EP3150761B1 - Machine for producing or treating a fibrous web with a steam heated cylinder and an apparatus for supplying the cylinder with steam, and method for recovering steam from a steam heated cylinder in a machine for producing or treating a fibrous web - Google Patents

Description

The invention relates to a machine for producing or processing a fibrous web according to the preamble of claim 1, as well as a method for vapor recovery of a steam consumer in the form of a steam-heated cylinder in a machine for producing or processing a fibrous web.

In the production or processing of fibrous webs usually steam-heated cylinders are used for drying the web. Particularly in the production of tissue webs, comparatively large cylinders, so-called Yankee cylinders, are used.

To heat these Yankee cylinders, steam is used at a certain pressure level (consumer pressure). The operation of the cylinder condenses the steam and a vapor-condensate mixture is removed from the cylinder. The steam contained therein could be used again to heat the Yankee cylinder. However, it has too low a pressure level so that it must be compressed by means of a thermocompressor back to the required consumer pressure.

In addition, the Yankee cylinder uses a hot air hood to dry the web. The hot exhaust air of this hood is usually used again for the production of steam. Various methods are known from the prior art for this purpose.

For example, according to the EP 2 085 514 Steam generated by relaxation of heated condensate directly on the consumer pressure. However, since most of the steam required for the Yankee is already available via the flash steam, this method limits the amount of steam that can be generated by heat recovery. This makes the process uneconomical.

Another option is, as in the EP 2 396 469 described, using heat recovery from heated condensate to generate steam at the pressure level of the plant's live steam network. Again, however, the producible amount of steam is limited. The required motive steam pressure of the thermocompressor is usually lower than the pressure level of the live steam network.

In the EP 2 775 030 a vapor collection tank is proposed, in which the steam generated in the steam generator is promoted. However, such an additional pressure vessel leads to increased investment costs and possibly also depending on local legislation an increased maintenance and testing costs.

It is the object of the present invention to obviate the weaknesses of the prior art, and specifically to maximize the amount of high quality motive steam produced by waste heat recovery.

This object is fully achieved by a machine for producing or processing a fibrous web according to the characterizing part of claim 1 and a method according to claim 11.

The inventive machine for producing or processing a fibrous web comprises a steam consumer in the form of a steam-heated cylinder, a live steam network which provides live steam at a first pressure level and a device for supplying the steam-heated cylinder. The device comprises a steam supply, which provides steam at a second pressure level for the steam consumer, and which is connectable to the live steam network. In addition, the device comprises a condensate return line for guiding the condensate removed from the steam consumer, in particular for return to an external steam generator, for example a power plant.

There is also provided a steam generating device for at least partially evaporating the condensate removed from the steam consumer, which comprises at least one heat exchanger, and a return feed line, which is connectable to the steam supply to feed back steam generated from the condensate in the steam supply.
According to the invention, it is provided that the steam supply can be decoupled from the live steam network by means of a valve or a throttling element and essentially consists of a line system without an additional storage container. In addition, it is provided that the second pressure level of the steam supply differs from the first pressure level of the live steam network.
Compared with the prior art, this machine according to the invention has the significant advantage that the pressure level of the steam supply can be optimally adapted independently of the pressure level of the live steam network of the installation. Since the live steam network of the system next to the steam consumer of the device according to the invention, so next to the Yankee still supplies one or more other steam consumers, the pressure in this steam mains will be so high that all connected consumers can be adequately supplied. However, this first pressure level is usually higher than the pressure level which is necessary for the supply of the steam consumer and / or possible further units in the device according to the invention. In addition, the device according to the invention does without an additional vapor collection for the generated steam.

Advantageous embodiments of the machine according to the invention are described in the subclaims.
For example, it may be advantageous that the device additionally comprises a thermocompressor for supplying the steam consumer. This thermocompressor is connectable to the steam supply such that steam at the second pressure level can be used as motive steam. In preferred embodiments, the thermocompressor can be used to steam a low pressure levels - in particular flash steam, which is obtained by relaxing the condensate removed from the steam consumer by means of the driving steam to the pressure level at which the steam is introduced into the steam consumer. In common applications steam is used in the steam consumer at a pressure of between 6 and 8.5 barg. The pressure can also be lower, eg at 3 barg or higher.

The inventive decoupling of live steam network and steam supply, it is now possible to provide a second pressure level in the steam supply, which can be selected independently of the first pressure level, and which can be tailored specifically to the requirements of the steam consumer and if available the thermocompressor. This second pressure level will usually differ from the first pressure level. In advantageous applications, the second pressure level will be lower than the first pressure level. Advantageously, the second pressure level is between 0.5 bar and 7 bar below the first pressure level, preferably between 2 bar and 4 bar below the first pressure level.

Usually, the pressure level required by the thermocompressor as motive steam is lower than the pressure level at which the steam comes from the steam generator, or as the first pressure level, which is maintained in the live steam network.

Thus, it is provided in advantageous embodiments, that the second pressure level is adapted to the driving steam pressure of the thermocompressor, which is necessary to supply the steam consumer. Preferably, the second pressure level can be selected as the minimum pressure level required for the thermocompressor. By choosing this low pressure level for the motive steam naturally a larger amount of motive steam is required, as in the choice of a higher motive steam pressure. Since this motive steam is generated according to the invention at least partially by the vapor recovery and can evaporate more condensate in the vapor recovery at low vapor pressure, thus the efficiency of the vapor recovery is increased. Thus, the economy of heat recovery can be significantly increased.

In advantageous embodiments of the invention, the steam generating device comprises in addition to a heat exchanger at least one throttle body to at least partially evaporate the condensate after passing through the at least one heat exchanger, and a separator (S2) to which the at least partially evaporated condensate can be fed, and to the the return feed line can be connected.

In particularly preferred embodiments, the at least partial evaporation of the condensate does not take place directly in the heat exchanger. Such direct evaporation can optionally lead to the formation of deposits in the heat exchanger, which in turn can lead to a reduction in performance or damage to the heat exchanger. Also, the cost of feedwater treatment or condensate treatment can be higher.

Advantageously, the throttle body can be a valve, a diaphragm or a similar device which is suitable for at least partially evaporating the condensate after it has passed through the heat exchanger.

In a further advantageous embodiment, it can also be provided that the condensate is vaporized directly at the inlet of the separator (S2) or in the interior of the separator (S2). In such an embodiment, the separator (S2) has the function of a flash tank. In such an embodiment, the separator and the throttle body form a functional unit.

The decoupling of the steam supply from the main steam network can be carried out in advantageous embodiments by means of a control or throttle valve. However, the invention is not limited to these embodiments.

Despite the described advantages of the decoupling of live steam network and steam supply, the connectivity of the two steam systems is advantageous. This can be used on the one hand for the initial filling of the steam supply and the steam consumer etc. The steam from the first Pressure level of the fresh steam network to the second pressure level of the steam supply relaxed. Furthermore, in the case of a complete or partial failure of the heat exchanger, for example, the required steam can also be supplied to the steam feed from the live steam network. In this case, a defined pressure level in the steam supply can be ensured by the valve or throttle member.

In a further advantageous embodiment, the device comprises a first pressure stage, which is designed to compress condensate from the condensate return line to a third pressure level. This first pressure stage is generated in advantageous embodiments of the invention by a make-up pump. This make-up pump can advantageously be designed so that it is suitable to bring the condensate to a pressure level of at least 20 barg, more preferably at least 25 barg.

The third pressure level will be higher in advantageous applications than the second pressure level. Often the third pressure level will be between 7.1 bar and 13 bar higher than the second pressure level. In particularly preferred embodiments, the third pressure level between 9 bar and 11 bar will be higher than the second pressure level. In this case, condensate can be removed from the condensate return line, which is brought by the make-up pump to the third pressure level.

In a further advantageous embodiment, the heat exchanger can be connected to the first pressure stage in such a way that the condensate is further heated at the third pressure level in the heat exchanger. This heated condensate can then be at least partially evaporated, for example.

In a further advantageous embodiment of the invention, the heat exchanger can be connected to an exhaust air line in such a way that the exhaust air can be used to heat the condensate. In a particularly advantageous embodiment, in the exhaust air line around the exhaust air line of a drying device of a machine for producing or processing a fibrous web. In particular, it may be the exhaust duct of the dryer hood of the steam consumer according to the invention. But it is also possible that it is the exhaust air a drying hood of another drying cylinder acts. Furthermore, it can be provided that it is the exhaust duct of any other aggregate, which is used in the production or processing of a fibrous web. In this case, however, in particular but not exclusively, the exhaust air line of a hot air or infrared drying of a coating system come into question.

Advantageously, at least one throttle device, such as a fitting, a diaphragm or the like may be provided in the device to at least partially vaporize the condensate after passing through the heat exchanger.

In a further embodiment it can be provided that the device comprises a separator to which the at least partially vaporized condensate can be fed, and to which the return feed line can be connected. In a further advantageous embodiment, it can also be provided that the condensate is vaporized directly at the inlet of the separator or in the interior of the separator. In such an embodiment, the separator has the function of a flash tank. In such an embodiment, the separator and the throttle body form a functional unit.

In a further advantageous embodiment, a device can be provided, with which the separator condensate are removed, and the heat exchanger can be supplied to the evaporation. This device may in particular comprise suitable lines and a second pressure increasing device, which is suitable for compressing this condensate to the third pressure level.

In a particularly advantageous embodiment, it is also possible to provide a combination in which the condensate removed from the condensate return line can be combined with condensate, which is the separator is taken. From there, the condensate from the two sources can then be fed together to the heat exchanger.

Often no means for increasing the pressure will be provided between the merge and the heat exchanger.

By means of the first pressure increase device and the second pressure increase device, the two condensate streams can be compressed independently of one another and brought to the third pressure level, for example. Then, at the merger, two condensate flows of the same pressure level can be mixed together.

This arrangement, in which the merging takes place on the pressure side of both the first and the second pressure increase devices is very flexible. For example, if one of the two pumps fails, at least the other partial flow of condensate can continue to be operated. By contrast, with a pump installed between the junction and the heat exchanger, the heat exchanger could no longer operate in the event of an accident or maintenance of the pump.

In a particularly preferred embodiment, the machine according to the invention comprises only a single steam consumer, which is connected to the steam supply. In this embodiment, the advantages of the decoupling of live steam network and steam supply according to the invention are particularly strong for carrying.

Alternatively, for example, it may also be provided that the steam supply is connected or connectable to two or more substantially identical steam consumers and / or two or more largely identical thermocompressors. Also in this case, the second pressure level can be optimally adjusted.

1. a) Entnahme von Kondensat aus dem Dampfverbraucher,
2. b) Verdichten des Kondensats auf ein drittes Druckniveau,
3. c) Erwärmen des Kondensats auf dem dritten Druckniveau in zumindest einem Wärmetauscher,
4. d) Verdampfen des Kondensats und Erzeugen von Dampf auf dem zweiten Druckniveau, und
5. e) Einspeisen des erzeugten Dampfes in die Dampfzuführung.

With respect to the method, the object is achieved by a method for vapor recovery of a steam consumer in the form of a steam-heated cylinder in a machine for producing or processing a fibrous web, wherein the machine comprises a live steam network which provides steam at a first pressure level, and wherein the steam heated cylinder is supplied from a steam supply with steam at a second pressure level, said steam supply consisting essentially of a piping system without an additional storage container and of the live steam network means a valve or throttle body is decoupled, the method comprising the steps:

1. a) removal of condensate from the steam consumer,
2. b) compressing the condensate to a third pressure level,
3. c) heating the condensate at the third pressure level in at least one heat exchanger,
4. d) evaporating the condensate and generating steam at the second pressure level, and
5. e) feeding the generated steam into the steam feed.

In a preferred embodiment of the method, steps c) and d) are separated from each other. The evaporation of the heated condensate is therefore not directly in the heat exchanger, but downstream, for example by means of a throttle body.

The feeding of the steam generated in the steam supply is advantageously carried out at the second pressure level.

Advantageous developments of the method are described in the subclaims.

Thus, it can be advantageously provided that the at least one heat exchanger for heating the condensate exhaust air of a drying device of a machine for producing or processing a fibrous web used, in particular exhaust air of a drying hood of a drying cylinder or the exhaust duct of a hot air or infrared drying a coating unit.

It can preferably be provided that steam from the steam supply is used as a propellant gas for a thermocompressor. Here, the thermocompressor be used to compress steam from a low pressure level so that it can be reintroduced into the steam consumer. For this purpose, a pressure level between 6 barg and 8.5 barg is necessary in usual applications. In special applications, lower pressure levels (eg up to 3 barg) or possibly higher pressure levels may be necessary.

The values for the second pressure level and the third pressure level may vary depending on the application. In particular, the second pressure level can, as already described above, for example, be adjusted by optimal adaptation to the requirement of the thermocompressor to increase the efficiency. In usual applications, the pressure difference between the first pressure level and the second pressure level between 0.5 bar to 7 bar, in particular between 2 bar to 4 bar amount. The pressure difference between the second pressure level and the third pressure level may advantageously be between 7.1 bar to 13 bar, in particular between 9 bar to 11 bar.

Advantageously, after the evaporation of the condensate, a separator may be provided before the generated steam is fed into the steam supply. In this separator, in an advantageous embodiment, the steam generated is separated from the condensate. The steam is fed from the separator into the steam supply in this embodiment. In a particularly advantageous embodiment, the condensate is removed from this separator, compressed by means of a second pressure stage to the third pressure level, fed to the heat exchanger and then evaporated.

Furthermore, it can be provided that the condensate removed from the separator is combined with the condensate removed from the steam consumer at a junction and fed together to the heat exchanger, wherein no further pressure increase takes place between the junction and the heat exchanger (5).

In the following the invention will be explained in more detail with reference to a schematic drawing. FIG. 1 schematically shows an embodiment of the machine according to the invention.

The steam consumer 1 in FIG. 1 is exemplified as Yankee 1 executed. Via an inlet 1a, steam is introduced into the Yankee cylinder 1 for heating. This vapor can have a pressure level between 6 and 8.5 barg. In special applications, lower pressure levels (eg up to 3 barg) or possibly higher pressure levels may be necessary. Via an outlet 1b, the Yankee cylinder 1 condensate can be removed. This condensate can be at a pressure level between 5 and 7.5 barg. In a first separator S1 steam is generated by expansion, which is returned by means of a line (12) back to the Yankee cylinder 1. The resulting condensate is discharged from the first separator S1 via a condensate return line.

Since the generated flash vapor has too low a pressure level, it is compressed by means of a thermocompressor 7 so far that it can be reintroduced into the Yankee cylinder. The motive steam required for this purpose relates to the thermocompressor from the steam feed 2. The steam feed 2 provides steam at a second pressure level. This second pressure level may advantageously be chosen to represent the minimum pressure level required by the thermocompressor 7 to sufficiently compress the vapor from the first separator S1. This second pressure level is usually above the pressure at which the steam is fed into the steam consumer 1. However, the required second pressure level is usually below the pressure level that provides the live steam network 10 of the system. Therefore, in the device according to the invention the steam supply 2 is decoupled from the live steam network 10. This decoupling takes place in the embodiment in FIG. 1 by means of a valve 8, for example, a control or throttle valve 8. The decoupling can also be done by a throttle body. Essential to the decoupling is that in the steam supply 2 and the live steam network 10, the pressure can be set independently. As a rule, the second pressure level of the steam feed 2 is lower than the first pressure level of the live steam network 10.

The condensate is removed from the first separator S1 by means of a condensate return line 3. Part of it will be routed back to Steam Generator 99. However, a part of it can be used to generate steam with the aid of a heat exchanger 5. If a large amount of condensate can not be returned to the steam generator 99, but can be directly evaporated again, the cost of the process increases significantly. In the in FIG. 1 For this purpose, condensate return line 3 condensate is removed, and brought by means of a first pressure stage 4 to a third pressure level. This third pressure level can be, for example, 7.1 to 13 bar above the second pressure level, advantageously about 9 to 11 bar above the second pressure level. The absolute values of the third pressure level can lie in advantageous embodiments between 20 barg and 30 barg, in particular between 22 barg and 27 barg. However, in individual cases, the values of the third pressure level may also deviate therefrom.

In a heat exchanger 5, the condensate is heated further at the third pressure level. In this case, the heat exchanger 5 can be operated, for example, with the exhaust air of the Yankee cylinder 1. However, it is possible according to the invention to use all types of hot exhaust air, which occur in the environment of the production or processing of the fibrous web. These may be, for example, exhaust air from the moisture-drying, gas turbine exhaust air or others. From the heated condensate is in the in FIG. 1 shown execution by means of a throttle body 9 generates steam. From a second separator S2, the steam is introduced via a return feed line 6 into the steam feed 2. The injected steam is fed in substantially at the second pressure level. This again shows an advantage of the invention. Due to the decoupling of steam supply 2 and live steam network 10, the injected steam does not have to be produced at the (high) first pressure level, but can be generated at the (lower) second pressure level, which is usually chosen as the minimum pressure required for the operation of the thermocompressor 7 is necessary. Since the thermocompressor 7 requires more motive steam at a lower pressure level, more condensate can be evaporated and less is needed Condensate be returned to the steam generator 99, thereby increasing the efficiency of heat recovery.

The condensate accumulating in the second separator S2 can, as in FIG. 1 shown by way of example, brought by means of a second pressure stage 11 back to the third pressure level, and the heat exchanger 5 are supplied.

Like in the FIG. 1 can be advantageously provided that the condensate return line 3 removed condensate, which is brought by the pressure increasing means 4 - usually a pump to the third pressure level, and the separator S2 removed condensate before being introduced into the heat exchanger 5. The merge 15 can advantageously be done before the heat exchanger 5. The merging 15 is preferably carried out on the pressure side of the second pump 11, that is, after the condensate has been brought from the separator S2 to the third pressure level. In this very advantageous embodiment, therefore, there is no means for increasing the pressure of the condensate between the junction 15 and the heat exchanger 5.

Claims (15)

1. Machine for producing or processing a fibrous web, having a steam consumer (1) in the form of a steam-heated cylinder (1); a fresh steam network (10) which makes available fresh steam at a first pressure level; and a device for supplying the steam-heated cylinder (1), comprising a steam infeed (1) which provides steam at a second pressure level to the steam consumer (1) and which is capable of being connected to the fresh steam network (10); a condensate return line (3) for guiding the condensate that is retrieved from the steam consumer (1), in particular for returning said condensate into an external steam generator; a steam generation device for at least partially evaporating the condensate that is retrieved from the steam consumer (1), said steam generation device comprising at least one heat exchanger (5); and a return feed line (6) which is capable of being connected to the steam infeed (2) so as to feed steam that is generated from the condensate back into the steam infeed (2), wherein the steam infeed (2) by means of a valve (8) or a throttle element is capable of being decoupled from the fresh steam network, and wherein the second pressure level differs from the first pressure level,
   characterized in that
   the steam infeed (2) is composed substantially of a line system (2) without any additional storage vessel.
2. Machine according to Claim 1, characterized in that the device additionally comprises a thermocompressor (7) for supplying the steam consumer (1), said thermocompressor (7) being capable of being connected to the steam infeed (2) in such a manner that steam at the second pressure level can be used as motive steam, and the second pressure level is adapted to the motive steam pressure of the thermocompressor (7).
3. Machine according to one of the preceding claims, characterized in that the steam generation device comprises at least one throttle element (9) so as to at least partially evaporate the condensate after passing through the heat exchanger (5), and a separator (S2) to which the at least partially evaporated condensate is capable of being fed and to which the return feed line (6) is capable of being connected.
4. Machine according to one of the preceding claims, characterized in that the decoupling of the steam infeed (2) from the fresh steam network (10) is performed by means of a control valve or throttle valve (8).
5. Machine according to one of the preceding claims, characterized in that the device comprises a first pressure-boosting installation (4) which is designed for compressing condensate from the condensate return line (3) to a third pressure level, and the heat exchanger (5) is capable of being connected to the first pressure-boosting installation (4) in such a manner that the condensate at the third pressure level can be fed to the heat exchanger (5) for heating.
6. Machine according to one of Claims 3 to 5, characterized in that an installation by way of which condensate can be retrieved from the separator (S2) and be fed to the heat exchanger (5) is provided, and said installation comprises a second pressure-boosting installation (11) which is suitable for compressing the condensate to the third pressure level.
7. Machine according to one of Claims 3 to 6, characterized in that an amalgamation unit (15) in which the condensate that has been retrieved from the condensate return line (3) can be amalgamated with condensate that has been retrieved from the separator (S2) is provided.
8. Machine according to Claim 7, characterized in that no further means for pressure boosting are provided between the amalgamation unit (15) and the heat exchanger (5).
9. Machine according to one of the preceding claims, characterized in that the heat exchanger (5) is capable of being connected to an exhaust-air line (13) in such a manner that the exhaust air can be used for heating the condensate.
10. Machine according to one of the preceding claims, characterized in that only a single steam consumer (1) is connected to the steam infeed (2).
11. Method for recovering steam of a steam consumer in the form of a steam-heated cylinder (1) in a machine for producing or processing a fibrous web, wherein the machine comprises a fresh steam network (10) which makes available steam at a first pressure level, and wherein the steam-heated cylinder (1) is supplied from a steam infeed (2) with steam at a second pressure level, wherein said steam infeed (2) is composed substantially of a line system (2) without any additional storage vessel, and is capable of being decoupled from the fresh steam network (10) by means of a valve (8) or a throttle element, wherein the method comprises the following steps:

    a) retrieving condensate from the steam consumer (1) ;

    b) compressing the condensate to a third pressure level;

    c) heating the condensate at the third pressure level in at least one heat exchanger (5);

    d) evaporating the condensate and generating steam at the second pressure level;

    e) feeding the steam generated into the steam infeed (2).
12. Method according to Claim 11, characterized in that the pressure differential between the first pressure level and the second pressure level is between 0.5 bar and 7 bar, in particular between 2 bar and 4 bar, and/or or the pressure differential between the second pressure level and the third pressure level is between 7.1 bar and 13 bar, in particular between 9 bar and 11 bar.
13. Method according to one of Claims 11 or 12, characterized in that after the at least partial evaporation of the condensate, or for at least partially evaporating the condensate, a separator (S2) is provided prior to the steam generated being fed into the steam infeed (2).
14. Method according to Claim 13, characterized in that condensate which is compressed to the third pressure level and is fed to the heat exchanger (5) is retrieved from the separator (S2).
15. Method according to Claim 13 or 14, characterized in that the condensate that is retrieved from the separator (S2) at an amalgamation unit (15) is amalgamated with the condensate that is retrieved from the steam consumer (1) and conjointly with the latter condensate is fed to the heat exchanger (5), wherein no further pressure boosting is performed between the amalgamation unit (15) and the heat exchanger (5).

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