Key Questions
The following key questions are answered in this module:
What are some of the weaknesses of conventional multi-cylinder dryer systems?
Multi-cylinder dryer systems have relatively low drying rates so require a lot of space, they respond rather slowly to control changes, and they inherently offer poor control of cross-machine moisture profiles.
Can Yankee dryers be used in the production of non-tissue grades?
Yankee dryers can also be used to produce machine-glazed (MG) papers. On these machines, there is no dryer coating, steam pressures and temperatures are lower, and additional dryers are necessary to assist in sheet drying.
How does through-air drying increase the bulk, softness, and water absorbency of the sheet?
Through-air drying machines do not employ any wet pressing, so the sheet is never crushed.
Infrared drying is not usually very economical, so why is it used at all?
Infrared dryers are small so they are sometimes used to add incremental drying capacity. They can also provide additional control over cross-machine moisture profiles, or non-contact drying for paper coatings.
What is air impingement drying?
Air impingement drying involves blowing hot dry air onto a wet sheet. Yankee dryer hood systems involve this type of drying, and air impingement is also used in flotation dryers.