EP2396469B1 - Device and method for drying a tissue paper web using steam recapture - Google Patents

Description

The present invention relates to tissue paper making and, more particularly, to an apparatus for drying a tissue paper web having a heatable cylinder, the so-called Yankee or creping cylinder, which is supplied with steam for heating thereof from a live steam network, and a hot air hood at the outer periphery of the cylinder for hot air to blow and suck on the tissue paper web, drying the tissue paper web through both the hot outer surface of the cylinder and the hot air. The evaporated water is sucked off and disposed of via the exhaust air of the hot air hood. Furthermore, the present invention relates to a method for vapor recovery when drying a tissue paper web with such a device.

By a tissue paper is meant a soft absorbent paper with a low basis weight. In general, a basis weight of 8 to 40 g / m ² , in particular 10 to 25 g / m ² per layer is selected. The total basis weight of a multi-ply tissue product is preferably up to a maximum of 120 g / m ² , more preferably up to a maximum of 60 g / m ² . Its density is typically below 0.6 g / cm ³ , preferably below 0.30 g / cm ^3, and more preferably between 0.08 and 0.20 g / cm ³ .

The production of tissue paper differs from papermaking due to the extremely low basis weight and the much higher tensile tear index (see DIN EN 12625-4 and DIN EN 12625-5). Paper and tissue also generally differ in terms of modulus of elasticity, which characterizes the stress-strain properties of these planar products as material parameters.

The high tensile rupture index comes from the outer or inner creping of the tissue. The former creping is performed by compressing the paper web on a dry cylinder as a result of the action of a creping doctor or, in the case of the latter creping, as a consequence of a difference in speed between two fabrics ("fabrics"). This causes the still wet, plastically deformable web to be broken internally by compression and shear, making it more ductile under load than an uncreped paper.

Wet tissue paper webs are usually dried by so-called Yankee drying, through air drying (TAD) or pulse drying.

The fibers contained in the tissue paper are primarily cellulosic fibers, such as chemical fiber pulp fibers (eg, kraft sulfite and sulfate pulps), mechanical pulp (eg, groundwood), thermomechanical pulp, chemomechanical pulp, and / or chemithermomechanical pulp ( CTMP). Fibers made from both hardwood, softwood or annual plants may be used. The fibers may also be or contain recycled fibers. The fibers can be treated with additives - for example fillers, plasticizers, such as quaternary ammonium compounds and binders, such as conventional dry strength agents or wet strength agents, used to facilitate the original paper making and used to adjust the properties thereof. The tissue paper may also contain other fiber types, e.g. Regenerated cellulose fibers or synthetic fibers which, inter alia, increase the strength, absorbency, smoothness or softness of the tissue paper.

The use of a steam-heated cylinder and a hot air hood by means of the hot air is blown onto the running around the heated cylinder tissue web, in the prior art z. B. from the DE 10 2007 006 960 A1 , of the EP 294 982 B1 or the EP 1 027 495 B1 known.

Due to the increasing energy costs, which are also reflected in the cost of steam extraction from the fresh steam network, there are efforts to reduce the required amount of steam and thus the energy costs that are necessary for paper production to reduce.

A device or a method having the features in the preamble of claims 1 and 9 is known from DE-A-35 01 584 known.

The object of the present invention is therefore to provide a device for drying a tissue paper web and a method for recovering steam when drying a tissue paper web, which make it possible to reduce the amount of steam required to dry the tissue paper web from a live steam network in a stable control loop, in particular at To reduce the paper production and in particular the drying costs incurred.

This object is achieved by a device having the features of claim 1 and a method having the features of claim 9.

The invention is based on the idea of using the exhaust air from the hot air hood, which has already been used for drying the tissue paper web, but has a high residual energy content, to evaporate condensate from the heated cylinder and the steam generated at a higher pressure level the Feed back fresh steam network. As a result, less steam from the live steam network is needed in the end, whereby the energy costs and thus the manufacturing costs for the tissue paper web can be reduced. In addition, a live steam network is a big buffer, making a more stable Loop can be achieved with the associated stable drying and thus stable paper quality.

Accordingly, the device for drying a tissue paper web comprises a heatable cylinder, the so-called Yankee or crepe cylinder. The cylinder is connected for heating with steam to a supply line which supplies the steam and which can be connected to a live steam network. For the purposes of the present invention, a live steam network means any mains that provides live steam and supplies at least two consumers with live steam at a first pressure level. One of the consumers is the heatable cylinder of a tissue paper machine. The other consumer can z. B. also be a heatable cylinder but another tissue paper machine. But other consumers are also conceivable. The condensate formed in the cylinder during drying is removed from the cylinder via a condensate line. In addition, the device comprises a hot air hood on the outer circumference of the cylinder to blow hot air in the direction of the outer periphery and thus in operation on the running around the heated cylinder tissue paper web. Thus, the tissue paper web is dried on the one hand by the hot outer circumference of the heated cylinder and on the other hand by the blown on the tissue paper web hot air of the hot air hood. After the hot air of the hot air hood has been used to dry the tissue paper, it is removed with the evaporated water via an exhaust air line from the hot air hood. The device according to the invention further comprises a first pressure stage, which is designed to compress condensate from the cylinder to the first pressure level of the Yankee cylinder. The pressure level reached there can deviate from the first pressure level by ± 2-7 bar. Furthermore, in the device according to the invention an evaporation device for at least partial evaporation of the condensate is provided with an energy transfer device. The energy transfer device is configured to generate energy Exhaust air in the exhaust duct to transfer to the condensate. The energy transfer can be adversely affected by the presence of vapor bubbles in the condensate, so that the energy transfer according to the invention takes place downstream of the first pressure stages. Increasing the pressure increases the boiling point of the condensate (water) and thus prevents the occurrence of vapor bubbles in the heat exchanger. Finally, the device of the present invention comprises a recirculation line, which is connectable to the main steam network to feed back steam generated from the condensate into the main steam network. As a result of the configuration according to the invention, the exhaust air from the hot air hood or its energy is used to generate steam from the condensate discharged from the cylinder, so that less live steam is required from a live steam network, whereby the energy or fresh steam costs can be reduced. Furthermore, the live steam network forms a sufficiently large buffer to provide a stable control loop which is necessary to achieve a constant temperature of the heated cylinder with the associated constant dry quality and paper quality.

In order to further improve the heat transfer between the exhaust air from the hot air hood and the condensate (water) and to further reduce the occurrence of vapor bubbles in the condensate, it is preferable to provide a second pressure stage which is designed to remove the condensate from the substantially first pressure level to compress to a second higher pressure level. The boiling temperature is further increased, thereby condensing possible vapor bubbles in the condensate and the occurrence of vapor bubbles is essentially excluded. The energy transfer device is thus connected downstream of the second pressure stage and preferably formed by a heat exchanger arranged in the exhaust air, in particular a tubular heat exchanger. The condensate, which has been compressed to the second pressure level, is heated via the heat exchanger.

Finally, it is further preferred to provide a third pressure stage configured to suddenly and suddenly vaporize the heated condensate, to which end the condensate is expanded from the second pressure level to the first pressure level, i. H. The evaporation takes place primarily in that the pressure level of the previously heated condensate is reduced so that the boiling temperature abruptly decreases and is thus exceeded and a phase transition from liquid to gaseous takes place. In addition, the expansion is intended to bring the generated steam to the pressure level of the live steam network to allow a return feed via the return line.

Furthermore, it is preferred according to the invention, in particular in order to achieve optimum separation of steam / condensate and to be able to build a control loop, that the device further comprises a first Kondensatabscheider which communicates with the condensate line and a first condensate connected to the first return line. In this case, the first pressure stage is formed by a first pump in the first return line. Furthermore, a second condensate separator is provided, which is in communication with the first return line. As it becomes clear below, the temperature in the second condensate is significantly higher than the temperature in the first condensate and thus the condensate, which is introduced via the first return line in the second Kondensatabscheider. To compensate for this temperature difference, the condensate is preferably introduced via a diffuser in the second condensate. Furthermore, a second return line is provided which is connected to the second condensate separator. The second pressure stage is in this case formed by a second pump in the second return line and the heat exchanger is the second pump downstream integrated into the second return line. The third pressure stage is according to this embodiment, preferably by a Heat exchanger downstream arranged expansion device, in the form of an expansion valve or a capillary or throttle in the second return line formed. Furthermore, the second return line of the expansion device is connected downstream with the second condensate separator. The return of the generated steam is also from the second Kondensatabscheider what the return line is connected to this.

Depending on the exit temperature of the condensate and the exhaust air temperature passing through the heat exchanger, the second pressure level is preferably in the range of 23-27 bar, preferably in the range of 24-26 bar, and most preferably 25 bar. This pressure range is selected so that when passing through the heat exchanger depending on the heat transferred to the condensate, the boiling temperature is not exceeded and thus still no steam is generated. This is to be generated according to the preferred embodiment only by the expansion in the third pressure stage.

The first pressure level is in the range of 10-15 bar, preferably 13-14 bar, and most preferably 13 bar, depending on the pressure of the live steam network.

As an alternative to the design of the energy transfer device in the form of a heat exchanger integrated into the second return line, it is also conceivable that the energy transfer device comprises a condensate separator, through which the exhaust air line preferably extends with a large surface, so that the heat transfer from the exhaust air to the condensate in the condensate , whereby the condensate evaporates in the condenser. In this embodiment, the steam generated in the condensate is also returned via the return feed line to the live steam network. The problem here is However, in this case, the condensate must be arranged with its large dimensions and its high weight in a high position, ie above the paper machine. This can lead to constructive and constructional problems. Advantage of this embodiment, however, can be dispensed with pumps and valves.

In order to achieve a sufficiently large heat transfer to the evaporation and thus to create an effective system, it is particularly preferred to use high-temperature hoods as hot air hoods, as for example in the EP 0 905 311 A2 are described. Such hot air hoods are designed to blow hot air at a temperature of more than 530 ° C on the tissue paper web. At the moment, a maximum of approx. 650 ° C is achieved. The exhaust air of such a high-temperature hood, depending on the application, a temperature of about 150 ° C less than the hot air and is thus at a maximum of 500 ° C.

In addition to the device according to the invention, a method for recovering vapor during drying of a tissue paper web with a cylinder fed from a live steam network and a hot air hood which flows hot air onto the tissue paper web is also proposed. The inventive method comprises the steps of removing condensate from the cylinder, compressing the condensate to a first pressure level corresponding to that of the live steam network, heating the condensate by heat exchange with the exhaust air from the hot air hood, evaporating the condensate and feeding the generated steam into the live steam network.

In accordance with the device, it is preferred to compress the condensate after compression to the pressure level and before heating the condensate with exhaust air from the hot air hood to a second higher pressure level, whereby the boiling temperature of the condensate (water) is raised and thus the occurrence of Steam bubbles is reduced. This makes a better heat transfer possible. Further is it is preferred that the condensate does not evaporate during the heat transfer from the exhaust air to the condensate, ie the pressure level is chosen sufficiently high and the evaporation takes place only after the heating of the condensate with exhaust air from the hot air hood by relaxation to the first pressure level.

The pressure ranges of the second and first pressure levels correspond to the above-mentioned pressure ranges as well as the exhaust air preferably has a temperature of more than 350 ° C.

• Fig. 1 einen Schemaplan einer erfindungsgemäßen Vorrichtung in einer ersten Ausführungsform zeigt; und
• Fig. 2 einen Schemaplan einer erfindungsgemäßen Vorrichtung in einer zweiten Ausführungsform zeigt.

In addition to the above-mentioned features which, unless contradictory to each other, may be used individually and independently of each other or in any combination, further individual features that can be combined with one or more of the above features are described below a preferred embodiment. This description is made with reference to the accompanying drawings, in which:

• Fig. 1 shows a schematic diagram of a device according to the invention in a first embodiment; and
• Fig. 2 shows a schematic of a device according to the invention in a second embodiment.

In Fig. 1 the elements of the tissue paper machine except for the steam-heated Yankee cylinder 10 and the associated hot air high-temperature hood 11 are not shown. The hot air hood 11 may be, for example, a hot air hood according to the EP 0 905 311 A2 act. Furthermore, a live steam power line 12 is shown, which is to represent the live steam network, from which the Yankee cylinder 10 is supplied with steam. The live steam network 12 provides live steam at a pressure of approximately 13 bar. The live steam network 12 and the Yankee cylinder 10 are connected to each other via a supply line 13. In the supply line 13, a pressure reduction via an expansion device 14 takes place. The steam supplied to the Yankee cylinder 10 at a pressure of 6-8 bar heats the Yankee cylinder 10, so that the tissue paper web (not shown) guided around the outer surface or part of the outer surface of the Yankee cylinder 10 is dried by thermal conduction ,

Along a portion of the outer surface of the Yankee cylinder 10, a so-called. Hochtemperaturheißlufthaube 11 is arranged in the illustrated embodiment, hot air in a temperature range of currently not more than 650 ° C on the outer surface of the Yankee cylinder 10 opposite side of the tissue paper web blows, whereby it is dried by convection. After hitting the tissue paper web, the hot air is discharged via exhaust ducts (not shown) of the hot air hood 11, for which purpose a fan 16 is arranged at the end of an exhaust air duct 15. The exhaust air is through an exhaust duct 15 via a bypass 40 with a flap 42 to open or close the bypass, via the fan 16 for hot water production, for heating the machine hall, in which the paper machine stands for fresh air preheating or to further heat recovery measures the blower 16 derived. Alternatively, and according to the present invention, the exhaust air via the exhaust duct 15 with open flap 43 via the line 41 through a built-in exhaust pipe 15 heat exchanger 38 before being fed via the blower 16 to the aforementioned heat recovery measures. The heat exchanger 38 may be a conventional tube heat exchanger.

When the Yankee cylinder 10 is heated, the vapor and condensate, which is in the region of the saturated steam temperature, condenses in a pressure range discharged between about 5-6 bar from the Yankee cylinder 10. For this purpose, a condensate line 17 is provided. The condensate line 17 opens into a first condensate separator 18, in which condensate is separated from steam. The upper portion of the Kondensatabscheiders 18 is further connected via a line 19 with a thermocompressor 20 (jet pump), which can be brought via a line 21 and a valve 23 with the live steam line 12 in fluid communication. As a result, the vapor which is in the first condensate separator 18 in a pressure range between 5-6 bar and at a temperature of about 150 ° C to 160 ° C, sucked via the thermocompressor 20 and again via the supply line 13 to the Yankee Cylinder 10 supplied. In the lower part of the first condensate collector 18, the condensate collects 22 (vapor water), ie water, which is located substantially in the vicinity of the saturated steam temperature. The condensate is fed via an expansion device (26) to a collecting container (not shown). In addition, the lower region of the first condensate separator 18 for discharging the condensate 22 is connected to a first return line 25. Via a valve 27, the condensate 22 in the first condensate separator 18 can flow into the first return line 25. Downstream of the valve 27, a first pump 28 is arranged (first pressure stage). The pump 28 leads to a compression of the condensate 22 to a pressure of about 13.5 bar and conveys the condensate to a second Kondensatabscheider 29. At the inlet of the second Kondensatabscheiders 29, the condensate has about a pressure of 13 bar and a temperature between about 150 ° C and 160 ° C. In the second condensate separator 29, however, a temperature of about 180 to 190 ° C. prevails (as described later). Due to the temperature difference between the introduced condensate and the medium in the second condensate separator 29, the condensate from the return line 25 is introduced via a diffuser 30 into the second condensate separator 29. In the lower section of the second condensate 29 collects substantially liquid condensate 31. The lower portion of the second Kondensatabscheiders 29 is connected to a second return line 33. Connected downstream of the condensate separator 29 is a second pump 34 (second pressure stage). The second pump 34 compresses the condensate 31 from the second Kondensatabscheider 29 to a pressure of about 25 bar.

The compressed condensate downstream of the pump 34 is approximately in a temperature range of about 180 ° C to 190 ° C, flows through the heat exchanger 38. In this case, energy is transferred from the exhaust air in the exhaust duct 15 to the condensate in the return line 33 and the condensate is heated. In this case, the pressure of the condensate is selected to be so high that during the heating of the condensate no evaporation of the condensate and in particular no vapor bubbles arise. Downstream of the heat exchanger 38, the condensate has approximately a temperature of 209 ° C at a pressure of 25 bar. Furthermore, an expansion valve 35 is provided downstream of the heat exchanger 38 in the return line 33. At the expansion valve 35, a portion of the condensate of 25 bar to about 13.5 bar is expanded, causing the condensate evaporates abruptly and a temperature reduction takes place at saturated steam temperature. Following the expansion valve 35 (expansion device), the second return line 33 into the second condensate separator 29 preferably opens into an upper region thereof. Consequently, in the region of the second condensate separator 29, steam produced from the condensate is in a pressure range between 13-14 bar and at a temperature of approximately 180-190 ° C.

Connected to the upper region of the second condensate separator 36 is a return feed line which can be brought into fluid communication with the live steam power line 12 via a valve 37. When the valve 37 is open, the steam generated from the second condensate 29 in the Main steam network or the live steam power line fed back, the pressure of the steam corresponds approximately to the pressure of the live steam network.

The function of the device according to the invention and thus the method according to the invention will be explained below.

The water vapor used for drying the tissue paper web (not shown) in the Yankee cylinder 10 is in the form of vapor water (condensate) present over the condensate line 17 from the Yankee cylinder 10 and in a pressure range between 5-6 bar dissipated. The condensate is fed to a first condensate separator 18. There is a first separation between the vapor and liquid phases. The liquid water (condensate) 22 collects in the lower region of the first condensate container 18 and is compressed with the valve 27 open via the first return line 25 by the first pump 28 (first pressure stage) to approximately 13.5 bar and conveyed to the second condensate separator 29 , The condensate is then fed via a diffuser 30 into the second condensate separator 29, where once again a separation between vapor and liquid phase takes place. The liquid condensate 31, which collects in the lower region of the second Kondensatabscheiders 29 is compressed via the valve 32 by the second pump 34 in the second return line 33 of the pressure prevailing in the second condensate 29 pressure between 13-14 bar to 25 bar and with a temperature of about 180 ° C in the heat exchanger 38 out. At the outlet of the heat exchanger 38, the condensate still has a pressure of 25 bar, but a significantly higher temperature of about 209 ° C. Exhaust air of the hot air hood flows through the heat exchanger 38 at a maximum temperature of 500 ° C., thereby heating the condensate from the starting temperature of 180 ° C. to approximately 209 ° C. By the expansion device in the form of the expansion valve 35, the pressure level of the heated condensate abruptly from 25 bar to 13.5 bar reduced, which also results in a temperature reduction to saturated steam temperature. By this pressure reduction, the condensate evaporates abruptly, so that the condensate passes into the vapor phase. The steam is discharged via the return line 33 into the second condensate separator 29 and can be fed back from there via the return feed line 36 into the live steam network when the valve 37 is open. As a result of the two pressure stages, in particular the second pressure stage with a pressure increase to 25 bar, the boiling temperature of the condensate is markedly increased, so that otherwise any vapor bubbles contained in the condensate are avoided. As a result, the heat transfer from the exhaust air to the condensate in the heat exchanger 38 can be made more efficient. As a result, a more efficient utilization of the energy content of the exhaust air can be achieved.

Due to the system according to the invention, it is possible for a paper machine with a steam consumption of 7-9 tons per hour to recycle 1-3 tons of steam per hour into the live steam network 12. As a result, the actual live steam demand from the grid is reduced by 1-3 tons, whereby the cost of the live steam can be significantly reduced (up to 1/3). In addition, the feedback in the live steam network from a control engineering point of view is particularly advantageous because there is no need fluctuations. The live steam network, which provides live steam in quantities of at least 20 tonnes, forms a large buffer and can buffer the 1-3 tonnes returned without any regulatory problems. Thus, there can be no over-supply of the Yankee cylinder with steam and thus to a large increase in temperature or fluctuations. If the outer surface of the Yankee cylinder is too hot, there is the problem that due to the moisture of the tissue paper web, vapor bubbles are generated and the paper lifts off from the Yankee cylinder. If the temperature profile on the Yankee cylinder varies by more than 10 ° C, there is considerable variation Production problems. This results in quality variations in the paper web, which are undesirable, but caused by an unstable drying. By means of the device according to the invention or the corresponding method, an "overheating or temperature fluctuations" of the Yankee cylinder with the associated problems mentioned with it can be avoided. The existing energy is fed back into the network and is thus removed from the control circuit.

As a further advantage, condensate return and vapor recovery can also reduce the amount of condensate that is to be removed via lines 24 and 26 to the condensate collector by 1-3 tonnes. The reduced amount of cooling water also leads to a reduction in production costs.

Thus, the present system represents a significant advantage over the prior art.

Alternative to that in relation to Fig. 1 However, it is also conceivable embodiment of the device according to the embodiment described in Fig. 2 make. Here, the same parts or similar elements with the same reference numerals and a further description is omitted.

Essentially, the design differs in Fig. 2 from the in Fig. 1 in that the second pressure stage with the second return line 33, the valve 32 and the pump 34 and the expansion valve 35 and the heat exchanger 38 is omitted.

Instead, the condensate 22 is compressed in the first condensate separator 18 via the pump 28 and the first return line 25 to 13 bar and via the diffuser 30 in the second Kondensatabscheider 29th fed. There, the liquid condensate collects in the lower region of the second Kondensatabscheiders 29. Preferably, through this area, the exhaust duct 15 in the form of a tubular heat exchanger (air - water) 39 out, so that the heat of the exhaust air in the exhaust duct 15, via the valve 43 and the conduit 41 flows into the helix 39 and is transferred directly to the condensate 31 contained in the second condensate separator 29 and evaporates it in the second condensate separator. Subsequently, the cooler exhaust air is supplied via the blower 16 to the above-mentioned other heat recovery measures. The steam generated in the second condensate separator 29 is in turn fed back via the recirculation line 36 with the valve 37 open into the live steam supply line 12 and thus into the main steam network.

The advantage of this embodiment is that it is possible to dispense with the second pressure stage and its element, as a result of which the investment costs can possibly be reduced. The structure of the device is so much easier constructively. A disadvantage of this embodiment compared to the embodiment in Fig. 1 is, however, that the second Kondensatabscheider 29 is provided at the top position, that is directly under or on the hall roof of the machine shop, which receives the paper machine. However, such a container has large outer dimensions and a weight between about 30-50 tons, which can result in structural problems.

Otherwise, the second embodiment offers the same advantages as those described with reference to FIG Fig. 1 explained.

In addition to the embodiments described above, of course, other embodiments and / or combinations of embodiments are conceivable. For example, the exhaust air could Fig. 1 leaving the heat exchanger 38, subsequently through the second Condensate 29 are guided to preheat the condensate there already. Also, other waste heat sources from the paper machine could, for example, be used to preheat the condensate at one or the other location (first or second condensate separator or other location). One skilled in the art, in light of the above, recognizes that various modifications and variations of the illustrated embodiments are conceivable and practicable without departing from the spirit of the present invention as defined in the following claims.

Claims (13)

1. Apparatus for drying a web of tissue paper, comprising
   a heatable cylinder (10);
   a supply pipe (13) which is connected to the cylinder for heating the cylinder with steam and can be connected to a fresh steam network (12);
   a condensate pipe (17) for the removal of condensate from the cylinder;
   a hot air hood (11) at the outer circumference of the cylinder to let hot air flow in the direction of the outer circumference;
   a waste air pipe (15) connected to the hot air hood for conducting the waste air out of the hot air hood; and
   an evaporation device for at least partial evaporation of the condensate, having an energy transfer device (38 or 39) for transferring energy from the waste air in the waste air pipe, mounted behind the first pressure stage, to the condensate; characterised by
   a first pressure stage (28) which is designed to compress condensate from the cylinder to substantially a first pressure level, wherein the fresh steam network supplies at least two loads with fresh steam at the first pressure level; and
   a feedback pipe (36) which can be connected to the fresh steam network for feeding steam generated from the condensate back to the fresh steam network.
2. Apparatus according to claim 1, in which the evaporation device further comprises:

   a second pressure level (34) which is designed to compress the condensate from the first pressure level to a second pressure level, wherein the energy transfer device is formed by a heat exchanger (38) which is arranged in the waste air pipe and which is mounted behind the second pressure stage for heating the condensate which has been compressed to the second pressure level; and

   a third pressure stage (35) which is designed to expand the heated condensate from the second pressure level to substantially the first pressure level and evaporate it.
3. Apparatus according to claim 2, further comprising:

   a first condensate separator (18) which is connected to the condensate pipe (17),

   a first return pipe (25) connected to the first condensate separator, wherein the first pressure stage is formed by a first pump (28) in the first return pipe,

   a second condensate separator (29) which is connected to the first return pipe, preferably via a diffuser (30), and heated with the hot waste air via a tube-type exchanger (39), wherein the steam produced in the condensate separator is discharged via the regulating valve (37) to the steam network (12).
4. Apparatus according to claim 2 or 3, further comprising:

   a second return pipe (33) connected to the second condensate separator, wherein the second pressure stage is formed by a second pump (34) in the second return pipe and the heat exchanger (38) is integrated in the second return pipe, mounted behind the second pump,

   wherein the third pressure stage is formed by an expansion device (35), in particular an expansion valve, behind the heat exchanger in the second return pipe, the second return pipe is connected to the second condensate separator, behind the expansion device, wherein the feedback pipe is connected to the second condensate separator.
5. Apparatus according to any of claims 2 to 4, in which the second pressure level is within a range of 23-27 bars, preferably 24-26 bars, most preferably 25 bars.
6. Apparatus according to any of the preceding claims, in which the first pressure level is within a range of 10-15 bars, preferably 13-14 bars, most preferably 13 bars.
7. Apparatus according to either of claims 1 or 6, in which the energy transfer device comprises a condensate separator (29) through which passes the waste air pipe (39).
8. Apparatus according to any of the preceding claims, in which the hot air hood is designed to let hot air flow at a temperature of more than 530°C in the direction of the outer circumference.
9. Method for steam recovery during the drying of a web of tissue paper with a cylinder (10) supplied from a fresh steam network (12) and a hot air hood (11 ) which lets hot air flow onto the web of tissue paper, comprising the steps of:

   removing condensate from the cylinder;

   heating the condensate by heat exchange with the waste air from the hot air hood; and

   evaporating the condensate; characterised by

   compressing the condensate to a first pressure level substantially corresponding to that of the fresh steam network; and

   feeding the steam generated to the fresh steam network.
10. Method according to claim 9, in which the condensate, after compression to the first pressure level and before heating of the condensate with waste air from the hot air hood, is compressed to a second pressure level and in which, after heating of the condensate with waste air from the hot air hood, the condensate is relieved of pressure to substantially the first pressure level for evaporation.
11. Method according to claim 10, in which the second pressure level is within a range of 23-27 bars, preferably 24-26 bars, most preferably 25 bars.
12. Method according to any of claims 9 to 11, in which the first pressure level is within a range of 10-15 bars, preferably 13-14 bars, most preferably 13 bars.
13. Method according to any of claims 9 to 12, in which the waste air has a temperature of more than 350°C.

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