Vacuum Drum Washer Troubleshooting

Vacuum drum washers are often used after the Kraft pulping process to separate the pulp fibers from the spent cooking liquor (called “black liquor”). These “brownstock washers” are typically arranged in multiple stages and utilize countercurrent washing, where the wash water flow is countercurrent to the pulp flow.

The recovery of the spent cooking chemicals and dissolved organics in the black liquor, while minimizing the use of wash water, is essential to the economic viability of the Kraft pulping process. Efficient washing is also desirable to minimize the “carryover” of black liquor in the pulp headed to the next process. This is especially true if the next process is chemical bleaching, as black liquor carryover increases the use of expensive bleaching chemicals and the organic load in the bleach plant effluent.

Learning Objectives