EP2396468B1 - Method and device for drying a fibrous web - Google Patents

Description

The invention relates to a process for drying a fibrous web, in particular cardboard, paper or tissue web, in which the moving fibrous web is subjected to steam and hot, moist air in the region of a preceding drying zone and is fed to a downstream drying zone following the preceding drying zone comprising a drying cylinder, in particular Yankee cylinder, as well as a hood associated therewith. It further relates to a machine for producing a fibrous web, in particular paper, board or tissue web, the specified in the preamble of claim 8 Art.

In the US Pat. No. 7,351,307 B2 and WO 2008/077874 A method is already described which serves to produce a voluminous tissue web and in which a so-called belt press in conjunction with a hot air hood and a steam supply for dewatering the fibrous web is used up to a certain dry content. In particular, for such tissue machines, it is important to reduce energy consumption, in particular during the drying process to achieve a predeterminable dry content. In addition, there is a need for an increase in dry matter content with the least possible expenditure of energy.

For example, from the EP 1 959 053 A1 It is also already known to supply exhaust air of the hood of the hot air hood assigned to a Yankee cylinder to a belt press.

The document WO 2009/117751 A1 discloses a drying device for moving material webs with at least two successive drying groups, each with a plurality of heatable drying cylinders. The drying cylinders of the first drying group are steam-heated drying cylinders, with a first heat cycle being provided for the steam. The drying cylinders of a second drying group are heated by the combustion of a combustible energy carrier and have a discharge for the waste heat. It is a first heat exchanger provided which couples the first heat cycle and the discharge for the waste heat.

The document WO 031078728 A2 describes a drying device with at least one drying cylinder group and at least one impingement drying unit, as well as a combustion turbine. The combustion gases of the combustion turbine are guided at least into the impingement drying unit as impingement air.

In the Yankee cylinder with associated drying hood or a belt press comprising drying units a lot of steam is consumed. The associated energy costs lead to correspondingly higher costs of paper production. Heretofore, the high energy exhaust air from the hood associated with the Yankee cylinder has been used primarily to preheat the hood combustion air for the Yankee dryer and water used in the paper machine.

The technology based on a belt press brings with it an even higher steam consumption compared to conventional tissue machines, resulting in an overall negative energy balance.

For this band press-based technology, more energy is needed for hot, humid air, for which exhaust air from the hood assigned to the Yankee cylinder has been used. It was previously necessary to mix the exhaust air from the Yankee hood with fresh air to reduce the temperature of the belt press air supplied to the value required in this belt press, but with which also the humidity and enthalpy of the heating air were reduced. The exhaust air temperature of the Yankee hood is usually higher than the temperature at which the belt press can operate.

The invention has for its object to provide an improved method and an improved device or machine of the type mentioned, in which the drying process is further optimized, in particular with regard to the energy requirements for the dewatering of the fibrous web. In this case, the drying process is to be optimized in particular in a combined drying in a belt press and a subsequent, a Yankee cylinder with associated drying hood comprehensive drying unit.

With regard to the method, this object is achieved in that the drying cylinder of the downstream drying zone associated hood hot air, in particular exhaust air is removed, that for generating at least a portion of the steam for the preceding drying zone by means of a first heat exchanger in the drying cylinder of the downstream drying zone condensate and / or fresh water is heated by the hood removed hot air.

In an advantageous practical embodiment, for the production of at least a portion of the hot, humid air for the preceding drying zone, the hot air removed from the hood and passed through the first heat exchanger is fed to the preceding drying zone.

Due to this design, the steam consumed from the steam generator is significantly reduced, thereby correspondingly reducing the total energy consumption. In particular, heat for the production of steam is recovered, which is then used in the papermaking process. The energy is used, which is released due to the enthalpy drop of the exhaust air of the dryer cylinder or Yankee cylinder associated hood. In the process, steam is generated on the one hand. On the other hand, the lower temperature hot air exiting from the heat exchanger is further used in the papermaking process, whereby the steam produced and the hot air cooled to a lower temperature can be further used, in particular in a belt press.

According to a preferred practical embodiment of the method according to the invention is from the supplied condensate and / or fresh water directly Steam is generated by means of the first heat exchanger and this steam is supplied to the preceding drying zone.

According to an advantageous alternative embodiment, the condensate and / or fresh water is first heated by means of the first heat exchanger. Following this first heat exchanger, the heated condensate and / or Fresh water then fed to a flash evaporator, in which case the vapor generated by the flash evaporation is supplied to the preceding drying zone.

Expediently, condensate obtained in the flash evaporation is returned to the first heat exchanger and heated therein by the hot air taken from the hood together with the condensate and / or the fresh water accumulating in the drying cylinder of the downstream drying zone.

According to a further advantageous embodiment of the method according to the invention, fresh air is heated by means of a second heat exchanger through the hot air removed from the hood and the fresh air thus heated is fed to the hood associated with the drying cylinder of the downstream drying zone as combustion air and / or make-up air. By "make-up air" is meant, for example, air for preheating the drying zone and / or the drying system. Preheating is carried out, for example, when starting the tissue machine.

The withdrawn hot air can advantageously be passed first through the provided for heating the condensate and / or fresh water first heat exchanger and then through the provided for heating the fresh air second heat exchanger before it is fed to the preceding drying zone.

According to an expedient alternative embodiment, however, it is also possible for the hot air removed from the hood to be heated first by the second heat exchanger provided for heating the fresh air and then by the first heat exchanger provided for heating the condensate and / or fresh water pass it before it is fed to the preceding drying zone.

The inventive machine for producing a fibrous web, in particular cardboard, paper or tissue web, is characterized accordingly by the fact that for generating at least a portion of the steam for the preceding drying zone, a first heat exchanger is provided, the hot air, in particular exhaust air, from the Dehumidifier cylinder is supplied to the downstream drying zone associated hood in order to heat condensate and / or fresh water obtained by the hood removed hot air in the drying cylinder of the downstream drying zone.

In an advantageous practical embodiment, at least part of the hot, humid air for the preceding drying zone is supplied by the hot air taken from the hood through the first heat exchanger to the preceding drying zone.

According to a preferred practical embodiment of the machine according to the invention, the preceding drying zone comprises an evacuated device, in particular suction roller, over which the fibrous web is guided together with at least one permeable band, in particular structured band or TAD band (TAD = Through Air Drying) permeable band and then the fibrous web are traversed by steam or hot, moist air.

In this case, the fibrous web is advantageously covered by at least one further permeable band, in particular press belt, wherein initially the Another permeable band or press belt, then the first permeable band or structural band and then the fibrous web are traversed by steam or hot, humid air. This results in the use of a press belt, a kind of belt press, in addition to the mechanical Pressure in particular a combined hot air and steam drying is applied.

In addition to the fibrous web, a dewatering belt, in particular felt belt, can be guided over the evacuated device or suction roll, first the further permeable belt or press belt, if present, then the first permeable belt or structural belt and the fibrous web and finally the additional belt Dewatering belt to be traversed by steam or hot, humid air.

The preceding drying zone may for example be fed directly by means of the first heat exchanger from the supplied condensate and / or fresh water produced steam.

However, as already mentioned, it is also conceivable to first only heat the condensate and / or fresh water by means of the first heat exchanger and to feed the condensate and / or fresh water heated by means of this first heat exchanger to a flash evaporation device. In this case, the vapor generated by the flash evaporation is supplied to the preceding drying zone.

The corresponding evaporation system can in particular also comprise one or more pumps for the circulation of the water. With these pumps, in particular, it can be achieved that the water circulating within the first heat exchanger has an increased pressure, wherein this pressure can be in particular in a range from about 3 to about 20 bar. The water absorbs heat from the air passing through the heat exchanger and is then relaxed.

In the case of flash evaporation, the water pressure is reduced, whereby steam is generated. The higher pressure water evaporates at a higher temperature. If the water is kept at a higher pressure, then its temperature can be increased without evaporation. If the pressure is then reduced to a value that has a boiling temperature below the previous temperature, the relaxation process begins automatically.

The steam generated can be deposited in a suitable chamber and used for the further drying process, in particular in tissue production.

Advantageously, a second heat exchanger is provided to heat fresh air through the hood removed hot air, wherein the thus heated fresh air of the drying cylinder of the downstream drying zone associated hood is supplied as combustion air and / or make-up air. As already mentioned, the term "make-up air" is understood as meaning, for example, air for preheating the drying zone and / or the drying system. Preheating is carried out, for example, when starting the tissue machine.

The present invention brings in particular advantages in terms of steam consumption and in particular when using a Yankee dryer and / or a belt press. The amount of steam generated depends on such conditions as, in particular, air mass flow, air temperature and humidity, the fact of whether or not an air-to-air heat exchanger is provided, etc.

It is particularly advantageous if at least one heat exchanger is provided with a preferably flow-regulated bypass for the hot air removed from the hood.

Fig. 1

ein schematisches Flussbild einer ersten Ausführungsform des erfindungsgemäßen Wärmerückgewinnungssystems,

Fig. 2

ein schematisches Flussbild einer weiteren Ausführungsform des Wärmerückgewinnungssystems,

Fig. 3

ein schematisches Flussbild einer weiteren Ausführungsform des Wärmerückgewinnungssystems mit einer Entspannungsverdampfungseinrichtung,

Fig. 4

ein schematisches Flussbild einer weiteren, eine Entspannungsverdampfungseinrichtung umfassenden Ausführungsform des Wärmerückgewinnungssystems und

Fig. 5

ein schematisches Flussbild einer weiteren, eine Entspannungsverdampfungseinrichtung umfassenden Ausführungsform des Wärmerückgewinnungssystems.

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing; in this show:

Fig. 1

a schematic flow diagram of a first embodiment of the heat recovery system according to the invention,

Fig. 2

a schematic flow diagram of another embodiment of the heat recovery system,

Fig. 3

a schematic flow diagram of another embodiment of the heat recovery system with a flash evaporation device,

Fig. 4

a schematic flow diagram of another, comprising a flash evaporator embodiment of the heat recovery system and

Fig. 5

a schematic flow diagram of another, a flash evaporator comprehensive embodiment of the heat recovery system.

Fig. 1 shows a schematic flow diagram of a first exemplary embodiment of the inventive heat recovery system of a machine for producing a fibrous web, which may be in particular a cardboard, paper or tissue web.

In this case, the moving fibrous web is first applied in the region of a preceding drying zone 10 with steam and hot, humid air. in the Connection therein, the fibrous web is fed to a downstream drying zone 12.

In this case, the preceding drying zone 10 may in particular comprise an evacuated device 42, preferably suction roll, over which the fibrous web is guided together with at least one permeable band, in particular structured band or TAD band, wherein first the permeable band and then the fibrous web of steam or hot, moist air to be flowed through.

The fibrous web can also be covered by at least one further permeable band, in particular press belt, in which case first the further permeable band or pressing band, then the first permeable band or structure band and subsequently the fibrous web of steam or hot, moist air be flowed through. This results in the use of a press belt, a kind of belt press, in which in addition to the mechanical pressure in particular the combined hot air and steam drying takes place.

In addition, in particular, a dewatering belt, in particular felt belt, may also be guided via the evacuated device 42, first the further permeable belt or press belt, if present, then the first permeable belt or structural belt and the fibrous web and then the additional belt Dewatering belt to be traversed by steam or hot, humid air.

The downstream drying zone 12 may in particular comprise a drying cylinder 14, in particular Yankee cylinders, and a hood 16 associated therewith, which may in particular be a hot air hood.

The hood 16 associated with the drying cylinder 14 is removed hot air 18, in particular exhaust air. To produce at least a portion of the steam for the preceding drying zone 10, condensate 22 and / or fresh water obtained by means of a first heat exchanger 20 in the drying cylinder 14 of the downstream drying zone 12 are heated by the hot air 18 taken from the hood 16.

To produce at least a portion of the hot, moist air for the preceding drying zone 10, the hot air 18 taken from the hood 16 and passed through the first heat exchanger 20 is fed to the preceding drying zone 10. Since the hot air 18 gives off heat to the condensate 22 or fresh water, its temperature is lowered, so that the moist hot air 18 'finally supplied to the preceding drying zone 10 has a temperature suitable for the specific drying in this drying zone 10. Thus, the hot air supplied to the heat exchanger 20, 18 for example, a temperature in the range of 360 ° C and the last of the preceding drying zone 10 supplied moist hot air 18 'have a temperature in the range of 200 ° C. The condensate 22 fed to the heat exchanger 20 may, for example, have a temperature in the region of 165 ° C.

In the present case, steam 24 is generated directly from the supplied condensate 22 and / or fresh water by means of the first heat exchanger 20, which is then supplied to the preceding drying zone 10.

As based on the Fig. 1 can be seen, in addition, a steam separator 26 may be provided, which is arranged between the cylinder 14 and a pump 28, via which the heat exchanger 20, the condensate 22 is supplied. Moreover, in this Fig. 1 to recognize a steam generator 30.

The heat exchanger 20 is an air / water heat exchanger.

Fig. 2 shows a schematic flow diagram of another embodiment of the heat recovery system, which differs from the embodiment according to Fig. 1 essentially differs in that heated by means of a second heat exchanger 32 through the hood 16 removed hot air 18 fresh air 34 and the thus heated fresh air 34 'of the drying cylinder 14 of the downstream drying zone 12 associated hood 16 is supplied as combustion air. The second heat exchanger 32 is thus an air / air heat exchanger.

In the present case, the hot air 18 removed from the hood 16 is first passed through the second heat exchanger 32 provided for heating the fresh air 34 and then through the first heat exchanger 20 provided for heating the condensate 22 and fresh water before it is fed to the preceding drying zone 10.

In principle, however, such a design is conceivable, for example, in which the removed hot air 18 is first passed through the first heat exchanger 20 provided for heating the condensate 22 and / or fresh water and then through the second heat exchanger 32 provided for heating the fresh air 34 it is fed to the preceding drying zone 10.

Incidentally, this embodiment has at least substantially the same structure as that of Fig. 1 , wherein like reference numerals are assigned to corresponding parts.

Fig. 3 shows a schematic flow diagram of another embodiment of the heat recovery system, which differs from the embodiment according to Fig. 1 essentially differs in that the condensate 22 and / or fresh water is heated by the first heat exchanger 20 under elevated pressure, which is for example in a range of about 3 to about 20 bar, under elevated pressure and heated by means of this first heat exchanger 20, under elevated pressure condensate 22 and / or fresh water is subsequently fed to a flash evaporation device 36. In this case, therefore, the steam 24 produced by flash flashing, which has a lower pressure than heated condensate 22 or fresh water, is supplied to the preceding drying zone 10.

The heat exchanger 20 may be provided with a preferably flow-controllable bypass 38 for the hood 16 removed hot air 18. This gives greater flexibility with regard to the amount of steam generated for the preceding drying zone 10, preheating the combustion air (cf., for example Fig. 4 ) or even an increase in the temperature in the drying or hot air hood 40 associated with the preceding drying zone 10.

As based on the Fig. 3 can be seen, in the flash evaporation condensate 22 'returned to the first heat exchanger 20 and are heated in this together with the costs incurred in the drying cylinder 14 of the downstream drying zone 12 condensate 22 and / or fresh water through the hood 16 removed hot air 18.

Incidentally, this embodiment can at least substantially the same structure as the embodiment according to Fig. 1 have, with corresponding parts corresponding reference numerals are assigned.

Fig. 4 shows a schematic flow diagram of another embodiment of the heat recovery system, which differs from the embodiment according to Fig. 3 essentially differs in that additionally heated by means of a second heat exchanger 32 through the hood 16 removed hot air 18 fresh air 34 and the thus heated fresh air 34 'of the drying cylinder 14 of the downstream drying zone 12 associated hood 16 is supplied as combustion air.

In the present case, the removed hot air 18 is first passed through the first heat exchanger 20 provided for heating the condensate 22 and / or fresh water and then through the second heat exchanger 32 provided for heating the fresh air 34 before it is fed to the preceding drying zone 10.

Also, the second heat exchanger 32, which is an air / air heat exchanger, may again be provided with a preferably flow-controllable bypass 38 for the hood 16 removed hot air 18.

Incidentally, this embodiment can at least substantially the same structure as the embodiment according to Fig. 3 have, with corresponding parts corresponding reference numerals are assigned.

Fig. 5 shows a schematic flow diagram of another embodiment of the heat recovery system, which differs from the embodiment according to Fig. 4 essentially differs in that the hot air 18 taken from the hood 16 is first passed through the second heat exchanger 32 provided for heating the fresh air 34, and then through the first heat exchanger 20 provided for heating the condensate 22 and / or fresh water, before the preceding one Drying zone 10 is supplied.

Incidentally, this embodiment, at least substantially again the same structure as that according to Fig. 4 have, with corresponding parts corresponding reference numerals are assigned.

In the following table, a concrete example is reproduced, which reproduces the potential for the steam generation according to the energy content of the exhaust air of the cylinder 14 of the downstream drying zone 12 associated hood or drying hood 16. The generated steam can be used at least partially, in particular, in a steam blower box assigned to the preceding drying zone 10 or even in the Yankee troeper. It is assumed for example by a heat recovery system, as it is in the Fig. 3 is reproduced, in which only the first heat exchanger 20 is provided for heat recovery.

• Temperatur der Abluft der Yankee-Haube: 360°C
• Feuchte der Abluft der Yankee-Haube: 450 g/kg
• Temperatur der Abluft der Yankee-Haube nach der Wärmerückgewinnung (WR): 250°C
• Yankee-Hauben-Abluftfluss: 6,45 kg/s (Trockenmasse)
• Kondensatdruck: 15 bar
• Kondensattemperatur vor der Wärmerückgewinnung: 110°C
• Kondensattemperatur nach der Wärmerückgewinnung: 183°C
• Druck des durch die Entspannungsverdampfung erzeugten Dampfs: 3 bar.

For this example, the following is required:

• Yankee hood exhaust air temperature: 360 ° C
• Yankee hood exhaust air humidity: 450 g / kg
• Yankee hood exhaust air temperature after heat recovery (WR): 250 ° C
• Yankee hood exhaust air flow: 6.45 kg / s (dry matter)
• Condensate pressure: 15 bar
• Condensate temperature before heat recovery: 110 ° C
• Condensate temperature after heat recovery: 183 ° C
• Pressure of the vapor generated by the flash evaporation: 3 bar.

The steam generation potential in this example is 2020 kg / h of steam at a pressure of 3 bar. <U> REFERENCE LIST </ u> 10 preceding drying zone 12 downstream drying zone 14 drying cylinders 16 Hood, drying hood 18 hot air 18 ' hot air 20 first heat exchanger 22 condensate 22 ' condensate 24 steam 26 steam separator 28 pump 30 steam generator 32 second heat exchanger 34 fresh air 34 ' fresh air 36 Flash evaporation device 38 bypass 40 Hood, drying hood 42 vacuumed device, suction roller

Claims (17)

1. Method for drying a fibrous web, in particular a board, paper or tissue web, in which the moving fibrous web has steam and hot, moist air applied to it in the area of a preceding drying zone (10) and, following the preceding drying zone (10), is supplied to a downstream drying zone (12), which comprises a drying cylinder (14), in particular a Yankee cylinder, and a hood (16) assigned to the latter, wherein
   hot air (18), in particular exhaust air, is removed from the hood (16) assigned to the drying cylinder (14) of the downstream drying zone (12) and, to produce at least some of the steam for the preceding drying zone (10), by means of a first heat exchanger (20), condensate (22) accumulating in the drying cylinder (14) of the downstream drying zone (12) and/or fresh water is heated by the hot air (18) removed from the hood (16).
2. Method according to Claim 1,
   characterized in that
   to produce at least some of the hot, moist air for the preceding drying zone (10), the hot air (18) removed from the hood (16) and led through the first heat exchanger (20) is supplied to the preceding drying zone (10).
3. Method according to Claim 1 or 2,
   characterized in that
   by means of the first heat exchanger (20), steam (24) is produced from the condensate (22) and/or fresh water supplied, and this steam (24) is supplied to the preceding drying zone (10).
4. Method according to Claim 1 or 2,
   characterized in that
   the condensate (22) and/or fresh water heated by means of the first heat exchanger (20) is supplied to an expansion evaporation means (36) following the first heat exchanger (20), and in that the steam (24) produced by the expansion evaporation is supplied to the preceding drying zone (10).
5. Method according to Claim 4,
   characterized in that
   condensate (22') accumulating during the expansion evaporation is fed back to the first heat exchanger (20) and, in the latter, together with the condensate (22) accumulating in the drying cylinder (14) of the downstream drying zone (12) and/or the fresh water, is heated by the hot air (18) removed from the hood (16).
6. Method according to one of the preceding claims,
   characterized in that
   by means of a second heat exchanger (32), fresh air (34) is heated by the hot air (18) removed from the hood (16), and the fresh air (34') heated in this way is supplied to the hood (16) assigned to the drying cylinder (14) of the downstream drying zone (12) as combustion air and/or make-up air.
7. Method according to one of the preceding claims,
   characterized in that
   the hot air (18) removed is led firstly through the first heat exchanger (20) provided for the heating of the condensate (22) and/or fresh water, and then through the second heat exchanger (32) provided for the heating of the fresh air (34), before it is supplied to the preceding drying zone (10).
8. Method according to one of Claims 1 to 6,
   characterized in that
   the hot air (18) removed from the hood (16) is led firstly through the second heat exchanger (32) provided for the heating of the fresh air (34) and then through the first heat exchanger (20) provided for the heating of the condensate (22) and/or fresh water, before it is supplied to the preceding drying zone (10).
9. Machine for producing a fibrous web, in particular a board, paper or tissue web, having a preceding drying zone (10), in the area of which steam and hot, moist air can be applied to the moving fibrous web, and having a further drying zone (12) downstream of the first, comprising a drying cylinder (14), in particular a Yankee cylinder, and a hood (16) assigned to the latter, in particular for carrying out the method according to one of the preceding claims, wherein
   to produce at least some of the steam for the preceding drying zone (10), a first heat exchanger (20) is provided, to which hot air (18), in particular exhaust air, from the hood (16) assigned to the drying cylinder (14) of the downstream drying zone (12) is supplied, in order, by means of this hot air (18) removed from the hood (16), to heat condensate (22) accumulating in the drying cylinder (14) of the downstream drying zone (12) and/or fresh water.
10. Machine according to Claim 9,
    characterized in that
    to produce at least some of the hot, moist air for the preceding drying zone (10), the hot air (18) removed from the hood (16) and led through the first heat exchanger (20) is supplied to the preceding drying zone (10).
11. Machine according to Claim 8 or 9,
    characterized in that
    the preceding drying zone (10) comprises an evacuated means (42), in particular a suction roll, over which the fibrous web is led together with at least one permeable belt, in particular a structured belt or TAD belt, wherein steam or hot, moist air flows firstly through the permeable belt and then through the fibrous web.
12. Machine according to Claim 11,
    characterized in that
    the fibrous web is covered by at least one further permeable belt, in particular a press belt, and steam or hot, moist air flows firstly through the further permeable belt or press belt, then through the first permeable belt or structured belt and then through the fibrous web.
13. Machine according to Claim 11 or 12,
    characterized in that
    a dewatering belt, in particular a felt belt, is additionally led over the evacuated means (42) together with the fibrous web and, if appropriate, steam or hot, moist air flows firstly through the further permeable belt or press belt, then through the first permeable belt or structured belt and the fibrous web and finally through the additional dewatering belt.
14. Machine according to one of the preceding Claims 9 - 13,
    characterized in that
    steam (24) produced from the supplied condensate (22) and/or fresh water by means of the first heat exchanger (20) is supplied to the preceding drying zone (10).
15. Machine according to one of Claims 9 to 13,
    characterized in that
    the condensate (22) and/or fresh water heated by means of the first heat exchanger (20) is supplied to an expansion evaporation means (36), and the steam (24) produced by the expansion evaporation is supplied to the preceding drying zone (10).
16. Machine according to one of the preceding Claims 9 - 15,
    characterized in that
    a second heat exchanger (32) is provided, in order to heat fresh air (34) by means of the hot air (18) removed from the hood (16), and in that the fresh air (34') heated in this way is supplied to the hood (16) assigned to the drying cylinder (14) of the downstream drying zone (12) as combustion air and/or make-up air.
17. Machine according to one of the preceding Claims 9 - 16,
    characterized in that
    at least one heat exchanger (20, 32) is provided with a preferably controllable-flow bypass (38) for the hot air (18) removed from the hood (16).

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