Paper drying process, involves constantly monitoring web dryness and altering exhaust air removal and steam pressure inside dryer cylinders if dryness deviates from chosen value

摘要

The moisture content of the web is monitored and in the event of a deviation from the desired dryness value, the amount of exhaust air removed and the pressure of the steam used for heating the cylinder are changed. A process for drying a web of material (4), preferably a paper web, comprises contacting the web with cylinders (3) heated internally with steam, and removing the liberated water vapour and steam with the exhaust air, whilst regulating steam pressure inside the cylinders and regulating the flow of exhaust air. The moisture content of the web is monitored and in the event of a deviation from the desired dryness value, the amount of exhaust air removed is either increased or reduced in order to increase or reduce the dryness respectively. A comparatively slow change is also made in the pressure of the steam used for heating the cylinder, such that an increase in pressure will increase the dryness, or vice versa.