04.04 Kiln Operations Guide Lines_ENG

KILN OPERATIONS

GUIDE LINES

•

Our objectives

•

To produce more

•

To produce with regularity

•

To produce cheaper

•

Stable kiln operation is key to achieving our

objectives

Rules

R1 -

Constant kiln volume load

R2 -

Constant cooler clinker bed depth

R3 -

Predefined tables for cooler fans

R4 -

Constant slightly negative kiln hood pressure

R5 -

Constant Oxygen and in excess at kiln back end

R6 -

Oxygen in excess at tower exit

R7 -

Constant ID fan outlet pressure

R8 -

Fuel amount proportional of to kiln feed rate –

Production ramp up

R9 -

Constant calcination

R10 -

Maximize production to minimize heat

consumption

Prerequisites

P1 -

Raw mix preparation

P2 -

Fuel preparation

P3 -

Burner adjustment

P4 -

Reliable sensors

Rules

R1 -

Constant kiln volume load

R2 -

Constant cooler clinker bed depth

R3 -

Predefined tables for cooler fans

R4 -

Constant slightly negative kiln hood

pressure

R5 -

Constant Oxygen and in excess at kiln back

end

R6 -

Oxygen in excess at tower exit

R7 -

Constant ID fan outlet pressure

R8 -

Fuel amount proportional of to kiln feed

rate – Production ramp up

R9 -

Constant calcination

R10 -

Maximize production to minimize heat

consumption

Because Operating the kiln with an irregular bed depth

• Makes the clinker pour irregularly into the cooler • Influences heat exchanges between gases and material • Impacts on the state of combustion in the burning zone

• Makes the kiln torque signal to be less representative of the kiln state

Why?

Indicators

Kiln speed/kiln feed ratio has

•

to be calculated by the process engineer

Takes into account kiln dimensions, process, clinker reactivity.

Recommended value

kiln speed = k · kiln feed The k factor characterizes each kiln

R1 – Constant kiln load volume

The kiln speed is proportional to the kiln feed

In general, maximum kiln speed is reached at maximum kiln feed

3.5 rpm 2 rpm 1.2 rpm 1.2 rpm Precalciner Preheater Grate preheater Wet kiln

To maximise & regularise heat recuperation

Constant bed depth

=

constant under grate pressure measured in the first chambers

=

Adjust cooler grate speed and never change the fan volume that impacts this under grate pressure…

Cooler bed depth must be maximized.

On new cooler generations, the clinker bed depth measured on the first grate can range from 500 to 800 mm.

For processwith grate coolers

Why?

Indicators

Recommended values

•

To maximise heat recovery

•

To supply secondary and tertiary air

•

To cool enough the clinker and avoid clinker transport problems and maintain cement mills operation efficiency

Air flows

Outlet cooler clinker temperature

•In the first chambers

•fluidized clinker bed

•fixed fan volume, air flow density must be constant

•In the last chambers

•non-fluidized bed

•cooler fan volume proportional to clinker production rate. Make specific air flow (Nm3_{/kg clinker) adjustments in the last chambers to keep a}

Airflow/Clinker ratio constant

•Clinker temperature at the cooler outlet

• Good performance = 100°C

• Unacceptable > 150°C (cement false set…)

• It is best to avoid having too cold clinker; the temperature inside the cement mill may not be sufficient to form enough semi-hydrates in the cement.

1 1,3

1,5 Air flow density (Nm3_/m2/.s)

3 2

1 Chamber#

Average air flow : 1,8 – 2,5 Nm3_{/kg clinker}

For processwith grate coolers

Why?

Indicators

Recommended values

•

Positive pressure gas/material puffing, spillages (safety issues)

Controlled by cooler exhaust fan which extracts excess air from the cooler

Kiln hood pressure setting point

•–2 to –7 mmWG.

•depends on its stability: the more stable the pressure, the closer to zero it can be.

CO

Secondary air

Discharge end ring 

Hood air inleak (false air) Risk of Impact If hood pressure is too negative

Why?

Levers

Recommended values

R4 – Constant slightly negative kiln

• To avoid formation of CO which gives less energy where we want it C + O₂ CO₂+ 97.6 kcal C + ½ O₂ CO + 29.4 kcal • To minimize volatilization & cyclic operations

• To guarantee uniform clinker quality especially sulfate fluctuations

• Kiln back end O₂

• Kiln back end O₂Standard deviation

•

For Precalciner kiln, the O₂set point ranges from 3 to 5%

•

Standard deviation measured by 1-minute average values over 24 hours

• Very good if

• Very bad if

If Increase Kiln back end O₂set point

> 2,5 % Hot meal analysis on stage 4

•SO₃

> 100 ppm CO level at kiln back end

% 2 . 0 2 < O

σ

Why?

Levers

Recommended values

R5 – Constant oxygen & in excess

at kiln back end

% 4 . 0 2 > O

σ

2 2,5 3 3,5 4 4,5 13 5 7 9 1113151719212 2 2 231 minut es 2 2,5 3 3,5 4 4,5 1 3 5 7 9 11 13 15 17 1921 23 25 27 29 31 mi nute s

•

Too low level of O₂will result in the formation of CO in preheater tower & possible explosion in the electrostatic precipitator: When the CO produced finds some oxygen, it burns as follows

CO + ½ O₂ CO₂+ 68.2 kcalExplosive reaction if there is a spark!

•

Too high level of O₂will result in possible loss of production

•Tower exit O₂ value

•Also Take into account

Carbon included in the raw material

False air

•

Generally 3% < O2 < 5%

Why?

Indicators

Recommended values

•

Stable pressure will prevent perturbations from raw mill, GCT to the kiln

•ID fan outlet pressure must be controlled by the EP fan damper or variable speed drive.

Depend on stability

ID fan outlet pressure must be slightly negative but as close to zero as possible (-10 mmWG).

If ID fan at the maximum limit with margin on EP fan, ID fan outlet pressure set point can be more negative.

For process with EP fan

If ID fan outlet pressure positive

ID fan volumetric flow Qv

O₂

Indicators

Recommended values

R7 – Constant ID fan outlet pressure

Why?

Circuit head loss Fan curve

Kiln feed increase

more material to be burned

proportional fuel increase

Fuel = A · kiln feed + B

B = constant function of heat wall losses

• Kiln specific heat consumption (SHC)

•

Create operation table for kiln feed to fuel rate taking in consideration

• Kiln specific heat consumption

• Heat wall losses

• Fuel calorific value

0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 0 10 20 30 40 50 60 70 80 90 100 Kiln feed t/h Fuel t/h A B

•

Questions to be raised in case of drift on SHC (A or B)

• Calibration of the feeders

• Raw mix chemistry

• Raw mix uniformity

Indicators

Recommended values

R8 – fuel amount proportional to kiln

feed rate – Production ramp up

Why?

Draft Kiln Speed

Feed rate

Ratio Burner Fuel Ratio Ratio 800 825 850 875 900 925 950 975 1000 1025 1050 1075 1100 1125 1150 1175 1200 18 23 28 33 38 43 48 53 58 Clinker t/h SHC Specific Heat Consumption kcal/k ck A B

To avoid a shift of the burning zone.

•

Calcination level is controlled by temperature probe considered as representative (bottom cyclones, riser duct) with a control loop acting on secondary burner fuel rate. Set point around 850°C

•

The main burner / secondary burner ratio must be mastered on continuous basis to detect any drift (probe build-ups…). The main burner / secondary burner ratio does not vary too much (example: Precalciner kiln main burner = 40%, secondary = 60%)

For process with secondary burner

Calcination 

Calcination

Ignition point = Start of liquid phase

%

calcination

Type of kiln 90 – 92% Preheater AS 55 - 70% Preheater AT

Indicators

Recommended values

R9 – Constant Calcination

Why?

Bottom cyclones and riser duct temperatures Calcination level of bottom cyclones hot meal

The maximum production minimizes the heat

consumption:

•If the ID fan is at nominal ventilation : the only actuator to maintain kiln condition is the feed rate

•If the ID fan is below nominal ventilation, give priority to feed rate and use fuel and ID fan to control combustion

ID fan draught margin

800 825 850 875 900 925 950 975 1000 1025 1050 1075 1100 1125 1150 1175 1200 18 23 28 33 38 43 48 53 58 SHC Specific Heat Consumption kcal/k ck

Indicators

Recommended values

R10 – Maximize production to minimize

Heat consumption

Why?

Prerequisites

P1 -

Raw mix preparation

P2 -

Fuel preparation

P3 -

Burner adjustment

P4 -

Reliable sensors

Raw mix residues targets
Lime saturation

1.43F)

6.72A

S

6

.

7

(

C

07

.

4

S

C

₃

=

−

_sol

+

+

P1 - Raw mix preparation

1%

200

µ

m

10%

100

µ

m

F

A

S

C

LSF

65

.

0

18

.

1

8

.

2

100

+

+

=

C

F

A

S

C

F

A

S

bc

+

+

+

−

+

+

=

∆

100

(

2

.

8

1

.

65

0

.

35

)

Range between 90 and 98 depending on fuel ashes and quality target

Range between –4 and +4 depending on fuel ashes and quality target

C3S is the potential C3S content of clinker when free lime is zero and calculation LOI=0. (Potential C3S target also depends on the chemical composition of the ashes generated by the fuel.)

Potential C3S contained in raw mix as target is more sensitive than _{bc, LSF but }_{bc, LSF calculations are} more robust since these 2 lime saturation factors are less influenced by FX drifts.

Effects of fuel ashes

• Fuel ashes exhibit a very significant deficit in C in relation to S content (very high lime deficiency)

• It must be compensated by using the lime from the raw mix to combine the excess S.

• The C₃S of the raw mix that have to be designed will be higher than the targeted C₃S in clinker.

Example

S

C

.

S

C

.

S

C

₃ clinker

=

a

₃ rawmix

+

b

₃ ashes with (a+b) = 1

P1 - Raw mix preparation

a

b

ashes clinker mix raw

S

C

.

S

C

S

C

₃

=

3

−

3

2

.

71

981

.

0

(-258)

019

.

0

65

S

C

₃ rawmix

=

−

=

fuel ker) (feed/clin fuel

PCI

.

Ratio

100

%Ash

.

SHC

b

=

Calorific Value (PCI) ash J/g % 24000 20,0 Fuel Heat Cons. (SHC) Feed / kk J/g kk 3500 1,54 Kiln

981

.

0

019

.

0

b

=

⇒

_a

=

Silica ratio

Alumina ratio

P1 - Raw mix preparation

F

A

S

SR

+

=

F

A

AR

=

SR: 2.3 to 3.0 constant at ± 0.05 AR: 1.3 to 2.0 constant at ± 0.05 Hard Easy Burning Low, high thermal load Excessive, attack to bricks Liquid phase No Too thick, unstable Coating Dusty, high free lime Balling, hard Clinker High Low Cement strength High Low SR

With low F, insufficient liquid phase is formed

(Viscous liquid phase) Fluid

Liquid phase

If AR<0,64 No C3A in clinker

Clinker

High early strength Low early strength

Cement strength

High Low AR

Kiln Feed Uniformity Index KFUI < 14

Average of the squared difference between a spot kiln feed sample C₃S value and the C₃S target, on a daily basis

•

if KFUI> 30, an emergency action plan must be implemented High KFUI: Possible reasons

P1 - Raw mix preparation

∑

= − = N i T i C S S C N KFUI 1 2 3 3 ) ( 1 Combustion regularity Heat consumption Kiln stability Brick life Clinker output Volatilization of SO₃ Equipment life Grindability (kWh/t)

Cement mill output

Clinker quality

Regular clinker quality

σC₃S σf-CaO σStrengths Cost CC/CK ratio Effects on PROCESS Effects on PRODUCT KILN FEED UNIFORMITY Mining Prehomogenization KILN FEED UNIFORMITY Blockages Analyser

Variable materials quality

Raw mill feeders accuracy

Homogenization

Solid fuel residues

*VM: volatile matter

Liquid fuel

• Keep viscosity <25 cSTto obtain satisfactory atomization

Viscosity decreases with higher fuel temperature

Fuel heating temperature to achieve required viscosity depends on fuel oil type

Example: 120°C minimum for a bunker C fuel oil (n° 6)

• Filter at 125 µm to protect pumps and nozzles injectors

• Fuel atomizer type MY

P2 - Fuel preparation

63 µm 90 µm < (0.5×VM*_{) %} 200 µm 0 % S fuel > 4% S fuel < 4% Target

The flow is adjusted by fuel pressure and operates adequately for a flow ranging between 80 and 100% of the fuel scale. If the flow differs, the orifice plate and

atomizer must be replaced.

On stabilized operations, pressure nozzle remains around 40 bars

The primary / secondary pressure differential allows the adjustment of the divergence angle of the streams jet (optimization)

Line up the burner with the kiln axis using laser beam

To avoid that the flame licks:

• Either the material in the zone with the risk of local formation of CO and thus volatilization of sulphates

• Either the walls with the risk of destroying coating and refractories

Flow rate at the burner must be constant at ± 1%

Flame must be:

a. Sharp b. Narrow c. Strong

d. Attached to the burner (30 cm black plume)

e. Such that flame licks neither the bricks nor the clinker bed

Lafarge burner

Influence of the rotational and Axial air on the flame

P3 – Burner adjustment

0,1 6,0 N.h. GCal-1 Coal 0,1 7,5 N.h. GCal-1 Coke 7,5 N.h. GCal-1 5,0 N.h. GCal-1 Impulse 0,05 0,1 Swirl Gas Liquid fuel

+ 10 / - 50 mmWG

ID fan outlet pressure

Immediate chamber after static part or 2nd _chamber

0 / 100 mbar

Cooler under grate pressure

Mandatory if fuel has high S content

0 / 30000 ppm

SO2

Measured with pyrometer 0 / 500°C

Clinker temperature Kiln amps

Measured in 3 points, using large diameter pipe tubes with

can be easily cleaned + 5 / - 10 mmWG

Kiln hood pressure

Measured with representative and well placed thermocouple

probe (far from buildups) 0 / 1000°C

Calcination temperature

Measured with pyrometric camera

0 / 2000°C

BZ temperature

Measured inside the kiln (50 to 80 cm in the Kiln), Probe positioned in the upper quarter

opposite the clinker bed 0 /10% O2 “ 0 / 3000 ppm CO NOx Sensors “ 0 / 2000 ppm Comments Scales

P4 - Reliable sensors

Free lime analyzer = the last direct indicator of the quality for clinker burning

•The free lime content is an indicator of the state of the burning

•Setting time is a function of the free lime content.

•Take into account trends and not only values

•Free lime signification for well proportioned raw material

• Free CaO > 2.0% under burning

• 0.5% < Free CaO < 2.0% well burnt

• Free CaO < 0.5% over burning

•Free lime stability

1

1

.

0

lime

free

2

.

0

lime free

<

+

×

=

σ

FLUI

P5 - Qualifiers sensors for free lime

Advance 46 mn Advance 35 mn Advance 25 mn Advance 15 mn Amps Gamma NOx T Zone F-CaO GLW NOx BZT Amps

TECHNICAL CENTER EUROPE-AFRICA Burning Environment Department

95, rue du Montmurier - BP 17

38291 St-Quentin-Fallavier Cedex - France Tel. + 33 4 74 82 16 16