Vertical Single Tier Drying: Technology and Application of Vertical Dryer Configurations for Increased Quality and Production, 2002 Technology Summit Proceedings

Stephen Halsall 

The need to fit the maximum number of drying cylinders into relatively confined spaces has led to the development of a number of novel configurations. Single-tier technology has allowed the designers to create custom-built dryer sections that address particular needs. By using the machine basement and the space above the existing dryers, sections can be added that increase production rate and sheet quality.

Single-tier drying with vacuum hitch rolls fully supports the sheet, giving better runnability. The sheet is also restrained from cross-machine shrinkage, leading to improved edge uniformity. Key quality improvements include reduced hygroexpansivity, better profiles, and increased stiffness.

The original basement installation at Korsnäs, Sweden consisted of 14 cylinders. The section was positioned at the maximum shrinkage location. Careful design eliminated the potential problems of running a sheet in the basement (broke handling, roll change, access, threading). The rebuild achieved all its design objectives.

In subsequent installations at Korsnäs and at AssiDomän Frövifors, also in Sweden, the design was developed into the vertical configuration we have today. These units have shown that far from being difficult to run, operation of the vertical single-tier section can have fewer problems than conventional sections.