Rotorless Knotter Inversion for Pulp Plugging
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Solution Overview
Problem
Conventional knotters used in pulp processing require an elutriation flow to prevent plugging, which dilutes the pulp stream and necessitates larger equipment in subsequent washing steps, and alternative designs with rotating components either replicate this issue or introduce mechanical complexity.
Innovation Solution
A rotorless knotter design that uses a stationary cylindrical screen with elutriation nozzles and a booster pump to maintain high tangential velocities and direct energy tangentially around the screening chamber, reducing the need for dilution and minimizing moving parts within the machine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an elutriation flow is used to prevent plugging in conventional knotters, then plugging is prevented, but the pulp stream is diluted and larger equipment is required in subsequent washing steps
Solution Approach 1:
The patent inverts the conventional approach by using a stationary screen cylinder with rotating hydrofoils instead of rotating screen cylinder with stationary hydrofoils. This inversion eliminates the need for elutriation flow to prevent plugging, as the rotating hydrofoils mechanically agitate the pulp to prevent knot accumulation on the screen surface, thereby preventing plugging without diluting the pulp stream
Solution Approach 2:
The patent replaces the fluid dynamic mechanism (elutriation flow) with a mechanical mechanism (rotating hydrofoils) to achieve plugging prevention. The hydrofoils physically interact with the pulp and knots on the screen surface, using mechanical agitation to prevent accumulation and plugging, eliminating the need for high-velocity diluting flows
2Ease of operation
If a rotating screen cylinder with stationary hydrofoils is used, then screening function is achieved, but mechanical complexity and moving parts are introduced
Solution Approach 1:
The patent inverts the conventional configuration by making the screen cylinder stationary and the hydrofoils rotating. This inversion simplifies the overall mechanical design because the stationary screen eliminates the need for precise rotational sealing and bearing arrangements required for rotating screens, while the rotating hydrofoils can be driven by a simple shaft connection to the drive mechanism
3Productivity
If elutriation flow is used to reinvigorate stock flow, then flow stoppage is prevented, but reject consistency becomes very low and secondary knotter workload increases
Solution Approach 1:
The patent replaces the fluid dynamic approach (elutriation flow) with a mechanical approach (rotating hydrofoils) to maintain flow continuity. The hydrofoils mechanically agitate and redistribute the pulp and knots on the screen surface, preventing flow stagnation and stoppage without introducing large volumes of diluting flow that would lower reject consistency
Solution Approach 2:
The rotating hydrofoils create a self-regulating system where the mechanical agitation automatically maintains flow continuity based on the actual pulp load and screen conditions, adapting to varying operating conditions without requiring external dilution flows to prevent plugging
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 effectively prevents plugging without diluting the pulp stream, simplifies maintenance, and reduces the rejects consistency by half, while maintaining high operational efficiency with no internal moving parts.
Implementation Method 1
a jet of high velocity dilution (known as the 'elutriation flow') is injected tangentially along the wall of the chamber. The energy in this flow (which is equal to the flow times the velocity head) reinvigorates the stock flow and avoids any chance that the flow could stop and plug.
Implementation Method 2
The knotter uses a barrier, or screen cylinder, with perforations in the 8 to 12mm diameter range being most common... Pulp stock passes through this screen cylinder, while the larger pieces of uncooked wood chips cannot pass through.
Implementation Method 3
there are two specially designed hydrofoils, mounted on a rotor and driven by a motor connected by V-belts, that produce an outward pulsation through the screen cylinder. It is the intent of these hydrofoils that they push any knots away from the inlet side of the screen cylinder so that the passing flow can carry them away.
Data Source
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AI summary
A device including a hollow body defining axially extending compartments therein for receiving a slurry of pulp fibers in a carrying flow. The device includes a stationary screen within the hollow body defining a slurry compartment on one side of the screen, and a screened compartment on the other side of the screen. The hollow body also includes a slurry inlet into the slurry compartment, an elutriation suction outlet in communication with the slurry inlet, and elutriation nozzles into the slurry compartment. The device also includes an elutriation pump outside of the hollow body, the elutriation suction outlet being in fluid communication the elutriation pump, and the elutriation pump being being in fluid communication with the elutriation nozzles.