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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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Reciprocating Grate Cooler (contd)
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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Reciprocating Grate Cooler (contd)
Overgrate
compartment
contains hot clinker &
hot airlined with
refractory
In most cases
refractory is a
combination of brick
& monolithics
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Reciprocating Grate Cooler (contd)
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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Reciprocating Grate Cooler (contd)
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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2. Constant Bed Depth (contd)
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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2. Constant Bed Depth (contd)
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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2. Constant Bed Depth (contd)
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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2. Constant Bed Depth (contd)
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
Recommended