Combustion training in Cement KilnsCement Kilns

Guess what it is?Guess what it is?

22 m

Coating in the preheaterCoating in the preheater4

3

2

o

t

m

e

a

l

[

%

]

strong coating

1

C

l

i

n

h

o

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 kiln Raw meal (limestone, kaolin, sand, iron scale) Fuels (oil, petcoke, olive residues)

Volitalisation Temperature profile of kiln (Burning zone) Burner (shape of the flame)

Fuel preparation Fuel preparation Combustion condition (CO)

Indirect factors Indirect factors Raw 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 clinker 14.1 g/kg clinker

90% oil10% olive residues10% olive residues 13.7 g/kg clinker

% 50% oil40% petcoke10% olive residues

19 8 /k li k 19.8 g/kg clinker

V lit li tiVolitalisation

volatile circuits at kilnvolatile circuits at kiln

K2SO4:Tmelting =1069C Tboiling=1689CN SONa2SO4:Tmelting =884C

Eutectic:Eutectic:Tmelting =823C

Mechanism of volitalisationMechanism of volitalisation

Volitalisation reaction of CaSO41 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

p

p

m

Fan capacity Heat consumption Temperature kiln inlet

400600800

S

O

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 formation Alignment of the burner Shape of flame Fuel flow uniformity Fuel preparation

Key 2: TemperatureKey 2: Temperature100

40

60

80

b

a

l

a

n

c

e 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

l

i

s

a

t

i

o

n 1000degC1200degC1400degC

0.2

0.4

v

o

l

i

t

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 speed Calcination degree

Flame 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 air Higher pressure ~ higher impulsion Higher impulsion => hot secondary air sucked in

quicker => faster combustion => shorter flameRadial air Radial air Higher pressure ~ higher swirl Higher swirl => flame gets wider (dont touch Higher swirl => flame gets wider (don t touch

refractory or clinker bed!) Central air

Higher 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 output

Secondary 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

f

l

o

w

2000

4000

f

u

e

l

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 g Adjust 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: R200m=0%,

R90m

Burner positionBurner position

Centered in and parallel to kiln axis, maybe a little offset to kiln top side

Moving 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 flame

higher risk for nose ring (temperature) more risk for snowman upwards deformed flame => less evaporation

I di t f tIndirect factors

Indirect factorsIndirect factors

Kiln feed uniformity Settings of kiln operation according to worse material

(e.g. high LSF) => overheating of good material Burnability

L b bilit ( hi h j t ) d hi h b i Low burnability (e.g. high rejects) needs high burning zone temperature

Stability of cooler operationStability of cooler operation Variations of cooler operation => variation of

secondary air temperature => variation of burning t tzone temperature

Monitoring combustionMonitoring combustion Free lime (ratio fuel / feed)

Kil i l t l Kiln 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 measurements Kiln 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 CO Increase flame / secondary air temperature Decrease burning zone temperature Decrease burning zone length Maintain fuel preparation targets

f Reduce raw mix fineness Increase free lime

Control the flame shape Control the flame shape