Advances in wet end steam shower design and performance - Smaller zone sizes has resulted in improved CD moisture profile control

Increasing wet end sheet temperature using steam showers or other sources o f heat, has long proven effective in improving water removal in the forming and pressing sections. Increasing sheet temperature assists in mechanical water removal by lowering water viscosity and reducing water surface tensio n. Steam showers have been successfully used at the wet end for many years for profile control, to increase machine speed and to enhance paper propert ies. In recent years, a number of improvements in their design have resulte d in increased performance and improved maintainability of the equipment. T his paper considers the trends to smaller zone sizes for improved cross-dir ection (CD) moisture profile control. In addition, the use of in-situ therm owells for optimizing steam temperature and resulting steambox performance is discussed. The use of removable screen plates for enhanced maintainabili ty is reviewed as is the use of wet end scanners for control. The benefits of using multiple steam boxes are also reviewed.