Fundamentals on

Grinding Workshops

GRINDING I – Training Session

 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 2

 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 3

 Fundamentals on Grinding Workshops

Why do we grind in the cement business?

• To create surface area for good chemical reactions

to occur

• Combination in the kiln (Raw grinding)

• Hydraulic reactions in the concrete (Cement grinding)

• Good combustion in the kiln flame (Coal grinding)

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 Fundamentals on Grinding Workshops

Where do we grind in the overall cement

manufacturing process

Quarry Storage Raw

Grinding

Fuel Combustion
Grinding

Storage

Cement
Grinding
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 Fundamentals on Grinding Workshops

What are the main challenges for cement

production

• Reduce power consumption

• Maximize production

• Optimize and improve product regularity

• Control maintenance costs

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 Fundamentals on Grinding Workshops

Grinding costs money

• Grinding uses approx. • Cheap power is no longer
60% of plant electricity true
60 €/MWh
Répartition des kWh dans une cimenterie

Broyage cru
40 €/MWh
19%
Autres
39%

20 €/MWh

Broyage
ciment
42% 0 €/MWh
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

• Today plant electricity bill is more important than

fuel bill
Specific power must be improved
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Fundamentals on Grinding Workshops

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 Fundamentals on Grinding Workshops

Grinding costs money

• Costs of wear parts increasing

• Joint visits between process and maintenance
departments upgrade the efficiency: wear takes place in
the process
PLN raw mill example:
• Change of iron source
• Wear before and after use
of this new raw material

• Material stays in the reject TOTAL WEAR FROM 1998 TO 01-2004

TOTAL WEAR FROM 02-2004 TO 04-2004

KUJ - July 2012 – Grinding I 9

 Fundamentals on Grinding Workshops

The different types of mill

• Three different mill types with specific purposes

• Raw mills (for slag, shale, limestone…)

• Size reduction (targeted rejects at 90 and 200µm)
• Drying the materials
• Cement mills (pure or compound cements)
• Size reduction (objectives in SSB)
• Management of gypsum dehydration
• Fuel mills (coal and pet coke)
• Size reduction (targeted rejects at 90µm)
• Drying the materials

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 Fundamentals on Grinding Workshops

Technologies and arrangements

• Different mill technologies

• Ball mills
• Air swept mill = materials released by ventilation air
• Compound mill = with end discharge
• Bi rotator mill = with central discharge
• Vertical mill
• Roller press
• Horomill
• Different architectures
• In open circuit
• In closed circuit
• With pre-grinding, hybrid grinding…

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 Fundamentals on Grinding Workshops

Origin of a current workshop

• Existing workshop design depends on

• Material feed specifications
• Feed size
• Moisture
• Outlet product specifications
• Flow rate
• Fineness target
• History of the plant and workshop

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 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 13

 Fundamentals on Grinding Workshops

The Ball Mill

KUJ - July 2012 – Grinding I 14

 Fundamentals on Grinding Workshops

The Ball Mill

• Compound with two compartments
Gas + dust
Intermediate diaphragm outlet

Outlet diaphragm
Fresh feed +
Inlet head
Separator C2 liners
Rejects C1 liners Discharge box
chute
Outlet seal

Material discharge

Fresh air inlet

Central ventilation ring

Shell

Supports

Inlet trunnion

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 Fundamentals on Grinding Workshops

The ball mill in open circuit

Fan
Dust
Collector

gas
Fresh material
Feed

Mill
Finished Product

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 Fundamentals on Grinding Workshops

The ball mill in open circuit

• Advantages
• Moderate investment costs
• Simple operation
• Simple maintenance
• Highest reliability
• Disadvantages
• little or no control of fineness
• not adapted to high fineness (possibility of overgrinding)
• broad particles size distribution
• higher temperature of products
• Limited drying capacity

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 Fundamentals on Grinding Workshops

The ball mill in closed circuit

Fan Fan
Dust Collector
Dust
Collector
Dynamic
Separator
Static
Separator

Rejects

Finished Product
Fresh
Feed
Mill Material
Gas

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 Fundamentals on Grinding Workshops

The ball mill in closed circuit

• General description
• Better regularity thanks to a real control of the fineness
• High fineness is possible
• Higher flexibility and possibility of optimisation by product
• Higher output, better efficiency
• Possibility of higher mill ventilation
• Better temperature control
• High mill ventilation
• Possibility to have a separated ventilation in the separator
• Narrow particle size distribution
• Higher investment costs

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 Fundamentals on Grinding Workshops

The Bi-rotator Mill

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 Fundamentals on Grinding Workshops

Material feed (separator rejects)

The Bi-rotator Mill
Central
discharge
Air
Material feed

Air

Grinding
chambers

Drying chamber

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 Fundamentals on Grinding Workshops

The Bi-rotator Mill in closed circuit

Material Fan
Gas
Dust Collector
Dynamic
Separator

Static
Separator
Rejects

Finished Product

Fresh
Feed
Mill

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 Fundamentals on Grinding Workshops

The Bi-rotator Mill

• Advantages
• High ventilation capacity for drying materials

• Disadvantages
• False air

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 Fundamentals on Grinding Workshops

The Air-Swept Mill Air + material

Intermediate
Material diaphragm

Air

Grinding
chamber

Drying
chamber

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 Fundamentals on Grinding Workshops

The Air-Swept Mill in closed circuit Fan

Dust Collector

Material
Dynamic
Gas
Separator

Rejects
Finished Product

Fresh
Feed
Mill

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 Fundamentals on Grinding Workshops

The Air-Swept Mill

• Advantages
• High ventilation capacity to dry materials

• Disadvantages
• High specific power consumption due to swept solution

KUJ - July 2012 – Grinding I 26

 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 27

 Fundamentals on Grinding Workshops

The Vertical Mill Fine Product

Separator
Drive

Feed Material
HE Separator

Rejects Cone

Grinding Roller

Pressure
frame
Grinding Table

Port ring
Hydraulic
tensioning
cylinder
Air or Hot Gases
Mill Drive

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 Fundamentals on Grinding Workshops

The Vertical Mill in closed circuit Hot Gas

Roller Mill Main Baghouse &
Fresh Feed Fan Vapour

Cyclone

Vent Fan
Recirculation Elevator

Product Flow 1 Product Flow 2

closed circuit

Hot Gas
Roller Mill

(Coarse Rejects) KUJ - July 2012 – Grinding I 29

 Fundamentals on Grinding Workshops

The Vertical Mill

• Advantages
• Good efficiency factor
• High drying capacity
• Combined grinder, separator and dryer in one unit
• Popular for coal and raw material grinding with high
moisture content

• Disadvantages
• Complex operation
• Reliability – maintenance costs
• Vibrations
• Management of gypsum dehydration in cement grinding

KUJ - July 2012 – Grinding I 30

 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 31

 Fundamentals on Grinding Workshops

Roller Press
feed
universal joint reducer

fixed roller

accumulators
flake

cylinders Floating roller

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 Fundamentals on Grinding Workshops

Roller Press
• Pneumatic slide choke plates on
both sides of feed hopper needed to
control intake and therefore power.

• Low reliability typical, but very

energy efficient.

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 Fundamentals on Grinding Workshops

Roller Press

• Advantages
• High efficiency factor
• Compact installation
• High production increase when used as pregrinding

• Disadvantages
• High investment costs
• Complex operation
• Reliabilty
• Limited drying capacity

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 Fundamentals on Grinding Workshops

Pregrinding with Roller Press

• Basic pregrinding
Feed
Fines

Recir-
culation

• Preground material could feed into an intermediate bin

• Approx. 30% increase of production
• Recirculation is required for pregrinder efficiency and stability

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 Fundamentals on Grinding Workshops

Pregrinding with Roller Press

• Hybrid pregrinding
Feed
Fines

Recir-
culation Reject

• Separator rejects are split (partly to ball mill and pregrinder)

• Approx. 50% increase of production
• Difficult to control
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 Fundamentals on Grinding Workshops

Pregrinding with Roller Press

• Combined pregrinding (series)
Semi-finished

Feed
Fines

• Each grinding machine has its own separator

• Up to 100% increase of production is possible

KUJ - July 2012 – Grinding I 37

 Fundamentals on Grinding Workshops

Content

• Fundamentals on grinding
• Different types of ball mills
• Vertical mills
• Roller press
• Horomill

KUJ - July 2012 – Grinding I 38

 Fundamentals on Grinding Workshops

Horomill

• General description

• Horizontal mill
• Single roller inside a motorized tube shell
• Slide shoe (thrust pad) bearings
• Girth gear and pinion drive
• Designed by FCB

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 Fundamentals on Grinding Workshops

Horomill
Scraper and feed
forward plate

roller

pinion shaft
cylinder

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 Fundamentals on Grinding Workshops

Horomill
feed vent

shell grinding track

roller
cylinder

discharge

slide shoe bearings

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 Fundamentals on Grinding Workshops

Horomill

17° nip angle

• Patented device to control

• Greatest nip angle (lowest retention time
amount of pressure) • RPM > V critical
• Virtually no shear - little • Internal recirculation results in
low vibration
wear claimed

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 Fundamentals on Grinding Workshops

Ways to upgrade a workshop

• Optimisation of workshop operations

• Ball charge design
• Ventilation balance
• Circulating load
• Increase of the ball mill speed (target of 75% Vcrit)

• Replacement of the workshop separator with a third

generation one

KUJ - July 2012 – Grinding I 43