Recycling of ECF Bleaching Plant Effluents Cleaned by Coagulation / Flocculation, 1997 Pulping Conference Proceedings

To close the kraft pulp mill circuits, the re-using of bleaching filtrates must be actual. The coagulation/flocculation can be one method to clean the filtrates before recycling. Conventional polymers are used to remove suspended solids, dissolved solids and colloids in acidic and alkaline bleach plant effluents of ECF bleaching of kraft pulp. A relationship between polluting loads and molecular weight distribution is established using gel permeation and ultra or nano-filtration. The trials have been performed on industrial filtrates. A specific mathematical method applied to laboratory trials has permitted to compute the carry-over to simulate an industrial recycling. According to the laboratory trials results, the implementation of some modules of coagulation/flocculation on the mill circuits are simulated. Some cases have been studied to recycle the treated bleaching filtrates to the bleaching process or/and to the brown stock pulp washing. A material and nergy balance of the whole mill including news coagulation/flocculation models is presented.