Cement Process Chemistry

“In the name of Allah, the Beneficent, the Merciful” About Cement 

Cement Chemistry  Cement is hydraulic material which develops strength when it reacts with water.  It is inorganic material which consists of oxides of calcium, silicon, iron, aluminum.  Phases in Cement    

C3 S (Alite) C2 S (Belite) C3 A C4 AF

C - CaO , S - SiO2 , A - Al2O3 , F - Fe2O3

About Cement 

Cement Reaction With Water 

Portland cement when mixed with water undergoes the process of Setting & Hardening



The initial stiffening or setting of PC pastes appears to be the result of the rapid hydration taking place on the surface of the cement particles. This rapid initial setting is controlled by the presence of calcium sulfate and for this reason a small proportion of gypsum is interground with cement clinker to control the rate of initial setting. Following this the principal reaction is the formation of single calcium silicate hydrate(C-S-H) from the various anhydrous calcium silicates present in the cement particles.

About Cement 

Cement Reaction With Water



C3S + 3H --> C-S-H + 2C-H rigid gel



C2S + 2H --> C-S-H + C-H rigid gel



C3A , C4AF have less hydraulic properties but useful for liquid formation in kiln.

C - CaO , H - H2O

About Cement 

Types of Cement  OPC - Ordinary Portland Cement   



PPC - Pozzolona Portland Cement 



Clinker + Gypsum 33 grade , 44 grade ,53 grade 33 grade :- develop strength upto 330kg/cm2 after 28 days

Clinker + Flyash + Gypsum

PSC - Slag Cement 

Clinker + Slag + Gypsum

Process Overview Additives i.e. Iron ore or Clay

Mining & Crushing Crushed Limestone

Packaging

Raw Mill Grinding

Blaine 300-350 m2/kg OR (45) Res. Clinker o Heating 1500 C in Kiln

Grinding

Clinker + Gypsum + Additives ------------> Cement

Process Overview 

Mining  First step in Cement Production  Drilling is used to drill deep holes in the soil  Blasting is done with the help of drilled holes & explosives  Blasted Limestone is excavated with excavator  Unearthed Limestone is transported to Crusher

Process Overview 

Raw Meal Preparation  Crushing Limestone from Mines 







Limestone from Quarry requires coarse size reduction as it is in the form of big boulders. Crushers are used in two or three steps for coarse size reduction. Types :Jaw Crusher , Hammer Crusher , Impact crusher.

Pre-homogenization of Limestone 



Limestone ,excavated from different benches, has different chemical composition.Hence homogenization is needed. In this Crushed limestone is stacked onto stock pile in such a way that inherent CaCO3 Inconsistency is evened out.

Process Overview 

Raw Meal Grinding  Pre-homogenized Raw Meal in addition with with additives ,e.g. sandstone, iron oxide,clay etc., is ground in Raw Mill.  



Types : VRM , Closed Circuit Ball Mill Hot air from Preheater is used for removing moisture in Raw Meal.

Homogenization of powdered Raw Meal is done in blending silo so that Chemical properties of Raw Meal gets equalized w.r.t. time.

Process Overview 

Pyroprocessing  The homogenous raw meal is preheated in Preheater.  The material is then calcined upto 90% in Calciner.  The Calicined raw meal is sintered into clinker in a rotary Kiln.  Fuel (Coal , Oil) is fired into Kiln to sinter the raw meal.  Red hot Clinker is cooled in cooler.  The cooled clinker is crushed in Clinker breaker & stored in silo or Gantry for finished grinding.

Process Overview 

Finished Grinding 

Crushed Clinker is mixed with gypsum & fed into Cement Mill for fine size reduction.  



Gypsum is added to control setting time of cement. Circuit Types : Open circuit Ball Mill , Closed circuit Ball Mill , Roller Press with Ball Mill,VRM with Ball Mill

Depending on final Cement requirements Flyash or Slag is added along with Crushed Clinker.

Process Overview 

Different Type of Process  Wet Process 

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Semi Wet Process / Semi Dry Process 



Raw feed fed to kiln contains 30-40% water by weight Raw feed, prepared by either the wet or dry methods according to the nature of the raw materials is formed into pellets or modules, which are fed into the kiln by way of a grate preheater in which the moving bed of nodulized material is dried and brought upto calcining temperature by heat from kiln.

Dry Process 

Raw Material fed to kiln contains 2-4% water by weight

Size Reduction in Cement Industry 

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

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Raw Meal Crushing  Jaw,Impact,Hammer,Gyratory Crusher Raw Meal Grinding  Ball Mill , Vertical Roller Mill (VRM) Clinker Crushing  Hammer Crusher Final Grinding  Ball Mill , VRM , Roller Press, Hybrid

Grinding in Cement Industry 

Objectives  Size Reduction  

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Drying  

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Reduces feed size increases reactivity Grinding Efficiency improves due to moisture removal Better thermal efficiency in kiln

Blending  

Raw material with different property get mixed Achieves better homogeneity

Grinding in Cement Industry 

Locations in Cement process 

Size reduction and drying of Raw meal. 



Size reduction and drying of Coal. 

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VRM , Ball Mill VRM , Ball Mill , E-Mill

Size reduction of cement clinker. 

VRM , Ball Mill , Roller Press

Grinding in Cement Industry 

Different Type of Grinding Equipment 

Ball Mill

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Vertical Roller Mill (VRM)

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Roller Press

Ball Mill 

Dry Grinding  Open Circuit 

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Closed Circuit 

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Mill Product is Fed to Air Separator & Coarse Material is fed back to mill Material from Mill to Separator is conveyed by Elevator

Air-Swept Operation 

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Mill Product is Final Product

Material from Mill to Separator is conveyed by Air

Wet Grinding  Open Circuit  Closed Circuit

Ball Mill 

Operational philosophy 

Grinding By Impact  





Primary size reduction process in first chamber of mill. Large diameter grinding media climbs along the mill lining due to centrifugal force. At the point when the weight of ball exceeds centrifugal force the ball falls down. The impact of the falling grinding charge with Mill lining causes particles entrapped between the charge & lining to fracture and undergo size reduction

Ball Mill 

Operational philosophy 

Grinding By Attrition 



Grinding action in the Fine grinding compartment is generally by abrasion & shearing action Small particles , which are in an agglomerated form before grinding, are sheared off from the surface due to rubbing between multiple large sized aggregates and/or the grinding media.

Air Separator 

Operational philosophy The performance of closed circuit mill very much depends upon performance of separator that is used. There are two broad categories of separator. These are 



Conventional Type Of separator (mechanical air separator) High Efficiency Separator (static separator)

Both types use Air for separation in which centrifugal force of circulating air separates fines from coarse.

Mechanical Air Separator 

Separation In this type of Separator Due to drag force of air separation of fines from coarse takes place. Fresh feed is fed to distributing plate, which disperse feed into air stream flowing up. Fines get entrained in air stream & coarse hits the wall of separator. After hitting the wall coarse gets collected into cone.

Mechanical Air Separator 

Fineness Control Circulating Air Volume in Separator is only MV that can control Fineness. The less is the volume more is Fineness. Auxiliary fan in separator can very the circulating air volume. As Auxiliary fan rpm increases circulating air volume decreases which intern decrease material dragged by air to fines of separator. Thus Fineness can be increased. Sp. Power requirement for such separator is around 6 kWh/ton.

Mechanical Air Separator 

Limitations High Fineness of product is difficult or can be achieved with high circulating load. Mismatches between sizes of mill & separator It is not possible to have selective size gradation (3-30 micron for cement.) In case of conventional separator 50% of fine (below 30 micron) if returned to mill.

High efficiency Static Air Separator 

Separation The Mill discharge material is fed on dispersion plate. The material then cascade down to separating (classifying zone) where tangential inlet air suspends feed particles against the opposing centrifugal force of the rotor. Intense shearing force breaks apart the particle agglomerates for highly efficient classification. Product size particles, controlled by rotor speed, pass through the rotor blades to the cyclone. Rejects fall down to the collection hopper & fed back to mill. An externally located fan sucks the fine. Air is again recirculated to the separator. Small amount of recirculated air is vented off.

High efficiency Static Air Separator 

Fineness Control Fineness can be controlled by rotor speed & air volume in separator. By increasing rotor speed feed material requires more turn & energy against centrifugal force to get through rotor blades. Due to this fineness of product increases. Also by decreasing air volume in separator increases fineness of product.

Ball Mill - Dry Grinding Close Circuit 

Process  Fresh feed is fed to ball mill with Separator rejects.  Ball mill product goes to Separator for separation  Rejects is fed back to mill Rejects

Recirculating Load

Ball Mill Fresh Feed TPH

Separator Mill Product

Accum Mill kW

TPH

Final Product RPM Damper

TPH Blaine/Residue

Ball Mill - Dry Grinding Close Circuit

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MV-CV relation

Ball Mill - Dry Grinding Close Circuit 

Abnormal Conditions & there control 

Sudden increase in Mill accumulation 



Cause : – Feed Size increase – Moisture increase in feed – Hardness of Feed increase Control: – Cut the fresh Feed

Ball Mill - Dry Grinding Close Circuit 

Abnormal Conditions & there control 

Separator Resonance 



Cause : – Mechanical structure natural frequency matches with Separator at certain RPM Control: – Prohibit RPM for resonance range

Ball Mill - Dry Grinding Close Circuit 

Malfunctions 

Decrease in Mill Output 

Cause : – Feed hardness & size – Worn out Mill charge – Blocked diaphragm – High moisture content – Fractured diaphragm

Ball Mill - Dry Grinding Close Circuit 

Malfunctions 

Product too coarse 

Cause : – Increased feed hardness – Grinding media too large – Too few grinding media – Diaphragm slots worn out – Mill feed overloading – Malfunction of separator – Mill fan damper jammed

Ball Mill - Dry Grinding Close Circuit 

Malfunctions 

Mill inlet pressure low 

Cause : – Low mill draught – Excessive wet feed

Ball Mill v/s VRM/Roller press Ball Mill

VRM/Roller Press

Grinding-Impact/Attrition

Grinding-Compressive stress

Lower fines

Greater Fines

Higher kWh/ton

Lower kWh/ton

Non flexible

Flexible for different products

Easy to maintain

Requires High skills

Vertical Roller Mill 

Operational philosophy 

Grinding by Compressive force Feed is ground between horizontal grinding table & two or more rollers , which are pressed against the grinding table under high pressure

VRM - Typical Raw Mill 

Process  VRM is widely used for Raw Meal Grinding.  Raw Material is fed to table . Raw Material get grounded between table & roller.  Hot air with re-circulation air enters from bottom of the mill through perforated plates.  Air carries ground material to separator inlet which is integral part of Mill.  Separator reject falls back to grinding table & fines are carried by air to cyclone.

Vertical Roller Mill 

Major Operating Parameters      

Mill Vibration Bed Layer Thickness Mill DP Fan Power Mill Outlet Temp. Residue/Blaine

: : : : : :

Health of Mill Stability Stability Air Volume Feed Moisture Drying Quality

Vertical Roller Mill 

MV - CV relation

Vertical Roller Mill 

Abnormal Conditions & there control 

Vibration High 

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Cause : – Imbalance between Material DP & Air DP Control: – Cut/Increase Feed – Increase Water Spray

Vertical Roller Mill 

Abnormal Conditions & there control 

High increase rate in DP or High DP 

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Cause : – Inlet Material Property changes e.g. Moisture , Grindability – High Feed rate Control: – Cut Feed

Roller Press 

Operational philosophy

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Grinding by Compressive force Feed is ground between horizontal grinding roll , one of which is pressed against the another immovable roll under high pressure

Roller Press 

Process  Roller Press is widely used for Finished Grinding in hybrid mode of operation.  Raw Material is fed to overhead silo . Material bed is always maintained above roller press.  Ground material is fed to separator by elevator.  Separator reject is fed to roller press & fines are carried by air to cyclone.  Sometime ground material doesn’t goto Separator. Only divider divides ground product ,one part of which goes back to Roller Press.

Roller Press 

Major Operating Parameters      

Roller Gap - Health of mill Back Pressure - Good grinding Over head Silo level - Choke feed Residue/Blaine Returns Mill Power

Modes of Operation 

Roller press & Ball mill for finished grinding can work in following modes   

One Pass Mode Pre-grinding Mode Hybrid Mode

Clinkerization Overview 

Main Aim of this section is to produce Clinker from Raw meal in energy efficient manner



Kiln Operation can be in following mode   

Wet Process : Kiln Feed Water 30 - 40% Semi Dry/Wet process Dry Process : Kiln Feed Water 2 - 3%

Clinkerization Overview 

The choice of the process to be used depends upon a complex combination of different factors This includes:  



The nature of the raw materials. The thermal efficiency of the different processes and their variations fuel and other energy prices

Clinkerization Overview 

Three sections in Dry Process  Preheater :  



Kiln : 

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Preheat the Kiln feed Using Waste Heat Gas Calcination Using Waste heat gas & Coal in Calciner Clinker Formation from Calcined Kiln feed using Coal fuel.

Cooler :  

Heat Recovery from Hot Clinker Cooling Clinker rapidly to form reactive clinker

Clinkerization Overview 

Reactions - Heating  30 - 300 



400 - 900  

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Removal of structural water and OH group from clay minerals Clacination

above 800 

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Evaporation of Water

Formation of C2S , intermediate product , aluminate , ferrite

above 1250  

Formation of liquid phase (aluminate & Ferrite melt) Crystalization of Alite ,Belite I.e Completion of phase formation

Clinkerization Overview 

Reactions - Cooling  1300 - 1240 

Crystalization of liquid phase into mainly aluminate & ferrite

Clinkerization Overview Raw Meal

Preheater

30oC to 900oC Removal of Water

Raw Meal Preheating

100oC to 300oC

30oC to 100oC

above 800oC

Liquid & Phase formation

Belite formation

Crystalization 1350oC to 1250oC

Clinker

CaCO3 -> CaO + CO2

(CaO)2.SiO2 + CaO -> (CaO)3.SiO2 Cooling

Kiln

Calcination Oxide Formation

CaO SiO2 Fe2O3 Al2O3

Above 1200oC

(CaO)3.(Al2O3) ----- C3A (CaO)4.(Al2O3).Fe2O3--- C4AF

CaO + SiO2 -> CaO.SiO2 CaO.SiO2 + CaO -> (CaO)2.SiO2

Preheater

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Different Type of Preheater System  4 , 5 , 6 stage ,One string - With or Without Calciner  4 , 5 stage ,Two String - Calciner String , Kiln String  4, 5 stage ,Two string - Both Calciner String Typical : 5 stage , Two String - Calciner & Kiln String



More Stages gets added in Preheater String  More Heat Recovery from Waste Heat Gas  More Capital Cost  Less Temperature For Raw Mill Grinding

Preheater 

Aim  Maximum Heat Recovery from waste heat gas  Maximum Calcination without melting raw meal

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Operational Philosophy  Heat exchange between Waste Heat Gas & Raw Meal takes place through Direct Heat Exchange in Riser Duct  Separation of Raw Meal Solid from Gas is carried out in Cyclone at each stage.  Maximum Calcination is carried out in Pre-Calciner by burning Coal.

Preheater 

Process  Gas enters from bottom cyclone  Raw meal enters from top cyclone  Gas is sucked by induced draft fan from kiln  Fan is placed at Preheater Outlet  From Last but One cyclone raw meal goes to PreCalciner where coal is fired  Tertiary air is sucked in Calciner from cooler  After Pre-Calciner Raw meal is carried to last cyclone by air & Separated raw meal from this cyclone goes to Kiln



Major Operating Parameter  PHOutlet Temp  PHOutlet CO

: Heat Recovery : ESP security, Oxygen Shortage : Completion of Calcination : Material Fusion Temp : Excess Air , Leakage : Cyclone Jamming

Calciner Outlet Temp  Kiln inlet Material Temp  PHOutlet Draft / O2  Cyclone Cone Draft Handles  PHOutlet Fan Damper /RPM : Air Quantity  Calciner Coal : Heat Quantity 



Preheater

Preheater 

MV-CV Relation

Preheater 

Abnormal Conditions & control  High PHOutlet CO 



Cause: – Less Oxygen for Coal Combustion – High Calciner Coal Feed rate Control: – Cut Calciner Coal – Increase PHFan RPM or Damper

Preheater 

Abnormal Conditions & control 

High Kiln inlet material temp 



Cause : – High Calciner Coal Feed rate – Less Raw Meal Rate – Secondary Burning of Coal in preheater Control: – Cut Calciner Coal

Preheater 

Abnormal Conditions & control 

High Calciner Outlet temp 



Cause : – High Calciner Coal Feed rate – Less Raw Meal Rate Control: – Cut Calciner Coal

Preheater 

Abnormal Conditions & control 

Low Cyclone cone draft 



Cause : – Less Air – Coating in cyclone – Brick lining failure , Flap damper Malfunction Control: – Cut Raw Meal Feed Rate

Kiln 

Aim  Maintain Clinker Quality  Minimize Heat Consumption



Operational Philosophy  Heat is generated by Coal combustion  High residence time i.e. 20 min  High Temp 1500oC  Maximum Contact area of Hot air & Material by circulatory motion (4 rpm)



Kiln

Process  Kiln is cylindrical rotating furnace (60 m length) & installed slightly slant (3-4degree) to carry the material to lower end when rotating.  At Lower end is the burner where coal is fired through using primary air for conveying.  Cooler Secondary air is sucked into Kiln which is at high temp ( Due to heat recuperation from hot clinker ).  Secondary Air from Cooler & Primary Air gets heated by combustion of coal.  This air travels opposite to material flow & Heat Exchange between air & material takes place

Kiln 

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Major Operating Parameter  Kiln Torque  Burning Zone Temp.  Clinker Lt..wt. & Free Lime  Kiln Hood Draft  Kiln inlet CO or O2 Handles  Kiln Feed  Kiln RPM  Kiln Coal

: : : : :

Clinker Quality Good Heat Content Clinker Quality Safety & Maintenance Oxygen Availability



Kiln

Clinker Quality  Clinker Phase Requirement C3 S (Alite) C2 S (Belite) C3 A C4 AF 

-

40 to 60% 20 to 30% 5 to 12% 5 to 12%

:Rapid Contribution to strength : Slow Contribution to strength : Rapid Contribution to strength : V. Slow Contribution to strnth

Indirect/Direct Measurement of Good Clinker  

Litre Weight (density) Free Lime (CaO)

- Represent phase% - Should be minimized



Clinker Quality 

Affecting Parameters      

Degree of Kiln feed mixing Kiln Feed Granulometry Burnability of kiln feed Degree of heating Retention time Clinker Cooling Rate

Kiln

Kiln 

MV-CV Relation

Kiln 

Abnormal Conditions & control 

High Kiln inlet CO 



Cause : – Less Air – More Kiln Coal Control: – Cut Kiln Coal – Increase PH fan RPM / Open Damper

Kiln 

Abnormal Conditions & control 

LOW kiln Torque/ Dusty Kiln 



Cause : – Less Heat Content in Kiln – High Kiln filling Control: – Reduce Kiln RPM & Increase Kiln Coal – Decrease Kiln Feed

Kiln 

Abnormal Conditions & there control 

Red Spot 



Cause : – Coating Deformation – Brick dislodging Control: – Reduce Kiln RPM – Stop Kiln

Cooler 

Aim  Recuperate Maximum Heat from Clinker  Maintain Clinker Quality  Minimize Clinker Temperature



Operational Philosophy  Maximum Heat Recuperation in first few compartments is achieved by keeping high bed height of Clinker  Lower Clinker temperature is achieved in last few compartments by Low Clinker bed height & High Air volume



Process  Types Of Cooler

Cooler



Reciprocating Grate Cooler – Perforated Grates moving one over other creating forward motion for clinker. – Air with high velocity flows vertically up 90 degree to Clinker flow.



IKN Cooler – Grates Doesn’t move. Forward motion for clinker is created by Horizontal Air Jet with very high velocity. – Air with very high velocity flows parallel to Clinker flow & then moves vertically up.





Major Operating Parameter  Under-Grate Pressure  Grate Drive Amps  Clinker Temperature  Secondary Air Temp.  Hood Draft  Cooler Vent Temperature Handles  Air Volume / Fan Damper /  Grate Drive Speed  Vent fan Damper / RPM

Cooler : : : : : :

Clinker Bed Clinker Bed Clinker property , Safety Recuperation Safety Heat Loss

Fan RPM

Cooler 

MV-CV Relation

Cooler 

Abnormal Conditions & control 

Grate Drive Amps High 



Cause : – High Clinker Bed Height – Lumps Control: – Increase Grate Speed