Drying section for a paper or cardboard web has a convection heater with a number of drying sections where the web is subjected to flows of hot air or steam from one or both sides in a closed path

摘要

The web drying section, at a papermaking or cardboard production machine, has at least one convection drier (10). It has at least one drying section (18-24) where the web (12) moves between two permeable fourdriniers (26-34) for hot air and/or hot steam to pass through it from one or both sides. The convection drier (10) has at least one straight or slightly curved drying section (18-24) on the direction (L) of web travel. It can have at least two drying sections (18-22), over each other or in succession. At least one drying section (18-24) is formed between two drying or jet hoods (36,36'-42,42'). The hoods have a steam or air suction extraction. The web (12) is enclosed at the sides, at least partially by the convection drier (10). The heaters at the drying sections (18-24) are controlled separately, at least partially, to set the heating levels. The convection drier (10) has at least one drying section (18-24) divided into zones across the direction (L) of web (12) travel. The web (12) has an enclosed travel path through the convection drier (10). The web deflection between the drying sections (18-24) is through suction rollers (44-50), which take the web (12) from the preceding fourdriniers (26,28,32,30). The hot air and/or hot steam applied to the web (12) in at least one drying section (18-24) is at a temp. of 150-450[deg]C, and especially at 200-400[deg]C, and at a flow speed of 60-120 m/s, especially 100 m/s. The convection drier (10) is located in front of a drying group of cylinders in one or two rows. On reaching the first drying cylinder (14), the web (12) has been dried to a dry content level of 55-65%. The convection drier (10) is placed after one or more cylinders or at least one web guide roller.