This document discusses tests that can be performed on ball mills for cement production to optimize performance. Key tests include axial sampling along the mill to analyze material fineness at different points, measuring power consumption, air flows, and material sampling at various points in the circuit. Issues like media coating, blockages, and ventilation can be identified. Maintaining proper media gradings, slot sizes, and chamber lengths is important for efficient grinding. Regular monitoring and mill internals inspections are needed to establish baseline performance and identify potential problems.

1. cement performance international

2. Cement Mill Testing

3. OBJECTIVES
BALL MILL TESTING
To describe some of the tests which can be carried
out on ball mills
in order to :
* Establish actual performance criteria
* Identify problem areas
* Resolve these problems and optimise the mill
This almost always requires a series of tests over a
period of time

4. Cement Mills at del Valle and
Colclinker
• Higher power consumption than expected
• Del Valle – on same product mill 8 more efficient
than mill 9, although line 8 in poor condition.
• Del Valle – product residues are high for a high
efficiency separator
• Del Valle – chamber 1 mill 8 is 7.52kWh/t, mill 9 is
15kWh/t
• Colclinker- all mills should have spare power
capacity
• Colclinker – chamber 1 power kWh/t – mill A 10.92,
mill B 10.22, mill C 11.16

5. Typical ball mill circuit with high efficiency separator
MILL FAN DAMPER
LIMESTONE RATIO CONTROL

6. Cement
Separator/Fan
Weigh
feeders
Mill Internals
Mill Fan Mill Dust filter
To storage
Elevator/Airslid
es
Potential Problem Areas
Main filter

7. Chemical effects
on mill
performance
Max. T.P.H.
t.p.h.
Kwh/T
1986 1987
C2S
C3S
Min C2S
Max. C3S
Lowest cement
grindability
Highest mill output
Grindability

8. Monitoring mill operation
“Establish the facts”
2.- Power Used Kwh -Mill + Ancillaries
3.- Product Residues
Surface area (Blaine/L+N)
4.- Feed quality Clinker/Gypsum ratio
Clinker chemistry
C3S/C2S
Feed size
5.- Temperature Degrees C
6.-Air flow Kg air/kg cement
7.- Water injection % on feed rate
1.- Mill throughput tonnes/h

9. With mill in operation
• Material samples from circuit
– Mill product
– Mill separator product
– Classifier feed
– Classifier fines
– Classifier coarse
– Final product

10. With mill in operation
• Air flows around circuit
– Mill inlet
– Mill outlet (before filter)
– Filter outlet
– Separator inlet
– Separator outlet
– Separator filter outlet
– Separator re-cycle (where it exists)

11. With mill in operation
• Other
– Mill only power consumption (kW)
– Mill circuit power consumption (kW)
– Mill feed rate (tph)
– Recycle rate from classifier to mill (tph)
– Temperatures around circuit

12. Motor power
Cos  from the motor nameplate
normally 0.85 - 0.9
Where V = Applied voltage
I = Motor current
Cos  = Motor power factor
3 = 1.732
W = x V x I x Cos
3

13. Ready to go into the mill
• Doors off –
– Stop
– Look from the door into the mill
– Record your first impressions
– Material levels
– Ball distribution
– Coating
– Diaphragm
– Obvious moisture

14. Axial Testing

15. 1. Powder loading level
2. Axial samples
3. Height above charge
4. Mill internal dimensions
5. Diaphragm dimensions and condition
6. Lining dimensions and condition
7. Inlet dimensions
8. Media size and distribution
Inside A Typical Two Chamber Cement Mill

16. INSPECTION POINTS
LINING PLATES
WATER INJECTION
AIR OUTLET
PRODUCT
DIAPHRAGMS
GRINDING
MEDIA
FRESH AIR INLET
SEALS
(SIZES - SAMPLES -CONDITION)
(SLOT SIZES - AVAILABLE SLOT AREA
- VENTILATION GRID)

17. Axial sample test
1.- OBSERVE STABLE MILL OPERATION BEFORE THE TEST.
MEASURE POWER CONSUMPTION AND PRODUCTION.
TAKE SAMPLES OF FEED AND PRODUCT.
TAKE SEPARATOR AND MILL CIRCUIT SAMPLES
2.- STOP BOTH MILL AND FEED SIMULTANEOUSLY.
3.- TAKE AXIAL SAMPLES (ALONG THE LENGTH OF THE MILL)
4.- DETERMINE FINENESS OF THE SAMPLES
FOR EXAMPLE RESIDUES AT 2.36 mm, 300 mic. 90 mic, 45 mic.
- CAN CALCULATE SURFACE AREA IF REQUIRED
5.- MEASURE - VOLUME LOAD = CALCULATE CHARGE WEIGHT
6. - CALCULATE POWER USED
NETT KW = 0.2846 x D x A x W x N)
7. - PLOT THE AXIAL GRAPH.

18. SSA vs. Position
Plot of SSA(m2/kg) V.s. position along mill
0.00
100.00
200.00
300.00
400.00
1a 1b 1c 2a 2b 2c 3a 3b 3c 3d 3e 3f
Position
SSA(m2/kg)
SSA

19. Axial samples can help identify the problem
% Retained
on the sieve
Inlet
Outlet
chamber 1 chamber 2
100
0
45 mic
2.36mm
2.36mm
300 mic
1.18mm
150mic
And as chamber 2
300micron
150micron
90micron
45 micron

20. Low reduction in 45 micron sieve residue
due to media coating and charge cushioning
with chamber overfilling.
Badly worn or incorrect gradings with
backmixing can have the same effect.
Axial samples can help identify the problem
Coarse material accumulation
% Retained
on the sieve
Inlet
Coarse accumulation due
to nibs leaving chamber 1.
Outlet
Targets for cement
mills with 6-8mm slots
Sample fineness here
Expect 20% max + 300 mic
1% + 2.36 mm (4% max)
chamber 1 chamber 2
100
0
45 mic
2.36mm
2.36mm
300 mic

21. Taking axial samples
Sample below the
surface of the material
and media Measure the height
above charge in each
chamber H1 +H2
x x x x
x
x
x
H2
H1

22. RATIO H/D
Ball mill volume load estimation
50
45
40
35
30
25
20
15
10
5
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85
H=HEIGHT ABOVE
CHARGE
D= INTERNAL DIA.
H

23. Volume Load Formula
% Volume Load =
400/PI*((0.25*Cos(2*(H/D-0.5)))
-((H/D-0.5)*((H/D-(H/D)^2)^0.5)))
H = HEIGHT ABOVE CHARGE (M)
D = MILL INTERNAL DIAMETER INSIDE LINING (M)

24. Changes in apparent volume load
due to charge expansion
H1 = Height above charge -Mill Crash Stop
H2 = Height above charge - Mill Run Out
Apparent Charge density Case %Volume load
t/m3
3.91 H1 Crash Stop 38%
H 1 H 2
4.50 H2 Without Material 33%
Charge Expansion 5%

25. Mill power calculation
- DAWN Formula
NETT KW = 0.2846 DAWN
Where D
= Internal Diameter of Mill
A = 1.073 - J
(Where J = Fractional Volume Load ie if VL = 30% then J = 0.3)
W = Charge weight in Tonnes from volume load and media
density (4.3 to 4.5)
N = Mill speed in RPM
Gross Power
The ratio of net to gross power is normally :-

26. Net and Gross mill power
Normal values for the ratio Net/Gross power
0.90 Normally for old and inefficient mills
0.92 Polysius Combiflex Drive
0.93 Girth gear driven mill
0.94 -0.95 Modern central drive mill
Unexpected values
0.88 High power losses possibly due to mill
chambers running empty.
0.97 - 1.00 Low power losses possibly due to charge
expansion and/or build up of clinker nibs.
If unexpected values occur : review the mill data

27. Media Blockage

28. Worn diaphragm

29. CHAMBER LENGTHS
Chamber 1 Chamber 2
CLOSED 28 -34 % 72 - 66 %
CHAMBER LENGTHS DEPEND UPON THE MILL
SPEED,THE INTERNAL DESIGN AND THE TARGET
SSA OF THE CEMENTS PRODUCED.

30. First Chamber Length-
Guidelines
28 % FIRST CHAMBER LENGTH.
• CEMENT S.S.A= 350 - 400 m2/kg
• MILL % CRITICAL SPEED = 75 - 78 %
• CLINKER SIZE FINE - 30 mm
• STEP LINER - STEP DISTANCE = 75 mm
34 % FIRST CHAMBER LENGTH
• CEMENT S.S.A=280 - 300 m2/kg.
• MILL % CRITICAL SPEED = 70 - 72 %
• CLINKER SIZE COARSE - 50 mm Plus
• STEP LINER - STEP DISTANCE = 50 mm (Change Design)
General :- Chamber 1 uses 9 to 11 Kwh/tonne Cement

31. Diaphragm Slot
Sizes And Areas
SLOT
SIZE MM
SLOT
AREA %
OPEN CIRCUIT
Chamber 1 to 2 6 mm 4-5 %
Chamber 2 to 3 7 mm 5-6 %
Outlet 8 mm 6-7%
CLOSED CIRCUIT-
UK
Intermediate
Outlet
CLOSED CIRCUIT-
USA
Intermediate
Outlet
6 mm
8 mm
6-8 mm
8-10 mm
5-6 %
6-8 %
Max >6 %
Max>8%
6
NOTE:-SLOT AREAS DO NOT INCLUDE VENT GRID AREA

32. Media Grading
• First Chamber requires crushing action
• Larger clinker needs larger balls
• Second Chamber finer grinding
• Optimum ball charge for clinker size reduction
– Must not restrict material flow through mill

33. MEDIA GRADINGS-CHAMBER 1
BALL SIZE
MM
COARSE
GRADING %
FINE
GRADING %
90 36.5 23
80 29.5 32
70 24 20
60 10 25
COARSE GRADING SUITS COARSE CLINKER,
SLOWER MILL SPEEDS,SHORTER CHAMBER 1,
HARD CLINKER ETC

34. UK MILLS- GRADINGS
CHAMBER 2 MEDIA
BALL
SIZE
MM
OPEN
CIRCUIT
MILLS %
CLOSED
CIRCUIT
MILLS %
30 - 25 20 30
20 20 30
17 – 15 60 40

35. Comparison of ball gradings
Chamber 1 Chamber 2
Ball
size
mm
% of effective mill length - % of charge
Blue Circle
(Current)
120
100
80
60
40
20
0
Base curve
(FLS)
Blue Circle
(Historical)
Old FLS
Blue circle
historical
current

36. Target levels for material fineness before the
intermediate diaphragm
Sieve size % Cumulative
Residue
2.36 mm 1 %
1.18 mm 6 %
300 um 20%
Basis - sieve about 0.5 - 1 Kg of material if
there are clinker nibs present.

37. CEMENT MILL - AIR FLOW TESTS
MEASURED AIRFLOW
= 200 m³/min
TEMP = 50 ºC
MILL EXIT = 115ºC
TO ELEVATOR
TOTAL FREE VOLUME
ABOVE CHARGE = 40 m³
APPARENT AIR CHANGES/MIN = 200 = 5
40
(TARGET 3 - 5 for OPEN CIRCUIT)
COLD AIR
20ºC
FRESH FEED AND
SEPARATOR REJECTS

38. INLEAKING
AIR
140 m3/min
FROM HEAT AND MASS BALANCE
ACTUALAIR CHANGES = 1·5 !!!!!
FRESH FEED AND
SEPARATOR REJECTS
COLD AIR
20ºC
MILL EXIT = 115ºC
TOTAL FREE VOLUME
ABOVE CHARGE = 40 m³
TO ELEVATOR
CEMENT MILL - AIR FLOW TESTS
MEASURED AIRFLOW
= 200 m³/min
TEMP = 50 ºC
30% OF TOTAL
AIRFLOW

39. Mill ventilation
Recommended airflow for mill ventilation
Circuit Open Closed
Air changes / min 3 5
Kg air / Kg Cement 0.25 0.4
Actual operating airflow may be lower - consider Mill Heat
Balance/clinker temperature/mill exit temperature/gypsum etc
False Air inleak
1.- Estimate the inleaking air by comparing temperatures at the mill
outlet and the filter outlet. Also measure airflow at the mill inlet by
anemometer and compare with the filter outlet flow.
2.- A typical inleak level over a filter system on a new mill is about =
30% of the flow passing through the mill.

40. PSD ROSIN-RAMMLER SLOPES
AT 350 M2
Kg-1
R – R
SLOPE
45mmRESIDUE
Open circuit 1.00 – 1.10 10 – 15
Conventional Closed Circuit 1.05 – 1.12 8 – 12
Med. Efficiency Closed Circuit 1.10 - .15 7 – 10
High Efficiency Closed Circuit > 1.2 < 6

41. Checklist-Look for Changes in:-
• Cement Grindability, chemistry, SO3,
Free lime, C2S, C3S, Gypsum, MAC %.
• Mill Absorbed Power, Kw per chamber.
• Mill Internals Inspection, Media size
grading, Liners -type/condition,
Diaphragm slot sizes/areas + % blockage.
• Powder levels, degree of coating, charge
expansion.
• Cement-Residue, SSA, SO3
• Mill Ventilation flow at mill inlet and
filter, Inleaking air, Water Injection rates.
• Ancillary plant limitations, B/Elevator etc.
MILLAXIAL SAMPLING TEST AND FULL
INTERNAL INSPECTION

42. cement performance international