Cross-flow filter for white liquor in polysulfide production
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Solution Overview
Problem
Conventional polysulfide production processes face interruptions and reduced availability due to the need for frequent regeneration of filter beds, leading to high operational costs and substantial loss of filtered white liquor, as they rely on granular filter beds that require frequent washing and cannot achieve complete removal of suspended solids, especially calcium carbonate particles.
Innovation Solution
Implementing a second filtration process using an essentially continuously operating cross-flow filter to achieve a high availability of filtered white liquor with low suspended solids, reducing the need for buffer tanks and high-capacity pumps, and maintaining filtering capacity over time with ceramic filters and thin membrane technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If granular filter beds are used for white liquor filtration, then suspended solids can be captured, but the filter bed requires frequent washing and regeneration causing process interruptions
Solution Approach 1:
The patent replaces granular filter beds with membrane filters that have thin filtering layers (1-100 μm) supported on porous structures. This membrane technology eliminates the need for frequent bed washing and regeneration, allowing continuous operation and improving both filter availability and polysulfide production continuity without sacrificing filtration effectiveness.
Solution Approach 2:
The patent substitutes the mechanical granular filter bed system with a membrane-based filtration system that uses pressure differential and membrane pore structures instead of gravity-driven flow through granular media. This substitution eliminates the fluidization and washing steps required for granular beds, enabling continuous operation.
2Ease of manufacture
If high-capacity pumps are used to fluidize filter beds for washing, then solids can be flushed out, but investment and operational costs increase
Solution Approach 1:
The patent extracts and removes the washing and regeneration functions entirely from the filtration system by using membrane filters that do not require backwashing or fluidization. The membrane structure allows for simple replacement or cleaning in place without requiring high-capacity pumps for bed expansion and solids removal, thereby reducing both device complexity and associated costs.
Solution Approach 2:
The patent employs membrane filters that can be easily replaced or cleaned without complex regeneration equipment. Instead of investing in expensive high-capacity pumps for bed regeneration, the system uses simpler, more economical membrane elements that can be disposed of or regenerated with minimal infrastructure, reducing both investment and operational costs.
3Productivity
If buffer tanks are used to store wash white liquor, then continuous flow can be maintained, but substantial volume of filtered white liquor is lost
Solution Approach 1:
The patent implements continuous filtration using membrane elements that operate without interruption. The cross-flow configuration and continuous cleaning mechanisms (such as air sparging or chemical cleaning in place) maintain constant filtration performance without requiring batch washing cycles, thereby maintaining continuous white liquor production without the need for large buffer tanks and minimizing liquor loss.
Solution Approach 2:
The patent introduces intermediary cleaning mechanisms (such as air sparging, chemical cleaners, or ultrasonic treatment) that act between the filtration and regeneration steps. These intermediaries allow for continuous operation by cleaning the membrane surface in place without requiring complete shutdowns and large buffer tanks for wash liquor storage, thereby reducing both equipment requirements and liquor loss.
4Manufacturing precision
If filter beds are washed frequently to remove captured solids, then filtering capacity is maintained, but process availability decreases
Solution Approach 1:
The patent uses thin membrane filtering layers (1-100 μm) with controlled pore sizes that maintain high suspended solids removal efficiency without requiring frequent washing. The membrane structure prevents particle penetration while allowing continuous operation, as the thin film can be cleaned in place or replaced without disrupting the overall polysulfide production process, thereby maintaining both manufacturing precision and process availability.
Solution Approach 2:
The patent replaces the mechanical granular filter bed system with membrane filtration that uses pressure differential and pore structure instead of gravity-driven flow. This substitution enables continuous operation with minimal interruption, as membrane cleaning or replacement is simpler and faster than bed washing and regeneration, thereby maintaining high suspended solids removal efficiency while improving process availability.
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 approach enables a stable and continuous polysulfide production process with reduced temporary shutdowns, lower operational costs, and improved plant economy by maintaining high filtering efficiency and minimizing the need for frequent acid cleaning, thereby increasing the overall availability of the polysulfide manufacturing system.
Implementation Method 1
passing the accept flow of white liquor through a second filtering process obtaining a filtered white liquor with a second order of suspended solids measured in ppm
Implementation Method 2
maintaining filtering capacity over time with ceramic filters and thin membrane technology
Implementation Method 3
passing the filtered white liquor through a polysulfide reactor with addition of an oxygen containing gas for promoting conversion of sulfides to polysulfide
Data Source
Figure 1
Figure 2
Figure 3~4b
AI summary
The invention is related to improved polysulfide production process wherein a specific second filtration process (Fx) is installed before the polysulfide reactor (Rc). According to the inventive method a cross flow filter (Fx) is used as the second filtration process reaching astonishing low levels of residual solids in the white liquor as well as extended availability of the second filtration process. The subsequent polysulfide reactor, either in form of an electrolytic cell or in form of a bed of active carbon, could then also be operated at increased availability. The invention increases the production volume of polysulfide and the retentate from the cross filtering process may be bled out continuously to a process position ahead of a first filtering or clarification stage, capturing most of the increased content of lime mud particles in the retentate and causing less disturbance of the process with a minimum of tanks and pumps.