Drying method, especially for paper, comprises altering water content of supplied air and steam pressure inside cylinders in response to change in web moisture content

摘要

If a deviation from the desired dryness of the dried web (4) is detected, the water content of the air supplied to the dryer (1) is reduced, and the steam pressure inside the dryer cylinders (3) is increased in order to reduce the moisture content of the outgoing air. A method for drying a web of material, especially a paper web, comprises contacting the web with cylinders which are internally heated with steam, and removing the water vapor expelled from the web with the process air, some of which is optionally recirculated. The non-recirculated process air is replaced with a corresponding amount of hot air with a low moisture content. Steam pressure inside the cylinders and the flow of air leaving the process are regulated throughout. If a deviation from the desired dryness of the dried web is detected, the water content of the supplied air is altered, by reducing the water content of the air if the web dryness is reduced, the water content of the air is reduced, and by altering the steam pressure inside the cylinders in accordance with the water content in the outgoing air, so that dryer outgoing air will increase steam pressure (or vice versa), in order to give a desired water content in the outgoing air. The latter step is relatively slow compared to the former step.