Patent ID: 6938359

Claim:
A method for controlling drying of a web-formed material moving through a drying plant having a plurality of upper and lower blow boxes arranged in a plurality of drying decks, the web-formed material floating above the lower blow boxes, which at their upper sides blow out hot process air against the web-formed material, thereby drying the web-formed material, comprising: detecting water content in the web-formed material downstream of the blow boxes; blowing process air on the web-formed material, wherein water escaping from the web-formed material is mixed with and discharged by the process air; re-circulating at least part of the process air, whereas the a non-circulated part of the process air is discharged as exhaust air, replacing the discharged exhaust air with a corresponding portion of supply air controlling the temperature of the process air, determining a deviation from a desired water content of the dried web-formed material by comparing the desired water content to the sensed water content; changing the volume flow of the process air in accordance with the deviation, whereby the volume flow of the process air is increased when the water content in the web-formed material is too high, and the volume flow of the process air is decreased when the water content in the web-formed material is too low, thereby rapidly regaining the desired water content of the dried web-formed material.