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

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.

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

Process Overview

From Coal Fired Fine Raw Meal

(120)Res. < 3% Lt. wt 1200-1350 Clinker 1) Gypsum 2) Flyash 3) Pozzolona 4) Slag 1) OPC 2) PPC 3) Slag Cement Blaine 300-350 m2_/kg OR (45) Res. <16% Cement

Process Overview

Limestone + Additives ---> Clinker

Clinker + Gypsum + Additives ---> Cement Heating 1500o_C

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

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 &

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 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

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

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

Grinding in Cement Industry

 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.

Grinding in Cement Industry

 Different Type of Grinding Equipment

 Ball Mill

 Vertical Roller Mill (VRM)

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

 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

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 Separator

Fresh Feed

Rejects

Mill Product Final Product

TPH Blaine/Residue TPH TPH Accum Mill kW RPM Damper Recirculating Load

Ball Mill - Dry Grinding Close Circuit

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:

Ball Mill - Dry Grinding Close Circuit

 Abnormal Conditions & there control

 Separator Resonance

 Cause :

– Mechanical structure natural frequency matches with Separator at certain RPM

 Control:

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 &

Vertical Roller Mill

 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

Vertical Roller Mill

Vertical Roller Mill

 Abnormal Conditions & there control

 Vibration High

 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

 Cause :

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

– High Feed rate

 Control:

Roller Press

 Operational philosophy

 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

 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

Clinkerization Overview

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 30o_{C to 100}o_{C 100}o_{C to 300}o_C 30o_{C to 900}o_C above 800o_C Above 1200o_C Cooling 1350o_{C to} 1250o_C 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

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

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

Preheater

 Abnormal Conditions & control

 High PHOutlet CO

 Cause:

– Less Oxygen for Coal Combustion – High Calciner Coal Feed rate

 Control:

– Cut Calciner Coal

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:

Preheater

 Abnormal Conditions & control

 High Calciner Outlet temp

 Cause :

– High Calciner Coal Feed rate – Less Raw Meal Rate

 Control:

Preheater

 Abnormal Conditions & control

 Low Cyclone cone draft

 Cause :

– Less Air

– Coating in cyclone

– Brick lining failure , Flap damper Malfunction

 Control:

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

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

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 strength

C₂ S (Belite) - 20 to 30% : Slow Contribution to strength

C₃ A - 5 to 12% : Rapid Contribution to strength

C₄ AF - 5 to 12% : V. Slow Contribution to strnth

 Indirect/Direct Measurement of Good Clinker

 Litre Weight (density) - Represent phase%

Kiln

 Clinker Quality

 Affecting Parameters

 Degree of Kiln feed mixing

 Kiln Feed Granulometry

 Burnability of kiln feed

 Degree of heating

 Retention time

Kiln

Kiln

 Abnormal Conditions & control

 High Kiln inlet CO

 Cause :

– Less Air

– More Kiln Coal

 Control:

– Cut Kiln Coal

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

Cooler

Cooler

 Abnormal Conditions & control

 Grate Drive Amps High

 Cause :

– High Clinker Bed Height – Lumps

 Control: