4 Different Types of pressure screen

Different types of pressure screens play a vital role in ensuring the quality and efficiency of the papermaking process. These machines are designed to remove impurities and contaminants from pulp, improving fiber quality and guaranteeing uniform sheet formation. Depending on the stage of production and the desired pulp characteristics, different types of pressure screens are used across paper mills. In this article, we will explore four different types of pressure screens, their working principles, and their specific applications within the pulp and paper industry. Discover everything about pressure screens in the paper industry. For a detailed overview of the equipment used in the paper industry, you can also refer to our article.

Pressure Screen in Paper Industry

Pressure screens for pulp and paper are essential in the industry. By using a pressure screen machine, paper manufacturers ensure high-quality pulp for producing superior paper products.

Screen performance is determined by two internal components:

• a cylinder with apertures that pass acceptable fibers and block oversize contaminants
• a rotor that clears the apertures of any blockages.

What is a Pressure Screen?

A pressure screen is a mechanical device that separates fibers from impurities in the pulp and paper industry.

Key Features:

• Removes contaminants like shives, plastics, and oversized fibers.
• Ensures uniform fiber distribution for consistent paper quality.
• Operates under pressure for higher throughput and efficiency.

How Does a Pressure Screen Work?

The working mechanism of a pressure screen in paper industry includes:

• Tangential Pulp Entry:
  • Pulp enters tangentially through the inlet pipe, creating a swirling motion.

• Centrifugal Separation:
  • Heavier impurities are pushed to the bottom by centrifugal forces and discharged through the reject outlet.

• Screening Area:
  • Pulp overflows into the screening area between the rotary drum and screen basket.
  • The rotor generates pulses to remove fibers that might get trapped in the slots of the screen.

• Screen Cylinder & Apertures:
  • Inside the screen, a cylinder with slotted or holed apertures allows acceptable fibers to pass.
  • Aperture size is critical:
    • Smaller apertures → higher contaminant removal, lower capacity.
    • Larger apertures → higher capacity, may let small contaminants pass.

• Accept and Reject Streams:
  • Accept stream: Cleaned pulp suitable for further processing.
  • Reject stream: Concentrated contaminants removed from the pulp.
  • Typical operating consistency is 1–5%, and about 10–30% of the feed exits through the reject outlet.

This mechanism ensures efficient fiber recovery , contaminant removal , stable operation , making pressure screens essential in modern papermaking.

Importance of Pressure Screens in Papermaking

materials such as boxes—recycled old corrugated containers (OCC) have emerged as a valuable raw material for the production of linerboards and corrugating mediums.

Unlike pulp produced directly from lignocellulosic materials, the use of OCC presents unique challenges in the papermaking process. This is mainly due to the variability in material quality, which can affect the performance and properties of the final paper products.

To alleviate these problems caused by OCC collection, several technological approaches have been applied, including:

• mechanical
• chemical
• fractionation
• substitution treatments

Among these strategies, fractionation is widely considered to be one efficient way to minimize pulp variability.

At the industrial scale, pulp fractionation is typically performed using pressure screens equipped with slotted or holed cylinders.

During fractionation, pulp fibers are separated into different fractions according to characteristics such as:

• Fiber length
• Fiber width
• Fiber coarseness

This separation allows papermakers to selectively use each fraction to produce specific paper grades, enhancing both product quality and consistency.

Different Types of Pressure Screens

Different pressure screen machines serve specific purposes in paper production:

• Inflow Pressure Screen / Low Consistency Screen: Smooth operation without pulsation due to multi-foil rotor design.
• Combo Screen: Handles light rejects, deflakes stock, and cleans/dewaters fibers simultaneously.
• Medium Consistency Vertical Screen: Rotor design minimizes positive pulses and enhances negative pulses for effective cleaning.
• Shield Screen: Optimized head geometry and eccentric basket placement prevent deposits, ensuring reliable operation at lower cost.

Inflow Pressure Screen:

Combo Screen:

Medium Consistency Vertical Screen

Shield Screen:

Types of Rotors Used in Pressure Screens

Rotors are critical for the efficiency of pressure screens in pulp and paper The primary role of the rotor is to keep the screen cylinder apertures clear of any fibres or contaminants that could plug the apertures and cause the screen to fail.

A rotor is thought to work in three ways:

1) generating pressure pulsations that backflush the apertures of any incipient blockages,

2) accelerating the pulp suspension on the feed side of the cylinder to a high tangential velocity and

3) inducing turbulence at the cylinder surface.

Common Types of Rotors Used in Pressure Screens:

• Multi-Foil Rotor: Reduces pulsation and provides smooth screening.
• Contoured Foil Rotor: Optimizes fiber separation efficiency.
• Positive/Negative Pulse Rotor: Dislodges trapped fibers for continuous operation.
• Two-Foil vs Three-Foil Designs: Two-foil rotors often offer higher capacity and lower energy consumption.

Advantages of Pressure Screens in Papermaking

1. Enhanced Paper Cleanliness & High Fiber Recovery

• Remove a wide range of contaminants, including shives and fiber bundles.
• Minimizes rejects and maximizes the yield of long fibers, improving paper quality.

2. Energy Efficiency & Cost Savings

• Reduce the need for expensive chemical bleaching treatments.
• Allow pulp to be fed forward without additional refining, saving energy.
• Lowers power consumption while maintaining high throughput.

3. Reliable and Stable Operation

• Smooth flow with minimal pulsation ensures stable performance.
• Fractionation of mechanical pulp enables flexible and efficient processing.

4. Maintenance Friendly & Process Reliability

• Automatic lubrication and seal water detection reduce downtime.
• Preserves fiber strength, extending the life and quality of the final product.

5. Optimized for Approach Flow Systems

• Ideal for high-capacity paper mills and modern papermaking lines.
• Supports higher recycling rates and sustainable production practices.

Conclusion

Pressure screens are indispensable in the pulp and paper industry, offering high fiber recovery, energy efficiency, and reliable operation. By understanding types of pressure screens, their mechanism, and rotor designs, paper mills can optimize both production efficiency and product quality.

References

1.Parason Machinery. (n.d.). Pressure Screens in the Paper Industry. Parason.
URL: https://www.parason.com/blog/pressure-screens-paper-industry

2.Salem, H. J., Gooding, R. W., Martinez, D. M., & Olson, J. A. (2013). Some Fundamental Aspects of Pulp Screen Capacity. In Advances in Pulp and Paper Research, Cambridge 2013, Trans. of the XVth Fundamental Research Symposium, Cambridge, 2013, (S.J. I’Anson, ed.), pp 261–299, FRC, Manchester, 2018.
URL: https://bioresources.cnr.ncsu.edu/wp-content/uploads/2019/03/2013.1.261.pdf

3.Koskenhely, K., Paulapuro, H., Ämmälä, A., & Jokinen, H. (2018). Effect of Refining Intensity on Pressure Screen Fractionated Softwood Kraft. Nordic Pulp & Paper Research Journal, 20(2), 169–175.
DOI: 10.3183/npprj-2005-20-02-p169-175