Defoaming in the Pulp and Paper Industry

Abstract

The pulp and paper industry is the world's biggest single user of defoaming agents. In chemical pulp production, wood chips are cooked at elevated temperatures in solutions of various chemicals in pressurized vessels called digesters. To make the kraft process economically viable, spent pulping chemicals must be recovered as efficiently as possible; hence, thorough washing is essential. The bleached pulp may be further screened and cleaned, and sent directly to the paper mill; alternatively, it may go to a pulp-drying machine, if it is to be sold as pulp. The three materials necessary for foam production are a liquid, a gas, and a surfactant. In the pulp and paper industry, the liquid is water, the gas is air, and the surfactants are numerous. One of the biggest foam-related problems in chemical pulp mills is maintaining rate and efficiency of washing on rotary drum washers. There are limitations and problems associated with the use of chemical antifoams.