Cement Kilns-Chlorine Impact on Process

Combustion training in Cement Kilns

Guess what it is?

2 µm

Coating in the preheater 4

Cl in ho otmeal [ % ]

3

strong coating 2

acceptable

1

coating ti low coating

0 0

1

2

3 SO 3 in hotmeal [ % ]

4

5

6

Factors 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 † Combustion condition (CO) Indirect factors † Raw mix (homogenity, burnability)

I Input t to t the th kiln kil

Input to the kiln „

Actual raw mix + † 100% oil „ 14.1 14 1 g/kg clinker †

90% oil 10% olive residues „ 13.7 g/kg clinker

†

50% % oil 40% petcoke 10% olive residues „ 19.8 19 8 g/kg /k clinker li k

V lit li ti Volitalisation

volatile circuits at kiln •K2SO4: Tmelting =1069°C Tboiling=1689°C •Na N 2SO4: Tmelting =884°C •Eutectic: Tmelting =823°C

Mechanism of volitalisation „

Volitalisation reaction of CaSO4

CaSO4 ⇔ CaO + SO2 + 1 O2 2 „

Law of mass action (Goldberg and Waage)

[CaO ]* [SO2 ]* [O2 ] k= [CaSO4 ] Constant (fuel, raw mix input)

keys to control volitalisation

SO2 2 ppm

Key 1: Oxygen 2000 1800 1600 1400 1200 1000 800 600 400 200 0

„

„

0.0 0.5 1.0 1.5 2.0 2.5 Oxygen %

Increase O2! † Limits: „ Fan capacity „ Heat consumption „ Temperature kiln inlet Above 900degC: 2 CO + 1 O2 => 2 CO2 Decrease CO!

Local 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: Temperature 100

balance

80 SO3 (in clinker) SO2 (in gas)

60 40 20 0 700

800

900

1000

1100

temperature degC

„

Decrease burning zone temperature! † Limit: „ Free lime

1200

1300

Keys 1&2: Oxygen and Temperature

volitalisation n

1 0.8

1000degC 1200degC 1400degC

0.6 0.4 0.2 0 0

1

2 O2 % 3

4

5

Key 3: time Which p profile causes more evaporation? p temperature profile

„

Maintain short burning zone! † Kiln speed † Calcination degree † Flame shape

20% more evaporation time

Flame / combustion theory

fuel

oxygen

temperature „ „ „

Increase oxygen! Increase secondary air temperature! Mix it properly!

Kiln burner Air gun

Axial air Rotational air

Jacket tubes

2 longitudinal expansion joints

Coal transfer

Central air (flame catcher)

Axial radial & central air Axial, „

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Axial air † Higher pressure ~ higher impulsion † Higher impulsion => hot secondary air sucked in quicker => faster combustion => shorter flame Radial air † Higher pressure ~ higher swirl † Higher swirl => flame gets wider (don’t (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 settings Axial air

Momentum Swirl Flame length Diameter

Rotational air

Momentum Swirl Flame length Diameter

Momentum Swirl Flame length Diameter

(1) Results are a function of the relative importance of the two actions (2) Central air as low as needed for cooling bluff body

Fuel burner nozzle „

secondary circuit Primary circuit

Orifice plate Orifice plate Secondary circuit primary

circuit Primary atomizer secondary

atomizer Secondary atomizer primary atomizer

2 pressure regulating valves † Primary valve adjust the output † Secondary valve adjust primary / secondary ratio => divergence

Fuel burner nozzle 12000 10000

fuel flow

8000 6000 4000 2000 0 20

25

30

35

40

pressure main valve (bar) 52 sec open 52 sec closed

„ „

64 sec open 64 sec closed

78 sec open 78 sec closed

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

Fuel preparation

Fineness of Petcoke (t (target: t R200µm=0%, 0% R90µm „

„ „ „

Shorter Sh t cooling li zone => >h hotter tt clinker li k iin cooler l => > hotter secondary air temperature => shorter flame higher risk for nose ring (temperature) more risk for snowman upwards deformed flame => less evaporation

I di t factors Indirect f t

Indirect factors „

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Kiln feed uniformity † Settings of kiln operation according to worse material (e.g. high LSF) => overheating of good material Burnability † Low L b burnability bilit ((e.g. hi high h rejects) j t ) needs d hi high hb burning i zone temperature Stability of cooler operation † Variations of cooler operation => variation of secondary air temperature => variation of burning zone temperature t t

Monitoring combustion „ „

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„ „ „

Free lime (ratio fuel / feed) Kil iinlet Kiln l t gas analyzer l † O2 (oxydizing atmosphere) † CO (reducing atmosphere) † NOx (flame / secondary air temperature) † SO2 ( (burning g zone temperature) 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 volitalisation volitalisation… „ „ „ „ „ „ „ „ „

Increase O2 Decrease CO Increase flame / secondary air temperature Decrease burning zone temperature Decrease burning zone length Maintain fuel preparation targets Reduce raw mix fineness f Increase free lime Control the flame shape