BENEFITS OF IMPLEMENTING A PAPER BRIGHTNESS CONTROL SYSTEM IN A TWO-MACHINE NEWSPRINT MILL

Paper brightness control is challenging, especially when there are frequent target changes. Manipulating bleaching chemicals manually to meet these targets can be difficult, and operations will prefer to err on the high side, resulting in over-bleaching at a cost. In the case of a mill with two paper machines fed with the same pulp, one more difficulty arises: maintaining two different targets on each machine using common bleach addition points. A control application was designed to use four manipulated variables in a multi-variable predictive control (MPC) strategy to maintain brightness targets on both machines and minimize the use of bleaching agents. Details of the controller design, control performance, and benefits are described in this paper.