EP3628953A1 - Workpiece processing system and method for operating same - Google Patents

Abstract

A drying and / or hardening system (10) for drying and / or hardening painted and / or coated and / or glued workpieces has a process chamber (18) for receiving workpieces (14) to be processed, which is connected to a process air line (40, 42, 44, 46, 50) for introducing and / or discharging process air into and out of the process chamber, a heating device (26-37) for heating process air to be introduced into the process chamber (18) and a control device (55) for controlling a quantity of process air introduced into and / or discharged from the process chamber and for controlling a heating power of the heating device. The control device (55) is designed in such a way that it adjusts, controls and / or regulates the process air volume and the heating output as a function of one another or in relation to one another.

Description

The present invention relates to a workpiece processing system, in particular for drying and / or hardening painted and / or coated and / or glued workpieces, and a method for operating a workpiece processing system, in particular for drying and / or hardening painted and / or glued workpieces. In particular, the invention relates to the field of continuous dryers, continuous hardening systems, chamber dryers and chamber hardening systems in which painted and / or glued bodies or body parts can be dried and / or hardened.

A drying and / or hardening system of this type is, for example, from the WO 2010/122121 A2 known. This conventional drying and / or hardening system has a process chamber with at least one zone for receiving workpieces to be processed, which is connected to a fresh air line for introducing fresh air into the process chamber and an exhaust air line for discharging exhaust air from the process chamber. To optimize the energy consumption of the drying and / or curing system, a fresh air and / or exhaust air quantity control is also provided for controlling the fresh air quantity to be introduced into the process chamber and / or the exhaust air quantity to be discharged from the process chamber. The fresh air and / or exhaust air quantity control is preferably carried out as a function of a number of workpieces currently supplied to the process chamber.

The in the WO 2010/122121 A2 The drying and / or curing system disclosed also has a thermal afterburning device (TNV), to which exhaust air from the process chamber is fed for the purpose of thermal exhaust air purification and the clean air which is output is fed to a plurality of recirculating air or fresh air recuperators in order to supply the recirculating air or fresh air to be introduced into the process chamber heat.

The DE 10 2011 114 292 A1 describes a thermal afterburning system in which the combustion chamber temperature is not adjusted to a fixed, maximum value, but in Dependence on a carbon monoxide content in the clean air output from the afterburning system is regulated. Due to the resulting, on average, lower combustion chamber temperatures, energy should be saved and the materials used there should be protected.

The DE 10 2008 034 746 B4 discloses a device for drying painted vehicle bodies with a thermal afterburning system, in which the pollutant concentration of organic solvents in the dryer is measured continuously. As the concentration of pollutants increases, on the one hand the fresh air supply to the process chamber is increased and the exhaust air discharge from the process chamber is reduced, and on the other hand the combustion chamber temperature is kept constant by reducing the fuel supply to the combustion chamber of the afterburning system.

In the DE 10 2012 023 457 A1 describes a method and a device for tempering, in particular for drying objects. All control and regulation processes of the dryer are coordinated by a control unit, through which valves, a process air blower, a fresh air blower and a burner are controlled. A combined control of process air volume and heating output is not provided here.

The DE 20 2009 013 054 U1 discloses a system for controlling the cabin interior temperature in a drying and / or painting cabin for refinishing vehicles and vehicle parts. A temperature sensor detects the temperature on the surface of the object to be heated and / or dried without contact, and a control and regulating device controls the blowers and the heating device as a function of the detected surface temperature of the object to be heated and / or dried. Combined control of process air volume and heating output is not provided here either.

The invention has for its object to provide an improved workpiece processing system and an improved method for operating a workpiece processing system with the lowest possible energy consumption.

This problem is solved by the teaching of the independent claims. Advantageous embodiments of the invention are the subject of the dependent claims.

The workpiece machining system according to the invention has a process chamber for receiving workpieces to be machined, which is connected to a process air line for introducing and / or discharging process air into and from the process chamber; a heating device for heating a process air to be introduced into the process chamber; and a control device for controlling a quantity of process air introduced into and / or discharged from the process chamber and for controlling a heating power of the heating device. The control device is designed in such a way that it adjusts, controls and / or regulates the process air quantity and the heating output as a function of one another and / or in relation to one another.

The combination of the controls (i.e. settings, controls and / or regulations) of the amount of process air introduced into and / or out of the process chamber and the heating power of the heating device creates further energy saving potential. In addition, the combination of the two controls can result in synergy effects, which can reduce the metrological effort for the system control and thus the cost. The invention is based in particular on the following considerations.

The aim is to operate the workpiece processing system as needs-based as possible and thus to save energy. Depending on requirements, for example, depending on production data or parameters (e.g. number of workpieces to be processed in the system), on the one hand, regulate the volume flow of the process air in the process chamber and, on the other hand, the heating output of the connected heating device. Such an improved regulation is possible because, for example, with a reduced number of workpieces in the process chamber, the hydrogen and / or carbon entry, in particular the entry of organic solvents and / or other hydrocarbon compounds and / or other volatile, combustible, ie oxidizable substances reduced in the plant. For a constant, process-capable process chamber atmosphere, the required fresh air and exhaust air quantities in and out of the process chamber are reduced accordingly. The specific pollutant load in the exhaust air, which is typically specified in the unit mass per volume (eg g / m ³ ), can be essentially constant in accordance with the smaller number of workpieces in the process chamber being held. The associated increase in the residence time of the exhaust air in the heating device with the lower exhaust air volume flow - with a smaller number of workpieces - results in an improved burnout (carbon monoxide content in the exhaust gas) and thus also improved emission values. Due to this effect, it is possible not only to reduce the fresh air and / or exhaust air volume flows with a smaller number of workpieces, but also the heating power of the heating device, and to continue to comply with the prescribed emission values. A reduction in the heating power of the heating device leads directly to energy savings.

Lowering the heating power of the heating device can also extend the service life of the workpiece processing system. For example, a purely exhaust air volume flow reduction can result in structural and / or process-related very high preheating temperatures in the preheating and / or heating zone of the heating device. In this case, a reduced heating power of the heating device can cause possible damage e.g. prevent by thermal overload at the end of the preheating zone of the heating device, especially also in the case of maximum preheating.

By integrating the heating power control with the process air volume control, an additional, usually complex measurement technology for detecting the pollutant content in the exhaust air or clean air emitted by the heating device can optionally be dispensed with.

In this context, the term process air is intended to encompass all types of air flows that can be introduced into the process chamber and / or can be discharged from the process chamber. These include, in particular, fresh air to be introduced into the process chamber, exhaust air to be discharged from the process chamber and recirculated air to be discharged from the process chamber and reintroduced into the process chamber. In this context, the term air is intended to encompass any type of gaseous fluid. This includes in particular (ambient) air in the actual sense and gases, each with and without impurities or pollutants.

The control device is intended to control the amount of process air and the heating power as a function of one another or in relation to one another. In this context, dependent control is to be understood to mean, in particular, controls in which there is a functional relationship between the two parameters process air quantity and heating output. There is preferably a fixed law for this functional relationship, preferably via the entire value range of the parameters. In this context, reference control is to be understood to mean, in particular, controls in which different dependencies, laws or special rules apply in different value ranges of the parameters. There is preferably a tabular assignment between the values of the two parameters, this assignment preferably being able to be determined empirically.

In a preferred embodiment of the invention, the control device can be designed to adapt the heating output of the heating device to the process air quantity or the process air quantity control or to adapt the process air quantity to the heating output or the heating output control. This configuration includes in particular several different operating modes. The process air volume control (master) can be superior to the heating output control (slave), so that a change in the process air flow would automatically result in a change in the heating output of the heating device. Alternatively, the heating output control (master) can be superior to the process air volume control (slave), so that a change in the heating output would automatically result in a change in the process air volume in or out of the process chamber. It is also conceivable for the air flow control and heating output control to be in principle the same, in which the master / slave ratio is only determined as a function of, for example, the production data or parameters of the workpiece machining system. Such a configuration or mode of operation of the control device can advantageously contribute to compliance with desired or prescribed emission limits of the system.

When adapting the heating output to the process air volume control or the process air volume to the heating output control, the assignment of heating output and process air volume cannot be fundamentally proportional to one another with this integrated control. Alternatively, under certain circumstances it can also be anti-proportional if, for example, with a reduced number of workpieces, the heating output has to be increased in a certain range in order to be able to provide sufficient clean gas enthalpy for the process heating when the process air flow is reduced.

In a preferred embodiment of the invention, the process air line can (at least) one fresh air line for introducing fresh air into the process chamber, (at least) one exhaust air line for discharging exhaust air from the process chamber and / or (at least) a recirculation line for discharging and reintroducing exhaust air from or into the process chamber. The control device is then preferably designed in such a way that it controls the fresh air quantity, the exhaust air quantity and / or the circulating air quantity.

In a further preferred embodiment of the invention, the heating device can have a combustion chamber. The control device is then preferably designed such that it controls a combustion chamber temperature of the combustion chamber. The combustion chamber temperature can be changed, for example, by changing the fuel gas supply.

In a further preferred embodiment of the invention, the heating device can have a thermal afterburning device (TNV), which is connected to an exhaust air line connected to the process chamber for supplying exhaust air from the process chamber to the afterburning device. The thermal afterburning device is preferably designed to carry out a thermal oxidation, preferably a regenerative or recuperative thermal oxidation of the combustible pollutants in the exhaust air stream from the process chamber.

In yet another preferred embodiment of the invention, the heating device can have (at least) a recirculating air recuperator and / or (at least) a fresh air recuperator, to which a clean gas resulting from combustion is fed.

• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der in der Prozesskammer aufgenommenen Werkstücke;
• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der der Prozesskammer pro Zeiteinheit zugeführten Werkstücke;
• Volumenstrom, Massenstrom, Temperatur, Qualität (z.B. Homogenität der Dichteverteilung, Flüchtigkeit, etc.) und/oder Menge des Bearbeitungsmediums und/oder -fluids (z.B. Lack, Beschichtungspulver, Klebstoff oder dergleichen);
• Schadstoffgehalt und/oder Temperatur und/oder Feuchtigkeit der Prozessluft in der Prozesskammer; und
• Schadstoffgehalt und/oder Temperatur und/oder Feuchtigkeit einer aus der Prozesskammer ausgeleiteten Abluft.

The control device is preferably designed in such a way that (when determining the process air quantity control as a master) it controls the process air quantity as a function of at least one parameter which is selected from:

• Number and / or weight and / or type and / or surface area of the workpieces accommodated in the process chamber;
• Number and / or weight and / or type and / or surface area of the workpieces fed to the process chamber per unit of time;
• Volume flow, mass flow, temperature, quality (eg homogeneity of density distribution, volatility, etc.) and / or quantity of the processing medium and / or fluid (eg paint, coating powder, adhesive or the like);
• Pollutant content and / or temperature and / or humidity of the process air in the process chamber; and
• Pollutant content and / or temperature and / or moisture in an exhaust air discharged from the process chamber.

• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der in der Prozesskammer aufgenommenen Werkstücke;
• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der der Prozesskammer pro Zeiteinheit zugeführten Werkstücke;
• Schadstoffgehalt und/oder Temperatur einer aus der Prozesskammer ausgeleiteten Abluft;
• Schadstoffgehalt und/oder Temperatur eines aus der Heizvorrichtung in die Umgebung ausgeleiteten Reingases;
• Temperaturdifferenz einer aus der Prozesskammer ausgeleiteten und wieder in die Prozesskammer eingeleiteten Umluft;
• Temperaturdifferenz zwischen einer einer Brennkammer der Heizvorrichtung zugeführten Abluft aus der Prozesskammer und eines aus der Brennkammer ausgeleiteten Reingases; und
• Stellung einer Reingas- oder Dosierklappe, die je nach Öffnungswinkel mehr oder weniger Reingasenthalpie an die Umluft abgibt.

The control device is preferably designed in such a way that it controls the heating power of the heating device as a function of at least one parameter, which is selected from:

• Number and / or weight and / or type and / or surface area of the workpieces accommodated in the process chamber;
• Number and / or weight and / or type and / or surface area of the workpieces fed to the process chamber per unit of time;
• Pollutant content and / or temperature of an exhaust air discharged from the process chamber;
• Pollutant content and / or temperature of a clean gas discharged from the heating device into the environment;
• Temperature difference of a circulating air discharged from the process chamber and reintroduced into the process chamber;
• Temperature difference between an exhaust air supplied to a combustion chamber of the heating device from the process chamber and a clean gas discharged from the combustion chamber; and
• Position of a clean gas or metering flap that releases more or less clean gas enthalpy to the circulating air, depending on the opening angle.

In a preferred embodiment of the invention, the heating power can be adjusted without detecting an additional measurement variable relating to a pollutant concentration in the process air (clean air) introduced into the process chamber and / or the process air (exhaust air) discharged from the process chamber. This adaptation is preferably carried out using an empirically or theoretically determined control algorithm. That is, No additional measuring system is required to adjust the heating power, but the control device can access data, parameters, measured variables, etc. that are already present.

In the method according to the invention for operating a workpiece machining system, workpieces to be machined are received in a process chamber, the process chamber being connected to a process air line for introducing and / or discharging process air into and out of the process chamber; a process air to be introduced into the process chamber is heated by means of a heating device; and a quantity of process air introduced into the process chamber and / or discharged from the process chamber and a heating power of the heating device are set, controlled and / or regulated depending on or in relation to one another.

With this method, the same advantages as with the workpiece machining system of the invention described above can be targeted. The above explanations regarding advantages, definition of terms and preferred configurations apply accordingly.

The present invention can preferably be used in drying and / or curing systems for drying and / or curing lacquered and / or coated and / or glued workpieces. The workpieces are, for example, vehicle bodies or vehicle body parts.

Fig. 1

den Aufbau einer Werkstückbearbeitungsanlage gemäß einem bevorzugten Ausführungsbeispiel der Erfindung;

Fig. 2

den Aufbau einer Werkstückbearbeitungsanlage gemäß verschiedenen Modifikationen des Ausführungsbeispiels von Fig. 1;

Fig. 3

den Aufbau einer Werkstückbearbeitungsanlage gemäß weiteren Modifikationen des Ausführungsbeispiels von Fig. 1; und

Fig. 4

den Aufbau einer Werkstückbearbeitungsanlage gemäß zusätzlicher Modifikationen des Ausführungsbeispiels von Fig. 3.

The above and other advantages, features and possible uses of the invention can be better understood from the following description of various exemplary embodiments with reference to the accompanying drawings. It shows, mostly schematically:

Fig. 1

the construction of a workpiece processing system according to a preferred embodiment of the invention;

Fig. 2

the construction of a workpiece processing system according to various modifications of the embodiment of Fig. 1 ;

Fig. 3

the construction of a workpiece processing system according to further modifications of the embodiment of Fig. 1 ; and

Fig. 4

the construction of a workpiece processing system according to additional modifications of the embodiment of Fig. 3 .

Fig. 1 shows a workpiece processing system 10 according to an embodiment of the invention, which is designed as an example as a drying and / or curing system. The structure of this drying and / or curing system 10 basically corresponds to that of WO 2010/122121 A2 . With regard to the structure of the system, the functionality of the individual components and possible modifications, we will therefore refer to them WO 2010/122121 A2 fully referenced.

The drying and / or curing system 10 can be part of a painting system. For example, the painting system can have one or more painting zones 12 in which workpieces 14 are painted. The drying and / or curing system 10 can be attached to these painting zones 12 and, in particular, can be connected downstream in a conveying direction 16. The drying and / or curing system 10 is usually followed by a cooling zone, not shown, in which the workpieces 14 are cooled for further process steps or work steps. The drying and / or hardening system 10 is particularly suitable for drying and / or hardening painted and / or glued components, in particular bodywork, bodywork parts or other assemblies (parts) of a land, water or aircraft.

For example, that is in the Fig. 1 Workpiece 14 shown designed as a painted body for a vehicle or aircraft. The workpiece 14 is in this case fastened on a suitable carrier (skid) 15 which can be moved in a conveying direction 16 in order to convey the workpiece 14 from the painting zones 12 into and through the drying and / or hardening system 10. The workpiece 14 can be transported continuously or discontinuously. However, the workpiece machining system 10 according to the invention is also suitable for other applications.

The drying and / or curing system 10 has a process chamber 18 with a plurality of zones 20-24. A first zone 20 is designed as a lock zone in the form of an inlet lock. A second zone 21 is configured as a first heating zone and a third zone 22 is configured as a second heating zone. Furthermore, a fourth zone 23 is designed as a holding zone and a last zone 24 is designed as a lock zone in the form of an outlet lock. When the drying and / or curing system 10 is in operation, the workpiece 14 first enters the inlet lock 20, the inlet lock 20 sealing the process chamber 18 of the drying and / or curing system 10 from an environment. With this sealing, there is also a certain thermal separation between the interior of the process chamber 18, which is being heated, and the environment. The lock zones 20 and 24 are preferably designed such that, in particular, a process air inside the process chamber 18 does not escape from it, or at least largely prevents escape.

The first heating zone 21 and the second heating zone 22 enable the workpiece 14 to be heated in (in this exemplary embodiment, two) stages. At full capacity, one or more workpieces 14 can be heated in each of the zones 21, 22, the workpiece 14 being conveyed into the zone 22 after the heating in the zone 21 in order to enable further heating. One or more workpieces 14 can remain in the holding zone 23 for a certain period of time in order to carry out drying and hardening of the workpiece 14 (possibly with the aid of electromagnetic radiation). Solvents (solvents) in the form of aliphatic and / or aromatic hydrocarbons, fluorohydrocarbons, fluorochlorohydrocarbons, esters, ketones, glycol ethers, alcohols, water and the like then accumulate - depending on whether they are low or medium - or high boilers - mainly in the area of the heating zones 21, 22 or the holding zone 23 in the air of the process chamber 18. The conditions under which the solvents escape in the drying and / or curing system 10 depend, however, on the respective solvent or the solvent component. Low boilers escape at low (<100 ° C), medium boilers at medium (100 ° C to 150 ° C) and high boilers at high (> 150 ° C) temperatures. For the drying and / or curing process in the holding zone 23, a certain time can be specified, after which the workpiece 14 is conveyed out of the drying and / or curing system 10 via the lock zone 24. The glued and / or lacquered workpiece 14 is then dried and / or hardened.

In the operation of the drying and / or curing system 10, a certain exchange of the process air provided in the process chamber 18 is required. Here, a certain amount of air can be removed from the drying and / or curing system 10 (exhaust air), which is replaced by fresh air. This process air exchange is necessary because the air in the process chamber 18 is enriched with solvents that get into the interior (usable space) of the process chamber 18 of the drying and / or curing system 10 from a paint film or an adhesive during the drying and / or curing process , and this enrichment must be counteracted. As a result, the process air enriched with solvent can be exchanged gradually, in particular continuously, in order to ensure that the process air can continue to absorb solvents. In this case, a certain threshold value can be predetermined, which, in order to maintain a proper drying and / or curing process, should not be exceeded or only slightly, in particular in terms of time and / or space. This process air exchange takes place in a targeted manner, an exchange via the lock zones 20, 24 being prevented as far as possible, since otherwise warm air from the process chamber 18 undesirably gets into the environment or - if the fresh air mainly via the lock zones 20, 24 into the process chamber 18 is drawn - too much cold outside air enters the process chamber 18.

The drying and / or curing system 10 also has a heating device 26-37. This heating device has a thermal afterburning device (TNV) 26, at least one, preferably several (here: three) recirculating air recuperators 28, 30, 32 and generally one (in rare cases none) fresh air recuperator 34.

The thermal post-combustion device 26 is preferably designed as a post-combustion device for regenerative or recuperative thermal oxidation of combustible pollutants in an exhaust air from the process chamber 18 and preferably has a gas burner 36. The hot clean air generated by the gas burner 36 in a combustion chamber 37 is passed through the recuperators 28, 30, 32, 34 and then released into the atmosphere, as indicated by the arrow 38. I.e. The hot exhaust gases (clean air) from the TNV 26 are used in the recuperators 28, 30, 32, 34 as an energy source for heating the circulating air or fresh air. Throttle valves are respectively provided in the recuperators 28, 30, 32, 34 in order to use a certain part of the thermal energy generated by the gas burner 36 in the respective recuperator and to forward the remaining part to the next recuperator.

The recuperators 28, 30, 32, 34 also each have a heat exchanger 29, 31, 33, 35. A suction side and an outflow side of a circulating air line 40 connected to the first heating zone 21 are assigned to the heat exchanger 29 of the first circulating air recuperator 28. The heat exchanger 29 is arranged together with a fan in the recirculation line 40. Depending on the position of the throttle valves of the first recirculating air recuperator 28, the circulating air flowing through the heat exchanger 29 and returned to the first heating zone 21 is heated to a greater or lesser extent in order to maintain a certain temperature during operation of the system 10 to reach and maintain the process air in the first heating zone 21 of the process chamber 18. Analogously, the second heating zone 22 of the process chamber 18 is connected via a recirculation line 42 to the second recirculation recuperator 30, which has a heat exchanger 31 arranged in the recirculation line 42, and the holding zone 23 of the process chamber 18 is connected to the third recirculation recuperator 32 via a recirculation line 44 connected, which has a heat exchanger 33 arranged in the circulating air line 44. In this way, the process air in zones 21, 22, 23 can be heated and its temperature can be kept at a desired level.

In addition, at least one exhaust duct 46 is provided. According to Fig. 1 a suction side of this exhaust air line 46 is arranged in the holding zone 23 of the process chamber 18, and an outflow side of the exhaust air line 46 opens into the combustion chamber 37 of the TNV 26. The oxygen required for burning a fuel gas can thus be extracted from the exhaust air flowing through the exhaust air line 46 Holding zone 23 can be obtained, wherein this exhaust air is heated. Here, the exhaust air from the holding zone 23 is thermally cleaned, so that in the direction of arrow 38 clean air is released to the atmosphere. A heat exchanger 27 is arranged in the exhaust air line 46 so that the exhaust air flowing into the combustion chamber 37 on the outflow side can be preheated. A throttle valve 47 and a fan 48, which is designed as a (frequency) controlled fan in particular, are also arranged in the exhaust air line 46.

In addition, the drying and / or curing system 10 has a fresh air line 50 with a fresh air inlet 52 through which fresh air can be drawn in. From the fresh air inlet 52, the fresh air is first passed through the fresh air line 50 through the fresh air recuperator 34, the heat exchanger 35 being arranged in the fresh air line 50. In this exemplary embodiment, the fresh air line 50 has a first outlet point on the lock zone 20 of the process chamber 18 and a second outlet point on the lock zone 24. In this case, throttle valves are arranged in front of these outlet points in order to regulate the proportion of the fresh air quantity which is fed to the outlet points and which is supplied via the fresh air line 50. As an option, adjustable grids or nozzles are provided at individual or at all outlet points in order to be able to adjust the throughputs. In addition, a (frequency) controlled fan 53 is also arranged in the fresh air line 50. In this exemplary embodiment, the fan 53 is arranged in the flow direction upstream of the heat exchanger 35 of the recuperator 34 in the fresh air line 50.

As in Fig. 1 shown, the drying and / or curing system 10 further comprises a control device 55. This control device 55 is in particular designed in such a way that on the one hand it controls the amount of fresh air introduced into the lock zones 20, 24 of the process chamber 18 via the fresh air line 50 and / or the amount of exhaust air discharged via the exhaust line 46 from the holding zone 23 of the process chamber 18 and on the other hand it controls the heating output of the TNV 26 controls. Furthermore, the control device 55 can also control the quantities of circulating air conducted via the circulating air lines 40, 42, 44.

For this purpose, the control device 55 with a control (e.g. an actuator) 56 of the fan 48 in the exhaust air line 46, with a control (e.g. an actuator) 57 of the fan 53 in the fresh air line 50, and with a control of the gas burner 36 in the Combustion chamber 37 of the TNV 26 connected. Alternatively or additionally, the control device 55 can also be connected to actuators of the throttles or throttle flaps in the exhaust air line 46 or the fresh air line 50 and / or throttle flaps / clean gas flaps for controlling the clean gas enthalpy in the recirculating air recuperators 28, 30, 32.

Deviating or supplementary to that in Fig. 1 Exhaust duct 46 shown can also be arranged on one side of the suction side in one or more heating zones 21, 22 or in the transition between two successive zones 21, 22, 23 and / or 24. The suction side of an exhaust air line 46 is preferably arranged in the area of the maximum concentration of combustible pollutants in the process air in the process chamber 18 or in an area of the process chamber 18 following a section or area of maximum concentration increase of combustible pollutants in the process air. The suction side of an exhaust air line 46 is particularly preferably arranged after the heating zone 21. If more than one exhaust air line 46 is provided, a controllable and / or adjustable throttle or shut-off valve 47 and / or a separate, controllable and / or controllable fan 48 for controlling a flow through the respective exhaust air line 46 can be provided in at least one of the exhaust air lines 46 be provided, which are advantageously connected to the control device 55.

The control device 55 can take into account one or more parameters for controlling the fresh air quantity introduced into the zones 20, 24 and the exhaust air quantity discharged from the zone 23. Corresponding parameters are advantageously stored in the control software, whereby the parameters can be changed depending on the operation of the system 10. Since the amount of solvent introduced into the process chamber 18 varies in different operating states, for example in the break mode, partial load mode or full load mode, the number of workpieces 14 accommodated in the process chamber 18 can serve as a parameter. As a rule, the quantity of solvent introduced into the process chamber 18 varies in direct dependence on the number of workpieces 14, so that the fresh air and exhaust air quantities can be varied in proportion to the number of workpieces 14. As in Fig. 1 For this purpose, the control device 55 is connected to a workpiece detection device 60, which can detect the number of workpieces 14 conveyed into the process chamber 18 of the drying and / or hardening system 10.

In this exemplary embodiment, a workpiece detection device 60 is provided, which is arranged in the conveying direction 16 between the lock zone 20 of the process chamber 18 of the drying and / or curing system 10 and the painting zone 12. As an alternative or in addition, at least one, preferably a plurality of workpiece detection device (s) can also be provided, which is / are connected downstream of the process chamber 18. In a further exemplary embodiment, such a separate workpiece detection device can also be dispensed with if an indicator for the number of workpieces is defined in another way via the system control. The workpiece detection devices 60 are preferably sensors or transmitter / receiver units that operate on the basis of electromagnetic waves, induction and / or weight force measurement. The workpiece detection device (s) 60 can be configured, for example, as a sensor (s) which, when passing through the carrier 15 or the workpiece 14, at least one clock signal or another measurement variable relating to and / or characterizing the carrier 15 or the workpiece 14 can / can transmit or transmit / transmit to the control device 55. From the clock signals received, the control device 55 can then determine the current degree of utilization of the drying and / or curing system 10. As an alternative or in addition, the position of the workpiece in the dryer can be determined from the clock signals and / or another measurement variable detected by the workpiece detection device 60 and relating to and / or characterizing the carrier 15 or the workpiece 14. Further alternatively or additionally, if necessary or advantageous, the amount of fresh air and / or exhaust air can be made dependent, in particular controlled, from this position of the carrier 15 or the workpiece 14, from the process progress (e.g. position in the heating zone or holding zone) and / or the measured variable and / or regulated. However, the workpiece detection device 60 can also be designed as a reading device, RFID reading device, barcode reader or the like. In such an embodiment, the workpiece detection device 60 can, for example, detect a workpiece number of the workpiece 14 or information related to the workpiece 14.

Alternatively or additionally, it is also possible to take into account other process parameters of the system 10, for example a size of the workpiece 14, a material of the workpiece 14 and the like. Other process parameters that can be considered alternatively or additionally are a volume flow, a mass flow, a temperature, a quality (e.g. homogeneity of the density distribution, volatility, etc.) and / or an amount of the processing medium and / or fluid (e.g. paint, Coating powder, adhesive or the like). The control device 55 can receive this information, for example, from a higher-level system control of the painting system.

In this way it is possible to counteract an excessive accumulation of solvents which get into the process chamber 18 of the drying and / or curing system 10 from the paint film, an adhesive or the like during the drying and / or curing process. For this purpose, sufficient fresh air can be continuously fed into the process chamber 18 and at the same time solvent-containing exhaust air can be discharged from the process chamber 18. The amount of exhaust air removed via the exhaust air line 46 can hereby be replaced by a corresponding amount of fresh air. The amount of fresh air introduced and the amount of exhaust air discharged are selected so that condensate formation in the area of the lock zones 20, 24 can be prevented and / or reduced. Furthermore, the amount of fresh air and the amount of exhaust air are optimized, that is, chosen as small as possible to save energy. In particular, energy is required in the fresh air recuperator 34 for heating the fresh air supplied via the fresh air line 50, the consumption of which can thereby be optimized. In addition, thermal exhaust air purification is preferably carried out in the TNV 26 for the discharged exhaust air.

A further energy saving is carried out by the control device 55 by adapting the heating output of the heating device 26-37, in particular the burner output of the TNV 26, to the fresh air and / or exhaust air quantity control. This adjustment of the heating output can optionally be carried out without additional measuring systems (e.g. to record the pollutant concentration in the clean air, for example downstream of the TNV 26 in the clean air or upstream of the TNV 26 in the exhaust air), based on the production data and parameters supplied by the system 10, which are already used by the control device 55 for fresh air and / or exhaust air quantity control.

The control device 55 enables the drying and / or hardening system 10 to be operated as required and thus saves energy. The improved system regulation proposed here is possible because, for example, with a reduced number of workpieces 14 in the process chamber 18, the water and carbon input, in particular the solvent and / or hydrocarbon entry in the system 10 is reduced. For a constant, process-capable process chamber atmosphere, the volume flows required for the fresh air to be introduced into the process chamber 18 and the exhaust air to be discharged from the process chamber 18 are correspondingly reduced. The specific pollutant load in the exhaust air, which is typically specified in the unit mass per volume (eg g / m ³ ), remains essentially constant due to the smaller number of workpieces in the process chamber 18. The increase in the dwell time of the exhaust air in the TNV 26, which is associated with the lower exhaust air volume flow, results in an improved burnout and thus also improved emission values for the clean air. This makes it possible not only to reduce the fresh air and / or exhaust air volume flows with a smaller number of workpieces, but also to reduce the burner output of the TNV 26 and still comply with the prescribed emission values.

Lowering the combustion chamber temperature of the TNV 26 is also technically sensible and may be necessary, since a reduction in the exhaust air volume flow can result in very high preheating temperatures in the heating zone of the TNV 26. Plant damage, e.g. due to thermal overload at the end of the preheating zone of the TNV 26. It is therefore advantageous to combine the process air volume control with the combustion chamber temperature control to form an integrated overall control.

As explained above, this combination can look such that the fresh air and / or exhaust air quantity control is superior to the combustion chamber temperature control. An increase or decrease in the exhaust air volume flow through the exhaust air line 46 would then automatically result in an increase or decrease in the combustion chamber temperature. The one here The control algorithm can be adapted, for example, by reference measurements as part of the emission value settings on the TNV 26 for the present system 10.

• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der in der Prozesskammer 18 aufgenommenen Werkstücke 14;
• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der der Prozesskammer 18 pro Zeiteinheit zugeführten Werkstücke 14.

The control device 55 can control the amount of fresh air and / or the amount of exhaust air into or out of the process chamber 18 of the drying and / or curing system 10, preferably as a function of one or more of the following process parameters of the system 10:

• Number and / or weight and / or type and / or surface size of the workpieces 14 received in the process chamber 18;
• Number and / or weight and / or type and / or surface area of the workpieces 14 supplied to the process chamber 18 per unit of time.

• Volumenstrom, Massenstrom, Temperatur, Qualität und/oder Menge des Bearbeitungsmediums und/oder -fluids;
• Schadstoffgehalt und/oder Temperatur und/oder Feuchtigkeit der Prozessluft in der Prozesskammer 18;
• Schadstoffgehalt und/oder Temperatur und/oder Feuchtigkeit der aus der Prozesskammer 18 ausgeleiteten Abluft.

Other possible process parameters on the basis of which the fresh air and / or exhaust air volume control can be carried out are:

• Volume flow, mass flow, temperature, quality and / or quantity of the processing medium and / or fluid;
• Pollutant content and / or temperature and / or humidity of the process air in the process chamber 18;
• Pollutant content and / or temperature and / or humidity of the exhaust air discharged from the process chamber 18.

Alternatively, the control device 55 can also provide a control architecture in which the control of the combustion chamber temperature of the TNV 26 can be carried out as a function of certain process parameters of the system 10 (master) with automatic adaptation of the fresh air and / or the exhaust air volume flow (slave).

• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der in der Prozesskammer 18 aufgenommenen Werkstücke 14;
• Anzahl und/oder Gewicht und/oder Typ und/oder Oberflächengröße der der Prozesskammer 18 pro Zeiteinheit zugeführten Werkstücke 14.

The control device 55 can also preferably control the combustion chamber temperature of the TNV 26 as a function of one or more of the following process parameters of the system 10:

• Number and / or weight and / or type and / or surface size of the workpieces 14 received in the process chamber 18;
• Number and / or weight and / or type and / or surface area of the workpieces 14 supplied to the process chamber 18 per unit of time.

• Schadstoffgehalt und/oder Temperatur der aus der Prozesskammer 18 ausgeleiteten Abluft;
• Schadstoffgehalt und/oder Temperatur des aus der Heizvorrichtung 26-37 in die Umgebung ausgeleiteten Reingases;
• Temperaturdifferenz der aus der Prozesskammer ausgeleiteten und wieder in die Prozesskammer eingeleiteten Umluft (Zonen 21, 22, 23);
• Temperaturdifferenz zwischen der der Brennkammer 37 der TNV 26 zugeführten Abluft aus der Prozesskammer 18 und des aus der Brennkammer 37 ausgeleiteten Reingases;
• Stellung einer Reingas- oder Dosierklappe, die je nach Öffnungswinkel mehr oder weniger Reingasenthalpie an die Umluft abgibt.

Other possible process parameters on the basis of which the combustion chamber temperature can be controlled are:

• Pollutant content and / or temperature of the exhaust air discharged from the process chamber 18;
• Pollutant content and / or temperature of the clean gas discharged from the heater 26-37 into the environment;
• Temperature difference of the circulating air discharged from the process chamber and reintroduced into the process chamber (zones 21, 22, 23);
• Temperature difference between the exhaust air supplied to the combustion chamber 37 of the TNV 26 from the process chamber 18 and the clean gas discharged from the combustion chamber 37;
• Position of a clean gas or metering flap that releases more or less clean gas enthalpy to the circulating air, depending on the opening angle.

Finally, it is also conceivable for the process air quantity control and the combustion chamber temperature control to be classified in principle. I.e. the respective master / slave ratio of these two regulations by the control device 55 is only determined during operation of the drying and / or curing system 10 as a function of the current production data or parameters.

Referring to Fig. 2 are now various modifications of the drying and / or curing system 10 of Fig. 1 explained, which can be provided individually or in any combination.

As mentioned above, the control device 55 can optionally also use at least one status parameter (for example moisture, temperature, pollutant content) of the process air in the process chamber 18 as a further process parameter. As in Fig. 2 shown, an appropriate process air sensor 62 can therefore optionally be installed in / on the process chamber 18. During this process air sensor 62 in Fig. 2 is positioned in / on the lock zone 20, one or more process air sensors can alternatively or additionally also be provided in / on one or more of the other zones 21-24 of the process chamber 18. The process air sensor (s) 62 can be used, for example, to determine the moisture as a moisture meter or hygrometer, to determine the temperature as a thermometer, infrared sensor, thermoelectric Element or the like and / or for determining a pollutant content as a flame ionization detector (FID), pellistor, electrochemical cell, optical gas sensors, galvanic concentration cell or the like.

As already mentioned above, the control device 55 can optionally also use a state parameter (for example temperature, pollutant content) of the exhaust air discharged from the process chamber 18 through the exhaust air line 46 as a further process parameter. As in Fig. 2 shown, therefore, at least one corresponding exhaust air sensor 64 can optionally be attached in / on the exhaust air line 46. As an alternative or in addition, the exhaust air sensor 64 can also be arranged or provided in the process chamber 18, preferably in the zone from which the extraction can take place or take place by means of the extraction line, in particular in the region of the extraction side of the extraction line 46. The exhaust air sensor 46 is in particular intended, provided and / or designed to determine at least one quality, property and / or a condition parameter, in particular a moisture, temperature and / or pollutant content of the exhaust air or the process air to be extracted. The exhaust air air sensor (s) 64 can be used, for example, to determine the moisture as a moisture meter or hygrometer, to determine the temperature as a thermometer, infrared sensor, thermoelectric element or the like and / or to determine a pollutant content as a flame ionization detector (FID), pellistor, electrochemical cell , optical gas sensors, galvanic concentration cell or the like.

As also mentioned above, the control device 55 can optionally also use a state parameter (for example moisture, temperature, pollutant content) of the clean air 38 output by the heating device 26-37 as a further process parameter. As in Fig. 2 A corresponding clean air sensor 66 can therefore optionally be provided downstream of the heating device. Alternatively or additionally, a clean air sensor can also be provided between the TNV 26 and the first recirculating air recuperator 28. The clean air sensor 66 can be used, for example, to determine the moisture as a moisture meter or hygrometer, to determine the temperature as a thermometer, infrared sensor, thermoelectric element or the like and / or to determine a pollutant content as a flame ionization detector (FID), pellistor, electrochemical cell, optical gas sensors, galvanic Concentration cell or the like.

As in Fig. 2 illustrated, various further exhaust air lines 68, 70, 72, 74 can also be provided.

A suction side of the further exhaust air line 68 is arranged in the holding zone 23 of the process chamber 18, as is the case with the exhaust air line 46. This further exhaust air line 68 is brought together with the fresh air line 50 in order to mix the fresh air from the fresh air inlet 52 with the exhaust air from the further exhaust air line 68. This mixture of fresh air and exhaust air is supplied to the lock zones 20, 24 of the process chamber 18 via the fresh air line 50. A throughput, in particular a frequency-controlled fan, and a throttle valve are preferably arranged in the further exhaust air line 68. In this embodiment, the control device 55 preferably takes into account a third criterion in addition to the two criteria of energy saving and avoidance of condensate, namely the limitation of the solvent concentration to below 25% of the lower explosion limit (LEL). In order to meet these criteria, a certain amount of exhaust air has to be discharged from the holding zone 23. The exhaust air removed from the process chamber 18 via the exhaust air line 46 is subjected to thermal exhaust air purification in the combustion chamber 37 of the TNV 26, while the part of the exhaust air which is led out of the holding zone 23 via the further exhaust air line 68 and which is introduced together with the fresh air into the lock zones 20, 24 Exhaust air in relation to the entire drying and / or hardening system 10 serves as circulating air and can distribute the process air enriched with the solvent over the process chamber 18. As a result, a high concentration of solvents in the process air of the holding zone 23 is reduced, the thermal energy being retained and the energy requirement thus being able to be reduced further. In addition, the part of the exhaust air quantity routed via the further exhaust air line 68 can replace a part of the fresh air quantity supplied. The air mixture from the exhaust air and the fresh air entering the lock zones 20, 24 is heated and is relatively low in solvent when it comes into contact with the lock air in the lock zones 20, 24, which is why the formation of condensate in these zones 20, 24 can be counteracted. Alternatively or additionally, the exhaust air serving as circulating air can also be taken from another zone of the process chamber 18, for example the first heating zone 21 and / or the second heating zone 22.

Via a further exhaust air line 70, 72, exhaust air serving as circulating air can be discharged from the holding zone 23 of the process chamber 18 and preferably directly, i.e. without mixing with fresh air, the lock zones 20, 24 are supplied. The two further exhaust air lines 70, 72 can optionally have separate suction points or a common suction point in the holding zone 23.

Via a further exhaust air line 74, exhaust air serving as circulating air can be removed from the first heating zone 21 of the process chamber 18 and fed to the lock zone 20. As a result, a certain amount of exhaust air can be conducted from the first heating zone 21 into the lock zone 20.

Although not shown, fans, throttles or throttle valves, filter devices and / or exhaust air sensors 64 can also be provided in the further exhaust air lines 68, 70, 72, 74.

Referring to Fig. 3 Various other modifications of the drying and / or curing system 10 of Fig. 1 explained. These further modifications can be carried out individually or in any combination and / or in any combination with one or more combinations of Fig. 2 be provided.

As in Fig. 3 an intermediate lock 25 can optionally be provided between the first heating zone 21 and the second heating zone 22. A branch line 51 branches off from the fresh air line 50, via which a fresh air flow curtain can be generated in the intermediate lock 25 by means of a nozzle.

There is also the possibility of supplying fresh air to one or more of the recirculated air lines 40, 42, 44. For this purpose, a further fresh air line 76 is provided, which branches off, for example upstream and / or downstream of the heat exchanger 35 of the fresh air recuperator 34, and for example downstream of the heat exchanger 29, 31, 33 of the respective recirculated air recuperator 28, 30, 32 into the corresponding recirculated air line 40, 42, 44 opens.

Further variants of the drying and / or curing system 10 have a flow measuring device 78 on the further fresh air line 76 and / or a flow measuring device 79 on the fresh air line 50.

Referring to Fig. 4 various additional modifications of the drying and / or curing system 10 of Fig. 1 explained, these here as additional modifications to the execution after Fig. 3 are shown. However, these additional modifications can also be used individually or in any combination and / or in any combination with one or more combinations of Fig. 2 be provided.

In addition, for example, to Fig. 3 At least one further exhaust air line 46 is provided, the suction side of which is arranged on the intermediate lock 25. A throttle valve 47, a fan 48 and / or an exhaust air sensor 64 can be provided or arranged in at least one exhaust air line 46, which advantageously characterize, determine and / or define a flow through the respective exhaust air line 46. The throttle valve 47 and / or the fan 48 are advantageously connected to an output line of the control device 55, the exhaust air sensor 64 in particular to an input line. With regard to the type and task of the exhaust air sensor 64, the description of the exemplary embodiment is referred to here Fig. 2 referred.

Optionally, it can also be provided that a clean air sensor 66 is provided in a path or a line of the clean air, as already described in the explanations Fig. 2 has been described, which is referred to at this point.

As already described in the description Fig. 1 is described on the heating device 26-37, in particular the TNV 26, after Fig. 4 a control flap for controlling a fuel or a fuel-air mixture supply is shown, which is connected to an output line of the control device 55. In addition to this control flap, the heating device 26-37, in particular the TNV 26, can optionally also be connected to an output of the ignition device and / or a combustion chamber monitoring sensor (also not shown) to an input of the control device 55, as a result of which the control advantageously also initiates an ignition process and / or can monitor the ignition and / or the combustion process.

In a further modification according to Fig. 4 it is further provided that the control device 55 is a process and / or supplementary or alternative to the data of the workpiece detection device 60 Product data 12A from the upstream painting and / or coating and / or gluing process, in particular from the painting, coating and / or gluing system, preferably from the painting cells 12, can be supplied and / or queried by the latter. Process and / or product data 12A relating to the working material used (for example paint, coating material, adhesive and / or auxiliaries, in particular with regard to composition, physical / chemical properties, etc.), application properties are particularly important for the workpiece machining system 10 or the method according to the invention. e.g. layer thickness) and / or workpiece quality (e.g. mass, volume, surface, shape) are important. These can be supplied, provided and / or queried by a process computer of the upstream painting and / or coating and / or gluing process, for example via a data bus, to the control device 55. As an alternative or in addition, it can also be provided that this process and / or product data 12A is passed on to or with the workpiece 14 or the carrier 15 and is preferably read out by means of the workpiece detection device 60 or another reading unit and forwarded to the control device 55 for processing. For example, certain parameter values, intervals and / or groups can be encoded in a preferably machine-readable code (eg barcode, QR code), the control device 55 advantageously having a corresponding decoding unit in order to process and / or product data transmitted in this way 12A to evaluate for processing. As an alternative or in addition, process and / or product data 12A can be stored in a coded or uncoded manner in a storage element on the workpiece 14 and / or carrier 15, the workpiece detection device 60 or another reading unit of the workpiece processing system 10 advantageously containing the process and / or or reads out product data 12A. In addition, a writing unit can be provided, for example, in or after the discharge zone 24, which stores process and / or product data 10A of the workpiece machining in the workpiece machining system 10 in the storage element of the workpiece 14 and / or carrier 15. As an alternative or in addition, the control unit 55 can also forward the process and / or product data 10A to a process control computer.

Claims (13)

Workpiece processing system (10), in particular for drying and / or hardening painted and / or coated and / or glued workpieces, comprising: a process chamber (18) for receiving workpieces (14) to be machined, the process chamber (18) having a process air line (40, 42, 44, 46, 50) for introducing and / or discharging process air into and out of the process chamber connected is; a heater (26-37) for heating process air to be introduced into the process chamber (18); and a control device (55) for controlling a quantity of process air introduced into and / or discharged from the process chamber and for controlling a heating power of the heating device, wherein the control device (55) is designed to adjust, control and / or regulate the process air quantity and the heating output as a function of one another or in relation to one another. Workpiece processing system according to claim 1, wherein the control device (55) is configured to adapt the heating power of the heating device to the process air quantity or the process air quantity control or to adapt the process air quantity to the heating capacity or the heating capacity control. Workpiece processing system according to one of the preceding claims, in which the process air line (40, 42, 44, 46, 50) a fresh air line (50) for introducing fresh air into the process chamber, an exhaust air line (46) for discharging exhaust air from the process chamber and / or has a recirculation line (40, 42, 44) for discharging and reintroducing exhaust air from or into the process chamber; and
the control device (55) is designed to control the fresh air quantity, the exhaust air quantity and / or the circulating air quantity. Workpiece processing system according to one of the preceding claims, in which the heating device (26-37) has a combustion chamber (37); and
the control device (55) is designed to control a combustion chamber temperature of the combustion chamber (37). Workpiece processing system according to one of the preceding claims, in which the heating device (26-37) has a thermal afterburning device (26) which is connected to an exhaust air line (46) connected to the process chamber (18) for supplying exhaust air from the process chamber into the afterburning device (26 ) connected is. Workpiece processing system according to one of the preceding claims, in which the heating device (26-37) has a recirculating air recuperator (28, 30, 32) and / or a fresh air recuperator (34); and
a clean gas resulting from a combustion is fed to the recirculating air recuperator (28, 30, 32) and / or the fresh air recuperator (34). Workpiece processing system according to one of the preceding claims, in which the control device (55) is designed to control the process air quantity as a function of at least one parameter which is selected from: - Number and / or weight and / or type and / or surface area of the workpieces (14) accommodated in the process chamber (18); - Number and / or weight and / or type and / or surface area of the workpieces (14) fed to the process chamber (18) per unit of time; - Volume flow, mass flow, temperature, quality and / or quantity of the processing medium and / or fluid; - Pollutant content and / or temperature and / or humidity of the process air in the process chamber (18); - Pollutant content and / or temperature and / or humidity of an exhaust air discharged from the process chamber (18). Workpiece processing system according to one of the preceding claims, in which the control device (55) is designed to control the heating power of the heating device as a function of at least one parameter which is selected from: - Number and / or weight and / or type and / or surface area of the workpieces (14) accommodated in the process chamber (18); - Number and / or weight and / or type and / or surface area of the workpieces (14) fed to the process chamber (18) per unit of time; - Pollutant content and / or temperature of an exhaust air discharged from the process chamber (18); - Pollutant content and / or temperature of a clean gas discharged from the heating device (26-37) into the environment; - Temperature difference of a recirculated air which is discharged from the process chamber and reintroduced into the process chamber; - Temperature difference between an exhaust air supplied to a combustion chamber (37) of the heating device from the process chamber (18) and a clean gas discharged from the combustion chamber; - Position of a clean gas or metering flap. Method for operating a workpiece processing system (10), in particular for drying and / or hardening painted and / or coated and / or glued workpieces, in which
Workpieces (14) to be machined are received in a process chamber (18), the process chamber (18) having a process air line (40, 42, 44, 46, 50) for introducing and / or discharging process air into and out of the process chamber connected is;
a process air to be introduced into the process chamber (18) is heated by means of a heating device (26-37); and
a quantity of process air introduced into and / or discharged from the process chamber and a heating power of the heating device are adjusted, controlled and / or regulated depending on or in relation to one another. Method according to claim 9, in which the heating power of the heating device is adapted to the process air quantity or the process air quantity control or the process air quantity is adapted to the heating capacity or the heating capacity control. Method according to Claim 9 or 10, in which the process air quantity is controlled as a function of at least one parameter which is selected from: - Number and / or weight and / or type and / or surface area of the workpieces (14) accommodated in the process chamber (18); - Number and / or weight and / or type and / or surface area of the workpieces (14) fed to the process chamber (18) per unit of time; - Volume flow, mass flow, temperature, quality and / or quantity of the processing medium and / or fluid; - Pollutant content and / or temperature and / or humidity of the process air in the process chamber (18); - Pollutant content and / or temperature and / or humidity of an exhaust air discharged from the process chamber (18). Method according to one of Claims 9 to 11, in which the heating power of the heating device is controlled as a function of at least one parameter which is selected from: - Number and / or weight and / or type and / or surface area of the workpieces (14) accommodated in the process chamber (18); - Number and / or weight and / or type and / or surface area of the workpieces (14) fed to the process chamber (18) per unit of time; - Pollutant content and / or temperature of an exhaust air discharged from the process chamber (18); - Pollutant content and / or temperature of a clean gas discharged from the heating device (26-37) into the environment; - Temperature difference of a recirculated air which is discharged from the process chamber and reintroduced into the process chamber; - Temperature difference between an exhaust air supplied to a combustion chamber (37) of the heating device from the process chamber (18) and a clean gas discharged from the combustion chamber; - Position of a clean gas or metering flap. Method according to one of Claims 9 to 12, in which the heating power is adjusted without detecting an additional measurement variable relating to a pollutant concentration of the process air introduced into the process chamber (18) and / or of the process air discharged from the process chamber (18), preferably by means of a control algorithm becomes.

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