Pulp Screen Rotor Openings Reduce Entry Velocity
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Solution Overview
Problem
As papermaking pulp screens increase in size, the entry velocity into the annular space between the drum-style rotor and the screen cylinder becomes excessively high due to the square relationship of the screen plate area with diameter, leading to unacceptably high pressure drops and performance degradation, which existing solutions attempt to mitigate by reducing the screen cylinder height, resulting in complex or costly designs.
Innovation Solution
A drum-type rotor with openings extending from its interior to exterior along at least a fourth of its length, allowing pulp suspension to flow through both the annular inlet and the rotor surface, thereby reducing entry velocity and maintaining efficient screening without increasing manufacturing complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the screen size is increased to handle larger pulp volumes, then the screening capacity is improved, but the entry velocity into the annular space becomes excessively high causing unacceptably high pressure drops
Solution Approach 1:
The rotor is segmented with multiple openings distributed along its length, dividing the single high-velocity entry point into multiple lower-velocity entry points. This segmentation of the entry area allows large screens to maintain lower entry velocities by distributing the pulp flow across multiple openings rather than forcing all flow through a single annular space.
2Stress or pressure
If the screen cylinder height is reduced to lower entry velocity, then the pressure drop is reduced, but the design becomes complex or costly
Solution Approach 1:
Instead of reducing the screen cylinder height (one-dimensional solution), the invention adds openings along the rotor length (extending into the longitudinal dimension). This dimensional approach allows velocity reduction by distributing flow across multiple openings while maintaining the full screen height and avoiding the complexity of shortened designs.
3Reliability
If multiple foils are used to perform impulse and screening functions, then the screening efficiency is improved, but the device complexity increases
Solution Approach 1:
The rotor openings serve multiple functions simultaneously: they distribute pulp flow to reduce entry velocity, they allow pulp to enter the screening space, and they work in conjunction with the foils to maintain screening efficiency. This multi-functionality reduces the need for additional separate components while achieving both velocity control and effective screening.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design maintains efficient pulp screening by distributing pulp flow effectively across the rotor length, reducing pressure drops and performance degradation while avoiding the complexities and costs associated with previous solutions, ensuring consistent performance across varying screen sizes.
Implementation Method 1
A rotating impulse member is positioned to operate adjacent a surface of the screen, which is commonly, but not always, an inner inlet surface, to maintain the stock suspension in a state of agitation and to provide pressure impulses to aid the screening function
Implementation Method 2
Separation of this undesirable material is referred to as screening, and requires passing the pulp slurry through very small openings; most typically slotted screen cylinders are used with slot openings of between 0.10 and 0.40 mm
Data Source
AI summary
A rotor adapted for mounting for rotation within a screen of a pulp screening apparatus, and for defining a screening space between the rotor and the screen so that pulp suspension flows into the screening space, with accepted pulp passing through the screen to a stock outlet and rejected pulp passing along a screen inlet surface in a screening flow direction to a rejects outlet. The rotor has an interior, and an exterior with pressure impulse protuberances thereon for rotation with the rotor in close proximity to the inlet surface. A stock inlet communicates with the screening space and the rotor interior. And the rotor has at least one opening extending in the screening flow direction from its interior to its exterior for over at least a fourth of screening flow length of the rotor for admitting a substantial portion of pulp suspension from the stock inlet and the rotor interior into the screening space.