EP2189741A2 - Method and device for drying and programming of drying process - Google Patents

Abstract

The method involves regulating a drying parameter e.g. temperature and air flow quantity, under consideration of a regulation difference (9) between an actual shrinkage of a finished or semi-finished component part and a preset component part-specific shrinkage reference profile (6). A process parameter of the regulated parameter is recorded to generate reference- and/or actuating variables for a drying process. The regulation is made based on measuring signals of relative moisture and/or temperature. Shrinkage measuring sensors (7, 8) are arranged at the parts for determining the shrinkage. An independent claim is also included for a drying device for executing a method for drying a finished or semi-finished component part that is either moist or shrunk while drying.

Description

The invention relates to a method for drying at least one moist and Trocknungsschwindungsbehäfteten semi-finished or finished component according to the teaching of claim 1.

Furthermore, the invention relates to a device for carrying out the method according to the invention according to the teaching of claim 16.

Drying processes known from the prior art are based on heat transfer and mass transfer between a semi-finished or prefabricated component subject to wetting and drying, a fabric component, generally water, being withdrawn through a dry medium, usually a hot air flow, to a finished or semi-finished component so that the component to be dried undergoes a volume decrease. If the volume decrease is not evenly distributed throughout the body, shrinkage tensions arise. The absolute amounts of the stresses are material specific and shape dependent, whereby the component can only absorb certain amounts of stress. The voltages stay close below a critical crack resistance limit, deformations can occur. When the crack resistance limit is exceeded, the component breaks.

Generic drying methods are used in particular in clay production, in the production of roof tiles, clinker, flower pots, brick slabs, tiles, fine ceramic products, etc. Furthermore, such drying methods are also used in the woodworking industry, especially in wood drying and veneer production. However, such drying methods can also be used in other areas of component production where wet components are to be dried.

The requirements of an economically interesting drying method are directed to the production of components of consistent definable quality, which are free of distortion and cracks with a defined residual moisture quickly and economically in large quantities and drying successive drying processes are reproducible to dry.

For this purpose, "try and error" drying methods are known from the prior art, in which an experienced expert tries to determine by manual adjustments optimal parameters in terms of short drying time, high product quality, low residual moisture, etc., in order to dry half or finished components , After several such "try and error" drying operations, many sequential drying operations are then carried out for series production based on the process parameters found out. This procedure usually requires a high number of manual test runs with corresponding Zeit-, labor and cost, which incurred in most cases a significant amount of semi or finished components as a committee.

The aim of an economically interesting drying process is, therefore, process parameters, in particular the parameters relative humidity and temperature, by means of actuators, which regulate the air flow and the heat generation, optimally adjust to achieve reproducible drying results.

The methods known from the prior art try to determine suitable setpoint curves of relative humidity and temperature for each new semi-finished or prefabricated component to be produced. However, this often fails due to the influence of the shape factor of the component and the unpredictable inequality factors of the dry chamber types. Above all, a control according to relative humidity and / or temperature with respect to the component in the drying device is only an indirect measurement and control method, which does not allow any statement on the actual drying or shrinkage behavior of the component to be dried.

Thus, the previous preparation of drying curves, which can serve for repeated execution of drying processes, an iterative process, in which only with existing drying results after drying time, quality and residual moisture again a new drying process, taking into account the relative humidity and temperature, etc. can be created , see also Fig. 1 , Thus, the quality of the drying processes of the prior art depends on a manual preparation and thus on the quality of the specified setpoint values for temperature, relative humidity and on the number of optimization steps. In this context, the relative humidity is understood to mean the percentage ratio between the instantaneous water vapor pressure and the saturation water vapor pressure over a pure and even water surface. The relative humidity therefore indicates immediately to what degree the air is saturated with water vapor, or how much water from the air can still be absorbed.

The state of the art is explicitly based on the dissertation by Uta Telljohann, "Theoretical and Experimental Investigations of the Drying of Molded Bricks", Faculty of Process and Process Engineering Systems Engineering, Otto von Guericke University Magdeburg, June 4, 2004 directed.

On the basis of the abovementioned prior art, the object thus arises of proposing a drying method and a device provided for this purpose, which provides a measurement-size-based and automatic determination of optimum drying parameters for any semifinished or finished components, whereby optimal parameters are already available after a few test runs and an efficient determination of drying parameters for the reproducible and qualitatively adjustable drying of a series of similar components is made possible.

This object is achieved by a method according to claim 1 and a device according to claim 16.

Advantageous embodiments of the invention are the subject of the dependent claims.

The inventive method is used to dry at least one humid and Trocknungsschwindungsbehäfteten half or finished component, wherein at least a first controlled drying process is performed, in which a control of drying parameters, such as temperature, air flow rate, etc. taking into account at least one control difference between actual shrinkage of the component and a predetermined component-specific Schwindungssollverlauf is enabled.

According to this teaching, the relevant course of shrinkage is regulated online and the resulting actual values of the drying parameters such as air circulation, drying temperature, etc. can be stored and made available as future program target values for subsequent drying operations. By taking into account the shrinkage of a component and its comparison with a component-specific Shrinkage follow-up curve requires only a small number of drying operations until optimal drying parameters are determined. The method can be used for target curve determination when introducing new components, but also serve to find out their optimal new setpoint curves after retrofitting existing equipment, as well as saving energy of the drying process for existing drying systems and a dynamic runtime adjustment to minimize the drying times with minimum energy drying curves enable.

Prerequisite for this is the submission of a component-specific shrinkage setpoint curve, which depends on the one material-dependent, on the other hand, but also on the form factor, ie the specific geometric design of the component. In order to find such a shrinkage setpoint curve, there are sufficient empirical values based on the knowledge of the overall shrinkage of the molding under process conditions. This shows Fig. 2 an idealized shrinkage behavior of ceramic masses by means of a Bourry diagram. It can clearly be seen that after the beginning of a drying process, the proportion of water dwindles to a so-called point of infiltration, at which the component reaches its final volume, in this case about 80% of the initial volume. As the degree of drying progresses, the water content decreases, without the volume shrinking further. As in the Fig. 3a and 3b As shown, the shrinkage setpoint curve changes depending on whether a "thin" or "thick" component is dried.

The determination of a shrinkage setpoint curve can be carried out quickly and easily by a person skilled in the art, even with new component geometries, and guarantees that no irregularities in the drying process and shrinkage cracks occur unless the shrinkage setpoint curve falls short of the shortest possible drying time or does not exceed the material and product-specific strength values become.

Thus, the inventive idea is that in the course of the drying process the shrinkage of the component is measured online and a shrinkage setpoint curve is readjusted, ensuring that the actual volume shrinkage curve never exceeds the maximum shrinkage gradients that depend on the drying progress.

In an exemplary embodiment, the process parameters of the controlled drying process are logged in order to be able to generate control and / or manipulated variables for subsequently controlled or controlled drying processes. Thus, after execution of the shrink-controlled drying process, its process parameters are logged in the course of the drying process and are available for subsequently controlled or merely controlled drying processes. In this context, a regulation means a feedback and comparison of controlled variables to reference variables for the generation of manipulated variables which influence the behavior of a controlled system. A controller has no such feedback and is used to influence a device according to a predetermined plan.

Furthermore, it is advantageously conceivable that the control loop comprises a further control as a temperature control with a temperature control difference and / or a humidity control for controlling the water vapor absorption capacity of the dehumidifying dry medium based on measurement signals of relative humidity and temperature within the drying chamber. Thus, the second control is based on either a temperature or a humidity, or a combination thereof. In addition, further control parameters for the second control loop are conceivable, which can provide information about the drying progress of the component. Thus, the value for the water vapor absorption capacity (.DELTA.g _steam / kg _air ) or a differential pressure, for example partial _{pressure of} water vapor to saturation partial pressure, a good basis of a control difference formation be. It should only be noted that previously two variables, such as temperature and relative humidity calculated to a size (such as the differential temperature between the cooling limit temperature and temperature of the drying device) can be transferred. A humidity control is particularly suitable if in the drying chamber a supply air flap, possibly parallel to an exhaust air flap and / or antiparallel is provided as a recirculation damper for controlling the humidity and a heat generator as a burner or heater or the like. can be operated by means of a temperature control.

Basically, as claim 1 indicates, the control loop comprises a shrinkage control. After the in Fig. 2 Bourry diagram shown is achieved in the course of the drying process at the point of so-called. Knickpunktsfeuchte a Schwindungsendmaß of the component, from which the water content decreases, but the component undergoes no change in volume and thus the degree of shrinkage can provide any information about the degree of dryness of the component , Thus, it is advantageously conceivable that the control also takes into account a temperature control, so that shrinkage and temperature are used to find optimal drying parameters.

A further development of the above-mentioned embodiment is that during a drying process within a first drying phase at least partially a shrinkage control and within a subsequent second drying phase at least partially carried out a temperature and / or humidity control.

Thus, as already explained in the above embodiment, the Bourry diagram, the volume decrease is regulated until reaching the Knickpunktsfeuchte means of shrinkage control, from then the drying control is continued by means of a temperature and / or humidity control until the component reaches the desired final moisture. Thus, it is advantageously conceivable that in the first drying phase Schwindungsregelung is made and uses a temperature and / or humidity control in the second drying phase.

Furthermore, it is advantageously conceivable that the control loop comprises at least two slave controllers, wherein the control value u _{1 of} a first slave controller K _{1 is used} as a reference variable w _{2 of} a second downstream slave controller K ₂ . By using a control loop by means of two slave controller K ₁ , K ₂ with the output of the first follower K ₁ serves as a reference variable of the second controller K ₂ , elegantly controlled two controlled variables can be compensated for each other, for example, the component shrinkage as a first controlled variable and the temperature difference or another second variable as a second controlled variable, wherein a first controller K ₁ performs a vibration control and a second controller K _{2 performs} a temperature and / or humidity control, or the adjustment of the second size.

From this follows the advantageous further design of the inventive method, wherein a first slave controller K ₁ performs a Schwindungsregelung, wherein the error signal e ₁ of Schwindungsregelung w a Schwindungsregeldifferenz between actual Bauteilschwindung y ₁ and a Schwindungssollverlauf is ₁ and the output value u ₁ w as a reference variable ₂ is used for a temperature control or for the control of a second size of the second sequence controller K ₂ , wherein the second control difference e _{2 is} a temperature control difference or a control difference of the second size.

While the first control difference as shrinkage control represents the difference between actual component shrinkage and a component-specific shrinkage setpoint course, the second controlled variable of the drying effect can be selected as desired. In an advantageous embodiment, the reference variable w ₂ and / or control variable y ₂ 'of the temperature control (input variables of the second regulator K ₂ ) can be derived from temperature y ₂₁ and relative humidity y _{22 of} the drying device (02) derivable physical difference quantity, in particular temperature difference between wet bulb temperature and dry temperature. In this case, the wet bulb temperature is defined as the cooling limit temperature, ie the lowest temperature which can be achieved by evaporative cooling, in which the water delivery of a moist surface is in equilibrium with the water absorption capacity of the surrounding atmosphere, so that the surrounding gas or the air is saturated with steam ,

However, it is likewise advantageously conceivable that a pressure difference between the water vapor saturation _partial pressure and instantaneous water vapor _partial pressure (in bar), a mass difference between maximum water vapor _{absorption capacity} in the saturation state and instantaneous water vapor content (in _water / kg _air ) or a similar difference _variable can be determined from temperature and relative humidity. which can be used as a controlled variable for the downstream drying effect control stage of the follower controller K ₂ .

The wet bulb temperature is difficult to determine directly by measurement. However, it is advantageous and obvious that instead of the wet bulb temperature, the relative humidity and temperature of a drying device is determined, from which the wet bulb temperature can be derived by calculation with known conversion formulas. Thus, it is advantageous to determine the temperature difference y ₂ 'by calculation from measured relative humidity y ₂₂ and temperature y _{21 of} a drying device.

According to the above, it is advantageous that the drying effect control difference (13) shows a difference e ₂ between a reference variable w ₂ obtainable from the shrinkage control u ₁ and one from relative humidity y ₂₂ and the temperature y _{21 of} the drying chamber (02). determinable controlled variable y ₂ 'is. In particular, lends itself for this purpose a control value resulting from the Schwindungsregelung u ₁ detectable temperature difference command value w ₂ between wet-bulb temperature and a dry temperature and a relative humidity of y ₂₂ and y ₂₁ of the drying chamber temperature determinable Temperature difference y ₂ 'between wet bulb temperature and dry temperature. In other words, this results in an advantageous embodiment of the drying method, in which a first controller performs a shrinkage control between an actual shrinkage of a component during a drying process and a Schwindungssollverlauf, the output of the first controller is interpreted as the difference between actual temperature and wet bulb temperature. This output control value u _{1 of} the first controller K ₁ then serves as differential control variable w _{2 of} the second controller K ₂ and can be regarded, for example, as a differential temperature between wet bulb temperature and dry temperature, wherein the controlled temperature y ₂ 'is the actual temperature difference between wet bulb temperature and dry temperature in the controller K ₂ , which can be derived from the directly to be measured temperature y _{21 of} the drying chamber and the relative humidity y ₂₂ , which prevails in the drying chamber. However, for the difference values, pressure difference or mass difference, which can be determined from relative humidity and temperature, can be used in the same way as suggested above.

Basically, the above-mentioned method is based on recording the actual shrinkage of the component during the drying process. To determine the actual shrinkage, it is advantageous if at least one Schwindungsmessaufnehmer is disposed on at least one component that absorbs the actual shrinkage of the component.

Furthermore, it is advantageously possible to arrange at least two Schwindungsmessaufnehmer on two components, wherein the first component is the fastest drying component and the second component is the slowest-drying component. The pre-selection of the slowest and fastest component is based on physical relationships and the experience of the person skilled in the art.

Since the drying rate increases with increasing rate of the water-receiving medium, i. As the air velocity increases and as the desiccant saturates with water (air saturation), the components blown directly from a hot air supply will be the fastest drying / dwindling components. The most remote components are due to the increasing saturation of the dry medium by the intervening drying components and the lower flow velocity because of the greater distance the slowest drying components. Furthermore, the user of the drying device usually knows "wet nests" which are based on circumstances that are not obvious at first sight and e.g. from uneven hot air supply through the fan or fans with different outputs. Therefore, it is easily possible to identify the location of the fastest and slowest-drying components and thus attach the Schwindungsmessaufnehmer to these components according to the advantageous development.

In addition, it is advantageously conceivable that, in a first drying phase of the shrinkage control, first the shrinkage of the first component, which shrinks fastest, is taken into account in the control and, at the end of the shrinkage phase, the shrinkage of the second component, which dries the slowest, for determining the shrinkage control difference e ₁ is used. Thus, the shrinkage of the fastest drying component is used for shrinkage control initially, at the end of its shrinkage process of this component, the slowest drying component continues to shrink. Thus, after completion of the shrinkage operation of the fastest-shrinking member, the shrinkage control can resort to the shrinkage behavior of the slowest-shrinking member, so that it is ensured that a shrinkage control is performed until the shrinkage of all the components to be dried is completed.

Furthermore, in an advantageous embodiment of the method, it is conceivable to carry out at least three drying operations, wherein a first drying operation is carried out with a predetermined drying time, a second subsequent drying operation is carried out while optimizing the setpoint curves, and a third drying operation is performed to verify the drying result. After the three processes have been carried out at the latest, optimum drying parameters should be present, so that, as proposed in a further embodiment of the method according to the invention, further drying operations, in particular as controlled drying operations on the basis of the logged drying parameters, can be carried out at least without shrinkage control.

Furthermore, the invention relates to a drying device for carrying out a method according to one of the aforementioned method claims. For this purpose, the drying device according to the invention comprises a drying device for drying at least one component, at least one adjusting device for setting drying parameters such as temperature, air flow rate, air circulation or the like in the drying device, a control device for controlling the drying operation by actuating the adjusting device by means of a control value u ₂ and at least a sensor for receiving a controlled variable y ₁ . The drying device is characterized in that the control device comprises at least one Schwindungssollkurveneinheit for outputting a component-specific Schwindungssollkurve least one component and at least one sensor is formed as Schwindungsmessaufnehmer that can absorb the shrinkage of the component in the course of a drying process as a controlled variable y ₁ , wherein the control device formed is to correct a Schwindungsregeldifferenz e ₁ between actual component shrinkage y ₁ and the Schwindungssollverlauf w ₁ .

In other words, the drying device comprises a control device with a shrinkage measuring transducer and a shrinkage setpoint curve unit, which specifies a shrinkage setpoint curve as a reference variable. The sensor absorbs the actual shrinkage of the component, whereby the control device is influenced by influencing the controlled system, i. Setting device and drying device ensures that the shrinkage of the component follows the Schwindungssollverlauf during the drying process.

In principle, the device can work with a shrinkage sensor. Advantageously, the device comprises at least two Schwindungsmessaufnehmer, wherein a first Schwindungsmessaufnehmer is disposed on a first fastest-drying component and a second Schwindungsmessaufnehmer on a second slowest-drying component.

In addition, the device is equipped with a temperature sensor and a sensor for detecting the relative humidity of the air within the drying device to provide from temperature and relative humidity within the drying means a second drying action controlled variable, for example, a differential temperature between wet bulb temperature and actual temperature to be able to determine a pressure difference between water vapor partial pressure and instantaneous water vapor partial pressure or a mass difference between maximum water vapor absorption capacity in the saturation state to instantaneous water vapor content.

It is advantageously conceivable that the control device comprises at least one first controller K ₁ , which is designed as a PID controller. A PID controller has the advantage, without overshooting and without remaining control difference, a uniform and rapid compensation of the control difference e .

Furthermore, it is advantageously conceivable that the control device comprises at least two controllers K ₁ , K ₂ , which are concatenated as slave controller (cascade controller), wherein the first slave controller K _{1 is} designed to control a Schwindungsregeldifferenz e ₁ and the second slave controller K ₂ designed is to correct a temperature control difference, wherein the manipulated variable u _{1 of} the first sequence controller K ₁ as a reference variable w _{2 of} the second sequence controller K ₂ is used. Again, it is advantageously possible to interpret the second follower K ₂ as a PID controller.

In addition, it is advantageously conceivable that the control device comprises a computing unit that is designed, from the measured values y ₂₁ , y _{22 of} the temperature sensor (10) and the sensor (11) of the relative humidity, a physical drying effect difference quantity (13), in particular Difference temperature between wet bulb temperature and dry temperature, pressure difference between water vapor saturation partial pressure and instantaneous water vapor partial pressure or mass difference between maximum water vapor absorption capacity in the saturation state to determine instantaneous water vapor content of the component. These derived parameters are used during the oscillation process in a simple manner as a guide parameter for shrinkage control.

In a further embodiment of the drying device, the latter comprises a protocol unit which is designed to record at least the output manipulated variable u ₂ and / or u ₁ (optionally a plurality of output manipulated variables u ₁ or u ₂ ) of the control device during at least one drying operation. The output manipulated variable u ₂ directly influences the adjusting device, which in turn controls direct drying parameters, such as temperature of the drying air within the drying device, air circulation speed, ventilation flap opening, etc. By means of the protocol unit, the manipulated variables u ₂ output during a first or second drying process can be logged and, in a further exemplary embodiment, in which the device comprises a control device, on the basis of the protocol unit The adjusting means u _{2 received by} the control device directly control the adjusting device of the drying device for carrying out further drying operations. Thus, after carrying out the inventive drying method, the initial control variables recorded by the protocol unit can be called up to carry out further, merely controlled drying operations. In addition, the manipulated variable u ₁ can also be recorded, so that a simple regulation according to the differential temperature can be carried out on the basis of the course of the manipulated variable u ₁ given by the protocol unit. Furthermore, a simple control by temperature and / or relative humidity is conceivable.

In the following the invention will be explained in more detail with reference to exemplary embodiments showing drawings.

Fig. 1:

Ein Verfahrensablauf eines Trocknungsverfahrens nach dem Stand der Technik;

Fig. 2:

ein Bourry-Diagramm eines typischen Trocknungsvorgangs;

Fig. 3:

schematische Schwingungssollverläufe von Bauteilen, mit Vergleich dickes/dünnes Bauteil und "realer" Schwindungsverlauf;

Fig. 4:

Regelkreise nach dem Stand der Technik und nach einem Ausführungsbeispiel;

Fig. 5:

ein Ausführungsbeispiel eines erfindungsgemäßen Regelkreises;

Fig. 6:

in schematischer Darstellung ein Ausführungsbeispiel einer erfindungsgemäßen Trocknungsvorrichtung.

Show it:

Fig. 1:

A process flow of a prior art drying process;

Fig. 2:

a Bourry diagram of a typical drying process;

3:

schematic oscillation setpoint curves of components, with comparison of thick / thin component and "real" shrinkage curve;

4:

Control circuits according to the prior art and according to an embodiment;

Fig. 5:

an embodiment of a control circuit according to the invention;

Fig. 6:

a schematic representation of an embodiment of a drying device according to the invention.

Fig. 1 shows schematically a drying method according to the prior art. Here, in a dryer 02 ceramic moldings as components, in this case tiles, dried. Here, a shrinkage over the time course of the drying process, whereby only the process parameters temperature and relative humidity in the drying device 02 are measured. Upon completion of the drying process, the user is evaluated for shrinkage, temperature and relative humidity and manually set temperature and relative humidity set points for subsequent drying operations. These specified drying parameters are used to re-dry components in a subsequent drying operation to repeat this process several times until optimized drying parameters are found for the components. Thus, the creation of optimal drying parameters is an iterative process, which is characterized by high costs and a large amount of energy and time and a high degree of rejects of the components to be dried.

Fig. 2 schematically shows a Bourry diagram representing the shrinkage process of a clay component. At the beginning of the drying process, the volume is 100%, wherein in the example about 28% of the component volume consists of water. In the course of the drying process, the water content decreases, whereby a shrinkage of the component size in the example to about 80 to 85% occurs. Upon reaching the so-called. Knick-point moisture, ie the temperature at which the decrease in water content leads to no further significant shrinkage, air pores are formed, so that the body volume remains constant.

In the Fig. 3a and 3b Schwindungssollkurvenverläufe are shown, where in Fig. 3a a Schwindungssollverlauf a "thin" and a "thick" component is shown. An example of a thin component may be a beaver tile, a thick component may be a solid brick brick. A thin molding can in principle due to the shorter diffusion paths and a larger surface / volume ratio faster than a thick, solid molding dry. With a standardized drying time, it can also be seen that the thin molded article requires a shorter phase of moisture from the point of contact to the same residual moisture. The easy-to-classify curves are highly similar, with the most significant difference being the molding or component geometry, ie, the surface or sphere model of the thin or thick molding. The shrinkage setpoints for the shrinkage are mainly determined by the component size and geometry, the reference distance on the component, the planned drying time, the mixture of raw materials and the water content.

In the Fig. 3b The angles (α ₁ , α ₂ and α _{3 represent} the start angle of the shrinkage process α ₁ , the angle of the moisture point of curvature α ₂ and the shrinkage curve end angle at the end of the drying time α _3. If cracks occur when the shrinkage target curves are being traversed, the type of cracks can be very high In the course of a drying process, the shrinkage gradient is adapted to the starting value of the gradient of the shrinkage setpoint curve, wherein a tangential setting of the shrinkage setpoint course to the respective drying case is achieved If the actual value of the shrinkage is too great from the outset despite the supply air being closed, the circulation capacity can be reduced, as far as the dryer equipment permits, and the drying speed can be slowed down so as to ensure that the actual flow rate is maintained tion the shrinkage setpoint course, as it is, for example, in Fig. 3b is shown, can be tracked. At the latest from the time at which the slowest dwindling molding reaches its shrinkage end size, the so-called break point moisture (angle α ₂ ), the shrinkage is no longer suitable as a measure of the drying process and thus to regulate the drying process to the desired residual moisture content.

Fig. 4a shows schematically a known from the prior art control loop. The input variable is the reference variable w , which is also referred to as the nominal value. From it, the controlled variable y , which is also referred to as the actual value and which is output at the end of the controlled system G , subtracted, so that a control difference e results. Controller K attempts to adjust the manipulated variable u in such a way that the control difference e disappears. The manipulated variable u is entered into the controlled system G , wherein the controlled system G generates a controlled variable / actual value y after the manipulated variable u . This control variable y is also subject to a disturbance d , which must be compensated by the control loop.

Fig. 4b schematically shows an embodiment of a control loop by means of a sequence control of the two controllers K ₁ and K ₂ according to an embodiment of the invention. Initially, the reference variable w ₁ serves as a desired shrinkage setpoint course, from which the actual shrinkage profile y _{1 is} subtracted, so that a shrinkage rule difference e ₁ 09 results. The controller K ₁ 12 outputs a manipulated variable u ₁ , which is entered as a reference variable w ₂ in the downstream controller K ₂ . At the input of the controller K ₂ , the drying effect controlled variable e ₂ 13, which is calculated as the difference of the reference variable w ₂ and an actual quantity y ₂ ', which results from conversion by means of the arithmetic unit from the actual size y ₂ . The controller K ₂ outputs a manipulated variable u ₂ , which flows into the controlled system G , in this case in the drying device 02 by influencing the adjusting device 03. By means of the sensor 05, the output quantities y ₁ are then supplied as manipulated variables of the shrinkage control and y ₂ as control variables of the temperature control.

Fig. 5 shows an embodiment of the drying method according to the invention by means of in Fig. 4 schematically illustrated control circuit components. In a drying device 02 roof tiles are dried by means of a dryer and hot oven exhaust air and a circulating air circulation (not shown), wherein the output variables y metrologically be determined by means of sensors 05. Furthermore, a Schwindungssollverlauf the components flows into the scheme and serves as Sollschwindung w ₁ . The actual shrinkage y ₁ is recorded by means of shrinkage sensors, for example strain gauges, potentiometers or optical systems, and transformed into a control value u ₁ by means of the PID controller K ₁ 12. This control value u ₁ serves as a reference variable w _{2 of} the downstream PID controller K ₂ 14 and is considered as the difference temperature between the current temperature and the cooling limit temperature of the drying device 02. In parallel, the actual temperature and the relative humidity of the air within the drying device 02, y ₂₁ and y _{22 are} recorded. From these, an arithmetic unit 15 can in turn determine an actual differential temperature between the current temperature and the wet bulb temperature of the drying device 02, which also enters the PID controller K ₂ 14 as a controlled variable y ₂ '. The PID controller K ₂ 14 determines therefrom a manipulated variable u ₂ , which directly controls the flap position 03 of the dryer 02 and thus influences the controlled system (drying device 02). Parallel to this, the determined temperature and relative humidity w ₁₁ , w _{22 are} logged and are available by means of the protocol unit 16 for subsequent drying operations. By the series connection of the two controllers K ₁ 12 and K ₂ 14, a shrinkage control is initially made, since the decrease in shrinkage of the component initially dominated in the control loop.

In principle, instead of the differential temperature between the current temperature and the cooling limit temperature, other physical variables derivable from the relative humidity and current temperature of the drying device (2) can enter the follow-up controller K ₂ 14 as controlled variable y ₂ ', in order to allow residual drying of the component after completion of shrinkage to reach. As an example of such difference sizes include the pressure difference between water vapor partial pressure and instantaneous water vapor partial pressure or mass difference between maximum saturation saturation water vapor capacity and instantaneous water vapor content.

At the latest from the time when the slowest molding has almost reached its shrinkage end size (point of contact moisture), however, the shrinkage is no longer suitable in order to continue an exact regulation up to the desired residual moisture. Therefore, by the second controller K ₂ after reaching the Schwindungsendmaßes, the reflected u ₁ at a constant value of the manipulated variable, On regulated by the temperature differential between the cooling limit temperature and temperature of the drying device ₂ as a control variable y. Since the differential temperature is generally not parallel to the signals temperature and relative humidity at the sensor outputs, the current temperature y ₂₁ and the relative humidity y _{22 are determined} in the drying device 02 and by means of a mathematical relationship to the actual differential temperature between the cooling limit temperature and temperature in the drying device formed by a computing unit 15. Thus, the difference between the output of the PID controller K ₁ 12 serves as a reference variable w ₂ and the actual differential temperature y ₂ 'as Trocknungswirkungs-control difference 13 of the downstream controller 14, which carries out a temperature control.

With the computational merger of the two physical quantities relative humidity and temperature y ₂₁ , y ₂₂ in the drying device 01 on a size of the differential temperature between the cooling limit temperature and temperature in the drying device, which corresponds to a defined drying capacity of the air, it is possible that the process control an actuator over the entire drying time can be performed optimally and stably even with fluctuating supply air temperature.

The shrinkage setpoints result from the choice of the reference section, the mix of raw materials, the shape size and geometry and the planned drying time. These easy-to-classify curves have a high similarity, with the most significant difference being the component or molding geometry (surface or sphere model). As in Fig. 2 illustrated, the point of contact moisture determines the time in which the shrinkage of the component is no longer suitable to serve as a reference variable for the control of the drying process. Visually, the moisture of the breakpoint is recognizable when the shape changes its color, because the moisture level sinks below the surface of the molding.

Since the sizes of the raw material composition and the water content of the components are kept constant within the scope of a constant production quality, the moisture point of the break point is always reproducible. Therefore, a predefinition of the value of the breakpoint humidity at which the shrinkage control is switched to the temperature control is possible and advantageous. However, the in Fig. 5 illustrated cascade control automatic switching, because after the components have reached their Schwindungsmaß according to the Knickpunktsfeuchte, is switched by the Schwindungsregler 12 to a parameter set for specifying the manipulated variable curve u ₂ , so that only the predetermined change in the differential temperature of the drying device 02 as a controlled variable the behavior of the temperature controller 14 determined. A predefinition of the break point value, for example, at approximately 5% of the shrinkage end dimension, can ensure that a reliable switchover is made between shrinkage control and temperature control.

The output u _{1 of} the Schwindungsreglers 12 has a control value of 0 to 100%, but which can also be issued in a size from 0 to 100 Kelvin and thus can be defined as the differential temperature of air temperature to the cooling limit temperature (wet bulb temperature). A lower shrinkage than specified by the setpoint increases the control value (differential temperature from the air temperature to the cooling limit temperature), and an excessively high shrinkage is reduced the control value. The larger the difference temperature between the air temperature and the cooling limit temperature, the stronger the drying effect of the air. For a non-oscillatory behavior of the control, only the controller must be parameterized accordingly.

At constant flow rate of the drying medium above the component and present too low shrinkage rate, the saturation of the drying medium is too high. Consequently, the saturation of the air is lowered, depending on the two variables temperature and relative humidity. A change of both each size, as well as both sizes (raising the temperature and / or lowering the relative humidity) has a change (decrease) in the saturation and thus increased moisture absorption capacity result, which in turn dry the molding faster and thus shrink faster leaves. As a measure of the absorption capacity of the dry medium, therefore, for example, the difference between the measured air partial pressure and the saturation partial pressure in Pascal, the water vapor absorption capacity in kilograms of steam per kilogram of dry air or the water absorption capacity in kilograms of water per kilogram of dry air or just the difference temperature of air temperature used to the cooling limit temperature be, with the above sizes, for example, for the building material ceramic behaves in conventional temperature ranges sufficiently linear and thus excellently offers as a controlled variable. All of the four variables listed above can be calculated from the measured temperature and the relative humidity, wherein this conversion carries out the arithmetic unit 15.

If the actual shrinkage y _{1 is} less than or equal to the geometry and material-dependent breakpoint _setpoint shrinkage w _{kink point} (see FIGS. 2 and 3 ), there is no further shrinkage of the component, so that a regulation of the drying process can no longer be based on the component shrinkage. At this time, a default the desired value w _{2 of} the following controller K ₂ 14 based on pre-logged values u _n -u _k , which are stored as parameter set values for the drying time after reaching the break point moisture of the molded article, which can be taken from the protocol of the parameter setpoint values 16.

Fig. 6 schematically shows an embodiment of a drying device 01, with the aid of an inventive drying method can be performed. The drying device 01 comprises a drying device 02 in which components, in this case roof tiles, are dried by means of dry, warm air (for example, furnace waste heat). For this purpose, the dry, warm air, in particular the waste heat from outside the drying device 01 come, ie the oven does not have to be part of the drying device. For this purpose, the supply air volume and an air circulation can be actuated by means of an adjusting device 03. Within the drying device 02 sensors are arranged 05. These sensors 05 comprise a first shrinkage measuring sensor 07 and a second shrinkage measuring sensor 08, wherein the first shrinkage measuring sensor 07 is arranged on the molding, which according to experience dries fastest. The second Schwindungsmessaufnehmer 08 is located on the molding that dries from experiments or experience known to slowest. Furthermore, the sensors 05 include a temperature sensor 10 and a sensor of the relative humidity 11. The measured variables of the shrinkage sensors 07, 08 are controlled variables y ₁ and the temperature of the temperature sensor 10 and the relative humidity of the air inside the drying device 02 by means of the relative humidity sensor 11 entered as a control variable y ₂ in a control device 04.

The control device 04 comprises a shrinkage setpoint progression unit 06 which determines a setpoint shrinkage course, which is component-specific and depends on the material, shape and other parameters of the component (s), outputs. Furthermore, the control device 04 comprises two slave controllers K ₁ 12 and K ₂ 14, which are connected in a control cascade. In addition, a computing unit 15 is provided which generates a derived controlled variable y ₂ 'from the controlled variables y ₂ by arithmetic calculations. Finally, the control device 04 comprises a protocol unit 16, which can log the output manipulated variable u _{2 of} the control device 04 in addition to the two controlled variables y ₁ and y ₂ . This protocol unit 16 is in turn connected to a control device 17 and, after repeatedly carrying out a drying operation and finding optimized drying parameters, allows a pure control of the drying device 02 by means of the control device 17 and the adjusting device 03.

During the entire drying process, the control takes place on the one hand with the Schwindungsgradienten recorded by the Schwindungsaufnehmer 07, 08 and the measured variables temperatures and relative humidity from which the size of the differential temperature between the cooling limit temperature and dry temperature can be determined by means of a computing unit 15. Until reaching the break point moisture content of the molded article or, more precisely to the switching between the Schwindungsregelung a Schwindungsregelung based on the measurement values y ₁ of the first and second transducers 07, 08 and the Schwindungssollverlauf 06, which are used as Schwindungsregeldifferenz 09 input into the controller K ₁ 12, carried out , If the break point moisture of the slowest drying component (shrinkage sensor 08) is reached, the shrinkage controller 12 switches over to a parameter set for specifying the manipulated variable curve u ₂ .

The values logged during a first drying process by the logging unit 16 can be optimized in a second drying process, wherein in a third downstream drying process the quality of the dried components can be verified again. At the latest after completion of three drying operations should be stored in the protocol unit 16 optimized values, so that by means of the control device 17 and the controller 03 subsequent drying operations can be performed only controlled with optimal control parameters with a consistent quality.

Claims (22)

Method for drying at least one semi-finished or prefabricated part subject to damp and drying, wherein at least one first controlled drying process is carried out, in which a control of drying parameters such as temperature, air flow amount etc. taking into account at least one control difference (09) between actual shrinkage of the component and a given component-specific Schwindungssollverlauf takes place. Method according to claim 1
characterized,
that process parameters of the controlled drying process are logged in order to be able to generate control and / or manipulated variables for subsequent controlled or controlled drying processes. Method according to one of the preceding claims
characterized,
that the control circuit (19) comprises a further control based on the measurement signals of relative humidity and / or temperature. Method according to claim 3
characterized,
that during a drying process within a first drying phase at least partially a shrinkage control and within a subsequent second drying phase at least partially a temperature control and / or a humidity control is carried out. Method according to claim 4
characterized,
that in the first drying phase, the shrinkage control is carried out, and in the second drying phase, the temperature control and / or the humidity control is carried out. Method according to one of the preceding claims
characterized,
in that the control loop (19) comprises at least two slave controllers (12, 14), wherein the control value u _{1 of} a first slave controller K ₁ serves as a reference variable w _{2 of} a second downstream slave controller K ₂ . Method according to claim 6
characterized,
that the first sequence controller K ₁ performs a Schwindungsregelung, wherein the error signal e ₁ of Schwindungsregelung w a Schwindungsregeldifferenz (09) between the actual Bauteilschwindung y ₁ and a Schwindungssollverlauf is _1, and the manipulated variable u ₁ as a command variable w ₂ for a temperature and / or Humidity control of the second sequence controller K ₂ is used, wherein the second control difference e _{2 is} a temperature and / or humidity difference (13). Method according to claim 7
characterized,
that the command variable w ₂ and / or controlled variable y ₂ 'of the temperature control of the slave controller K ₂ a of temperature y ₂₁ and relative humidity y ₂₂ of the drying device (02) derivable physical difference variable, in particular the temperature difference between wet-bulb temperature and a dry temperature, pressure difference between Wasserdampfsättigungspartialdruck and instantaneous Is partial pressure of water vapor or mass difference between maximum water vapor absorption capacity in the saturation state to instantaneous water vapor content. Method according to one of claims 7 or 8
characterized,
that the drying effect control difference (13) a difference e ₂ between a resulting from the Schwindungsregelung manipulated value u ₁ determinable setpoint value w ₂ and one of relative humidity y ₂₂ and temperature y ₂₁ of the drying chamber (02) determinable controlled variable y ₂ '. Method according to one of the preceding claims
characterized,
in that, to determine the actual shrinkage, at least one shrinkage measuring sensor (07) is arranged on at least one component which absorbs the actual shrinkage of the component. Method according to claim 10
characterized,
in that at least two shrinkage measuring sensors (07, 08) are arranged on two components, wherein the first component is the fastest-drying component and the second component is the slowest-drying component. Method according to claim 11
characterized,
that in the first drying phase of the first Schwindungsregelung the shrinkage of the first component and the end of the Schwindungsphase the shrinkage of the second component to determine the Schwindungsregeldifferenz e ₁ (09) is used. Method according to one of the preceding claims
characterized,
in that at least three drying operations are carried out within the scope of the method, wherein a first drying operation is carried out with a predetermined drying time, the second drying operation is carried out with optimization of the setpoint curves and a third drying operation is carried out for verification of the drying result. Method according to claim 2
characterized,
that further drying operations are carried out at least without a shrinkage control, in particular as controlled drying operations on the basis of the logged drying parameters. Drying device (01) for carrying out a method according to one of the preceding method claims comprising a drying device (02) for drying at least one component, at least one adjusting device (03) for setting drying parameters such as temperature, air flow rate, air circulation or the like in the drying device (02) , a control device (04) for controlling the drying process by actuating the adjusting device (03) by means of a control value u ₂ and at least one sensor (05) for receiving a controlled variable y ₁
characterized,
in that the regulating device (04) comprises at least one shrinkage setpoint curve unit (06) for outputting a component-specific shrinkage setpoint curve of at least one component, and at least one sensor (05) is designed as shrinkage measurement receiver (07, 08) which determines the shrinkage of the component during the course of a drying process as a controlled variable y ₁ , wherein the control device (04) is designed to correct a shrinkage control difference e ₁ (09) between actual component shrinkage y ₁ and the shrinkage setpoint course w ₁ . Device (01) according to claim 15,
characterized,
in that the device (01) comprises at least two shrinkage measuring sensors (07, 08), wherein a first shrinkage measuring transducer (07) is arranged on a first fastest drying component and a second shrinkage measuring transducer (08) on a second, slowest drying component. Device (01) according to one of the preceding device claims,
characterized,
in that the device comprises at least one temperature sensor (10) and a sensor (11) of the relative humidity of the air inside the drying device (02). Device (01) according to one of the preceding device claims,
characterized,
that the control device (04) comprises at least a first controller K ₁ (12), which is designed as a PID controller. Device (01) according to one of the preceding device claims,
characterized,
that the control device (04) comprises at least two controllers K _1, K ₂ (12, 14) which are chained as a sequence controller, wherein the first slave controller K ₁ (12) is adapted auszuregeln a Schwindungsregeldifferenz (09), and the second slave controller K ₂ (14) is designed to correct a temperature and / or humidity difference (13), wherein the manipulated variable u _{1 of} the first sequence controller K ₁ (12) as a reference variable w _{2 of} the second slave controller K ₂ (14). Device (01) according to claim 17
characterized,
in that the regulating device (04) comprises a computing unit (15) which is designed to use the measured values y ₂₁ , y _{22 of} the temperature sensor (10) and the sensor (11) of the relative humidity to produce a physical drying effect difference variable (13), in particular a differential temperature between wet bulb temperature and dry temperature, pressure difference between water vapor partial pressure and instantaneous water vapor partial pressure or mass difference between maximum water vapor absorption capacity in the saturation state to determine instantaneous water vapor content of the component. Device (01) according to one of the preceding device claims,
characterized,
that the control device (04) comprising a protocol unit (16), which is designed to monitor u ₂ of the control device (04) during at least one drying process at least the output control value. Device (01) according to claim 21,
characterized,
in that the device (01) further comprises a control device (17) which is designed to adjust the setting device (03) of the drying device ( ₃ ) based on the manipulated variables u ₁ and / or u _{2 received} by the protocol unit (16) of the control device (04). 02) to control further drying operations.

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