WELCOME TO

LECTURE ON PROCESS FOR NONPROCESS

ENGINEERS

K.P.Pradeep kumar

Cement is a substance (often a ceramic) that by a chemical reaction binds particulates aggregates into a cohesive structure.( hydraulic binder). The quality of raw material is the main pointin maintaining of quality of cement. The mineral compoundscontaining the main components of cement: lime, silica, alumina and iron oxide are used in cement manufacturing process. Therefore it is usually necessary to select a measured mixture of a high lime component with a component which is lower in lime, containing however more silica, alumina and iron oxide(clay component). The purpose of calculating the composition of the raw mix is to determine the quantitative proportions of the raw components, in order to give the clinker the desired chemical and mineralogical composition

What is cement ?

In 1824, Joseph Aspdin, a British stone mason, obtained a patent for a cement he produced in his kitchen. The inventor heated a mixture of finely ground limestone and clay in his kitchen stove and ground the mixture into a powder create a hydraulic cement-one that hardens with the addition of water.Aspdin named the product portland cement because it resembled a stone quarried on the Isle of Portland off the British Coast. With this invention, Aspdin laid the foundation for today's portland cement industry

History of Cement

Manufacture of cement has a history, which traces back to millennia. The Romans who were prolific builders used burnt calcareous (calcium bearing) rocks along with pozzolanic materials in an era Before Christ. The structures built by them, like the Pantheon, are still there for us to see proving the goodness of cementitious materials as input material for construction. The Roman called it as Opus cementum and pozzalana as Pozzolui. Post industrialization and as infrastructure development started globally, demands for cement have been growing steadily both quantitatively & qualitatively.

BackgroundAlthough the use of cements (both hydraulic and non-hydraulic) goes back many thousands of years (to ancient Egyptian times at least), the first occurrence of portlandcement" came about in the 19th century. In 1824, Joseph Aspdin, a Leeds mason took out a patent on a hydraulic cement that he coined "Portland" cement (1824) He named the cement because it produced a concrete that resembled the color of the natural limestone Quarried on the Isle of Portland, a peninsula in the English Channel Since then, the name "portland cement" has stuck and is written in all lower case because it is now recognized as a trade name for a type of material and not a specific reference to Portland, England.

few years later, in 1845, Isaac Johnson made the first modern Portland Cement by firing a mixture of chalk and clay at much higher temperatures, similar to those used today. At these temperatures(1400C-1500C), clinkering occurs and minerals form which are very reactive and more strongly cementitious.While Johnson used the same materials to make Portland cement aswe use now, three important developments in the manufacturing process lead to modern Portland cement:- Development of rotary kilns- Addition of gypsum to control setting- Use of ball mills to grind clinker and raw materialsRotary kilns gradually replaced the original vertical shaft kilns used for making lime from the 1890s. Rotary kilns heat the clinker mainly by radiative heat transfer and this is more efficient at higher temperatures, enabling higher burning temperatures to be achieved. Also, because the clinker is constantly moving within the kiln, a fairly uniform clinkering temperature is achieved in the hottest part of the kiln, the burning zone.

Raw materials required to make cement

• Lime stone ( calcareous material , Calcium carbonate)

• Shale , low grade lime stone , clay ( argillaceous materials, Silica)

• Aluminous mateial ( clay, bauxite or Laterite)

• Ferrous material, haematite ( iron ore , ferric oxide )

Cement quality – type of cement

Clinker quality

Fuel chemistry

Raw mix design

OPC, PPC, WC, OWC, SRC,SC

Ordinary portland cement,Pozalona portland cementWhite cement,Oil well cement,Sulfate resistant cement,Slag cementOther cements for special application

Gpsum&fly ash orOther additive quality

quality

Factors influencing the cement quality

1. Mechanical handling of clinker2. Chemical and mineralogical

composition of raw mix3. Chemical and mineralogical composition

of clinker4. Burning process & cooling process5. Chemical composition of fuels (ash)6. Circulation phenomena (volatiles)

Mining

crushing

preblending

Raw meal preparation

Raw meal blending

Pyroprocess

Clinkercooling

Cement grinding

Packing & despatch

Process stepsDust collection&

pollution control

Quality control

Process flow diagram in general

Mining

• Core drilling (bore) holes to explore the mines

• Drill holes for blast

• Blasting

• Excavation and haulage

• Transportation to crusher

• Size reduction for process requirements

MiningQuarry planning

• Ensure - that the required quality & quantity on daily / monthly/ yearly is available to the plant

• Minimise – total operating and capital costs

• Optimise - raw feed quality

• Fulfil – all the safety and legislative requirement

• Maximise – return on capital employed

• Achieve - peak quarring / plant efficiency

overburden

Good quality lime stone

Moderate quality

Poor quality

overburden

Good quality lime stone

Moderate quality

Poor quality

selfish mining – short term benefits

Efficient mining –for well blended – long term benefits

Well developed mineLong term benefits

Bench = 10 M

Picture of a well developed mineAll benches are used effectivelyto improve the mine blend and increase the reserve for long term business

Mining on hill & under ground miningis challenge to the mining engineer

Geology and location of boreholes

Rock drilling machine

Before blasting drill holes are drilled

The released energy of the explosiveis converted into various other formsof energy

• heat

• seismic energy ( stress waves)

• new surface energy ( rock fragmentation)

• concussion and noise ( airblast)

Explosion

• kinetic energy of spoil ( throw) rockdisplacement

Surface miners

Drill machine

Dumpers

excavators

Whell loaders

Material breakage involved in crushing process

Impact Attrition shearing compression

Crushing process

Size reduction stages

Primary n = 5

secondary n = 8

Tertiary n = 6

impact ( crushing)impact

fragmentation

shearing

attrition

compression

fractured fragmented

CrushingCrushing is a process which does size reductionCrushers are chosen depending upon the material characteristicssuch as hardness ,abrasiveness, feed input size, moisture content etcThe commonly used crushers are hammer crushers,Impact crushers, roll crushers, gyratory crushers, jaw crushers.Size reduction depends upon the grinding system to be adopted ie., ball mill or vertical mill

Size reduction ratio Max feed size ( linear edge dimension)

Maximum feed size of crushed product=---------------------------------------------------

( linear edge dimension)

Fracture phenomenon

Stress type-1Between two solidSurfaces( compression,Shearing)

Stress type-2at solidSurface( impact)

Stress type-3Not at a solidSurface , but by action ofThe surrounding medium(shear stress)

Stress type-4Non mechanical introductionOf energy ( thermal shock,explosive shattering & electro hydraulic)

crushersJaw crushers

Gyratory crushers

cone crushers

roll crushers

impact crushers

Hammer crushers

MMD crusher (Roll crusher)It can crush lime stone with high % of moisture

Selection of crushers for different product size

Crushing and grinding

PreblendingVariation is a devil in any process

Types of stackingChevron method

Window method

Axial stacking

Strata method

Single cone shell stacking

double cone shellstacking

Storage systemCircular storage

Linear stacker & storage

Front acting machine Side acting machine

Advantage and disadvantages of circular and linear piles

Circular pileAdvantages• space saving and hence low capital cost• end cone problem is avoided• un interrupted operation

Disadvantages• pile correction is not possible and it depends on mines operation with less variation

Linear pileAdvantages

• it occupies more space• while shunting the operation has interruption• end cone problem

Disadvantages• Pile correction is possible if quality varies

Chevcon method ( at Ariyalur)

Chevcon - was developed for a circular stockpile arrangement. the stacker boom slews back and forth over the curved stockpileridge maintaining a constant pile length. With each individual movement, the end of one movement or the start of the next movement is advanced by the dimension ∆L. In that way many layers - similar to the Chevron mode - are superimposed and the stockpile grows continuously in one direction.

Chevcon configuration refers on to circular stock piles and relates to Chevronwhen it is applied to a circle. In this cofiguration the chevcon layers areinclined as in the side of a cone , each layer runs from the full height of the stock pile to the ground

Well blended slice without end cone

End cone problems

Linear stock pile

Blending ratio = S in / S out

More variation, high std

Less variation, low std

X (t)

Quantity(t)

X (t)

Reclaiming Slices transversely

Stacking in Equal layers

Material quantityPer layer = t

Material quantityPer slice = q

Variations in the raw material composition homogenisedin the blending bed

∆τ ∆τ∆Q ∆Q

∆Q ∆Q

∆τ

∆τ∆τ

Assessment of blending methodS in

S out

Blending ratio = S inS out

Blending efficiency n n = number of layers

n = V*(S*3600) / d d = volume discharged cum/hrS = cross sectional area, sq mV = travelling speed of the stacker

η

Homogenising systems

3.1 Variabilitv and standard deviation The normally accepted method of measuring variability is in the form of a term called standard deviation. The standard deviation of a property can be calculated by taking a number of measurements on the property (such as LSF, SR etc.), and applying the following formula:-

Where X is the measured variable (e.g. LSF)X is the variable mean (or average)N is the number of measurements or observationsTable 1 illustrates a worked example using actual kiln feed LSF data:-

Blending ratio = Std in/ Std out , = 1 for an ideal blending system.

σ = Σ ( X - X ) 2

N - 1

Main parameters for raw mix design

Lime saturation factor = CaO / (2.8 SiO2+1.65Al2O3 + 0.65 Fe2O3)( LSF)

Silica modulus = SiO2 / ( Al2O3+Fe2O3)

Alumina modulus = Al2O3 / Fe2O3AlM

Here we have apply the formula (as per British Standard)

CaO-0.7SO3

(2.8*SiO2 + 1.2* Al2O3 + 0.65*Fe2O3)

(SIM)

LSF =

Lime saturation factor on clinker basis

If MgO is below 2 %

LSF = 100( CaO – free CaO+0.75 MgO)(2.85 SiO2) + ( 1.18 Al2O3) +(0.65 Fe2O3)

If MgO is above 2 %

LSF = 100( CaO – free CaO+1.5 MgO)(2.85 SiO2) + ( 1.18 Al2O3) +(0.65 Fe2O3)

95 –harder to burn, tendency to high free lime & C3S clinker, high early strength high fuel consumption

< 95 , easy to burn , excess coating , excess liquid phase ,possible brick infiltration reduced cement strength , low free limeacceptable standard deviation = 1.2

Raw meal preparation

Raw mills

Ball mill

Roller press & Ball mill

Vertical roller mill

Horizontal roller mill

Grinding media for ball mills

Ball mills

toeDead zone

Mill rotation

qopEffective interval

q >>> qop ; balls hit each other, not grinding material

At critical speed

qmax

q <<< qop ; The ball waves through the material

= 42.3/ D effectiveCritical speed

cascading

cataracting

Ball mill grinding

toe

Mill rotationcataracting

toe

Mill rotationCascading

toe

Mill’s critical rpm

Influence of mill speed onTrajectory of balls

Ball millsOpen circuit Closed circuit

separator product

product

Coarse return

Vertical mills are closed circuit millswith built in separators

separator

Circulation factor =1 Circulation factor = 2 to 2.5

Vertical mill

Vertical roller mills

Vertical mill operation ( over view)

Separator

Residue = 12 – 18 % on 90 µ= 1.5 – 2.5 % on 212 µ

An efficient separator is one which operates with no finesin coarse return ( rejects) and no coarse in product fines

Air drag

Gravitational force

Centrifugal force

Stationary vanes

Rotary cage

Function of separator

Centrifugal force

Gravitation force

Air

drag

for

ce

Separation space

Stationary vanesGuide vanes

rotor

Particle size distribution curve

Advantages of vertical mills

• Energy consumption is less compared to ball mills

• Flexiblity in operation as all forces can be controlled

• Drying capcity is better than ball mills

• Noise level (noise pollution) is much less than ball mills

• Particle size distribution better than ball mills

Roller pressoperation

Roller press

compressed & Caked material

Compression zone

In homogeneous homogeneous

Kiln feed uniformity index (KFUI)

KFUI= n ( C3S actual - C3S target )2

ni - n

C3S actual = the calculated C3S of one instantaneous daily sample of kiln raw mix feedC3S Target = the C3S target established for the mill productn = number of samples ( calculation of average C3S is done monthly)Target for KFUI is < 10( an instantaneous sample is one made up of 5 consecutive increments taken at short intervals)

PreblendingVariation is a devil in any process

Blending silo

The efficient blending silo does efficient blending with minimum energy

The variation in chemistry at the silo outlet is to be at the minimum possible ,Standard deviation of LSF < 1Standard deviation of CaO < 0.2Standard deviation of Silica ratio < 0.1Standard deviation of A/F < 0.01

Flow properties of powders :

• Importance of measuring flow properties

• Various problems in powder handling and storage

Arching Channeling Segregation

Different blendingsystems

Different blending systems

Blending silo

Controlled flowinverted coneblending SiloCapacity = 18000 t

18 M

40 MAdvantages• low inventory• low capital cost

Disdvantages• can not be operated on low stock as raw mill operation directly affectsilo effciency and hence the quality and production.

• as the buffer stock is only for 1 day the incoming raw meal std mustbe < 1 for LSF and Silical modulus < 0.1

Controlled flowInverted cone silo

60 o10 o

Pyro process

Kiln rotation

refractory

charge

flame

KILN

KILN

Pyro process

• Wet process

• Semi dry process

• Semi wet process

• Dry process

( wet milling and slurry is fed into the kiln )

(dry milling , water sprinkled to makenodulation, nodules are fed into the kiln)

(wet milling , dried in vacuum drier, cakeddried , powedered and fed into kiln

(dry milling , dry meal is fed into kiln)

• VSK processVertical shaft kiln

( First process invented in cement process )

Vertical shaft kiln

Wet process Semi wet process

Semi wet process Semi dry process

Long dry process kiln

Dry kiln , suspension preheater kilnDry kiln , suspension preheater kilnWith pre calciner

Kiln = 4500 tpd4.35 M * 67 M% filling = 9 – 11 %Material retention time =18 mts

calciner

Clinker manufacture

• Calcite – CaCO3

• Dolomite –CaMg(CO3)2

• Quartz – SiO2

• Clay minerals• Micas• Feldspars• Aluminum oxide• Pyrite• Iron oxide• Gypsum / anhydrite

• Alite,C3S• Belite,C2S• Aluminate,C3A• Ferrite,C4AF• Free lime(un wanted)• Periclase(un wanted)• Alkali

sulfates(unwanted)

Mineral phases in raw meal Mineral phases in clinker

Temperature

PressureTim

e

AliteCaO

Belite

Liquid

CaCO3

Beta quartz

Gammaquartz C3A

Calcining zone Transition zone Burning zone coolingzone

1400

1200

1000

800

600

400

200

1450 OCDeg C

Pre heating zone

C12A7 C2(A, F)C4AF

Clinkering process

Refractories

The function of the refractories are

• to protect the shell from the heat

• to insulate to reduce heat losses

• to withstand thermal stresses

• to with stand thermo-chemical stresses

• to withstand thermo-mechanical stresses

Kiln refractory lining

Refractories are lined inside the kiln shell and preheater cyclones to the metalfrom heat as well as to insulate to conserve heat.The bricks used are lowalumina , high alumina bricks, magchrome bricks and spinel bricks. Mag chromebricks are banned due to health hazard.Chromium is poisenous.For severe conditions special bricks like zirconia based , are used.

1400-1500 deg C

1200 -1250 deg C1000-1100 deg C

1100-1200 degc Gas temperature

Refractory brick

Always to be remembered

If coal is mixed it is burnt

If flame is wrong everything goes wrongwhatever you may do with chemistry or higher heat input through calciner or kiln.The burning zone needs heat and it can beonly obtained from well shaped radiantflame.i.e., short, snappy and convergent flame .

Flame

Flame of an efficient burner

7 8 9

Burner positioning We do positioning of the burner for centering the flame.The positions1,2,3, 4 and 7are close to the refractory and they are away from the charge.Positions9 and 8 are close to charge .

Only 5 is close to charge and refractory and this is best as the flame in this gives the best thermal distribution to do effective burning.Position 8 & 9 is very close to charge if coal is trapped it has serious negativeimpact.Position 1,4 & 7 is very close to refractory and it can burn the refractory.

4 5 6

1 2 3

Heat exchange in kiln is • mainly radiation of heat from flame to refractory walland to charge

• conduction of heat from refractory and to charge

• convection of heat within the charge ( particle to particlecontact)

radiationconduction

convection

Heat flows from hotter body to colder body Gases flow from high pressure area to low pressure area

1800 deg c

1300 deg C

1400 deg C

1500 deg C

1600 deg c

1700 deg c

radiation

conduction

convection

Lower rpm , high % filling , less activeLayer , high free lime, high radiationlosses

high rpm , low % filling , more activeLayer , low free lime and low radiationlosses

Influence of revolutions / minute on kiln operation

Optimum % filling = 9 – 11 with raw meal retention time of 20 -25 minutes

unfavorable favorable

Passive layer

active layer

Different flames

Normal flame

Flame with lowSecondary air tempDistorted nozzle

Flame –poorhood geometryOr distorted nozzle

Flame at the center

Flame downward

Flame upward

Flame length

Long flame, unstable coating,High back end temp Low shell temperature

Short intense divergent flameGood for burningLow back end temperaturePoor refractory life, highShell temperature

Convergent flameGood for burningGood for refractoryStable coatingLow shell temperature

The Ideal Flame

hot !short !stable !

T"long" flame

"short" flame

Complete combustion:- CO = 0- SO2, NOX ↓

Homogeneous:- no temperature peaks- no local CO on the clinker bed

Longer flame increase the back end temperature resulting inHeat loss at kiln exit and hot meal clogging

Burning zone, Flame-profile• Low momentum burner

• High momentum burner

rings12m (~3xD) burning zone

Rotaflam ~16 m Flame !☺!

rings

~23 m Flame

17m (~4xD) burning zone

! !

Burner Operation

Clinker cooling

Satellite cooler

rotary cooler

grate cooler

Recuperation z one C ooling zone

static gratedirect aeration chamber aerationchamber aeration

Grate coolerWith stationaryinlet

Walking floorpyrofloor

Cross bar cooler

Improvement in

technology

Rotary disc cooler

MMD cross bar

IKN

Poly trackPyro floor

?

Pyro step

Cooler ( heat recuperator)

Heat transferby radiation

and convection Heat movesto clinker edgeby conduction

Air flows overclinker cooling

surface

How cooling is accomplished

800 O C

100 O C

• Convection - Surface to Air• Conduction - Inside to Surface• Heat transfer is driven by temperature

difference

• Takes place at the clinker surface

• To maximize it:– Increase the air/material contact time

with:• Deeper bed ( ⇒ more power)• Slower air flow (⇒ larger cooler)

Heat transfer in clinker

CounterflowParallel flow

Co-current

Air

Material

Air

Material

Cross-flow

Material

Air

material

air

T

material

air

T

material

T

Heat exchanger types

Old conventional grate platescreate sand blasting effect or fluidizationThis creates poor heat exchange

Modern cooler plates flow resistancebranch off the air , createsless fluidization , better heat exchange

Cross flow Counter current

Mechanical flow regulator

Temperature

Bed

thic

knes

s

clinker

air

Fixed bed

Fluidized bed

Air in

Air out

Clinker

Air in

Air out

Clinker

Temperature

Bed

thic

knes

sclinker

air

More efficient recovery with fixed bed

Air flow requirementHas reduced from4 kg air/ kg.cl to2.2 kgair / kg cl

Heat exchange between clinker and air

1. The hotter the inlet temperature the hotter the clinker outlet temperature.

2. The hotter the cooling air temperature the hotter the clinker outlet temperature.

3. The longer the air/material contact time the cooler the clinker outlet temperature.

General truths ( all coolers)

4. Quicker the clinker cooling ( quenching) the smaller thecrystals, results in micro cracks of the minerals, improvesthe soundness of the clinker ( when MgO % exceeds 1.5 %)

C4AF

C3S

C2S

Mgo

CaO

C3A

Pictoral representation of clinker micrograph

• MicroscopicA mixture of different mineral phasesParticle size ≈ 0 – 100 µm

• MacroscopicA gray, granulated, rocky materialGrain size ≈ 0 – 50 mm

What is portland cement clinker

Uniform nodule Sizes

Rather uniform-sized nodules are ingeneral an advantage regarding burning efforts and uniform degree of burning.

Quickly cooled clinkers are favourable for the early strength potential; no alite is lost. The fine crystalline liquid phase prevents aluminate from an early hydration. The influence of aluminate on the setting time is limited in quickly cooled clinker.

Influence of cooling on clinker phases

Fast coolingWell distributedsmall crystals

Slow cooling Larger crystals

C3S

Clinker when it is quenched in cooler it creates micro cracks whichneeds less energy for comminution during grinding.

C3S

Clinker cooling

C2S

Fuels used in cement industry

• Solid fuels ( coal , pet coke, lignite, anthracite )

• Liquid fuels ( furnace oil)

• Gas fuels ( natural gas)

• Alternate fuels ( shredded tyres,waste woodchemical waste, animal meal)

Solid fuel preparation

Fuel lumps are crushed to suitable size depending on the grinding systemand Hard groove index of fuel. The residue depends on the volatile matter

Fuel preparation

(solid)

Fuel properties

crushing

Design offiring system

Selection of Grinding system

drying

storage

fineness

Coal grinding

Inert grindingO2 % < 12 % ( preheater gases&Hot air generators)

Non inert grindingO2 % > 12 % ( cooler air)

Coal grinding is designed also on the basis of explosion index( safety index) , residue , HGI

Ball mill circuit

Vertical mill circuit

Non-inert operation

mills with inert operation

mills with non inert operation

Using cooler gases for drying the coal is non inert operation as it contains > 20 % O2

The acceptable feed size is2 % of the roller diameter

Built in separator

Grinding table

Grinding roller

Vertical mill for coal grinding

For pet cokeand anthracite

For bituminous coal

The residue on 90 microns is 50 % of the volatiles as a thumb rule

Residue vs volatiles

Relationship between coal types,compositionand grinding fineness

Petcoke < 10 < 1.04%< + 0.09 mm0 %< + 0.2 mm

Normally the residue on 90 mic is50 of the % volatiles.

Cement grinding

Clinker + Gpsum + Pozalonic Material ( Fly ash , Slag)

OPC , Clinker = 92 – 97 %, Gypsum = 3 – 7 %

PPC , Clinker = 60 – 70 %, Gypsum = 3-7 % , Fly ash = 25 -30 %

Slag cement, clinker = 50 – 60 %, Gypsum = 3 – 7 % , Slag= 45 – 55 %

Cement grinding

Ball mill

Roller press

Horizontal mill

Vertical rollermill

Roller press•Pressure applied to material varies from 3,000 a 4,000 kg/cm2. They are over dimensioned in order to operate at lower pressures (2500).•Requires a subsequent de-lump, in order to separate the resulting paste, except in the case the roller press feeds a ball mill. •Pressure application angle should be around 6°.•Press consumes 20 to 25 kWh/ton of cement.•Circulation factors range from 6 to 10.•Requires great maintenance.•Wear out elements expected lifetime: 10,000 hours

Horizontal roller mill•Rotates at hypercritical speed (1.2 times critical speed), having no feed.•Pressure on material ranging from 700 to 1,000 kg/cm2.•Pressure application angle: 15 to 20°.•Circulation factors: 3 a 8.•Requires great maintenance.•Consumes 25 to 30 kWh/ton of cement.•Expected lifetime: 10,000 hrs.Roller and ball mills hybrid. Being the most recent one, its utilization is not widespread.

Tubular mill (ball mill)•Rotates at 0.7-0.8 of critical speed.•Lacks pressure system.•Lacks application angles.•Consume 35 to 40 kWh/ton.•Circulation factors: 1 to 3.•Requires little maintenance.•Expected lifetime measured in years.It is the most widely used for cement milling. Its drying capacity is proportional to D2, so in cement the L/D proportion is 3.In raw meal milling L/D is 1.5, if humidity is not greater than 3%, a single chamber mill is recommended. In case the material has humidity greater than 7%, it is necessary to incorporate a flash dryer or change to a vertical mill. The % of material in suspension will determine which type of mill should be used.

Cement mill cooling

The setting properties depend the water molecules of Gypsum CaSO4.2H2OIf water is dehydrated ( at 125 deg C) it results in false setIf it is partially dehydrated, CaSO4.1/2 H2O, called Hemihydate it contributes to initial strength. Hence cement temperature is to be maitained > 100 deg c and < 125 deg C

Ettringite

3 CaO.Al2O3 + 3 CaSO4 +26 H2O 3 CaO .Al2O3.3 CaSO4.32H2O

Vertical mill (roller mill)•Pressure on material:300 to 500 kg/cm2. •Application angle: 12°. The width of the material layer is proportional to this angle and to the rollers diameter.•Consumes 25 to 35 kWh/ton of cement.•Circulation factors: 3 to 5.•Requires great maintenance.•Wear out elements expected lifetime: 15,000 hrs.•Recommended in cases where humidity is greater than 7%, taking into consideration that abrasive content must remain low. This is why it is commonly used in raw meal milling. It works better than a ball mill on plastic materials (clay).

Combined grinding

Dust collecting equipments

ESPElectro staticprecipitators

Bag filters scrubbers

cyclone

ESPAt Ariyalur cooler ESP

Operational Resistivityin a Cement Plant

Applying ESP Technology in a Cement Plant

• Control Critical– Collection Efficiency Effected by

• Dust Characteristics– Particle size ( migration velocity)– Resistivity– Composition– Stickiness

• Gas Conditions– Humidity– Temperature– Composition– Flow rate

– Upstream Gas Conditioning Sensitive (i.e. cooling tower)

– Most Importantly Upstream Process Equipment Sensitive

Dust resistivity characteristics as afunction of moisture content

MicromistWater spray

Principles of the function of ESP

Collecting plate

Charged dust particles

Dust removal

Dust layerGas molecules and ions

Corona generation

Discharge electrodes

H2O

SO2O2N2

Gas flow

T/R set

Gravitational force

Air drag

Migration velocity

corona

Negative electrode

Positive electrodeForces acting on dust particlePositive electrode

Migration velocity and collection efficiency

η

ω =q Ep

( 4 π µ r)

= 1 – exp ( - W.A / Q)

ω = migration velocity

Ep = strength of field in which particles are collected , volts/ meter

µ = Viscosity of gas Pa-s

r = radius of the particle- µ m

η = fractional collectional efficiency

A = collection surface of the particlesQ = gas volumetric flow rate W = drift velocity

PulseCleanGas/dust distribution

Clean gas outlet

Raw gas with dust inlet

Dust drop out

Collected dust

Dust up flowbetween bags

Cake formation

Pleated bags

No dampers:Only possible to do on-line cleaning.Maintenance:On-line not possible.

Example A One dirty gas chamber.One clean gas chamber.

With inlet and outlet dampers:Possible to do on and of-line cleaning.Maintenance:On-line possible when separate hoppers

Multiple dirty gas chambers.Multiple clean gas chambers.

Example B

Fabric FilterOptional Arrangements

Properties of cement

Cement quality tests

• Compressive strength (mortar)• Modulus of rupture ( bending strength)• Fineness( blaine or Particle size distribution)• Expansion ( Le Chatelier & Auto clave)( soundness)

• Setting time

Influencing parameters onCement strength

1 3 7 28 90 days

Strength MPa

C3S

C2S

C3A

C4AF60

0

20

30

40

50

= f (C3S)

28

7

3

1

MPa 70

60

50

40

30

20

10

40 45 50 55 60 65 % C3S

= f (Wk)

28

7

3

1

0

MPa 70

60

50

40

30

20

10

0 0.5 1.0 % Wk

A 1% increase in LOIresult in decrease instrength

1 day by 25 %2 8days by 3 % and90 days by 2 %

Compressive strength – influencing parameters

Compressive strength

1 d 3 d 7 d 28 d

Influencing Normal range 5 – 15 20 – 35 30 - 45 45 - 60Parameters OPC

C3S 45 – 65 % + + + +

C3A 6 – 12 % + + + +

Ks 0.2 – 1.5 % + + +/0/- -

SO3 2 – 4 % +/0/- +/0/- +/0/- +/0/-

Blaine 280 – 300 + + + +m2/kg

Wk 0 - 0.3% - - - -

Quantitative rules of thumb

C3S : 1 – 28 d : + 0.5 Mpa / %

Ks ; 1 d : + 4 Mpa / % : 3 d : + 4 Mpa / %: 7 d : - 2 Mpa / %: 28 d : - 10 Mpa / %

(SO3) tot : 1 - 28 d : - 5 Mpa / % from optimum

Blaine : 1 d : + 0.04 Mpa / (m2/ kg) 3- 28 d : + 0.08 Mpa / (m2/ kg)

One day strength is contributed mainly byC3A , Soluble alkalies, and C3S

3 day is contributed mainly by C3S

7 days strength is contributed by mainlyC3S

28 days strength is mainly contributed byC2S

Apart from the above cement strength is enhanced byhigher fineness of cement Less C3S crystal size achieved by rapid burningand quenching the clinker in coolerHigher fineness of rawmeal also reduces the crystal size of clinker minerals , ie ., C3S & C2S whichenhances the hydraulic reactivity

Cement strength – influencing parameters

Wk , prehydration of clinker

Prehydration of clinker minerals can occur

1. As a result of incorrect internal water cooling in cement mill

2. when storing too hot cement in a silo

3. When clinker and especially cement is exposed to humidity

Please note:If clinker has more soluble alkalis and sulfates it is highly hygroscopic especially when pet coke is fired. In cement silos they form Syngenite , K2SO4.2 CaSO4. H2O which forms lumps and block the cement silos. Hence venting is mustto evacuate moisture and silo cleaning.cements having soluble alkalis and sulfates preferably packed inpaper bags to avoid depletion of strength.

Thumb rule formulae for prediction of strength

FLS predicted the formula for cement ground to 300 kgs/ m2

With 4 % gypsum

strength,

d28 = 52 - 10.( Ks) + 0.15.(C3S)

The content of soluble alkalis Ks is dependent on the total alkalicontent and SO3 content in clinker.

As per Knofel it is

F 28 = (3*C3S)+ (2*C2S) + C3A – C4AF N / mm2

Strength prediction

for 3 d = 97 + 35.8 Ma + 38.1K2SO4 + 28.7 Ms – 1.3 C3S Kg/ cm2

7 d = 300 + 13.4 Ms + 2.8 C2S + 56.1 Ma – 15.4 K2SO4 + 15.5 Na2O 28 d = 490 – 55.3 K2SO4 + 1.3 C3S (or)

= 490 – 86 K2O + 2 C3S – 26 Na2O

Influence of fineness on cement strength

For cements with the same specific surface the increase of the uniformity factor results in increase of strength of all ages.

1. The specific surface , the percentage of fractions 3- 32 mm and theuniformity factor n really influences the development of cement strength.The influence of 3 - 32 mm fraction and the uniformity factor is higher incement with higher in specific surface ( > 3400 cm2/ g)

2. The fractions with particle size less than 3 mm contributes only to earlystrength while the fraction with particle size more than 24 mm influencesstrength development significantly.

3. While the fractions 3 – 16 mm and 16 – 32 mm seems to be more significant factor for specific surface 3500 – 4000 cm2/ g) . This is relevant only if the granulometric distribution is continuous and steep.

4. The optimistic granulometric distribution of a cement is a continuousand steep ( with high uniformity factor) distribution with a high (65 %)content in 3 – 32 mm fraction and specifically in 16 - 24 mm fraction andlow content of fine particles ( < 3 mm , 10 % ) and specific surface of2500 – 3000 cm2/ g according to Blaine.( high efficiency separator andgrinding media distribution plays significantly here)

Properties of cement minerals

Characteristics C3S C2S C3A C4AF

Setting quick slow rapid nil

Hydration rapid slow rapid nil 3 days heat 1.1 cal / g 0.4 cal / g 2 cal / g nil liberation Early strength high upto low upto not much nilContribution 14 days 14 days beyond one day

Late strength less later high later nil nil contribution

Resistance to moderate high poor highChemical attack

Drying shrinkage nil low nil nil

Problems and solutions

1. Grinding problemsa) False set lower cement mill temperature

add less gypsumadd part anhydrite

b) reduced strength high mill temperatureless water cooling correct water cooling

2. Silo storagea) False set short storage time

cooling of cement < 70 deg c

b) reduced strength increase gypsum dehydration inmill

c) lump formation and add less gypsum, use partlysilo blockage (syngenite anhydrate , decrease K2O contentformation, K2SO4.2CaSO4.H2O to avoid the formation of Syngenite

Problems solutions

3 ) Bag storage

a. reduced strength short storage time

b. lump formation add TEA during grinding(tri ethanal amine)add hydrophobic agents

c. crust formation plastic coated bags

d. abnormal setting plastic covering pallets

Packing and dispatch

Customer is the king. He is a better business man than you.Tomorrow’s market is competitive with quality/ price ratio.Customer creates the customers.Bon’t brand the quality alone , brand your service too.

Hope you had a fruitful training

Wish you all the best– Pradeep kumar

Thank you for your kindattention