Dryer section, paper production

Sheet Drying. At a water content of ca 1.2—1.9 parts of water per part of fiber, additional water removal by mechanical means is not feasible and evaporative drying must be employed. This is at best an efficient but cosdy process and often is the production botdeneck of papermaking. The dryer section most commonly consists of a series of steam-heated cylinders. Alternate sides of the wet paper are exposed to the hot surface as the sheet passes from cylinder to cylinder. In most cases, except for heavy board, the sheet is held closely against the surface of the dryers by fabrics of carefuUy controUed permeabiHty to steam and air. Heat is transferred from the hot cylinder to the wet sheet, and water evaporates. The water vapor is removed by way of elaborate air systems. Most dryer sections are covered with hoods for coUection and handling of the air, and heat recovery is practiced in cold climates. The final moisture content of the dry sheet usually is 4—10 wt %. 

The mill had the choice either to shut the machine or upgrade to improve the stretch and TEA values and the profiles in the cross direction. The mill acted to address the CD profile problems by upgrading the dryer section of the paper machine to improve dryer pocket humidity profiles. At the same time, the mill also decided to upgrade the product quality from flat sack to semi-extensible sack papers. Semi-extensible sack paper is an ideal sustainable packaging solution where high pressure and high-speed filling are... 

The purpose of the press section is to increase the dry content of the paper web as much as possible by compression. This kind of mechanical dewatering reduces steam consumption in the dryer section and increases the strength of the web in order to avoid web breaks during production. 

Dryers for Films and Sheets The construction of dryers where both the feed and the product are in the form of a sheet, web, or film is markedly different from that for dryers used in handling particulate materials. The main users are the paper and textile industries. Almost invariably the material is formed into a very long sheet (often hundreds or thousands of meters long) which is dried in a continuous process. The sheet is wound onto a bobbin at the exit from the dryer again, this may be 1 or 2 m in diameter. Alternatively the sheet may be chopped into shorter sections. 

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