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Based on: Industry Standards and Best Practices

Languages: English

Sample Transcript

Infrared dryers heat a wet sheet using radiant heat transfer. A hot surface gives off infrared radiation, which is absorbed by the fibers and the water around the fibers. The absorbed energy quickly heats the water to its evaporation temperature and drives the water from the sheet. Infrared radiation can be generated either by electrical elements or by passing natural gas through a catalyst coated material, which burns the gas without a flame to create a very hot surface. Although the drying rate created by infrared heaters is much higher than conventional steam heated dryer cylinders, the overall economics are not as favorable. For that reason, infrared heating is used only in specialty situations.

Paper Machine Alternative Drying Systems

Training Time: 31 minutes

On most conventional paper and board machines, the energy required to dry the sheet to the desired moisture target at the reel is supplied by a series of rotating steam-heated dryer cylinders or cans. This module briefly covers the principles behind this system of drying. It will discusses applications where this system is not the best choice, and where alternative drying techniques can be used. These alternatives include: Yankee drying, through-air drying, infrared drying, impulse drying, and air impingement drying.

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Infrared dryers transfer radiant heat to the fibers and water in the sheet, which causes the water to evaporate.

Many steam-heated Yankee dryers increase their drying capacity by using a second form of drying called air impingement.

In a through-air dryer (or TAD), hot air is blown through the sheet and a perforated drum.

Learning Objectives

  • Identify and describe the major components of a multi-cylinder dryer section
  • Describe the principles of operation of multi-cylinder dryer sections
  • List some the drying alternatives to multi-cylinder drying
  • List the advantages and disadvantages of multi- cylinder drying
  • Describe the process and typical components for Yankee drying
  • Identify typical products in which Yankee drying is applied
  • Describe the process and typical components for through-air drying
  • Identify typical products in which through-air drying is applied
  • Describe the process and typical components for impulse drying
  • Identify typical products in which impulse drying is applied
  • Describe the process and typical components for infrared drying
  • Identify typical products in which infrared drying is applied
  • Describe the process and typical components for air flotation drying
  • Identify typical products in which air flotation drying is applied
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Paper Machine Alternative Drying Systems FAQs

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.

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