Process and dryer section for drying a running web in a paper or board

Abstract

A dryer section of a paper or board making machine has a plurality of dryers. In a first group of dryers, each dryer heats the web somewhat more, but not to the level of the maximum evaporation rate of the moisture contained in the web. As the web is passing the end of the first group, the web is heated to such a high temperature that it reaches the maximum evaporation rate of the moisture in the web. The dryers in the first group have smaller diameters, which may gradually increase up to the region of the maximum evaporation rate, or they may all be of one smaller size. The dryer section has a second group of dryers in which each dryer heats the web to the maximum evaporation rate of the moisture contained in the web. The dryer at the beginning of the second group has the largest diameter. The following dryers in that group can have a smaller diameter. The dryers in the second group may be grouped in groups of decreasing size, or may gradually decrease in size. Advantageously, each group of dryers (A,B) is divided into subgroups (A.sub.1 ; A.sub.2 ; B.sub.1 ; B.sub.2 ; B.sub.3 ; B.sub.4) wherein first, one side of the web contacts all the dryers of one subgroup (for example A.sub.1), and then the other side of the web contacts all the dryers in the next subgroup (for example A.sub.2), and each subgroup is associated with one and only one fabric belt such as a felt or wire.