Green Liquor Clarification via Dregs Recirculation and Flocculation
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Solution Overview
Problem
Existing methods for clarifying green liquor in pulp mills, such as sedimentation and filtration, face inefficiencies in sedimentation rate and require large equipment or high costs, and recirculating clarified liquor negatively impacts sedimentation.
Innovation Solution
Recirculating a portion of settled dregs back into the sedimentation tank after passing through turbulence generators to break them into smaller fractions, combined with the addition of polymeric flocculants, enhances sedimentation rate and clarity by increasing the dregs' surface area and interaction with raw green liquor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional sedimentation tanks are used for green liquor clarification, then the process is simple and low cost, but the sedimentation rate is slow and large tank volumes are required
Solution Approach 1:
The patent applies preliminary action by pre-coagulating dregs with flocculants before they enter the sedimentation tank. This pre-treatment causes fine dreg particles to aggregate into larger flocs that settle much faster, thereby increasing the sedimentation rate without requiring larger tank volumes. The pre-coagulation process prepares the particles in advance to optimize their settling behavior.
Solution Approach 2:
The patent changes physical parameters by introducing polymeric flocculants that alter the surface properties and aggregation state of dreg particles. This parameter change transforms fine, slow-settling particles into larger, faster-settling flocs, directly addressing the contradiction between sedimentation rate and tank volume requirements.
2Productivity
If polymeric flocculants are added to increase sedimentation rate, then the sedimentation efficiency improves, but the operational cost increases
Solution Approach 1:
The patent optimizes the concentration parameter of flocculants by using polymeric flocculants at controlled dosages. These polymers are highly effective at low concentrations, achieving rapid sedimentation without requiring excessive amounts of chemical additives, thus balancing productivity improvement with cost control.
Solution Approach 2:
The patent employs composite flocculation systems combining different types of polymeric flocculants (anionic and cationic) to enhance sedimentation efficiency. This composite approach allows for synergistic effects that improve particle aggregation at lower overall dosages, reducing the quantity of substances required while maintaining high sedimentation rates.
3Manufacturing precision
If cross-flow filters are used to achieve effective filtering, then the green liquor clarity improves, but the equipment complexity and operational cost increase
Solution Approach 1:
The patent extracts and removes the complex filtration system from the process by replacing it with a simplified sedimentation approach. By using flocculants to pre-aggregate particles and then allowing gravity-based sedimentation, the system eliminates the need for complex cross-flow filter equipment while still achieving effective separation and acceptable clarity.
Solution Approach 2:
The patent substitutes expensive, complex filtration equipment with a simpler, more economical sedimentation system using chemical additives. This replacement uses inexpensive polymeric flocculants and basic sedimentation tanks instead of costly filter systems, reducing both equipment complexity and operational costs while maintaining effective separation.
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 significantly improves sedimentation rate and clarity of green liquor, reducing the need for large equipment and operational costs by utilizing the recirculated dregs' increased surface area and flocculant efficiency.
Implementation Method 1
the upper layer of clarified green liquor raises due to difference in the density of the green liquor and the dregs, which dregs have a higher density and thus settle towards the bottom
Implementation Method 2
provide for an even distribution of the raw green liquor at a low flow velocity in the lower half of the sedimentation tank via a rotating distributor sweeping over the cross section of the sedimentation tank
Implementation Method 3
passing through turbulence generators, which are able to break up some of the dregs into smaller fractions, before reaching the mixing chamber
Implementation Method 4
addition of polymeric flocculants, enhances sedimentation rate and clarity by increasing the dregs' surface area and interaction with raw green liquor
Data Source
AI summary
The invention relates to a method for clarification of raw green liquor in a sedimentation tank. According to the invention is a part of dregs separated in the sedimentation tank recirculated back into the inflow of raw green liquor, and preferably after passing the dregs through at least one turbulence generator (30, 31) that could break up larger dregs particles into smaller dregs particles, and thus create larger total surface on the dregs particles, improving sedimentation rate in the sedimentation tank. In a preferred embodiment is the recirculated dregs added into the flow of raw green liquor before a flocculant is added into the flow of raw green liquor and mixed recirculated dregs.