Setting the stage

The figure below shows the process flow diagram of a typical paper mill process. The specifics aren't important right now. The diagram should outline the major systems that comprise the paper mill:

Source: https://www.yokogawa.com/us/library/resources/application-notes/pulp-paper-instruments-and-solution-for-pulp-paper-industry/

Creating paper is done by making pulp from wood. For the process, trees are debarked and cut up into chips by a chipper. The chipper is a giant tree grinding machine that can cut up a tree in a matter of seconds. The wood chips are then chemically treated inside a digester. The digester is comparable to a giant pressure cooker. The chemical pulping process inside a digester separates lignin from cellulose fibers. This is accomplished by dissolving lignin in a cooking liquor so that it can be washed from the cellulose. The liquor is a combination of harsh chemicals. The wood chips and liquor are mixed up and cooked under pressure in the digester until...