Woven Mesh Screen Assembly for Pulp Digester Clogging and Fatigue

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Solution Overview

Problem

Existing screens in pulp digesters and impregnation vessels face issues such as limited open area, scale deposits, mechanical failures due to cyclic pressure differences, and cumbersome maintenance, leading to clogging, fatigue, and high maintenance costs.

Innovation Solution

A woven non-welded mesh screen assembly with a flexible construction, utilizing stainless steel wire mesh with high open area and suitable weaves, attached via side clamps, end clamps, and fastening bolts to a support frame, allowing for self-cleaning and reduced mechanical stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional screen plates with slots or holes are used, then liquor extraction is enabled, but the open area is limited restricting flow through the screen openings

Engineering Contradiction:

Improveliquor flow rateVSAvoidopen area of screen

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The patent applies a woven mesh screen made of wire or rod material that forms a porous structure with interconnected openings. This porous construction provides significantly greater open area compared to conventional solid screen plates with discrete slots or holes, enabling enhanced liquor flow rates while maintaining effective separation of liquor from fibrous material.

Inventive Principle:

Principle #31Porous materials

2Productivity

If screen plates are used with long parallel slots, then liquor flow is improved, but chips are able to pass through the screen during chip column movement

Engineering Contradiction:

Improveliquor flow rateVSAvoidchip retention

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The woven mesh screen creates a porous barrier with interconnected openings that are too small for chips to pass through, yet large enough to allow efficient liquor flow. The mesh structure forms a continuous filtering surface that prevents chip penetration while maintaining high productivity.

Inventive Principle:

Principle #31Porous materials

3Strength

If rigid screen construction is used, then mechanical strength is improved to withstand pressure differences, but the screen becomes heavy and maintenance becomes costly

Engineering Contradiction:

Improveresistance to pressure differenceVSAvoidscreen weight

Core Design Contradiction:

StrengthVSWeight of stationary object

Solution Approach 1:

The patent employs a flexible woven mesh screen that can deform under pressure differences rather than requiring rigid construction. This flexible membrane approach maintains mechanical strength to withstand cooking pressures while significantly reducing screen weight and associated maintenance costs compared to massive rigid screen plates.

Inventive Principle:

Principle #30Flexible shells and thin films

4Productivity

If conventional screen plates are used, then liquor extraction is achieved, but scale deposits accumulate on the screen increasing limitation of open area

Engineering Contradiction:

Improveliquor flow rateVSAvoidscale deposit accumulation

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The woven mesh screen's porous structure with its interconnected openings and three-dimensional wire configuration resists scale deposit accumulation more effectively than flat screen plates. The mesh geometry prevents scale from forming continuous blocking layers, maintaining open area and liquor flow rates over extended operation periods.

Inventive Principle:

Principle #31Porous materials

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 solution enhances liquor flow, reduces clogging and maintenance time, and extends the operational period between outages by providing a lightweight, flexible, and self-cleaning screen assembly resistant to mechanical stress.

Implementation Method 1

Screens, such as screen plates, are used in conventional digesters for the production of chemical cellulose pulp, e.g. kraft pulp, for both continuous and batch digesters. Screens are filters that allow liquor to be extracted from a digester but prevent the extraction of fibrous material.

Methodology Applied

Scientific EffectPhysical filtration: Filter (physical)

Implementation Method 2

A novel screen assembly for digesters and other treatment vessels, such as impregnation and pre-hydrolysis vessels has been developed comprising a woven non-welded mesh screen. The screen assembly is formed of a plurality of screen panels, which are attached by side clamps and bolts to each other and to the support frame

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS11255046B2Screen assembly for pulp digesters and other treatment vessels in pulp production

Publication Date: 2022.02.22 ANDRITZ OY

AI summary

A screen assembly for a digester, impregnation vessel or other treatment vessel for separation of cooking liquor or treatment liquor from lignocellulosic material, typically in a form of chips, in the production of chemical cellulose pulp, which screen assembly includes a plurality of screen panels (17) of woven wire mesh cloth and attachment device configured to attach the screen panels to a support frame of the digester or vessel.