Introduction
This document is one of several white papers that summarize
readilyavailableinformationoncontroltechniquesandmeasuresto
mitigategreenhousegas(GHG)emissionsfromspecificindustrial
sectors. These white papers are solely intended to provide basic
informationonGHGcontroltechnologiesandreductionmeasures
in order to assist States and local air pollution control agencies,
tribal authorities, and regulated entities in implementing
technologiesormeasurestoreduceGHGsundertheCleanAirAct,
particularly in permitting under the prevention of significant
deterioration(PSD)programandtheassessmentofbestavailable
controltechnology(BACT).Thesewhitepapersdonotsetpolicy,
standards or otherwise establish any binding requirements; such
requirementsarecontainedintheapplicableEPAregulationsand
approvedstateimplementationplans.
Cementmanufacturingrawmaterials
Ifyouhappentobeageologist,therawmaterialsquarryisprobably
themostinterestingpartofacementworks,maybeunlessyouview
the clinkering process as igneous rocks in the making.
Themostcommonrawrocktypesusedincementproductionare:
Limestone(suppliesthebulkofthelime)
Clay,marlorshale(suppliesthebulkofthesilica,aluminaand
ferricoxide)
Othersupplementarymaterialssuchassand,flyash/pulverised
fuel ash (PFA), or ironstone to achieve the desired bulk
composition
Quarry management is an art; most quarries will probably have
"goodmaterial"fromwhichcementcaneasilybemade.Theymay
alsohavesomematerialthatisnotasgood.Thismightbeharderto
grind,orbeoflessconvenientcomposition.
Limestoneblocksbeingtakenawayforcrushing.(Picturecourtesy
CastleCement.)
Ifthe'goodstuff'isallusedupfirst,itmaybemoredifficultto
makecementoutofwhatisleft.Carefulselectiononadaytoday
basisisneededtomakethebestuseofallthematerialsavailable.
Raw materials are extracted from the quarry, then crushed and
groundasnecessarytoprovideafinematerialforblending.Mostof
thematerialisusuallygroundfinerthan90micronsthefinenessis
oftenexpressedintermsofthepercentageretainedona90micron
sieve.
Once the the raw materials are ground fine enough, they are
blendedintheproportionsrequiredtoproduceclinkerofthedesired
composition.
Theblendedrawmaterialsarestoredinasilobeforebeingfedinto
thekiln.Thesilostoresseveraldays'supplyofmaterialtoprovidea
bufferagainstanyglitchesinthesupplyofrawmaterialfromthe
quarry.
Technically,acementproducercanhavealmostcompletecontrol
over clinker composition by blending raw materials of different
compositionstoproducethedesiredresult.Inpractice,however,
clinkercompositionislargelydeterminedbythecompositionsof
thelocallyavailablerawmaterialswhichmakeupthebulkofthe
raw meal.
Supplementarymaterialsareusedtoadjustthecompositionofthe
rawmealbutcostandavailabilityarelikelytodeterminetheextent
towhichtheyareused.Transportcostsinparticular
ManufactureProcessofCement
ThemanufactureproceduresofPortlandcementisdescribedbelow.
Mixingofrawmaterial
Burning
Grinding
Storageandpackaging
1.Mixingofrawmaterial
The major raw materials usedinthemanufactureof cement are
Calcium,Silicon,IronandAluminum.Thesemineralsareusedin
differentformaspertheavailabilityoftheminerals.
TableshowstherawmaterialsforPortlandcementmanufacture
Themixingprocedureofthemanufactureofcementisdonein2
methods,
Dryprocess
Wetprocess
a)DryProcess
The both calcareous and argillaceous raw materials are firstly
crushedinthegyratorycrusherstoget25cmsizepiecesseparately.
Thecrushedmaterialsareagaingrindedtogetfineparticlesinto
ballortubemill.
Each finely grinded material is stored in hopper after screening.
Nowthesepowderedmineralsaremixedinrequiredproportionto
getdryrawmixwhichisthenstoredinsilosandkeptreadytobe
sentintorotarykiln.Nowtherawmaterialsaremixedinspecific
proportionssothattheaveragecompositionofthefinalproductis
maintainedproperly.
Fig:ManufactureofCementbyDryProcess
b)WetProcess
Therawmaterialsarefirstlycrushedandmadeintopowderedform
andstoredinsilos.Theclayisthenwashedinwashingmillsto
removeadheringorganicmattersfoundinclay.
Thepowderedlimestoneandwaterwashedclayaresenttoflowin
the channels and transfer to grinding mills where they are
completelymixedandthepasteisformed,i.e.,knownasslurry.
Thegrindingprocesscanbedoneinballortubemillorevenboth.
Thentheslurryisledintocollectingbasinwherecompositioncan
beadjusted.Theslurrycontainsaround3840%waterthatisstored
instoragetanksandkeptreadyfortherotarykiln
Fig:ManufactureofCementbyWetProcess
ComparisonofdryprocessandwetprocessofCementManufacture
2.BurningofRawMaterials
Theburningprocessiscarriedoutintherotarykilnwhiletheraw
materialsarerotatedat12rpmatitslongitudinalaxis.Therotary
kilnismadeupofsteeltubeshavingthediameterof2.53.0meter
andthelengthdiffersfrom90120meter.Theinnersideofthekiln
islinedwithrefractorybricks.
Thekilnissupportedonthecolumnsofmasonryorconcreteand
restedonrollerbearinginslightlyinclinedpositionatthegradient
of1in25to1in30.Therawmixofdryprocessofcorrectedslurry
ofwetprocessisinjectedintothekilnfromtheupperend.Thekiln
isheatedwiththehelpofpowderedcoaloroilorhotgasesfromthe
lowerendofthekilnsothatthelonghotflamesisproduced.
Asthekilnpositionisinclinedanditrotatesslowly,thematerial
chargedfromupperendmovestowardslowerendatthespeedof
15m/hr. In the upper part, water or moisture in the material is
evaporated at 400oC temp, so this process is known as Drying
Zone.
The central part i.e. calcination zone, the temperature is around
10000C, where decomposition of lime stone takes place. The
remainingmaterialisintheformofsmalllumpsknownasnodules
aftertheCO2isreleased.
CaCO3=CaO+CO2
Thelowerpart(clinkeringzone)havetemperatureinbetween1500
17000C where lime and clay are reacts to yielding calcium
aluminatesandcalciumsilicates.Thisaluminatesandsilicatesof
calciumfusetogathertoformsmallandhardstonesareknownas
clinkers.Thesizeoftheclinkerisvariesfrom510mm.
The lower part i.e. clinkering zone has the temperature around
15001700C.Intheregionlimeandclayreactstoyieldcalcium
aluminatesandcalciumsilicates.Thisproductsofaluminatesand
silicatesofcalciumfusestogethertoformhardandsmallstones
knownasclinkers.Thesizeofthesmallandhardclinkersvaries
from5to10mm.
2CaO+SiO2=Ca2SiO4(declaimsilicate(C2S))
3CaO+SiO2=Ca3SiO5(tricalciumsilicate(C3S))
3CaO + Al2O3= Ca3Al2O6(dicalcium aluminate (C2A)) 4CaO +
Al2O3+Fe2O3=Ca4Al2Fe2O10(tetracalciumaluminoferrite(C4AF))
Theclinkercomingfromtheburningzoneareveryhot.Tobring
downthetemperatureofclinkers,airisadmittedincountercurrent
direction at the base of the rotary kiln. The cooled clinkers are
collectedinsmalltrolleys.
GrindingofClinkers
Thecooledclinkersarereceivedfromthecoolingpansandsentinto
mills.Theclinkersaregrindedfinelyintopowderinballmillor
tube mill. Powdered gypsum is added around 23% as retarding
agentduringfinalgrinding.Thefinalobtainedproductiscement
thatdoesnotsettlequicklywhencomesincontactwithwater.
Aftertheinitialsettingtimeofthecement,thecementbecomesstiff
andthegypsumretardsthedissolutionoftricalciumaluminatesby
formingtricalciumsulfoaluminatewhichisinsolubleandprevents
tooearlyfurtherreactionsofsettingandhardening.
3CaO.Al2O3+xCaSO4.7H2O=3CaO.Al2O3.xCaSO4.7H2O
4.Storageandpackaging
Thegrindedcementisstoredinsilos,fromwhichitismarketed
eitherincontainerloador50kgbags.
CementIndustryinWorld
No. of
Rank Company/Group Country Capacity (Mt/yr)
plants
1 Lafarge France 225 166
2 Holcim Switzerland 217 149
3 CNBM China 200 69
4 Anhui Conch China 180 34
5 HeidelbergCement Germany 118 71
6 Jidong China 100 100
7 Cemex Mexico 96 61
8 China Resources China 89 16
9 Sinoma China 87 24
10 Shanshui China 84 13
11 Italcementi Italy 74 55
12 Taiwan Cement Taiwan 70 -
13 Votorantim* Brazil 57 37
14 CRH** Ireland 56 11
15 UltraTech India 53 12
16 Huaxin China 52 51
17 Buzzi Italy 45 39
18 Eurocement Russia 40 16
19 Tianrui China 35 11
20 Jaypee*** India 34 16
STEPS TAKEN FOR QUALITY CONTROL:
A Quality Assuarance deptt. at Corporate office with
representativesateachcementmanufacturingplantisthebackbone
of Quality, for the product manufactured by CCI. This cell is
directly reporting
to C&MD regarding all quality matters.
One executive of Production deptt at each unit has been made
responsibleforqualityassurance.Alltheseexecutivesatunitlevel
areresponsibleforfollowingjobs:
CONCLUSION
Asbestoscementproductsweredevelopedinaneraofingenuityfor
creatingeasytoinstallandeconomicbuildingmaterials.Although
asbestoscementhasacquiredapoorreputationbyassociationofits
title,ithasnotgainedthatreputationthroughalackofdurabilityor
utility. In order to preserve this twentiethcentury material,
understandingwhatmakes,ordoesnotmake,asbestosahazardis
trulyimportant.Inthiscase,nohazardiscreatedwhenasbestos
cement building materials are sound and left in place, or when
treatmentsincorporatenonabrasivemeans.
References
http://www.hse.gov.uk/pubns/cis26.pdf
http://www.cementaustralia.com.au/wps/wcm/connect/website/pac
kaged products/home/hintsandtips/FAQ Safety/#FAQsafety
PPE.html
http://www.tdi.texas.gov/pubs/videoresource/stpcement.pdf
Cement'sbasicmolecularstructurefinallydecoded(MIT,2009)
CONTENTS
1. Introduction
2. Raw Material
3. Manufacture of Cement
a. Dry Process
b. Wet Process
c.Burning of Raw materials
d. Grinding of Clinkers
4. Storage and Packaging
5. Cement Industry in World
6. Quality Control
7. Conclusion
8. References
