Polysulfide Kraft Cooking Liquor Carbohydrate Stabilization

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Solution Overview

Problem

Conventional kraft cooking methods face challenges with high alkali concentrations that are detrimental to pulp viscosity, leading to inefficient alkali consumption and reduced pulping yield, particularly during the initial neutralization of wood acidity.

Innovation Solution

A method involving a low temperature pretreatment stage with a high polysulfide cooking liquor concentration and liquor-to-wood ratio of 2.0 to 3.2, followed by a cooking stage, which stabilizes carbohydrates and reduces alkali consumption, maintaining high alkali concentration during the impregnation stage to achieve improved pulping yield.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high alkali concentrations are charged to the top of the digester in conventional cooking, then the initial neutralization of wood acidity is effective, but pulp viscosity is reduced detrimentally

Engineering Contradiction:

Improveneutralization effectivenessVSAvoidpulp viscosity reduction

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The alkali charge is divided into two separate stages: first, black liquor with residual alkali is charged to neutralize wood acidity during impregnation; second, additional alkali is charged at the top of the digester after the harmful peak concentration period has passed. This segmentation allows effective neutralization while avoiding detrimental high alkali concentrations at the start of cooking.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The neutralization of wood acidity is performed in advance during the impregnation stage using black liquor with residual alkali, before the main cooking process begins. This preliminary action removes the need to charge high alkali concentrations at the top of the digester, thereby preventing pulp viscosity reduction while still achieving complete neutralization.

Inventive Principle:

Principle #10Preliminary action

2Temperature

If large volumes of alkali treatment liquors are charged to meet high alkali consumption, then alkali concentration in top of digester is reduced, but liquor to wood ratio increases

Engineering Contradiction:

Improvealkali concentration at top of digesterVSAvoidliquor to wood ratio

Core Design Contradiction:

TemperatureVSQuantity of substance

Solution Approach 1:

The process changes the timing and form of alkali charging: black liquor with residual alkali is used during impregnation instead of charging large volumes of dilute alkali liquor at the top of the digester. This parameter change allows meeting alkali consumption requirements while maintaining lower liquor to wood ratios and avoiding high alkali concentrations at the top of the digester.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If polysulfide cooking liquor is used to stabilize carbohydrates, then pulping yield increases, but alkali consumption increases

Engineering Contradiction:

Improvepulping yieldVSAvoidalkali consumption

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

Black liquor with residual alkali from earlier cooking phases is reused during the impregnation stage to neutralize wood acidity. This self-service approach allows the system to meet alkali consumption requirements for polysulfide cooking and carbohydrate stabilization without requiring additional fresh alkali charges, thereby increasing pulping yield without proportionally increasing total alkali consumption.

Inventive Principle:

Principle #25Self-service

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 increases pulping yield by maintaining high polysulfide concentration and reducing alkali consumption, resulting in kraft pulp with desired kappa numbers and improved carbohydrate stabilization, while minimizing pulp viscosity reduction.

Implementation Method 1

concentration of polysulfide should be kept high in a low temperature pretreatment stage at relatively long retention time before cooking... The stabilization effect of carbohydrates, the major objective for polysulfide addition, has shown to be improved dramatically

Methodology Applied

Scientific EffectCarbohydrate stabilization:

Implementation Method 2

the lignin-containing cellulosic material is heated to a temperature in the range 50-100° C.

Methodology Applied

Scientific EffectThermal heating: Heating

Data Source

PatentUS9580864B2Kraft cooking method using polysulfide cooking liquor

Publication Date: 2017.02.28 VALMET AB

AI summary

The method is 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 a first impregnation stage using polysulfide cooking liquor is implemented at high alkali and polysulfide concentration and at a low temperature. Knots are added to a high-pressure conduit extending between an impregnation vessel and a digester.