Proportionally operable diverting gates between the 4th preheater stage and kiln inlet provide benefits when firing certain fuels in the kiln. Diverting some raw meal reduces coating formation from high-ash coals, petcoke with sulfur above 1.5% evaporation factor, or when alkali levels exceed 0.5%. This is because the raw meal absorbs ash and reduces stickiness. There is a misconception that raw meal will drop into the kiln when diverted, but high gas velocities above 15 m/s lift all material to the calciner. Diverting raw meal slightly increases retention time and reduces fuel use.

1. Benefits of proportional
diverting gates or swivel gates
in kiln preheater ( 4 th stage to
Kiln inlet)

2. Proportionally operatable
diverting gates
TYPICAL INLINE CALCINER
WITH A 5 -STAGE PREHEATER

3. Diverting gate is used to create
Hot temp zone when fuels which
needs long ignition and combustion
time for fuels like Petcoke ,anthracite
and shredded tires are used.( very low
volatile)
Diverting gate is used when there is
tendency to form coating esp when
high ash coal is used or petcoke
with sulfur is used. When sulfur
cycle is more than 150% or the
Evoporation factor is > 1.5 then
raw meal can be diverted to reduce
Stickiness of raw meal thereby reduces
the coating tendency. For alkalis the
Effect is less.
Hot zone
1100 To 1150 deg C

4. Coal firing
nozzles
Area prone for
Coating formation
Raw meal diverting gate -2
for diverting ( proportioning)
4 th stage raw meal
to kiln inlet and calciner cone

5. When coal has more ash, it can fuse at the firing point
when the hot zone is clear without raw meal cloud and
can stick to the refractory walls of the kiln inlet or on the
cone of the Calciner .This reduces the gas flow and the
production too. When raw meal is diverted from 4 stage it
absorbs the ash and reduces the coating formation.
When we fire pet coke Or when hot meal has alkalis or
sulfur,coating forms. By all means diverting material
from 4 th stage to kiln inlet is beneficial.
Good oxidising conditions and intense short flame are
favorable to reduce the coating tendency. CO formation
enhance the volatile cycle and makes the raw meal
sticky. Moreover the CO burns at the inlet and shoot up
the inlet gas temperature. If it is more than > 1000 deg C
hot clogging takes place.
Reasons for coating formation at kiln inlet

6. ILLUSION
There is an apprehension or illusion ( created by old timers), that raw
meal drops into the kiln when 4 th stage material Is diverted to kiln inlet
and the kiln runs dusty . The gas velocity at kiln inlet is > 15 m/s and it
can lift the entire quantity of material to the calciner . If the illusion is
true, then in calciner where the velocity is 6 to 7 m/s , all the material
must drop Into the kiln inlet . Mind that, there are kilns operated with 80 to
90 % cross over feeding comfortably.
Curved castable l ining
will not allow drop out
Of raw meal into the inlet.
Moreover the velocity of gases
Is > 15 m/s
Raw meal flow
profile

7. Molar ratio( clinker basis)
K2O = 0.5
SO3 = 0.3
C l =0.015
ASR = 0.541
This shows there will be excess alkalis which has volatile
recycle. The excess alkali melts in transition zone,volatilize and
condense at the kiln inlet called the transition chamber. Over a
period of time it builds and blocks kiln inlet. Hence diversion
of the 4 th stage to kiln inlet will reduces the coating
formation.Or to reduce the coating we can use petcoke with
little high S ie., 4 to 5 % to make the ASR to 1.
ASR ,Alkali – sulfur ratio

8. Conclusion
Advantages on the operation of 4 th stage material
diversion to kiln inlet .
It reduces the coating formation which is due the
melting of high ash content of the coal or the
excess alkali or sulfur .
It increases the retention time of raw meal by 0.4
secs as it travels 5 to 6 meter extra apart from the
entire calciner. This will reduce fuel marginally,
being fired in calciner.

9. Thanks
K.P.PRADEEP KUMAR
Sr.G.M.OPERATION
CHETTINAD CEMENTS LTD
ARIYALUR