Batch Digester Hydrolysis Packing Degree and Recovery
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Solution Overview
Problem
Current methods for recovering concentrated hydrolysate in batch digesters are inefficient, leading to dilution and uneven treatment, which affects pulp quality and energy balance, particularly due to the lack of effective monitoring and compaction of wood chips during steam hydrolysis.
Innovation Solution
The method involves a two-phase hydrolysis process where cellulose material undergoes steam phase hydrolysis at 150-170°C to achieve a significant packing degree increase, followed by a liquid phase hydrolysis with controlled Liquor-to-wood ratio, allowing for efficient recovery of concentrated hydrolysate by circulating the liquid and draining free liquid, thereby minimizing dilution and optimizing carbohydrate extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a separate washing stage is used to recover hydrolysate before neutralization, then carbohydrate recovery is improved, but processing time increases and energy balance deteriorates
Solution Approach 1:
The invention combines the hydrolysis and washing operations into a single integrated process. The hydrolysis liquid itself is used as the washing medium, eliminating the need for a separate washing stage. This merging of operations recovers carbohydrates efficiently while reducing processing time and improving energy balance, as the same liquid serves dual purposes: hydrolyzing hemicellulose and washing/extracting the hydrolysate.
2Ease of manufacture
If wood chips are loosely packed in the digester, then filling is easier, but hydrolysate concentration decreases due to excessive void volume
Solution Approach 1:
The invention applies preliminary compaction to the wood chips before the hydrolysis-washing process. By pre-compressing the chips to reduce void volume, the system creates optimal conditions for concentrated hydrolysate recovery without requiring complex filling mechanisms. This preliminary action maintains ease of operation while significantly improving hydrolysate concentration.
3Loss of substance
If steam phase hydrolysis is used, then hemicellulose removal is improved, but hydrolysate dilution occurs due to steam condensate
Solution Approach 1:
The invention optimizes the steam phase hydrolysis parameters, specifically controlling temperature, pressure, and duration to minimize condensate formation while maximizing hemicellulose hydrolysis. By carefully adjusting these parameters, the system achieves effective hemicellulose removal with reduced dilution of the hydrolysate.
Solution Approach 2:
The invention uses a composite approach combining steam phase hydrolysis with a specifically formulated hydrolysis liquid that has optimized properties for both hydrolysis efficiency and minimal dilution. This composite process leverages the advantages of steam phase treatment while mitigating the dilution issue through careful selection and control of the liquid phase characteristics.
4Loss of substance
If conventional recovery methods are used, then hydrolysate is recovered, but dilution and uneven treatment reduce pulp quality
Solution Approach 1:
The invention implements a feedback mechanism where the hydrolysis liquid is circulated back through the chip mass multiple times. This circulation ensures uniform distribution of the hydrolysis medium and consistent extraction of hydrolysate throughout the material. The feedback loop maintains even treatment conditions, preventing localized dilution or incomplete hydrolysis, thereby preserving pulp quality while achieving comprehensive hydrolysate recovery.
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 substantial increase in packing degree, enabling the recovery of undiluted hydrolysate with high carbohydrate concentration, improving energy efficiency and pulp quality by effectively capturing dissolved carbohydrates and maintaining pulp strength.
Implementation Method 1
the only liquid brought into the steam phase hydrolysis is the liquid that is brought into the digester with the cellulose material, preferably most of it as bound liquid, and the steam condensate that heats the cellulose material
Implementation Method 2
The prehydrolysis is carried out at acidic conditions either as a water or steam phase prehydrolysis, or in the presence of a catalyst. In the steam hydrolysis processes, organic acids liberated from lignocellulose during the process, i.e. the wood acidity, perform a major part of the acidification for the hydrolysis
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
A method for obtaining a strong hydrolysate from cellulose material after a hydrolysis in a batch digester. According to the invention is the cellulose material exposed to a 2-stage hydrolysis with a first steam phase hydrolysis followed by a liquid phase hydrolysis, and wherein the steam phase is conducted to such an extent that the packing degree of the cellulose material is resulting in a packing degree increase of at least 20% and up to 100%. The liquid phase hydrolysis is established by adding hot and preferably acidified hydrolysis liquid not establishing higher total L/W ratio above 3.5, but sufficient to keep the cellulose material under the level of the hydrolysis liquid.