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7/31/2019 2 Stock Preparation & Approach System
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2010 04 / CGK 1
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
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 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
Stock preparation & approach system
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Process detail
2.1 Slushing / pulper station with auxiliaries
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
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
Stock preparation & approach system
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Process detail
2.1 Slushing / pulper station with auxiliaries
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
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