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.

Bleach plants also often use vacuum drum washers to remove the spent bleaching chemicals from one stage so that the chemicals do not get sent on with the pulp to the next process. If the next process is another bleaching stage, any leftover chemicals will increase the amount of bleaching chemicals needed in that stage.

The separation of pulp fibers from cooking and bleaching chemicals is critical for economic, operating, and environmental reasons, which is why it is so important to take action to get vacuum drum washers back to their desired state when an issue develops. This course covers the key operating variables for vacuum drum washers, common issues, possible causes and corrections for those issues, and best practices for troubleshooting vacuum drum washers.