Two-Stage Lignin Precipitation from Black Liquor
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Solution Overview
Problem
The existing lignin separation processes from black liquor require high amounts of fresh chemicals, leading to increased operational costs and environmental concerns, and face challenges with the disposal of odorous H2S gases and adapting to changing chemical compositions in the pulping process.
Innovation Solution
A method that divides the precipitation process into two phases with individual acidifier supplies, utilizing acidifying gases such as carbon dioxide from flue gases and sulfuric acid, and optimizing flow paths to minimize acidifier usage and prevent lignin particle blockage, allowing for efficient lignin extraction while maintaining the heat value of the treated black liquor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-stage acidification process is used to precipitate lignin from black liquor, then the process is simple to operate, but high amounts of fresh chemicals are required leading to increased operational costs
Solution Approach 1:
The acidification process is divided into two distinct stages: a first acidification stage using mill-generated waste acid flows to reduce pH from 13 to 11.5, and a second acidification stage using additional acidifier to reach pH 10-11 for lignin precipitation. This segmentation allows optimization of acidifier usage in each stage, reducing total fresh chemical requirements while maintaining process control.
2Quantity of substance
If mill-generated waste acid flows are used as acidifiers, then fresh chemical charges are reduced and environmental impact is lessened, but the process requires adaptation to varying chemical compositions
Solution Approach 1:
The process incorporates pH monitoring and control systems that provide feedback to adjust acidification rates and rates of subsequent steps. This allows the process to adapt to variations in mill-generated waste acid flow composition while maintaining consistent lignin precipitation performance, enabling effective use of variable waste streams.
3Productivity
If the pH is lowered rapidly from 13 to precipitate lignin, then the acidification process is faster, but excessive acidifier is consumed due to the logarithmic pH scale
Solution Approach 1:
The first acidification stage performs preliminary pH reduction from 13 to 11.5 using waste acid flows before the main lignin precipitation stage. This preliminary action consumes acidifier when the black liquor composition is more resistant to pH change, preparing the system for more efficient lignin precipitation in the second stage while reducing total fresh chemical requirements.
4Object-affected harmful factors
If H2S gases are routed to another part of the pulp mill for disposal, then the odorous emissions are managed, but transport and storage risks increase
Solution Approach 1:
The process converts the harmful H2S gas byproduct into a useful resource by routing it to the sulfidity unit where it serves as a sulfur source for pulping operations. This eliminates the need for separate H2S disposal infrastructure, removes transport and storage risks, and provides a benefit to the pulping process by maintaining sulfidity levels.
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 reduces the need for fresh chemicals, minimizes environmental impact, and achieves high lignin yield with a 'green' fuel product, effectively addressing the cost and environmental issues of the existing processes.
Implementation Method 1
The first phase reaching this pH level typically reduce the pH level from about pH 13 in the original black liquor down to a pH level about 11,5... As the precipitation of lignin requires acidification of alkaline black liquor flows
Implementation Method 2
LignoBoost is a process for precipitating lignin from black liquor... the precipitation process should be divided into at least two distinctive phases
Data Source
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AI summary
The present invention relates to a method for separation of lignin from original black liquor (BLIN) comprising the following phases in sequence; a first precipitation phase (PR1) for precipitation of lignin by a first acidification of the original black liquor by adding a first acid or mixture of acids (G1a); followed by a second precipitation phase (PR2) for precipitation of lignin by a further acidification of the original black liquor by adding a second acid or mixture of acids (G1b). According to the invention is the first phase implemented to lower the pH while avoiding any larger amount of precipitation, i.e. less than 2-5%, while the second phase is implemented in order to obtain the larger part of the precipitation. In total is 40-70% of the total lignin content of the original black liquor precipitated while the residual black liquor after precipitation is still strongly alkaline.