Pressure Pulsation of High Consistency Machine Screening
Silakoski, Ville (2023)
2023
Konetekniikan DI-ohjelma - Master's Programme in Mechanical Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-06-02
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202306016388
https://urn.fi/URN:NBN:fi:tuni-202306016388
Tiivistelmä
Pressure fluctuation on headbox slice flow causes basis weight variation in machine direction and quality issues to end product. Machine screen is a typical source of short-term and recurring pressure fluctuation and pulsation. Suction pulses and pressure fluctuation created by screen rotor is mandatory for dominant screen design to avoid plugging of screen cylinder apertures because of fibers. Increased headbox feed consistency demands more aggressive cleaning pulse from screen rotor to avoid plugging which increases pulsation after screen and at headbox.
The aim of this thesis is to determine which factors affect to pulsation magnitude created by screen and determine what is the current state of the screening technology regarding pulsation. This study examines if current screening technology can operate at low pulsation while feed consistency increases and still maintain good end product quality.
Experimental section of this thesis consists of trial runs and pulsation measurements on pilot facility. With trial procedures, it is possible to research effects of different rotors and operating parameters to pulsation on standardized environment. Effects of excess factors can be minimized, and factors of pulsation can be characterized. Magnitude of pulsation is measured inside the screen and on accept pipe of the screen in various measurement points which enables possibility to research development of pulsation after the screen. Fundaments for trial runs are created in form of literature review and analysis of prior measurements. Peer reviewed studies are complemented with internal measurements and studies of company to provide profound and diverse research material regarding the topic.
As a result of the research, factors and design parameters affecting to the magnitude of screen pulsation, can be characterized. Cross-section and disposition of rotor foils are most influential design features affecting to the magnitude of pulsation that screen creates. The magnitude of pulsation can be increased for example by increasing chord length, thickness, attack angle or camber of the foil. Regarding operational parameters, foil tip speed has most significant influence on pulsation magnitude, but also factors such as increasing feed flow or reducing reject amount, increase pulsation. Disposition of foils can be used to determine how foil pulsation effects on accept pipeline. Inclination, dividing foils to shorter sections, and use of staggered disposition are measures to reduce relative magnitude of pulsation transferring to accept pipeline. On literature, effect of consistency to pulsation is partially inconsistent and unclear but based on the experimental section of this research, it can be said that consistency does not affect to magnitude of created pulsation directly.
On trial runs, different rotors are compared to each other regarding pulsation. If compared to traditional machine screen rotor that was used as reference, one fine screen rotor model was able to operate at lower pulsation on same trial environment. In theory, cleaning ability of this fine screen rotor is better than ability of machine screen rotor because of foil disposition. Fine screen rotor provides more suction energy with lower pulsation magnitude. Important result of this research is that the particular fine screen rotor or new machine screen rotor developed from this fine screen rotor is a possible solution to increased pulsation caused by increasing headbox consistency.
The aim of this thesis is to determine which factors affect to pulsation magnitude created by screen and determine what is the current state of the screening technology regarding pulsation. This study examines if current screening technology can operate at low pulsation while feed consistency increases and still maintain good end product quality.
Experimental section of this thesis consists of trial runs and pulsation measurements on pilot facility. With trial procedures, it is possible to research effects of different rotors and operating parameters to pulsation on standardized environment. Effects of excess factors can be minimized, and factors of pulsation can be characterized. Magnitude of pulsation is measured inside the screen and on accept pipe of the screen in various measurement points which enables possibility to research development of pulsation after the screen. Fundaments for trial runs are created in form of literature review and analysis of prior measurements. Peer reviewed studies are complemented with internal measurements and studies of company to provide profound and diverse research material regarding the topic.
As a result of the research, factors and design parameters affecting to the magnitude of screen pulsation, can be characterized. Cross-section and disposition of rotor foils are most influential design features affecting to the magnitude of pulsation that screen creates. The magnitude of pulsation can be increased for example by increasing chord length, thickness, attack angle or camber of the foil. Regarding operational parameters, foil tip speed has most significant influence on pulsation magnitude, but also factors such as increasing feed flow or reducing reject amount, increase pulsation. Disposition of foils can be used to determine how foil pulsation effects on accept pipeline. Inclination, dividing foils to shorter sections, and use of staggered disposition are measures to reduce relative magnitude of pulsation transferring to accept pipeline. On literature, effect of consistency to pulsation is partially inconsistent and unclear but based on the experimental section of this research, it can be said that consistency does not affect to magnitude of created pulsation directly.
On trial runs, different rotors are compared to each other regarding pulsation. If compared to traditional machine screen rotor that was used as reference, one fine screen rotor model was able to operate at lower pulsation on same trial environment. In theory, cleaning ability of this fine screen rotor is better than ability of machine screen rotor because of foil disposition. Fine screen rotor provides more suction energy with lower pulsation magnitude. Important result of this research is that the particular fine screen rotor or new machine screen rotor developed from this fine screen rotor is a possible solution to increased pulsation caused by increasing headbox consistency.