Combustion training in Cement KilnsCement Kilns

Guess what it is?Guess what it is?

22 µm

Coating in the preheaterCoating in the preheater4

3

2

otm

eal

[ % ]

strong coating

1

Cl i

n ho

acceptableti

lowcoating

coating

SO 3 in hotmeal [ % ]

0

0 1 2 3 4 5 6

Factors influencing SO in hotmealFactors influencing SO3 in hotmeal

Input to the kilnRaw meal (limestone, kaolin, sand, iron scale)Fuels (oil, petcoke, olive residues)

VolitalisationTemperature profile of kiln (Burning zone)Burner (shape of the flame)Fuel preparationFuel preparationCombustion condition (CO)

Indirect factorsIndirect factorsRaw mix (homogenity, burnability)

I t t th kilInput to the kiln

Input to the kilnInput to the kiln

Actual raw mix +100% oil

14 1 g/kg clinker14.1 g/kg clinker

90% oil10% olive residues10% olive residues

13.7 g/kg clinker

%50% oil40% petcoke10% olive residues

19 8 /k li k19.8 g/kg clinker

V lit li tiVolitalisation

volatile circuits at kilnvolatile circuits at kiln

•K2SO4:Tmelting =1069°C Tboiling=1689°C

N SO•Na2SO4:Tmelting =884°C

•Eutectic:•Eutectic:Tmelting =823°C

Mechanism of volitalisationMechanism of volitalisation

Volitalisation reaction of CaSO4

1 OSOCaOCaSO ++⇔ 224 21 OSOCaOCaSO ++⇔

Law of mass action (Goldberg and Waage)

[ ] [ ] [ ][ ]

22 ** OSOCaOk = [ ]4CaSO

Constant(fuel, raw mix input)

keys to control volitalisationkeys to control volitalisation

Key 1: OxygenKey 1: Oxygen

160018002000 Increase O2!

Limits:Fan capacity

100012001400

2 pp

m

Fan capacityHeat consumptionTemperature kiln inlet

400600800SO

2

Above 900degC:2 CO + 1 O2 => 2 CO2Decrease CO!

0200

0.0 0.5 1.0 1.5 2.0 2.5Oxygen %

Local reducing conditionLocal reducing condition

Fuel burns locally with lack of O2 -> CO formationAlignment of the burnerShape of flame Fuel flow uniformityFuel preparation

Key 2: TemperatureKey 2: Temperature100

40

60

80

bala

nce SO3 (in clinker)

SO2 (in gas)

0

20

700 800 900 1000 1100 1200 1300

Decrease burning zone temperature!

temperature degC

Limit:Free lime

Keys 1&2: Oxygen and TemperatureKeys 1&2: Oxygen and Temperature

0.8

1

n 1000degC

0.6

lisat

ion 1000degC

1200degC1400degC

0.2

0.4

volit

a

00 1 2 3 4 5O2 %0 1 2 3 4 5O2 %

Key 3: timeKey 3: time

Which profile causes more evaporation?

temperature profile

p p

Maintain short burning zone!Maintain short burning zone!Kiln speedCalcination degreeFlame shape

20% more evaporation time

Flame shape

Flame / combustion theoryFlame / combustion theory

fuel oxygen

Increase oxygen!Increase secondary air temperature!

temperature

Increase secondary air temperature!Mix it properly!

Kiln burnerKiln burner

Air gun

Axial air

Jackettubes

2 longitudinalexpansion joints

Rotational air

Coal

expansion joints

Coaltransfer

Central air (flame catcher)Central air (flame catcher)

Axial radial & central airAxial, radial & central air

Axial airHigher pressure ~ higher impulsionHigher impulsion => hot secondary air sucked in quicker => faster combustion => shorter flame

Radial airRadial airHigher pressure ~ higher swirlHigher swirl => flame gets wider (don’t touchHigher swirl => flame gets wider (don t touch refractory or clinker bed!)

Central airHigher pressure => more cooling of bluff body,but less dp => flame farer away from burner tip

Burner settingsBurner settingsAxial air

Momentum

Flame length

Swirl

Flame length

Diameter

MomentumRotational

Flame length

Swirl

Diameter

Rotationalair

Momentum

Swirl(1) Results are a function

of the relative importanceFlame length

Diameter

of the two actions(2) Central air as low as

needed for cooling bluff body

Fuel burner nozzleFuel burner nozzle

2 pressure regulating valves

Primary valve adjust the

Primary circuitsecondary circuit

Primary valve adjust the outputSecondary valve adjust primary / secondary

Orifice plateOrifice plateprimary / secondary -ratio => divergenceSecondary circuit

Primary atomizersecondary

primary circuit

Secondary atomizerprimary atomizer

atomizer

Fuel burner nozzleFuel burner nozzle

10000

12000

6000

8000

flow

2000

4000fuel

020 25 30 35 40

pressure main valve (bar)52 sec open 64 sec open 78 sec open52 sec open 64 sec open 78 sec open52 sec closed 64 sec closed 78 sec closed

Adjust flow with primary valve or change of orifice set!j p y gAdjust flame shape with secondary valve!

Fuel preparationFuel preparation

Fuel flow uniformity (± 1%)Fuel flow uniformity (± 1%)Fuel preparation

Fineness of Petcoke (t t R 0%

Atomizing of oil (target: 17 St t b ) (target: R200µm=0%,

R90µm<0.5•%VM)

90100

6

7

17cSt at burner)

4050607080

isco

sity

cSt

HVOfuel #6

3

4

5

6

rnin

g tim

e s

900 degC1500 degC

0102030

80 90 100

110

120

130

140

150

160

170

180

190

200

vi

0

1

2

0

0 05 0.1 0 15 0.2 0 25 0.3

bu

8 9 10 11 12 13 14 15 16 17 18 19 20

fuel temperature degC 0.0 0 0.1 0 0.2 0

Coal particle size mm

Maintain oil temperature and petcoke fineness targets!

Burner positionBurner position

Centered in and parallel to kiln axis, maybe a little offset to kiln top sideMoving of burner tip between 0m and 1m inside kiln

Less deeper inside (closer to nose ring) => Sh t li > h tt li k i l >Shorter cooling zone => hotter clinker in cooler => hotter secondary air temperature => shorter flamehigher risk for nose ring (temperature)more risk for snowmanupwards deformed flame => less evaporation

I di t f tIndirect factors

Indirect factorsIndirect factors

Kiln feed uniformitySettings of kiln operation according to worse material (e.g. high LSF) => overheating of good material

BurnabilityL b bilit ( hi h j t ) d hi h b iLow burnability (e.g. high rejects) needs high burning zone temperature

Stability of cooler operationStability of cooler operationVariations of cooler operation => variation of secondary air temperature => variation of burning

t tzone temperature

Monitoring combustionMonitoring combustionFree lime (ratio fuel / feed)Kil i l t lKiln inlet gas analyzer

O2 (oxydizing atmosphere)CO (reducing atmosphere)CO (reducing atmosphere)NOx (flame / secondary air temperature)SO2 (burning zone temperature)2 ( g p )

Temperature measurementsKiln inlet (burning zone length)Tertiar air (flame length)

Shell scanner, kiln amps (burning zone length)Colour of clinker (burning zone temperature)White steam from cooler (burning zone temperature)

In order to minimize volitalisationIn order to minimize volitalisation…

Increase O2

Decrease COIncrease flame / secondary air temperatureDecrease burning zone temperatureDecrease burning zone lengthMaintain fuel preparation targets

fReduce raw mix finenessIncrease free limeControl the flame shapeControl the flame shape