[0001] The present invention refers to a machine for drying tissue paper, according to the
preamble portion of claim 1.
BACKGROUND OF THE INVENTION
[0002] In the paper industry machines for drying tissue paper are known, that are provided
with a hood that blows hot air with a great velocity against the tissue paper, and
a rotatable drying cylinder called Yankee partially covered by said hood. The tissue
paper is dried thanks to the combination of the drying cylinder that transmits heat
by contact and the hood that dries by heat and mass transfer.
[0003] Generally, the machines for drying tissue comprise hood that operate with air at
temperatures of 300, 400 and 500°C. Recently, hoods that operate at 650 and 700°C
were made, but they have problems regarding the material expansion, so that the manufacturers
of said hoods use materials and manufacturing systems developed with finite element
models. The speeds of the blown air can reach values from 90 to 160 m/s.
[0004] The hood must be placed very near from the drying cylinder and the paper, leaving
a distance of about one inch. However, the hood must have a separation mechanism when
there is no paper, to prevent the air to be directed against the opposed cylinder
because it would be dangerous, and also the separation mechanism permits the access
to an operator for service.
[0005] The hood is divided into two parts, called respectively wet part and dry part, so
that the tissue paper firstly passes by the wet part and then by the dry part of the
hood.
[0006] The division of the hood is carried out according to the cylinder axis, because the
wet and dry parts are symmetrical. At the wet part of the hood the yield is higher
and more water is extracted, so it seems that a symmetrical hood is not suitable.
However, in the market there are symmetrical hoods for spare parts reasons, decreasing
the costs.
[0007] Each part of the hood has its own air circuit, so that each circuit comprises a motor
fan that blows air, which is heated by heating means before it enters inside the corresponding
part of the hood. Said heating means of blown air can be of several kinds, such as
vapour radiators, thermal oil radiators, or more usually gas burners in air vain.
In the case of gas burners, each receives a mixture of combustible gas, e.g. natural
gas, and air to feed the flame of the burner.
[0008] The hood extracts water evaporated from the paper. This vapour is concentrated in
the circulation air so a quantity of air must be drained to outside. To compensate
it, fresh air must enter from outside. The hood includes respectively a feeding air
input for the wet part and a feeding air input for the dry part. The part of the hood
on the Yankee cylinder comprises, at its external surface, a plurality of openings
that are communicated with the internal part of the hood. Some openings permit the
air to pass and other ones recover the wet air.
[0009] In operation, the wet tissue band enters the drying machine adhering it on the surface
of the Yankee cylinder to be dried, and the hot air enters inside the hood to be applied
against the cylinder to enter in contact with the wet tissue band. Therefore, when
the cylinder rotates, the tissue band is dried, passing firstly under the wet part
of the hood and then under the dry part of it.
[0010] From both parts of the hood, the wet one and the dry one, is extracted a portion
of air, the exhausted one, to prevent air in the circuit with a humidity of 100%.
Until now, to do this there are two practices: one consists on extracting the air
purge from both wet and dry hoods and send it to a heat recuperator, and the other
one consists on circulate the purge from the dry hood, where the air has less content
of humidity, to the wet hood, and from it to outside. This is carried out this way
because the two parts of the hood are symmetrical.
[0011] Up to date it is feasible in a tissue paper plant to use a cogeneration central,
because the greater thermal consumption is carried out in the hood. As stated previously,
this consumption is carried out normally with heated air by the combustion of natural
gas in air vain. Therefore, temperatures of 500°C are achieved quickly, even though
hoods with temperatures up to 700°C are also reached.
[0012] Because the production of paper and the evaporation depend on the humidity difference
between the limit layer of the air in contact with the paper and the blown air, and
also on the quantity of heat transported by the air, it is very difficult to find
a solution for the cogeneration. The hoods have been designed up till now by the recirculation
of wet air with the extraction of the purge to maintain a maximum humidity.
[0013] Currently, the development of the hood to be adapted to a cogeneration central is
carried out passing all the cogeneration combustion gases by the two parts of the
hood, the wet one and the dry one. Optionally, a burner in vain of these gases increases
the temperature. At the exit of the hood, without recirculation, the gases pass by
the aquotubular boiler to produce the vapour necessary for the Yankee cylinder. In
a circuit like this, the humidity is very low.
[0014] Patent application
WO99/57367 describes a method and an apparatus for improving the drying capacity of a hood covering
a Yankee cylinder, when drying a web with a Yankee cylinder while conveying the web
over the cylinder by blowing hot air jets against the web at the region of a first
hood, said hot air jets having a temperature mainly lower than 550 °C. The drying
capacity of the drying hood is increased by blowing hot air jets against the web conveyed
over the cylinder at the region of a second hood, a so called hot air hood, said hot
air jets having a temperature which is higher than the temperature of the hot air
jets blown against the web at the first hood, or mainly higher than 550 °C.
[0015] The object of the machine for drying tissue paper provided with a cogeneration system
of the present invention is to solve the drawbacks of the drying machines of the state
of the art, providing a greater efficiency and permitting to be adapted to a cogeneration
central.
[0016] The machine for drying tissue paper is characterised in that the machine is provided
with a cogeneration system and in that the air purge is recirculated from the wet
part to the dry part before it exits the hood, and in that the dry part of the hood
receives the gases from the cogeneration system.
[0017] Therefore, it is obtained a machine for drying tissue paper with a greater efficiency,
obtaining also the following advantages.
[0018] The asymmetric hood permits to obtain a wet part with a greater drying surface and
operating at a greater temperature, to obtain a greater yield in the drying process.
[0019] The cogeneration is carried out at the dry hood, because it has a lower yield and
it is where the most savings can be obtained. The wet hood is for increasing the production,
because it has a better yield.
[0020] As the air purge is conducted from the wet part to the dry part, contrary to the
teachings to the state of the art, it is possible to increase the flow rate of said
dry part and, therefore, the blowing velocity, increasing the yield. Furthermore,
it is possible to keep a necessary good humidity level, because said dry part operates
with gases from the cogeneration, with a relatively low humidity.
[0021] According to a preferred embodiment of the invention, the wet part, with an embrace
angle with the cylinder of 145°, operates at 650°C and at an air velocity of 160 m/s,
and the dry part, with an embrace angle of 105°, operates at 405°C and at an air velocity
of 145 m/s.
[0022] Preferably, the heating means for the air that enters into the hood are gas burners
in air vain. Both circuits, the wet part and the dry part, of the hood have a closed
operation, so that the air at the exit of the fan passes by the gas burner in vain,
enters the hood, and it exits to enter again inside the fan.
[0023] To start the machine it is necessary to star the air circuit with the burner to finally
permit the entrance of the cogeneration gases.
[0024] Advantageously, the machine comprises a recovery boiler connected to the air purge
exit of the dry part of the hood.
[0025] Said recovery boiler permits to obtain vapour at a temperature and pressure suitable
for the machine.
[0026] Preferably, the recovery boiler is of pyrotubular kind. However, another kind of
boiler can be used such as, e.g. aquatubular boilers.
[0027] Advantageously, the recovery boiler comprises a gas recovery zone and another zone
with a housing with a gas burner.
[0028] Preferably, both zone of the recovery boiler are placed into the same shell. Therefore,
the quality of the vapour does not change if it is carried out with recovery or not.
[0029] Advantageously, at the exit of the recovery boiler two economisers are provided,
one for each zone of said boiler.
[0030] Advantageously, at the exit of the recovery boiler an air-to-air recuperator is provided,
that heats by heat exchange with the gases form the recovery boiler, a fresh airflow
that is blown to said burners of the wet and dry parts of the hood, and to the fresh
air entrance of the wet part of the hood.
[0031] Also advantageously, at the exit of the air-to-air recuperator a low-pressure, preferably
0.5 bar, vapour boiler is provided, to heat the process water.
[0032] Advantageously, a thermo-compressor is provided, that mixes the vapour produced by
the recovery boiler and the flash or vapour evaporated of condensates from the Yankee
cylinder and extracts vapour at the feeding pressure.
[0033] Advantageously, a first expansion tank is provided through which the condensates
of the Yankee cylinder pass to produce vapour flash to be recovered in the thermo-compressor,
and a second expansion tank, at a lower pressure, through which a second flash at
a lower pressure, preferably 2 bar, is produced, to feed the vapour box.
[0034] Advantageously, the vapour produced at the exit of the second expansion tank serves
to feed a vapour box that heats the tissue paper before it enters into the Yankee
cylinder, and also to heat the machine water.
[0035] This solution, even though is usual for a conventional paper machine, is new for
tissue paper machines, where vapour boxes are usually not used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] To facilitate the description of what has be disclosed previously, some drawings
are attached in which, diagrammatically and only as a non-limitative example, a practical
case of embodiment of the machine for drying tissue paper provided with a cogeneration
system of the invention is shown, in which fig. 1 is a diagrammatical view that shows
the machine for drying tissue paper of the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0037] As it can be seen from fig. 1, the machine 1 for drying tissue paper 2 of the invention
comprises a drying hood 3 divided into two parts, a wet part 3a and a dry part 3b,
that blows hot air with a great velocity into a Yankee rotatable cylinder 4 on which
the tissue paper 2 is placed, and each part 3a, 3b of the hood 3 including a motor
fan 5a, 5b and a gas in vain burner 6a, 6b that heats the air from the fan 5a, 5b
before it enters into the corresponding part of the hood 3a, 3b. Both circuits, wet
part 3a and dry part 3b, of the hood 3 have a closed operation, so that the air at
the exit of the fan 5a, 5b passes through the gas in vain burner 6a, 6b, it enters
inside the hood 3, and it exits to return to the fan 5a, 5b.
[0038] The hood 3 is geometrically asymmetric, so that the wet part 3a presents a greater
drying surface and it works at a higher temperature with respect to the dry part 3b.
Hence, it is obtained a higher yield in the drying process.
[0039] At the hood 3 it is provided an exit for extracting a purge of exhaust air 7, in
this case the purge 7 is recirculated from the wet part 3a to the dry part 3b before
it exits said hood 3.
[0040] Furthermore, the dry part 3b of the hood 3 receives the gases 8 from a cogeneration
system. The cogeneration is carried out in the dry hood, because it is the one that
has a lower yield and it is where more savings can be obtained. The wet hood is specialised
in increasing the production, because it has a better yield.
[0041] As the purge is conducted from the wet part to the dry part, opposed as it is done
in the state of the art, it is possible to increase the flow rate of said dry part
and, therefore, the blowing velocity, increasing the yield. Furthermore, it is possible
to keep a good humidity level because the dry part operates with gases from the cogeneration.
[0042] Hence, it is obtained a machine for drying tissue paper with a greater efficiency.
[0043] The wet part 3a of the hood 3, with an embracement angle with the cylinder of 145°,
operates at 650°C and with an air velocity of 160 m/s, and the dry part 3b, with an
embracement angle with the cylinder of 105°, operates at 405°C and with a velocity
of 145 m/s.
[0044] On the other hand, the machine comprises a recovery boiler 9, of pyrotubular kind,
connected to the air purge exit 7 of the dry part 3b of the hood 3.
[0045] Therefore, if the cogeneration gas enters at 405°C, at the exit the dry part of the
hood the gases are at 310°C yet, with a humidity of 0.0851 Kg H
2O/Kg dry.
[0046] Said recovery boiler 9 is a mixed boiler, with a gas recovery zone and another zone
with a housing with a gas burner, both zones being placed inside the same shell, so
that the quality of the vapour does not change if it is carried out with recovery
or not. At the exit of the recovery boiler 9 there are two economizers 10, one for
each zone of the boiler 9. The recovery boiler 9 provides vapour at 17 bars and at
a temperature of 222°C.
[0047] Furthermore, at the exit of the recovery boiler 9 there is an air-to-air recuperator
11 that heats, by heat exchange with the gases from the recovery boiler 9, a fresh
airflow 12 that is blown to the burners 6a, 6b of the hood 3 and to the entrance of
the wet part 3a of the hood 3.
[0048] At the exit of the air-to-air recuperator 11, downstream in the circuit, a vapour
boiler 13 at 0.5 bars is provided to heat the process water and the manufacturing
section.
[0049] A thermo-compressor is provided, that mixed the vapour at 17 bars produced by the
recovery boiler 9 and the condensate flow from the Yankee cylinder 4, and it extracts
vapour at 8 bars, that is the feeding pressure.
[0050] It is also provided a first expansion tank, through which the condensates of the
Yankee cylinder pass to promote the flow to be recovered, and a second expansion tank
through which said flow to be recovered passes to produce vapour at 3 bar.
[0051] The vapour produced at the exit of the second expansion tank serves to feed a vapour
box that heats the tissue paper before it enters inside the Yankee cylinder, and to
heat the machine water. This solution, even tough is usual for a conventional paper
machine, is new in the case of tissue paper machines, where vapour boxes are usually
not used.
[0052] The exit gases from the boiler are finally at 155°C.
[0053] Finally, the water of the recovery boiler, whose entrance is at 47°C, will be heated
by a plate exchanger with the water from the cogeneration central, it will pass by
a degasifier and it will enter inside the boiler at 105°C. The gases at the degasifier
exit will be at 148°C.
[0054] To calculate the energy used in the high yield hood 3, the model with no post-combustion
has been fixed, operating the hood 3 only with the recovery gases. Once fixed the
reached production, another model is carried out, this time with cogeneration central,
keeping the production of the paper machine 1, and therefore the evaporation inside
the hood 3.
[0055] The boiler 9 in these conditions produces less vapour than that the machine 1 needs
to operate. The production calculation serves to determine the yield of the assembly.
Only in the case of heating of water, it is supposed that it will be for all the produced
vapour.
[0056] The production will be of 4,800 kg/h of vapour at 17 bars and 3,510 kg/h vapour at
2 bars, with a recovery in the boiler of 5,503 kw. The used hot water will be used
to heat the loss of condensates in the operation of live vapour (vapour box) 4,000
kg/h of fresh water of the boiler from 15°C to 80°C, temperature at which it will
enter inside the degasfier. Furthermore, 16 m3/h of fresh feeding water of the paper
machine will be heated to 70°C. In this step of heating water 1,345 kw will be recovered.
[0057] During the transit of the gases by the high yield hood 3 the heat will be recovered,
passing from 405°C to 310°C, using 3,614 kw. The recovered assembly will be of 3,614
+ 5,503 + 1,345, that is a total of 10,462 kw. If the gases at the exit of the cogeneration
central had a power of 10,563 kw, the recovery yield is, therefore, of 99,9%.
[0058] The cogeneration central is based in an 18V34SG motor.
[0059] The management of this complex cogeneration central-forced air hood must permit to
operate if the cogeneration central is stopped. This is a cogeneration principle that
never can be omitted. Therefore, it is necessary that the hood could operate with
recirculation of air and that the vapour boiler could work without the addition of
gases from the hood.
1. Machine (1) for drying tissue paper (2), comprising a drying hood (3) divided into
two parts, a wet part (3a) and a dry part (3b), that blows hot air at high velocity
to a Yankee rotatable cylinder (4), on which the tissue paper (2) to be dried is placed,
and each part (3a, 3b) of the hood (3) includes a motor fan (5a, 5b) and heating means
(6a, 6b) that heat the air from the fan (5a, 5b) before it enters into the corresponding
part of the hood (3a, 3b), and the hood (3) including an exit for extracting an exhaust
air purge (7), the hood (3) being geometrically asymmetric, the wet part (3a) presenting
a greater drying surface and operating at a temperature higher than that of the dry
part (3b), characterised in that the machine is provided with a cogeneration system and in that the air purge (7) is recirculated from the wet part (3a) to the dry part (3b) before
it exits from the hood (3), and in that the dry part (3b) of the hood (3) receives the gases (8) from the cogeneration system.
2. Machine (1) according to claim 1, characterised in that the wet part (3a), with an embrace angle with the cylinder of 145°, operates at 650°C
and at an air velocity of 160 m/s, and the dry part (3b), with an embrace angle of
105°, operates at 405°C and at an air velocity of 145 m/s.
3. Machine (1) according to claim 1, characterised in that said heating means of the air that enters into the hood (3) are gas burners in air
vain (6a, 6b).
4. Machine (1) according to any of the previous claims, characterised in that it comprises a recovery boiler (9) connected to the air purge exit (7) of the dry
part (3b) of the hood (3).
5. Machine (1) according to claim 4, characterised in that the recovery boiler (9) is of pyrotubular kind.
6. Machine (1) according to claim 4 or 5, characterised in that the recovery boiler (9) comprises a gas recovery zone and another zone with a housing
with a gas burner.
7. Machine (1) according to claim 6, characterised in that both zones of the recovery boiler (9) are placed into the same shell.
8. Machine (1) according to claim 6 or 7, characterised in that at the exit of the recovery boiler (9) two economizers (10) are provided, one for
each zone of said boiler (9).
9. Machine (1) according to any of the previous claims, characterised in that at the exit of the recovery boiler (9) an air-to-air recuperator (11) is provided,
that heats by heat exchange with the gases form the recovery boiler (9), a fresh airflow
(12) that is blown to said burners (6a, 6b) of the wet (3a) and dry (3b) parts of
the hood (3), and to the fresh air entrance of the wet part (3b) of the hood (3).
10. Machine (1) according to claim 9, characterised in that at the exit of the air-to-air recuperator (11) a low-pressure, preferably 0.5 bar,
vapour boiler (13) is provided, to heat the process water.
11. Machine (1) according to any of the previous claims, characterised in that a thermo-compressor is provided, that mixes the vapour produced by the recovery boiler
(9) and the flash or vapour evaporated of condensates from the Yankee cylinder (4)
and extracts vapour at the feeding pressure.
12. Machine (1) according to claim 11, characterised in that a first expansion tank is provided through which the condensates of the Yankee cylinder
(4) pass to produce vapour flash to be recovered in the thermo-compressor, and a second
expansion tank, at a lower pressure, through which a second flash at a lower pressure,
preferably 2 bar, is produced, to feed the vapour box.
13. Machine (1) according to claim 12, characterised in that the vapour produced at the exit of the second expansion tank serves to feed a vapour
box that heats the tissue paper (2) before it enters into the Yankee cylinder (4),
and also to heat the machine water.
1. Maschine (1) zum Trocknen von Tissue-Papier (2) mit einer Trocknungshaube (3), die
in zwei Teile aufgeteilt ist, einem feuchten Teil (3a) und einem trockenen Teil (3b),
die heiße Luft bei hoher Geschwindigkeit zu einem drehbaren Yankeezylinder (4) bläst,
auf dem das Tissue-Papier (2), das getrocknet werden soll, platziert ist, wobei ein
jeder Teil (3a, 3b) der Haube (3) ein Motorgebläse (5a, 5b) und eine Heizeinrichtung
(6a, 6b) umfasst, die die Luft von dem Gebläse (5a, 5b) aufheizt, bevor sie in den
entsprechenden Abschnitt der Haube (3a, 3b) eintritt, und wobei die Haube (3) einen
Ausgang zum Extrahierten einer Abgasluftreinigung (7) umfasst, wobei die Haube (3)
geometrisch asymmetrisch ist, der feuchte Teil (3a) eine größere Trocknungsoberfläche
aufweist, und bei einer Temperatur arbeitet, die höher ist als die des trockenen Teils
(3b), dadurch gekennzeichnet, dass die Maschine mit einem Kraft-Wärme-Kopplungssystem versehen ist, und dass die Luftreinigung
(7) von dem feuchten Teil (3a) zu dem trockenen Teil (3b) zurückzirkuliert wird, bevor
sie die Haube (3) verlässt und dass der trockene Teil (3b) der Haube (3) die Gase
(8) von dem Kraft-Wärme-Kopplungssystem erhält.
2. Maschine (1) nach Anspruch 1, dadurch gekennzeichnet, dass der feuchte Teil (3a) mit einem Umschließungswinkel mit dem Zylinder von 145°, bei
650° C und einer Luftgeschwindigkeit von 160 m/s arbeitet, und der trockene Teil (3b)
mit einem Umschließungswinkel von 105°, bei einer Temperatur von 405° C und bei einer
Luftgeschwindigkeit von 145 m/s arbeitet.
3. Maschine (1) nach Anspruch 1, dadurch gekennzeichnet, dass die Heizeinrichtung der Luft, die in die Haube (3) eintritt, Gasbrenner in Luftadern
(6a, 6b) sind.
4. Maschine (1) nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass sie einen Erholungsboiler (9) aufweist, der mit dem Luftreinigungsausgang (7) des
trockenen Teils (3b) der Haube (3) verbunden ist.
5. Maschine (1) nach Anspruch 4, dadurch gekennzeichnet, dass der Erholungsboiler (9) von der Art eines Pyrorohres ist.
6. Maschine (1) nach Anspruch 4 oder 5, dadurch gekennzeichnet, dass der Erholungsboiler (9) eine Gaserholungszone und eine weitere Zone aufweist, mit
einem Gehäuse mit einem Gasbrenner.
7. Maschine (1) nach Anspruch 6, dadurch gekennzeichnet, dass beide Zonen des Erholungsboilers (9) in dieselbe Schale gesetzt sind.
8. Maschine (1) nach Anspruch 6 oder 7, dadurch gekennzeichnet, dass am Ausgang des Erholungsboilers (9) zwei Abgasvorwärmer (10) vorgesehen sind, einer
für jede Zone des Boilers (9).
9. Maschine (1) nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass am Ausgang des Erholungsboilers (9) ein Luft-zu-Luft-Wärmetauscher (11) vorgesehen
ist, der mittels Wärmetausch mit den Gasen von dem Erholungsboiler (9) heizt, wobei
ein frischer Luftstrom (12), der auf die Brenner (6a, 6b) des feuchten (3a) und trockenen
(3b) Teils der Haube (3) und zu dem Frischlufteingang des feuchten Teils (3b) der
Haube (3) geblasen wird, aufheizt.
10. Maschine (1) nach Anspruch 9, dadurch gekennzeichnet, dass an dem Ausgang des Luft-zu-Luft Vorwärmers (11) ein Niederdruck-, vorzugsweise 0,5
bar, Dampfboiler (13) vorgesehen ist, um das Prozesswasser aufzuheizen.
11. Maschine (1) nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Wärmekompressor vorgesehen ist, der den Dampf, der von dem Erholungsboiler (9)
erzeugt wird, und den Austrieb oder Dampf, von Kondensaten von dem Yankeezylinder
(4) verdampft, mischt, und den Dampf unter Zuführdruck ausbringt.
12. Maschine (1) nach Anspruch 11, dadurch gekennzeichnet, dass ein erster Expansionstank vorgesehen ist, durch den die Kondensate des Yankeezylinders
(4) hindurchströmen, um eine Dampfausbringung zu erzeugen, die in dem Wärmekompressor
rückgewonnen werden muss, und ein zweiter Expansionstank vorgesehen ist, bei einem
niedereren Druck, durch den eine zweite Ausbringung bei niedererem Druck, vorzugsweise
2 bar, erzeugt wird, um die Dampfbox zu speisen.
13. Maschine (1) nach Anspruch 12, dadurch gekennzeichnet, dass der an dem Ausgang des zweiten Expansionstanks produzierte Dampf dazu dient, eine
Dampfbox zu speisen, die das Tissue-Papier (2) aufheizt, bevor es in den Yankeezylinder
(4) eintritt und auch das Maschinenwasser aufheizt.
1. Machine (1) pour sécher du papier essuie-tout (2), comprenant une hotte de séchage
(3) divisée en deux parties, une partie humide (3a) et une partie sèche (3b), qui
souffle de l'air chaud à grande vitesse vers un cylindre rotatif Yankee (4), sur lequel
est placé le papier essuie-tout (2) à sécher, chaque partie (3a, 3b) de la hotte (3)
comprenant un moto-ventilateur (5a, 5b) et des moyens de chauffage (6a, 6b) qui chauffent
l'air venant du ventilateur (5a, 5b) avant qu'il entre dans la partie correspondante
de la hotte (3a, 3b), et la hotte (3) comprenant une sortie pour évacuer une purge
d'air d'échappement (7), la hotte (3) ayant une géométrie asymétrique, la partie humide
(3a) présentant une surface de séchage plus grande et fonctionnant à une température
plus élevée que celle de la partie sèche (3b), caractérisée en ce que la machine est équipée d'un système de cogénération et en ce que la purge d'air (7) est remise en circulation de la partie humide (3a) vers la partie
sèche (3b) avant qu'elle sorte de la hotte (3), et en ce que la partie sèche (3b) de la hotte (3) reçoit les gaz (8) du système de cogénération.
2. Machine (1) selon la revendication 1, caractérisée en ce que la partie humide (3a), formant un angle de recouvrement (« embrace angle ») de 145°
avec le cylindre, fonctionne à 650 °C et à une vitesse d'air de 160 m/s, et la partie
sèche (3b), formant un angle de recouvrement (« embrace angle ») de 105°, fonctionne
à 405 °C et à une vitesse d'air de 145 m/s.
3. Machine (1) selon la revendication 1, caractérisée en ce que lesdits moyens de chauffage de l'air qui entre dans la hotte (3) sont des brûleurs
à gaz à veine d'air (6a, 6b).
4. Machine (1) selon l'une quelconque des revendications précédentes, caractérisée en ce qu'elle comprend une chaudière de récupération (9) raccordée à la sortie de purge d'air
(7) de la partie sèche (3b) de la hotte (3).
5. Machine (1) selon la revendication 4, caractérisée en ce que la chaudière de récupération (9) est de type pyrotubulaire.
6. Machine (1) selon la revendication 4 ou 5, caractérisée en ce que la chaudière de récupération (9) comprend une zone de récupération de gaz et une
autre zone avec une enceinte avec un brûleur à gaz.
7. Machine (1) selon la revendication 6, caractérisée en ce que les deux zones de la chaudière de récupération (9) sont placées dans la même enveloppe.
8. Machine (1) selon la revendication 6 ou 7, caractérisée en ce qu'il est prévu, à la sortie de la chaudière de récupération (9), deux économiseurs (10),
un pour chaque zone de ladite chaudière (9).
9. Machine (1) selon l'une quelconque des revendications précédentes, caractérisée en ce qu'il est prévu, à la sortie de la chaudière de récupération (9), un récupérateur air/air
(11) qui chauffe, par échange thermique avec les gaz provenant de la chaudière de
récupération (9), un flux d'air frais (12) qui est amené auxdits brûleurs (6a, 6b)
des parties humide (3a) et sèche (3b) de la hotte (3), et à l'entrée d'air frais de
la partie humide (3b) de la hotte (3).
10. Machine (1) selon la revendication 9, caractérisée en ce qu'il est prévu, à la sortie du récupérateur air-air (11), une chaudière à vapeur (13)
basse pression, de préférence 0,5 bar, pour chauffer l'eau du procédé.
11. Machine (1) selon l'une quelconque des revendications précédentes, caractérisée en ce qu'il est prévu un thermocompresseur, qui mélange la vapeur produite par la chaudière
de récupération (9) et la vaporisation éclair ou la vapeur évaporée des condensats
du cylindre Yankee (4) et évacue la vapeur à la pression d'alimentation.
12. Machine (1) selon la revendication 11, caractérisée en ce qu'il est prévu un premier réservoir d'expansion, à travers lequel passent les condensats
du cylindre Yankee (4) pour produire la vaporisation éclair destinée à être récupérée
dans le thermocompresseur, et un second réservoir d'expansion, à une pression plus
basse, à travers lequel une seconde vaporisation éclair est produite à une pression
plus basse, de préférence 2 bars, pour alimenter le coffret de vapeur.
13. Machine (1) selon la revendication 12, caractérisée en ce que la vapeur produite à la sortie du second réservoir d'expansion sert à alimenter un
coffret de vapeur qui chauffe le papier essuie-tout (2) avant qu'il entre dans le
cylindre Yankee (4), et à chauffer également l'eau de la machine.