Yankee drying hood arrangement, a Yankee drying cylinder fitted with a Yankee drying hood arrangement and a method of drying a fibrous web

A Yankee drying hood arrangement (1) which is shaped to be fitted over a rotatable Yankee drying cylinder (2) having an axial extension (A) and a circular cylindrical surface (3) such that the Yankee drying hood arrangement (1) covers a part (4) of the circular cylindrical surface (3) of the Yankee drying cylinder (2), the Yankee drying hood arrangement (1) comprising:

• a plurality of nozzle boxes (5) distributed around an imaginary axis (X) which is coincident, or substantially coincident, to the axis of rotation of the Yankee cylinder, such that, when the Yankee drying hood arrangement (1) is fitted over a Yankee drying cylinder (2), the nozzle boxes (5) are spaced from the circular cylindrical surface (3) of the Yankee drying cylinder (2) and form a curved structure (6) that follows the outer contour of the circular cylindrical surface (3) of the Yankee drying cylinder (2), each nozzle box (5) having a longitudinal extension in a direction parallel to the axial extension (A) of the Yankee drying cylinder (2) and each nozzle box (5) having a plurality of openings (7) distributed along the longitudinal extension of the nozzle box (5) through which openings (7) a fluid such as hot air can exit the nozzle boxes (5) and stream towards the circular cylindrical surface (3) of the Yankee drying cylinder (2) at different points along the longitudinal extension of each nozzle box (5) such that the fluid streaming from the openings (7) reaches the circular cylindrical surface (3) of the Yankee drying cylinder (2) at different points along the axial extension of the Yankee drying cylinder (2);
• a plurality of distributor conduits (8) for a fluid such as hot air, the distributor conduits (8) extending in the circumferential direction around the curved structure (6) formed by the nozzle boxes (5) and each distributor conduit (8) being in communication with one or more nozzle boxes (5) such that a fluid such as hot air streams from each distributor conduit (8) to said one or more nozzle boxes (5);
• at least one first temperature main supply conduit (9) for a fluid including one or more of hot air, hot air and steam, or water vapor, at a first temperature T1, and at least one second temperature main supply conduit (10) for a fluid including one or more of hot air, hot air and steam, or water vapor, at a second temperature T2 which is not the same as T1, said first temperature and second temperature main supply conduits (9, 10) being in communication with the distributor conduits (8) such that fluids from the first temperature and second temperature main supply conduits (9, 10) flow into the distributor conduits (8) and be mixed,
• wherein at least one distributor conduit (8) is provided with damper means (31) for changing the ratio between the flow rate of fluid at temperature T1 from the first temperature main conduit and the flow rate of fluid at temperature T2 from the second temperature main conduit into said at least one distributor conduit (8).