142 | Metso Paper Technology Days 2005For a conventional dry crepe tissue machine to be competitive today, it must have the ability to effi ciently produce high-quality paper at a high utilization rate and at the lowest possible total production cost. The drying section, consisting of a Yan-kee cylinder and an AirCap plays an important role. Its dimensioning and design should be optimized for the specifi c process. It is also important that the components work together in order to guarantee the required drying load at the minimum energy cost. The Yankee dryer and AirCap must also be designed and manu-factured for safe and reliable use with the least possible downtime for maintenance and service.1. The drying process – a brief introductionThe drying process is a combination of cylinder (Yankee dryer) and im-pingement drying (AirCap) (Fig. 1).Energy for the drying of the tis-sue sheet is supplied both by high-pressure steam condensing inside the Yankee cylinder and by hot air blown onto the sheet in the AirCap, which covers a large area of the Yan-kee surface. Conductive drying on the Yankee cylinder initiates from the fi rst press roll nip and contin-ues as long as the sheet remains in contact with the dryer. Convective and radiant drying begin under the area covered by the AirCap. The Yan-kee drying process is very intensive with drying rates of 150 – 240 kg H20/hm2, versus 20 – 30 kg H20/hm2 Fig. 1 Yankee drying is a combination of conductive cylinder drying and convective and radiant impingement drying. 1. Yankee hood air, 2. Diff usion vapor, 3.Conducted heat.Vice President, SalesTissue Business LineMetso PaperGeneral Sales ManagerMetso Paper GoriziaSales Manager, Yankee DryersTissue Bus...
