Polymer-enhanced displacement of lignin solution from model packed beds

Researchers have concluded that poor displacement efficiencies occur on commercial drum washers because the pulp pads are not uniform. Laboratory results using model beds saturated with black liquor have indicated that improved displacement washing can be achieved by the addition of cationic polymers to the displacement water. Flow visualization experiments in a transparent cell support the proposed mechanism that, in areas of high flow in the pulp bed, the cationic polymer reacts with the lignin to form a precipitate. Selective precipitation in the high permeability channels means that overall washing is improved because less wash water is wasted by escaping through the most open channels. Results obtained with reactive cationic polymers are compared with those obtained with water and non-reactive anionic polymer solutions.