41 vertical mills_v2-0

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Vertical Roller Mills


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2Mombasa / June 2009

Vertical Roller Mills

The term Vertical Mill denotes equipment with the following

characteristics

A rotating, circular grinding table that turns around a vertical shaft

Spherical, cylindrical, tapered rollers that are pressed on to roller paths

on the surface of the table

A source of pressure on the rollers

A stream of gases flowing upwards around the table, entraining anddrying the material

A separator mounted directly on the mill housing


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Vertical Roller Mills in the TCEA zone

Very common to grind fuel (FCBmill: E type)

More and more common on Rawmeal

New on cement

France; 5

UK; 8

Spain; 4

Maroc; 5

France; 2

UK; 2

Spain; 2

Maroc; 4

Kenya; 1

Nigeria; 1

France; 1

UK; 1

Spain; 1

0

5

10

15

20

25

Fuel mill Raw Mill Cement Mill

(Project)


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Vertical Roller Millsadvantages and disadvantages

Very compact workshop

Larger feed size

Better grinding efficiency and thuspower consumption

Accept very wet material (moistureup to 20%)

Advantages Disadvantages

Investment cost

Prone to vibrations

Need a good maintenancemastery


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Mills technologies


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VRMs - Variations by supplier

Table design

Roller number and design (shape)

Ease of roller change

Roller tensioning arrangement


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The Grinding Tracks

Raymond-LM-

F

G

A

Loesche-LM-

A

F

G

Raymond-LM-

G

A

F

Pfeiffer-TG-

F

G

A

Onoda-Kobe-LM-

F

G

A

Kawasaki-LM-

F

G

A

Polysius-TG-

F

G

AFLS-LM-

A

F

G

BabcockCPAG-TG-

F

A

G



VRMs TechnologyTwo main types

Track guided Polysius

Pfeiffer (Allis Chalmers, KHD)

Babcock

Claudius Peters

Lever mounted

Loesche (Fuller-Loesche)

Kawasaki (CKP)

IHI

Raymond

OK (Onoda/Kobe - Fuller)



Polysius Design

Track GuidedCharacteristics

Rollers are held in place by the tabletrack

Hydraulics are used as springs andsome grinding pressure

Excellent on limestone. Difficulty withhard materials

High replacement due to lost track andwheel shape. Rollers wont stay in the

track



Pfeiffer MPS Design

3 rollers held by a triangular frame

Hydraulic cylinders at each corner

Low external recirculation

High internal velocity and wear

Air port design critical



FCB Design

Several balls (blue)

1 rotating table in the lower

part (brown)

1 fix table in the higher partwhich is pressed on the balls(green)



Lever Mounted - Grinding

Larger cylinders

Smaller rollers

Large linking elements requiredbetween hydraulic cylinder androller arm

Hydraulics critical

Loesche Design



Lever Mounted - Characteristics

Uses external shaft to hold roller inplace. Not dependent on trackcondition

Usually no roller to table contact

Coal mills use springs, other designuse complex hydraulics

Rollers are smaller, more emphasison hydraulics

Roller speed monitoring on latestmodels

ABB Raymond HP Coal Mill



CKP Internal

Spherical rollers

Tapered track

6 cylinders

Center feed

Scrapers to bottom

discharge

Feed

Roller

ReducerTable

Hydraulic Cylinder

Dedusting



Main flow across Vertical Mills



Operation principle

Mill feeding by the table center

Combined drying/grinding

Material travels outwards andpasses under rollers

External and Internal recirculation ofcoarse particles

Product leaves mill with gas flow



Gas flow circulation

Inlet gas can come from:

Mill outlet (re-circulated gas) Hot gas source

Cold gas source


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Materials flows: the table rejects

Go back in the millwith the fresh feed

Constitute theEXTERNAL circulating

load


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Material flows: the internal rejects

Constitute theINTERNAL

circulating load

The mill DP is animage of the internal

circulating load


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Material flows: the final product

Fines fromthe table


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Theoretic approach on the grinding

by compression applied on VM


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Action of the grinding rollers

The grinding theory is based on 2 main angles:

The nip angle:

The pressure angle:


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Grinding theory: nip and pressure angles

Depend on:

Dam ring height

Quantity of material on the table

Material propriety

Roller surface state


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Grinding theory: angle variations


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Grinding theory: angle variations


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Synthesis: and angles variations

For the same hydraulic pressure

High grinding bed (angle high) Low pressure inside the material bed

Low grinding efficiency

Pressure resultant less vertical (high angle)

Increase of the absorbed power

Leads to

High recirculation

High mill delta P

Low vibrations

Low grinding bed (angle low)

Reverse consequences on grinding efficiency and mill absorbedpower

Leads to:

Sensitive of vibrations


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Typical values for material and gas flow

Concerning material flow: Circulating loads range: from 500% - 1000%

External circulation allows reduced airflows. Spill Over Ranges from 0 to 50%, depending on manufacturer and mill

operations

Bed thickness: From 30 mm to 60 mm

Concerning gas flow

Gas speed at the ventilation ring From 40 to 90 m/s depends on the VRM supplier


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Hydraulic units


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Hydraulic circuit for grinding rollers

Equipment present in all hydraulic circuit type

1 hydraulic pomp

1 cylinder

1 or several nitrogen accumulators

Typical arrangement:

Nitrogen


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The nitrogen accumulators

Two main types:

Bladder accumulators

Piston accumulators


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Hydraulic circuit operations

PH=0

Nitrogen pressure increase

Hydraulic pressure increase

PH=P

w= 2 x P

N

Nitrogen pressure = PN

Cylinder moving dueto instability


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Nitrogen pressure and hydraulic rigidity

1st case:

PW= 100 bars PNinit= 0.8 * PW = 80 bars

2ndcase:

PW= 100 barsPNinit=0.4 * PW = 40 bars

PH= 0

PN= 80 barsVN= Vaccu= 5 liters

PH= PW = PN = 100 barsVN= V1 = 4 liters

PH= 0PN= 40 barsVN= Vaccu= 5 liters

PH= PW =PN = 100 barsVN= V1 = 2 liters

Moving of 1.3litres due toinstability

Moving of 1.3litres due toinstability

VN= V2= V11.3 liters= 2.7 litersPFinal= PH * V1 / V2 = 148 bars

VN= V2 = V11.3 liters = 0.7 litersPFinal= PH * V1 / V2 = 286 bars


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Grinding equipments wear:

Table, Rollers and Dam ring


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Typical Wear cycle

T/H

TIME

Newrollers

Rollers partlywornpeak

efficiency

Rollers need to be replaced.Grinding efficiency worsens as you lose roller

shape.

Vibration worsens


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Roller Shear Forces

m/s

From center

Synchronized speeds

Fine grinding

Crushing

Difference in surface speeds,creates shear forces that helpgrinding, BUT accelerate wear

(fine grinding zone).


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Main roller wear in the FOS /MER slag mill

-20

-15

-10

-5

0

0 100 200 300 400 500

Origin (mm) 15/10/2003 01/03/2004 24/05/2004 Limit After welding


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-20

-15

-10

-5

0

0 100 200 300 400 500

Origine (mm) Limite 14/02/2007 04/04/2007 20/06/2007 09/11/2007

Main roller wear in the BORDEAUX slag mill


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Wear patterns

QUADROPOL

EWEKORO

Fuller/Loesche


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Dam ring function and impact of its wear

Main function:

Keep the material on the table and under the rollers

Main impacts on the VM operations:

Direct impact on bed height

Acts on the absorbed power and the grinding efficiency

Acts on the mill vibrations


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Dam ring following

The dam ring is a VM key point, thus it must be followed properly

Mechanical state, continuity

Its height should be adapted to the table wear.

Objective: keep constant height between track bottom and dam ring high part.

How to follow the table wear and the dam ring height:

Regularly draw the track profile Reduce the dam height as the table wear or

Recharge the table profile regularly to keep constant the global dam ring height

a a


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1,5

2

2,5

3

3,5

4

4,5

5

6

7

8

9

10

11

12

Vibrations sparateur vertic (mm/s) KWh/T

nettoyage en

profondeur

circuit

injecteurs

2003

3.2 mm / s

20052004 2006 2007ADF Sept 03Nvle cerce 60mm

dcoupe cercepassage de 60

40mm

dcoupe cercepassage de 40

30mm

ADF Jv05

nv profiltable/galets

nvle cerce60mm

dcoupe cerce

- passage de 60 50mm dc06- puis 50 30mm ADF Jv07

mm/s kWh/t

Dam ring following: PLNRM example

Kiln shutdown10/2003

New dam ring:60 mm

Dam ring cutfrom 60 to

40mm

Dam ring cutfrom 40 to

30mm

Kiln shutdown01/2005:

- New table &rollers

- New dam ring:60 mm

Waterinjectionsystemcleaning

Dam ring cut:-12/2006: from 60 to 50mm- Kiln shutdown 01/2007: from50 to 30mm

Separator vertical vibrations (mm/s)


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Separation process in VM


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VM separation: 3 stages

1st separation: table rejectGo to the external recirculation

2ndseparation: settling in the mill body

Go back to the table

3rd

separation: separator selectionGo back to the table

Dynamic


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Types of Separators

Adjustable Blades

Ventilation+ final product

Rejects Cone

Ventilation +Final Product +

Rejects

Static Separator

Static

SeparatorVariable speed

Rejects

Rejects Cone (option)

DynamicOld design

Ventilation+ final product

Ventilation +Final Product +Rejects

DynamicNew design

Rejects

Rotating cage

Fixed blades

Gas + Rejects+ Final product

Gas + Final product


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Standard flow sheets

and control loops


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Typical flow sheet


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Gas flow circuit: key points

P

T

Constant flow throughthe separator

Gas speed throughthe ventilation ring

T

Final product

dry


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Gas flow circuit: control loops

P

T

Mill gas flow rate:controlled by the mill fan

Mill inlet pressure:controlled by the

recirculation damper

Mill outlet T; controlledby hot gas sources


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Normal Grinding

Coarse material isground under the roller.If the table material ispresented uniformly, theroller passes over the

bed smoothly.

Table rotation

Fines (and some coarse)fall over the edge of the table


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Over Loaded Table

More ungrounded material

is spilled over the edge

Causes:

-Too much feed-High internal recirculation-Not enough grinding-Speed of de-aeration

The roller tries to rideover the bed, butswims through it.Causes a lowfrequency vertical

movement.

Snow-plowingpushes at the roller,causing a twist in themill body. When itsnaps back, causesa higher frequencytorsional vibration.

As long as it is not snowplowing, a deeperbed is generally a quieter mill, BUT drawshigher kW.


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Unstable beds

Flushes create thick and thin bedzones

Irregular feed

Irregular size (fines)

Material fluidity

Poor gas control

Too much recycling makes bedtoo fine and unstable


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Material feed rate: key pointsThe three main sensors which are useful to fix the mill throughput:

Mill DP, Vibration, kWh/t

Mill DP

Vibrations Mill kWh/t


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Parameters to follow up: direct impact on performances

Periodic control ofnitrogen pressure

False airreduction

Maintain in good state thebelt height sensors, have a

proper calibration

Reduction of the gap

Between the table and theNozzle ring

Continuous control of the airflow measurement (annubar vs

exhaust fan efficiency)

Water injection

peripheral: cloggingon-line detection.Water injection ontable inconclusive

Dam ring: height

regularly controlled. Toadapt to table profile


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Main differences between grinding:Raw materials or slag compare to cement

Raw material or slag Cement

Wet material Dry material

No quality impact of water injection Quality impact of moisture

No gypsum dehydrationmanagement

gypsum dehydration management


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Conclusions

Main Advantages of Vertical Roller Mills Better grinding efficiency Better production costs (higher energy savings)

Drying capacity (up to 20%)

Quick product change (cement mills)

One single machine for drying, grinding and separation

Restrictions Maintenance

Frequent recharge of rollers (automatic)

Sensitive to vibrations Water injection, dam ring height adjustment

Few industrial references at high Blaine Slag grinding tests at 6000 Blaine

41 vertical mills_v2-0

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