Refiner Plate Corrosion and Coating Prevention via Segmented pH Control
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Solution Overview
Problem
The existing methods for producing pulp from lignocellulose using sodium sulphite and sodium bisulphite face issues with corrosion and coating on refiner plates due to varying pH levels, leading to reduced service life and increased energy consumption.
Innovation Solution
Feeding a mixture of sodium sulphite and sodium bisulphite directly into the refiner with adjusted pH levels of 6.0-7.5 for impregnation and 4.0-5.5 for additional chemicals, optimizing the chemical distribution to prevent corrosion and coating, while maintaining effective pulp treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chemicals from sodium sulphite and sodium bisulphite mixture are used for impregnation at low pH (4.0-5.5), then corrosion is prevented and SO2 emissions are controlled, but coating forms on refiner plates reducing their service life
Solution Approach 1:
The patent divides the chemical addition process into two separate stages with different pH conditions: first stage at low pH (4.0-5.5) for corrosion prevention, and second stage at higher pH (6.0-7.5) to prevent coating on refiner plates. This segmentation allows each stage to optimize for its specific function without compromising the other.
Solution Approach 2:
Different pH conditions are applied to different locations/stages of the process: the low pH environment is applied where corrosion is a concern (in the digester/refiner), while the higher pH environment is applied during impregnation where coating prevention is the priority. This local quality approach ensures each region has the optimal conditions for its specific requirements.
2Duration of action of stationary object
If chemicals are added at higher pH values (6.0-7.5), then coating on refiner plates is reduced, but corrosion occurs and SO2 emissions increase
Solution Approach 1:
The chemical treatment process is segmented into two distinct stages: the first stage uses higher pH (6.0-7.5) chemicals to prevent coating on refiner plates, while the second stage uses low pH (4.0-5.5) chemicals to prevent corrosion. This segmentation allows each stage to address its specific problem without exacerbating the other.
Solution Approach 2:
The patent applies preliminary action by first treating the wood chips with chemicals at higher pH to prevent coating formation on refiner plates before the grinding process occurs. This preliminary treatment ensures that the refiner plates remain free of coating during subsequent operations.
3Device complexity
If single pH level chemicals are used throughout the process, then the process is simple, but both corrosion and coating problems occur simultaneously
Solution Approach 1:
The patent segments the chemical addition process into two separate stages with different pH levels: the first stage uses chemicals at pH 6.0-7.5 for impregnation to prevent coating, and the second stage uses chemicals at pH 4.0-5.5 added directly to the refiner to prevent corrosion. This segmentation resolves the contradiction by showing that the additional complexity enables simultaneous prevention of both coating and corrosion, improving overall system reliability.
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 extends the service life of refiner plates, reduces energy consumption, and avoids salt formation, resulting in substantial cost savings and improved pulp quality.
Implementation Method 1
the lignocellulose material is impregnated with chemicals from a mixture of sodium sulphite and sodium bisulphite
Implementation Method 2
The gaseous SO2 as the product of bisulphite decomposition can occur in the pre-treatment stage but also during grinding
Data Source
AI summary
A method for producing a fibrous material from lignocellulose from wood, preferably in the form of wood chips. The lignocellulose material is impregnated with a mixture of sodium sulfite and sodium bisulfite and subsequently undergoes a comminution process in a refiner. Additional chemicals from a mixture of sodium sulfite and sodium bisulfite are directly introduced into the refiner, allowing optimal conditions to be set for both additive flows of chemicals such that the process can be operated in an energetically advantageous manner and corrosion and scale formation in the refiner and subsequent aggregates can be prevented as much as possible.