ball mill understanding & optimisation

8/10/2019 Ball mill understanding & optimisation

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Grinding with Ball Mill Systems

EDM


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HGRS Tikaria_Mill Workshop SEPT-07

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

5 2

1

4

5 6 7

35 2

1

4

5 6 7

3


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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

12 12


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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

ball mill understanding & optimisation

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