Polysulfide Kraft Cooking Liquor for Yield and Viscosity
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Solution Overview
Problem
Conventional kraft cooking methods face challenges with high alkali concentrations that negatively impact pulp viscosity and require excessive alkali usage, leading to inefficient alkali consumption and reduced pulping yield.
Innovation Solution
A method involving a high polysulfide concentration at a low temperature pretreatment stage with a liquor-to-wood ratio of 2.0 to 3.2, followed by cooking stages, where the initial impregnation stage maintains high alkali and polysulfide concentrations to stabilize carbohydrates without initial delignification, allowing for reduced alkali consumption and improved yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high alkali concentrations are charged to top of digesters in conventional cooking, then alkali consumption is reduced, but pulp viscosity deteriorates
Solution Approach 1:
The cooking process is divided into two distinct stages: a pretreatment stage using polysulfide cooking liquor at low temperature, and a subsequent cooking stage. This segmentation allows alkali to be consumed efficiently in the pretreatment stage without exposing the pulp to high alkali concentrations during the critical cooking phase, thus maintaining pulp viscosity while reducing total alkali consumption.
Solution Approach 2:
The invention changes the temperature parameter during the pretreatment stage, maintaining it below the cooking temperature. This parameter change enables effective alkali consumption and carbohydrate stabilization without the detrimental effects of high temperature and high alkali concentration combination, preserving pulp viscosity.
2Quantity of substance
If large volumes of alkali treatment liquors are charged to meet high alkali consumption, then alkali concentration in top of digester is reduced, but process complexity increases
Solution Approach 1:
The pretreatment stage performs preliminary alkali consumption and carbohydrate stabilization before the main cooking process. By conducting this action in advance at low temperature with polysulfide liquor, the system avoids the need to charge large volumes of dilute alkali treatment liquors during cooking, simplifying the overall process while maintaining appropriate alkali concentrations.
3Productivity
If polysulfide treatment liquor is drained after pretreatment stage, then black liquor treatment efficiency is improved, but alkali concentration is reduced
Solution Approach 1:
The invention merges the pretreatment stage with the cooking stage by continuously charging polysulfide cooking liquor throughout the cooking process. This combination ensures that alkali concentration is maintained at appropriate levels while the pretreatment functions are achieved, avoiding the need to drain the liquor and subsequent recharging operations.
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 results in a kraft pulp with a kappa number below 40 and significantly increased pulping yield, with over 90% of the total alkali charge used in the first impregnation stage, reducing alkali concentration and maintaining pulp viscosity, while achieving a high polysulfide concentration and stabilization effect.
Implementation Method 1
high polysulfide concentration and stabilization effect
Implementation Method 2
the cellulosic material is heated to a temperature in the range 50-100 °C
Implementation Method 3
a large part of the alkali consumption is due to the initial neutralization of the wood acidity
Data Source
Figure 1A~1C
Figure 2
Figure 3
AI summary
The invention is related to a method for the preparation of kraft pulp with increased pulping yield from lignin-containing cellulosic material using polysulfide cooking liquor. In order to increase carbohydrate stabilization and hence the yield from a kraft cooking process is a first impregnation stage using polysulfide cooking liquor implemented at high alkali and polysulfide concentration and at low temperature.