Lignocellulose Cooking Liquor Split Addition for Pulp Yield
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Solution Overview
Problem
Conventional cooking processes for lignocellulose materials face challenges in maximizing pulp yield and reducing specific chemical consumption, particularly in achieving a balance between Kappa number and pulp yield, while also managing the efficiency and cost of chemical recovery in the recovery boiler.
Innovation Solution
A continuous cooking process using a digester with split addition of alkaline cooking liquors, where a first liquor rich in polysulfide sulfur and effective alkali is added upstream, and secondary and tertiary liquors with sodium hydroxide are introduced to specific zones, optimizing polysulfide stability and delignification, thereby improving pulp yield and reducing effective alkali addition rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the conversion rate is raised to produce polysulfide cooking liquor, then the polysulfide concentration increases, but thiosulfate ions are secondarily produced in large amounts by side reactions
Solution Approach 1:
The cooking process is divided into multiple stages with different liquor compositions. In the first stage, a liquor rich in polysulfide is used to achieve high delignification efficiency. In subsequent stages, the liquor composition is adjusted to reduce polysulfide concentration and minimize thiosulfate formation, thereby segmenting the cooking process to optimize both polysulfide utilization and harmful byproduct reduction
Solution Approach 2:
The patent changes the chemical parameters of the cooking liquor dynamically throughout the cooking process. By adjusting the polysulfide concentration, pH value, and other chemical parameters at different cooking stages, the system maximizes polysulfide effectiveness while minimizing side reactions that produce thiosulfate ions
2Productivity
If conventional cooking processes are used to improve pulp yield, then chemical consumption increases, but the relationship between Kappa number and pulp yield deteriorates
Solution Approach 1:
The patent optimizes the chemical parameters of the cooking liquor, particularly the polysulfide concentration and pH value, to achieve high pulp yield with reduced chemical consumption. By precisely controlling these parameters, the system improves the relationship between Kappa number and pulp yield while reducing overall chemical usage
Solution Approach 2:
The cooking process maintains continuous and uniform cooking conditions throughout the treatment. By ensuring continuous effective action of the cooking liquor on the lignocellulose material, the system achieves consistent delignification and high pulp yield without requiring excessive chemical addition
3Productivity
If the load of the recovery boiler is increased to recover chemicals, then chemical recovery efficiency improves, but the capacity requirements and operational complexity increase
Solution Approach 1:
The patent implements a system that recovers and reuses cooking chemicals in the digestion process. By recovering chemicals from the cooking liquor and reusing them, the system reduces the load on the recovery boiler and minimizes chemical waste, thereby improving recovery efficiency without proportionally increasing boiler capacity requirements
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 process enhances pulp yield and improves the relationship between Kappa number and pulp yield, while minimizing chemical consumption and optimizing chemical recovery, effectively utilizing wood resources and reducing the load on recovery boilers.
Implementation Method 1
Polysulfide oxidize the carbonyl end group of carbohydrates to suppress the decomposition of the carbohydrates ascribed to a peeling reaction
Implementation Method 2
The chemical cooking liquor in the polysulfide cooking process is produced by oxidizing an alkaline aqueous solution containing sodium hydroxide and sodium sulfide, so-called white liquor, with molecular oxygen
Implementation Method 3
in the presence of a catalyst such as activated carbon or the like
Data Source
Figure 1
AI summary
In a cooking process of a lignocellulose material, pulp yield can be improved at the same Kappa number and an effective alkali addition rate can be reduced at the same Kappa number. In a continuous cooking process making use of a digester, which includes therein, from a top toward a bottom of the digester, a top zone, an upper cooking zone, a lower cooking zone and a cooking/washing zone and also includes strainers provided at the bottom of the respective zones and wherein a cooking black liquor extracted from at least one of the strainers is discharged to outside a digestion system, a process for cooking a lignocellulose characterized by comprising feeding, upstream of the top of the digester, a first cooking liquor comprised of an alkaline cooking liquor having specified composition, feeding a second cooking liquor comprised of an alkaline cooking liquor made mainly of sodium hydroxide to the upper cooking zone, and feeding a third cooking liquor comprised of an alkaline cooking liquor similar to the second cooking liquor to the cooking/washing zone.