Polysulfide Pulping Yield via Staged Alkali Exchange
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modified Kraft pulping processes are not fully compatible with current commercial polysulfide pulping technology, resulting in suboptimal pulping yields and pulp strength due to incomplete utilization of polysulfide additives.
Innovation Solution
A method that employs a modified cooking process in conjunction with polysulfide pulping, where 100% of the alkali dosage is added as polysulfide liquor at the impregnation stage, with controlled liquor exchanges to maintain a uniform effective alkali concentration profile, similar to that of modified cooking, thereby maximizing pulping yield and pulp strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polysulfide pulping technology is applied to modified cooking, then pulping yield can be increased, but the effectiveness is reduced because only 45-75% of polysulfide is added at the beginning of the cook
Solution Approach 1:
The invention segments the polysulfide addition process into two parts: (1) adding 45-75% of total polysulfide at the beginning of the cook to establish initial effectiveness, and (2) adding the remaining 25-55% of polysulfide at intermediate cooking stages when temperature is between 100-140°C and polysulfide retention time is at least 15 minutes. This segmentation allows full utilization of polysulfide benefits while maintaining compatibility with modified cooking's staged alkali addition approach.
Solution Approach 2:
The invention applies preliminary action by adding a portion of polysulfide at the beginning of the cook (45-75% of total) to prepare the system for enhanced pulping yield from the start, while reserving the remaining polysulfide for later intermediate stage addition. This preliminary positioning of polysulfide ensures optimal conditions are established before the main cooking action occurs.
2Productivity
If total alkali charge is added at the beginning of the cook, then polysulfide can be fully utilized, but excessive effective alkali concentration causes losses in pulping yield and pulp strength
Solution Approach 1:
The invention segments the alkali addition into two independent components: (1) staged alkali addition (45-75% at beginning, remainder at intermediate stages) to control effective alkali concentration and prevent losses, and (2) staged polysulfide addition (45-75% at beginning, 25-55% at intermediate stages) to maximize pulping yield. This dual segmentation resolves the contradiction by allowing full polysulfide utilization without excessive early-stage effective alkali concentration.
Solution Approach 2:
The invention applies local quality by creating different chemical environments at different cooking stages: early stage has moderate alkali with polysulfide for yield enhancement, intermediate stages have controlled alkali addition with supplemental polysulfide for continued yield improvement, and late stage completes the cooking. Each stage has optimized local conditions rather than uniform conditions throughout.
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 achieves higher pulping yields and pulp strength by ensuring full utilization of polysulfide benefits while maintaining a uniform alkali concentration, overcoming the limitations of prior art by integrating polysulfide pulping into modified cooking.
Implementation Method 1
essentially all polysulfide has reacted with lignocellulosic material to stabilize carbohydrates for pulping yield increase
Implementation Method 2
heating up the cook from about 60°C to 120°C in 15 minutes; heating up the cooking to full cooking temperature of about 157°C (315°F) in 30 minutes
Implementation Method 3
heating up the chips with low-pressure steam; cooling the cook down to below 100°C
Data Source
Figure 1a~1b
Figure 2
Figure 3~4
AI summary
A method for Kraft pulping employing a modified cooking process in conjunction with polysulfide pulping technologies to obtain higher pulping yields than obtained in the prior art. The total required alkali charge (polysulfide liquor) is added to the beginning of a cook, and after all polysulfide has essentially reacted with lignocellulosic material at temperature below that at which no significant carbohydrate degradation occurs, a first quantity of the cooking liquor high in effective alkali (EA) concentration is removed from a first point in the pulping process and replaced with a cooking liquor low in EA concentration removed from another process point. The first quantity is then added elsewhere in the pulping process, where the EA concentration is low. This cooking liquor "exchange" obtains the full yield benefit from polysulfide pulping and a more uniform EA concentration profile to retain the major benefits of modified cooking.