Foam and its Control in Pulp and Paper Manufacturing: A Review of Chemical Principles and Governing Factors

Abstract

This review article considers factors contributing to the development of problematic levels of foam, as well as ways to control foam, with emphasis on two critically important unit operations in pulp and paper manufacturing plants, namely the brownstock washing system and the paper machine. In general terms, hard-to-break foam bubbles can be expected when an aqueous system is subject to a means of air entrainment (such as agitation), when an air phase is present, when there are surface-active agents present, and when the solution also contains significant levels of water-soluble polymers. Brownstock washers and paper machines have all of these ingredients, and sometimes they are at problematic levels. The resulting stabilized foam bubbles can hurt production rates, interfere with displacement of pulping liquor from the fiber mat during washing, and contribute to blemishes in paper products. Considerable progress has been made over many years in understanding these phenomena and also in understanding the work of foam-control products. Engineers in modern pulp and paper mills can make use of efficient foam-control products as well as monitoring equipment. This article provides a tutorial review of such issues, based on published findings.