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The main objective of the drying section of the paper machine is to remove any residual moisture in the web that has not fallen out, been sucked out or been pressed out.

There are a variety of drying techniques

By far the most common is contact drying, where the paper web is passed around steam heated drying cylinders. Holding the paper web in close contact with the cylinders using tensioned dryer fabric to ensure the sheet has close contact with the cylinder surface, this assists in heat transfer. Evaporation mainly occurs in the open draws between cylinders, but can also occur through the fabric whilst the sheet is in contact with the cylinder. This depends on the air permeability of the fabric.

The drying section for multi cylinder contact drying is usually divided into three zones. Early drying cylinders are used to warm up the paper gently. Cylinders in the middle zone are heated to much higher temperatures and are responsible for the majority of the evaporation. There are different practices for the final zone, some are kept at high temperatures while others are lower than the middle zone.

Drying cylinders can be single tier, two-tier or sometimes a combination of both.

On two tier drying systems the top and bottom set of cylinders each have their own dryer fabric. The cylinders drive the fabric. There are systems known as silent drive, where the fabric drives the cylinders.

A more modern system is known as the slalom. In this system, there is only one dryer fabric. It follows the path of the paper over both top and bottom drying cylinders. It was this system that led to the single tier drying system.

On some machines there is only one large drying cylinder. On a traditional paper or board machine this is called the MG cylinder, (machine glazing), on a tissue machine it is called a Yankee cylinder.

When considering the dryer section it is important to have a good understanding of heat transfer and mass transfer.

As energy prices increase and environmental awareness becomes more acute, there is increased awareness of the importance of steam and condensate systems.

View my short video about drying on You Tube by clicking on the link below

Introduction to Drying


Compact Engineering

Spooner Industries Limited

Pages in category "Drying"

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