Tissue papermaking machine and a method of manufacturing a tissue paper web
A tissue papermaking machine is described, comprising a wet section and a press section comprising a single press with first and second press elements forming a press nip, and with a press felt running through the press nip in contact with the formed fiber web, whereby the second press element is arranged inside the loop of the press and felt, and a smooth belt runs through the press nip in contact with the formed fiber web, whereby the first press element is arranged inside the loop of the belt, and a transfer roll arranged inside the loop of the belt forming a transfer nip with a drying surface, whereby the smooth belt carries the fiber web between the press nip and the transfer nip. A pre-dewatering device is arranged upstream of the press to dewater the fiber web to a dry content of 15-30%. Associated methods are also provided.
1. A tissue papermaking machine for manufacturing a tissue paper web ( 1 ″), comprising:
a wet section ( 2 ) for forming a fibre web ( 1 ′),
a press section ( 3 ) for pressing the fibre web ( 1 ′), said press section ( 3 ) comprising:
a single press ( 11 ), comprising:
a first press element ( 12 ),
a second press element ( 13 ), said press elements ( 12 , 13 ) forming a press nip (N 1 ) therebetween with a predetermined pressure,
a press felt ( 17 ) running in an endless loop around a plurality of guide rolls ( 18 ) and through said press nip (N 1 ) together and in contact with the formed fibre web ( 1 ′), the second press element ( 13 ) being arranged inside the loop of the press felt ( 17 ),
a smooth belt ( 14 ) running in an endless loop around a plurality of guide rolls ( 15 ) and through said press nip (N 1 ) together and in contact with the formed fibre web ( 1 ′), the first press element ( 12 ) being arranged inside the loop of the belt ( 14 ), and
a transfer roll ( 16 ) arranged inside the loop of the smooth belt ( 14 ),
a dry section ( 4 ) for final drying of the fibre web ( 1 ″) pressed in the press nip (N 1 ), said dry section ( 4 ) comprising a drying surface ( 20 ) for final drying of the pressed fibre web ( 1 ″),
said transfer roll ( 16 ) being arranged to form a transfer nip (N 2 ) together with the drying surface ( 20 ) for transfer of the fibre web ( 1 ″) to the drying surface ( 20 ), whereby the smooth belt ( 14 ) is arranged to carry the pressed fibre web ( 1 ″) between the press nip (N 1 ) and the transfer nip (N 2 ), wherein:
a pre-dewatering device ( 25 ) is arranged substantially adjacent the press felt ( 17 ) at a location upstream of and spaced apart from the first press element ( 12 ) and the second press element ( 13 ) of the press ( 11 ), and prior to any contact between the fibre web ( 1 ″) and the smooth belt ( 14 ), the pre-dewatering device ( 25 ) being configured to pre-dewater the fibre web ( 1 ′) to a dry content of 15-30% before the fibre web ( 1 ′) runs into the press nip (N 1 ) of the press ( 11 ); and
the press felt ( 17 ) and the smooth belt ( 14 ) are arranged to be separated from each other immediately after the exit of the press nip (N 1 ) and define therebetween an angle α, which is at least 5° in order to prevent rewetting of the pressed fibre web ( 1 ″).
2. The tissue papermaking machine according to claim 1 , wherein the smooth belt ( 14 ) is impermeable to water.
3. The tissue papermaking machine according to claim 1 , further comprising a pre-dewatering device ( 25 ) for pre-dewatering of the fibre web ( 1 ′) to a dry content of 15-30% without compressing.
4. The tissue papermaking machine according to claim 1 , further comprising a pre-dewatering device ( 25 ) which has a suction device.
5. The tissue papermaking machine according to claim 1 , wherein the press ( 11 ) is a press with an extended nip.
6. The tissue papermaking machine according to claim 5 , wherein the press ( 11 ) is a shoe press.
7. The tissue papermaking machine according to claim 1 , wherein the specific pressure in the press nip (N 1 ) is 4-6 MPa and the linear load is 400-600 kN/m.
8. The tissue papermaking machine according to claim 7 , wherein, for grammages of the fibre web ( 1 ″) in the range of 12-42 g/m 2 the press is arranged to dewater the fibre web ( 1 ″) so that the fibre web ( 1 ″) obtains a dry content of 46-52% after the press ( 11 ).
9. The tissue papermaking machine according to claim 7 , wherein, for grammages of the fibre web ( 1 ″) in the range of 15-25 g/m 2 , the press is arranged to dewater the fibre web ( 1 ″) so that the fibre web ( 1 ″) obtains a dry content of 46-52% after the press ( 11 ).
10. The tissue papermaking machine according to claim 1 , wherein the smooth belt ( 14 ) provides an adhesion of the fibre web ( 1 ″) against it whereby the machine speed can be increased to 1300-2200 m/min.
11. The tissue papermaking machine according to claim 1 , wherein the press ( 11 ) provides a recovery of the thickness of the fibre web ( 1 ″) at the exit of the press nip (N 1 ).
12. The tissue papermaking machine according to claim 1 , wherein the pre-dewatering device ( 19 ) comprises a suction roll ( 25 ) located within the loop of the press felt ( 17 ), and a steam box ( 26 ) located on the outside of the loop of the press felt ( 17 ) opposite the suction roll ( 25 ).
13. The tissue papermaking machine according claim 1 , further comprising a preheating device ( 27 ) arranged downstream of the press ( 11 ) to increase the temperature of the fibre web ( 1 ″) before the fibre web ( 1 ″) reaches the drying surface ( 20 ).