At the end of this module, you will be able to:
- Explain the purpose of coarse screening
- Describe why coarse screening systems often use multiple stages
- Identify and describe the major components of cylindrical screens
- Identify and describe the major components of disk screens
- Describe the process flows for coarse screening
- Identify the characteristics of screen openings which influence screen performance
- Explain why a different design is typically used in the final stage of coarse screening
- List safety hazards and guidelines associated with coarse screening systems
The following key questions are answered in this module:
What is the goal of coarse screening in an OCC facility?
Coarse screening is one of the first separation processes in a recycled fiber facility and its purpose is to remove contaminants that are significantly larger than the fibers.
What is the purpose of the rotor in a cylindrical screen?
Shaped elements on a spinning rotor in a cylindrical screen create pressure pulses which assist with fiber flow through the screen and help prevent screen plugging.
What process variables can be used to determine if a screen is plugged?
If the pressure differential between the inlet to the screen and the screen accepts stream increases, there is a good chance that the screen is plugging.
What is the primary advantage a disk screen offers over a cylindrical screen?
The rotor in a disk screen is effective at breaking up fiber bundles which would otherwise be rejected.
Why do some screening systems use multiple stages of screening?
Multiple stages of screening permit the reprocessing of rejects which increases the overall retention of acceptable fiber.
Below is a transcript of the video sample provided for this module:
In cylindrical pressure screens, the OCC pulp is usually fed through the inlet piping into a space between the rotor and screen basket, and the rotating motion of the rotor imparts motion to the pulp slurry. The incoming flow plus the rotating motion of the rotor help push the pulp slurry against the screen basket. Depending on the size of the openings, particles of different sizes and shapes pass through. Depending on the screen design, the pulp can travel either inward or outward through the openings. The portion of the pulp that successfully passes through the screen openings is called the accepts while the portion that does not pass through is called the rejects.
Use the additional resources and links below to learn more about this topic: