Cement Process & Energy Saving

October, 2006
The Energy Conservation Center, JapanTaichiro Kawase
Laos 2006.101

Bird-eye View of Japanese Cement Factory
Coal yard

Water

SP &calciner
Waste tireyard

Electrostatic
Precipitator

Rotary kiln
Raw millcrusher

Cement silo

Shipping pierLayout of one Japanese cement factory

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2

Chemical Compositionof Raw Materials and Cement Product
Raw Materials
CaO(%)
Limestone

SiO2(%)

Al2O3(%)

SO3(%)

47-55

CO2(%)
37-43

Clay45-78

Silica

77-96

10-26

Iron-ore
Gypsum

Fe2O3(%)

3-9

40-90
26-41

37-59

Cements
CaO(%)

SiO2(%)

Al2O3(%)

Fe2O3(%)

SO3(%)

Portland cement

63-65

20-23

3.8-5.8

2.5-3.6

1.5-2.3

Blended cement(BF slag)

52-58

24-27

7.0-9.5

1.6-2.5

1.2-2.6

Laos 2006.10

others3Temperature Profile in Wet Process Kiln
Temperature, ℃
2000
Gas temperature
1000

Material temperature
Calcining

DryingPreheating
Water content of raw meal :Sintering
Zoning

Cooling
Clinker temp : 80 – 100 ℃

38 – 40%
Fuel

Raw meal
Kiln

Cooler

Chain Curtain Zone:
20- 25% extension

ClinkerFigure 5 Temperature Profile in Wet Process Kiln
Laos 2006.104Chemistry of Cement Process
Heating (℃)
dryingcalciningsintering

100〜110

Vaporization of physically adsorbed water

110〜700

Vaporization of chemically bonded water

700〜750

Decomposition of MgCO3750〜900

Decomposition of CaCO3, Formation of 2CaO・SiO2

950〜1200

Transition to β・ 2CaO・SiO2

1200〜1300

Formation of 3CaO・Al2O3, 4CaO・Al2O3・Fe2O3

1300〜1450

Formation of 2CaO・SiO2, Sintering of Al2O3, Fe2O3, Na2O,
K2O, etc
During a course of cooling, pebble-like black colored clinker
is formed, which consists of the following components;

cooling

150〜200

3CaO・SiO2: referred to as Alite or C3S

2CaO・SiO2: referred to as Belite orC2S

3CaO・Al2O3: referred to as aluminate phase or C3A

4CaO・Al2O3・Fe2O3 : referred to as ferrite phase or C4AF

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5

Raw Materials and Energy
required for production of 1 ton of Cement
Energy Consumption
Raw Materials (kg)

Fuel (*1)

105
99Limestone

1,095Electric power (kWh)Clay204

Silica78(*1) : kg of coal equivalent
where HHV of coal is 6,200kcal/kg.

Iron-ore30

Gypsum

34

total

1,439

Fuel by kind (%)
Coal78Petroleum coke

13

Combustible waste

5

Heavy oil4

Base : 1 ton of cement

Laos 2006.106

Dry Process Kiln with Suspension Preheater (SP・NSP)
Raw material(Suspension) preheater:
Raw material (fine powder) is
preheated in suspension stateby hot gas coming from kiln.

Suspension
preheater(pre-calciner)

Kiln:
Raw material is calcinedand sintered by fuelburning. Calcining is CO2
removal reaction. Sintering
is formation of molten
clinker by heating.
fuelexhaust gas

exhaust gas

coolerCooler:Molten clinker
is quenchedby cold air.

air

Pre-calciner:
A part of calcining reaction
is made in pre-calciner inmodern NSP process.

clinkerstackstack

Electrostatic precipitator (EP):
Dust-containing gases arededusted in EP or bag filter.

Laos 2006.10

SP

Suspension Preheater

EPElectrostatic Precipitator

F

FanS

Stabilizer (conditioner)

AQC(Air Quenching) Cooler7

Cement Production Process
FinishingsectionDry
Process
SilicaLimestone
Slag

Clay

Clinker
Burning
sectionRaw
Material
sectionWater

Fly ashSilicaDryer
Weigher

CoolerBurnerAdmix millCement mill

Lepol Kiln

Blending
SiloGypsum

CoalBurner

Lepol Grate

Raw MillDryer

Heavy oil

Ordinary
Kiln
Pelletizer

Crusher

Clinker BF slag

Elec Generator
Dust Collector

Weigher

CoolerCementSiloWeigher

WHB
Dry Powder

Mixer

Suspension
preheater
Water

Mixer
Slurry tank

Wet
Process

BurnerCement Silos

SP/NSP Kiln
Cooler

Raw Mill

FilterLong Kiln

Weigher

Shipping
BurnerBulk loader

PackerPackerCoolertankertruckFreight shipcar

Packing center

Figure 1 Cement Production Process
Laos 2006.10

Marketing8

Factory 1

Heat Requirement in Burning Section
Kiln

kcal/kg-cl

Source(1)Nm3/kg-cl(2)Shaft kiln

940

Yogyo Kogaku
H/B1.65

Dry long kiln

1,487

JCTA(1961)

2.62

Wet kiln

1,357

〃

2.38

Lepol kiln

954

〃

1.68

SP kiln

797

JCTA(1981)

1.40

NSP kiln

773

〃

1.35

Note 1: JCA means Japan Cement Technology Association
2: Estimated based on 1.40 Nm3/kg-cl in SP kiln
Factory 2

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9

Dry Process Raw Material Grinding System
aa. Open Circuit

EP
Dryer

Dryer and raw mill are
installed separately.
Dust made in milling is
not recovered.

StorageRaw mill

BTST

Pre-heater & kiln

Dryer
Heat generatorbb. Closed Circuit

EPCollector
StorageSeparator is added.
Coarse dust made in
milling is separated andrecycled to mill. Drying
is done within mill.

Separator

BT : Blending tank
ST : Storage tank
EP : Electrostatic precipitator
BT & ST

Raw mill
Pre-heatercEnergy-efficient verticalroller mill (VRM) isemployed. VRM is also
space-saving.

Factory 2EP
Storagec. Closed Circuit

Factory 1 ?

F : fanCollector
BT & ST
Raw mill
Pre-heater

Figure 4 Dry Process Raw Material Section
Laos 2006.10

10Vertical Roller MillLower part : Classifier

Upper part : roller millVertical roller mill (VRM)
is energy-efficient andalso space-saving.

Laos 2006.1011

Energy Management System(Cement Factory)
AspectOrganization

Monitoring

Major Activity
Accountability

Employee education (awareness)

Organization

EE&C promotion committee
Energy manager

Monitoring

Data recording & reporting to employee

TargetingSpecific energy consumption (SEC)
Key efficiency parameters

Technology
Operation &maintenance (O&M)

Technical review (energy audit)
House keeping

Product yield (avoid off-spec product)
Preventive maintenance (avoidunscheduled shutdown)

Laos 2006.1012

Energy Saving Measures in Cement Factory
Raw material section

Clinker burning section

First step

1)Selection of raw materials2)Management of particle
fineness3)Management of grindingmedia1)Prevention of unscheduled
shutdown
2)Selection of fuel3)Prevention of leakage

1) Management ofparticle fineness2) Management ofgrinding media

Secondstep

1)Replacement of fan rotor2)Improvement oftemperature and pressure
control system
3)Improvement of mixing &homogenization system
4)Installation of closed circuit
mill (separator)

1)Use of industrial waste(waste tire, etc)
2)Heat recovery of pre-heater
exhaust gas and cooler
exhaust gas (drying of raw
material and generation ofelectricity)
3)Replacement of cooler dust
collection from multiclone toEP

1)Installation ofclosed circuit mill(separator)
2)Installation of feed
control system

Third step1)Conversion from wetprocess to dry process2)Replacement of ball or tube
mill by vertical roller mill
3)Pneumatic transfer of raw
material to mechanicaltransfer1)Conversion of fuel frompetroleum to coal2)Conversion of SP to NSP
3)Conversion of planetary
cooler to grate cooler

1)Use of industrial
waste (slag, pozzolan)

Laos 2006.10

Finishing section13Boundary of Heat Balance (Measurement)
Exhaust gas
F

Raw material
TTFgas flow

Tmaterial flow

O2

Air leakPre-heater Section

TKiln SectionT

1ry air

O2
O2

Fuel oilF

TT

Cooler exhaustventT

Air leakT

Cooler Section

Trial & Error MethodTTmeasured or assumed

2ry airT

calculated
ClinkerF

exhaust gas rate

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14

Prediction of Maximum Attainable Production Capacity(Tool : Heat Balance Method)
1

Principle of prediction:
Production capacity is approximately proportional toexhaust gas rate which flows through kiln.

2Calculate exhaust gas rate at pre-heater exit or kiln exit
(m3N/kg-cl) by heat balance method

3Compare with exhaust gas rate of well-designed kiln asshown below;- SP kiln with Grate cooler : 1.4 m3N/kg-cl- SP kiln with Satellite cooler : 2.0 m3N/kg-cl- Dry kiln : 2.6 m3N/kg-cl- Wet kiln : 2.4 m3N/kg-cl

Laos 2006.1015

Air Leakage Measurement
possible air leakage

combustion air
fuelcoolingairstackEPO2

preheaterrawmillO2

Air leakage may bringabout an increase ofboth fuelconsumption and fanpower consumption.

O2kilncooler
FO2

Air leakage occurred in kiln andpre-heater increases fuelconsumption in order for heating
leaked cold air up to processtemperature.

Laos 2006.10

However, air leakage in EP
and raw mill does notnormally increase fuelconsumption, but it
increases required powerof fan motor.

16

Calculation of Energy Loss due to Air Leakage
Location

Leak Amount(m3N/h)Fuel Increase(kg-oil/h)

Elec Power Increase(kWh/h)Burner0Kiln Exit

5530

48.9(*1)

18.7(*2)

Preheater Exit

8690

76.8(*1)

29.3(*2)

Raw Mill Exit

36340

28.2(*3)

EP exit57670

33.1(*4)

Calc Equation of Fuel Loss :(*1)⊿ fuel = Leak (m3N/h) x 0.31 kcal/m3N・degC x (320 – 30) (degC) /10170
Calc Equation of Elec Power Loss :(*2) ⊿ elec (kiln fan) = Leak (m3N/h)/60 x (320+273)/273 x 400mmAq /6120 /0.7(*3) ⊿ elec (RM fan) = Leak (m3N/h)/60 x (90+273)/273 x 150mmAq /6120 /0.7(*4) ⊿ elec (EP fan) = Leak (m3N/h)/60 x (130+273)/273 x 100mmAq /6120 /0.7
Note : LHV of fuel oil = 10170 kcal/kg⊿P mmAq Kiln fan(50) Preheater(400) Raw Mill(150) EP(100)Laos 2006.1017

Monitoring of SEC & Key Variables
SectionMonitored Item

UnitRaw MillSEC = Electric Power / Raw
Material Charge(kWh/kg-raw mat’l)

Clinker
Burning

SEC = Fuel / Clinker production
O2% of Kiln Exhaust Gas(kcal/kg-cl)(%)

Cement MillSEC = Electric Power / Cement
Production(kWh/kg-cement)

Laos 2006.1018

Recording of SEC on the Graph
Watch raw mill SEC daily and add grinding balls in right timing→ 10% energy saving expectedSEC should bemonitored daily, andwhen SEC arrives atcertain level, grinding
balls is compensated.

Raw mill SEC

Ball diameter shrinks astime passes due toerosive effect. This leads
to gradual increase ofraw mill SEC.

Addition of Grinding Balls(kWh/kg-mat’l)Filling level of grinding
balls is also important ingrinding efficiency.
Optimum level of fillingshould be maintained.

Oct.2

Oct.9

Oct.16

Laos 2006.10

Oct.23

Oct.30Nov.6

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Example of Monitoring Sheet(Wet Process)Eng. unit

10/2

Raw Material Charge

ton/d760

Clinker Production

ton/d500

Cement Production

ton/d520

Elec Cons in Raw Mill

kWh/d38000

103xkcal/d750

Elec Cons in Cement
MillkWh/d36000

O2 in Kiln Exhaust Gas

vol%

4.5

SEC of Raw Mill Sect.

kWh/kg-rm

50

SEC of Kiln Sect.

kcal/kg-cl

1500

SEC of Finishing MillSect.

kWh/kg-ce

69.2

Fuel Cons in Kiln

10/3

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10/4

10/5

10/6

10/7

10/820