High Yield Wood Pulping via Segmented Chemical and Mechanical Processing
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Solution Overview
Problem
Current wood pulping processes face challenges in achieving a significant yield increase while maintaining high strength and stiffness of pulp fibers, with conventional methods only achieving 2-5% yield improvement and often resulting in lower tear strength and increased raw material costs for paperboard production.
Innovation Solution
A novel wood pulping method involving chemical pulping to high kappa numbers, followed by high consistency mechanical pulping of rejects to generate additional pulp fibers, which are then blended to produce paperboard with enhanced strength and stiffness at lower basis weights, reducing the need for phenolic resin in laminates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chemical pulping is used to remove lignin, then fiber strength and bleachability are improved, but pulp yield decreases to 45-53%
Solution Approach 1:
The pulping process is segmented into two distinct stages: first, chemical pulping removes a portion of lignin to improve fiber strength and bleachability; second, mechanical pulping processes the rejected material to extract additional pulp fibers. This segmentation allows the process to achieve both high fiber quality and high overall yield by treating different fractions of the wood input differently.
2Productivity
If mechanical pulping is used to separate fibers, then pulp yield increases to 85-98%, but fiber strength deteriorates due to high energy consumption and fiber degradation
Solution Approach 1:
The process segments the wood input into two streams: rejected material from chemical pulping (which undergoes mechanical pulping to maximize yield) and liberated fibers (which maintain high strength). By segmenting the treatment path based on material characteristics, the process optimizes both yield and strength for different fractions.
Solution Approach 2:
The process changes the operational parameters of mechanical pulping by applying it specifically to rejected material at high consistency with controlled refining energy (5-30 hpd/ton), rather than applying intensive mechanical pulping to all wood input. This parameter optimization reduces fiber degradation while maximizing pulp recovery from the rejected fraction.
3Productivity
If rejects are recooked in the digester, then fiber yield increases, but pulp brightness decreases and dirt level increases
Solution Approach 1:
The process replaces the chemical cooking method (recooking in digester) with a mechanical pulping method (refining in high consistency refiner). This substitution allows extraction of pulp fibers from rejected material through mechanical action rather than chemical digestion, preserving fiber quality, brightness, and cleanliness while still achieving high yield.
4Strength
If refining energy is increased to improve fiber properties, then fiber strength improves, but energy consumption increases significantly
Solution Approach 1:
The process optimizes refining parameters by operating at high consistency (50-90%) with controlled refining energy input (5-30 hpd/ton), rather than using low consistency refining with high energy input. This parameter change reduces energy consumption while maintaining effective fiber separation and strength development.
Solution Approach 2:
The chemical pulping stage performs preliminary lignin removal before mechanical pulping, which prepares the rejected material for more efficient mechanical treatment. This preliminary action reduces the refining energy required in the second stage while still achieving the desired fiber strength and 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 method achieves an 8-20% yield increase, providing paperboard with improved stiffness and strength at lower basis weights, comparable to conventional pulps, and reduces the amount of phenolic resin required, thus lowering production costs and material usage.
Implementation Method 1
Chemical pulping reacts wood chips with chemicals under pressure and temperature to remove lignin that binds pulp fibers together
Implementation Method 2
Thermomechanical pulping (TMP) grinds wood chips under steam at high pressures and temperatures
Implementation Method 3
Within the past 10 years, the industry has begun to use alkaline hydrogen peroxide as an impregnation chemical and as a chemical directly applied to a high consistency refiner treatment for CTMP pulping
Data Source
AI summary
A method of wood pulping having a significantly increased yield is disclosed. Wood chips are chemically pulped to a high kappa number, providing a first accepts component and a first rejects component. The first rejects component is subjected to a high consistency pulping process such as a substantially mechanical pulping process to generate a second accepts component and a second rejects component. The first accepts component may be used in the production of saturating kraft paper with excellent saturability and resin pick up. The second accepts may be used as a second fiber source in the production of multiply linerboard and unbleached paperboard with enhanced stiffness, strength, and smoothness. Alternatively, the first accepts component may be blended with the second accepts component to produce fiber blends, which may be used in a production of paper-based products having enhanced strength and stiffness at low basis weight.