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