Batch Digester Displacement Liquor Temperature Gradient
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing pulp production methods, particularly in prehydrolysis-kraft cooking, face challenges in achieving uniform pulp quality due to temperature gradients during the displacement phase, leading to uneven H-factor and P-factor exposure across the digester, resulting in variations in pulp quality between the top and bottom contents.
Innovation Solution
A method involving a temperature gradient in the displacement liquor is introduced, where a first displacement liquor with a lower temperature is added to the bottom of the digester, followed by a second displacement liquor with a higher temperature, and optionally a final displacement liquor, to reduce residual heat exposure and promote uniform temperature profiling, thereby reducing differences in pulp quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a constant temperature displacement liquor is used throughout the displacement phase, then the heating system is simple to operate, but temperature gradients persist in the digester causing non-uniform pulp quality
Solution Approach 1:
The displacement liquor is divided into multiple temperature zones: colder liquor is introduced at the bottom while hotter liquor is introduced at the top. This segmentation of temperature control along the vertical axis of the digester eliminates temperature gradients and ensures uniform pulp quality throughout the cooking chamber.
Solution Approach 2:
Different temperatures are applied to different locations within the digester. The bottom region receives colder displacement liquor while the top region receives hotter displacement liquor, creating local temperature optimization that prevents thermal stratification and ensures uniform cooking conditions throughout the entire volume.
2Manufacturing precision
If excessive heating is applied to maintain high temperature throughout displacement, then temperature uniformity is improved, but energy consumption increases significantly
Solution Approach 1:
The temperature parameter of the displacement liquor is varied spatially rather than maintained uniformly. By introducing colder liquor at the bottom and hotter liquor at the top, the system achieves temperature uniformity through parameter differentiation rather than parameter homogenization, significantly reducing the total heating energy required.
Solution Approach 2:
Instead of heating the entire displacement liquor to a high uniform temperature, the system inverts the approach by using colder liquor at the bottom and only heating the portion introduced at the top. This inverted temperature distribution strategy achieves the same temperature uniformity effect while minimizing energy consumption.
3Reliability
If large heating accumulators are used to store hot displacement liquor, then temperature stability is improved, but equipment size and investment cost increase
Solution Approach 1:
The heating accumulator is segmented into zones corresponding to different displacement liquor temperatures. Rather than one large accumulator storing all hot liquor, the system uses smaller accumulators or heating zones that supply specific temperature levels to specific locations, reducing total equipment volume while maintaining temperature stability.
Solution Approach 2:
Instead of heating and storing large volumes of displacement liquor at high temperatures, the system applies partial heating only where needed (at the top introduction point). This partial action approach maintains temperature stability in the critical zones while avoiding the energy waste and equipment size associated with heating entire liquor volumes excessively.
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 ensures more uniform pulp quality by reducing the difference in H-factor and P-factor exposure across the digester, conserving energy by reducing the need for excessive heating, and minimizing the size of heating accumulators.
Implementation Method 1
a first displacement liquor with a first lower temperature T1 which is more than 20°C below the treatment temperature in the heated treatment phase... continuing to add the same first displacement liquor to the bottom liquid exchange position, but the first displacement liquor now having a higher second temperature T2
Implementation Method 2
adding a first displacement liquor to the bottom liquid exchange position... filling a part of the digester with a first volume of the first displacement liquor
Data Source
AI summary
A method for producing pulp in batch digesters is disclosed. More particularly, the invention concerns a method for ending a treatment phase of the digester content. In order to obtain a more uniform pulp quality from the process is the treatment phase ended by displacing a liquor volume (WLP) through the digester vessel with an imposed increasing temperature in the displacement liquor added to digester.