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Based on: Industry Standards and Best Practices

Languages: English

Sample Transcript

The most common brown stock washing system uses a series of vacuum drum washers. The primary element of a vacuum drum washer is a large compartmentalized cylinder or drum, which has its outer surface covered with a fine mesh. This drum is partially submerged in a vat filled with diluted pulp. As the drum slowly turns through the pulp suspension in the vat, a partial vacuum within the drum causes a mat of fiber to form on the surface as liquor is pulled into the drum. Once out of the vat, liquor continues to be pulled from the mat.

Brown Stock Washing

Training Time: 32 minutes

The black liquor and pulp must be separated after they exit the digester so that the pulp can go on to the papermaking process. This separation occurs on brown stock washers, where water is used to wash the black liquor from the pulp. At the end of this module, you will be able to describe the importance of countercurrent washing and identify the process variables that effect washing.

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Black liquor washer from brown stock is reclaimed in the recovery and recaust area of the mill.

The vacuum in most drum washers is derived from gravity pulling the filtrate removed from washer down a dropleg.

In diffusion washers, pulp flows up through concentric rings as wash liquor is injected into the pulp between the rings.

Learning Objectives

  • Describe the makeup of black liquor
  • List the reasons for washing cooked pulp
  • Identify and describe the primary process flows
  • Describe the importance of countercurrent washing
  • Identify and describe the components of a vacuum drum washer
  • Describe the principles of a vacuum drum washer operation
  • Identify and describe the components of an atmospheric diffuser
  • Describe the principles of an atmospheric diffuser operation
  • Identify the key process variables that effect washing
  • Describe some of the safety hazards working around washing equipment
  • Explain the relationship between brown stock washing and overall mill operating costs
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Brown Stock Washing FAQs

Why is it important to remove black liquor from pulp after cooking?
There are two reasons. 1) Cooked pulp could not be made into paper without removing the black liquor, and 2), the inorganic chemicals in the black liquor can be reused once they are separated.

What is the principle behind countercurrent washing?
Countercurrent washing takes advantage of the fact the very dirty pulp can be washed with somewhat dirty liquor. This allows wash liquor to be reused multiple times.

What is the source of vacuum for most vacuum drum washers?
The vacuum in most drum washers is derived from gravity pulling the filtrate removed from washer down a dropleg.

What are some of the factors which affect the performance of a drum washer?
Some of the factors which affect washer performance are shower and stock temperature, shower flow and distribution, drum speed and vat consistency.

What are three different configurations of brown stock washers?
Washer types include drum, belt, and diffusion washers.

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