EP3034975A1 - Method and a drying plant for drying plastic granulate - Google Patents

Abstract

The present invention discloses a method and a drying plant with a drying container for drying a drying material in the drying container by passing a drying medium through the material to be dried. In the process and in the drying plant (1), the following process steps are carried out repeatedly:
- determining a consumption of the material to be dried (30);
- Determining a filling amount and / or a mass of the material to be dried (30) in the drying container (10);
- Calculating an actual residence time (IV) of the material to be dried (30) in the drying container (10) taking into account the consumption of the material to be dried (30) and taking into account the capacity of the material to be dried (30) and / or the mass of the material to be dried (30) in the drying vessel (10); and
- Outputting a control signal for filling the drying container (10) with Trocknungsgut (30) in the event that the actual residence time (IV) is less than the desired residence time (SV).

Description

The present invention relates to a method and a drying plant for drying a material to be dried, in particular of plastic granules, by passing a drying medium through the material to be dried.

In the plastics processing industry, the plastic raw materials mostly present in the form of granules are dried before processing. For drying the plastic granules, dry air serving as the drying medium flows through a drying container in drying systems known from the prior art, wherein the plastic granules are taken up in bulk in the drying container. Usually, the drying container is designed as a funnel, from which the plastic granulate is successively discharged into a further processing device, for example a plasticizer. The drying medium is introduced by means of a blower in the drying tank and flows around the particles of the plastic granules. In this process, heat is released from the drying medium onto the plastic granules and at the same time moisture of the plastic granules is taken up by the drying medium and removed by means of the drying medium. The moisture-mixed drying medium is then usually regenerated in a separate process and then returned to the drying container in a closed circuit. In the regeneration process, the drying medium flows through a regenerating agent, for example a so-called molecular sieve, through which the moisture contained in the drying medium is adsorbed.

The EP 1 006 329 A1 describes a process for drying plastic raw materials, in which a gaseous drying medium flows through drying material located in a drying container, the flow of the drying medium being pulsed. By an appropriate method, the drying process is increased in its efficiency. The drying container is always completely filled.

For further processing provided for plastic granules has a dependent on the ambient conditions moisture. This can lead to problems during further processing, for example in an injection molding process. Excessive moisture content causes hydrolytic degradation during processing, which can lead to surface defects of the injection-molded component in the form of streaks. If the moisture content is too low, ie if the plastic granules are overdried, the melt viscosity of the plastic increases, which can cause decomposition streaks in the finished product.

For the plastics processing industry, it is therefore of central importance that the plastic granulate (drying material) provided for further processing be dried in such a way that it has a moisture content in an acceptable range for further processing. This moisture content correlates with a residence time of the material to be dried in the drying container.

The known from the prior art drying equipment for drying of drying material are designed as a rule after the maximum plastic granule consumption to at highest utilization to ensure an acceptable predrying. In order to prevent over-drying, the temperature of the drying medium in the flow and return is measured in the prior art. If the difference between the two temperatures is within a defined tolerance band, the drying temperature is lowered to a lower value. A standby mode is activated. If fresh plastic granulate is sucked in again, or no plastic granules are removed from the drying container for a predetermined time, the standby mode is deactivated to prevent rewet of the plastic granules. The drying process is then continued with the original setting. The stationary state of a moisture balance of a hygroscopic plastic mainly depends on the dryness of the ambient air, that is, on the dew point set in the dryer. Since only the temperature is lowered in standby mode, this does not change the stationary state of the moisture balance, but only the drying speed. Consequently, an overdrying of the plastic granules by a long dwell time within the drying container is also possible.

The object underlying the present invention is to provide a method for drying a drying material in a drying container, which ensures a moisture content of the material to be dried within a predetermined moisture content regardless of the consumption of a further processing plant, which is downstream of a drying plant.

This object is achieved by a method having the features of claim 1. Advantageous embodiments of the method are described in the dependent of claim 1 claims.

Furthermore, the present invention has the object to provide a drying plant with a drying container for drying drying material located in the drying container, which ensures a moisture content of the material to be dried within a predetermined moisture content regardless of the consumption of the drying plant downstream processing equipment.

This object is achieved by a drying plant with the features of claim 4. Advantageous embodiments are described in the dependent of claim 4 claims.

• Ermitteln eines Verbrauchs des Trocknungsgutes;
• Ermitteln einer Füllmenge und/oder einer Masse des Trocknungsgutes im Trocknungsbehälter;
• Berechnen einer Ist-Verweilzeit des Trocknungsgutes im Trocknungsbehälter unter Berücksichtigung des Verbrauchs des Trocknungsgutes und unter Berücksichtigung der Füllmenge des Trocknungsgutes und/oder der Masse des Trocknungsgutes im Trocknungsbehälter; und
• Ausgeben eines Steuersignals zum Befüllen des Trocknungsbehälters mit Trocknungsgut in dem Fall, dass die Ist-Verweilzeit kleiner als die Soll-Verweilzeit ist.

More specifically, the object underlying the present invention is achieved by a method for drying a drying material in a drying container by passing a drying medium through the material to be dried, the method having the following repetitive method steps:

• Determining a consumption of the material to be dried;
• Determining a filling quantity and / or a mass of the material to be dried in the drying container;
• Calculating an actual residence time of the material to be dried in the drying container, taking into account the consumption of the material to be dried and taking into account the filling quantity of the material to be dried and / or the mass of the material to be dried in the drying container; and
• Outputting a control signal for filling the drying container with material to be dried in the event that the actual residence time is less than the desired residence time.

These process steps are thus arranged in the form of a repetitive loop and are repeated at predetermined intervals in order to adjust the actual residence time of the desired residence time reliably over a longer period of time and with changing consumption conditions.

An appropriate method ensures that regardless of consumption of the drying plant downstream processing plant, the residence time of the material to be dried in the drying tank is always within a predetermined time range, so that the subsidized from the drying tank or from the drying plant plastic granules always has a moisture content within a predetermined Moisture range is. For if the actual residence time is less than the desired residence time, i. If the actual residence time of the material to be dried in the drying container is shorter than the desired residence time, which is linked to the desired moisture content of the material to be dried, then the inventive method ensures that a control signal is output, which causes a filling of the drying container with Trocknungsgut. As a result, further drying material is conveyed into the drying container, so that the actual residence time is prolonged and consequently approaches the desired residence time.

If, for example, polyamide 6.6 is used as the drying material, then the residual moisture of the plastic granules should preferably be between 0.04% and 0.10%, so that the plastic granules can then be easily further processed by a further processing facility. A corresponding residual moisture is achieved if, under normal drying conditions, the plastic granules remain between 2.5 hours and 8 hours in the drying tank.

In the absence of the control signal for filling the drying container, i. in the event that the actual residence time is greater than or equal to the desired residence time, the drying container is therefore not filled with further Trocknungsgut. Consequently, there is a staircase-like approximation of the actual residence time to the desired residence time.

The material to be dried can also be referred to as plastic granules and / or as plastic raw material. The actual residence time is the calculated emptying time of the drying tank. The consumption of the material to be dried is the consumption of a further processing device downstream of the drying container, for example a plasticizer. The drying medium may be, for example, air which is adjusted to a predetermined temperature and humidity. However, it is of course also possible to use as the drying medium another gaseous drying medium.

The consumption of the material to be dried can be determined, for example, by means of a flow meter downstream of a drying container outlet downstream. It is also possible to provide a plurality of flowmeters, which are connected upstream of further processing devices.

It is particularly advantageous if the consumption of the material to be dried is determined by means of an MES system (Manufacturing Execution System). An MES system is a link between the planning level of a company and the manufacturing level with the manufacturing / production processes.

Of course, it is also possible that the flow rate of the drying medium is adjusted by the drying tank. The drying speed of the material to be dried is influenced by a corresponding setting, so that also the desired residence time of the material to be dried in the drying container is changed.

The determination of the filling quantity and / or the mass of the material to be dried in the drying container is carried out by measuring and / or calculating the filling quantity or the mass of the material to be dried. More specifically, the determination of the filling amount in the drying tank by measuring the level, that is, the filling level of the material to be dried in the drying tank and subsequent calculation of the filling takes into account the geometry, in particular the cross-sectional geometry of the drying container and the density of the material to be dried. The determination of the mass of the material to be dried in the drying container can also be done by using a balance. By using a balance to determine the filling amount of the drying container, the material to be dried in the drying container may have any distribution, for example, form a pour cone, it being ensured that the filling quantity is reliably determined in this case.

The filling level or the filling amount of the material to be dried in the drying container can be determined in a variety of ways. For example, capacitive sensors can be used. Furthermore, ultrasonic sensors and / or light barriers can also be used to determine the filling quantity. With regard to the investigation procedure for determining the filling quantity of the material to be dried in the drying container and with regard to the use of different level sensors, there are no restrictions whatsoever.

The calculation of the actual residence time of the material to be dried in the drying container can be done by dividing the filling amount by the consumption amount. More specifically, the calculation of the actual residence time by dividing the mass of the drying material in the drying container by the consumption mass of the material to be dried by the drying tank downstream processing equipment done. The consumption quantity is given in mass per unit of time. Furthermore, it is possible to determine the actual residence time by dividing the volume of the material to be dried in the drying container by the consumption volume of the material to be dried. The consumption volume is given in volume per unit of time.

Advantageously, the method further comprises a method step for outputting a second control signal for stopping the filling of the drying container with material to be dried in the event that the actual residence time is equal to or greater than the desired residence time. A corresponding method may be necessary for a drying plant, in which a filling opening for the plastic granules in the drying container in the absence the control signal for filling the drying container is not automatically closed.

Further preferably, the method comprises an initial step of inputting and / or setting the desired residence time of the material to be dried in the drying container. It is thereby achieved that a drying plant using or carrying out the method according to the invention can be set rapidly to different drying material and / or to different throughflow rates, temperatures and moisture contents of the drying medium through the material to be dried.

The object underlying the present invention is also achieved by a drying system with a drying container for drying drying material in the drying container by passing a drying medium through the material to be dried, the drying system a level sensor for determining the level of the material to be dried in the drying container and / or a weight sensor for Determining the weight of the material to be dried in the drying container. Furthermore, the drying system has a control device, which is connected to the level sensor and / or the weight sensor via a signal line. The control device is designed to receive a consumption signal representing the consumption of the material to be dried via the signal line and / or via a further signal line. Furthermore, the control device is designed to calculate an actual residence time of the material to be dried in the drying container based on the consumption of the material to be dried and the filling amount of the material to be dried and / or the mass of the material to be dried in the drying container, wherein the control device is further configured to to issue a control signal for filling the drying container with material to be dried, if the actual residence time is less than the desired residence time.

By a corresponding drying plant ensures that regardless of the consumption of the drying plant downstream processing equipment, the residence time of the material to be dried in the drying tank is always within a predetermined time range, so that the conveyed from the drying tank or from the drying unit plastic granules always has a moisture content within a predetermined residual moisture range lies. For if the actual residence time is less than the desired residence time, i. If the actual residence time of the material to be dried in the drying container is shorter than the desired residence time, which is linked to the desired moisture content of the material to be dried, then the control device of the drying system, that a control signal for filling the drying container is output with Trocknungsgut. As a result, further drying material is conveyed into the drying container, so that the actual residence time is prolonged and consequently approaches the desired residence time.

The control device is designed such that the determination of the level of the material to be dried in the drying container, the determination of the consumption of the material to be dried, the calculation of the actual residence time of the material to be dried in the drying tank based on the consumption of the material to be dried and the amount of material to be dried and the output of a control signal for filling the drying container with drying material, if the actual residence time is less than the desired residence time, in Repeatedly executed in the form of a repeat loop.

By outputting the control signal for filling the drying container, a magnetic switch can be actuated or activated, for example, by means of which a closure flap, which closes a filling opening of the drying container in its closed position, is transferred from its closed position into its open position. The closure cap can be biased alternatively or additionally by means of a force spring device in its closed position. Alternatively, the drying system may also be designed such that when a control signal for filling the drying container, the filling opening of the drying container is opened for a predetermined time, so that a predetermined amount of material to be dried is introduced into the drying container. After the predetermined time has elapsed, the closing flap automatically closes the filling opening of the drying container, whereupon the method steps described above are carried out again by the control device. In this way, a gradual adaptation of the actual residence time to the desired residence time takes place.

By means of the control signal for filling the drying container but could also be a conveyor, such as a vacuum pump can be controlled, which causes a conveying of the material to be dried in the drying container.

The signal line may be an arbitrarily designed signal line, which may be formed, for example, wired or radio-based.

In a preferred embodiment of the drying system, the control device is designed to output a second control signal for stopping the filling of the drying container with material to be dried in the event that the actual residence time is equal to or greater than the desired residence time. A suitably designed drying plant allows the use of a shutter that is not automatically transferred from the open position to its closed position when a control signal for filling the drying tank fails.

Preferably, the level sensor is designed as a capacitive level sensor. A corresponding design of the drying plant is structurally particularly simple and therefore inexpensive to implement, since corresponding level sensors are inexpensive to buy and can be easily implemented or installed in existing drying systems.

Preferably, the level sensor extends parallel to a longitudinal axis of the drying container. Thereby, the level of the drying container can be determined continuously, i. not only only discrete filling states can be determined. Furthermore, only a single level sensor is necessary to determine over the entire longitudinal extent of the drying tank whose level with Trocknungsgut.

Preferably, the drying plant has a plurality of level sensors. This can increase the reliability.

The individual fill level sensors can be configured as light barriers, wherein in each case a light transmitter is arranged opposite a light receiver. Due to the large number of light barriers, there is a certain amount of redundancy, so that increased reliability is ensured.

Further preferably, the individual level sensors are arranged at different axial heights of the drying container. By appropriate training discrete filling conditions of the drying container can be determined. A corresponding design of the drying plant is structurally simple.

The individual level sensors need not be arranged equidistant in the drying container, but the distances from adjacent level sensors may be smaller in the bottom region of the drying container than the distances of adjacent level sensors in the region of an upper lid of the drying container.

Figur 1:

eine schematische Darstellung einer erfindungsgemäßen Trocknungsanlage;

Figur 2a:

ein Flussablaufdiagramm eines erfindungsgemäßen Verfahrens zum Trocknen von Trocknungsgut gemäß einer ersten Ausführungsform der vorliegenden Erfindung;

Figur 2b:

ein Flussablaufdiagramm eines erfindungsgemäßen Verfahrens zum Trocknen von Trocknungsgut gemäß einer zweiten Ausführungsform der vorliegenden Erfindung; und

Figur 3:

eine schematische Darstellung des realisierten Regelkreises zum Angleichen einer Ist-Verweilzeit des Trocknungsgutes an eine Soll-Verweilzeit.

Further advantages, details and features of the invention will become apparent from the illustrated embodiment. In detail:

FIG. 1:

a schematic representation of a drying system according to the invention;

FIG. 2a:

a flow chart of a method according to the invention for drying drying material according to a first embodiment of the present invention;

FIG. 2b:

a flow chart of a method according to the invention for drying Trocknungsgut according to a second embodiment of the present invention; and

FIG. 3:

a schematic representation of the realized control loop for adjusting an actual residence time of the material to be dried to a desired residence time.

In the following description, like reference numerals denote like components or like features, so that a description made with respect to a figure with respect to a component also applies to the other figures, so that a repetitive description is avoided. Furthermore, individual features described in connection with one embodiment may also be used separately in other embodiments.

FIG. 1 shows a drying system 1 according to the invention, which has a drying container 10 for drying of drying material 30 located in the drying container 10. The drying material 30 is dryable by passing through a drying medium. Any suitable gaseous drying medium, for example air, can be used as the drying medium. The drying material 30 is usually a plastic raw material in the form of granules, which is also referred to as plastic granules 30. The drying plant 1 has an inlet opening 11 for filling the drying container 10 with material to be dried 30 and an outlet opening 15 for removing the material to be dried 30 from the drying container 10. In the illustrated embodiment, the inlet opening 11 can be closed by means of an inlet flap 12. At the inlet flap 12, a switch 13 is provided in the form of a magnetic switch 13, by means of which the inlet flap 12 between a in FIG. 1 shown Closed position and is pivotable at an open position. The inlet opening 11 is in fluid communication with a suction power 14 for sucking drying material 30 from a storage volume (not shown). The suction box 16 and thus also the outlet opening 15 are in fluid communication with an outlet line 17 for conveying the material to be dried to a further processing device (not shown).

The drying plant 1 has a fill level sensor 18 for determining the fill level of the drying container 10 with material 30 to be dried. In the illustrated embodiment, the level sensor 18 is designed as a capacitive level sensor 18. Of course, however, other sensors, such as acoustic or optical sensors (photoelectric sensors) can be used as level sensors 18. The level sensor 18 extends parallel to a longitudinal axis of the drying container 10 over a large part of its total longitudinal extent. Consequently, with the level sensor 18, the level of the drying container 10 can be continuously determined between an (approximately) empty and a (fully) filled state.

Furthermore, the drying installation 1 has a control device 19, which is connected to the fill level sensor 18 via a signal line 20. In the illustrated embodiment, the signal line 20 as an electrical (galvanic) connection between the level sensor 18 and the controller 19 is shown. However, 20 may be realized as a signal line 20 as a radio-based signal line.

The control device 19 receives from the level sensor 18 via the signal line 20 a signal representing the level of the drying container 10. Furthermore, the control device 19 receives a consumption signal, which represents a consumption of the material to be dried 30, via a further (second) signal line 21. The consumption of the material to be dried 30 can be determined, for example, by means of a flow meter, which is not shown and arranged downstream of the outlet 16 or suction box 16 of the drying container 10. Furthermore, the consumption of the material to be dried 30 can also be determined by means of an MES system.

How out FIG. 1 it can be seen open in the control device 19 further signal lines 21, via which, for example, information about the flow of the drying medium through the drying container 1, the temperature of the drying medium and / or the moisture content of the drying medium can be transmitted to the control device 19.

The operation of the controller 19 will be described below with reference to FIG FIG. 2a illustrated flowchart. In a first method step S1, the consumption of the material to be dried 30 is determined. In a subsequent method step S2, a filling quantity of the material to be dried 30 in the drying container 10 is determined by means of the level sensor 18. Subsequently, in a method step S3, the control device 19 calculates an actual residence time IV of the item to be dried 30 in the drying container 10, taking into account the consumption of the item to be dried 30 and taking into account the capacity of the item to be dried 30 in the drying container 10. The actual residence time corresponds while the actual residence time of the material to be dried 30 in the drying tank 10 and is determined by dividing the filling amount of the material to be dried 30 in the drying tank 10 by the consumption of the material to be dried 30. It is then checked whether the actual residence time IV is smaller than a desired residence time SV of the material to be dried 30 in the drying container 10th

The desired residence time SV is specific to the plastic granules 30 and depends on the flow rate of the drying medium through the drying vessel 10, on the temperature and the moisture content of the drying medium. The desired residence time SV can be input to the control device 19 in a method step preceding the method step S1. This can be done for example by means of an input device, not shown here, which is connected to the control device 19.

If the actual residence time IV is smaller than the desired residence time SV, then the control device 19 outputs in a method step S4 a control signal for filling the drying container 10 with material 30 to be dried. In the illustrated embodiment, a signal is output to the magnetic switch 13 to open the inlet door 12 via a signal output line 22. As a result, further drying material 30 is introduced into the drying container 10, thereby prolonging the actual residence time IV in the drying container 10. Subsequently, the method steps are carried out again beginning at step S1 until the actual residence time IV is not less than the desired residence time SV. In this case, no control signal for filling the drying container 10 is then output with 30 more drying because the actual residence time IV is sufficiently large, so that the drying material 30, regardless of the amount consumed by downstream processing equipment always has a predetermined and suitable for further processing residual moisture.

The drying plant 1 shown can be configured such that when receiving a control signal for filling the drying container 10 with 30 Trocknungsgut the magnetic switch 13 opens the inlet flap 12 for a predetermined time, so that a predetermined amount of Trocknungsgut 30 is filled into the drying tank 10, whereupon Inlet flap 12 is automatically closed. After filling the predetermined amount of drying material 30, the method steps S1 to S4 are carried out again until the actual residence time IV is no smaller than the desired residence time SV. A corresponding procedure leads to a stepwise adaptation of the actual residence time IV to the desired residence time SV.

With reference to the in FIG. 2b Flowchart shown flowchart is explained below, the operation of the control device 19 for the case in which the inlet flap 12 must be actively transferred from the open position to the closed position. In this case, the control device 19 is adapted to output a second control signal for stopping the filling of the drying container 10 with the material to be dried 30, if the actual residence time IV is equal to or greater than the desired residence time SV. If the actual residence time IV is equal to or greater than the desired residence time SV, then in a method step S5 a second control signal for stopping the filling of the drying container 10 with material 30 to be dried is output. Upon receipt of this signal, the switch 13 transfers the inlet door 12 from its open position their closed position. The remainder of the operation of the controller 19 is identical to that described with reference to FIG FIG. 2a explained operation of the control device 19 so that a repetitive description is avoided.

In FIG. 3 the realized control loop of the drying plant 1 is shown. The desired residence time SV is compared with the actual residence time IV. More specifically, the difference .DELTA.t between the actual residence time IV and target residence time SV is formed. This result .DELTA.t is further processed by a control software contained in the control device 19 together with further information, which are indicated by arrows opening into the control device 19. The control software then outputs to a conveyor system 25 control data. If the difference Δt <0, ie if the actual residence time IV (emptying time) is greater than the desired residence time SV, then a mass m _{FÖ of} the material to be dried 30 is _fed into the dryer 10. By filling the material to be dried 30 in the drying tank 10, the level h increases. From this level h is still a level reduction h _V deducted, resulting from the temporal integration of the actual Trocknungsgutverbrauchs. Subsequently, in the control device 19 of the thus corrected level h * and the measured consumption amount or the measured consumption mass of the material to be dried 30 is used to calculate the actual residence time IV. This information is then used again to calculate the difference .DELTA.t with further assistance of the desired residence time SV.

LIST OF REFERENCE NUMBERS

1

drying plant

10

drying container

11

inlet port

12

intake flap

13

magnetic switches

14

suction

15

outlet

16

Outlet / suction box

17

outlet pipe

18

level sensor

19

control device

20

signal line

21

further / second signal line

22

Signal output line

25

conveyor system

30

Drying material / plastic granulate / plastic raw material

IV

Actual residence

SV

Shall dwell

h _V

level reduction

H*

corrected level of the drying tank

m _FÖ

in the drying tank conveyed mass of the material to be dried

.delta.t

Difference between actual residence time IV and target residence time SV

Claims (9)

Process for drying a drying material (30) located in a drying container (10) by passing a drying medium through the material to be dried (30), characterized by the following repetitive method steps: - Determining a consumption of the material to be dried (30) and a filling amount and / or a mass of the material to be dried (30) in the drying container (10); - Calculating an actual residence time (IV) of the material to be dried (30) in the drying container (10) taking into account the consumption of the material to be dried (30) and taking into account the capacity of the material to be dried (30) and / or the mass of the material to be dried (30) in the drying vessel (10); and - Outputting a control signal for filling the drying container (10) with Trocknungsgut (30) in the event that the actual residence time (IV) is less than the desired residence time (SV). A method according to claim 1, characterized in that the method further comprises a method step for outputting a second control signal for stopping the filling of the drying container (10) with material to be dried (30) in the event that the actual residence time (IV) is equal to or greater than the desired residence time (SV) is. Method according to one of the preceding claims, characterized in that the method comprises an initial step of inputting and / or setting the desired residence time (SV) of the material to be dried (30) in the drying container (10). Drying plant (1) with a drying container (10) for drying drying material (30) located in the drying container (10) by passing a drying medium through the material to be dried (30),
characterized by the following features: - The drying plant (1) has a level sensor (18) for determining the level of the material to be dried (30) in the drying container (10) and / or has a weight sensor for determining the weight of the material to be dried (30) in the drying container (10); - The drying plant (1) has a control device (19) which is connected to the level sensor (18) and / or the weight sensor via a signal line (20); - The control device (19) is adapted to receive via the signal line (20) and / or via a further signal line (21) a consumption signal representing a consumption of the material to be dried (30); - The control device (19) is adapted to, based on the consumption of the material to be dried (30) and the filling amount of the material to be dried (30) and / or the mass of the material to be dried (30) in the drying container (10) an actual residence time (IV) of Drying material (30) in the drying tank (10) to calculate, and is further adapted to, if the actual residence time (IV) is less than a desired residence time (SV), a control signal for filling the drying tank (10) with drying material (30 ). Drying plant (1) according to claim 4, characterized in that the control device (19) is adapted to a second control signal for stopping the filling of the drying container (10) with Trocknungsgut (30) in the case that the actual residence time (IV) is equal to or greater than the target residence time (SV). Drying plant (1) according to one of claims 4 or 5, characterized in that the level sensor (18) is designed as a capacitive level sensor (18). Drying plant (1) according to claim 6, characterized in that the filling level sensor (18) extends parallel to a longitudinal axis of the drying container (10). Drying plant (1) according to claim 4 to 7, characterized in that the drying plant (1) has a plurality of level sensors (18). Drying plant (1) according to claim 8, characterized in that the level sensors (18) are arranged at different axial heights of the drying container (10).

Images