External Circulation System for Screening Reject Separation
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Solution Overview
Problem
Existing screening apparatuses in the pulp and paper industry face challenges in efficiently removing heavy reject fractions, leading to the passage of high-quality fibrous material into the reject and disturbance of accept flow through the screening surface.
Innovation Solution
An external circulation system is implemented, increasing pulp flow volume and utilizing a pressure difference to separate heavy particles into a junk trap, with a bypass flow that dilutes the pulp and prevents non-pulp particles from re-entering the main apparatus, enhancing junk collection capability without direct contact with other processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heavy reject fraction is removed from fibrous pulp, then junk separation capability is improved, but high-quality fibrous material may pass into the reject
Solution Approach 1:
The reject removal conduit is divided into multiple zones: a feed zone, a diluted pulp flow zone, and a junk trap zone. This segmentation allows different functions to be performed in different sections, enabling effective junk separation while protecting high-quality fibers from being lost in the reject stream.
Solution Approach 2:
An external circulation system acts as an intermediary, introducing additional pulp flow through a bypass. This intermediary flow dilutes the static pulp layer, creating conditions that allow heavy junk particles to settle and be separated without causing high-quality fibers to be incorrectly directed to the reject outlet.
2Productivity
If reject particles are removed from the screening surface, then screening efficiency is improved, but disturbance is caused to the passing of accept through the screening surface
Solution Approach 1:
The reject removal system extracts heavy reject particles from the pulp flow before they can disturb the accept flow through the screening surface. By taking out the harmful reject particles in advance through the external circulation and junk trap mechanism, the screening process operates with minimal disturbance to the accept stream.
Solution Approach 2:
The reject removal conduit provides localized treatment where heavy particles are separated in a controlled environment with diluted flow conditions. This local quality improvement ensures that reject particles are removed without creating disturbance that would affect the broader screening process and accept flow.
3Manufacturing precision
If external circulation increases pulp flow volume, then junk collection capability is intensified, but water consumption increases
Solution Approach 1:
The external circulation system utilizes the existing reject removal conduit and integrates with the existing junk trap infrastructure. The system serves itself by using the available flow paths and structures, minimizing the need for additional water consumption while intensifying junk collection capability through optimized flow dynamics.
Solution Approach 2:
The system changes the flow parameters (velocity, volume, distribution) in the reject removal conduit to intensify junk collection. By optimizing these parameters rather than simply increasing water quantity, the system achieves enhanced separation capability with controlled water consumption.
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
The external circulation system improves junk separation and collection efficiency, preventing high-quality fibers from entering the reject and minimizing disturbance to the accept flow, while maintaining the operation of the junk trap similar to existing systems.
Implementation Method 1
The pressure difference provides for the required and essential flow in the external circulation
Implementation Method 2
The increase of the static pressure is due to the decelerating of the flow prior to the outer foil
Implementation Method 3
the decrease of the static pressure is due to the accelerating of the flow between the outer foil and the screen drum
Implementation Method 4
so that the pulp is simultaneously preferably diluted, heavy particles in the layer being diluted are allowed to be separated onto the bottom of the reject removal conduit
Implementation Method 5
heavy particles in the layer being diluted are allowed to be separated onto the bottom of the reject removal conduit and therethrough into a separate junk trap
Data Source
Figure 1
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Figure 4
AI summary
The present invention relates to an arrangement in screening apparatuses of the pulp and paper industry, said arrangement comprising a conduit (2) for removing reject formed in a screening process. It is essential that circulation of material is arranged between the reject removal conduit and the interior of the screening apparatus from the removal conduit into the interior of the screening apparatus via a conduit (5) external to the screening apparatus. When such a by-pass flow is arranged for pulp via external circulation, heavy particles in the layer being diluted are allowed to be separated onto the bottom of the reject removal conduit and therethrough e.g. into a separate junk trap (3) .