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) 2 x Pre-grinding 100 t/h (OPC) 2 x Semi-finish grinding 270 t/h (OPC) 1 x VRM 120 t/h
Cement bag dispatching
Contact e-mail:
[email protected]
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KHD Fuller KHD Loesche (LM46.2 +2C)
Contents 1. 2. 3. 4.
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Objective of Ball mill optimization Mill performance test Air flow and diaphragm Separator performance test
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 improvement or Production improvement
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Ball mill optimization Ball mill optimization
Mill charge 1. Mill sampling test 2. Charge distribution 3. Regular top-ups
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Air flow & Diaphragm 1. Mill ventilation 2. Water injection 3. Diaphragms
Separator 1. Tromp curve 2. Separator air flow 3. Separator sealing
When: Do optimization 1. 2.
In some period (1 month, 1 Quarter, 1 Year or ???) To assess the reason/cause of disturbance
3.
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When abnormal operation Poor performance of grinding system Low mill output or poor quality product High operation or maintenance costs
Keep operation in a good efficiency
Conventional grinding system
Clinker
Gypsum Limestone
To Cement Silo
Cement Mill
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1. 2. 3. 4. 5.
Main Machine Feeding system Tube mill Dynamic separator Dedusting (BF/EP) Transport equip.
Mill charge optimization
Clinker
Gypsum Limestone
To Cement Silo
Cement Mill
8
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.
-Fine grinding
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2nd compartment
Coarse material grinding
Fine material grinding
Piece weight (or knocking weight)
Specific surface
Average weight/piece of grinding media in each compartment (g/piece) Piece weight Impact force
Average surface area of (ball) grinding media in each compartment (m2/t) Specific surface Attrition force
Need small ball size
Need large ball size 10
Ball charge composition 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)
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Ball charge composition Check piece weight and specific surface Compartment 1 Fraction (mm), d 90 80 70 60 50 40 Total #1
Charge calculation
(t) 5.0 11.0 13.6 15.3 5.6 2.5 53.0
% 9% 21% 26% 29% 11% 5% 100%
Compartment 2 Fraction
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Specific surface, Surface, O o pcs. (m2/t) (m2) 1,673 8.5 43 5,240 9.6 106 9,671 11.0 149 17,277 12.8 196 10,927 15.4 86 9,528 19.2 48 54,317 11.8 628
Weight, W weight Piece weight, I no., n (g) 2,989 2,099 1,406 886 512 262 976
Piece weight: 976 g/piece Specific surface: 11.8 m2/t
Charge calculation Specific surface, Surface, O o pcs. (m2/t) (m2) 0 15.4 0 0 19.2 0 45,170 25.6 128 749,309 30.7 1,476 1,143,35 38.4 1,441 4 2,308,58 45.2 2,102 5 4,246,41 37.6 5,147 7
Weight, W weight Piece weight, I no., n
(mm), d 50 40 30 25
(t) 0.0 0.0 5.0 48.0
% 0% 0% 4% 35%
(g) 512 262 111 64
20
37.5
27%
33
17
46.5
34%
20
Total #1
137.0
100%
32
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 **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
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B : Maximum ball size (mm.) F80 : Feed material size for 80% pass (µm) W i : Bond work index (kWh/t) C s : N/Nc (normally ~ 0.7-0.75) Sg : 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. • 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 1/2 1/2 1/3 B = 36x(13.4) x[(3x13)/(100x0.7x4 )] Maximum ball size = 86 mm.
Maximum steel ball size Maximum ball size (mm.) : Clinker Wi 13.0 kWh/t, Cs 0.7, Sg 3
Max Ball Size (mm.)
180 160 140 120 100 80 60 40 20 0
2
5
10
15
20
Feed Size (mm.), F80
** Typical fresh clinker : 5% residue 25 mm. or F80 = 13.4 mm. 15
25
30
Example Given • • • • •
Feed size = 5% res. 20 mm. Wi = 12.0 kWh/t Cs = 0.7 Sg = 3.0 t/m3 De = 2.5 m.
Find: required maximum ball size F80 Maximum ball size (mm.)
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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 5. Evaluation of test
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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 Fan drive power
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2. Air flow measurement Air flow measurement Air flow rate Temperature Static pressure
Mill ventilation air
Clinker
Gypsum Limestone
To Cement Silo
Cement Mill
19
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/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. 20
M
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 Temperature 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 ? m/sec
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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.)
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Preparation of sampling equipment Lock switch
Plastic bag
PPE
Crash stop
Meter Lighting
Shovel Meter Scoop
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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
Liner
Diaphragm
Ball charge
25
Clogging
Clean block slot
3. Crash stop and visual inspection Material level in compartment #1 and #2
M
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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
Effective length, L
Free height, h M
Inside diameter, Di
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Ball charge quantity (Filling degree)
H
De
h Ball level
h = H- (De/2)
Degree of filling (%)
60.0 50.0 40.0
30.0
N ormal range 28-32%
20.0 10.0 0.0 Meter
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0.000
0.100
0.200
0.300 h/De
0.400
0.500
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
0.5 1m 1m 1m 0.5 0.5 1m 1m 1m 1m
1.1 1.1
1.2 1.2
1.3 1.3
1.4 1.4
2.1
2.2
2.3
2.4
1m 1m 0.5
2.5
Material sampling point in mill
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Deep 20 cm.
2.6
2.7
Take sampling
0.5 1m 1m 1m 0.5 0.5 1m 1m 1m 1m
1.1 1.1
1.2 1.2
1.3 1.3
1.4 1.4
2.1
2.2
2.3
2.4
1m 1m 0.5
2.5
2.7
2.6
Front view
Side view
0.5 m.
0.5 m. 1
2
3
4
5
6
7
8
9
1 0
1
2
3
4
5
6
7
8
9
1 0
1 1
1
2
3
4
5
6
7
8
9
1 0
1 1
Take 1 sample
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Top view
1 1
•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
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 Position m. cm2/g
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16
8
4
2
1
0.50
0.20
0.09
mm
mm
mm
mm
mm
mm
mm
mm
mm
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 1 pt.1
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
0.00
0.00
2.00
19.00
pt.5
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9.5
0.5 1 2 3 4 4. 5
0. 1 2 3 4 5 6 7 8 9 9.5 5 0.5 m
Size Reduction Progress
100 90 80 70 60 50 40 30 20 10 0
2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800
0.5 m
32.000 mm 16.000 mm 8.000 mm
Blaine (cm^2/g)
% Residue on sieve
Typical grinding diagra m : OPC 3000 cm2 /g
4.000 mm 2.000 mm 1.000 mm 0.500 mm 0.200 mm 0.090 mm Blaine cm2/g
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 Length (m.) 34
Comp. 1
Comp. 2
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
35
Evaluation of mill test standard reference Size reduction along mill axis Sieve residues and Blaine value in front of the diaphragms Compartme nt
First comp.
Particle size
FLSmidth
Holderbank
Slegten
+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.)
+0.2 mm.
20-30%
20-30%
15-25% (at 0.1 mm.)
Second comp.
36
+0.5 mm.
Max 5%
Max 5%
-
Blaine (cm2/g)
-
2,100
-
Size Reduction Progress
100 90 80 70 60 50 40 30 20 10 0
2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800
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 Comp. 1
Compartm ent
First comp.
32.000 mm 16.000 mm 8.000 mm
Blaine (cm^2/g)
% Residue on sieve
Evaluation of mill test
4.000 mm 2.000 mm 1.000 mm 0.500 mm 0.200 mm 0.090 mm Blaine cm2/g
Length (m.)
Comp. 2
Particle size
FLSmidth
Holderban k
Slegten
Mill test
Result OK?
+0.5 mm.
15-25%
12-25%
-
28%
+0.6 mm.
10-20%
-
-
-
+1.0 mm.
7-14%
-
-
12.5%
+2.0 mm.
Max 4%
Max 3%
Little much coarse particle size from compartmen t1
Max 5%
(at 2.5
10.5%
mm.)
+0.2 mm.
20-30%
20-30%
15-25% (at 0.1
2%
mm.)
Second comp. 37
+0.5 mm.
Max 5%
Max 5%
-
0%
Blaine (cm2/g)
-
2,100
-
2,120
Good!
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 Clear diaphragm slot
38
Good condition liner
Broken liner
Inspection
Bad condition step liner
39
Slot blockage
Common problems! Compartment
First comp.
Second comp.
40
Liner/Diaphragm
Result
Ball charge
Over limit of particle size in front of diaphragm 1 st comp.
-Increase impact force in 1 st comp. -Revise ball charge and need larger ball size (piece weight)
-Low lifting efficiency (visual inspection) -Clean block at diaphragm (nib)
Over limit of particle size in front of diaphragm 2 nd comp.
-Wait for revise charge in 1 st comp.
-Wait for improve liner in 1 st comp.
1 st comp. OK but 2 nd 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
Operation
Mill vent.
-Feed too much (visual inspection)
-Too high velocity (check air flow)
-Feed too much (visual inspection)
-Too high velocity (check air flow)
Case mill test, CM6 STS (Aug,2008) 70.0
2500
2,314
2,058
abnormal
1,927
60.0
1,739
2000
1,807
1,626
Diaphragm
50.0
40.0
30.0
1,487
1500
1000
20.0 500 10.0
0.0
0 0
2
5.6 mm.
41
2 mm.
4
0.5 mm.
6
0.212 mm.
8
0.09 mm.
10
0.075 mm.
12
0.045 mm.
14
blaine
Blaine (cm2/g)
2,333
Diaphragm
% residue
80.0
Evaluate and correction Reference standard
Compartme Particle nt size
FLSmidth
Holderba Slegten nk
Mill test
+0.5 mm.
15-25%
12-25%
-
31%
+0.6 mm.
10-20%
-
-
-
+1.0 mm.
7-14%
-
-
-
+2.0 mm.
Max 4%
Max 3%
Result OK? Abnormal size reduction (in front of diaphragm), should clear blockage diaphragm slot
First comp.
Second comp.
42
Max 5% (at 2.5 mm.)
15-25%
23%
+0.2 mm.
20-30%
20-30%
(at 0.1 mm.)
52%
+0.5 mm.
Max 5%
Max 5%
-
51%
Blaine (cm2/g)
-
2,100
-
2,314
Abnormal size reduction (in front of diaphragm), should clear blockage diaphragm slot
Case Mill test from : VDZ congress 2009 Cement plant in Europe
• Chamber 1 : good size reduction efficiency • Chamber 2 : 45 micron shown results that grinding has stopped midway through the 2nd chamber 43
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.) 44
Separator performance test
Clinker
Gypsum Limestone
To Cement Silo
Cement Mill
45
What is separator?
• • • •
46
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
Advantage of grinding system with separator
“Maximized separator performance” “Maximized power saving” 47
Separator performance test Steps 1. Recording of related operational data 2. Air flow measurement 3. Sampling within grinding system 4. Evaluation of test
48
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 Separator fan power (kW)
49
2. Air flow measurement Air flow measurement Air flow rate Temperature Static pressure
Separator circulating air
Clinker
Gypsum Limestone
To Cement Silo
Cement Mill
50
Dynamic Separator circulating air Purpose Distribute and disperse cement dust Classify cement dust at rotor Take out fine particle from separator to be product
Separator feed (t/h)
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
Circulating air flow (m³/h)
Dust load (fine) less than 0.75-0.8 kg fine / m3 = Fine product / Circulating air
Return
51
Fine product (t/h)
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) 1
Clinker
Gypsum Limestone 3 2
To Cement Silo
Cement Mill
53
Sampling
Sampling point in process
Return (reject)
Separator feed or mill output 54
Scoop
Fine product
Sampling test Point
55
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
Particle size distribution analysis
56
Thung Song Plant Result: from “Laser analysis” -Range 1.8-350 um -Test time
