Paper Drying

Paper drying is an expensive method to remove water. The energy consumption is high and the investment cost for the drying section is considerable. As a result it is mostly the high investment cost for the drying section that limits the production on a paper machine.

In the wire section and later in the press section, large amounts of water are mechanically removed. The dry solids content of the web, when it enters the dryer section, is normally somewhere between 35 and 52%. The dry solids content in the finished paper is in most cases between 90 and 96%.

Water, impossible to remove mechanically, must be thermally removed; evaporated. Even if the amount of water to be evaporated is less than 1% of the amount removed during the forming and the press operation, there is still a lot of water left to evaporate. Counted in tons it is about as much as the produced paper.

Drying a paper web means that the water leaves the paper machine’s drying section as vapour, going to the atmosphere.

Source : Metso