382602 Development and Evaluation of a Novel Non-Traditional Processing Aid for the Pulp and Paper Industry
In the paper making process the pulp mill operation is critical to the final paper quality as well as overall process optimization. Brown stock washing is a crucial part of the pulp mill operation as it impacts downstream processes such as bleaching, evaporators and caustic recovery among others. The objective of brown stock washing is to remove the maximum amount of black liquor solids from the pulp while using as little wash water as possible (1). Due to the presence of soap and lignin, a significant amount of foam is generated, and a foam control agent is needed to increase production rate, optimize and continue operations (2).
Foam is generated by the presence of surface active components (e.g. surfactants, fatty acids, particles, etc.) and the addition of energy (e.g. mixing). Foam bubbles are structured as liquid polyhedral cells entraining gas, and the cells are separated by a thin liquid-air face called the lamella and stabilized by the surfactants. These surfactants can have the form of traditional liquid surfactants as well as amphiphilic solid particles. Both forms preferentially adsorb at the liquid-air interface and act as foam stabilizers. Thus, in order for a defoamer to be effective it must penetrate the foam or bubble lamella as droplets when emulsified in the foaming medium. As the defoamer droplet approaches the foam surface, a three phase film consisting of oil (or other defoaming active ingredient), water and air is formed. After the defoamer droplet penetrates the surfactant film at the foam surface it spreads into a lens at the liquid-air interface. As the lens spreads it destabilizes the bubble wall disrupting the foam structure.
Traditionally, silicone defoamers are used in brown stock washing applications; although this chemistry is proven to be very effective in foam control, it can also present issues of carryover (hydrophobic content) to the paper machine that can negatively impact the final product. An effective non-traditional product may present a solution for the industry as it will not only help with foam control, but also decrease carry over issues, enhance the cleaning of the pulp and improve drainage. Kemira has developed a new non-silicone processing aid for the pulp and paper industry that has been successfully trialed. Kemira’s process aid has shown many operational improvements, such as improved drainage and washing, lower dirt count, increased black liquor solids, decreased soda loss, and reduced pulp hydrophobic (stickies) content as well as improved defoaming. Examples will be drawn from these trials as well as lab evaluations to highlight the improved performance of this new chemistry.
(1) Handbook for Pulp and Paper Technologists, 3rdEdition, G. Smook
(2) Emulsions, Foams, and Suspensions: Fundamentals and Applications, L. Schramm