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7/27/2019 verticalrawmill-pradeepkumar-130515030859-phpapp02

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Vertical raw mill

K.P.PRADEEP KUMAR

Sr G M OperationKarikkali Works

Chettinad Cements Ltd


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The principle of vertical mill

resembles like ammi kallu, attaankallu,

Or ennai chekku vandi


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History of grinding technology


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GrindingSeparation

DryingConveying

Four functions in one machine makesVRM a compact grinding system

Functions of Roller Mill


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Vertical mill


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General Design


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material to air ratio

,0.5 0.6 kgs/m3


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Vertical mills of various suppliers Loesche

mill

Raymond mil FLS Atox mill

Gebr Pfeiffer , MPS

Krupp Polysius

Williams mill

CP Mill (claudius Peters)

Babcock E ring mill


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Raw mills of different designers


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Investigation of the feed material

Different materials are characterized by

high resistance to grinding

severe abrasiveness

in homogeneous grindability , moisture content and grain sizes

tendency not to form a stable bed , so that the material leaves

the grinding bowl prematurely

I ti ti f th f d t i l


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High resistant to grinding - coal below 45 hard groove or petcoke

- lime stone above 9 kwh/t at 12% on 90

microns- clinker

Flowabity - poor drawing in behavior - poor bed formation properties

- tendency for quartz accumulation on

grinding bowl

Combination of different - low and high grindability

properties - moist and dry

- coarse and fine fractions

Abrasiveness - high quartz content,particularly above 90

microns particles

- pyrites- felspars

- shelly lime stone

Investigation of the feed material

3.2 How does a vertical mil work?


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The raw materials are fed directly to the centre of the grinding plate,which, thanks to

centrifugal forces and the pushing effect of the incoming materials themselves (both fresh

and separator coarse material), are distributed evenly under the grinding rollers. The turning

speed of the grinding plate, together with the pressure of the grinding rollers, create thenecessary friction for grinding the materials. After being ground, the material is transported to

the dynamic separator by the (more or less hot) gas flow, where the selection of the material

takes place.

The gas flow, besides transporting the material, performs other important tasks:

First material selection; the coarse particles tend to fall back on thegrinding plate.

Thermal exchange; more efficient compared to tubular ball mills,

thanks to the complete mix of gases and materials.

The coarse material coming from the separator is directed back to the

centre of the grinding plate in order to be ground again.

The grinding process starts with the preparation of the so-called grinding

bed, where the coarse material is crushed. Then the material in compressed

and ground by the grinding rollers. For a stable grinding procedure the

following parameters are important: The vibrations of the grinding plate.

The P of the grinding system.

The height of the grinding bed

(formed by a small border on the grinding plate).

The pressure of the grinding rollers.The speed of the grinding plate.


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P.GUNASEKARAN

MECHANICAL FOREMAN.


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Common aspects of operation with regard to the grinding process

and generally exhibits the following characteristics.

Compression is the main mechanism of size reduction , although some

elements of attrition , shear and impact will be present

Grinding takes place selectively, with most of the initial grinding action applied

to the larger particles at the start of the process .Then progressively with the

time the mill starts to ac on the mass of smaller particles resulting from the

reduction of the larger , more friable ones

The resistance of the rollers to motion through the product decreases as the

material bed becomes shallower .Consequently , the power absorbed by the

grinder decreases with the decrease of the crushed flow and vice versa.

The effective grinding in the mill depends on many parameters . Important

among them are area , gripping angle, nip angle, maximum grinding pressure ,grinding bed thickness between grinding surfaces , rolling friction factor -


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Grinding theory of vertical roller mill

Grinding in roller mill is effected by shear and compaction.

The effective grinding In the mill depends on many parameters .

Important among them area : the gripping angle , nip angle,

maximum grinding pressure , grinding bed thickness between the

Grinding surfaces , rolling friction factor-

Gripping angle(ligament angle)

It is the angle between the surface of roller and table. The

material throughput Between the grinding surfaces is determined

by the maximum angle. From the diagram it Is understood that

the increase in the gripping angle will result in a Thicker bed .

But the maximum gripping angle is limited by the internal friction

and the Stability of the material.

C i ti P i R ll Mill


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Comminution Process in Roller Mills


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Material Track

Grinding Action in Roller Mill


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Grinding Action in Roller Mill


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Multiple point contacts by particles on a particle: inter particle


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Multiple point contacts by particles on a particle: inter particle

comminution

C i ti P i R ll Mill


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Comminution Process in Roller Mills


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The raw materials are fed directly to the centre of the grinding plate,which,

thanks to centrifugal forces and the pushing effect of the incoming materialsthemselves (both fresh and separator coarse material), are distributed evenlyunder the grinding rollers. The turning speed of thegrinding plate, together with the pressure of the grinding rollers, create the

necessary friction for grinding the materials. After being ground, the material istransported to the dynamic separator by the (more or less hot) gas flow, wherethe selection of the material takes place.The gas flow, besides transporting the material, performs other importanttasks:

First material selection; the coarse particles tend to fall back on the grinding plate

Thermal exchange; more efficient compared to tubular ball mills,

thanks to the complete mix of gases and materials. The coarse material comingfrom the separator is directed back to the centre of the grinding plate in order to beground again. The grinding process starts with the preparation of the so- calledgrinding bed, where the coarse material is crushed. Then the material in

compressed and ground by the grinding rollers. For a stable grinding procedure thefollowing parameters are important:


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The material , which flows over the damn ring is caught by the

vertical gas flow from the nozzle ring and lifeted up. Coarse

particles fall back to the grinding table and Finer ones are sweptup to the separator for being classified. The internal circulation

Rate depends mainly on the grindability of the ground material

and can amount up to 15 to 25 cycles.

Reducing the gas speed in the nozzle ring adjustment of the open Arealeads ti falling through of larger particles. The fall through material has to be

Extracted with scrapers and mechanically recirculated to the mill feed.

SeparationThe use of modern separators in roller mils is state of the art.

A sharp separation Improves the rawmeal quality and avoids

Over grinding ( saving of energy). Coarse Tailings , fed through the

tailings cone to the center of the grinding table, helps theFormation of a more stable grinding bed. The raw meal fineness

is easily controlled By the adjustment of the cage rotor speed.


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Friction factor : t affects the material movement on the table.Material with low Friction factor tends to have high radial

velocity in relation with the table speed and has The backward

sliding tendency. So certain amount of material falling on the

table flows To the table edge without passing under the roller.

The increases with increasing pressure;However thecapacity of the mill does not grow in proportional to the

pressure. So it is economical if we design a slightly larger mill

with lower Specific pressure that allows a less strained designand an longer life Of the machinery instead of sizing a mill with

high grinding pressure.

The amount of material passing between the grinding surfacesis The product of grinding bed thickness , roller width , roller

diameter And the density of the pressed material. For a certain

roller speed and material and material , the capacity of the

roller mill is directly Proportional to the grinding thickness.

Power taken by the mill


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Power taken by the mill

The power taken up by the vertical roller mill is given\

by the following expression

N =( I. .KT .DR .W.Dm. .n ) / 60 K W

Where ,I = no.of rollers

= friction factor (0.07-0.14 for raw materials , 0.09-0.1 for coal

T = specific roller pressure , kN/m2

(400 800 for raw and coal)DR = roller diameter , m

W = roller width , m

Dm = mean diameter of the track , m

N = table speed , rpm

For a given mill design, the expression reduces to

N = (constant) .m .KT.Do 2.5


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Roller Specific


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Roller Specific

force curve


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2 1 ti l ll ill ib ti i t l


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2.1 vertical roller mill vibration is too large:

(1) Feed uneven, when the mixture into the vertical roller millover the powder, the vertical roller mill's loading rate, leading to

the vertical roller mill on the thin material, and even disc direct

contact with the roller,resulting in mechanical milling; when into

the vertical roller mill multimaterial mixture materials for the

block, the resulting pressure grinding roll instability, resulting in

mechanical milling. The solution is to stabilize

the particle size of materials into the vertical roller mill, theappropriate adjustment of feed rate or reduce the grinding

pressure, the assurance required under the premise of the

fineness of materials, appropriate to reduce the classifier speed.

(2) Metal piece into the vertical roller mill, check the metal

detectors

Controlling Vibrations


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Controlling VibrationsKnow the vibration limit and optimum grinding bed thickness for your

mill

Have reliable, calibrated bed depth monitorsAdjust the mill dam ring height to compensate for table wear

Match grinding pressure to mill throughput establish relationship

between feedrate and hydraulic pressure. Consider control loop beddepth vs hydraulic pressure

Maintain an even bed, avoid big stones in mill, avoid excessive fines

in mill feed, avoid uncontrolled feed variations, even distribution of

material to each of the rollers, feed to the centre of the table,

adjustment of feed chute and or use of guide vanes (ploughs)

Apply stable water spray to the control bed, normally fed to the feed

side of each roller, check flow consistency on each sprayKnow the critical level of gasflow and pressure drop for your mill

Maintain stable mill gasflow to keep internal circulation consistent

apply automatic control loop

Avoid magnetic and non-magnetic objects entering mill


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1 Operation points


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1.Operation points

1.1 Stable Beds: to maintain stability and bed material, which is

grinding roller grinding bed basis, the normal operation of the

key. Material thickness can be adjusted to adjust the height of

retaining ring material, a suitable thickness and their

relationship with the correspondence between the verticalroller mill output should be in the debugging stage of the first

to find out. Lower fuel layer thick grinding efficiency, material

layer is too thin will cause vibration. Such as roll up,then finepowder generated much thinner material layer; roll reduction,

disc material thicker, more appropriate to return the materials,

material layer thickening. vertical roller mill speed increase,increase in internal circulation, material layer thickness,

reducing the wind speed, reducing the inner loop, material

layer thinning. Under normal operation by the vertical roller

mill feed roller bed thickness after compaction should not be

less than 40 ~ 50ram.

1 2 Cont ol of g inding p ess e


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1.2 Control of grinding pressure:

The pressure is affecting the grinding mill output,power mill grinding efficiency and the main factor. vertical rollermill is to impose by means of the material bed crushing pressure

and the pressure to increase production increased, but reacheda certain critical value does not change, the pressure increasefollowed by a increase in power, resulting in unit powerconsumption increase, so the appropriate roll to production andenergy consumption both. This value depends on materialproperties, particle size and volume of feed. In the testproduction grinding to find the right pressure and wind pressure

can form a reasonable good internal circulation, so that thematerial layer disc proper, stable, high grinding efficiency. In theproduction process, when the wind area of a certain ring, the

wind speed from the wind decide. Production capacity with thecorrespondence between, to ensure the grinding effect.


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1.2 Control of grinding pressure: the pressure is affecting thegrinding mill out put,power mill grinding efficiency and the

main factor. vertical roller mill is to impose by means of thematerial bed crushing pressure and the pressure toincrease production increased, but reached a certain critical

value does not change, the pressure increase followed by aincrease in power, resulting in unit power consumptionincrease, so the appropriate roll to production and energy

consumption both. This value depends on material properties,particle size and volume of feed. In the test productiongrinding to find the right pressure and wind pressure canform a reasonable good internal circulation, so that the

material layer disc proper, stable, high grinding efficiency. Inthe production process, when the wind area of a certain ring,the wind speed from the wind decide. Production capacity

with the correspondence between, to ensure the grindingeffect.

1 3 Th t f th i di t t ti l ll


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1.3 The guarantee of the grinding temperature: vertical rollermill is drying and grinding system, the ground temperature is a

measure of whether the normal drying operation comprehensiveindex. In order to ensure good drying of raw materials, thegrinding of materials is less than 0.5% moisture, the general

control of mill outlet temperature at 90 ~ C or so. If thetemperature is too low then finished water, causing the efficiencyof grinding efficiency and reduce the separator, dust collectionsystem may cause condensation; If too high, humidity isnot enough that gas cooling, dust collection will also affect theresults.

2. Exception handling


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p g

2.1 vertical roller mill vibration is too large:

(1) Feed uneven, when the mixture into the vertical roller mill

over the powder, the vertical roller mill's loading rate, leading

to the vertical roller mill on the thin material, and even discdirect contact with the roller, resulting in mechanical milling;

when into the vertical roller mill multimaterial mixture materials

for the block, the resulting pressure grinding roll instability,resulting in mechanical milling. The solution is to stabilize

the particle size of materials into the vertical roller mill, the

appropriate adjustment of feed rate or reduce the grinding

pressure, the assurance required under the premise of the

fineness of materials, appropriate to reduce the classifier

speed.

(2) Metal piece into the vertical roller mill, check the metaldetectors


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Static separators: Produce wide psd, fineness adjustment by


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vanes cause high P and poor efficiency

Conventional rotor type: Fineness adjustment by rotor speed,wide psd, low P, tailings fall spread over grinding table

Cage rotor with guide vanes: Operate with high air speed (4.5-6

m/s), produce narrow psd steep slope R200/R90 = 0.02-0.05


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Air drag

Centrifugal force

Generated by rotor cage

Gravitational force

Function of classifier


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Air drag

Gravitational force

Centrifugal force

Stationary vanes

Rotary cage

15 18 m/s

5 m/s

Classifier


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Classifier

S t Cl ifi


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Separator or Classifier


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Loeshe mill separator inlet stationary vanes


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If product has more coarse then classifier seal needs inspection


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and rectification. Production drops drastically.

Classifier rotor seal


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100% Ideal separatorGround material to separator


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1000 500 400 100 90 80 70 60 50 40 30 20 mic

rejects

80

60

30

10

100%

80

60

30

10

1000 500 400 100 90 80 70 60 50 40 30 20mic

1000 500 400 100 90 80 70 60 50 40 30 20mic

Sharpness = d75 / d 25

Value =0.8 0.85 is a very

Efficient classifier

Size fraction

By pass fraction


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Mill exit velocity = 10 m/s

Cage rotor with guide vanes:

Operate ith high air speed (4 5 6 m/s)


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Nozzle ring velocity

45 60 m/s

velocity above roller

V = 1.5 Do to 2.5 Do

Velocity through rotor

vanes = 5.0 m/s

Grinding bed thickness = 1 - 2 % of Do

For cement grinding = 0.2 % of Do

Mill Dp = 350 Do m

Operate with high air speed (4.5-6 m/s),

produce narrow psd

steep slope R200/R90 = 0.02-0.05

operating rpm , N = 56 / Do

5 6 m/s


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Counter measures in wear parts


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p


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Atox mill dimensions and characteristics


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Foster wheeler energy company


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Innovation and patented


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Innovation and patented


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Thank you for your kind attention

K.P.Pradeep Kumar

Sr G.M.OperationKarikkali works

Chettinad cements Ltd

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