Ball mill understanding & optimisation
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Transcript of Ball mill understanding & optimisation
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Grinding with Ball Mill Systems
EDM
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Ball Mill
Ball Mill
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What is a End Discharge Mill (EDM)?
Intermediate diaphragm
Mill feed arrangement
1stCompartment
(Coarse Grinding)
2stCompartment
(Fine Grinding)
Mill discharge
Air outlet
Air inlet
Gearbox with pinions
Drive
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EDM
EDM =
End Discharge Mill
Product discharge
at mill end
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Elements of Ball Mill - Overview
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Mill Drive Concepts
Single pinion concept(< 2'500 kW)
Double-pinion concept(< 5'000 kW)
Girth gear Drives
Single drive withtwo pinions
(< 5'000 kW)
Double drive withfour pinions(< 10'000 kW)
Girth gear units
Two-way power splittingreducer
(< 6'000 kW)
Planetary gear reducer(< 12'000 kW)
Central drives
Drive Concepts for
Ball mills
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Example Planetary Gear Drive
Planetary gear reducer concept MAAG
Two gear stages with three planets
All shafts with friction bearings
Pinions, planets surface-hardened
Annulus through-hardened
Annulus
Sun pinionsDrive arrangement
Planets
Gear coupling
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Gear Box Internals
Parallel shaft gear reducer (two way power branch)
Low speed gearstage
All gears surface-hardened andground
All shafts with roller bearings
Key point::
Face load distribution of the
LS-gear stage
Bearings with excentric sleeves
to optimise the face load distribution
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Potential Technical Problems Drive
Girth gear drives - Fundamental
Problems
Dynamic behaviour
A lot of individual rotating masses
risk of resonance vicinities Torsional/structural vibrations
Pinion shaft bending vibrations
1. Axial/radial runout
2. Alignment of the drive trains
3. Uneven power splitting
4. Centre distances variable
5. Face load distribution
6. Sealing of the girth gear
7. Girth gear is through hardened
only, fatigue strength is limited
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1
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5 6 7
35 2
1
4
5 6 7
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Gearboxes
Polysius Combiflex Gear reducer
Planetary Gear
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Potential Damages Drives
Breakage damage (pinions)
Cause: Inadequate transverse
load distribution, brittle material
Secondary damage:
Tooth breakage
Initial damage:
Pitting on the pitch line
Fatigue breakage
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Potential Problems Drive
Single pinion drive (2300 kW)
Breakage failure of the pinion in thegear reducer
Heavy (active) pitting on the drive
pinion
Possible Cause:
- Inadequate load distribution (1)
- Overload of the tooth flanks (2)
1
2
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Mill Bearing
Advantages slide shoe bearings:
No size and capacity limitation of themill
Simple design of wear plates
Far higher limit of gas temperature at
mill inlet (e.g. for drying with heat
generator)
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Feed Arrangements for Ball Mills
Preferred design today
(Slurry mill)
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Feed Arrangement (Example Step Feeder)
Advantages
Good mill ventilation
Easy to maintain
Simple design
Ventilation air
Material feed
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Elements of Ball MillOverview (Internals)
Mill feedarrangement Mill head Mill shell arrangement
Mill dischargedriveMill
bearingMill
Grindingmedia
Shell Intermediatering
Retention
Internalelements
elements
External
liners diaphragmDischargediaphragmliners
Head
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Overview Internal Elements
A Coarse grinding
compartment
B Intermediate
diaphragm
C Fine grinding
compartment D Discharge
diaphragm
E Grinding media
F Retention ring
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Liners for Coarse Grinding
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h0
h
h > 0.5 ho
Lifting Height Requirements (1stChamber)
This criteria has to be
confirmed case by case
through evaluation of thecoarse grinding.
Rule of thumb: h must be
greater than 50 [mm]
1st chamber lining at end of lifetime
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Classifying Liner for Fine Grinding (2ndChamber)
Rotation sense
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Intermediate Diaphragm
1stCompartment
Coarse Grinding
2ndCompartment
Fine Grinding Intermediate diaphragm
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Function of Intermediate Diaphragm
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Intermediate diaphragm
Slot opening in 1stchamber
Material flow control system
Centre screen
Grates in the second chamber
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Discharge diaphragm
Discharge diaphragm
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Discharge Diaphragm
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Life Time of Shell Liners
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Grinding in Ball Mill
Coarse grinding (1stchamber)
Cataracting of grinding media
Fine grinding (2nd chamber)
Cascading of grinding media
A
A
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Ball filling degree (f)
f [%]20 40 - 4530
75
Power[%]
85
93
98
25 35
Typical range
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Steps of Grinding
Coarse
Grinding
Medium
Grinding
Fine
Grinding
C G i di P t f O ti i i
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Coarse Grinding: Parameters for Optimising
Power parameters
Filling degree Chamber length Mill diameter
Liner design and condition Mill speed
Efficiency parameters
Ball charge (filling degree &
composition)
Liner design
Intermediate diaphragm settings Mill ventilation
G i di M di
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Grinding Media
Bulk weight of a grinding media charge in a two chamber mill with
classifiying liner
4,4 [t/m3] 4,6 [t/m3] 4,7 [t/m3]
G i di M di (1st C t t)
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Grinding Media (1stCompartment)
1.Co m p artm ent
Ball [mm] Weight [ t ] Percent [%]
90 25.0 25.0
80 35.0 35.0
70 25.0 25.0
60 15.0 15.0
Total 100.0 100
Average ball weight [ g ] 1667
Spec. media surface [m2 / t ] 10.2
Holcim Standard for 1stCompartment
G i di M di (2nd C t t)
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Grinding Media (2ndCompartment)
Holcim Standard for OPC > 3200 [cm2/g], closed circuit
system
2.Co m partm ent
Ball [mm] Weight [ t ] Percent [%]
50 20.0 10.0
40 20.0 10.0
30 32.0 16.0
25 32.0 16.0
20 42.0 21.0
17 54.0 27.0
15
Total 200.0 100
Average ball weight [ g ] 41
Spec. media surface [m2 / t] 32.8
Material Quality of Grinding Media
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Material Quality of Grinding Media
Specific Wear Rates of Grinding Media
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Specific Wear Rates of Grinding Media
Mill Efficiency
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Mill Efficiency
[%R]
acc.[cm2/g]Blaine
mill length [m]
longitudinal sieving graph
[m]
Blaine Value
Sieve Residues
Chamber 1
(coarse grinding)
Chamber 2
(fine grinding)
Lifting Liners Effects
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Lifting Liners Effects
Liner-Lifting : low high
Optimum Material Level 1st Chamber
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Optimum Material Level 1 Chamber
Optimum Material level 2nd chamber
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Optimum Material level 2 chamber
Mill Ventilation
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Mill Ventilation
Main Tasks Mill Ventilation:
Material transport Cooling
Removal of fines Fluidisation of material
Cooling and Heating Possibilities
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Cooling and Heating Possibilities
Cooling air
Cooling air
Moist additive
Hot clinker
Hot gases H2O H2O
H2O
Product
Product
Air
Dust ladden air
H2OHot gases
Fine Grinding and Mill Cooling
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Fine Grinding and Mill Cooling
SOLUTION
Adapted mill cooling,playing with:
Clinker temperature
Mill ventilation
Water injection
Use of grinding aid
(temporary solution
because expensive)
PROBLEM
Insufficient mill coolinglead to material
agglomeration on balls
and liners
The grinding is not any
more done by balls
against material but by
material against material
Water Injection Systems
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j y
80
90
100
110
120
130
Producttemp. [C]
Mill length
countercurrent
no waterinjection
co-currentAir fromblower
Air fromblower H2OH2O
H2O
H2O
1st 2nd Comp.
1st 2nd Comp.
2nd Comp.
1st Comp.
(Double)Rotary union
counter current
co-current