Disc Filter Precoat Thickness Control via Axial Scraper Movement
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Solution Overview
Problem
Disc filters used in the chemical pulp industry face issues with precoat layer clogging and uneven production rates when filtering viscous lime sludge, leading to increased engine power requirements, equipment size, and potential production interruptions due to simultaneous precoat thickness reduction across all filtering surfaces.
Innovation Solution
The precoat thickness reduction is performed non-simultaneously on some filter discs, with the central shaft moving axially to control scraper distance and maintain even material streams through the drop chute, reducing the need for complex internal moving mechanisms and allowing for precise control of precoat thinning motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If precoat thickness reduction is performed simultaneously on all filtering surfaces, then the precoat layer is effectively reduced, but the production rate fluctuates significantly and causes clogging in drop chutes
Solution Approach 1:
The patent divides the filtering surfaces into separate groups, each with independent scraper control. Instead of reducing precoat thickness on all discs simultaneously, the system segments the operation so that only some discs undergo precoat reduction at any given time, while others continue normal filtration. This segmentation maintains stable production rates in active filtration zones while preventing clogging in drop chutes.
Solution Approach 2:
The system dynamically adjusts scraper positions and activates different scraper groups based on real-time filtration needs. The control system monitors cake thickness and production rates, dynamically switching between normal operation mode and precoat reduction mode for different disc groups, thereby maintaining overall system stability while achieving periodic precoat maintenance.
2Reliability
If multiple scrapers are moved simultaneously towards the filtering surface, then precoat reduction is achieved, but the amount of filtered solid matter increases remarkably causing excessive filling of drop chute
Solution Approach 1:
The patent segments the scraper operation by controlling different scraper groups independently. When precoat reduction is needed, only specific scraper groups are activated to move towards their respective filtering surfaces, while other scrapers maintain normal scraping operations. This prevents the simultaneous removal of large amounts of solid matter that would otherwise excessively fill drop chutes.
Solution Approach 2:
The system applies partial action by activating only the necessary portion of scrapers for precoat reduction at any given time. Instead of moving all scrapers simultaneously (excessive action), the control system selectively activates specific scraper groups based on which filtering surfaces require precoat renewal, thereby removing just enough solid matter to maintain precoat layers without overfilling drop chutes.
3Reliability
If the apparatus is dimensioned for maximum momentary production flow, then clogging is prevented, but the apparatus becomes excessively large and expensive
Solution Approach 1:
The system dynamically manages production flow by switching between different operational modes for different disc groups. During normal operation, filtration proceeds at standard rates. When precoat reduction is performed on specific discs, the system dynamically redirects or manages the solid matter flow from those discs, preventing sudden peaks that would require oversized apparatus dimensions for clogging prevention.
Solution Approach 2:
By segmenting the filtration operation into active filtration zones and precoat reduction zones, the system prevents concentrated peaks of solid matter flow. The drop chutes receive steady, manageable flows from actively filtering discs, while discs undergoing precoat reduction are managed separately, allowing the apparatus to be dimensioned for normal operating conditions rather than maximum momentary peaks.
4Device complexity
If all scrapers are actuated by one common actuator moving simultaneously, then the process is simple, but the engine power required for rotating filter discs is substantially increased
Solution Approach 1:
The patent segments the actuator system into multiple independent actuator groups, each controlling specific scraper groups on different discs. This segmentation allows the engine to rotate filter discs at constant speed while individual actuator groups independently adjust scraper positions only when needed for precoat reduction, avoiding the power surges that would result from all scrapers moving simultaneously against the rotating discs.
Solution Approach 2:
The system dynamically controls scraper actuation based on real-time needs, activating different actuator groups at different times rather than operating all scrapers simultaneously. This dynamic approach maintains constant disc rotation speed (reducing engine power requirements) while still achieving periodic precoat reduction through coordinated, non-simultaneous scraper movements.
Data Source
Figure 1
Figure 2~3c
Figure 4a~4c
AI summary
Method and apparatus for reducing the thickness of a precoat-layer (57) accumulated on the filtering surface (56) of a filter disc (12) from a solids-containing suspension in a basin (40) of a disc filter, said disc filter having two or more filter discs arranged on a shaft (10) and between them at least one drop chute (38) provided with a scraper (20) on both sides, which scraper (20) scrapes the cake filtered from the suspension on the filtering surfaces (56) of the filter discs (12) into the drop chute (38), by means of which scraper (20) the layer thickness of the precoat (57) on the filtering surface (56) is reduced by shortening the distance between the tips of the scrapers (20) and the filtering surface (56) and the precoat (57) thickness reduction is accomplished for the precoats (57) on the filtering surface (56) of the two filter discs (12) on both sides of the drop chute (38) non- simultaneously.