Supplemental and Recycled Fiber – Fiber Prep and Screening
Wood fiber accounts for more than 90% of the raw material used in the production of paper and board products, and it can come from a variety of sources. These sources can be slushed virgin fiber that is produced onsite, market pulp from other pulp mills, or recycled/secondary fiber. This course will cover the preparation and screening of market pulp and recycled fiber at papermaking facilities.
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Learning Objectives
• Define the terms: “market pulp,” “recycled fiber,” “pre-consumer waste,” and “post consumer waste”
• Identify and describe the primary process flows of a repulper
• Identify and describe the main components of a repulper
• Describe the consequences of improper level and consistency control in a repulper
• Explain the purpose of deflaking
• Identify and describe the main components of a disk deflaker
• Explain the purpose of screening
• Describe the equipment and process flows in coarse screening and fine screening systems
• Identify and describe safety hazards and safety guidelines associated with repulping, deflaking, and screening equipment
Specs
| Course Level | Intermediate |
| Languages | English |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What is market pulp?
Market pulp is the term applied to virgin fiber which has been produced at a pulp mill, partially dried, and then shipped to a paper mill to be repulped and made into paper.
What is the difference between “pulping” and “repulping”?
Pulping uses chemicals or intense mechanical action to break down raw sources of cellulose, typically wood, to produce fibers which can be made into paper. Re-pulping is the mixing and agitation of existing paper or market pulp with water to create a fiber suspension which can be used to re-manufacture paper or board products.
What are important repulper operating variables?
Efficient fiber repulping requires controlling the consistency and level in the repulper.
What is “deflaking”?
After recycled paper is repulped, there usually are fiber bundles or flakes which would interfere with papermaking. Deflaking is a mechanical shearing process which breaks up the fiber bundles.
What is the purpose of screening pulp?
Screening is used to remove oversize fiber bundles and contaminants from the fiber suspension before it is used to make paper.
Sample Video Transcript
Deflaking is sometimes necessary to break down fiber flakes that remain in the pulp slurry after repulping. Flakes result from the presence of size, coated, and wet strength grades in recycled fiber bales. Deflakers are similar to refiners in design and operation. Disc deflakers consist of one or two stationary discs and one rotating discs all fitted with slotted raised rings. The pulp slurry enters at the center of the discs and travels outward radially passing through the slots at the periphery. The acceleration and sheer forces present in the slots help break apart the fiber flakes. Heat and chemicals can be added to the pulp before deflaking to weaken the flakes and improve results. Very difficult to repulp grades may require two or even three deflaking stages.
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