Ball Mill Audit and Optimization

8/20/2019 Ball Mill Audit and Optimization

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Ball mill optimization

Dhaka, Bangladesh

21 March 2010

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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

Contact e-mail: [email protected]

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Contents

1. Objective of Ball mill optimization

2. Mill performance test

3. Air flow and diaphragm

4. Separator performance test

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Objective

1. Audit performance of grinding system

2. Show the key areas for optimization the ball

mill system3. Provide the basic information for changes or

modifications within grinding system

4. Reduce power consumption, Qualityimprovement or Production improvement

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5


Mill charge Air flow & Diaphragm Separator

1.Mill sampling test2. Charge distribution3.Regular top-ups

1.Mill ventilation2. Water injection3.Diaphragms

1.Tromp curve2.Separator air flow3.Separator sealing


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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

3. Keep operation in a good efficiency

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Conventional grinding system

To Cement Silo

Cement Mill

Clinker Gypsum Limestone

Main Machine

1. Feeding system2. Tube mill

3. Dynamic separator4. Dedusting (BF/EP)

5. Transport equip.

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Mill charge optimization

To Cement Silo

Cement Mill


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What is function of mill?

9

M

Size reduction along the mill-Coarse grinding 1st compartmentNormal feed size 5% residue 25 mm.

Max feed size 0.5% residue 35 mm.-Fine grinding 2nd compartment


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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

10

Coarse material grindingCoarse material grinding Fine material grindingFine material grinding

Need large ball size

Need small ball size


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Calculation (for steel ball)

Piece weight : i = [3.143/6] x d3

x 7.8 ;g/pcs.Specific surface : o = 123 / i (1/3) ; m2 /ton

Note : d = size of ball (cm)

Ball charge composition

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Check piece weight and specific surface

Compartment1

Charge calculation

Fraction Weight, W weight Piece weight, I no., nSpecific surface,

oSurface, O

(mm), d (t) % (g) pcs. (m2/t) (m2)90 5.0 9% 2,989 1,673 8.5 4380 11.0 21% 2,099 5,240 9.6 10670 13.6 26% 1,406 9,671 11.0 14960 15.3 29% 886 17,277 12.8 196

50 5.6 11% 512 10,927 15.4 8640 2.5 5% 262 9,528 19.2 48

Total #1 53.0 100% 976 54,317 11.8 628

Compartment2

Charge calculation

Fraction Weight, W weight Piece weight, I no., nSpecific surface,

oSurface, O

(mm), d (t) % (g) pcs. (m2/t) (m2)50 0.0 0% 512 0 15.4 0

40 0.0 0% 262 0 19.2 030 5.0 4% 111 45,170 25.6 12825 48.0 35% 64 749,309 30.7 1,476

20 37.5 27% 331,143,35

438.4 1,441

17 46.5 34% 202,308,58

545.2 2,102

Total #1 137.0 100% 324,246,41

737.6 5,147

Piece weight: 976 g/pieceSpecific surface: 11.8 m2/t

Piece weight: 32 g/piece

Specific surface: 37.6 m2/t

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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

**depend on product fineness!!

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Maximum steel ball size (Bond equation)

B=36 x (F80)1/2 x [(SgxWi)/(100xCsxDe1/2)]

1/3

Where

B : Maximum ball size (mm.)

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

W i : Bond work index (kWh/t) Cs : N/Nc (normally ~ 0.7-0.75)

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

De : Effective diameter of mill (m.)

F80 = log [(0.20)size residue(mm.)

]/log(%residue)

Example;

Given

• Feed size = 5% res. 25 mm.

• Wi = 13.0 kWh/t

• Cs = 0.7• Sg = 3.0 t/m

3

• De = 4.0 m.

• F80 = log(0.20)25 /log(0.05)

• F80

= 13.4 mm.

Find : Maximum ball size

B = 36x(13.4)1/2

x[(3x13)/(100x0.7x41/2

)]1/3

Maximum ball size = 86 mm.

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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 l l S i z e ( m m

. )

Feed Size (mm.), F80

Maximum ball size (mm.) : Clinker Wi 13.0 kWh/t, Cs 0.7, Sg 3

** Typical fresh clinker : 5% residue 25 mm. or F80 = 13.4 mm.

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Example

Given• Feed size = 5% res. 20 mm.

• Wi = 12.0 kWh/t

• Cs = 0.7• Sg = 3.0 t/m

3

• De = 2.5 m.

Find: required maximum ball size

F80

Maximum ball size (mm.)

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Mill performance testSteps

1. Recording of related operational data

2. Air flow measurement

3. Crash stop and visual inspection in mill

4. Sampling in mill

5. Evaluation of test

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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 Fan drive power

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Air flow measurement Air flow rate

Temperature

Static pressure

To Cement Silo

Cement Mil l

Cl inker Gypsum Limestone

19

Mill ventilation air


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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 / dehydrationof 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

20

Mm/sec

**Min 0.5 m/s tend to result inefficient over grinding and excessiveheat generation with possible coating problem.**Max > 1.4 m/s drag particle out of mill before they have beensufficiency ground.


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Agglomeration and ball coating

Cause:

Temperature too high tendency of thematerial forming agglomerates/coating ongrinding media and liner plates

Grinding efficiency will be reduceTemperature outlet mill range 110-120 C.

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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 ?

22

Mm/sec


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3. Crash stop and visual inspection

Stable operation before crash stop

Emergency stop or Crash stop Tube mill / A ll auxiliary equipment

Mill Ventilation

Disconnect main circuit breaker (Safety !)

Preparation of sampling equipment (shovel, scoop, plastic bag, meter,

lighting etc.)

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Preparation of sampling equipment

Lighting Shovel

Scoop

Meter

Meter

Plastic bagLock switch

PPE

Crash stop

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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

Clean block slot

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Material level in compartment #1 and #2

M

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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

Effect ive length, L

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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 r e e o f f i l l i n g

( % )

h/De

h

HDe

Meter

Normal range 28-32%

Ball level

h = H- (De /2)

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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 takenfrom 0.5 m off the wall or diaphragms

1m 0.5 0.50.5 1m 1m 1m 1m 1m 0.51m

1.1

1m 1m

1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 2.71.1 1.2 1.3 1.4

Deep 20 cm.

Take sampling Material sampling point in mill

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1m 0.5 0.50.5 1m 1m 1m 1m 1m 0.51m

1.1

1m 1m

1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 2.71.1 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

10

10

10

11

11

11

0.5 m.

Take 1 sample

•Get total 11 collectedsamples along the mill•1 kg per sample

Side view Front view

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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

Plot size reduction chart (graph)

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Sieve test equipment

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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 t.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

t.2 4.0 0.10 3.00 5.00 7.00 8.00 10.50 22.00 46.00 65.00

t.3 4.5 0.05 4.00 7.50 9.00 10.50 12.50 28.00 48.50 68.00

artition **

Compt 2 t.1 0.5 940 1.00 8.00 32.00 56.00

t.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

t.3 7.0 1880 0.00 0.22 4.00 21.00

t.4 8.0 2000 0.00 0.01 3.00 19.50

9.0 2120 0.00 0.01 1.50 18.50

t.5 9.5 0.00 0.00 2.00 19.00

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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 l a i n e ( c m ^ 2

/ g )

% R

e s i d u e o n s i e v e

Length (m.)

Size Reduction Progress32.000 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

0.5 4 4.

5

321 0.

5

4 5321 6 9.5987

0.5 m 0.5 mTypical grinding diagram : OPC 3000 cm2 /g

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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 MillCement Mill

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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 2.5mm.)

Second comp.

+0.2 mm. 20-30% 20-30% 15-25% (at 0.1mm.)

+0.5 mm. Max 5% Max 5% -

Blaine(cm2/g)

- 2,100 -

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Evaluation of mill test

Compartment

Particlesize

FLSmidth Holderbank

Slegten Mill test Result OK?

First comp.

+0.5 mm. 15-25% 12-25% - 28% Little muchcoarse

particle sizefrom

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%

Secondcomp.

+0.2 mm. 20-30% 20-30% 15-25% (at 0.1mm.)

2%

Good!+0.5 mm. Max 5% Max 5% - 0%

Blaine

(cm2/g)

- 2,100 - 2,120

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 l a i n e ( c m ^ 2 / g )

% R

e s i d u e o n s i e v e

Length (m.)

Size Reduction Progress32.000 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

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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

OperationMill ventilation

Clear diaphragm slot

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39

Bad condition step liner

Broken liner

Good condition liner

Slot blockage

Inspection


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Common problems!

Compartment Result Ball charge Liner/Diaphragm Operation Mill vent.

First comp.

Over limit of particle size in

front of diaphragm1st comp.

-Increase impactforce in 1st comp.

-Revise ballcharge and need

larger ball size(piece weight)

-Low lift ingefficiency (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.

-Wait for revisecharge in 1st

comp.

-Wait for improveliner in 1st comp.

1st comp. OK but2nd comp. over

limit of particle sizein front of

diaphragm

-Revise ballcharge and may

need to increasespecific surface

or Piece weight

-Check ballcharge

distribut ion alongthe mill

-Classifier linerefficiency-Clean block at

diaphragm

-Feed too much(visual

inspection)

-Too high velocity(check air flow)

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Case mill test, CM6 STS (Aug,2008)

1,4871,626

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 i a p h r a g m

D i a p h r a g m

% r

e s i d u e

B l a i n e ( c m 2 / g )

abnormal

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Evaluate and correction

ompartment

Particlesize

FLSmidthHolderba

nk Slegten

Milltest

Result OK?

First comp.

+0.5 mm. 15-25% 12-25% - 31% Abnormal size reduction(in front of diaphragm),

should clear blockagediaphragm slot

+0.6 mm. 10-20% - - -

+1.0 mm. 7-14% - - -

+2.0 mm. Max 4% Max 3%Max 5%

(at 2.5 mm.)23%

Secondcomp.

+0.2 mm. 20-30% 20-30%15-25%

(at 0.1 mm.) 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

Reference standard

42

C Mill f VDZ 2009


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Case Mill test from : VDZ congress 2009

43

Cement plant in Europe

• Chamber 1 : good size reduction efficiency• Chamber 2 : 45 micron shown results that grinding hasstopped midway through the 2nd chamber

E l t d ti


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Evaluate and correction

44

• 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 ballsize diameter (to 42 g. and 22 mm.)

S t f t t


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Separator performance test

To Cement Silo

Cement Mill


45

Wh t i t ?


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What is separator?

46

• Advantage of grinding systemwith 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

Advantage of grinding system with separator


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Advantage of grinding system with separator

47

“Maximized separator performance” “Maximized power saving”

Separator performance test


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Separator performance testSteps



3. Sampling within grinding system

4. Evaluation of test

48

1 Recording of related operational data


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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

Separator fan power (kW)

49

2 Air flow measurement


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Air flow measurement Air flow rate

Temperature

Static pressure

To Cement Silo

Cement Mil l

Cl inker Gypsum Limestone

Separator circulating air

50

Dynamic Separator circulating air


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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 airDepend 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

51

3 Sampling within grinding system


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3. Sampling within grinding system

Operation period Determined suitable sampling point

Stable operation

6-12 hours duration of performance test Taking samples every ~1 hour

52

Sampling plan (stable operation period)


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Sampling plan (stable operation period)

To Cement Silo

Cement Mill


Sampling

1

2

3

53

Sampling point in process


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Sampling point in process

Separator feedor mill output

Return (reject) Fine product

Scoop

54

Sampling test


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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)

55

PSD analysis equipment


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PSD analysis equipment

Particle size distribution analysis

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ThungSong PlantResult: from “Laser analysis” -Range 1.8-350 um

-Test time


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( )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 40.5200 4.9 0.0 11.0

TOTAL: 636.9 492.3 814.9

% % %

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Meaning sieve size 32 um 52.2% of separator feed

residue on sieve size 32 um

80.9% of reject residue onsieve 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 40.5200 4.9 0.0 11.0

TOTAL: 636.9 492.3 814.9

59

4. Evaluation of performance test


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Separator efficiency Data for evaluation

Particles size analysis of sample within grinding system◊ - Separator feed R m

◊- Separator fine R f

◊ - 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) Separator specific loads / Dust Load

60

Tromp curve


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p

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)

Circulation Factor = 1.81

61

Tromp curve


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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

Tromp value (32-48 um) = 31.5%

62

Example Find Circulation factor (CF) of


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Find Circulation factor (CF) of

particle size 32 um and 48 um 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

Find Tromp value of size in range32-48 um Tr (d1,d2)=[(R g1-R g2)/(R m1-R m2)]x[1-

(1/CF)]x100

where Tromp (range d1,d2) : Fract ion of particles size

between d1 and d2

R g= % 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 40.5200 4.9 0.0 11.0

TOTAL: 636.9 492.3 814.9

63

Tromp value meaning “Tromp value (32-48 um) = 31.5%”


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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”

64

Tromp value Plot “Tromp curve”


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65

Rm Rf Rg

Size (um) Feed

%residue Fines

%residue Rejects

%residue CF

Size avg(um)

Trompvalue

1 96.4 95.1 98.1 1.76 0.5 22.9

2 93.9 91.7 96.5 1.85 1.5 29.34 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 8.932 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:

Plot “Tromp curve”


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Sieve size (um)

Particle size in range 32-48 um-31.5% go to be “Return” -68.5% go to be “Fine product”



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Tromp curve of “Ideal and Actual separator”


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Ideal separatorNo coarse in product and No fine in

return/reject

Actual separator

Have some coarse in product and Have

some fine in return/reject

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Ideal separator Actual separator

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Tromp curve


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Sieve size (um)

d50

Cut size : d50 = 60 um•The cut size of the separationbeing made is the particle sizewhere the tromp value is 50%•Meaning : Size 60 um has anequal chance to go either toproduct or to rejects

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Tromp value meaning Cut size (d50)


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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 goeither to product or to rejects

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Tromp curve


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Sieve size (um)

d75

Sharpness = d25/d75•Sharpness = 0.38•Steeper tromp curve, the betterthe separation

•Ideal separator sharpness = 1

d25

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Tromp curve


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Sieve size (um)

Minimum value

Bypass = 8.9%•Meaning : Bypass is anindication of the amount ofmaterial that essentiallybypasses the separator.•The lower the bypass, the moreefficiency the separation.

•3rd generation bypass < 15%

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Evaluation of separator performance test


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Item Units Typical range Result Evaluate

Circulation factor - 2-3 1.81 little less

Cut size(d50) microndepend 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 available2. 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 increase5. Power consumption of mill went down.

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Improvement Tromp curve


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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


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Improvement Tromp curve


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e c o v e r y t o r e t u r n ( r e j e c t )

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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


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General separator improvement


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•Separator feed chuteo 100% feed on dispersion plate(over the rotor) good distribution

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Feed point and dispersion plate



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•Make sure symmetry feed on rotor good distribution

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KHD “Sepmaster” and Fuller “O-Sepa”



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• Adjust guide vane good air flowdistribution to rotor

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Guide vane



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•Check rotor blade condition (wear anddeform) normal classification

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Rotor blade condition



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•Upper and Lower seal condition goodclassification•Grinding aids goodclassification/reduce bypass

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Summary


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Mill charge Air flow & Diaphragm Separator

1.Mill sampling test

2. Charge distribution3.Regular top-ups

1.Mill ventilation

2. Water injection3.Diaphragms

1.Tromp curve

2.Separator air flow3.Separator sealing

1. Every 6 months

2. Every 1 Year3. 1,000 hours

1. Check and maintain

2. 1,000 hours check 3. 1,000 hours check

1. Every 3 months

2. Optimized and maintain3. Every 3 months

Q & A


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Performance test Mill test and Separator test

Evaluation

Visual inspection Size reduction graph and Tromp curve

Improvement

Charge composition, Operation, ect.

Results Energy saving, Quality improvement

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Ball Mill Audit and Optimization

Documents

Transcript of Ball Mill Audit and Optimization