Pre-hydrolysis Reactor Extraction Screens for Pseudolignin Removal
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Solution Overview
Problem
The buildup of pseudolignins and lignin fragments on wood chips and equipment during pre-hydrolysis and Kraft cooking processes interferes with the operation of reactors, blocking pores and disrupting the flow of cellulosic feed material, particularly in acidic environments.
Innovation Solution
A pulp cooking system with multiple extraction points and a pre-hydrolysis vessel that includes a center pipe for discharging wash liquids and extraction screens to remove pseudolignins, along with pH management using hydrolysate and bisulfite compounds to prevent deposition, ensuring controlled flow and efficient processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pre-hydrolysis is performed in an acidic environment to dissolve pulp, then the hydrolysis reaction is enhanced, but pseudolignins and lignin fragments build up on wood chips and equipment surfaces
Solution Approach 1:
The patent introduces a separate extraction zone that physically removes pseudolignins and lignin fragments from the hydrolyzed cellulosic fiber feed material as they are formed. This extraction system continuously extracts the harmful substances from the acidic hydrolysis environment, preventing their accumulation on chips and equipment while allowing the hydrolysis reaction to proceed efficiently.
Solution Approach 2:
The patent uses an intermediary extraction zone that acts as a buffer between the hydrolysis reaction zone and the downstream equipment. This intermediary zone captures and removes pseudolignins and lignin fragments before they can deposit on equipment surfaces, while still allowing the acidic hydrolysis environment to be maintained in the reaction zone for optimal productivity.
2Productivity
If pseudolignins and lignin fragments are allowed to form during hydrolysis, then pulp dissolution is achieved, but pores in wood chips are blocked preventing alkali penetration
Solution Approach 1:
The extraction zone continuously removes pseudolignins and lignin fragments from the hydrolyzed material, preventing these substances from blocking the pores in wood chips. This ensures that when the material transitions to the Kraft cooking stage, the alkali can penetrate the chip pores effectively, maintaining reliable processing while still achieving thorough pulp dissolution during hydrolysis.
3Productivity
If pseudolignins and dissolved lignins build up on equipment surfaces, then the hydrolysis process continues, but flow passages are blocked and equipment operation is interfered with
Solution Approach 1:
The patent introduces a dedicated extraction zone that continuously removes pseudolignins and dissolved lignins from the hydrolysis stream before they can deposit on equipment flow passages. This extraction system maintains equipment operability by preventing buildup, while allowing the hydrolysis process to continue uninterrupted in the reaction zone.
4Object-generated harmful factors
If multiple extraction points are added to remove pseudolignins, then buildup is reduced, but device complexity increases
Solution Approach 1:
The patent divides the extraction function into multiple discrete extraction points distributed along the length of the reactor. Each extraction point handles a specific zone, allowing pseudolignins to be removed at multiple locations where they are most likely to form. This segmented approach reduces deposition effectively while keeping each individual extraction point relatively simple in design.
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
The system effectively reduces the buildup of pseudolignins and lignin fragments, maintaining uniform pH levels and enhancing the flow of feed material through reactors, thereby improving the efficiency and operation of pre-hydrolysis and Kraft cooking processes.
Implementation Method 1
Hydrolysis of comminuted cellulosic fiber feed material, such as wood chips, before Kraft cooking
Implementation Method 2
The pseudolignins and lignin fragments tend to build up on the surfaces of chips and equipment most when in an acidic environments
Data Source
Figure 1
Figure 2
AI summary
A pulp cooking system including: a cellulosic material feed system, a pre-hydrolysis reactor vessel and a Kraft cooking reactor vessel. The feed material system includes a steaming chip bin (10) and a high pressure transfer device (12). The pre-hydrolysis reactor vessel maintains the feed material in a mildly acidic condition and allows hydrolysate to be extracted through screens (60) below a hydrolysis zone (56) in the vessel. A wash zone (66) is below the screens and allows wash liquid to flow through the feed material in a cross-current direction. The wash liquid and hydrolysate removed from the feed material is extracted from the wash zone through the screens (60). The feed material is maintained in a mildly acidic condition through the pre-hydrolysis reactor vessel until the material enters the Kraft cooking vessel where the feed material is treated with alkaline cooking liquors.