DE102021000618A1 - Process for controlling the drying process of a product in a dryer - Google Patents

Abstract

The invention relates to a method for controlling the drying process of a product (1) in a dryer (2), with a blower (3) for conveying drying air (L) to the product (1), with a heating device (4) for heating the Drying air (L) and with a control and / or regulating device (5) for controlling a device (6) for controlling the temperature (TL, 1) and / or the humidity (ϱ) in the dryer (2).To a method to specify the regulation of a drying process of a product, which can be carried out with little measuring and control engineering effort and which enables the achievement of predeterminable final qualities of the drying product, it is provided that when controlling the moisture (ϱ) by the control and/or regulating device ( 5) on the temperature (TL) of the drying air (L) and/or the product (T1) and when controlling the temperature (TL) of the drying air (L) and/or the product (1) on the humidity (ϱL,1 ) in the T rocker (2) and/or the product (1) is closed.

Description

The invention relates to a method for controlling the drying process of a product in a dryer, with a blower for conveying drying air to the product, with a heating device for heating the drying air and with a control and/or regulating device for regulating a device for controlling the temperature and/or the humidity in the dryer, according to the preamble of claim 1.

Industrial products, but also products from agricultural production of plant or animal origin and also products derived from them for the manufacture of pharmaceuticals are usually processed using dryer types suitable for the product in question, such as belt dryers, shaft dryers, batch dryers or chamber or tray dryers transferred, in which they can either be processed further in the case of industrial products, as semi-finished products or end products or put to a specific use by a customer, or in the case of products from agricultural production, storage stability while at the same time maintaining the product quality over a period of time long enough for the end consumer reach.

Agricultural products in particular have a natural initial moisture content of around 35% or more and their storage stability is usually only achieved at a moisture content of 15% for plant products and below 20% for products of animal origin.

In order to achieve the desired final qualities of drying products of an industrial nature, but also in particular of agricultural origin, such as strength values of dried building materials or ingredients of products of agricultural origin, such as nutrient content, vitamin content, acidity or sugar content, but also the color and texture of the dried product, it has hitherto been necessary to determine and monitor not only the temperature and the relative humidity of the drying air but also its moisture content and often also its flow rate over the duration of a drying process.

Customers often make specific specifications and requests for the end or drying product to be achieved, which overall make a process and a dryer carrying it out complex and expensive to implement or purchase.

the EP 2 184 999 B1 describes a drying system consisting of a drying chamber with a fresh air supply with devices for conditioning the fresh air, a process air discharge with a monitoring and control device for monitoring and controlling the air flows, the humidity and the temperature in the drying system. The drying system is complex.

Proceeding from this prior art, the invention is based on the object of specifying a method for controlling the drying process of a product which can be carried out with little measurement and control effort and which enables the achievement of predeterminable final qualities of the dried product.

The object is achieved with a method having the features of claim 1 in its entirety.

Due to the fact that the influence of a plurality of physical parameters of the drying air to be monitored on the final qualities to be achieved of the drying product of the drying process is controlled and monitored, i.e. when regulating the moisture in the dryer and/or the product by the control and/or control device on the temperature of the drying air and/or the product and when controlling the temperature of the drying air and/or the product on the humidity in the dryer and/or the product is a process and a technical measure specified, which allows a simplification of the process and a simplification of the design effort in a dedicated dryer. Here, a sufficient number of random samples of dried products and their quality characteristics from the drying processes carried out during the development of the method are used and, for example, only the temperature of the drying air or the drying material is monitored and regulated, or only the humidity of the drying air or the product is monitored and regulated, while the temperature of the drying air remains constant.

Despite this step of simplification, it is nevertheless possible to achieve surprisingly precisely specified quality features of the drying product. Usually associated with a reduction in drying time.

Preferred embodiments result from the dependent claims.

A particular advantage of the method is that the method makes it possible for only the control of the temperature or the humidity of the drying air or the product that important product properties of the product after drying is not or would be difficult and difficult to monitor during drying, or which cannot be determined by non-destructive analysis, can nevertheless be achieved.

The process is thus characterized by structural and process engineering simplicity and good controllability and ultimately enables the desired product properties to be achieved.
For example, surface hardness or tensile and compressive strength of industrial products, their colors and surface properties can be defined after the end of drying by controlling the temperature of the drying air alone.

In the case of products of agricultural origin, starting from the respective product properties, for example vitamin, acid content, protein content, colour, content of sugars, content of essential oils and the like can be derived. Furthermore, the physical properties of the material, such as weight, specific weight, volume or surface area or texture after drying.

Therefore, no additional sensors and measuring technology are required in order to be able to successfully carry out the method according to the invention.

In a further advantageous embodiment of the method, subsequent drying processes can be carried out by exclusively controlling the temperature over the duration of the process using temperature profiles derived from a moisture profile during drying,

The purely temperature-controlled drying process is therefore preceded by several calibration or standardization processes with detection of the moisture and the course of the purely temperature-controlled drying process is maintained by the manufacturer of a dryer capable of carrying out the drying process according to the invention. For example in the form of files in a data memory of the open-loop and/or closed-loop control device.

In a dryer that can be produced particularly inexpensively for carrying out the method according to the invention, the device for controlling the temperature and/or the humidity in the dryer is designed in the manner of a flap influencing the flow channel cross section for drying air towards the product. As a result, the flow channel cross-section, for example, can be changed many times during the drying process and at intervals of a few seconds, and the temperature can therefore be influenced and controlled.

In the simplest case, the drying process is only controlled via a fixed temperature-time axis. With many products, especially products of agricultural origin, there is a characteristic moisture profile in the drying air and thus also in the product itself during drying.

For example, extensive representative tests have shown that, in a first phase after the start of drying, the relative humidity in the dryer develops an approximately linear course, with the humidity being able to remain the same or else to fall linearly.

After this first drying phase, the relative humidity falls in a characteristic manner and only specifically for the respective product, so that the temperature of the drying air can be lowered to a new, preset value before this fall.

Depending on the characteristics of the behavior of the product when it releases moisture over the drying period, the drying process can be divided into a first phase (usually higher temperature) and a second phase or other phases. In the first phase, in addition to the obligatory monitoring of the temperature, the humidity can also be monitored.

In the phases of the drying process, the control and/or regulating device can specify either the temperature or the humidity and the time intervals, so that the user of the method, which is preferably integrated in a dryer and its control optimized for this purpose, has no special knowledge of drying of corresponding products, thus has a very easy-to-use dryer at hand compared to dryers according to the prior art.

A contributing factor here is that the control and/or regulation device includes a program controller, which can also be programmable, which, based on the initial moisture content of the product or a product or air moisture content after a warm-up phase of the dryer, determines a basic drying process from a large number of drying processes or programs selects.

The drying programs can be based on data that were determined by the manufacturer of the dryer itself in long series of tests. However, it can also be advantageous to partially or completely control the data for controlling the drying process from a cloud (IoT) or a server system.

The updating of this data for controlling the course of drying can also come from the provision of data from a few or many companies carrying out the method.

It is advisable to carry out a plausibility check of the data before using this data. As mentioned, a simple control of the temperature of the drying air on the product is made possible by the fact that only one flap is to be arranged in the flow channel carrying the drying air, which partially or completely opens or also closes it.

The flap can also work in the manner of an iterative fully opening or fully closing control element in the flow channel and open and close again, so to speak, in a sawtooth operation at short intervals of, for example, one or a few seconds, whereby the temperature of the drying air on the product and the Product temperature is controllable.

It goes without saying that the flap can also be designed and operated in an infinitely variable manner.

A recuperator can be installed upstream or downstream of the device in order to significantly save energy and/or to change the temperature of the drying air. This can be able to save up to 90% heating energy. In addition, it has a dampening effect on the regulation of the temperature and there is a certain dehumidification of the drying air. The recuperator can also be used instead of the flap.

In particular, the flap opens a large cross section of the flow channel when the temperature of the drying air is lower than a target temperature and/or the humidity of the drying air is greater than a target humidity.

• 1a Einen schematischen, nicht maßstäblichen Längsschnitt durch einen als Hordentrockner gebildeten Trockner zur Durchführung des erfindungsgemäßen Verfahrens,
• 1b einen schematischen, nicht maßstäblichen Längsschnitt durch einen als Hordentrockner gebildeten Trockner mit einer als Rekuperator gebildeten Einrichtung zur Steuerung der Temperatur und/oder der Feuchte in dem Trockner,
• 2 einen Phasenverlauf der Ansteuerung der Einrichtung zur Steuerung der Temperatur und/oder der Feuchte in dem Trockner am Beispiel der Öffnung- und Schließzeiten einer den Strömungskanalquerschnitt steuernden Klappe,
• 3 einen Temperaturverlauf der Trocknungsluft bei dem Verfahren gemäß 2,
• 4 einen Temperaturverlauf der Oberflächentemperatur des zu trocknenden Produktes und einen Temperaturverlauf der Trocknungsluft über die Trocknungszeit aufgetragen,
• 5 ein weiteres Beispiel eines typischen Verlaufes der Temperatur der Trocknungsluft über die Trocknungszeit aufgetragen,
• 6 ein weiteres Beispiel eines Phasenverlaufes der Ansteuerung der Einrichtung zur Steuerung der Temperatur und/oder der Feuchte in dem Trockner am Beispiel der Öffnungs- und Schließzeiten einer den Strömungskanalquerschnitt steuernden Klappe,
• 7 einen Temperaturverlauf über die Trocknungszeit, wobei die Temperatur nicht konstant ist, sondern entsprechend des Verlaufes der Feuchte der Trocknungsluft geregelt wird; und
• 8 Verläufe der Feuchte in Abhängigkeit von der Trocknungsdauer und der Regelung der Temperatur der Trocknungsluft.

The procedure is explained below using the drawing. Show in the drawing:

• 1a A schematic, not to scale, longitudinal section through a dryer designed as a tray dryer for carrying out the method according to the invention,
• 1b a schematic longitudinal section, not to scale, through a dryer designed as a tray dryer with a device designed as a recuperator for controlling the temperature and/or the humidity in the dryer,
• 2 a phase curve of the activation of the device for controlling the temperature and/or the humidity in the dryer using the example of the opening and closing times of a flap controlling the flow channel cross section,
• 3 according to a temperature profile of the drying air in the method 2 ,
• 4 a temperature profile of the surface temperature of the product to be dried and a temperature profile of the drying air plotted over the drying time,
• 5 another example of a typical course of the temperature of the drying air plotted against the drying time,
• 6 a further example of a phase curve of the activation of the device for controlling the temperature and/or the humidity in the dryer using the example of the opening and closing times of a flap controlling the flow channel cross-section,
• 7 a temperature profile over the drying time, the temperature not being constant, but rather being regulated according to the moisture profile of the drying air; and
• 8th Moisture curves depending on the drying time and the regulation of the temperature of the drying air.

In 1a 1 is a schematic, not-to-scale longitudinal section in the vertical direction of a dryer 2 designed as a tray dryer for drying products 1, such as industrial series parts such as semi-finished products containing water containing building materials or products of agricultural origin such as fruit, vegetables, meat products or agricultural products 1 for the production of pharmaceuticals are shown.

The dryer 2 has a cube or cuboid housing in which the product 1 to be dried is shown arranged schematically.

On one, facing up 1a left end wall, a flow channel 7 is arranged, which continues over the bottom of the dryer 2. The flow channel 7 serves to transport drying air L, which is arranged at an opening 10 in the upper left corner of the dryer 2, opening to the surroundings of the dryer 2. This is formed by a movable flap 9, which serves as a device 6 for controlling the temperature T _L,1 and/or the humidity ϱ _L,1 in the dryer 2 and/or on the product 1. In the direction of view 1a a blower 3 is arranged in a lower, left-hand corner of the flow channel 7, which draws in drying air L from the opening 10 via a heating device 4 downstream of the blower 3 and conveys it to the product 1 at a temperature T _L .

The device 6 formed as a flap 9 is controlled by a control and/or regulating device 5 in its pivoting angle and thus in its The degree to which it opens or closes the opening 10 is controlled.

Correspondingly, when the flap 9 is in an open position, ambient air, which is generally cooler than the drying air L, can flow into the flow channel 7, or when the flap 9 is closed, the temperature T _L of the drying air L and thus usually also the Temperature T ₁ are raised.

In principle, it is therefore possible to influence and regulate the temperature T _L,1 in the dryer 2 . Even if the heating device 4 always heats the drying air L to a constant, preset value.

In 1a With the opening 10 closed, a recirculation mode is shown, ie the drying air L passing through the product 1 and flowing through it or along it is again passed over the heating device 4 and passed back to the product 1 by the blower 3 via the flow channel 7 .

When the flap 9 is open or partially open, drying air L enriched with moisture escapes through the opening 10 or another opening (not shown) outside of the dryer 2.

In 1b 1 is a schematic, not-to-scale longitudinal section in the vertical direction of a dryer 2 designed as a tray dryer for drying products 1, such as industrial series parts such as semi-finished products containing water containing building materials or products of agricultural origin such as fruit, vegetables, meat products or agricultural products 1 for the production of pharmaceuticals shown, where instead of the flap 9, as in 1a shown, a recuperator R is provided, which replaces the basic function of the flap 9.

In 2 is an example of many possible methods according to the invention, a phase curve of a device 6 controlled by the control and/or regulation device 5 for controlling the temperature T _L,1 and/or the humidity ϱ _L,1 in the dryer 2 in the form of the 1a shown flap 9 shown.

At the beginning of the drying process, the flap 9 remains closed in order to quickly reach the desired setpoint temperature in the dryer 2. The flap 9 remains open for a longer period of time only when drying products 1 with high surface moisture. As in the too 2 adjoining 3 shown, this is necessary in order to raise the product temperature T ₁ as quickly as possible to a then constant temperature in order to enable the greatest possible moisture release per unit of time.

As the 2 and 3 to clarify, after this first phase I, in which the flap 9 is open and maximum moisture is thus transported from the product 1 through the opening 10 to the outside, in the second phase II the flap 9 is opened in a controlled operation at discrete intervals and getting closed. Depending on the selected interval length, the temperature T ₁ of the product 1 or the drying air L can then be lowered even if the temperature of the heating device 4 and the drying air L emitted by it remains constant (cf. 6 , 7 ).

The in the 2 and 3 The methods shown are also characterized by the fact that the flap 9 is fully open or closed, i.e. the cross section A of the flow channel 7 is full of fresh drying air, which has been discharged from the area surrounding the dryer 1 or is completely traversed by circulating air in the dryer 2 . That in the 2 and 3 The method illustrated is carried out when or as long as a product 1 has a high surface temperature.

The selected temperatures T _L of the drying air L are in the in 2 until 7 derived from previous drying processes and their moisture profiles during the drying of the respective product 1. This guarantees specific quality features of the respective end product of a respective drying process. The products 1 do not have to be examined for their quality characteristics during the drying process using complex methods that are not always non-destructive.

For this purpose, the control and/or regulating device 5 preferably has a programmable program controller and a data memory. Depending on the type of product in question and its initial moisture content, a selection can be made from a large number of stored drying programs.

As 1a,b show, the control and/or regulation device 5 or its data memory can also be provided with data from previous drying processes as well as data from a cloud.

4 shows in the further curve a temperature curve T ₁ of the product 1 over the drying time. The air temperature T _L of the drying air L set and regulated for the drying of the product 1 is plotted above this.

In a first phase I of drying, the temperature T _L of the drying air L is selected to be higher, so that a desired moisture release from the product 1 is achieved and the surface temperature of the product 1 is brought to a temperature T ₁ selected for rapid moisture release.

After the desired surface temperature T ₁ of the product 1 has been reached, the drying air temperature T _L is adjusted to approximately the same value as the surface temperature T ₁ and maintained.

5 shows a simplification of the temperature control T _L of the drying air L to this result of the surface temperature T ₁ , as in 4 shown to be able to achieve. This in 5 The course of the temperature of the drying air L shown enables humidity courses as shown in 8th are shown. With many products 1, especially from agriculture, the characteristic drop in product moisture ϱ ₁ shown occurs during the drying process, with the temperature T _L of the drying air L then decreasing as in 5 shown can be reduced.

Reference List

(1)

product

(2)

dryer

(3)

fan

(4)

heating device

(5)

Control and/or regulation device

(6)

furnishings

(7)

flow channel

(8th)

cloud

(9)

flap

(10)

opening

(L)

drying air

(r)

recuperator

(TL)

drying air temperature

(T1)

temperature of the product

(ϱL)

humidity of the drying air

(ϱ1)

moisture of the product

(a)

cross-section

(v)

air speed

(I)

phase

(ii)

phase

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2184999 B1 [0006]

Claims (16)

Method for controlling the drying process of a product (1) in a dryer (2), with a blower (3) for conveying drying air (L) to the product (1), with a heating device (4) for heating the drying air (L) and with a control and/or regulating device (5) for regulating a device (6) for controlling the temperature (T _L,1 ) and/or the humidity (ϱ) in the dryer (2), characterized in that in the Regulating the moisture (ϱ) by the control and/or regulating device (5) on the temperature (T _L ) of the drying air (L) and/or the product (T ₁ ) and when regulating the temperature (T _L ) of the drying air (L) and/or the product (1) on the humidity (ϱ _L,1 ) in the dryer (2) and/or the product (1) is closed. procedure after claim 1 , characterized in that the course of the humidity (ϱ _L,1 ) or the temperature (T _L,1 ) during the drying of the product (1) as an indication of product properties of the product to be dried which cannot be determined, or only with difficulty, or cannot be determined non-destructively (1) is used. Procedure according to one of Claims 1 or 2 , characterized in that subsequent drying processes are carried out by exclusively controlling the temperature (T _L,1 ) over the duration of the process by means of a temperature profile derived from a moisture profile during the drying process. Procedure according to one of Claims 1 until 3 , characterized in that the device (6) for controlling the temperature (T _L,1 ) and the humidity (ϱ _L,1 ) as a device for controlling the cross section (A) of a flow channel (7) for drying air (L) to the Product (1) is designed out, which repeatedly changes the flow channel cross section (A) during the process. procedure after claim 4 , characterized in that a drop in moisture (ϱ _L ) of the drying air (L) is detected, which indicates a change in the speed (v) of the drying air (L) in the flow channel (7) for drying air (L) to the product (1st ) initiated. procedure after claim 4 , characterized in that a drop in humidity (ϱ _L ) of the drying air (L) is detected, which indicates a change in the drying air temperature (T _L ) and/or the flow channel cross-section (A) for drying air (L) to the product (1) initiated. Procedure according to one of Claims 1 until 6 , characterized in that the drying process is divided into at least a first phase (I) and a second phase (II). procedure after claim 7 , characterized in that in the first phase (I) the drying air temperature (T _L ) is always regulated and the air humidity (ϱ) is monitored. procedure after claim 7 or 8th , characterized in that in the first and/or second phase (I, II) the drying process is carried out according to fixed temperature, or humidity, or time specifications. Procedure according to one of Claims 1 until 9 , characterized in that the control and/or regulating device (5) comprises a programmable program controller which uses the initial moisture content (ϱ ₁ ) of the product (1) or a moisture content (ϱ _L ) after a warm-up phase of the dryer (2) to calculate a basic drying process from a variety of drying programs. procedure after claim 10 , characterized in that the drying programs are initially partially provided with data obtained before or during the drying process or data from a cloud (8). Procedure according to one of Claims 1 until 11 , characterized in that the device (6) is designed as a flap (9) which is moved steplessly. Procedure according to one of Claims 1 until 12 , characterized in that the device (6) has a recuperator (R) which preheats the drying air (T) and dehumidifies to a certain extent. Procedure according to one of Claims 1 until 13 , characterized in that the device (6) opens a large cross section of the flow channel (7) when the temperature (T _L ) of the drying air (L) _is lower than a target temperature (T set ) and/or the humidity (ϱ _L ) of the drying air (L) _is greater than a target humidity (ϱ target ). Procedure according to one of Claims 1 until 14 , characterized in that the device (6) remains open at fixed time intervals, for example 5 seconds, and its function is controlled by the control and/or regulating device (5) at variable time intervals. Procedure according to one of Claims 1 until 15 , characterized in that the product (1) is an agricultural product or a product for the manufacture of pharmaceuticals.

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