Stretching installation with heat recovery from exhaust air

Abstract

The invention relates to a stretching installation (1) for plastics films (2), comprising a device (3) having a heat exchanger (3.1) for recovering heat from exhaust air (3.3), by means of which thermal energy that has been recovered and can be transferred to the heat exchanger (3.1) is supplied to the treatment zones (Bn). The heat is recovered by means of a temperature control device (13) at a temperature level which is sufficiently high that no oligomer condensation occurs on heat exchange surfaces of the heat exchanger (3.1) under any operating conditions. The thermal energy is exchanged using a liquid heat-transfer medium (4). The delivery point (B1, B2) of the thermal energy transported using the heat-transfer medium is decoupled from the receiving point (B9).

Description

[0001] Stretching plant with heat recovery from exhaust air

[0002] The invention relates to a heat recovery system for a transverse stretching line for plastic films for supplying recovered heat energy to defined treatment zones according to the preamble of claim 1.

[0003] In principle, it is known that the high energy required for the treatment of plastic films should be used as optimally as possible and that as little of this energy as possible should be released unused into the environment in the form of heat energy.

[0004] For example, EP 2 576 188 B1 describes a device for drawing a film made of synthetic material, in which energy recovered from the exhaust air of the system is fed to a heating zone by means of a water circuit, and heat present in the exhaust air is fed to preheating cylinders for the heating zones of the heating zone by means of a second fluid circulation circuit using thermal oil. Although cyclone separators are provided through which the exhaust air is passed, the exhaust air itself is heated directly with the interposition of a gas burner, so that the recovered energy is not used for the actual transverse stretching. The disadvantage of recirculating the exhaust air into corresponding treatment zones is that an accumulation of oligomers can even occur in the treatment zones, which adversely affects the quality of the film produced.

[0005] EP 3 650 199 B1 describes a film stretching plant in which exhaust air from treatment zones of the plant is fed back to other treatment zones, but the exhaust air, which still contains a significant proportion of thermal energy, is fed directly to the corresponding treatment zones, so that such a recirculation can also lead to enrichment with oligomers in the treatment zones.

[0006] Furthermore, CN 21 39 72 553 U describes a heat recovery system for a stretching line in which warm exhaust air is fed to a heat exchanger via a heat recovery system, but the recovered heat is fed back into the initial treatment areas of the line. Thus, in such a line, the energy required to treat the film, especially in the transverse stretching area, is not utilized, especially since, in a line according to this prior art, the problems that can arise from oligomer condensation on heat exchanger surfaces are not described. The deposition of oligomers on component surfaces generally leads to increased maintenance and cleaning costs for the line, which entails significant economic disadvantages for the operation of such a line.

[0007] In contrast, the object of the present invention is to provide a heat recovery system for a transverse stretching line of a stretching plant for plastic films, which can be operated essentially maintenance-free.

[0008] This object is achieved with a stretching system for plastic films with a heat recovery device having the features according to claim 1. Appropriate further developments are defined in the dependent claims.

[0009] According to the invention, a stretching system for plastic films is provided with a maintenance-free heat recovery device. The heat recovery device according to the invention supplies recovered heat energy to desired treatment zones to which this recovered heat energy is to be applied by transferring the recovered heat to a liquid heat transfer medium so that it can be used at virtually any location. According to the invention, heat recovery takes place at a temperature level so high that condensation of oligomers on heat transfer surfaces does not occur. The term "oligomers" is a collective term for hydrocarbon compounds that evaporate from the product upon heating and transform from a gaseous consistency into a solid, powdery consistency upon cooling. This is the case, for example, in the processing of PET (polyester).This means that the temperature level on the heat transfer surfaces is higher than the condensation temperatures of oligomers. This keeps the heat transfer surfaces clean, as oligomers do not deposit on them. The heat recovery system therefore comprises a heat exchanger, with the recovered heat energy being dissipated via a liquid heat transfer medium. And at these heat transfer surfaces, through which the heat energy is transferred, temperatures above the condensation temperature of oligomers prevail. By transferring the heat energy to a liquid heat transfer medium, the release point of the heat energy transported by the heat transfer medium, which was previously absorbed by the heat transfer medium, is decoupled from its absorption point.The advantage of a liquid heat transfer medium is that the recovered heat energy can be directed to any treatment zone; the only requirement is that the treatment zones are operated at process temperatures below the liquid temperature of the heat transfer medium.

[0010] The heat recovery device according to the invention for stretching systems for plastic films ensures that the heat transfer surfaces on the heat exchanger transfer the returned energy from the exhaust air to a liquid heat transfer medium, which can also be in the form of heat transfer oil or water, and that these remain warm enough that their temperatures are above the condensation temperature of oligomers and so no so-called "cold spots" arise at which the oligomers / VOCs otherwise present in the exhaust air in gaseous form would precipitate. This keeps the heat exchanger surfaces clean and therefore maintenance-free. The liquid heat transfer medium can then be easily transported to another location using a pump, where it in turn releases the absorbed energy via a heat exchanger. The temperature of the heat transfer medium after the energy has been released is above the critical temperature at which the oligomers begin to precipitate.The liquid heat transfer medium then returns to the heat exchanger, which is supplied with hot, oligomer-laden exhaust air, and absorbs new energy from this exhaust air. The circuit operated in this way ensures continuous operation of this heat recovery system without operator intervention. Furthermore, the system according to the invention offers the advantage that not only is the system maintenance-free, but the thermodynamic properties of the heat transfer conditions do not change suddenly during operation, as the heat transfer surfaces remain clean and the heat transfer coefficients thus remain within their design range. Slow changes in the exhaust air temperature also change the transferred waste heat energy. However, since this happens very slowly, the temperatures change very slowly, so that the control system can easily compensate for these changes.This is not the case with currently state-of-the-art systems with automatic cleaning of the heat exchanger surfaces. In these systems, the heat output suddenly drops, sometimes even to zero, leading to temperature deviations in the treatment zones that require considerable additional effort to prevent. In the following, a distinction will be made between zones and areas. For example, a distinction can be made between the heating area, the stretching area, the fixing area and the treatment zone, in that the respective areas consist of several zones. For example, the heating area can consist of three heating zones, i.e. three treatment zones; the stretching area can consist of three stretching zones, i.e. three treatment zones; and the fixing area can consist of three fixing zones, i.e. three treatment zones.

[0011] According to the invention, energy is recovered from the hot exhaust air by transferring this energy to a heat transfer medium using a heat exchanger. This recovered energy, which is transferred to the heat transfer medium, is fed to treatment zones, such as the stretching zones of the stretching area and / or the heating zones of the heating area. Through heat transfer from the hot exhaust air, the energy absorbed by the heat transfer medium is transported to a different location, where the energy absorbed by the heat transfer medium is released again. This means that the release location of the energy from the heat transfer medium to a treatment zone and the absorption location of this recovered energy from the hot exhaust air are decoupled from one another. With appropriate control and operation of the system at a temperature level that prevents condensation of oligomers on the heat transfer surfaces, the heat exchanger can be operated maintenance-free.

[0012] This type of heat recovery is particularly suitable for PET film lines. In these lines, a heating and stretching section at approximately 90°C to 150°C is followed by a fusing section at approximately 180°C to 240°C. The heating section, in particular, requires a high level of energy to heat the film from approximately 30°C to approximately 100°C and to evaporate any water present in an inline coating.

[0013] The film, stretched in the stretching area consisting of several stretching zones, then enters a fusing area consisting of several fusing zones, where the film is treated at a film temperature of approximately 220°C. A large portion of the oligomers mentioned above, which must be specifically flushed out, are also produced in this fusing area. Therefore, the exhaust air is taken from this area.

[0014] As long as the exhaust air temperature does not fall below the condensation temperature of the oligomers, the oligomers remain there as a gas. In practice, temperatures of approximately 110°C to 130°C are still achievable without oligomer precipitation. The exhaust air temperature from the fusing area is 220°C to 230°C, resulting in a usable temperature range of approximately 100 K. The corresponding heat is transferred to a liquid heat transfer medium with an inlet temperature of approximately 120°C entering the exhaust air heat exchanger and an outlet temperature of approximately 140°C leaving the exhaust air heat exchanger. In a large polyester plant, this amounts to approximately 400 kW, which can be recovered maintenance-free.

[0015] This amount of heat roughly corresponds to the heat demand of the heating zone. Since this zone operates at approximately 100°C, the liquid heat transfer medium is ideal for use in the heat exchangers installed there.

[0016] To ensure that the heating zones maintain a stable temperature even if the recovery rate is slightly too low, the heat transfer medium is connected to an external heating network. If the amount of heat recovered is slightly too low, which can happen if the exhaust air flow is throttled, this external system supplies the missing heat. If the amount of recovered heat exceeds demand, the return temperature rises, and the system adjusts itself automatically. Alternatively, the stretching area can be connected as a consumer.

[0017] Preferably, the heat energy from the hot exhaust air is absorbed by the heat transfer medium, i.e., the absorption location for the heat energy, in a treatment zone designed as a fixation zone. The fixation zones of the fixation area have a relatively high treatment temperature compared to the entire stretching process, thus requiring a relatively high and continuous energy supply. The treatment temperatures in the fixation zones are preferably in the range of 180°C to 240°C.

[0018] The release point for the thermal energy supplied to the heat transfer medium in the heat recovery device is at least one treatment zone of a heating area and / or one treatment zone of a stretching area of ​​the transverse stretching, which comprises the treatment areas heating area, stretching area, fixing area and cooling area. In this context, the term treatment area is understood to mean the respective treatment zones of the transverse stretching comprising a treatment area, so that, for example, a heating area can consist of several heating zones and a stretching area can consist of several stretching zones. The temperatures of the release point for the thermal energy, i.e. the heating zones of the heating area and / or stretching zones of the stretching area, are preferably in a temperature range of 90°C to 150°C, whereby in the sense of a positive temperature gradient the temperature of the heat transfer surfaces must be above the specified temperature range.

[0019] Preferably, the delivery location can also be a longitudinal stretching machine (MDO). The longitudinal stretching machine is positioned upstream of the transverse stretching machine, i.e., upstream of it in the direction of travel of the plastic film.

[0020] This discharge location makes sense when the product being produced requires particularly cleanliness, which requires larger exhaust air volumes. Since the longitudinal stretching machine is also heated with liquid heat transfer media, this is easily achieved. The temperature level of the longitudinal stretching machine, at approximately 90°C, also matches the temperature level of the heat recovery circuit, with a flow temperature of approximately 120°C to 140°C.

[0021] According to a further development of the invention, the stretching system is preferably designed as a BOPET system.

[0022] If at least one treatment zone, for example the heating area, requires additional energy to be supplied in addition to the recovered thermal energy, it is further preferably provided that an additional electrical heating device is present and switched on.

[0023] Such heat recovery is also possible when there is no liquid heating. More and more of these systems are operated without combustible heat transfer media. Such systems are then usually equipped with electric heat exchangers. Therefore, heat recovery can also be carried out using a hot water circuit. In this case, a treatment zone in the heating area is provided with a second hot water heat exchanger, which is connected upstream of the electric heating register. If energy from the heat recovery system is lacking, the downstream electric heating register automatically takes over the difference between the supplied recovered energy and the required energy. Furthermore, it is preferably provided that the temperature level at which no condensation of oligomers occurs on the heat transfer surfaces can be regulated by means of a temperature control device so that the heat exchanger is maintenance-free.By means of the control device it is therefore possible to carry out or implement only as much heat recovery as is necessary to ensure that oligomers do not precipitate on the heat transfer surfaces due to temperatures that are too low. Heat recovery is therefore not carried out “at any price”, so to speak, but the amount of heat recovery is limited with the help of the temperature control device so that under no operating conditions do temperatures occur on the heat transfer surfaces at which oligomers could precipitate. This makes the system according to the invention not only very advantageous from an energy perspective, but also superior to previously known systems in terms of maintenance costs. If, for example, oligomers were to condense in the range from 110°C to 120°C, the heat exchanger surface temperature would have to be at least approx. 10 K above 120°C, i.e. at approx.130°C, to prevent condensation on the heat exchanger surfaces. This clearly shows that heat recovery is applied to the treatment areas or zones, i.e., heat recovery is carried out from those treatment zones or zones that have the highest temperatures for the heat treatment of the plastic films. Of course, it is also conceivable to carry out heat recovery from treatment zones that have temperatures above the condensation temperatures of the oligomers and where the surface temperature of the heat exchanger is at least 10 K higher.

[0024] Further advantages, features, and possible applications of the invention will now be explained in detail with reference to the accompanying drawings for several exemplary embodiments. The drawings show:

[0025] Figure 1 is a schematic diagram of a film stretching system with heat recovery from a treatment zone of a fixing area according to a first embodiment;

[0026] Figure 2 shows a further embodiment according to the invention, in which the

[0027] Heat is recovered from a treatment zone in the fixing area and the treatment zones are brought to treatment temperature using electric heating registers;

[0028] Figure 3 shows a further embodiment according to the invention, in which, compared to the embodiment according to Figure 1, a longitudinal stretching machine is additionally included, which is supplied by means of energy recovered from a treatment zone of the fixing area; and

[0029] Figure 4 shows a further embodiment of the invention in which the thermal energy recovered from a treatment zone of the fixing area is used to preheat the supply air.

[0030] Figure 1 shows a stretching system 1 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 runs into the stretching system 1 as a narrow film 17 into the heating zone 6 and leaves the stretching system 1 as a wide film 18 after the cooling zone 22. The stretching system 1 has several treatment zones Bi to B™ arranged one behind the other. A heating zone 6 with the treatment zones Bi, B2 and B3 referred to as heating zones treats the passing plastic film 2 in a temperature range from 100°C to 150°C. The heating zone 6 is followed by a stretching zone 7 which has the treatment zones B4, B5 and Be referred to as stretching zones and which is operated in a temperature range from 100°C to 150°C. This is followed by a fixation area 5, which has the treatment zones B7, Bs and B9, referred to as fixation zones.In these treatment zones, the film is treated within a temperature range of 180°C to 240°C. The fusing zone 5 is followed by the cooling zone 22, which has a temperature range of 40°C to 120°C in treatment zone B™. The heating zone 6, stretching zone 7, fusing zone 5, and cooling zone form the transverse stretching zone 8.

[0031] In a schematic representation, the clip chains 11 running around both sides are shown, which hold and fix the plastic film 2 at its respective edges as it passes through the stretching system 1.

[0032] In a manner known per se, each treatment zone B nas shown in detail X, a device for implementing a corresponding air circuit in the respective treatment zone. This device has a heat exchanger 14 for the treatment zone, through which energy is supplied to adjust the temperature required in the respective treatment zone. Via a return air intake 15, the air is fed through the heat exchanger 14 and, via a fan 12 for air circulation in the treatment zone, to nozzles 16 for blowing the passing plastic film 2. Between the heat exchanger 14 and the fan 12, a temperature sensor 13 is provided, by means of which the respective treatment temperature in the treatment zone can be checked and, if necessary, adjusted.

[0033] The stretching system 1 according to the invention has a heat recovery device 3, which has a heat exchanger 3.1 for recovering heat from exhaust air 3.3 from the treatment zone Bg of the fixing area 5. The heat recovery device 3 transfers the heat energy recovered from the oligomer-laden exhaust air 3.3 to a liquid heat transfer medium 4 in the form of heat transfer oil, also referred to as thermal oil, circulating in a pipe system. The circulation pump 3.2 transports the heat transfer medium 4 from the heat exchanger 3.1 in a flow line 3.4 via respective control valves 21 for the inlet and return to the heat exchanger 14 of the treatment zones, which transfers the recovered heat energy, according to the present example, to the treatment zones B1 and B2 of the heating area 6. The exhaust air 3.3 from the treatment zone B9 of the fixing area 5 has a temperature of, for example, 220°C.The corresponding recovered energy is transferred to the liquid heat transfer medium 4 in the heat exchanger 3.1. Due to the recovered thermal energy removed, the exhaust air at the outlet of the heat exchanger 3.1 has a temperature of, for example, 150°C. In this example, the usable recovery of energy is possible based on a temperature difference of 70 K. For inspection purposes, a bypass line 3.7 is provided around the heat exchanger 3.1, by means of which the supply of the exhaust air 3.3 obtained from the corresponding fixing zone B9 of the fixing area 5 can be bypassed by the heat exchanger 3.1 if it needs to be inspected or repaired.

[0034] After the recovered energy has been supplied to the liquid heat transfer medium 4 via the flow line 3.4 to the respective heat exchanger 14 in the treatment zone Bi or B2, whereby the temperature in the flow should be at least 130°C, the liquid heat transfer medium 4 returns to the heat exchanger 3.1 from the heat exchangers 14 in the treatment zones Bi or B2 via a return line 3.5 back to the heat exchanger 3.1. The temperature of the liquid heat transfer medium 4 in the return line 3.5 is, for example, 120°C. This temperature of the heat transfer medium 4 in the return line 3.5 is the coolest temperature that the exhaust air 3.3 can approximately assume. According to the invention, the heat exchanger 3.1 is dimensioned such that the lowest temperature at the surfaces of the heat exchanger 3.1 is higher than the temperature at which oligomers would condense and deposit.If this temperature criterion is maintained, oligomers are essentially prevented from precipitating on the surface of heat exchanger 3.1. The surfaces of heat exchanger 3.1 are thus free of oligomers and remain clean. They are therefore maintenance-free throughout the entire operation of the system.

[0035] If the operating conditions of the stretching system 1 are such that the thermal energy recovered by the heat recovery device 3 and supplied to the liquid heat transfer medium 4 is insufficient to achieve the process-required treatment temperatures in the treatment zones Bi and B2 of the heating area 6, an additional heating boiler is provided, from which an inlet 19 is realized via a line from the heating boiler to the flow line 3.4, so that the temperature required for the treatment to be carried out in these treatment zones is achieved via the control valves 21 in the heat exchangers 14 in the treatment zones Bi and B2. After heat has been released in the heat exchanger 14, the cooled heating medium is fed back to the heating boiler via the return line 20.To regulate this additional heating to the recovered heat energy, a control valve 26 for the treatment zones Bi and B2 of the heating area 6 is provided in the inlet 19 from the boiler, which control valve is opened in the event that the target temperature in the said treatment zones of the heating area 6 is not sufficiently high by means of the energy recovered from the heat recovery.

[0036] Figure 2 shows a further embodiment of the invention for a stretching system 1, which corresponds in the basic structure of the transverse stretching device 8 to the first embodiment described in Figure 1. In contrast to the embodiment according to Figure 1, in the embodiment shown in Figure 2, the heat exchanger 14 in the respective treatment zone is replaced by an electric heating register 10 as the primary energy source. The treatment temperatures required in the respective treatment zones are thus achieved via an energy supply via the electric heating device or the electric heating register 10. Only in the treatment zones B1 and B2 of the heating area 6 are additional heat exchangers 14 of these treatment zones present in analogy to the embodiment according to Figure 1, which obtain their energy supply via heat recovery, ievia the heat recovery device 3, from the treatment zone B9 of the fixing area 5 via the heat exchanger 3.1, in which, according to the invention, the energy from the exhaust air 3.3 is transferred to the liquid heat transfer medium 4 and supplied to the heat exchangers 14 in the treatment zones Bi and B2. In addition to the respective heat exchangers 14, an electric heating register 10 is provided in the treatment zones Bi and B2, which is switched on and supplies additional energy to the corresponding treatment zones in the event that the energy obtained via the heat recovery is not sufficient to achieve or ensure the required temperatures in the treatment zones Bi and B2 of the heating area 6. This is also shown in the enlarged detail X.

[0037] Due to the fact that a separate supply of energy to the respective treatment zones is possible and adjustable according to treatment requirements using the electric heating registers 10, the embodiment shown in Figure 2 does not provide for the "firing" of energy from an additional boiler if the recovered thermal energy is insufficient. The structure described in the embodiment shown in Figure 1 is otherwise similar in the embodiment shown in Figure 2, so to avoid repetition, this will not be described again.

[0038] Figure 3 shows a further embodiment of the invention in which, in addition to the heat recovery and integration of the recovered thermal energy into the treatment zones Bi and B2 of the heating area 6, a longitudinal stretching machine (MDO) 9 arranged in front of the transverse stretching machine 8 is connected.

[0039] From the illustration in Figure 3, it can be seen that the longitudinal stretching machine 9, as an independent element of the stretching system 1, is arranged in the production direction of the plastic film 2 upstream of the transverse stretching machine 8 or upstream of its heating zone 6. For this purpose, the feed line 3.4 of the heat recovery device 3 from its heat exchanger 3.1 is routed not only to the heat exchangers 14 of the treatment zones B1 and B2 of the heating zone 6, but, if sufficient thermal energy is available, also via the control valve 24 to a heat exchanger 3.8 of the longitudinal stretching machine (MDO) 9. In this heat exchanger 3.8, at least a portion of the thermal energy recovered from the fixing zone 5 by means of the heat exchanger 3.1 is transferred to a liquid heat transfer medium 4, which is supplied to the treatment zones (not shown in detail) of the longitudinal stretching machine 9 by means of a further circulation pump 3.6.9 checks whether the required target temperature in the MDO is reached. This temperature is, for example, around 110°C. If the recovered thermal energy is not sufficient to reach the target temperatures in the treatment zones of the MDO, an additional heating boiler is provided, as in the exemplary embodiment according to Figure 1, so that energy can be supplied from the heating boiler via the inlet 19 to the treatment zone of the MDO and the cooled heating medium from the treatment zones can be returned to the heating boiler via the return 20. The function of the control valve 26 is analogous to that in the exemplary embodiment according to Figure 1. In this way, at least part of the energy required by the longitudinal stretching machine 9 for the corresponding longitudinal stretching in the treatment zones can be provided from the exhaust air 3.3 of the fixing area 5 (treatment zone Bg), so that the overall energy balance of the stretching system 1 can be significantly improved.

[0040] Figure 3 also shows, analogously to Figure 1, detail X, which shows the air circuit in the corresponding treatment zone B1 or B2 in an enlarged view. The other parts or elements not specifically mentioned here in connection with the exemplary embodiment according to Figure 3 correspond, with regard to the basic structure of the transverse stretcher 8, to the exemplary embodiment according to Figure 1 or Figure 2 and are therefore not explained separately again.

[0041] Figure 4 shows a further exemplary embodiment which, in terms of its basic structure, corresponds to the transverse stretching machine 8 - including detail X for the air circuit of the treatment zones - according to the exemplary embodiment in Figure 1 and shows a first heat exchanger 3.1.1 for heat recovery from the treatment zone B9 of the fixing area 5 from the exhaust air 3.3.1. Figure 4 shows that, for the stretching system 1 shown, a second heat exchanger 3.1.2 for heat recovery is provided in the sense of a cascade connection, by means of which the exhaust air 3.3.2 from the treatment zone Be of the stretching area 7 is branched off. The device 3 has a heat exchanger 3.1.1 for heat recovery from the treatment zone B9 of the fixing area 5, whereas the heat recovery from the treatment zone Be of the stretching area 7 has a heat exchanger 3.1.2.1 transfers the recovered thermal energy from the fixing area 5 to the liquid heat transfer medium 4, which in turn heats fresh air, which heated fresh air 25 is fed to the treatment zones Bi of the heating area 6 or Be of the stretching area 7. The heat exchanger 3.1.2 for heat recovery transfers thermal energy recovered from the exhaust air 3.3.2 of the treatment zone Be of the stretching area 7 in the sense of a cascade circuit to the heat transfer medium 4, which is led to the heat exchanger 3.1.1. In the circuit, the circulating pump 3.2 is provided in the area of ​​the return line to the heat exchanger 3.1.2. In the flow line from the heat exchanger 3.1.1, devices are provided for transferring the recovered thermal energy from the fixing area 5 (treatment zone Bg) from the liquid heat carrier 4 to fresh air 25, which is preheated by the recovered thermal energy and guided into the corresponding treatment zone, in the present embodiment into the treatment zone Be of the stretching area 7 and the treatment zone Bi of the heating area 6.

[0042] What all embodiments have in common is that the heat exchangers 3.1.1 or 3.1.2 or 3.1 or 3.8 are each designed such that as much recovered heat as possible can be effectively fed back into the circuit or to the respective treatment zones, but that during heat transfer the surfaces in the respective heat exchangers always have a higher surface temperature than the condensation temperature of the oligomers contained in the exhaust air 3.3.1, 3.3.2 or 3.3. By adhering to this essential criterion, it can be ensured that the heat transfer surfaces in the aforementioned heat exchangers remain clean, i.e. condensed oligomers do not precipitate on their surfaces, so that the heat exchangers remain clean and therefore maintenance-free.

[0043] List of reference symbols

[0044] 1 stretching system

[0045] 2 plastic film

[0046] 3 Heat recovery device

[0047] 3.1 Heat exchanger heat recovery

[0048] 3.1.1 Heat exchanger fixing area

[0049] 3.1.2 Heat exchanger stretching area

[0050] 3.2 Circulation pump

[0051] 3.3 Exhaust air

[0052] 3.3.1 Exhaust air fixing area

[0053] 3.3.2 Exhaust air stretching area

[0054] 3.4 Supply line

[0055] 3.5 Return line

[0056] 3.6 additional circulation pump

[0057] 3.7 Bypass for inspection

[0058] 3.8 Heat exchanger M DO

[0059] 3.9 additional temperature sensor

[0060] 4 liquid heat transfer medium

[0061] 5 Fixing area

[0062] 6 Heating area

[0063] 7 Horizontal bar area

[0064] 8 cross bars

[0065] 9 Longitudinal stretching machine

[0066] 10 electric heating devices / electric heating registers

[0067] 11 rotating clip chain

[0068] 12 fans air circulation treatment zone

[0069] 13 Temperature sensor treatment zone

[0070] 14 Heat exchanger treatment zone

[0071] 15 Return air intake treatment zone

[0072] 16 nozzles film blowing treatment zone

[0073] 17 Narrow film (inlet)

[0074] 18 film wide (outlet)

[0075] 19 Inlet from the boiler 20 Return to the boiler

[0076] 21 control valves for inlet and return to or from the heat exchanger treatment zones

[0077] 22 Cooling area

[0078] 24 Control valve MDO

[0079] 25 heated fresh air

[0080] 26 Boiler control valve

[0081] B n Treatment zones

Claims

PATENT CLAIMS 1 . Stretching plant (1) for plastic films (2) with a device (3) having a heat exchanger (3.1) for heat recovery from exhaust air (3.3), by means of which device (3) treatment zones (B n ) and transferable to the heat exchanger (3.1), characterized in that the heat recovery takes place by means of a temperature control device (3.9, 13) at a temperature level which is so high that condensation of oligomers on heat transfer surfaces of the heat exchanger (3.1) does not occur, the heat energy is transferred by means of a liquid heat carrier (4) and the release location of the heat energy transported by means of the heat carrier (4) is decoupled from its absorption location.

2. Stretching system (1) according to claim 1, characterized in that the receiving location for the thermal energy on the part of the heat carrier (4) is a treatment zone of a fixing area (5) designed as a fixing zone.

3. Stretching system (1) according to claim 2, characterized in that the fixing area (5) is operated with a temperature range of 180°C to 240°C.

4. Stretching system (1) according to one of claims 1 to 3, characterized in that the release location for the thermal energy from the heat carrier (4) is at least one treatment zone of a heating area (6) designed as a heating zone and / or a treatment zone of a stretching area (7) of a transverse stretching line (8) designed as a stretching zone.

5. Stretching system (1) according to claim 4, characterized in that the heating area (6) and / or the stretching area (7) can be operated with a temperature range of 90°C to 150°C.

6. Stretching system (1) according to one of claims 4 or 5, characterized in that the delivery location is a longitudinal stretching machine (9).

7. Stretching system (1) according to one of claims 1 to 6, characterized in that it is designed as a BOPET system.

8. Stretching system (1) according to one of claims 1 to 7, characterized in that the heat transfer medium (4) is heat transfer oil or water.

9. Stretching system (1) according to claim 4, characterized in that a treatment zone of at least the heating area (6) additionally has an electrical heating device (10).

10. Stretching system (1) according to one of claims 1 to 9, characterized in that the temperature level at which no condensation of oligomers occurs on the heat transfer surfaces can be regulated by means of a temperature control device and the heat exchanger (3.1) is maintenance-free.

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