Brown Stock Washing - A Review of the Literature

摘要

Brown stock washing is a complex, dynamic process which separates dirty wash water or weak black liquor (dissolved organic and inorganic material obtained from the pulp cooking process) from pulp fibers. The use of material balance techniques is of great importance in order to identify potential problems and determine how well the system is operating. The kraft pulping industry was the first known to combine pulp washing with the recovery of materials used and produced in the wood cooking process. The motivation behind materials recovery is economic and more recently, environmentally driven. The chemicals used in the kraft process are expensive as compared to those employed in the sulfite process. In order for the kraft process to be economically viable, it is imperative that a very high percentage of the cooking chemicals be recovered. To reach such high efficiency, a variety of washing systems and monitoring parameters have been developed. Antifoam additives and processing aids have also played an important role in increasing washing effectiveness. Antifoam materials help attain washing effectiveness by preventing entrapped air from forming in the system which allows for an easier, unimpeded flow of filtrate through the screens and washers.