Ball Mill Testingjune99
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Transcript of Ball Mill Testingjune99
Ball Mill TestingCement / Raw Mills
D.Baird /Sean Haseldine
OBJECTIVES
• To Establish Actual Performance Criteria
• To Identify the Problem Areas
• To resolve the Problems and Optimise the mill
Product Residues (Raw Meal)Surface Area (Blaine / L+N)
Feed Quality Clinker / Gypsum ratioClinker chemistryC3S / C2SFeed size
Monitoring mill operation“Establish the facts”
Mill Throughput Tonnes /h
Power Used kWh - Mill + Ancillaries
Temperature Degrees C
Air Flow Kg air /Kg cement
Water injection % on Feed rate
Motor power
Cos φφφφ from the motor nameplatenormally 0.85 - 0.9
Where V = Applied voltage
I = Motor current
Cos φφφφ = Motor power factor
3 = 1.732
W = x V x I x Cosφφφφ3
Effect of Gypsum, Limestone + Pozzolan On mill performance
• 1% SO3 = m2/kg Surface Area• 1% Gypsum = Production• 1% Gypsum = m2/kg Surface Area• 1% Limestone = % B.C.I Grindability • 1% Pozzolan = to % B.C.I.
Grindability
+30+5%
+12-2.5
-0.4 -0.67
Relationship between power consumption and Chemistry for two closed circuit mills
No 2 Mill SRC
Nº1 Mill (OPC)
Nº1 Mill (OPC)
Nº2 Mill (SRC)
Mill Only Kwh/t
L.S.F.
LSF
C2S
C3S
32.5 33.0 33.5
C3S
C2S
C3S
C2S
Mills under AutomaticTotal Feed
Control
Chemical effects on mill
performance
Max. T.P.H.
t.p.h.
Kwh/T
1986 1987
C2S
C3S
Min C2S
Max. C3S
Lowest cementgrindability
Highest mill output
Grindability
Axial Testing
Procedure1. 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 SAMPLESFOR EXAMPLE RESIDUES AT 2.36 mm, 1.18 mm, 300 mic. 90 mic, 45 mic.
- CAN CALCULATE SURFACE AREA IF REQUIRED
5.- MEASURE - VOLUME LOAD = CALCULATE CHARGE WEIGHT
6. - CALCULATE POWER USEDNETT kW = 0.2846 x D x A x W x N
7. - PLOT THE AXIAL GRAPH.
Taking axial samples
Sample below the surface of the material
and media
x x x x
xxx
Measure the heightabove charge in each chamber H1 +H2
H2H1
Material Flow
% V
olum
e lo
ad
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 ABOVECHARGE
D= INTERNAL DIA.
H
VOLUME LOAD FORMULAVOLUME 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)
Changes in apparent volume load due to charge expansion
H1 = Height above charge -Mill Crash Stop
Apparent Charge density Case %Volume loadt/m3
3.91 H1 Crash Stop 38%H 1 H 2
H2 = Height above charge - Mill Run Out
4.50 H2 Without Material 33%
Charge Expansion 5%
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 i.e. if VL = 30% then J = 0.3)
W = Charge weight in Tonnes
N = Mill speed in RPM
Net and Gross mill powerNormal values for the ratio Net/Gross power
0.90 Normally for old and inefficient mills0.92 Polysius Combiflex Drive0.93 Girth gear driven mill0.94 -0.95 Modern central drive mill
Unexpected values0.88 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
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.
Axial samples can help identify the problem
% Retainedon the sieve
InletOutlet
chamber 1 chamber 2
100
0
Coarse accumulation dueto nibs leaving chamber 1.
45 mic
2.36mm2.36mm
300 mic
Targets for cement mills with 6-8mm slots
Sample fineness hereExpect 20% max + 300 mic
1% + 2.36 mm (4% max)
Low reduction in 45 micron sieve residuedue to media coating and charge cushioning with chamber overfilling. Badly worn or incorrect gradings withbackmixing can have the same effect.
Coarse material accumulation
% Retained v.s.Position C em en t M ill E xam p le
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
1a 1b 1c 2a 2b 2c 3a 3b 3c 3d 3e 3f
P osition A long M ill
% R
etaine
d
19,000
9500
6700
2360
1180
600
300
150
90
+ 45
SSA v.s Position
P lot of SSA (m 2/kg) V .s. position along m ill
0.00
100.00
200.00
300.00
400.00
1a 1b 1c 2a 2b 2c 3a 3b 3c 3d 3e 3f
P osition
SSA(m
2/kg)
S S A
INSPECTION POINTS
LINING PLATESWATER INJECTION
AIR OUTLET
PRODUCTDIAPHRAGMS
GRINDINGMEDIA
FRESH AIR INLET
SEALS
(SIZES - SAMPLES -CONDITION) (SLOT SIZES - AVAILABLE SLOT AREA- VENTILATION GRID)
Sampling closed circuit mills
Fresh Feed
Separator rejects
Mill Product (Separator feed)
SeparatorFines
Finished Product
Filter Product
CEMENT MILL - AIR FLOW TESTSMEASURED AIRFLOW= 200 m³/min
TEMP 50 ºC
MILL EXIT = 115ºC
TO ELEVATOR
TOTAL FREE VOLUMEABOVE CHARGE = 40 m³
APPARENT AIR CHANGES/MIN = 200 = 540
(TARGET 2 - 3 OPEN CIRCUIT 5 - 7 CLOSED CIRCUIT)( 0.25 0.4 KG AIR/KG CEMENT )
COLD AIR20ºC
FRESH FEED ANDSEPARATOR REJECTS
FALSE AIR INLEAK
ACTUAL -FROM HEAT AND MASS BALANCE
= 1 · 5AIR CHANGES !!!!!
MEASURED AIRFLOW= 200 m³/min
TEMP 50 ºCFRESH FEED ANDSEPARATOR REJECTS
COLD AIR20ºC
30% OF TOTALAIRFLOW
COLD AIR20ºC MILL EXIT = 115ºC
TOTAL FREE VOLUMEABOVE CHARGE = 40 m³
APPARENT AIR CHANGES/MIN = 200 = 540
(TARGET 2 - 3 OPEN CIRCUIT 5 - 7 CLOSED CIRCUIT)( 0.25 0.4 KG AIR/KG CEMENT )
TO ELEVATOR
CEMENT MILL - AIR FLOW TESTS
MILL TESTING EXAMPLEor
Your Time To Think• A Closed Circuit Cement Mill has
recently been overhauled with new internals.
• Output is up by 15% and you are promoted to Works Director.
• After 6 months, output drops by 25%.
• What will YOU do to avoid being demoted to Tea Boy?Your Boss hears about
the 20% drop in output !
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, R-R Slope.• Mill Ventilation flow at mill inlet and
filter, Inleaking air, Water Injection rates.• Ancillary plant limitations, B/Elevator etc.• Separator inspection, Efficiency, Bypass.MILL AXIAL SAMPLING TEST AND FULL
INTERNAL INSPECTION
Worn diaphragm
Media Blockage
1st ChamberLining
Worn Chamber Lining