04_Process Functions RevAB

8/13/2019 04_Process Functions RevAB

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DR

MediathequeLafarge

Process functions


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Clinker Cooler Fundamentals


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Clinker Cooler Fundamentals

Five Functions of the Clinker Cooler

Quenching

Clinker cooling

Heat recuperation

Transportation

Size Reduction


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Quenching

Quick clinker cooling maintains crystalline structure (C2S,

C3S), or freezes it (C4AF, C3A), & by doing so, maintains

hydraulic properties.

If cooling process is too slow

C2

S forms non hydraulic crystals, resulting in decrease in

strength

C3S C2S () + free CaO, resulting in decrease in strength

Formation of large C3A & C4AF crystals that are less

hydraulic, results in decrease in strength


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Quenching (contd)

Clinker quality highly affected by speed of cooling

Quick quenching freezes interstitial material & improves

clinker reactivity

Quenching required to prevent formation of periclase

(crystallized magnesia) - can generate delayed swelling Rapid cooling is important to stabilize the unstable C3S, to

prevent decay into C2S & lime, this reducing reactivity of

clinker


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Clinker Cooling

From 1300-1400C down to 50-100C clinker exit temp

Cooling required to

Protect clinker evacuation equipment

Maintain reasonable clinker storage temp

Reduce mill operating temps & water spray reqts Especially critical when plant inventories are low


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Heat Recuperation

Heat recovery through thermal exchange between hot

clinker bed & air traveling through it

Efficient coolers can recover more than 70% of clinkers heat

Recovered heat is used for:

Combustion - Secondary/tertiary air

Drying

Auxiliary air take off for raw mill, coal mills

Good heat recuperation makes the difference between

efficient & non-efficient kiln systems


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Transportation

Clinker cooler can be considered as part of clinker

evacuation system, transporting material from point A to

B (Cooler Inlet To Cooler Discharge)


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Size Reduction

Material exiting Clinker Cooler is reduced in size by

Clinker Breaker or Roll Crusher

Provides consistent feed size conducive to first

compartment ball charge design of finish mills


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Reciprocating Grate Cooler

Reciprocating Grate Cooler The name refers to the

motion of cooler grateplates that moves back &forth under action of gratedrive(s)

Divided into 2 main areas: Overgrate area - contains

clinker & heated air

Undergrate area - cold air isblown with fans, divided intoseveral compartments,sealed from each other,

improves air flow along axiallength of cooler


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Reciprocating Grate Cooler (contd)

Cooler Fans providing airflow to individual or multiple

compartments are controlled by variable speed drives or

by adjusting position of flow control damper using damper

drives


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12Shop air Secondary air Exhaust

Fans

750 - 850 C

to the dedusterto kiln

Grate cooler Fuller, air circuit


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Cooling air forced through grate plates & clinker bed to

provide forced convection

Incline of cooler grates have evolved from very steep (10)

to 5 &

then 3

New coolers have horizontal grate sections


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Overgrate

compartment

contains hot clinker &

hot airlined with

refractory

In most cases

refractory is a

combination of brick

& monolithics


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Reciprocating cooler made

up of sections of fixed &

movable rows of grates

Coolers can have single or

multiple grate sections

driven independently

Typically multiple grate

driven sections operate with

close ratio of speed from one

section to next


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Movable rows connected to grate drive/s which can be

electro mechanically, or hydraulically driven

Fixed rows of cooler grates are connected directly to cooler

structure


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Clinker Breaker

Discharge end of cooler

supplied with grizzly & hammer

crusher

Grizzly - parallel bars mounted

@ an angle

Grizzly designed to retain large

clinker pieces until theyve

been adequately sized bybreaker to pass through


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Clinker Breaker (contd)

Crushers rotation is such that hammers swing up thru

grizzly & expels oversized material back into cooler

In reverse rotation, hammers would push clinker against

grizzly - quickly plugging

By throwing oversized pieces back into cooler, hot core of

original clinker lump is now exposed - allows for further

cooling

Protection of cooler refractory from flying clinkerPlants

install chain curtains up stream of breaker across full width

of cooler to contain material


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Roll Crusher

Another type ofclinker breaker

Clinker broken underaction of rollers that

turn in oppositedirections to oneanother

Reduces clinker tomore uniform size &generatessignificantly less dust


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Roll Crusher (contd)

Can be installed between grate sections outside

recuperation zone as temp capacity is 400-500C

Large lumps broken down to more uniform size

increasing surface area, improving heat transfer &

cooling efficiency


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Clinker Cooler Principles

Hotter inlet temp = hotter clinker outlet temp

Increasing inlet temp shifts entire clinker profile upwards

Hotter cooling air temp = hotter clinker outlet temp

Explains why cooling is easier in winter months in cold

climates

Longer air/material contact time = cooler clinker outlet

temp

Longer contact time means increased residence time. This is

why lower cooler loading results lower outlet temp

Increasing production rate reduces residence time for a

constant bed depth


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Clinker Cooler Control Strategies

1. Maintain a constant air to clinker ratio

2. Maintain a constant bed depth

3. Control all excess cooling (exhaust) air


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1. Constant Air To Clinker Ratio

Maintain stable secondary air temp - critical to maintainconstant ratio of cooling air to amount of clinker moving

thru cooler

Need to increase airflow to cooler as production increases

decrease amount of airflow if production decreases

Airflow change accomplished by changing position of fans

variable damper or by changing set point of fans variable

speed drive


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2. Constant Bed Depth

Ensures stable secondary air temp by maintaining constantheight of material in cooler & therefore, a consistent

pressure drop thru clinker bed

Pressure drop measured as Undergrate Pressure

Positive static pressure measured in undergrate compartment

itself, or in fan duct

Pressure increases/decreases as a function of clinker bed

height & flow rate of compartment fan

Typically measured in 1st 2 and / or 3 inlet compartments

Most stable reading used as process indication for controlling

grate speed Consider this the control compartment


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2. Constant Bed Depth (contd)

Pressure indication in control compartment is used in acontrol loop against a target set point

As pressure increases/decreases, grate speed is

increased/decreased to maintain pressure set point

Close control over undergrate set point, maintains bed

depth constant

With multiple grate sections, speed of 1st section is

controlled & remaining sections follow by close ratio


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Example

Grate drive #1 8.0 strokes/minute

Grate drive #2 ratio is 1.2 9.6 strokes/minute

Grate drive # 3 ratio is .95 to # 2 9.1 strokes/minute


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Note

1st rule of cooler control strategy indicates need to maintain

constant clinker to air ratio

As production increases or amount of clinker entering

cooler increases, amount of cooling air is increased tomaintain stable operation

Impact?


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Simple increase in airflow on control compartment alongwith rest of cooler, means increase in undergrate

pressure

Increase is not the result of more material being measured

above gratesit is due to an increase in airflow which

increases pressure reading


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How do we manage an increase in air flow in controlcompartment?

As airflow is increased with an increase in clinker production,

an increase in undergrate pressure set point must be made in

order to maintain same bed depth


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3. Excess Cooling Air

Air is pushed into cooler by the action of cooler fans

Air is pulled out of cooler by the action of other major

system fans

Secondary & tertiary air with kiln ID fan/s

Coal mill air by coal circuits main system fan

Raw mill by furnace draft fan or circuits main system fan

Excess air by cooler vent fan


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3. Excess Cooling Air (contd)

Fans controlled independently

Example - kiln ID fan used in controlling oxygen & ID fan flow

rate increases/decreases with kiln production

Since all output fans are pulling air out of cooler, all have

negative pressure at duct inlet

There is a point in cooler where pressure gets to 0

This is referred to as the coolers Neutral point


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3. Excess Cooling Air (contd)

Vent fan purpose - remove excess air (not reqd forcombustion) from cooler

Stability in control of excess air requires static pressure

measured in kiln hood

Vent fan flow rate increases/decreases (by damper or fan

speed) to maintain slightly negative set point

Ensures hot material/gases are maintained inside process

(critical to plant safety)

Controlling hood pressure beyond slightly negative results

in increased inleakage or false air (becomes combustion

air to kiln @ low temp which displaces hot secondary air &

impacts fuel consumption)


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Cooler Control Review

Maintain constant air to clinker ratio

Increase cooler air flow proportionally with kiln production

Use LUCIE cooler automation, or control charts

Maintain a constant bed depth

Use cooler grate speed to control undergrate pressure to set

point

Compensate undergrate pressure set point for changes in

airflow as production increases/decreases

Remove all excess cooling (exhaust) air

Maintain hood pressure slightly negative by adjusting vent fan

flow rate as required


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Clinker Cooler

Documents

04_Process Functions RevAB