Cement manufacturing process

© Confederation of Indian Industry
Presentation on
Process Optimization in Cement
Industry
Presented by :-
Nitin Asnani

CEMENT MANUFACTURING PROCESS

UNIT - I UNIT - II
BLENDED L/S BLENDED L/S
RAW MEAL RAW MEAL
KILN FEED FINE COAL FINE COAL KILN FEED
CRUSHING AND STACKING PROCESS
L/S FROM MINES
HOT CLINKER
CRUSHED LIMESTONE
STOCK PILE
RAW MEAL GRINDING
PROCESS
CB SILO RAW MEAL
STORAGE & HOMOG.
COLD CLINKER
LATERITE
PYRO PROCESS
CF SILO RAW MEAL
STORAGE & HOMOG.
RAW MEAL GRINDING
COLD CLINKER
PYRO PROCESS
C E M E N T M A N U F A C T U R I N G P R O C E S S
RECLAIMING PROCESS RECLAIMING PROCESS
CLINKER STOCK PILE
HOT CLINKER
CLINKER COOLER CLINKER COOLER
CRUSHED COAL
CLINKER STOCK PILE
PROCESS
COAL CRUSHING
STACKING & RECLAIMING
COAL GRINDING
PROCESS
UNIT-I UNIT-II

CRUSHER

Crushing
 Input Size-1-2m
 Product Size
 25 mm for Ball mills
 50 - 75 mm for VRM
 (Based on mill size)

Pre-Homogenizing of Materials
 Objective:
 Homogenizing of Raw Materials
 Raw Material Storage
 Raw material Stacking
 Raw material Reclaiming

Stacker / Reclaimer

Raw Material Grinding
RAW MATERIAL
STACKING / RECLAIMIN
/ MIXING
RAW MATERIAL GRINDIN
FUEL GRINDING
CLINKER GRINDING
FUEL FIRING
Limestone
Quarrying
Crushing
3 - 5% Gypsum
l
RAW MIX FEED
Feed Size 60 - 100 mm
Raw Meal Product
12% R90  sieve
Input Size 50-75
mm
VRM
Product size 15%
on 90 micron

Raw Mill-Operating Principle
45 – 60 m/s
1500 – 3000
%
Nozzle Ring
Recirculation 10-25%
100 %
10 – 25%
New Feed 100%

HOT GASES FROM
PH FAN EXIT
Process Flow Sheet Raw Mill

Quality Parameters for Raw Mix
Design
 Silica Modulus
 Increase in Silica ratio – Difficult to burn.
 Hard to burn.
 Lower sintering temperature
3
2
3
2
6
/
O
Fe
O
Al
SiO
R
S



Design
 Alumina Modulus:-
 Ratio indicates the quantity of initial liquid
phase present during burning
3
2
3
2
/
O
Fe
O
Al
F
A 

Design
 LSF-Lime Statutaration Factor
3
2
3
2
2
3
2
3
2
2
7
.
0
1
.
1
8
.
2
64
.
0
/
35
.
0
6
.
1
8
.
2
64
.
0
/
O
Fe
O
Al
SiO
CaO
LSF
F
A
O
Fe
O
Al
SiO
CaO
LSF
F
A









Lime Saturation Factor
 Lime-Saturation Factor = 1:- The clinker is
difficult to burn.
 High free lime content.
 Over limed – LSF = 0.97.
 Excellent indicator.
 Permissible range of variation of free-lime
contents – 0.4 and 1.2%.

Raw Mix Design
 Depending Factors
 Type of Coal(Pet coke or coal)
 Lime Stone Quality
 Sulphur alkali ratio in Case of petcoke

Pyro process Optimization
 Inputs:- Outputs
 Kiln Feed Clinker
 Primary Air PH exit Gases
 Cooling Air Cooler vent
 Coal Return dust

of coal ash on clinker composition
Component Kiln Feed Ash Potential clinker
SiO2 20.71 47.00 21.50
Al2O3 4.84 27.00 5.50
Fe2O3 2.78 20.00 3.30
CaO 67.43 3.00 65.50
MgO 2.58 0.00 2.50
SO3 0.15 Trace 0.15
Na2O 0.22 Trace 0.83
K2O 0.85 Trace -

ILC –Double String Kiln System

ILC –Kiln System

SLC - Kiln System

Primary Air
 Just enough to carry and mix with the fuel
thoroughly
 May vary from 5 to 15 % of total air fed to kiln
system but should be as little as possible
 Burner nozzle velocity : 80-120 m/sec
 Primary air to fuel ratio : 0.8-1.3

Effects of Primary Air on Combustion
 Decrease in flame temperature
 Decrease in thermal efficiency of kiln and cooler
 Increase in fuel consumption
Increase in primary air causes :
Decrease in primary air leads to :
 Choking in primary air conveying pipe
 Improper mixing/turbulence

Secondary Air
 It is the main part of the combustion air (85 – 95%
of total air fed)
 Preheating of air is done in contact with hot
outgoing clinker in the cooler
 Temperature
700-8500c for wet process
900-10500c for dry process
 Velocity of the secondary air : 9-11 m/sec
 Flame direction is usually affected by the
buoyancy of secondary air

Effects of Increasing Secondary Air on
Combustion
 Increases thermal efficiency of kiln and cooler
 Increases flame temperature
 Increases coal consumption
 Affects flame direction

Chemical Reactions Inside kiln and
Preheater
Temp
(Deg C )
Process Chemical
Transformation
< 100 Drying, removal of
water
H 2O (l)  H 2O (g)
100-400
Decomposition of
clay with formation
of kaolinite
Al 2(OH) 8Si 4O 10
 2(Al 2O 3. 2SiO 2)
+4H 2O
600-900
Decomposition of
metakaolinite to a
mixture of free
reactive oxides
Al 2O 3. 2SiO 2 Al 2O 3. +
+2SiO 2

600- 1000 Decomposition of
limestone and
formation of CS
and CA
CaCO 3  CaO +CO 2
3CaO+ 2SiO 2+2Al 2O3
 2( CaO.SiO z) +
CaO.Al 2O3
800-1300 Decomposition of
limestone and
formation of C 2S,
C3A and C 4AF
2CaO +SiO 2
 2CaO.SiO 2
CaO.Al 2O3+2CaO
 3CaO.Al 2O3
CaO.Al 2O3+3CaO
+Fe 2O3 
4CaO.Al 2O3.Fe zO3
1250-
1450
Further binding of
lime by C 2S to form
C3S
2CaO 2.SiO 2 CaO 
3CaO.SiO 2
Chemical Reactions Inside kiln And
Preheater

Chemical Reactions Inside kiln and
Preheater
MgCO3 : MgCO3 - > MgO +CO2
Organic Carbon : C + O2 -> CO2
Sulfur as pyrites : 2 FeS2 + 6 1/2 O2 +
2 CaCo3 -> Fe2O3 +
2 SO2+2CaSO4 +2 CO2
Sulfur in fuel : 2S + 3 O2 -> 2SO3
CaO + SO3 -> CaSO4
Recarbonation : CO2 + CaO - > CaCO3 + heat

27/11/2021
(Optional) File source,
Department or division, Creator
HGRS_Master
Heat And Mass Balance Inputs
Fuels
Primary
air
Kiln feed
Fuels
Cooling air False air
Kiln HB
border
Cooler HB
border

27/11/2021
(Optional) File source,
Department or division, Creator
HGRS_Master
Heat and Mass Balance Outputs
Clinker
Cooler waste / middle
air
Radiation
and
Convection
PH
exhaust
gas/dust
Kiln HB
border
Cooler HB
border

Heat Input
INPUT
Mass flow Specific heat Temperature Heat Input
kg/kg
clinker
Kcal/Kg0
C 0C
Kcal/Kgclinker
Sensible heat of kiln feed 1.60 0.213 75 25.60
Sensible heat of kiln feed
moisture 0.02 0.446 75 0.803
Sensible heat of Fine Coal 0.09 0.289 70 1.87
Sensible heat of Primary air 0.08 0.238 32 0.58
sensible heat of cooling air 2.57 0.238 32 19.58
Sensible heat of conveying air 0.06 0.238 32 0.49
NCV of fuel
heat of fuel 738.34
sensible heat of fine coal
moisture 0.002 0.446 68 0.056
4.36
Total Heat Input 48.98

Heat Output
OUTPUT
Mass flow Specific heat
Temperatur
e
Heat Output
kg/kg clinker Kcal/Kg0
C 0
C Kcal/Kg clinker
Sensible heat preheater exit gases
string1 2.277 0.26 296.000 178.02
Sensible heat of raw meal return dust 0.10 0.24 296.000 6.87
Sensible heat of cooler exit gases 1.67 0.24 281.00 113.36
Heat of Formation of clinker 400
Cooler & Kiln Hood Radiation 2.99
Kiln Radiation 26.79
T.A .D. radiation 1.3735
Preheater Radiation 41.91
Sensible Heat of clinker 1 0.19 85 16.28
5.04
TOTAL HEAT OUTPUT 787.33
overall radiation loss(kcal/kg clinker) 73.07
%over all heat loss in radiation 9.28

Optimum Parameters
 Cooling air for new generation:-2.2 kg air/kg
clinker
 Preheater Gas Volume-1.5 Nm3/kg Clinker(Pet-
coke) & 1.3-1.5 Nm3/kg Clinker(Coal).
 Cooler Vent air-1.0 Nm3/Kg Clinker.
 Overall radiation loss -7-8%
 False air -8% across preheater
 Preheater O/L Temp-250 degree C for 6 Stage.
 Pressure drop 450-500 mmwg for 6 stage.

Cooling Air Requirement per kg
Clinker
50
75
100
125
150
175
200
225
250
275
300
1.4 1.9 2.4
Specific Cooling Air [Nm3/kg Clinker]
Clinker
End
T
[°C
above
Ambient]

Cooling Air requirement for different
Generation Coolers

Effect of grate resistance on air distribution
Cooler Bed Height Depends on Material
characteristics

Effect of resistance grates
FINE SIDE
cooling
UNEVEN AIR
FLOW
PROFILE
TRADITIONAL COOLER
air fan
KILN
cooling air
cooling air
cooling air sealing air
EVEN AIR
FLOW
PROFILE
COOLAX-CFG COOLER
KILN
FIGURE 25

Cooler Efficiency

Simplified Cooler Balance
Conventional
TOTAL COOLER LOSS: 160 kcal/kg
STD. COOLER LOSS : 130 kcal/kg
DEPENDENT
UPON
EXCESS AIR
FIGURE 35

Simplified Cooler Balance
Modern Cooler
TOTAL COOLER LOSS: 105 kcal/kg
STD. COOLER LOSS : 85 kcal/kg
FIGURE 47

Optimized Cooler Loss
A. PLANETARY COOLER
Radiation 97
Clinker (150ºC) 25
122 kcal/kg
B. ROTARY COOLER
Radiation 75
Clinker (225ºC) 45
120 kcal/kg
C. CONVENTIONAL GRATE COOLER
Radiation 6
Excess Air (1.85 kg/kg @ 240ºC) 108
Clinker (90ºC) 17
131 kcal/kg
D. AIR-BEAM GRATE COOLER
Radiation 6
Excess Air (1.2 kg/kg @ 240ºC) 70
Clinker (90ºC) 17
93 kcal/kg
E. CROSS-BAR COOLER
Radiation 6
Excess Air (1.0 kg/kg @ 240C) 58
Clinker (90C) 17
81 kcal/kg

IMPACT OF PROCESS PARAMETERS ON QUALITY
SNo. PARAMETER SIGNIFICANCE
1. Raw Meal
Composition
 Influences Burnability and Fuel consumption
 Mixes with high LSF and/or high SM require
more fuel for burning and vice versa
 Inhomogeneity and non-uniformity of the mix
affect the kiln operation
1.1 Raw Meal
Fineness
 Influences the heat transfer rate and kinetics
of reactions
 Affects Burnability
 Coarse particles (+0.2 mm) of silica cause
problems in burning if their percentage
exceeds 0.5

S.No. PARAMETER SIGNIFICANCE
2 Fuel (coal) quality
VM  Affects grindability
 Affects flame length and shape
Ash content  Influences grindability
 Affects the calorific value
 Affects the mineral composition of clinker
 Coal ash with low fusion point causes ash ring
Moisture Content  Affects grindability
 Affects power consumption output of mill
 Affects the flame temperature depending on the
firing system
 Residual moisture content in fine coal will be
abnormal in the case of ball mills when raw coal
moisture content is >10% (except where
separate dryers are used)
Impact of Process Parameter on
Quality

Fixed carbon  Influences the burning time of coal particles
 Influences the heating value of coal
 Influences the flame length when coal is coarsely
ground
Calorific value  The higher the net CV the lower the quantity of
coal required per unit clinker and vice versa
 Changes/variations in net CV of coal affect the
proportion of primary air
Oxygen content  Influences the combustion air requirement
Sulphur  When present in appreciable quantity causes
‘SO3’ cycles, ring formation etc.
2.1 Fineness of
pulvarized coal
 Influences the combustion efficiency
 Influences the burning time
Fineness of p.f.
(coal)
 Affects the rate of heat generation
Quality

3.0 Flame
Temperature
 Affects the sintering reactions
 Affects the temperature profile, temp. gradient and heat
transfer rate
3.1 Excess air  Necessary for ensuring complete combustion of fuel
 Influences in fuel consumption of above optimum –
power consumption and production also affected
3.2 Secondary air
temperature
 Signifies the efficiency of heat recovery from clinker
 Influences the flame temperature
3.3 Primary air
quantity
 Affects the flame temperature and length
 Affects the tip velocity and turbulence
4.0 Burning zone
temperature
 Influenced by the Burnability of mix
 ‘Hard’ burning mixes characterized by high LSF and
or high SM require high BZ temperature
Quality

4.1 Kiln speed  Controls the transport velocity of meal in the
kiln to maintain BZ temperature
 Influenced by the degree of filling and
Burnability of meal
4.2 Fuel feed rate  Controls BZ temperature
4.3 Kiln torque  Reflects the BZ condition
4.4 Clinker litre weight
and free lime
 Indicate the quality of clinker/efficiency of
burning
4.5 Kiln shell
temperature
 Trends indicates unusual coating formation, ring
formation, wearing of refractory, hot spot etc.
5.0 Temperature of
kiln exhaust
gases
 Indicates whether or not the required heat is
absorbed by the meal. In other words whether
temperature profile is maintained or not
Impact of Process Parameter on Quality

5.1 CO & O2 in exh. gases  Indicative of completeness of
combustion of fuel
 Indicates excess air quantity
 Indicates amount of ‘false’ air
5.2 NOx in exh. gases  Very fast indicator of changes in burning
zone temperature
6.0 Suspension Preheater
Temperature &
Draught in different
stages
 Indicates whether heat transfer and dust
load in the respective stages are OK or
not
6.1 Temperature drop (gas)
across the preheater
 Indicative of the thermal efficiency of the
preheater

6.2 Temperature of gases at
kiln inlet
 Indicates whether the temperature
profile across the kiln is in order
or not
6.3 Temperature of preheater
exhaust gases
 Indicative of the performance of
the preheater
6.4 Degree of calcination at
Ph outlet
 Indicative of the efficiency of heat
transfer in the Ph
7.0 Precalciner Outlet
gas Temperature
 Indicative of ‘equilibrium’
conditions inside the precalciner
Secondary fuel feed rate  Controls DC & precalciner outlet
gas temperature
Tertiary air quantity  Regulated through set point
controller

8 Clinker cooling in grate coolers :
8.1 Cooling air
quantities and flow
rates
 Maintained as required by operation of the
individual fan dampers by P.I.D. controller
8.2 Bed thickness  Controlled by pressure under the 1st grate
Compt. through regulation of the 1st grate
speed and the other grates proportionately
8.3 Hood pressure  Maintained by manipulating the vent gas fan
damper
 Deviation from set point indicates a shift of the
null point
8.4 Exhaust air
temperature
 Variation in the temperature indicates cooling
air flow rates in the ‘after cooling’ zone are
fluctuating, fluctuation in the granulometry of
clinker or shifting of ‘null’ point

MILL OPTIMIZATION

VERTICAL ROLLER MILL
Grinding table
Roller
Housing
Adjustable nozzle
ring
Gear box
Separator
Feed
chute

Optimization of VRM
 Optimization of feed size
 Optimization of Dam Ring height & Nozzle
Ring velocity
 Optimization of air quantities & Temp in
Mill circuit
 Minimization of false air in the circuit
 Optimization of product residue
 Operation of Mill with high level control
system

Nozzle Ring Velocity
 Minimum velocity is required to lift
material.
 Raw mill-35-50 m/sec
 Coal mill petcoke-45-60 m/sec
 Coal mill-40-60 m/sec

Nozzle Ring Velocity
 Optimum air velocity at nozzle ring m/Sec
 With recirculation system : 40 to 45 m/sec
 Without recirculation system : 60 to 65 m/sec

Dam Ring Height
 Generally-2-4% of Table Dia
 Observations:-
 Dam ring height too high
 High mill motor current
 Low Mill DP

Dam Ring Height
 Generally-2-4% of Table Dia
 Observations:-
 Dam ring height too LOW
 Low mill motor current
 Low Mill DP
 High rejects level
 Low mill output
 High Vibration than Normal

Mill Grinding Pressure
 Operating Pressure as per
supplier.
 Observations:-
 Low grinding pressure
 Low mill motor current
 Low capacity for given air flow and DP.
 High rejects level
 High DP across nozzle ring and separator.

Nozzle Modification

Electrical Energy Consumption Per
Section

Latest Inhouse Modifications In
Cement plants
 Suction Box Modifications of Process
fans
 Pressure drop stick inside the cyclones.
 Installation of Baffle plate in Cooler.
 Nozzle ring design in Mills.

Suction Box Modification in Raw MILLS
Raw Mill 2fan 1 UOM Before After
Flow m3/
hr.
789550 779600
Pressure at fan
I/L
mmw
g
-940 -910
Fan speed rpm 965 935-950
Fan Kwh kWh 3200-
3250
3150-
3200
Raw Mill 1fan1 UOM Before After
Flow m3/h
r.
810000 800000
Pressure at fan
I/L
mmw
g
-1100 -1040
Fan speed rpm 965 950
Fan Kwh kWh 3000 2850
1. Raw mill1 Fan inlet suction box
increased by extending the
width by 330mm.
2. Raw mill 2 fan inlet suction box
increased by extending the
width by 385mm.

Modification in Pyrosection
 TAD Ramp has been made to increase the
oxygen percentage at kiln inlet.
 Around 35% blocked the area.
 Shifting of cooler water spray nozzles from
take off duct to centre of cooler wall.

Modification in coal mill for pet coke
grinding
Parameters Before
modification
After modification
Dam Ring height(mm) 145 120
Nozzle ring
velocity(m/s)
41 60
Static vanes gap(mm) 35-40mm 30mm
Mill outlet dust
load(gm/m3)
170 210
Residue(90 micron) in
pet coke.
8% 1.2% - 3%

Installation of Baffle Plate at null
point in cooler
Before After
Input Cooling air(kg
air/kg clinker)
2.6 2.36
Specific power of
cooler ID fan(kwh/t
clinker)
0.714 0.542
Cooler Vent
Volume(Nm3/hr)
276834 234164
Specific heat
consumption(Kcal/kg
clinker)
690 685

Thank You!

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