grinding technologies
TRANSCRIPT
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Innovation and optimisationin cement grinding
Martin Schneider, Düsseldorf, Germany
CSI / TERI / ECRA Forum
New Delhi, 19/20 September 2008
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Electrical energy demand for cement production
• Extraction and blending 5 %
• Raw material grinding 24 %
• Raw material homogenisation 6 %
• Clinker production 22 %
• Cement grinding 38 %
• Conveying, packing, loading 5 %
100 %
total demand ~ 110 kWh/tcement
more than60 % forgrinding
processes!
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Grinding and its impact on quality
Cement grinding as an example:
quality parameters:
• workability
• water demand
• strength
• durability of concrete
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Particle size distribution in RRSB-diagram
Description of cement fineness with RRSB position parameterand slope:
1.05 to 1.1Horomill
1.0 to 1.1high pressuregrinding rolls
0.85 to 1.1vertical rollermill
0.85 to 1.1ball mill
slopegrindingsystem
example: cement from ball mill, n = 0,88
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Specific energy consumption of different grindingsystems
VRM (60 %)
Ball mill (100 %)
Horomill® (70 %)
HPGR (50 %)spec
ific
ener
gyco
nsum
ptio
n
specific surface
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Evolution of comminution technologies
Chronology:
Manual comminution
Hammer mechanism (ca. 1512)
Edge runner (ca. 1800)
Ball mill (ca. 1890)
Vertical roller mill (ca. 1930)
High pressure grinding rolls (ca. 1985)
Horomill®
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Manual comminution (16th century)
from: Georg Agricola, „De Re Metallica“
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Hammer mechanism (16/17th century)
from: Georg Agricola, „De Re Metallica“
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Edge runner (18/19th century)
from: Johann Georg Krünitz, „Ökonomisch-technologische Encyclopädie“
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Evolution of comminution technologies
F
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Comminution mechanisms in differentgrinding systems
F’
FF’
F
friction
F
F
compression
vimpact
ball mill
FF F
VRM
HPGR
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Comminution mechanisms in the ball mill
F’
FF’
F
friction F
F
compression
vimpact
ball mill
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Ball mill for dry grinding
Coarse grinding chamberLifter plate lining100 mm – 60 mm balls
Fine grinding chamberClassifying plate lining50 mm - 15 mm balls
Intermediate diaphragm
Discharge diaphragm
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Ball mill
Advantages
• combined drying and grinding
• reliable - long service life
• wide PSD
• high fineness
• good for abrasive materials
Disadvantages
• for high moistureexternal dryingnecessary
• high energy demand
• no explicit stress area
still widely used in cement plants
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Potentials for ball mills
Exact adjustment of grinding media and linings to requirement
separator adjustment
���� optimisation of mill and separator
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Grinding systems for efficient comminution
Objectives
• Lower grinding energy demand than ball mills
• Comminution to a large extent by using thecompression
• Comminution in an explicit “compression zone”
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Principle design of vertical roller mills
FF Fgrinding table
gear box
grits
grinding roller
separator
mill feed
air or hot gas
air and fines
rejects
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Vertical roller mills for raw material grinding
• Combined drying, grinding and separation
• Energy consumption 60 - 70 % comparedto a ball mill
• Moisture contents up to 25 %
• Compared to a ball mill 10 to 20 % highercapital costs
• Used in 90 % of all new plants as raw mill
• Throughput up to 840 t/h, feed size upto 200 mm
• Installed power up to 7 000 kW, grindingtable diameter up to 6 700 mm
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Vertical roller mill for cement and slag grinding
• Energy consumption:
70 % of a ball mill for cement
50 % of a ball mill for slag
• Fineness:max. 4 500 cm²/g for cement
max. 6 000 cm²/g for slag
• Moisture required for stabilising thegrinding bed – less influence oncement quality
• Low wear costs
• Throughput up to 300 t/h
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High pressure grinding rolls
Compacted cakes
Feed material
Fixed roller
Floating roller
Grindingpressure
• Defined grinding area
• Feed up to 60 mm
• Grinding pressure from50 to 400 MPa
• Compacted cakes upto 40% fines andcoarse particles
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High pressure grinding rolls – main features
• First application 1984
• Today worldwide more than600 mills in operation
• Throughput rates up to 1 300 t/h
• Grinding force from2 to 20 Mega-Newton
• Efficiency
1.8 to 3.5 times higher than ball mill
1.1 to 1.4 times higher than vertical roller mill
• cement finish grinding limited by PSD
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Example:High pressure grinding rolls for raw material grinding
• Advantages:
- Energy consumption 50 % lower than ball mill
- Extremely low roller wear (min 0.25 g/t)
• Disadvantages:
- Drying capacity is limited to 4 % feed moisture
- Application only for non-abrasive raw materials, due towear of deglomerator
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Application of high pressure grinding rolls for cementgrinding
Pregrinding Semi-finish grinding Finish grinding
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Comminution by compression: operating principles
12°
6° 18°
Horomill®
HPGR
VRMSpeed:
Limited by centrifugationof material
Bed thickness:
Medium
Speed:
Limited to 1 - 1,5 m/sbecause of vibrations
Bed thickness:
Low
Speed:
Upper value not yet known
Bed thickness:
2 to 3 times HPGR
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Operating principle of Horomill®
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Horizontal roller mill (Horomill®)
For wet materials external dryer necessary
Wear costs comparable to build-up welded high pressuregrinding rolls
Raw material grinding
• Energy consumption 50 % compared to a ball mill
Cement grinding
• Max. cement fineness 4 000 cm²/g
• Energy consumption 70 % compared to a ball mill
Slag grinding
• Max. cement fineness 4 800 cm²/g
• Energy consumption 60 % compared to a ball mill
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Technological parameters for different grinding systems
*) open - closed circuit
7050 to 6060 to 70100%specific energy
demand(closed circuit)
1.05 to 1.11.0 to 1.10.85 to 1.10.85 to 1.1 *)--RRSB slope
4 0004 0004 500> 6 000cm²/gproduct fineness
(Blaine)
Horomill®High pressuregrinding rolls
Verticalroller mill
Ball millUnitParameter
Comparison of different systems for cement grinding
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Comparison of service lives of the grinding elements from differentgrinding systems when grinding granulated blastfurnace slag
3 to 6120 to 150g/tspecific wear
partial or complete hardfacing of theworking surfaces at intervals of 2 to 3 months
3 to 6aservice life of
grinding media
hardfacedroller
surfaceshardfaced rolls
hardfaced rollers,grinding table
lining,grinding balls
--wearing parts
< 4 800> 5 500> 6 000> 6 000cm²/gproduct fineness
(Blaine)
HoromillHigh pressuregrinding rolls
Verticalroller mill
Ball millUnitParameter
Comparison of different systems for slag grinding
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Influence of grinding system on cement properties
Compressive strengthsof the B 3 000 clinkers
Phase contents of the < 20 µm fractionof the B 3 000 clinkers
Grinding the same clinker in a ball mill, a VRM and a HPGR
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Slag grinding and properties of slag cement
Compressive strengths of theblastfurnace cements
Slag particle
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0,10,1
1
1
10
10
100
100
1000
1000
10000
10000 100000
quartzlimestoneclinker
clinker
raw meal
single particle comminution
bulk comminution
spec
.siz
ere
duct
ion
ener
gy[k
Wh/
t]
particle size [µm]
Size reduction energy
Höffl, „Zerkleinerungs-und Klassiermaschinen“
Single particlecomminutionwith highestefficiency!
(target orientedstress)
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Energy utilisation of compression and impacten
ergy
utili
satio
n�
SM
/WM
[cm
²/J]
mass specific work WM [J/g]
Impact
Compression
Pahl:„Zerkleinerungstechnik“
Higher efficiencyof comminution bycompression!
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Throughput-speed-behaviour of different mill types
P/MM•
P/MM•
P/MM•
M•
M•
M•
1,0 2,0 3,00,0
1,00
~2,0
0
Spe
cific
pow
erde
man
d[k
Wh/
t]
Circumferential speed of the grinding track [m/s]
Thr
ough
put[
t/h]
oper
atin
gpo
int
Vertical roller mill
High pressure grinding rolls
Modified horizontal roller mill
• VRM: depends on grinding-table-diameter and number ofrollers
• HPGR: linear correlation onlyfor low circumferential speed ofrolls
• Modified horizontal roller mill:linear correlation also for highcircumferential speed (limit notyet known)
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Direction of new developments
Example:limestone0...6 mm
0
2
4
6
8
10
12
0,0 0,2 0,4 0,6 0,8 1,0
related grinding force
power demand
Bond index
Rel
ated
gri
nd
ing
forc
e[k
N/m
m]
Po
wer
dem
and
[kW
]
Bo
nd
ind
ex[k
Wh
/t]
Dimensionless feed throughput
limit of free dosedmaterial feeding
HPGR:
• Operation pointnot adjustable
• Independentadjustment ofgrinding force andthickness ofgrinding bed notpossible
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Objectives for future developments
• Comminution only by compression
• Compression of a grinding bed with defined thickness
• Independent adjustment of grinding force and thickness ofgrinding bed
• Low specific energy demand
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Modified horizontal roller mill
Independentadjustment ofgrinding force andthickness of grindingbed
Compression of agrinding bed withdefined thickness
Comminution bycompression
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Other comminution technologies for cement grinding?
• HEM High Energy Milling: very small particles � high reactivitymechanical activation of particles (< 2µm); tested for cementgrinding
• Ultrasonic-comminution (Patent DE 102 59 456 B4)energy-transfer by acoustic pulse; tested for slag grinding
• Plasma comminution (European Patent EP0976457)comminution in a liquid by shock waves; tested for semiconductormaterial
• Low temperature comminution (Internat. Application No.PCT/EP2007/010159)reducing particle size by rapidly reduction of energy level
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Summary (1)
Ball mill
• High energy consumption
• Reliable - long service life of the wearing parts
• Limitation in feed moisture – at high feed moisture externaldrying necessary
High pressure grinding rolls
• High energy savings
• Limitation in feed moisture – with external drying nolimitation in material moisture
• Maximum achievable fineness 4 000 cm²/g (clinker)
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Summary (2)
Vertical roller mill
• High energy savings
• Very high material moisture contents (up to 25 %) can beprocessed
• Low wear costs
• Maximum achievable fineness 4 500 Blaine for OPC
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Summary (3)
Horizontal roller mill (Horomill)
• Energy savings of 30 to 40 %
• Maximum achievable fineness 4 000 Blaine for OPC and4 800 Blaine for slag
No comminution without energy input
Highest efficiency of comminution by compression
Objectives
• Optimisation of known grinding processes necessary
• Development of new comminution processes:comminution by compression in an explicit stress area
• Comminution in one process without postrefining
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Thank you for your attention!