Applying Automatic Chemical Control from Stock Prep to the Machine

Abstract

For many years. retention-aid dosage has been controlled by the white water consistency in newsprint, fine paper and board applications. This control strategy is well known and has proven efficient and beneficial. However, combining retention-aid control and charge demand control with coagulant or fixative in the thick-stock area provides additional benefits. An on-line charge analyzer, measuring the incoming furnish charge level, allows controlled coagulant addition so that downstream additives are applied more efficiently and economically. This control strategy provides substantial cost savings to the mill. Costly functional additive consumption is reduced and other chemical control loops, such as retention-aid addition, are improved.This paper explains the impact of white-water consistency on paper machine outcomes such as basis weight variation, steam consumption and wet-end stability. White-water consistency, dewatering and charge demand control approaches are discussed, and practical examples are used to describe how short circulation and chemical composition of the pulp affects final product quality. Mill experiences with the on-line units, and proposed gains and benefits of these measurements to papermakers will be demonstrated.