Ball Mill Optimization

Ball mill optimization

Dhaka, Bangladesh

21 March 2010

Introduction

Mr.Peramas Wajananawat

Experience: 13 Years (2 y in engineering,11 y in production)

 Engineering department  Kiln and Burning system

 Siam Cement (Ta Luang) Kiln system, Raw material grinding and Coal grinding

 Siam Cement (Lampang)  Cement grinding and Packing plant

The Siam Cement (Thung Song) Co,Ltd

Production Engineer

 Cement grinding 7 lines

 2 x Conventional mill 150 t/h (OPC) _{ KHD}

 2 x Pre-grinding 100 t/h (OPC) _{ Fuller}

 2 x Semi-finish grinding 270 t/h (OPC) _{ KHD}

 1 x VRM 120 t/h _{ Loesche (LM46.2 +2C)}

 Cement bag dispatching

Contents

1.

Objective of Ball mill optimization

2.

Mill performance test

3.

Air flow and diaphragm

Objective

1.

Audit performance of grinding system

2.

Show the key areas for optimization the ball

mill system

3.

Provide the basic information for changes or

modifications within grinding system

4.

Reduce power consumption, Quality

Ball mill optimization

Ball mill optimization

Mill charge Air flow & Diaphragm Separator

1. Mill sampling test 2. Charge distribution 3. Regular top-ups 1. Mill ventilation 2. Water injection 3. Diaphragms 1. Tromp curve

2. Separator air flow 3. Separator sealing

When: Do optimization

1. In some period (1 month, 1 Quarter, 1 Year or ???)

2. To assess the reason/cause of disturbance

 When abnormal operation

 Poor performance of grinding system

 Low mill output or poor quality product

 High operation or maintenance costs

Conventional grinding system

To Cement Silo

Cement Mill Clinker Gypsum Limestone

Main Machine 1. Feeding system 2. Tube mill 3. Dynamic separator 4. Dedusting (BF/EP) 5. Transport equip.

Mill charge optimization

To Cement Silo

Cement Mill Clinker Gypsum Limestone

What is function of mill?

M

Size reduction along the mill

-Coarse grinding  1st _compartment

Normal feed size 5% residue 25 mm. Max feed size 0.5% residue 35 mm.

Piece weight (or knocking weight)

Average weight/piece of grinding media in each compartment

(g/piece)

Piece weight Impact force

Specific surface

Average surface area of (ball)

grinding media in each compartment (m2/t)

Specific surface Attrition force

Coarse material grinding

Coarse material grinding Fine material grinding Fine material grinding

Calculation (for steel ball)



Piece weight : i = [3.143/6] x d

3

_{x 7.8 ;g/pcs.}



Specific surface : o = 123 / i

(1/3)

_{; m}

2

_/ton

Note : d = size of ball (cm)

Ball charge composition

Check piece weight and specific surface

Compartment

1 Charge calculation

Fraction Weight, W weight Piece weight, I no., n Specific surface,

o Surface, O (mm), d (t) % (g) pcs. (m2/t) (m2) 90 5.0 9% 2,989 1,673 8.5 43 80 11.0 21% 2,099 5,240 9.6 106 70 13.6 26% 1,406 9,671 11.0 149 60 15.3 29% 886 17,277 12.8 196 50 5.6 11% 512 10,927 15.4 86 40 2.5 5% 262 9,528 19.2 48 Total #1 53.0 100% 976 54,317 11.8 628 Compartment 2 Charge calculation

Fraction Weight, W weight Piece weight, I no., n Specific surface,

o Surface, O (mm), d (t) % (g) pcs. (m2/t) (m2) 50 0.0 0% 512 0 15.4 0 40 0.0 0% 262 0 19.2 0 30 5.0 4% 111 45,170 25.6 128 25 48.0 35% 64 749,309 30.7 1,476 20 37.5 27% 33 1,143,35 4 38.4 1,441 17 46.5 34% 20 2,308,58 5 45.2 2,102 4,246,41

Piece weight: 976 g/piece Specific surface: 11.8 m2/t

Piece weight: 32 g/piece Specific surface: 37.6 m2/t

Ball charge composition

General we use (Product Blaine 4,500 cm2/g) for “Conventional”

 Cpt.1 : Piece weight 1,500-1,600 g./piece

 Cpt 2 : Specific surface 30-35 m2/t

For “Pre-grinding system”  “R/P + Conventional”

 Cpt.1: PW ~1,100-1200 g/pc

 Cpt.2: SS ~35-40 m2/t

Maximum steel ball size (Bond equation)

B=36 x (F₈₀)1/2 _{x [(S}

gxWi)/(100xCsxDe1/2)]1/3

Where

 B : Maximum ball size (mm.)

 F₈₀ : Feed material size for 80% pass (µm)

 W_i: Bond work index (kW h/t)

 C_s: N/Nc (normally ~ 0.7-0.75)

 S_g: Specific gravity of raw material (t/m3)

 D_e: Effective diameter of mill (m.)

 F₈₀ = log [(0.20) size residue(mm.)]/log(%residue)

Example;

Given

• Feed size = 5% res. 25 mm.

• W_i = 13.0 kWh/t • C_s= 0.7 • S_g = 3.0 t/m3 • D_e = 4.0 m. • F₈₀ = log(0.20)25/log(0.05) • F₈₀ = 13.4 mm.

Find : Maximum ball size

B = 36x(13.4)1/2x[(3x13)/(100x0.7x41/2)]1/3 Maximum ball size = 86 mm.

Maximum steel ball size

0 20 40 60 80 100 120 140 160 180 2 5 10 15 20 25 30 M a x B a ll S iz e ( m m .) Feed Size (mm.), F80

Example

Given

• Feed size = 5% res. 20 mm.

• W_i = 12.0 kWh/t

• C_s = 0.7

• S_g = 3.0 t/m3

• D_e = 2.5 m.

Find: required maximum ball size

 F₈₀

Mill performance test

Steps

1.

Recording of related operational data

2.

Air flow measurement

3.

Crash stop and visual inspection in mill

4.

Sampling in mill

1. Recording of related operational data

Tube Mill

 Feed rate, Return, Grinding aids, Water injection, Mill drive power (kW)

Static separator

 Vane position

Mill ventilation fan

 Damper position, Air flow rate (if have instrument), Pressure

2. Air flow measurement

Air flow measurement

 Air flow rate

 Temperature

 Static pressure

To Cement Silo

Cement Mill Clinker Gypsum Limestone

Mill ventilation air

Purpose

 Forward movement of the material  retention time

 Take out fine particles and so diminish the risk of coating

 Cooling of the material in mill  Diminish coating / dehydration of gypsum

Usual ranges of ventilation:

Air speed in mill

 Open circuit : 0.8 to 1.2 m/sec

 Closed circuit : 1.2 to 1.5 m/sec

M

m/sec

**Min 0.5 m/s  tend to result inefficient over grinding and excessive heat generation with possible coating problem.

**Max > 1.4 m/s  drag particle out of mill before they have been sufficiency ground.

Agglomeration and ball coating

Cause:



Temperature too high tendency of the

material forming agglomerates/coating on

grinding media and liner plates



Grinding efficiency will be reduce

Test 2

Mill dimension



Inside diameter

3 m.



Degree of filling 28% in both compartment

Mill ventilation check



Flow 22,000 m3/h

Check Air ventilation speed in mill ?

M

3. Crash stop and visual inspection

Stable operation before crash stop

Emergency stop or Crash stop

 Tube mill / All auxiliary equipment

 Mill Ventilation

Disconnect main circuit breaker (Safety !)

Preparation of sampling equipment (shovel, scoop, plastic bag, meter, lighting etc.)

Preparation of sampling equipment

Lighting _Shovel Scoop Meter Meter Plastic bag Lock switch PPE Crash stop

3. Crash stop and visual inspection

Visual inspection

 Liner and Diaphragm condition  wear, block

 Ball size distribution along the mill  classify liner

 Water spray nozzle condition  clogging

 Foreign material ?

 Ball charge condition  agglomeration, coating

Clogging Liner

Ball charge

Diaphragm

3. Crash stop and visual inspection

Material level in compartment #1 and #2

3. Crash stop and visual inspection

Ball charge quantity (Filling degree)

Measurement by free height

 Measure average internal diameter, Di

 Measure height, h, in three different points along axis for each grinding compartment

M

Inside diameter, Di Free height, h Effective length, L

Ball charge quantity (Filling degree)

0.0 10.0 20.0 30.0 40.0 50.0 60.0 0.000 0.100 0.200 0.300 0.400 0.500 D e g re e o f fi ll in g (% ) h/De h H De Meter N ormal range 28-32% Ball level h = H- (De/2)

4. Sampling inside mill (mill test)

Sampling of material

 Take ~1 kg sample every 1 m along mill axis

 Each sample collected from 3 point in the same cross section

 Removed some balls and taken sample

 First and last sample in each compartment should be taken from 0.5 m off the wall or diaphragms

1m 0.5 0.5 0.5 1m 1m 1m 1m 1m 1m 0.5 1.1 1m 1m 1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 2.7 1.1 1.2 1.3 1.4 Deep 20 cm. Take sampling

1m 0.5 0.5 0.5 1m 1m 1m 1m 1m 1m 0.5 1.1 1m 1m 1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 2.7 1.1 1.2 1.3 1.4 Top view 1 1 1 0.5 m. 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 1 0 1 0 1 0 1 1 1 1 1 1 0.5 m. Take 1 sample

•Get total 11 collected samples along the mill

•1 kg per sample

4. Sampling inside mill (mill test) –cont.

After work inside the mill

 Calculation quantity of ball charge and filling degree

 Sample sieve analysis

 1st compartment

◊ Sieve : 16 , 10 , 6 , 2 , 1.25 , 0.5 , 0.2 mm

 2nd compartment

◊ Sieve : 1.25 , 0.5 , 0.2 , 0.12 , 0.09 , 0.06 mm., Blaine Fineness

Results: Sieve and Fineness analysis from mill test

Sample Location % residue on sieve (by weight)

Blaine 32 16 8 4 2 1 0.50 0.20 0.09 Position m. cm2/g mm mm mm mm mm mm mm mm mm Compt 1 pt.1 0.5 7.00 18.00 34.00 47.00 57.00 64.00 71.00 81.00 90.50 1.0 9.00 21.00 36.00 45.00 52.00 60.00 69.00 79.00 89.00 2.0 3.00 7.00 13.00 18.00 20.50 31.00 48.00 67.00 83.00 3.0 0.50 1.00 3.00 5.50 8.00 19.50 29.50 52.00 71.00 pt.2 4.0 0.10 3.00 5.00 7.00 8.00 10.50 22.00 46.00 65.00 pt.3 4.5 0.05 4.00 7.50 9.00 10.50 12.50 28.00 48.50 68.00 Partition ** Compt 2 pt.1 0.5 940 1.00 8.00 32.00 56.00 pt.2 1.0 1080 2.00 9.00 33.00 59.00 2.0 1260 0.50 7.00 24.00 50.00 3.0 1300 0.01 4.00 18.00 42.00 4.0 1500 0.00 1.50 12.00 39.00 5.0 1600 0.00 1.00 9.00 32.00 6.0 1700 0.00 0.50 5.00 27.00 pt.3 7.0 1880 0.00 0.22 4.00 21.00 pt.4 8.0 2000 0.00 0.01 3.00 19.50 9.0 2120 0.00 0.01 1.50 18.50

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 0 10 20 30 40 50 60 70 80 90 100 0.5 1.0 2.0 3.0 4.0 4.5 ** 0.5 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 9.5 B la in e ( cm ^2 /g ) % R e si d u e o n s ie ve

Size Reduction Progress

32.000 mm 16.000 mm 8.000 mm 4.000 mm 2.000 mm 1.000 mm 0.500 mm 0.200 mm 0.090 mm Blaine cm2/g 0.5 _{4 4.} 5 3 2 1 _0. 5 4 5 3 2 1 6 7 8 9 9.5 0.5 m 0.5 m

5. Evaluation of performance test

Grinding efficiency

 Data for evaluation

 Result from visual inspection inside tube mill

 Sample analysis from longitudinal sampling inside tube mill  Size reduction graph

Cement Mill Cement Mill

Evaluation of mill test  standard reference

Size reduction along mill axis

Sieve residues and Blaine value in front of the diaphragms

Compartme nt

Particle size FLSmidth Holderbank Slegten

First comp.

+0.5 mm. 15-25% 12-25%

-+0.6 mm. 10-20% -

-+1.0 mm. 7-14% -

-+2.0 mm. Max 4% Max 3% _{Max 5%} (at 2.5 mm.) Second comp. +0.2 mm. 20-30% 20-30% _15-25% (at 0.1 mm.) +0.5 mm. Max 5% Max 5% -Blaine (cm2/g) - 2,100

-Evaluation of mill test

Compartm ent Particle size FLSmidth _Holderban k

Slegten Mill test Result OK?

First comp. +0.5 mm. 15-25% 12-25% - 28% _{Little much} coarse particle size from compartmen t 1 +0.6 mm. 10-20% - - -+1.0 mm. 7-14% - - 12.5%

+2.0 mm. Max 4% Max 3% Max 5% (at 2.5 mm.) 10.5% Second +0.2 mm. 20-30% 20-30% 15-25% (at 0.1 mm.) 2% Good! +0.5 mm. Max 5% Max 5% - 0% 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 0 10 20 30 40 50 60 70 80 90 100 0.5 1.0 2.0 3.0 4.0 4.5 ** 0.5 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 9.5 B la in e ( c m ^2 /g ) % R e s id u e o n s ie v e Length (m.)

Size Reduction Progress

32.000 mm 16.000 mm 8.000 mm 4.000 mm 2.000 mm 1.000 mm 0.500 mm 0.200 mm 0.090 mm Blaine cm2/g Comp. 1 Comp. 2

Evaluation of mill test

Test result : provide information to

 Improvement of ball charge composition

Maximum ball size and composition

Charge composition (PW and SS)

 Modification/Replace inside grinding compartment

Liners

Diaphragms

 Operation

Mill ventilation

Bad condition step liner

Broken liner

Good condition liner

Slot blockage Inspection

Common problems!

Compartment Result Ball charge Liner/Diaphragm Operation Mill vent.

First comp. Over limit of particle size in front of diaphragm 1st_comp. -Increase impact force in 1st_comp. -Revise ball charge and need larger ball size (piece weight) -Low lifting efficiency (visual inspection) -Clean block at diaphragm (nib)

-Feed too much (visual

inspection)

-Too high velocity (check air flow)

Second comp.

Over limit of particle size in front of diaphragm 2nd_comp.

-W ait for revise charge in 1st

comp.

-W ait for improve liner in 1st_comp.

1st_{comp. OK but}

2nd_{comp.  over}

limit of particle size in front of

diaphragm

-Revise ball charge and may need to increase specific surface or Piece weight -Check ball charge distribution along the mill -Classifier liner efficiency -Clean block at diaphragm

-Feed too much (visual

inspection)

-Too high velocity (check air flow)

Case mill test, CM6 STS (Aug,2008)

1,487 1,626 1,739 1,927 1,807 2,058 2,333 _2,314 0 500 1000 1500 2000 2500 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 0 2 4 6 8 10 12 14 5.6 mm. 2 mm. 0.5 mm. 0.212 mm. 0.09 mm. 0.075 mm. 0.045 mm. blaine D ia p h ra g m D ia p h ra g m % r e si d u e B la in e ( cm 2 /g ) abnormal

Evaluate and correction

Compartme nt Particle size FLSmidth Holderba nk Slegten Mill

test Result OK?

First comp.

+0.5 mm. 15-25% 12-25% - 31%

Abnormal size reduction (in front of diaphragm),

should clear blockage diaphragm slot

+0.6 mm. 10-20% - - -

+1.0 mm. 7-14% - -

-+2.0 mm. Max 4% Max 3% _{(at 2.5 mm.)}Max 5% 23%

Second comp.

+0.2 mm. 20-30% 20-30% _{(at 0.1 mm.)}15-25% 52%

Abnormal size reduction (in front of diaphragm),

should clear blockage diaphragm slot

+0.5 mm. Max 5% Max 5% - 51%

Blaine

(cm2/g) - 2,100 - 2,314

Case Mill test from : VDZ congress 2009

Cement plant in Europe

• Chamber 1 : good size reduction efficiency

Evaluate and correction

• Average ball size in chamber 2 is too small (average 16 mm, PW 17 g.)

• Take charge distribution more coarse to increase PW and average ball size diameter (to 42 g. and 22 mm.)

Separator performance test

To Cement Silo

Cement Mill Clinker Gypsum Limestone

What is separator?

• Advantage of grinding system with separator

• Reduce the number of fine particle to be ground in mill

• Increase production capacity and Reduce mill power consumption

• Increase % of Active particle in fine particle of Cement

Separator performance test

Steps

1.

Recording of related operational data

2.

Air flow measurement

3.

Sampling within grinding system

1. Recording of related operational data

Tube Mill

 Feed rate, Return, Grinding aids, Water injection, Mill drive power (kW)

Dynamic separator

 Rotor speed, Damper/vane position

 Separator drive power (kW)

Separator circulating fan & Separator ventilation

 Flow rate (if have instrument), Damper position

2. Air flow measurement

Air flow measurement

 Air flow rate

 Temperature

 Static pressure

To Cement Silo

Cement Mill Clinker Gypsum Limestone

Dynamic Separator circulating air

Purpose

 Distribute and disperse cement dust

 Classify cement dust at rotor

 Take out fine particle from separator to be product

Usual ranges of circulating air

Depend on separator feed and production rate

 Separator load  1.8-2.5 kg feed / m3

 = Separator feed / Circulating air

 Dust load (fine)  less than 0.75-0.8 kg fine / m3

 = Fine product / Circulating air

Circulating air flow (m³/h) Separator feed (t/h) Return Fine product (t/h)

3. Sampling within grinding system

Operation period

 Determined suitable sampling point

 Stable operation

 6-12 hours duration of performance test

Sampling plan (stable operation period)

To Cement Silo

Cement Mill Clinker Gypsum Limestone

Sampling

1

2

Sampling point in process

Separator feed or mill output

Return (reject) Fine product

Sampling test

Point _{Sampling point Weight Required sieve analysis}

1 _{Separator feed  “m”} 0.5 kg PSD Laser test, Blaine (cm2/g) 2 _{Separator return  “g”} 0.5 kg PSD Laser test, Blaine (cm2/g) 3 _{Separator fine  “f”} 0.5 kg PSD Laser test, Blaine (cm2/g)

PSD analysis equipment

Thung Song Plant

Result: from “Laser analysis” -Range 1.8-350 um

Particle Size Distribution (PSD)

Rm Rf Rg

Size (um) Feed

%residue Fines %residue Rejects %residue 1 96.4 95.1 98.1 2 93.9 91.7 96.5 4 89.0 85.3 93.7 8 81.5 74.6 89.9 16 68.8 55.1 85.6 24 60.3 41.2 83.9 32 52.2 28.9 80.9 48 39.4 13.0 71.9 64 32.3 7.4 62.9 96 18.2 0.0 40.5 200 4.9 0.0 11.0 TOTAL: 636.9 492.3 814.9 0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % R e s id u e

Sieve size (um)

Meaning sieve size 32 um

 52.2% of separator feed residue on sieve size 32 um

 80.9% of reject residue on sieve size 32 um

Rm Rf Rg

Size (um) Feed

%residue Fines %residue Rejects %residue 1 96.4 95.1 98.1 2 93.9 91.7 96.5 4 89.0 85.3 93.7 8 81.5 74.6 89.9 16 68.8 55.1 85.6 24 60.3 41.2 83.9 32 52.2 28.9 80.9 48 39.4 13.0 71.9 64 32.3 7.4 62.9 96 18.2 0.0 40.5 200 4.9 0.0 11.0 TOTAL: 636.9 492.3 814.9

4. Evaluation of performance test

Separator efficiency

 Data for evaluation

 Particles size analysis of sample within grinding system

◊ - Separator feed Rm

◊ - Separator fine Rf

◊ - Separator tailing or Reject R_g

 Tromp curve or Fractional recovery

 The tromp curve shows what fraction of particles of different sizes in the feed material is going in to the coarse fraction (often called Return or Tailing)

Tromp curve

Calculation

 Circulation factor (CF)

CF = (R_f - R_g)/(R_m - R_g) where

 R_f = % residue on sieve of fine

 R_g = % residue on sieve of coarse

 R_m = % residue on sieve of feed

 In this case (size 48 um)

Tromp curve

Calculation

 Tromp value

Tromp (range d1,d2) = [(R_g1-R_g2)/(R_m1-R_m2)]x[1-(1/CF)]x100 where

Tromp (range d1,d2) : Fraction of particles size between d1 and d2

R_g = % residue on sieve of coarse (return/reject)

R_m = % residue on sieve of separator feed

 In this case

Example

Find Circulation factor (CF) of particle size 32 um and 48 um

 CF = (R_f - R_g)/(R_m - R_g)

where

 Rf= % residue on sieve of fine

 R_g= % residue on sieve of coarse

 R_m = % residue on sieve of feed

Find Tromp value of size in range 32-48 um

 Tr (d1,d2)=[(R_g1-R_g2)/(R_m1-R_m2 )]x[1-(1/CF)]x100

where

 Tromp (range d1,d2) : Fraction of particles size between d1 and d2

 Rg= % residue on sieve of coarse (return/reject)

 R_m= % residue on sieve of separator feed

Rm Rf Rg

Size (um) Feed

%residue Fines %residue Rejects %residue 1 96.4 95.1 98.1 2 93.9 91.7 96.5 4 89.0 85.3 93.7 8 81.5 74.6 89.9 16 68.8 55.1 85.6 24 60.3 41.2 83.9 32 52.2 28.9 80.9 48 39.4 13.0 71.9 64 32.3 7.4 62.9 96 18.2 0.0 40.5 200 4.9 0.0 11.0 TOTAL: 636.9 492.3 814.9

Tromp value meaning “

Tromp value (32-48 um) = 31.5%”

For separator feed size between 32-48 um = 100 % “Separator feed”

Separator

31.5% to coarse fraction “Reject/Return” 68.5% to fine fraction “Fine product”

Tromp value  Plot “Tromp curve”

Rm Rf Rg

Size (um) _%residueFeed _%residueFines _%residueRejects CF Size avg _(um) Tromp _value

1 96.4 95.1 98.1 1.76 0.5 22.9 2 93.9 91.7 96.5 1.85 1.5 29.3 4 89.0 85.3 93.7 1.79 3 25.2 8 81.5 74.6 89.9 1.82 6 22.8 16 68.8 55.1 85.6 1.82 12 15.2 24 60.3 41.2 83.9 1.81 20 8.9 32 52.2 28.9 80.9 1.81 28 16.6 48 39.4 13.0 71.9 1.81 40 31.5 64 32.3 7.4 62.9 1.81 56 56.9 96 18.2 0.0 40.5 1.82 80 71.4 200 4.9 0.0 11.0 1.80 148 98.8 TOTAL: 636.9 492.3 814.9 1.81 TOTAL:

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Plot “Tromp curve”

Particle size in range 32-48 um -31.5% go to be “Return”

-68.5% go to be “Fine product” Particle size in range 8-16 um -15.2% go to be “Return”

-84.8% go to be “Fine product” Particle size in range 2-4 um -25.2% go to be “Return”

Tromp curve of “Ideal and Actual separator”

Ideal separator

No coarse in product and No fine in return/reject

Actual separator

Have some coarse in product and Have some fine in return/reject

0 10 20 30 40 50 60 70 80 90 100 1 % r e c o v e ry t o r e t u rn ( re je c t )

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Tromp curve

d50

Cut size : d50 = 60 um

•The cut size of the separation being made is the particle size where the tromp value is 50%

•Meaning : Size 60 um has an equal chance to go either to product or to rejects

Tromp value meaning  Cut size (d50)

For separator feed size between 48-64 um = 100 % “Separator feed”

Separator

50% to coarse fraction “Reject/Return” 50% to fine fraction “Fine product”

Size ~ 60 um: equal chance to go either to product or to rejects

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Tromp curve

d75

Sharpness = d25/d75

•Sharpness = 0.38

•Steeper tromp curve, the better the separation

•Ideal separator sharpness = 1

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Tromp curve

Minimum value

Bypass = 8.9%

•Meaning : Bypass is an indication of the amount of material that essentially bypasses the separator.

•The lower the bypass, the more efficiency the separation.

Evaluation of separator performance test

Item Units Typical range Result Evaluate Circulation factor - 2-3 1.81 little less

Cut size(d50) micron depend on rotor speed _{and fineness level} 60 micron seems high

Sharpness (d25/d75) - 0.5 0.38 little less

Bypass % 5-15% 8.90% OK

Separator load kg/m3 1.8-2.5 1.7 OK

Product load kg/m3 0.75 0.6 OK

Action :

1. Increase circulation factor (CF)  Separator load has available

2. Need to increase speed of rotor (due to higher CF  coarser separator feed) 3. Tromp curve move to finer side and d50 change to be less than 60 um.

4. Bypass slightly increase

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Improvement Tromp curve

1. Improve product: Reduce cut size -Increase circulation factor to 2-3

-Increase rotor rotation speed

-%Bypass may slightly increase  OK -Check separator load and dust load ?

Result:

-Better active particle size of product -Strength improve

0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 % r e c o v e ry t o r e t u rn ( re je c t )

Sieve size (um)

Improvement Tromp curve

2. Improve production rate: Reduce %bypass

-Improve separator feed distribution -Check separator load and dust load ?

-Separator ventilation flow -Check mechanical seal or leak

-Check guide vane and rotor blade ?

Result:

-Increase production rate -Reduce power consumption

Ideal separator

Actual separator

Test result : provide information to :

Adjustment of separator settings



Circulation load



Separating air flow, fan speed ,etc

Modification inside separator



Mechanical adjustment ,etc

Mechanical seal

Dispersion plate

General separator improvement

•Separator feed chute

o 100% feed on dispersion plate

(over the rotor)  good distribution

General separator improvement

•_{Make sure symmetry feed on rotor }

good distribution

General separator improvement

•_{Adjust guide vane  good air flow}

distribution to rotor

General separator improvement

•Check rotor blade condition (wear and deform) normal classification

General separator improvement

•_{Upper and Lower seal condition  good}

classification

•_{Grinding aids  good}

Summary

Ball mill optimization

Mill charge Air flow & Diaphragm Separator

1. Mill sampling test 2. Charge distribution 3. Regular top-ups 1. Mill ventilation 2. Water injection 3. Diaphragms 1. Tromp curve

2. Separator air flow 3. Separator sealing

1. Every 6 months 2. Every 1 Year 3. 1,000 hours

1. Check and maintain 2. 1,000 hours check 3. 1,000 hours check

1. Every 3 months

2. Optimized and maintain 3. Every 3 months

Q & A

Performance test

 Mill test and Separator test

Evaluation

 Visual inspection

 Size reduction graph and Tromp curve

Improvement

 Charge composition, Operation, ect.

Results