Mechanical Pulp Bleaching via Reject Fraction Segmentation
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Solution Overview
Problem
Traditional mechanical pulp production methods face challenges in achieving high strength and energy efficiency, particularly in the bleaching process, where the reject fraction often has low pliability, opacity, and high energy consumption.
Innovation Solution
A novel process that separates the pulp into accept and reject fractions during screening, bleaches the reject separately, and then remixes it with the accept, using small doses of alkali and peroxide-based bleaching chemicals to enhance strength and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the reject fraction is bleached together with the accept fraction, then the bleaching process is simpler, but the drainability of the main fraction becomes poor and normal filtration bleaching cannot be used
Solution Approach 1:
The pulp stream is segmented into accept and reject fractions through screening, allowing each fraction to be processed separately. The reject fraction is diverted to a separate bleaching line while the accept fraction continues through the main process, enabling optimized processing for each fraction's specific characteristics.
Solution Approach 2:
The reject fraction is extracted from the main pulp stream using a screen, separating it from the accept fraction. This extraction allows the reject to be treated independently with appropriate bleaching conditions without affecting the main fraction's drainability and processing.
2Productivity
If traditional chlorine compounds and sulphur compounds are used for bleaching, then the bleaching effectiveness is high, but environmental pollution and safety issues occur
Solution Approach 1:
The bleaching chemistry is changed from chlorine and sulphur compounds to hydrogen peroxide and organic peracids. This parameter change in chemical composition eliminates the formation of harmful chlorinated and sulfonated compounds while maintaining effective bleaching through oxidation mechanisms.
Solution Approach 2:
Hydrogen peroxide and organic peracids are used as strong oxidizing agents to bleach the pulp. These oxidants effectively remove lignin and other chromophores from the mechanical pulp, achieving the desired brightness and whiteness without the environmental harm associated with traditional chlorine-based bleaching.
3Strength
If high doses of alkali are used in bleaching, then the strength of the pulp increases, but the alkali consumption and cost increase
Solution Approach 1:
Instead of using high doses of alkali throughout the entire bleaching process, a small amount of alkali (0.01-0.05 equivalents per mole of peroxide) is added specifically during the peroxide bleaching stage. This partial application of alkali is sufficient to enhance pulp strength without the excessive alkali consumption that would occur with traditional high-dose alkaline bleaching.
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 significantly increases the strength of the pulp and reduces energy used in refining, while maintaining low alkali consumption, resulting in improved pulp properties and energy savings.
Implementation Method 1
Later, new types of bleaching compounds were used, among others, hydrogen peroxide and organic peroxy acids, such as peroxy formic acid and peroxy acetic acid
Implementation Method 2
the pulp is bleached in alkaline conditions
Data Source
AI summary
Method for the production of mechanical or chemi-mechanical pulp as raw material for paper or cardboard. According to this method, the pulp is fibrillated and the fibrillated pulp is bleached in alkaline conditions. According to the present invention, the pulp is screened to separate the reject from the accept, at maximum approximately 60% of the total amount of pulp is separated as the reject, the reject is bleached separate from the accept, and, after that, the bleached reject is remixed with the accept. When operating according to the present invention, the strength of the pulp increases and the energy used for refining is reduced, which is seen both in the refining of the reject and in the post-refining of the final mechanical pulp.