EnglishViews: 0 Author: Site Editor Publish Time: 2025-07-29 Origin: Site
Pressure screen is an extremely important screening equipment in modern production, mainly used to remove impurities such as colloids, gravel, plastics, etc. in pulp. Its separation can be divided into centrifugal pressure screen and differential pressure screen based on pulp and paper making process and fluid theory. Centrifugal pressure screen generates centrifugal force field through high-speed rotation of internal rotor to achieve solid-liquid separation, which is suitable for coarse screening (0.5-2.0mm particle size separation), while differential pressure screen relies on feed pressure gradient to drive pulp screening, which is suitable for fine screening (0.05-0.5mm accuracy).
The centrifugal pressure screen has a rotor to generate additional pressure. The rotor is usually located in the screen basket and is driven by a driving device to rotate at high speed. When rotating, the blades exert force on the surrounding pulp, causing the pulp to produce rotational motion and axial flow. In this process, the rotation of the rotor will generate additional pressure under the pulp, further increasing the power of the pulp to pass through the screen. In addition, the contact between the blades and the slurry during the rotation of the rotor is periodic, which will form a pulse effect in the slurry to help break the floccules and impurity layers on the surface of the screen, so that the fibers can pass through the screen more smoothly, maintaining permeability and preventing the screen from being blocked.
The slurry of the differential pressure screen enters the pressure screen from the feed port at a certain pressure under external power. This pulp inlet pressure is the initial driving force for the pulp to flow in the screen (the pulp inlet pressure will be maintained within a certain range to ensure that the pulp can smoothly enter the pressure screen and perform subsequent screening operations). Since the pressure screen is equipped with a screen basket and a screen mesh, there is a spatial difference between the inside and outside of the screen basket. When the pulp enters the screen basket, due to the barrier effect of the screen mesh on different components in the pulp, a pressure difference will gradually form on both sides of the screen mesh (the pressure difference is the key driving force for pushing qualified fibers in the pulp through the screen mesh)
Under the combined influence of the pressure difference and the additional pressure and pulse effect generated by the rotor, qualified fibers in the pulp, that is, fibers with a size smaller than the screen mesh aperture or gap width, will be pushed through the screen mesh by pressure and enter the collection area outside or inside the screen basket (depending on whether the pressure screen is an outflow type or an inflow type), becoming good pulp after screening, discharged from the discharge port, and entering the subsequent process.
Impurities in the pulp, such as particles, fiber bundles, adhesives, etc., whose size is larger than the mesh aperture or gap, cannot pass through the mesh and will be retained inside the mesh. As the pulp flows, they are eventually discharged from the slag outlet, thus achieving the separation of fibers and impurities and achieving the purpose of screening and purifying the pulp.
(1) Separation of large particle impurities: In the initial stage of pulping, the raw pulp often contains various large particles (wood chips, gravel). The coarse screen in the pressure screen can use the larger mesh holes and gaps to intercept and separate these impurities through centrifugal force or pressure difference, preventing impurities from entering the subsequent process and causing wear, blockage and other damage to the equipment.
(2) Removal of tiny impurities: For tiny fiber bundles such as gravel and adhesives in the raw pulp, the fine screen and purification screen of the pressure screen can play an effective role. These tiny impurities can be removed from the pulp through the smaller mesh holes or mesh gaps on the screen basket, thereby improving the purity of the pulp and laying the foundation for subsequent high-quality paper production.
(3) Grading by fiber length: The fibers used in paper making are of different lengths, which have different effects on paper properties. The pressure screen grades and screens the fibers according to the specifications and working principles of the screen. (In the production of special paper, fibers of specific lengths are required. The pressure screen separates these long or short fibers, so that the fibers in the subsequent process can be more uniform, greatly improving the strength and uniformity of the paper)
(4) During the pulping process, the quality of the fibers also varies. Some fibers may not be fully dissociated or have defects. The pressure screen can distinguish between fibers of better quality and fibers of poorer quality through screening, ensuring that the fibers used for paper making have better quality and performance, thereby improving the overall quality of the paper.
(5) Stabilizing the pulp concentration: The uniformity of the pulp concentration is extremely important for the quality of paper. During the screening process, the pressure screen further stirs and mixes the pulp to make the fiber and water distribution in the pulp more uniform, thereby stabilizing the pulp concentration. This helps to achieve a stable paper quantity during the paper making process and avoid problems such as uneven thickness and inconsistent strength of the paper.
(6) Promote uniform slurry flow: The rotor of the pressure screen will produce a specific flow state in the slurry during operation. This flow state is conducive to breaking the flocs in the slurry, making the fibers more dispersed, and making the slurry flow more evenly throughout the screen cylinder. Uniform slurry flow can ensure uniform fiber distribution during the paper forming process, improve the uniformity and appearance quality of the paper.
(7) Optimize production process: Through effective screening by pressure screen, impurities and non-compliant fibers in the pulp can be separated, making the subsequent paper making process smoother (using pressure screen before paper making can improve the quality of pulp entering the paper machine, reduce the probability of problems such as breakage and pulp jumping during paper machine operation, and improve paper machine operation efficiency and production stability.)
(8) Reduce equipment maintenance costs: The pressure screen can remove impurities in the pulp in advance, reduce the blockage and wear of impurities on subsequent pulping machines and paper making equipment, reduce failure rate and maintenance frequency, and extend the service life of equipment.
