Digester Washing Liquid Circulation for Pulp Hydrolysate Recovery
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing prehydrolysis-sulfate cooking processes for producing high-alpha cellulose pulps face inefficiencies in hydrolysate recovery, leading to uneven treatment, energy inefficiency, and dilute carbohydrate solutions, which affect pulp quality and sulfur contamination.
Innovation Solution
A displacement batch pulping process that introduces hot washing liquid from the bottom of the digester, circulates it through suction screens, and neutralizes the digester contents with alkaline liquor to recover hydrolysate and steam condensate, preventing fiber loss and achieving high concentration of dissolved sugars, while maintaining controlled pH levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a separate washing stage is used to recover hydrolysate, then carbohydrate recovery is improved, but the process becomes time-consuming and produces a very dilute carbohydrate solution
Solution Approach 1:
The patent combines the washing stage with the cooking stage by introducing washing liquid into the digester during the cooking process. The washing liquid is circulated through the chips during the cooking phase, allowing simultaneous washing and cooking operations. This eliminates the need for a separate washing stage, reducing process time while maintaining carbohydrate recovery efficiency.
Solution Approach 2:
The patent implements continuous circulation of washing liquid through the chips during the cooking process. The washing liquid is pumped from the bottom of the digester, circulated through the chips via suction screens, and returned to the top, creating a continuous flow that maintains constant contact between the liquid and chips throughout the cooking phase.
2Quantity of substance
If trickle-bed type down-flow recovery is used, then concentrated hydrolysate is obtained, but the recovery step is too slow and channeling occurs
Solution Approach 1:
Instead of using a trickle-bed type down-flow recovery method, the patent inverts the approach by introducing washing liquid from the bottom of the digester and circulating it upward through the chips. This upward circulation through suction screens ensures even distribution of the washing liquid throughout the chip mass, preventing channeling while maintaining high recovery speed and concentrated hydrolysate.
3Reliability
If traditional neutralization with alkaline neutralizing liquor is used, then hydrolysate is neutralized, but sulfur contamination occurs in the recovered hydrolysate
Solution Approach 1:
The patent extracts and removes the harmful sulfur-containing components from the hydrolysate by using a washing liquid that does not contain sulfur. The washing liquid circulates through the chips, selectively removing carbohydrates while leaving sulfur-containing compounds behind in the solid phase. This extraction method produces sulfur-free recovered hydrolysate while maintaining effective neutralization.
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 ensures even treatment of digester contents, improves energy efficiency, and produces high-grade pulp with essentially pure sulfur-free hydrolysate, enhancing the processing of carbohydrates and maintaining fiber quality.
Implementation Method 1
In the prehydrolysis stage carried out in a steam phase, direct steam is introduced to the chip column in the digester
Implementation Method 2
neutralizing of the digester contents by displacing the washing liquid with alkaline liquor
Data Source
Figure 1
AI summary
A method for producing pulp is disclosed. More particularly, the invention concerns a displacement batch cooking process comprising a steam-phase prehydrolysis step, wherein the recovery of the by-products is improved. In the recovery step of the present invention, after the target P-factor in the prehydrolysis stage is reached, hot washing liquid is introduced into the digester from the bottom thereof. The washing liquid is circulated via the suction screens to the top and to the bottom of the digester until the prehydrolyzed chips are under the washing liquid. The hot washing liquid containing by-products is recovered from the digester and the digester contents are neutralized by displacing the washing liquid with alkaline liquor.