Stretching installation with heat recovery from exhaust gases

Abstract

The invention relates to a stretching system (1) for a plastic film (2), comprising a device (3) having a heat transfer device (3.1) for heat recovery from exhaust gas (3.3), by means of which heat energy recovered and transferable to the heat transfer device (3.1) is supplied to a treatment zone (Bn). According to the invention, the heat recovery is carried out by means of the temperature control device (13) at a temperature level that is so high that condensation of oligomers on the heat transfer surface of the heat transfer device (3.1) does not take place under all operating conditions. Thermal energy is transferred by means of the liquid heat carrier (4). The release point (B1, B2) and the absorption point (B9) of the thermal energy conveyed by means of the heat carrier (4) are separated.

Description

Technical Field

[0001] The present invention relates to a heat recovery system for a transverse stretching portion of a plastic film according to the preamble of claim 1, the heat recovery system being used to supply the recovered heat energy to a defined processing area. Background Technology

[0002] In principle, it is known to make the best use of the high energy required to process the plastic film and to release that energy back into the environment unused as heat as possible.

[0003] Thus, EP 2 576 188 B1 describes an apparatus for stretching films made of synthetic materials, in which energy recovered from the facility's exhaust gas is supplied to a heating zone via a water circuit, and heat present in the exhaust gas is supplied to a preheating cylinder of the heating zone via a preferred second fluid circulation circuit using heat transfer oil. Although a cyclone separator is provided to guide the exhaust gas through it, the exhaust gas itself is directly heated with a gas burner connected in the middle, so the recovered energy is not used for the actual lateral stretching. Returning the exhaust gas to the corresponding processing zone has the disadvantage that oligomers can even accumulate there, which adversely affect the quality of the manufactured film.

[0004] EP 3 650 199 B1 describes a film stretching facility in which, although exhaust gas from the facility’s treatment zone is resupplyed to other treatment zones, exhaust gas containing a significant amount of thermal energy is also directly supplied to the respective treatment zones, and this resupply can also lead to the accumulation of oligomers in the treatment zones.

[0005] Furthermore, CN 21 39 72 553 U describes a heat recovery device for a stretching facility, in which, although still warm exhaust gas is supplied to a heat exchanger via a heat recovery system, the recovered heat is then supplied again to the initial processing area of ​​the facility. Therefore, in such a facility, the energy consumption for processing the film is particularly not used in the transverse stretching section, especially in facilities according to this prior art, where the problem can arise from oligomer condensation at the heat transfer surfaces. The deposition of oligomers on the component surfaces typically leads to increased maintenance and cleaning costs, resulting in a significant economic disadvantage for the operation of such facilities. Summary of the Invention

[0006] In contrast, the object of the present invention is to provide a heat recovery system for the transverse stretching section of a stretching facility for plastic films, which can operate essentially without maintenance.

[0007] This task is accomplished using a stretching facility for plastic films with a heat recovery device, featuring the characteristics of claim 1. Suitable improvements are defined in the dependent claims.

[0008] According to the present invention, a stretching facility with a maintenance-free heat recovery device for plastic films is provided. The heat recovery device according to the invention supplies recovered heat energy to a desired processing area to be loaded with the recovered heat energy by transferring the recovered heat to a liquid heat carrier so that the recovered heat can be used at virtually any location. According to the invention, heat recovery is carried out at a temperature level so high that condensation of oligomers on the heat transfer surface does not occur. The concept of "oligomers" refers to a general term for hydrocarbons that evaporate from the product upon heating and transition from a gaseous consistency to a solid powdery consistency upon cooling. This is, for example, the case in the processing of PET (polyester). This means that the temperature level on the heat transfer surface is higher than the condensation temperature of the oligomers. Therefore, the heat transfer surface remains clean because the oligomers do not accumulate on it. Therefore, the heat recovery device has a heat transferor in which the recovered heat energy is drawn away by means of a liquid heat carrier. And at the heat transfer surface through which the heat is transferred, there is a temperature higher than the condensation temperature of the oligomers. By transferring heat energy to a liquid heat transfer medium, the release point of the heat energy previously absorbed by the heat transfer medium and transported by the heat transfer medium is separated from its absorption point. The advantage of liquid heat transfer medium is precisely that the recovered heat energy can be directed to any processing zone, provided that the processing zone operates at a process temperature lower than the liquid temperature of the heat transfer medium.

[0009] The heat recovery device according to the invention for a stretching apparatus for plastic films ensures that the heat transfer surfaces at the heat transfer unit transfer the recovered energy from the exhaust gas to a liquid heat carrier (which can also be constructed as heat carrier oil or water) and that they remain warm, i.e., at a temperature above the condensation temperature of the oligomers and without any so-called "cold spots" where oligomers / VOCs otherwise present in the exhaust gas would precipitate. Therefore, the heat transfer surfaces remain clean and are thus maintenance-free. The liquid heat carrier can then be easily pumped to another location where it releases the absorbed energy again via the heat transfer unit. After energy release, the temperature of the heat carrier is here again above the critical temperature at which the oligomers begin to precipitate. The liquid heat carrier then returns to the heat transfer unit loaded with hot exhaust gas carrying the oligomers and absorbs new energy from the exhaust gas. This loop ensures continuous operation of the heat recovery without operator intervention. Furthermore, the system according to the invention offers the advantage that not only is the system maintenance-free, but also, because the heat transfer surfaces remain clean and thus the heat transfer coefficient remains within its designed range, the heat transfer coefficient does not change abruptly during operation due to its thermodynamic characteristics. Slow changes in exhaust gas temperature also alter the transferred waste heat energy. However, because this occurs very slowly, the temperature changes very gradually, allowing control to easily compensate for the changes. This is not the case in currently operating systems according to the prior art with automatic cleaning of heat transfer surfaces. In these systems, the heat power can drop even suddenly to zero, leading to temperature deviations in the treatment zone that must be prevented with significant additional costs. In the following, a distinction should be made between the terms "zone" and "region." For example, a distinction can be made between a heating zone, a stretching zone, a fixing zone, and a treatment zone, in such a way that the corresponding region comprises multiple zones. Thus, a heating zone can consist of three heating zones, i.e., three treatment zones; a stretching zone can consist of three stretching zones, i.e., three treatment zones; and a fixing zone can consist of three fixing zones, i.e., three treatment zones.

[0010] According to the present invention, energy is recovered from hot exhaust gas by means of a heat transfer device transferred to a heat carrier. This recovered energy, transferred to the heat carrier, is supplied to a processing zone, such as the stretching zone of a stretching area and / or the heating zone of a heating area. Through heat transfer from the hot exhaust gas, the energy absorbed by the heat carrier is transported to a different location where it is released. This means that the point of energy release from the heat carrier to the processing zone is separate from the point of absorption of the recovered energy from the hot exhaust gas. The heat transfer device can operate maintenance-free when the system is appropriately regulated and operated at a temperature level (i.e., where condensation of oligomers on the heat transfer surface is prevented).

[0011] This type of heat recovery is particularly suitable for PET film facilities. In these facilities, a stationary zone with temperatures ranging from 180°C to 240°C is followed by a heating zone and a stretching zone with temperatures ranging from approximately 90°C to 150°C. High energy requirements exist, especially in the heating zone, to heat the film from approximately 30°C to approximately 100°C and to evaporate any water that may be present in the online coating.

[0012] The film, stretched in a stretching zone consisting of multiple stretching zones, then reaches a fixing zone consisting of multiple fixing zones, where the film is treated at a film temperature of approximately 220°C. Most of the oligomers are also generated in this fixing zone, which must be selectively washed away. Therefore, waste gas is extracted from this zone.

[0013] Provided the exhaust gas temperature does not fall below the oligomer's condensation temperature, the oligomer remains gaseous there. In fact, temperatures of approximately 110°C to 130°C can be achieved without oligomer precipitation. The exhaust gas temperature from the stationary area is 220°C to 230°C. This results in a usable temperature range of approximately 100K. The corresponding heat is transferred to the liquid heat transfer medium, entering at approximately 120°C and exiting at approximately 140°C. In large polyester facilities, this amounts to approximately 400kW, which can be recovered maintenance-free.

[0014] This heat roughly corresponds to the heat demand of the heating zone. Since it operates at approximately 100°C, a liquid heat transfer medium is ideally suited for use in the heat transfer device installed there.

[0015] To ensure a stable temperature in the heating zone even with slightly low recovery rates, the heat transfer fluid is connected to an external heating network. If slightly less heat is recovered (as is the case with throttled exhaust gas), the external system supplies the missing heat. If the recovered heat exceeds the demand, the return temperature is increased, and the system adjusts itself, or optionally, the extended zone can be connected as a consumer.

[0016] Preferably, heat energy is absorbed from the hot exhaust gas via a heat transfer medium (i.e., an absorption point for thermal energy) in a treatment zone configured as a stationary zone. The stationary zone has a relatively high treatment temperature relative to the entire stretching process, thus requiring a relatively high and sustained energy supply. In the stationary zone, the treatment temperature is preferably in the range of 180°C to 240°C.

[0017] The heat energy supplied to the heat carrier in the heat recovery equipment is released from at least one processing area of ​​the heating region and / or at least one processing area of ​​the stretching region of the transverse stretching section, which includes a processing area, a heating area, a stretching area, a fixing area, and a cooling area. Here, the processing area is understood to be a corresponding processing area of ​​the transverse stretching section that includes a processing area, such that, for example, the heating area may consist of multiple heating areas and the stretching area may consist of multiple stretching areas.

[0018] The temperature of the heat release point (i.e., the heating zone of the heating area and / or the stretching zone of the stretching area) is preferably in the temperature range of 90°C to 150°C, wherein, in the sense of a positive temperature gradient, the temperature of the heat transfer surface must be higher than the given temperature range.

[0019] Alternatively, the release point can be a longitudinal stretching machine (MDO). The longitudinal stretching machine is arranged before the transverse stretching section, and thus positioned forward of the transverse stretching section in the direction of travel of the plastic film.

[0020] This release point is meaningful when the products being produced must be exceptionally clean, thus requiring a larger volume of exhaust gas. Since the longitudinal stretching machine also utilizes a liquid heat transfer medium for heating, this is easily achieved. Similarly, the temperature level of the longitudinal stretching machine, at approximately 90°C, is well-suited to the temperature level of the heat recovery circuit, which has a feed temperature of approximately 120°C to 140°C.

[0021] According to an improved embodiment of the present invention, the stretching facility is preferably constructed as a BOPET facility.

[0022] If additional energy must be supplied to at least one processing area, such as a heating zone, in addition to the recovered heat energy, it is preferable to additionally provide and connect an electric heating device.

[0023] This type of heat recovery is also feasible if liquid heating is not available. An increasing number of such facilities operate without flammable heat transfer fluids. These facilities are typically equipped with electrothermal transfer devices. Therefore, heat recovery can also be performed using a hot water circuit. A second hot water heat transfer device is then introduced into the processing zone within the heating area, preceding the electrothermal register. If the energy from heat recovery is insufficient, the subsequent electrothermal register automatically compensates for the difference between the supplied recovered energy and the required energy.

[0024] Furthermore, it is preferably configured such that the temperature level at which oligomer condensation does not occur on the heat transfer surface can be regulated by means of a temperature control device, i.e., making the heat transfer device maintenance-free. It is therefore feasible by means of a control device to perform or realize heat recovery only to such an extent that oligomers are always prevented from precipitating at the heat transfer surface due to excessively low temperatures. Heat recovery is therefore not performed "at any cost," but the amount of heat recovery is limited by means of a temperature control device such that, under any operating conditions, a temperature at which oligomers could potentially precipitate does not occur at the heat transfer surface. This makes the system according to the invention not only highly energy-efficient but also superior in terms of maintenance costs compared to systems known to date. If, for example, the oligomers condense in the range of 110°C to 120°C, the surface temperature of the heat transfer device must be at least 10K above 120°C, i.e., about 130°C, so that condensation does not occur at the heat transfer surface. It is thus evident that heat recovery is applied to the processing area or zone, i.e., to the processing area or zone with the highest temperature for the heat treatment of the plastic film. Of course, it is also conceivable to perform heat recovery in the following processing zones, i.e., those with temperatures exceeding the condensation temperature of the oligomer and where the surface temperature of the heat transfer device is at least 10K above the condensation temperature. Attached Figure Description

[0025] Further advantages, features, and applications of the present invention will now be explained in detail with reference to the accompanying drawings, which illustrate various embodiments. In the drawings: Figure 1 A schematic diagram of a thin film stretching facility with heat recovery from a processing zone in a fixed area according to a first embodiment is shown; Figure 2 Another embodiment of the invention is shown, in which heat recovery from a fixed processing zone is performed and the processing zone is brought to the processing temperature using an electric heating register; Figure 3 Another embodiment of the invention is shown, wherein, relative to the embodiment according to Figure 1 The embodiments additionally include a longitudinal stretching machine, which is supplied with energy recovered from a processing area in a fixed region; and Figure 4 Another embodiment of the invention is shown, in which heat recovered from the processing area of ​​a fixed region is used for gas preheating. Detailed Implementation

[0026] Figure 1A stretching facility 1 is shown, which, according to its basic structure, has a heating zone 6, a stretching zone 7, a fixing zone 5, and a cooling zone 22. A plastic film 2, as a narrow film 17, enters the stretching facility 1 into the heating zone 6 and exits the stretching facility 1 as a wide film 18 after passing through the cooling zone 22. The stretching facility 1 has multiple processing zones B1 to B2 arranged sequentially. 10 Heating zones 6, including processing zones B1, B2, and B3, process the traveling plastic film 2 within a temperature range of 100°C to 150°C. A stretching zone 7 immediately follows the heating zone 6, having processing zones B4, B5, and B6, and operating within a temperature range of 100°C to 150°C. A fixing zone 5 immediately follows the stretching zone, having processing zones B7, B8, and B9, also called fixing zones. In these processing zones, the traveling film is processed within a temperature range of 180°C to 240°C. A cooling zone 22 immediately follows the fixing zone 5, and operates within the heating zone B... 10 It has a temperature range of 40°C to 120°C. The heating zone 6, the stretching zone 7, the fixing zone 5, and the cooling zone form a transverse stretching section 8.

[0027] The schematic diagram shows clamping chains 11 surrounding both sides, which hold and fix the plastic film 2 at its respective edges as it travels through the stretching device 1.

[0028] In a manner known per se, each processing zone B n View detail X includes a device for implementing corresponding air circuits in the respective processing zones. This device has a heat transfer unit 14 for the processing zones, through which energy is introduced to adjust the required temperature in the respective processing zones. Air is supplied through the heat transfer unit 14 via a return air intake 15 and to nozzles 16 via a fan 12 for air circulation in the processing zones to blow air onto the traveling plastic film 2. A temperature sensor 13 is disposed between the heat transfer unit 14 and the fan 12, by means of which the corresponding processing temperature in the processing zones can be checked and adjusted as necessary.

[0029] The stretching facility 1 according to the invention has a heat recovery device 3, which has a heat transferr 3.1 for heat recovery from waste gas 3.3 from processing zone B9 of fixed zone 5. The heat recovery device 3 transfers the heat energy recovered from the waste gas 3.3 loaded with oligomers to a liquid heat transfer fluid 4 in the form of heat transfer oil, also known as heat transfer oil or hot oil, circulating in the piping system. A circulation pump 3.2 delivers the heat transfer fluid 4 from the heat transferr 3.1 in a feed line 3.4 via corresponding regulating valves 21 for entry and return to the heat transferr 14 of the processing zone, and the heat transferr releases the recovered heat energy to processing zones B1 and B2 of heating zone 6 according to the present example. The waste gas 3.3 from processing zone B9 of fixed zone 5 has a temperature of, for example, 220°C. The corresponding recovered energy is transferred to the liquid heat transfer fluid 4 in the heat transferr 3.1. Due to the withdrawn recovered heat energy, the waste gas has a temperature of, for example, 150°C at the outlet of the heat transferr 3.1. In the current example, energy recovery based on a temperature difference of 70K is feasible. For inspection purposes, a bypass line 3.7 is provided around the heat transferor 3.1, through which the supply of exhaust gas 3.3 from the corresponding fixed area B9 of the fixed area 5 can be diverted to bypass the heat transferor 3.1 if the heat transferor 3.1 must be inspected or repaired.

[0030] After the recovered energy at the liquid heat carrier 4 is supplied to the corresponding heat transfer device 14 in processing zone B1 or B2 via feed line 3.4 (where the temperature in the feed line should be at least 130°C), the liquid heat carrier 4 is returned from the heat transfer device 14 in processing zone B1 or B2 to heat transfer device 3.1 via return line 3.5, which again leads towards heat transfer device 3.1. The temperature of the liquid heat carrier 4 in return line 3.5 is, for example, 120°C. The temperature of the heat carrier 4 in return line 3.5 is, for example, the coldest temperature that the exhaust gas 3.3 can accept. According to the invention, heat transfer device 3.1 is now designed and sized such that the lowest temperature at the surface of heat transfer device 3.1 is higher than the temperature at which oligomers condense and accumulate. If this temperature standard is followed, the precipitation of oligomers on the surface of heat transfer device 3.1 is substantially prevented. Therefore, the surface of heat transfer device 3.1 is free of oligomers and thus remains clean. Therefore, it is maintenance-free throughout the operation of the facility.

[0031] If the operating conditions of the stretching facility 1 are such that the heat energy recovered and supplied to the liquid heat carrier 4 by means of the heat recovery equipment 3 is insufficient to reach the processing temperatures required for the processes in processing zones B1 and B2 of the heating zone 6, an additional heating boiler is provided. This heating boiler is connected via piping to the inlet 19 of the feed line 3.4, thereby achieving the required temperatures for the processes to be performed in processing zones B1 and B2 via regulating valve 21 in the heat transfer devices 14. After heat release in the heat transfer devices 14, the cooled heating medium is supplied back to the heating boiler via the return section 20. To regulate this heating for the recovered heat energy, regulating valve 26 for the processing zones B1 and B2 of the heating zone 6 is provided in the inlet 19 from the heating boiler. This valve opens when the theoretical temperature in the aforementioned processing zones of the heating zone 6 is not sufficiently high due to the energy obtained from heat recovery.

[0032] Figure 2 Another embodiment of the invention for the tensioning device 1 is presented, which differs from that for the transverse tensioning portion 8 in its basic structure. Figure 1 Corresponding to the first embodiment described. And according to Figure 1 The implementation methods differ, in Figure 2 In the embodiments presented, the heat transfer device 14 in the corresponding processing zone is replaced by an electric heating register 10, which serves as the main energy source. Therefore, the required processing temperature in the corresponding processing zone is achieved through an energy supply caused by the electric heating device or the electric heating register 10. Similar to the embodiment described above, only in processing zones B1 and B2 of heating zone 6 are there similar heat transfer devices. Figure 1 The additional heat transfer device 14 of the embodiment's processing zone obtains its energy supply from the processing zone B9 of the fixed area 5 via heat recovery, i.e., via the heat recovery device 3, through the heat transfer device 3, in which energy from the exhaust gas 3.3 according to the invention is transferred to the liquid heat carrier 4 and supplied to the heat transfer devices 14 in the processing zones B1 and B2. Attached to the respective heat transfer devices 14, an electric heating register 10 is also provided in the processing zones B1 and B2, which is turned on and additional energy is brought into the respective processing zone when the energy obtained via heat recovery is insufficient to reach or ensure the required temperature in the heating zone 6 of the processing zones B1 and B2. This is also shown in enlarged detail X.

[0033] Because it is feasible to supply energy individually to the corresponding processing area using the electric heating register 10, and this energy can be adjusted according to the processing requirements, based on... Figure 2 In this embodiment, no additional heating boiler is provided to "supplement" the energy, if the recovered heat energy is insufficient. According to... Figure 1 The structures described in the embodiments are based on Figure 2The embodiments are consistent in other respects, so this will not be described again to avoid repetition.

[0034] Figure 3 Another embodiment of the invention is shown, in which, in addition to heat recovery and incorporation of the recovered heat energy into the processing zones B1 and B2 of the heating zone 6, a longitudinal stretching machine (MDO) 9 arranged before the transverse stretching section 8 is also connected.

[0035] From the basis Figure 3 As is evident from the view, the longitudinal stretching machine 9, as a separate component of the stretching facility 1, is arranged in the production direction of the plastic film 2 before the transverse stretching section 8 or before its heating zone 6. For this purpose, the feed line 3.4 of the heat recovery device 3 leads from its heat transferor 3.1 not only to the heat transferors 14 of the processing zones B1 and B2 of the heating zone 6, but also, if sufficient heat energy is available, via regulating valve 24 to the heat transferor 3.8 of the longitudinal stretching machine (MDO) 9. In this heat transferor 3.8, at least a portion of the heat energy recovered from the stationary zone 5 via the heat transferor 3.1 is transferred to the liquid heat carrier 4, which is supplied to the processing zone of the longitudinal stretching machine 9 (not shown in detail) by means of another circulating pump 3.6. The required theoretical temperature in the MDO is checked by means of another temperature sensor 3.9. For example, this temperature is approximately 110°C. If the recovered heat energy is insufficient to reach the theoretical temperature in the processing zone of the MDO, then, as in... Figure 1 In the embodiment, an additional heating boiler is provided so that energy can be supplied from the heating boiler to the processing area of ​​the MDO via the inlet 19, and cooled heating medium can be supplied from the processing area back to the heating boiler via the return section 20. The function of the regulating valve 26 is as follows: Figure 1 The function is similar in the embodiments. In this way, at least a portion of the energy required in the processing zone for the longitudinal stretching machine 9 used for the corresponding longitudinal stretching can be provided by the exhaust gas 3.3 of the fixed zone 5 (processing zone B9), thereby significantly improving the overall energy balance of the stretching facility 1.

[0036] Figure 3 China is also with Figure 1 Similar detail X is presented, showing the air circuit in the corresponding processing area B1 or B2 in a magnified view. This is combined with... Figure 3 Other components or elements not specifically mentioned in the embodiments regarding the basic structure of the transverse stretching portion 8 are similar to those in the embodiments. Figure 1 or Figure 2 The embodiments are consistent and therefore will not be specifically explained again.

[0037] exist Figure 4Another embodiment is presented, which, in the basic structure of the transverse stretching section 8 (including details X of the air circuit for the processing area), is based on... Figure 1 The embodiment is consistent with that described, and a first heat transfer device 3.1.1 is shown for heat recovery from waste gas 3.3.1 in treatment zone B9 of fixed zone 5. From Figure 4 It is evident that, for the presented stretching facility 1, a second heat transferor 3.1.2 for heat recovery is shown in a cascaded manner, by means of which the exhaust gas 3.3.2 from the treatment zone B6 of the stretching zone 7 is branched. The device 3 has a heat transferor 3.1.1 for heat recovery from the treatment zone B9 of the fixed zone 5, while the heat recovery from the treatment zone B6 of the stretching zone 7 has a heat transferor 3.1.2. The heat transferor 3.1.1 transfers the recovered heat energy from the fixed zone 5 to the liquid heat carrier 4, which itself heats fresh air 25, which is supplied to the treatment zone B1 of the heating zone 6 or the treatment zone B6 of the stretching zone 7. The heat transferor 3.1.2 for heat recovery transfers the heat energy recovered from the exhaust gas 3.3.2 of the treatment zone B6 of the stretching zone 7 in a cascaded manner to the heat carrier 4, which is guided to the heat transferor 3.1.1. A circulation pump 3.2 is provided in the loop in the area of ​​the return section to the heat transferor 3.1.2. In the feed from the heat transferr 3.1.1, there is a device for transferring the recovered heat energy from the fixed area 5 (processing area B9) from the liquid heat carrier 4 to the fresh air 25, which is preheated by the recovered heat energy and guided to the corresponding processing area. In the current embodiment, it is guided to the processing area B6 of the stretching area 7 and the processing area B1 of the heating area 6.

[0038] What is common to all embodiments is that heat transfer devices 3.1.1, 3.1.2, 3.1, or 3.8 are designed such that, while as much recovered heat as possible can be effectively resupplyed to the loop or corresponding processing area, the surfaces in the respective heat transfer devices always maintain a higher surface temperature than the condensation temperature of the oligomers contained in the exhaust gas 3.3.1, 3.3.2, or 3.3. Adherence to this important criterion ensures that the heat transfer surfaces in the aforementioned heat transfer devices remain clean, i.e., condensed oligomers do not deposit on their surfaces, thus keeping the heat transfer devices clean and therefore maintenance-free.

[0039] Reference number list 1. Tensioning facilities 2. Plastic film 3 Equipment for heat recovery 3.1 Heat recovery from heat transfer devices 3.1.1 Fixed area of ​​heat transfer device 3.1.2 Tensioning Zone of Heat Transfer Device 3.2 Circulation Pump 3.3 Exhaust Gas 3.3.1 Fixed Area for Exhaust Gas 3.3.2 Exhaust Gas Stretching Zone 3.4 Feed Piping 3.5 Return piping 3.6 Other circulating pumps 3.7 Bypass for inspection 3.8 Heat Transfer Device MDO 3.9 Other temperature sensors 4. Liquid heat transfer fluid 5 Fixed Area 6 Heating Zones 7. Stretching area 8. Lateral stretching section 9. Longitudinal stretching machine 10 Electric heating equipment / electric heating register 11. Encircling clamping chain 12 Fan air circulation processing area 13 Temperature sensor processing area 14 Heat transfer device processing area 15 Return to the air intake processing area 16 Nozzle film blowing treatment area 17. Narrow membrane (inlet) 18. Film width (exit) 19 From the inlet of the heating boiler 20 Return section to the heating boiler 21. Control valve for inlet to or return from heat transfer unit (processing zone). 22 Cooling Zone 24 Control valve MDO 25. Heated fresh air 26. Regulating valve for heating boiler B n Processing area

Claims

1. A stretching facility (1) for a plastic film (2) having a device (3) for heat recovery from exhaust gas (3.3) with a heat transferr (3.1), wherein the recovered heat energy, transferable to the heat transferr (3.1), can be supplied to a processing area (B). n ), Its features are, The heat recovery is carried out by means of temperature control equipment (3.9, 13) at a temperature level that is so high that the condensation of oligomers on the heat transfer surface of the heat transfer device (3.1) does not occur, the heat energy is transferred by means of liquid heat carrier (4), and the release point of the heat energy transported by means of heat carrier (4) is separated from its absorption point.

2. The tensioning device (1) according to claim 1, characterized in that, The heat transfer medium (4) is a fixed region (5) with a fixed absorption point for the heat energy, which is a processing area.

3. The tensioning device (1) according to claim 2, characterized in that, The fixed area (5) operates in a temperature range of 180°C to 240°C.

4. The tensioning device (1) according to any one of claims 1 to 3, characterized in that, The heat release point of the heat carrier (4) is the heating area (6) of the transverse stretching part (8) which is a heating zone, and / or the stretching area (7) is a stretching zone, which is a processing area of ​​at least one heating zone.

5. The tensioning device (1) according to claim 4, characterized in that, The heating zone (6) and / or the stretching zone (7) can operate in a temperature range of 90°C to 150°C.

6. The tensioning device (1) according to any one of claims 4 or 5, characterized in that, The release point is the longitudinal stretching machine (9).

7. The tensioning device (1) according to any one of claims 1 to 6, characterized in that, The stretching facility is constructed as a BOPET facility.

8. The tensioning device (1) according to any one of claims 1 to 7, characterized in that, The heat transfer medium (4) is either oil or water.

9. The tensioning device (1) according to claim 4, characterized in that, At least the processing area of ​​the heating zone (6) is additionally equipped with an electric heating device (10).

10. The tensioning device (1) according to any one of claims 1 to 9, characterized in that, The temperature level at which oligomers do not condense on the heat transfer surface can be adjusted by means of a temperature control device, and the heat transfer device (3.1) is maintenance-free.

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