Brown Stock System Basics
The purpose of a brown stock system is to process the brown stock, and, usually in this order: remove high density trash, break down or remove uncooked wood, and wash black liquor from the brown stock. This module will explain the process steps within a brown stock system, and the various types of equipment which are used to accomplish each operation.
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Learning Objectives
• Describe the purpose of a brown stock system
• Identify and describe the major equipment
• Identify and describe the primary process flows
• Describe the function of a rock trap
• Describe the function of a screen
• Describe the function of a washer
• Differentiate between a fibrilizer and a refiner
• Describe countercurrent washing
• Identify and describe the safety hazards in the brown stock system
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What is brown stock?
Brown stock is the name for the mixture of cooked wood chip and cooking liquor that is discharged from a digester.
What is the goal of a brown stock system?
The purpose of a brown stock system is to remove all components of the cooked, discharged pulp mixture from the digester that would interfere with paper or board making.
Why is are rock trap located immediately after the digester?
The rock trap removes dense components such as rocks that might damage downstream equipment.
What is the purpose of brown stock screening?
Brown stock screening relies primarily on size differences to remove components which are no suitable for paper or board making.
What is being washed from the pulp in brown stock washers?
Spent cooking chemicals, or “”black liquor””, is washed from the cooked pulp in the brown stock washers.
Sample Video Transcript
The brown stock discharge from the digester also contains small pieces of uncooked wood or shives, and other small materials such as rocks, metal, and plastic. These smaller sized contaminants are removed from the brown stock by low consistency screens. The screens contain a cylindrical metal plate that has small holes or slots that allow the acceptable brown stock fibers to pass through, while blocking the contaminants. A screen has a rotor that turns at high speed to sweep the screen plate and prevents plugging by creating a back pressure pulse.
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