Lyocell Web Washing with Two-Stage Coagulation and Dewatering
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Solution Overview
Problem
Current lyocell melt-blown processes face challenges in washing cellulose filaments, requiring control over filament merging, diameter variation, minimizing damage, controlled liquor exchange, water consumption, and reducing equipment and energy costs, with no prior art achieving all these requirements effectively.
Innovation Solution
A two-stage washing process and device are introduced, where the first stage involves delivering wash liquor to lyocell solution threads before web formation to partially coagulate filaments, and the second stage uses modular washing modules with controlled wash liquor application and vacuum suction to form and dewater the web, optimizing residence time and module configuration for efficient solvent removal and web formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wash liquor is delivered to lyocell solution threads before web formation to partially coagulate filaments, then filament structure development is controlled and solvent removal is efficient, but water consumption and equipment costs increase
Solution Approach 1:
The washing process is divided into multiple modular washing zones with different functions: a first washing zone with spray nozzles for initial solvent removal and partial coagulation, and a second washing zone with curtain washers for further washing. This segmentation allows optimized water usage in each zone rather than uniform washing throughout
Solution Approach 2:
The first washing zone performs preliminary solvent removal and partial coagulation of filaments before the web formation step. This preliminary action controls filament structure development early in the process, reducing the water burden on subsequent washing zones
2Productivity
If high line speeds are used for web production, then productivity increases, but control over filament merging and diameter variation becomes more difficult
Solution Approach 1:
The first washing zone applies wash liquor to threads before web formation to induce partial coagulation and control filament diameter. This preliminary action occurs at high speed compatible with modern production rates, establishing filament structure before the web formation step
Solution Approach 2:
Spray nozzles in the first washing zone deliver wash liquor as a fine spray to the threads, providing controlled solvent removal and uniform filament coagulation at high line speeds. The hydraulic spray system ensures consistent application across the web width
3Reliability
If multiple washing modules are used for efficient solvent removal, then washing effectiveness improves, but device complexity and investment costs increase
Solution Approach 1:
The washing device is segmented into functional modules: a first washing zone with spray nozzles for initial solvent removal, and a second washing zone with curtain washers for further washing. Each module has a specific function, allowing optimized solvent removal without requiring excessive washing stages
Solution Approach 2:
The washing device performs multiple functions within a single integrated structure: solvent removal, filament coagulation control, and web formation assistance. This multi-functionality reduces the need for separate dedicated equipment for each function
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 allows for high-speed production of cellulose-based webs with controlled filament structure development, reduced water consumption, and minimized equipment costs, achieving line speeds from 5 m/min to 1000 m/min while maintaining web integrity and solvent recovery efficiency.
Implementation Method 1
delivering wash liquor to the solution threads directly after extension and prior to web formation, whereby partially coagulated cellulose filaments are formed
Implementation Method 2
the solvent has to be removed from the thermoplastic cellulose/solvent threads in a controlled manner (prior to, during and after web formation) to begin developing fibre structure
Implementation Method 3
a dewatering device for at least partially dewatering the web
Implementation Method 4
the web forming device has porosity sufficient to allow gas stream and wash liquor to be extracted through it
Data Source
AI summary
This invention relates to a process and a device for manufacturing cellulose-based webs which are directly formed from lyocell spinning solution and in particular for the washing of directly formed cellulose webs.