Clinker Coolers Holcim-1

Clinker Coolers
Cement Manufacturing Course Asia Pacific
Thane, September 27, 2011
Urs Gasser (CMS - TPT)
© Holcim Group Support Ltd 2011
Clinker Coolers: Table of Content
• Definitions and Theory
• Grate Coolers

The Three Golden Rules for Grate Coolers

Four Facts for Grate Coolers

Grate cooler operation (basics)

Dimensioning Rules

The Typical Problems of Grate Coolers
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
TPT/Ga
Clinker cooler performance is decisive for the pyroprocess!
Clinker
Air / O2
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Cement Manufacturing Course
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Tasks of the Clinker Cooler
1) Recuperation
= Return heat from hot clinker back to process
2) Cooling
= Reduce temperature of clinker
Approach to achieve this:
• Hot clinker is exposed to a stream of cold air for
a certain period of time (= residence time)
• The generated hot air is used for combustion
• The clinker is conveyed at a controlled speed
• The cooler is tight for clinker and air
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Cement Manufacturing Course
10.8.2011
TPT/Ga
Definitions
Recuperation is the recovery of heat contained in the hot clinker
(1300 to 1450°C) at the kiln discharge that is returned to the kiln
system to be used for the pyro process, reducing fuel consumption.
Combustion air is the total air required for stoichiometric combustion
of the fuels in the kiln and the precalciner;
i.e. = primary + secondary + tertiary air
Waste air of (grate) clinker coolers is the cooling air that is in excess of
the combustion air and is blown to ambient (via dedusting system).
The only purpose of this air is to further cool down the clinker.
(Please see also definitions in section „precalciners“)
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Cement Manufacturing Course
10.8.2011
TPT/Ga
Cooler Recuperation Efficiency h cooler
h cooler =
S Q loss
Q hot air to comb.
=
1 -
Q clinker from kiln
Q clinker from kiln
Heat in hot clinker Q cli = m cli * cp cli * (t cli - t ref)
Heat in hot air
Radiation loss
Q air = v air * cp air * (t air - t ref)
Q rad = C R * e * A{(tshell/100)4 - (tamb/100)4)}
Important:
Because the amount of recuperated heat depends on the air flow for combustion,
an h cooler is only meaningful, if the system heat consumption is known!
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
TPT/Ga
The clinker cooler can recover ~25% of process heat!
Fuel Consumption
3020 kJ/kg
Total Energy
To Kiln
4160 kJ/kg
Radiation &
Convection
20 kJ/kg
Hot Clinker
1450°C
1590 kJ/kg
Waste Air
285 °C
350 kJ/kg
Recuperated Air
1050 °C
1140 kJ/kg
Cold Clinker
120°C
80 kJ/kg
Recuperation Efficiency
72%
Cooling Air
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How to Improve Recuperation Efficiency
• Factors influencing recuperation efficiency:



Air flow for combustion (secondary and tertiary air)
 determined by system fuel requirement + excess air
Temperature of sec & tert air
 determined by heat exchange in recuperation zone
Clinker temperature from kiln
 determined by process; difficult to measure; ~1450°C
• Conclusion:
Our efforts must focus on achieving the highest
possible combustion air temperatures by optimizing
the heat exchange in the recuperation zone!
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
TPT/Ga
Grate Coolers: Definition
Grate Cooler:
The clinker is discharged onto an air permeable grate
where it forms a layer. Cooling air is pressed across this
bed from below through the grate while the clinker is
moving from feed end to discharge end in 15 to 20 min,
continuously giving heat to the passing air.
• Types of Grate Coolers (differ by conveying system):




Travelling Grate Coolers (until ~1985)
Reciprocating Grate Coolers (most common today)
Fixed Bottom Coolers (since 1998)
Moving Bottom Coolers (since 2002)
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Cement Manufacturing Course
10.8.2011
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Cooling Principle in Grate Coolers
Hot combustion air to kiln
Hot waste air to filter
Hot clinker in
Slightly negative pressure!
Grate
Positive pressure!
Cooled
clinker out
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Cooling Curve
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The Three Golden Rules of Clinker Cooling
1st Golden Rule:
Keep the clinker on the grate
Avoid clinker fall through  maintain narrow gaps
The cooler structure underneath the grate is
not heat resistant and must not get in contact
with hot clinker, else it will be DEFORMED!
2nd Golden Rule:
Ensure correct airflow
Minimize air losses
 keep the cooler tight so air cannot escape
3rd Golden Rule:
Maintain the highest bed depth
Keep grate speed low
 get maximum residence time on grate
The longer the clinker is exposed to cooling air,
the more heat is exchange; this results in
maximum utilization of our cooler grate size!
The cooling air has to follow the intended way
into the clinker ensuring that the clinker is cooled
by the correct amount of air on the entire grate.
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Cement Manufacturing Course
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Key to Optimum Grate Cooler Performance
• Operate at the highest possible bed depth,
i.e. 600–1000 mm, depending on clinker granulometry
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Key to Optimum Grate Cooler Performance
This requires
• Even clinker bed depth across grate width
• Sufficient installed fan delivery pressure
• No air escaping through gaps

Between plates

Between grate plate rows

Grate plates and wall

Between under grate compartments
TIGHT!!
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Cement Manufacturing Course
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Clinker Bed Depth
Low clinker bed (< 500 mm)
High clinker bed (> 600 mm)
Short clinker retention time in cooler
Long clinker retention time in cooler
Limited air retention time in clinker
Short cooling time
Low heat transfer
Risk of grate plate overheating
High clinker exit temperature
Low secondary air temperature
Higher air retention time in clinker
Increased cooling time
Improved heat transfer
Best protection for grate plates
Lower clinker exit temperature
Higher secondary air temperature
Limited heat recuperation
Increased heat recuperation
Frequent equipment overheating
Increased cooler availability
Poor cooler efficiency
Good cooler efficiency
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Tight Cooler  No Air Losses!
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Cement Manufacturing Course
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Fact 3:
Temperature effect on pressure drop & chamber pressure
pexp = f(T)
p, T
p1 > p 2 > p 3 >..... p n
pexp
pexp
pcli
p c li
x
p1
p2
p3
p4
p5
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Compartment Sealing
“Light check” reveals
holes in partition wall !!!
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Static Cooler Inlet
Advantages:
•
Rapid initial clinker cooling to avoid clinker agglomeration
•
Better clinker distribution from the drop point to the entire grate
width
•
Static (dead) clinker layer on the grate plates
 Reduced thermal exposure of the grate surface and supporting
structure
 no burnt plates  better availability
•
No moving parts in impact and high temperature zone
•
100% sealed (no air losses)
•
Proven good possibility to upgrade older grate coolers!
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Cement Manufacturing Course
10.8.2011
TPT/Ga
HGRS Dimensioning Rules for Grate Coolers
• Installed cooling air:
>= 2.2 Nm3/kgcli
• Grate size / specific loading
<= 40 t/(m2d)
• Grate width load:
1000 – 1500 t/(m d)
• First fan pressure:
>=100 mbar
 >1.01 Nm3/(s m2)
• If the cooler is designed according to the above rules, the following
operating parameter can be expected:
 Grate speed*
10 to 15 strokes/min
 Clinker temperature
~90 + t ambient
 Efficiency at 3100 kJ/kg
>70 %
* traditional reciprocating grate
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
TPT/Ga
Typical Problems of Grate Coolers
Thin
bed
Geyser
(air blow-through)
Red
river
Fritting /
caking
Poor UG
seal
Snowman
Burnt
plates
High fall
through
Dust
leakage
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
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Red River
• A Red River is fine clinker
fluidized by cooling air on top
of and on one or both sides of
the clinker bed (like airslide).
• Travelling faster than the
clinker bed, it has less
retention time, is hotter than
the clinker below and radiates
on top of black clinker.
• Effect:


Damage on grate side seal
Reduced heat exchange
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Cement Manufacturing Course
10.8.2011
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Snowman
• A snowman starts when hot
clinker sticks to the cooler, often
in the in the drop area, and the
following clinker keeps piling up.
• If not removed in time (by air
blaster e.g.) the snowman can
reach the kiln nose ring and must
be manually removed.
 1 – 2 days kiln stop!
• Effect:


Disturbed clinker distribution
Kiln stop (see above)
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© Holcim Group Support Ltd 2011
Cement Manufacturing Course
10.8.2011
TPT/Ga