grinding technologies

Innovation and optimisationin cement grinding

Martin Schneider, Düsseldorf, Germany

CSI / TERI / ECRA Forum

New Delhi, 19/20 September 2008

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!

Grinding and its impact on quality

Cement grinding as an example:

quality parameters:

• workability

• water demand

• strength

• durability of concrete

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

Specific energy consumption of different grindingsystems

VRM (60 %)

Ball mill (100 %)

Horomill® (70 %)

HPGR (50 %)spec

ific

ener

gyco

nsum

ptio

n

specific surface

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®

Manual comminution (16th century)

from: Georg Agricola, „De Re Metallica“

Hammer mechanism (16/17th century)

from: Georg Agricola, „De Re Metallica“

Edge runner (18/19th century)

from: Johann Georg Krünitz, „Ökonomisch-technologische Encyclopädie“

Evolution of comminution technologies

F

Comminution mechanisms in differentgrinding systems

F’

FF’

F

friction

F

F

compression

vimpact

ball mill

FF F

VRM

HPGR

Comminution mechanisms in the ball mill

F’

FF’

F

friction F

F

compression

vimpact

ball mill

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

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

Potentials for ball mills

Exact adjustment of grinding media and linings to requirement

separator adjustment

���� optimisation of mill and separator

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”

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

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

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

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

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

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

Application of high pressure grinding rolls for cementgrinding

Pregrinding Semi-finish grinding Finish grinding

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

Operating principle of Horomill®

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

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

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

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

Slag grinding and properties of slag cement

Compressive strengths of theblastfurnace cements

Slag particle

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)

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!

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)

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

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

Modified horizontal roller mill

Independentadjustment ofgrinding force andthickness of grindingbed

Compression of agrinding bed withdefined thickness

Comminution bycompression

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

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)

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

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

Thank you for your attention!