unit 15 has a passive element in the form of a shading element 20. The shading element 20 is embodied as a gabled roof. The shading element 20 protects the conveying line 6 arranged thereunder from external environmental influences 21, which are illustrated symbolically in FIG. 1. The external environmental influences 21 can cause temperature changes in the environment and/or act directly on the conveying line 6, e.g. in the form of direct solar radiation or in the form of rain on the conveying line 6. A change in the ambient temperature influences the temperature on and in the conveying line 6. Relevant environmental influences 21 are solar radiation, cloud cover, precipitation, such as rain, hail, snow, storms, thunderstorms and a change in daylight and/or seasons, for example.

(22) According to the illustrative embodiment shown, the condensation tempering unit 15 extends along a length which is less than 20% of the total length of the conveying line 6. The total length of the conveying line 6 is obtained from the conveying path between the feed location 7 and the target location 16. The total length of the conveying line 6 corresponds to the sum of the individual lengths of the various conveying line sections. The condensation tempering unit 15 can also extend over at least 50% of the total length of the conveying line, in particular over at least 60%, in particular over at least 70%, in particular over at least 80%, in particular over at least 90% and, in particular, over the entire conveying length of the conveying line 6.

(23) In particular, it is conceivable that the condensation tempering unit is arranged in a section of the conveying line 6 which directly adjoins the feed location 7.

(24) In particular, an initial section of the conveying line 6 which is arranged between the feed location 7 and the start of the condensation tempering unit 15 is provided. In particular, no condensation tempering unit 15 is arranged in the initial section. The length of the initial section of the conveying line 6 is, in particular, at least 2% of the total length of the conveying line 6, in particular at least 5% of the total length of the conveying line 6, in particular at least 10% of the total length of the conveying line 6, in particular at least 20% of the total length of the conveying line 6 and, in particular, at least 50% of the total length of the conveying line 6.

(25) According to the illustrative embodiment shown, the condensation tempering unit 15 is arranged in a region in which the conveying line 6 extends horizontally. The condensation tempering unit 15 can also be arranged in all other sections of the conveying line 6, in particular also where the conveying line 6 slopes relative to the horizontal and, in particular, where it is oriented vertically.

(26) The pneumatic conveyance of the plastic granulate 13 in the conveying system 1 is explained in greater detail below. The plastic granulate 13 is fed into the feed location 7 of the conveying line 6 from the receptacle 2 by means of the feed metering unit 5, and is subjected to pressure with humidified conveying gas 14 via the compressed air line 12. The pressurized conveying gas 14 and the plastic granulate 13 are conveyed pneumatically along the conveying line 6 from the feed location 7 to the target receptacles 17 at the target location 16, in particular by suspended conveyance or conveyance in strands. The humidification of the conveying gas is, in particular, performed in such a way that the conveying gas is supersaturated, i.e. has a relative humidity of more than 100%. The state of saturation of the conveying gas is, in particular, dependent on the pressure and temperature in the conveying line 6.

(27) Particularly owing to the temperature control of the conveying line 6 by means of the condensation tempering unit 15, the conveying conditions in the conveying line 6 are selectively influenced in such a way that the conveying gas is in a supersaturated state, with the result that the liquid in the conveying gas condenses. The condensed liquid is precipitated on an internal wall 23 of the conveying line 6 and forms a liquid film 24, which serves as a sliding film for the plastic granulate 13. The sliding film 24 can be formed in some section or sections along the circumference on the internal wall 23 and/or along the longitudinal axis 25 of the conveying line 6. In particular, the sliding film 24 is formed over the entire surface along the circumference of the internal wall 23.

(28) By means of the condensation tempering unit 15, the temperature T.sub.IW at the internal wall 23 of the conveying line 6 can be set in an advantageous temperature range, which corresponds to between 15° K less than the temperature of the conveying flow T.sub.F and the temperature T.sub.F of the conveying flow. The temperature T.sub.F of the conveying flow is a blended temperature T.sub.G comprising that of the conveying gas 14 and the temperature TK of the plastic granulate 13.

(29) Another embodiment is described below with reference to FIG. 4 and FIG. 5. Parts of identical design are given the same reference signs as in the previous embodiment, to the description of which attention is drawn herewith. Parts that are different in design but functionally similar are given the same reference signs followed by a.

(30) One difference is that the condensation tempering unit 15a has a plurality of passive elements, which, according to the illustrative embodiment shown, are each embodied as thermal insulating elements 26. The thermal insulating elements 26 are formed separately from one another. The thermal insulating elements 26 are embodied in an identical way, apart from their length. Depending on the temperature control to be achieved, it is conceivable to provide thermal insulating elements of different designs, which develop different thermal insulating effects, i.e. different temperature control effects, along the conveying line 6.

(31) According to the illustrative embodiment shown, the thermal insulating element 26 is embodied as an insulating layer in the form of an annular cylinder, which is arranged around the entire circumference of the conveying line 6 on an external wall 27 arranged opposite the internal wall 23. It is also conceivable for the thermal insulating element 26 to be embodied as an insulating layer which extends only over a certain region or regions along the outer circumference of the conveying line 6. The insulating layer can consist of a plurality of layer sections, which are arranged along the outer circumference on the external wall 27 of the conveying line 6.

(32) According to the illustrative embodiment shown, the insulating layer 26 has a layer thickness s.sub.I which, in particular, is greater than the wall thickness s.sub.L of the conveying line 6. In particular: s.sub.I≥5.Math.s.sub.L, in particular s.sub.I≥10.Math.s.sub.I, in particular s.sub.I≥15.Math.s.sub.L and in particular s.sub.I≥20.Math.s.sub.L.

(33) In particular, the layer thickness s.sub.I is less than an outside diameter D of the conveying line 6. In particular: s.sub.I≤0.6.Math.D, in particular s.sub.I≤0.2.Math.D and in particular s.sub.I≤0.1.Math.D.

(34) According to the illustrative embodiment shown, individual sections of the conveying line 6 are embodied without thermal insulating elements 26. In particular, pipe bends 28 are embodied without thermal insulating elements 26.

(35) The conveying line 6 has a target section 29, which is adjacent to the target location 16. The target section 29 has a target section length l.sub.Z. The target section length l.sub.Z is determined in such a way that a conveying pressure difference Δp.sub.F, l.sub.Z along the target section 29 does not exceed a defined maximum value. According to the illustrative embodiment shown, the defined maximum value is at most 30% of the total conveying pressure p.sub.F. The total conveying pressure is the conveying pressure with which the conveying gas 14 is fed to the conveying line 6 by the compressed air line 12 at the feed location 7. The conveying pressure difference is the result of the difference between the conveying pressure at the start of the target section p.sub.FA and the conveying pressure at the end of the target section 29 p.sub.FE.

(36) By virtue of the fact that the condensation tempering unit 15a is deliberately dispensed within the target section 29, liquid can evaporate in the conveying gas 14. Condensate formation is thereby reduced and, in particular, prevented. The risk that liquid will reach the target location 16, in particular will get into the target receptacles 17, is reduced and, in particular, prevented.

(37) In addition or as an alternative, an evaporation tempering unit 42 can be provided in the target section 29, said unit being explained in greater detail below by means of the embodiment shown in FIG. 7.

(38) In conveying system 1a, the condensation tempering unit 15a is arranged along the conveying line 6, along an initial section 30. The initial section 30 begins at the feed location 7 and extends as far as the target section 29. According to the illustrative embodiment shown, the conveying line 6 consists exclusively of the initial section 30 and the target section 29. The conveying line 6 has a total length l.sub.ges which corresponds to the sum of the initial section length l.sub.A and the target section length l.sub.Z.

(39) Another embodiment is described below with reference to FIG. 6. Parts of identical design are given the same reference signs as in the previous embodiments, to the description of which attention is drawn herewith. Parts that are different in design but functionally similar are given the same reference signs followed by b.

(40) One significant difference with respect to the previous embodiments is that the condensation tempering unit 15b is embodied in such a way that the conveying line 6 is substantially fully insulated by means of insulating elements 26 within the initial section 30. In particular, insulating elements 26 are also arranged at pipe bends 28.

(41) In addition or as an alternative, an evaporation tempering unit 42 can be provided in the target section 29, said unit being explained in greater detail below by means of the embodiment shown in FIG. 7.

(42) Another embodiment is described below with reference to FIG. 7. Parts of identical design are given the same reference signs as in the previous embodiments, to the description of which attention is drawn herewith. Parts that are different in design but functionally similar are given the same reference signs followed by c.

(43) One significant difference with respect to the previous embodiments is that the condensation tempering unit 15c has active elements in the form of active cooling elements 31. The active cooling element 31 is embodied as a double tube apparatus, having an additional tube 32, which is arranged concentrically with the conveying line 6. A cooling liquid, in particular water, in the interspace between the additional tube 32 and the conveying line 6 can be used to cool the external wall 27 of the conveying line 6. Cooling liquid is fed into and discharged from the interspace in such a way that the flow direction 33 of the cooling liquid is oriented counter to the conveying direction 34 of plastic granulate 13 and conveying gas 14. The active cooling element 31 is operated by the countercurrent method.

(44) By means of the active cooling elements 31, the heat dissipation at the external wall 27 of the conveying line 6 can be selectively influenced. In particular, adapted heat dissipation in accordance with the conveying conditions and/or the external environmental conditions is possible. In particular, the heat dissipation which is made possible by means of an active cooling element 31 can be influenced by means of the temperature of the cooling liquid and/or the flow rate of the cooling liquid.

(45) Conveying system 1c furthermore has a schematically illustrated control unit 35. The control unit 35 allows the control of the temperature T.sub.IW at the internal wall 23 of the conveying line 6. The control unit is in signal communication, in particular, with the condensation tempering unit 15c, in particular with the active cooling elements 31. For reasons of illustration, this signal link 36 is illustrated schematically for just one of the active cooling elements 31 in FIG. 7.

(46) Moreover, the control unit 35 is in signal communication with an ambient temperature sensor 37a and with an ambient humidity sensor 37b.

(47) The control unit 35 is furthermore in signal communication with a pipe wall temperature sensor 38 and a conveying gas temperature sensor 39. The pipe wall temperature sensor 38 is used to measure the temperature T.sub.IW at the internal wall 23 of the conveying line 6. The pipe wall temperature sensor 38 can be arranged on the external wall 27 or on the internal wall 23 of the conveying line 6.

(48) The control unit 35 is furthermore in signal communication with at least one sensor 40 for measuring the relative humidity of the conveying gas 14. A plurality of humidity sensors 40 can be provided along the conveying line 6. The conveying gas temperature sensor 39 and the at least one humidity sensor 40 are arranged within the conveying line 6 and/or in the compressed air line 12, between the pressure generator 10 and the feed location 7.

(49) The signal link between the control unit 35 and the sensors 38, 39, 49 can be embodied in a wired manner but can also be embodied wirelessly. The wired signal links are not shown in FIG. 7 for reasons of illustration. Wireless signal links are characterized by the schematic radio communication symbol 41 in FIG. 7.

(50) Depending on the measured values for the ambient temperature, the temperature T.sub.IW at the internal wall 23, the temperature T.sub.F of the conveying flow and the relative humidity of the conveying gas, a setpoint value for the temperature T.sub.IW at the internal wall 23 is determined in the control unit 35 and correspondingly influenced by an actuating signal to the active cooling elements 31. By means of the control unit 35 and the signal links 36, 41, there is the possibility, in particular, of a closed control loop in order to ensure constant sliding film formation on the internal wall 23.

(51) It is possible to provide the conveying system section by section with separate sensors, which are each independently in signal communication with the control unit 35. As a result, the various sections of the conveying system 1 can be controlled independently of one another. It is thereby possible to set the conveying conditions selectively in the various sections and, in particular, independently of the other sections of the conveying system 1.

(52) It is conceivable to keep the temperature T.sub.IW at the internal wall 23 so far below the temperature T.sub.F of the conveying flow that even a small addition of liquid brings about local, pressure-induced saturation in order to induce local sliding film formation. In particular, the temperature T.sub.IW at the internal wall 23 is 15° K less than the temperature T.sub.F of the conveying flow, in particular less than 10° K, in particular less than 5° K and, in particular, less than 1° K. The total quantity of liquid to be added can thereby be reduced and/or the friction-reducing effect of the sliding film intensified.

(53) In particular, it is conceivable to set the temperature difference to a level such that it is possible to dispense with a separate addition of liquid, particularly in the form of water, wherein a steady sliding film is formed on the internal wall 23 of the conveying line 6. This method is particularly advantageous since instruments for metered addition of liquid are superfluous. The outlay on apparatus is reduced. The water displaced from the sliding film can be reabsorbed by the conveying gas as soon as it heats up to the temperature T.sub.F of the conveyed material again. This takes place comparatively quickly, particularly within the conveying flow. As a result, an exchange of the conveying air ahead of the target location 16 is superfluous. Consequently, an exchange gas unit of the kind known from EP 3 366 618 A1 is superfluous. This method is suitable especially for short conveying lines 6 with which, on the one hand, only low conveying-pressure-induced supersaturation levels can be achieved and, on the other hand, the initial section within which, in particular, cooling of the conveying line 6 takes place is made relatively short.

(54) Another difference with respect to the previous embodiments is that not only has the condensation tempering unit been dispensed with but that, in addition, an evaporation tempering unit 42 is provided in the target section 29. According to the illustrative embodiment shown, the evaporation tempering unit 42 extends along the entire length L.sub.Z of the target section 29. The evaporation tempering unit 42 has a plurality of active elements in the form of active heating elements 43. The active heating elements 43 are embodied in a manner substantially identical with the active cooling elements 31, wherein a heat transfer fluid in the form of hot water, which is guided in co-current flow and not in countercurrent flow with respect to the conveying direction 34 of the plastic granulate 13, is used instead of a coolant.

(55) Depending on the ambient conditions, it is also conceivable to use active heating elements for the condensation tempering unit 15c instead of the active cooling elements.

(56) By virtue of the fact that the evaporation tempering unit 42 is used in the target section 29, condensate formation in the target section 29 can be excluded even more reliably.

(57) In particular, it is conceivable for the control unit 35 to be in signal communication with corresponding sensors 38, 39 and 40, which are then arranged in the conveying line 6 in the region of the target section 29, in order to ensure control of the temperature T.sub.IW at the internal wall 23 of the conveying line 6 in the target section 29.

(58) A distribution unit, which is used for selective distribution of the sliding film 24 formed on the internal wall 23 of the conveying line 6, is explained in greater detail below with reference to FIGS. 8 and 9.

(59) The flow direction of the conveying gas is characterized by the flow arrow 14 in FIG. 8. The distribution unit 44 shown in FIG. 8 has a plurality of swirl vanes 45, according to the illustrative embodiment four swirl vanes. The four swirl vanes 45 are arranged at equal intervals along the circumference of the internal wall 23. The swirl vanes 45 are each embodied as sheet metal strips, which have a curvature along the longitudinal axis 25 of the conveying line 6 such that the conveying flow 14 is deflected. In particular, a helical flow direction, which extends along the internal wall 23 of the conveying line 6, is produced by the distribution unit 44 with the swirl vanes 45. This helical conveying flow is illustrated downstream of the distribution unit 44 in FIG. 8. By virtue of the helical conveying flow, the contact of the heated conveying gas with the cold internal wall 23 of the conveying line 6 is intensified, resulting in an increase in condensate formation. The distribution unit 44 causes an additional formation of the sliding film.

(60) The swirl vanes 45 are embodied in an identical manner and are equally spaced along the circumference of the conveying line 6, i.e. are arranged at an angular spacing of 90° to one another. The distribution unit 44 can also have more than four swirl vanes 45. The distribution unit 44 can also have fewer than four swirl vanes 45, in particular precisely three swirl vanes 45, in particular precisely two swirl vanes 45 and, in particular, precisely one swirl vane 45. It is conceivable for the swirl vanes 45 of a distribution unit to be embodied differently from one another.

(61) The swirl vanes 45 each have a sheet metal thickness a in the range of from 2 mm to 10 mm. In particular, the sheet metal thickness a is 0.5 times to 10 times the wall thickness s.sub.L of the conveying line 6, in particular 1 times to 3 times the wall thickness s.sub.L.

(62) The swirl vanes 45 each have a sheet metal height h of between 20 mm and 200 mm. It is advantageous if the sheet metal height h is 0.1 times to 0.9 times the outside diameter D of the conveying line 6, in particular 0.2 times to 0.5 times the outside diameter D.

(63) The swirl vanes 45 have a length L.sub.DB of from 100 mm to 1000 mm along the conveying line 6. In particular, the length L.sub.DB is 1 times to 10 times the outside diameter D of the conveying line 6, in particular 2 times to 5 times the outside diameter D.

(64) The swirl vanes 45 each have a twist angle α to generate the helical conveying flow. The twist angle α is between 10° and 180°, in particular between 30° and 90°.

(65) In addition, the helical flow of the conveying gas brings about distribution of the sliding film on the internal wall 23.

(66) In particular, the distribution unit 44 with the swirl vanes 45 is arranged in a rectilinear section of the conveying line, in particular in a horizontal section of the conveying line 6. Fewer than four or more than four swirl vanes 45 can be provided in the distribution unit 44.

(67) It is particularly advantageous if the distribution unit 44 with the swirl vanes 45 is arranged along the conveying line 6 in the region of the second quarter up to the end of the last quarter of a horizontal section of the conveying line 6. Ideally, the distribution unit 44 with the swirl vanes 45 is arranged in the region of the second and third quarters of a horizontal section of the conveying line 6. The swirl vanes are advantageously arranged at an axial distance from pipeline bends 28, wherein the axial distance corresponds to 20 times to 200 times, in particular 50 times to 150 times, the outside diameter D of the conveying line 6.

(68) Another embodiment of a distribution unit is described below with reference to FIG. 10.

(69) According to the illustrative embodiment shown, the distribution unit 44 has a guide groove 46 in the form of an impressed feature, which is integrated in the form of a helix in the internal wall 23 of the conveying line 6. The guide groove 46 is, in particular, worked, in particular impressed, as a channel into the surface of the internal wall 23. The guide groove 46 can have a rectangular or semicircular contour.

(70) The guide groove 46 brings about deflection of the condensed liquid on the internal wall 23, in particular from a bottom region 47 of the conveying line 6 into the conveying gas flow and/or over the circumference of the internal wall 23. It is also possible for more than one guide groove 46 to be provided. In addition or as an alternative, the distribution unit 44 can also have baffles, which bring about deflection of the liquid flow in a manner similar to the guide grooves 46. The guide grooves 46 and/or the baffles form guide elements which allows selective distribution of the liquid film produced in order to form and maintain the sliding film.

(71) The guide elements are preferably used in straight sections of the conveying line 6, in particular in horizontal sections of the conveying line 6. A plurality of guide elements can be arranged one behind the other and/or side-by-side along the conveying line.

(72) It is advantageous if the guide elements are arranged in the region of the second quarter up to the end of the last quarter of a horizontal section of the conveying line 6 and, in particular, in the region of the second and third quarters of the horizontal section of the conveying line 6. In particular, the guide elements are arranged at an axial distance from pipeline bends 28, wherein the axial distance corresponds to 20 times to 200 times the outside diameter D of the conveying line 6 and, in particular, 50 times to 150 times the outside diameter D.

(73) Another embodiment of a distribution unit 44 is explained below with reference to FIG. 11.

(74) In the illustrative embodiment shown, the distribution unit 44 has at least one gas injection element in the form of an air nozzle 48. The air nozzle 48 is coupled directly to the conveying line 6. In particular, the air nozzle 48 is connected in the bottom region 47 of the horizontally arranged conveying line 6. In particular, the air nozzle 48 is arranged substantially tangentially on the conveying line 6, with the result that the air injected into the conveying line 6 by the air nozzle 48 follows a substantially tangential flow direction along the internal wall 23 of the conveying line 6. In superposition with the flow direction of the conveying gas 14, a substantially helical flow direction, which is characterized by the flow arrow 49 in FIG. 11, results for the air injected by means of the air nozzle 48.

(75) The injected helical air flow along the internal wall 23 of the conveying line 6 brought about an advantageous distribution of the condensed liquid and hence an improved arrangement of the sliding film. Installation of static elements within the conveying line 6 which could impair and/or hinder conveyance of the plastic is thereby avoided.

(76) In particular, the air nozzle 48 is connected to straight sections of the conveying line 6, in particular to horizontal sections of the conveying line 6. It is conceivable to use a plurality of air nozzles 48, which can be arranged spaced apart along the longitudinal axis 25. It is also conceivable to arrange a plurality of air nozzles 48 in a plane perpendicular to the longitudinal axis 25 along the circumference of the conveying line 6.

(77) It is advantageous if the air nozzles are arranged in the region of the second quarter up to the end of the last quarter of a horizontal section of the conveying line 6 and, in particular, in the region of the second and third quarters of the horizontal section of the conveying line 6. In particular, the air nozzles are arranged at an axial distance from pipeline bends 28, wherein the axial distance corresponds to 20 times to 200 times the outside diameter D of the conveying line 6 and, in particular, 50 times to 150 times the outside diameter D.

(78) In the embodiments of the distribution unit 44 explained above and shown in FIGS. 8 to 11, it is additionally or alternatively conceivable for the internal wall 23 to have a hydrophilic wetting surface. Improved wetting of the internal wall 23 with the liquid is thereby achieved. A contact angle, which can also be referred to as the wetting angle, which a liquid droplet forms on the hydrophilic wetting surface is advantageously less than 90°, in particular less than 50° and, in particular, less than 10°.

(79) For all the embodiments, it is the case that individual features can be combined in any desired manner. In particular, it is also possible for conveying systems 1, 1a and 1b to be embodied with an evaporation tempering unit 42. All the distribution units 44 can be used independently of one another in combination or individually in all the conveying systems mentioned.