ABSTRACT
CONTROL OF CONTINUOUS PULP DIGESTERS IN PAPER MAKING The basic material of paper is fiber and the quality of the finished paper product is absolutely dependent on this raw material. In extremely simplistic terms, a sheet of paper or card is formed by laying a uniformly thick mat of a pulp slurry, formed by a mixture of very fine wood, other fibers, and water, deposited onto a mesh screen that is fine enough to trap the solid fibers, but at the same time allow the huge amount of entrained water to drain away. In ancient times, when reasonably drained of the excess liquid, the still limp mat of fibers was subjected to a press operation carried out by laying a heavy block of stone on the limp fibrous mat. Nowadays the limp mat of fibers is made to pass between a series of pairs of heated rollers that are squeezed together, with the force applied to each pair being adjusted so that they form a progressively increasing applied force. These rollers serve three important functions:
• They squeeze yet more water out at each stage as the mat passes through. • They ensure complete uniformity of thickness. • They dry the fibers.
