Countercurrent washing

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Solution Overview

Problem

Existing washing processes for filaments, such as Lyocell, are inefficient in removing residual solvents like NMNO due to the large excess of washing liquid used, leading to environmental and economic inefficiencies, and fail to meet stringent chemical-free product requirements.

Innovation Solution

A countercurrent washing method where fresh washing liquid is applied in the final stage and used washing liquid is recycled through preceding stages, minimizing liquid contact and exposure to minimize solvent accumulation, using optimized washing elements and separation enclosures to maintain efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large volume of washing liquid is used to wash filaments, then washing effectiveness is improved, but water consumption increases and environmental friendliness decreases

Engineering Contradiction:

Improvewashing effectivenessVSAvoidwater consumption

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent applies countercurrent washing where the washing liquid flows in the opposite direction to the filament movement. Fresh washing liquid is applied at the exit end where solvent residues are lowest, while used washing liquid progresses to the entrance end where solvent residues are highest. This inversion of the conventional washing approach maximizes the effectiveness of each portion of washing liquid and minimizes overall water consumption while achieving complete solvent removal.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the concentration parameter of the washing liquid along the washing path. By progressively concentrating the washing liquid as it moves through the washing zones (from fresh at the exit to used at the entrance), the system optimizes washing effectiveness at each stage while minimizing total water usage. The washing liquid parameters are dynamically adjusted to match the local contamination level.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If washing liquid is recirculated and reused in the same area, then water consumption is reduced, but washing performance decreases over time

Engineering Contradiction:

Improvewater consumptionVSAvoidwashing performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The washing process is divided into multiple sequential washing zones (first, second, and optionally third washing zones) arranged in series. Each zone handles a specific portion of the washing task, with washing liquid flowing progressively through each zone. This segmentation allows the system to maintain washing performance by ensuring that each zone receives washing liquid with appropriate contamination levels, preventing performance degradation that would occur with simple recirculation in a single area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of recirculating used washing liquid back to the beginning of the washing path, the system inverts the flow by directing fresh washing liquid to the exit end and allowing used liquid to progress to the entrance end. This prevents the mixing of highly contaminated liquid with fresh liquid, maintaining washing effectiveness throughout the process while minimizing water consumption.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If fresh water is continuously added to maintain washing quality, then washing effectiveness is maintained, but water consumption and costs increase

Engineering Contradiction:

Improvewashing qualityVSAvoidwater consumption

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The system accepts and utilizes changes in washing liquid parameters (increasing contamination concentration) along the washing path rather than attempting to maintain constant freshness. By matching the washing liquid contamination level to the local filament contamination level in each zone, the system maintains washing effectiveness without requiring continuous addition of fresh water. The parameter changes are optimized to achieve complete solvent removal with minimal water consumption.

Inventive Principle:

Principle #35Parameter changes

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

Reduces solvent residues by over 80% with minimal water usage, enhancing washing efficiency and reducing overall water consumption while meeting chemical-free product standards.

Implementation Method 1

washing the filaments, which removes any remaining solvent (NMNO), as well as other components of the spinning solution and/or the precipitation bath

Methodology Applied

Scientific EffectDissolution: Solvation

Implementation Method 2

only a small portion of the water comes into direct contact with the filament. At the same time, the accumulation of, for example, washed-out solvents leads to an enrichment of these components in the wash bath

Methodology Applied

Scientific EffectMass transfer: Diffusion

Implementation Method 3

countercurrent washing method where fresh washing liquid is applied in the final stage and used washing liquid is recycled through preceding stages

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentEP4065755B1Countercurrent washing

Publication Date: 2025.10.29 LENZING AG

AI summary

The present invention relates to a process for washing filaments.