2 stock preparation & approach system

7/31/2019 2 Stock Preparation & Approach System

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Stock preparation & approach system

Process detail

2.1 Slushing / pulper station with auxiliaries

2.2 Screening and cleaning2.3 Fractionation

2.4 Flotation

2.5 Dispersion2.6 Refining

2.7 Stock mixing

2.8 Approach system


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Coarse screen

Virgin fiber

Recycle fiber


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Stock line coarse screeningTasks

To remove coarse impurities

Separates coarse particles such as grit, sand and wires

Increases the lifetime of refining fillings


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Stock line coarse screening

Requirements

To remove impurities with minimized fiber loss

High-consistency range up to 5 % Low installation cost

Compact machine size due to feed consistency up to 5 %

Low operation cost Low energy consumption

Low basket cost as the rotating basket is protected from

heavy particles by centrifugal force Low fiber loss due to low and controllable reject rate


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Stock line process

coarse screenas option to HC Cleaner


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Coarse screen

Virgin fiber

Recycle fiber


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Coarse screenApplications

Coarse screening must handle a variable load of sand,

glass, staples and other wearing impurities

The best solution for coarse screening is rotating baskettechnology with continuous reject removal.

When heavy loads of wearing impurities are expected,the inclusion of a medium-consistency cleaner system is

recommended in order to protect the tailing coarsescreen from wear.


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Coarse screen

Requirements Mild screening

Avoid impurity disintegration

If the screening conditions on the surface of screenbasket are harsh, the soft stickies may be forcedthrough the slot

High runnability Wide operation range Protect subsequent process stages

Low operating costs Energy efficient and low maintenance requirements High system operation consistency

Low installation costs


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Coarse screening system


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Coarse screening

Overview


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Coarse screening

Rotating screen basket

MPDU I 2034 298-02

Feed

Accept

RejectJunk


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Coarse screening

Light reject removal


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Coarse screening

Intermediate centrifugal cleaning

HC Cleaner

1= Feed

2= Accept

3= Reject

4= Flushing water- upper; stops rotation- lower; fills trap andlifts suspension limitto glass tube

5= Exhaust

45

12

3

4


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Fine screen


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Particle size and contaminant removal efficiency

Distribution ofcontaminantsin pulper

Efficiency ofcontaminantremoval

Number ofparticles

Particle size( Microns )

0.1 1 10 100 1,000 10,000

0.1 1 10 100 1,000 ( 1 mm ) 10,000 ( 1 cm )

Hydrophilic nature

Hydrophobic nature

Specific gravity

CleaningStiffness size

Washing

Flotation Screening


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Screen operational philosophy

Cleanliness

Capacity


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Consistency limits for screening of pulp

0

5

10

15

20

0 1 2 3 4

Pulp Consistency %

m/s,

kW/l

Passing Speed m/s

Fluidization energy

kW/l


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Conventional screen Feed

Accept

Reject

MPDUI2200

610-0

2


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Ideal screen Feed

Accept

Reject


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The factors influence production capacity

and cleanliness efficiency

Screen area :Higher total system screen area : higher production capacityor higher cleanliness efficiency

Screen opening area :Dependence on type & size of opening ; higher screenopening area : higher production capacity

Rotor linear speed :Higher linear speed : higher production capacity, higherenergy consumption, higher reject thickening effect, too low

linear speed might caused screen basket plugging problem

Pulse frequency :Effect on screen cleanliness efficiency

Screen profile


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Screen basket profile angle

Controlled boundary layer fluidization


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Flow pattern in screen bars


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Effect of profile angle and slot width on

cleanliness efficiency

Same profile angle1, 0.1mm slot cleanliness efficiency > 0.15mm slot

While1>2, 0.15mm slot cleanliness efficiency > 0.1mm slot

This is due to boundary layer fluidization


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Effect of screen basket slot width on

cleanliness efficiency for sticky removal


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Different cleanliness efficiencies of hard and soft

stickies depending on specific flow through screen


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Effect of mean screen through velocity

on removal of stickies


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Effect of slot width on reject thickening factor

At same through velocity


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Effect of mean screen through velocity on

reject thickening factor


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Cleanliness efficiency vs thickening factor with

different slot width in same screen


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Change of size spectrum of stickies influenced

by screening stages


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Effect of screen basket slot width on reject

thickening factor of different stages


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Screen mechanism

Improve specific loading capacity

Improve cleanliness

Avoid thickening

Reduce specific energy consumption


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Screen capacity

Screen area

Screen opening area

- Slot / Hole size

- Bar / Pitch width

- Conventional slotted screen basket

( slot opening length / blank length )

Rotor linear speed

Pulse frequency


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Screen capacity

Gap between leading edge of rotor foil and basket

- Narrow gap higher pulse ?

- Narrow gap higher capacity ?

Shape of bar surface

Stock consistency

Power input


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Screen efficiency

Cleanliness of screened pulp

Reject ratio Infeed pulp cleanliness

- Dirt size, dimension, amount, distribution Slot size, hole diameter Through put speed Pulp consistency acceptance Differential pressure Risk of dirt dispersion

- Gap, power input, consistency


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Screen efficiency

Efficiency vs reject ratio


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Screen efficiency

Efficiency vs through put speed


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Screen operational philosophy

Slot sizevs

Cleanliness


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Relative sizes


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Fractionation vs barrier separation

P b bilit f j ti ti l h di i i


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Probability of rejecting particles whose dimensions isone, two or all three dimensions are smaller than

screen perforations vs screen contact frequency


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Mass balance and definitions in a separation

system


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Definition in a separation system


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Key points dimensioning screen

Screen area- Specific loading capacity

Screen opening area Slot / hole dimension

Through put speed

Reject ratio Consistency - acceptance


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Fine screening system


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Multistage low-consistency fine-screening

system


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Cleaning plant



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Process detail


2.2 Screening and cleaning

2.3 Fractionation

2.4 Flotation

2.5 Dispersion

2.6 Refining

2.7 Stock mixing

2.8 Approach system


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Separation diagram

Separation diagram for debris long fibers and


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Separation diagram for debris, long fibers and

short fibers

The differences between screening and


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The differences between screening and

fractionation goals

Fractionation


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Fractionation

Requirement

One or two-stage fractionation

Narrow slots and high reject rate give clean accept( short and medium fiber fractions )

High fractionation degree, CSF SF/LF >250 ml

Modified for fractionation ( high reject flow )

Fractionation


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Fractionation

What should happen in successful fractionation

Difference in cleanliness

Difference in fiber properties

Difference in consistency

Fractionation


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Fractionation

Fractionation efficiency

Fractionation


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Fractionation

Fractionation efficiency

Fractionation


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Fractionation

How many fractionation stagesTwo stage

Improved pulp quality

Higher reject rate

screening stage

Wide operatingwindow

Higher investmentcost

Single stage

Standard pulp quality

Lower mass reject

rate Needs more control

Lower investment cost

Fractionation


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2-stage

Quality

RRm

Single2-stage

F ti ti


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Fractionation

Coarsescreening

Short fiberstoring

Long fiberscreening

DW-pump

CsWpump

Fractionator 1R R Fractionator 2



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Process detail



2.3 Fractionation

2.4 Flotation

2.5 Dispersion

2.6 Refining

2.7 Stock mixing

2.8 Approach system

Flotation


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Tasks and requirements

Tasks:

To remove ink

To remove stickies and other hydrofobic particles, e.g.fillers, coating components

Requirements:

Minimum fiber losses

Minimum specific energy consumption

Easy operation and maintenance of the system

Optimization tools

Flotation cell


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Flotation cell

Flotation cell is based on basic physical phenomenon

- The difference in pulp density between the aeration and

separation sectors of the flotation cell

Fl t ti ll


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Flotation cell

The performance of flotation cell

( with given raw material and specific chemistry )

- depends on the optimization of pulp aeration

air removal and reject removal

Flotation


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Pressurized air

Previous stage

N e x t S t a g e

R

DW-Pump

Pressurized air

DW-pump

Previous stage Next stage

System

Primary stageSecondary

stage

Flotation


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Key parameters

Control of key parameters of flotation:

Air-to-pulp ratio Average bubble size

Reject properties



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Process detail



2.3 Fractionation

2.4 Flotation

2.5 Dispersion

2.6 Refining

2.7 Stock mixing

2.8 Approach system

Dispersion


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Target of dispersion result

75 - 85 % Reduction in visible ink specks 90 - 100 % Reduction in macro hotmelts

10 - 20 % Improvement in pulp strength

Dispersion plant form 1949


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p p


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Target of dispersion


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Target of dispersion

1. Reduction in speck size

2. Freeing of inks from fibers

3. Dispersion of hotmelts and stickies

4. Homogenous pulp

5. Development of pulp properties

Dispersion Plant


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Overview

Dispersion


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Temperature

Impurity

Bitumen

Waxs

Hotmelts

Inks

Newsprint ink

UV-Varnishes

Softening temperature

100 - 110oC

85 - 110o

C

85 - 100o

C

85 - 120o

C

85 - 90o

C

85 - 120o C

Dispersion


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5-10%

30%

80-120oC

0-100kPa

4-8%

Dilution water( in pressurized modenot necessary )

Steam

1-5%

Dispersion at atmospheric / pressurized

2 stock preparation & approach system

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