Cement Process Chemistry

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

“In the name of Allah, the Beneficent, the Merciful”

About Cement Cement Reaction With Water

Portland cement when mixed with water undergoes theprocess of Setting & Hardening

The initial stiffening or setting of PC pastes appears tobe the result of the rapid hydration taking place on thesurface of the cement particles. This rapid initial settingis controlled by the presence of calcium sulfate and forthis reason a small proportion of gypsum is intergroundwith cement clinker to control the rate of initial setting.Following this the principal reaction is the formation ofsingle calcium silicate hydrate(C-S-H) from the variousanhydrous calcium silicates present in the cementparticles.

About Cement Cement Reaction With Water

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

C2S + 2H --> C-S-H + C-Hrigid 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 Clinker + Gypsum 33 grade , 44 grade ,53 grade 33 grade :- develop strength upto 330kg/cm2 after 28

days

PPC - Pozzolona Portland Cement Clinker + Flyash + Gypsum

PSC - Slag Cement Clinker + Slag + Gypsum

Process Overview

Mining &Crushing

Raw MillGrinding

Raw MealHomogenization

Pyro ProcessingClinkerization

FinalGrindingPackaging

Crushed Limestone

Additives i.e.Iron ore orClay

Coal AshFrom Coal Fired

Fine Raw Meal(120)Res. < 3%

Lt. wt 1200-1350Clinker

1) Gypsum2) Flyash 3) Pozzolona 4) Slag

1) OPC2) PPC 3) Slag Cement

Blaine 300-350 m2/kgOR(45) Res. <16%

Cement

Process Overview

Limestone + Additives ------------> Clinker

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

Heating 1500oC in Kiln

Grinding

Grinding

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 Raw feed fed to kiln contains 30-40% water by weight

Semi Wet Process / Semi Dry Process Raw feed, prepared by either the wet or dry methods

according to the nature of the raw materials is formed intopellets or modules, which are fed into the kiln by way of agrate preheater in which the moving bed of nodulizedmaterial is dried and brought upto calcining temperature byheat from kiln.

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

Size Reduction in Cement Industry

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

Reduces feed size increases reactivity

Drying Grinding Efficiency improves due to moisture removal Better thermal efficiency in kiln

Blending Raw material with different property get mixed Achieves better homogeneity


Locations in Cement process

Size reduction and drying of Raw meal. VRM , Ball Mill

Size reduction and drying of Coal. VRM , Ball Mill , E-Mill

Size reduction of cement clinker. VRM , Ball Mill , Roller Press


Different Type of Grinding Equipment

Ball Mill

Vertical Roller Mill (VRM)

Roller Press

Ball Mill Dry Grinding

Open Circuit Mill Product is Final Product

Closed Circuit 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 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


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

Ball Mill SeparatorFresh Feed

Rejects

Mill Product Final Product

TPHBlaine/Residue

TPHTPH AccumMill kW

RPMDamper

Recirculating Load

Ball Mill - Dry Grinding Close Circuit

MV-CV relation


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



Separator Resonance Cause :

– Mechanical structure natural frequency matches with Separator at certain RPM

Control:– Prohibit RPM for resonance range


Malfunctions

Decrease in Mill Output Cause :

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


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


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


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.


Major Operating Parameters

Mill Vibration : Health of Mill Bed Layer Thickness : Stability Mill DP : Stability Fan Power : Air Volume Mill Outlet Temp. : Feed Moisture Drying Residue/Blaine : Quality


MV - CV relation



Vibration High Cause :

– Imbalance between Material DP & Air DP Control:

– Cut/Increase Feed– Increase Water Spray



High increase rate in DP or High DP Cause :

– Inlet Material Property changes e.g. Moisture , Grindability

– High Feed rate Control:

– Cut Feed

Roller Press


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%

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


Three sections in Dry Process Preheater :

Preheat the Kiln feed Using Waste Heat Gas Calcination Using Waste heat gas & Coal in Calciner

Kiln : Clinker Formation from Calcined Kiln feed using Coal fuel.

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


Reactions - Heating 30 - 300

Evaporation of Water

400 - 900 Removal of structural water and OH group from clay minerals Clacination

above 800 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


Reactions - Cooling 1300 - 1240

Crystalization of liquid phase into mainly aluminate & ferrite



Raw MealPreheating

Removal of

Water

CalcinationOxide Formation

Belite formationLiquid &

Phaseformation

CaOSiO2Fe2O3Al2O3

CaCO3 -> CaO + CO2

CaO + SiO2 -> CaO.SiO2

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

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

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

Clinker

Kiln

Preheater

Raw Meal

30oC to 100oC 100oC to 300oC

30oC to 900oC

above 800oC

Above 1200oC

Cooling

1350oC to1250oC

Crystalization

Preheater 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

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 Pre-

Calciner 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

Preheater Major Operating Parameter

PHOutlet Temp : Heat Recovery PHOutlet CO : ESP security, Oxygen

Shortage Calciner Outlet Temp : Completion of Calcination Kiln inlet Material Temp : Material Fusion Temp PHOutlet Draft / O2 : Excess Air , Leakage Cyclone Cone Draft : Cyclone Jamming

Handles PHOutlet Fan Damper /RPM : Air Quantity Calciner Coal : Heat Quantity

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


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


High Calciner Outlet temp Cause :

– High Calciner Coal Feed rate– Less Raw Meal Rate

Control:– Cut Calciner Coal


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 Major Operating Parameter

Kiln Torque : Clinker Quality Burning Zone Temp. : Good Heat Content Clinker Lt..wt. & Free Lime : Clinker Quality Kiln Hood Draft : Safety & Maintenance Kiln inlet CO or O2 : Oxygen Availability

Handles Kiln Feed Kiln RPM Kiln Coal

Kiln Clinker Quality

Clinker Phase Requirement

C3 S (Alite) - 40 to 60% :Rapid Contribution to strengthC2 S (Belite) - 20 to 30% : Slow Contribution to strengthC3 A - 5 to 12% : Rapid Contribution to strengthC4 AF - 5 to 12% : V. Slow Contribution to strnth

Indirect/Direct Measurement of Good Clinker

Litre Weight (density) - Represent phase% Free Lime (CaO) - Should be minimized

Kiln 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 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

Cooler Process

Types Of 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.

Cooler Major Operating Parameter

Under-Grate Pressure : Clinker Bed Grate Drive Amps : Clinker Bed Clinker Temperature : Clinker property , Safety Secondary Air Temp. : Recuperation Hood Draft : Safety Cooler Vent Temperature : Heat Loss

Handles Air Volume / Fan Damper / Fan RPM Grate Drive Speed Vent fan Damper / RPM

Cooler MV-CV Relation

Cooler Abnormal Conditions & control

Grate Drive Amps High Cause :

– High Clinker Bed Height– Lumps

Control:– Increase Grate Speed

Cement Process Chemistry

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