Bypass

1. BY PASS SYSTEM
CIRCULATION PHENOMENON

2. Kiln Chemistry
Kiln Volatile Cycles
Normal atmosphere
96-99%
60-90%
30-70%
20-40%
Reducing atmosphere
97-99%
90-100%
30-70%
20-40%
Cl
SO3
K2O
Na2O

3. AIR SEPARATE CALCINER
Calciner exit gas 1000 C
Back-end Fuel
Calciner exit gas 880 C
Kiln fuel
Preheater exit gas
360 C
Normal operation
760 net kcal/kg clinker
Preheater exit gas 440 C
Abnormal operation
830 net kcal/kg clinker
High BET and risk of blockages

4. BY-PASS GAS REMOVAL
PREHEATER
PH
HORNO
VOLATILES
PRECALCINER
VOLATILES
HORNO
PH
P/C
HIGHER
CONCENTRATION
OF VOLATILES
P.H.
KILN
P.C,
KILN
BY PASS

5. Air Separate Pre-Calciner
Back-end Fuel
Tertiary Air duct
Calciner vessel

6. PROBLEMS OF BLOCKAGES IN KILN RISER
AND KILN BACK-END
BUILD UPAREAS
EFFECT OF LOWER
ENTRY FOR STAGE
3 MATERIAL
UPPER STAGE 3
MEAL FEED
UPPER STAGE 3
MEAL FEED

7. 330 - 360 °C
530 - 560 °C
680 - 720 °C
800 - 840 °C
1010 - 1100 °C
Five stage
310
490
630
750
820
1000-1100

8. Build-ups
1500-1600 °C
1150-1200 °C
800-850 °C
650-700 °C
350-400 ° C
500-550 °C
Chloride based build-up
Sulphur based Build-up
Ash rings

9. process adverse materials
 These harmful materials are sulfur, chlorine and
alkali elements i.e. sodium and potassium. Their
behaviors in the kiln and preheater atmosphere
leads to build-up of layers of these components
and trapping huge quantity of kiln dust. This build-
up forces the kiln operator to shutdown the kiln
system to clear this build-up. The kiln operation
suffers because the build-up in the riser pipes and
cyclones increases pressure drop in the system

10. Circulation phenomenon
This term is used to represent the
phenomena caused by the presence of the
volatiles in system i.e. alkali chlorides,
Sulphates and other related components in
the dry kiln system with preheater and
precalciner

11. Internal and External Circulation
Phenomena
 1-INTERNAL CIRCULATION PHENOMENON is
between preheater tower lower stages and
the kiln-burning zone.
 2-EXTERNAL CIRCULATION PHENOMENON
Their cycle from preheater to electrostatic
precipitator to kiln feed and back again to
the kiln system

12. % By-pass = % chlorine as Cl in
the raw materials x 100
 This procedure is applied to chlorine
because it is nearly impossible to control the
evaporation of chlorine in the kiln burning
zone or control its concentration in the
process by any mean.

13. Example
 The raw materials contain chlorine [raw
meal basis] =0.25 %. What is the bypass
%?
 The required bypass% = 0.25x100=25%

14. The main compounds made are:
 Alkali sulfate [K, Na]2 SO4
 Alkali chloride KCl, NaCl
 Alkali carbonate [K, Na]2 CO3
 Calcium sulfate Anhydrite CaSO4
 Sulfate spurrite 2C2 S CaSO4
 Sulfo-spurrite [K, Na] 2 SO4

15. Circulation Mechanism
 The circulating elements enter the kiln with the kiln
feed that travels through the preheater to the kiln
inlet.
 Starting from lower most cyclones the temperature
starts reaching 800ºC in the kiln system. From this
temperature, part of these elements is volatilized
and becomes part of the kiln atmosphere.
 KCl NaCl CaCl2 K2SO4 Na2SO4 CaSO4
775 772 801 1069 884 1450ºC
[melting temperature]

16. Circulation Mechanism
 When the material reaches burning zone, all
the chlorine will be evaporated with part
from sulfate, sodium, and potassium [the
harder the kiln feed to burn the higher will
be the evaporation rate of the volatiles and
this takes place also in case of a very strong
flame in the main burner]

17.  Chloride reacts primarily with the alkalis,
forming NaCl and KCl. Any excess of
chlorides will react with calcium oxide
available in the system to form CaCl2. A part
of the alkalis in excess of chloride combine
with sulfur to form Na2SO4, K2SO4 and
double salts as Ca2K2(SO4)2. Alkalis not
combined with chloride or sulfur is present as
Na2O and K2O embedded in the clinker
mineral

18. An Example
 If we introduced 1 kg of potassium each hour with
the feed and when the reactions achieve a state of
equilibrium of volatiles in the system, then we will
have the following condition:
 0.811 kg of potassium will leave with the clinker
 In the system the concentration of potassium will
be 2.573 kg
 In the by-pass dust the concentration of potassium
will be 0.221 kg.
 In the exhaust gas dust the concentration will be
0.042 kg of potassium.

19. Evaporation Rates of Different Elements
 The evaporation factor E =
 1 – (% within the clinker / % at kiln inlet
loss on ignition free basis )
basis
free
ignition
on
loss
inlet
kiln
At
%
clinker
e
Within th
%

20. Example: 1
 The concentration of the sulfate in the
clinker in one sample is 1.05 %, SO3
concentration in cyclone 4 materials which is
collected from the material pipe of cyclone 4
to the kiln inlet is 2 % and the loss on
ignition of this same sample is 3.5%
 What is the evaporation factor of sulfate
[SO3] in this system?

21. Evaporation Rates of Different Elements
 % SO3 at the kiln inlet loss on ignition free
basis = (2/100-3.5) * %
= ( 2/96.5 ) * %
= 2.0725
 Evaporation factor
E = 1 – (1.05/2.0725 )
= 1 - 0.507
= 0.493

22. Example 2
 The loss on ignition of the sample for
chlorine is 3.8 %. Its concentration in the
clinker is 0.03 % and its concentration in the
hot meal [kiln feed] from cyclone 4 to the
kiln inlet is 0.65 %. What is the evaporation
factor of chlorine in this system?

23. Solution
 % Chlorine at the kiln inlet loss on ignition
free= ( 0.65 / 100-3.8) * %
= ( 0.65/96.2) * % = 0.676
Evaporation factor E of chlorine
= 1 - ( 0.03/0.676)
= 1 - 0.04
= 0.96

24. Example 3
 The loss on ignition of the sample for
potassium in kiln feed is 3.5% and the
concentration of potassium in the clinker
0.29% and its concentration in the hot raw
meal from cyclone 4 to the kiln inlet 0.39%.
What is the evaporation factor of potassium
in this system?

25. Solution:
 The % of potassium at the kiln inlet loss on
ignition free = (0.39/ 100-3.5) * 100
= ( 0.39/96.5) * 100
= 0.4
Evaporation factor E of potassium
= 1 – (0.29/0.4)
= 1 - 0.725
= 0.275

26.  When E = 1 indicate that all volatile
elements evaporate and none leave
with the clinker
 This is clearly indicated in the case of
Example 2 of chlorine where the solution
proved in a very unmistakable way this fact.
[E in the example is nearly one].

27.  When E = 0 indicate that none of the
volatile elements evaporate and all
leave with the Clinker.
 This is clearly indicated in the case of
Example 3 of potassium where the solution
proved in a very unmistakable way this fact.
[E in the example is very small )

28. Average evaporation factors
 Alkali SO3 0.2 - 0.9
[have a relatively high melting point of 1074ºC,
boiling at 1689ºC]
 Excess SO3 0.75
 KCl 0.990 - 0.996
[have low melting point of 768ºC, boil at 1411ºC]

29. KCl, CaCl2 and NaCl
 Chloride compounds KCl, CaCl2 and NaCl
are seen to have an evaporation factor of
0.990-0.996 in the kiln at 800ºC. These
compounds melt and boil at 1400ºC

30. Excess sulfur
 Alkali sulfates have evaporation factors from
0.2 to 0.90 but they are mostly in the lower
part of the range, while excess sulfur that
cannot find alkali to react with has an
evaporation factor of 0.75, therefore it is
best that all sulfur react with alkalis to the
highest extent

31. Molecular Ratio of Sulfur and Alkalis
 If the alkalis are in the right proportion with
the sulfur in the system, both will combine
together and become built in salts in the
clinker minerals. But in the absence of
alkalis i.e. if there is excess sulfur in the
system, the more volatile calcium sulfate will
be formed in the kiln system, and it has a
higher evaporation factor

32.  SO3 /Alk =
( SO3/ 80)
K2O /94 + 0.5 * ( Na2O / 62 )
= 1.1
Estimation of optimum molecular ratio between
sulfur and alkalis in the system:

33. Estimation of optimum molecular ratio
between sulfur and alkalis in the system:
 If the sulfur and alkalis ratio exceeds 1.1 it
means that the amount of sulfur present in
the kiln feed material that react with the
alkalis is in excess and the remaining excess
sulfur will react to form CaSO4

34. Example 1
 A kiln feed sample contains the following
concentration
 SO3=0.45 % K2O=0.37 % Na2O=0.38 %
 What is the sulfur and alkalis molecular ratio
in this system?

35. Solution
The result is indicating that there is no excess
sulfur in the system.

36. Example 2
 A kiln feed sample contain the following
concentration
 SO3=0.57% K2O =0.21 % Na2O=0.15 %
 What is the sulfur and alkalis molecular ratio
in this system?

37. Solution
The result is indicating that there is excess sulfur in the
system that will react to form CaSO4

38. The amount of excess sulfur is expressed in gram
SO3 per 100kg clinker
 E.S = 1000x SO3 –850x K2O – 650x
Na2O [gram SO3/100kg clinker]
The limit on the excess sulfur is given to
be in the range of 250-600g/100clinker

39. Example
 A kiln feed sample contain the following
concentration
 SO3=0.57% K2O =0.21 % Na2O=0.15 %

40. Solution
 E.S = 1000 x SO3 –850x K2O – 650 x Na2O
[gram SO3/100kg clinker]
E.S = 1000x 0.57 – 850 x 0.21 –650 x 0.15
= 570 – 178.5 –97.5
= 294 gram SO3/100kg clinker

41. comment
 This kiln feed contains a relatively small
amount of excess sulfur. But if the material
of the kiln feed is hard to burn or the flame
is very strong a coating problem may cause
some trouble due to build-up in the
preheater and the pressure loss may
increase in the preheater

42. Optimum range of molecular of sulfur
and alkalis in the presence of chlorine
Therefore the optimum range is nearly
0.8 to 1.1.

43. comment
 Since the chlorine affinity for reaction with
alkalis is higher than the sulfate therefore
the following equation is applied to
determine the optimum sulfate alkali ratio
where the chlorine is subtracted from the
alkalis

44. Coating and Ring Formation in Kiln and
Preheater
In certain stage of build-up a new material starts to
exist and causes more trouble in the system.
The formation of spurrite [2 C2S . CaCO3] and sulfo
spurrite [2 C2S . CaSO4] in case of the excess sulfur will
exist in abundance

45. Where does the build-up occur in the kiln and
preheater system?
Cyclone preheater
Preheater with Precalciner

46. Why?
 What is the reason that makes
suspension-preheater-kilns
with precalciner
more sensitive to the volatiles problem
than the suspension –preheater kilns?

47. How to Decrease the Effect of Volatile
Matters on the Kiln System?
 Frequent kiln stops due to cyclones blocking
which need additional time for cooling and
cleaning.
 Higher heat consumption due to this frequent
stops, additional fuel used for reheating the
system and higher kiln’s brick consumption.
 Reduced kiln production since the operator will
try to continue work with less draft in the kiln
and in most cases in reducing atmosphere with
much CO in the system.

48. Reducing the burning zone
temperature
 This means the reduction of the volatility of
the alkalis, chloride and sulfate components.
This can be done by reducing the burning
zone temperature. The volatility of the sulfur
compounds especially calcium sulfate is a
function of the burning zone temperature.
Calcium sulfate starts to decompose at
1220ºC and this thermal decomposition can
be avoided by lowering burning zone
temperature

49. This can be done also by other means
as
Decreasing the silica ratio of the kiln feed and
thus making the kiln feed easier to burn.
Finer grounding of coarser particles especially
the free silicates if present in the kiln feed
therefore easier to burn kiln feed. The result will
be lower sintering temperature in the burning
zone decreasing the volatility .
Accepting higher free-lime in the clinker. This
requires less fuel in the burning zone, and there
will be no overheating of the burning zone.

50. Controlling volatile content
 Controlling volatile content in the raw
material used for grinding and used as kiln
feed.
 That means observing the optimum
molecular of sulfur to alkali and ensuring
that the excess sulfur is minimized

51.  Controlling Oxidation condition in kiln
atmosphere. When we have the oxygen level
in the kiln in the higher side, the condition in the
kiln will be oxidation condition. The dissociation
of sulfate compounds achieves balance in the
favor of forming alkali sulfate in the oxidation
condition in the kiln. If we have reduction
condition the alkali sulfate tends to dissociate to
alkali oxide and oxygen.

52. Controlling the reduction condition
in the kiln atmosphere
 Calcium sulfate + Carbon → Calcium oxide
+SO2 + Carbon mono-oxide
 Alkali sulfate + Carbon → Alkali oxide + SO2
+ Carbon mono-oxide
These reactions increase sulfur circulation in
the system

53. Installation of a kiln By-pass
system
 A modern by pass system consists of an air
quench chamber, a shut-off valve, a water
quench chamber and a dust collector. The
air quench chamber is used to mix ambient
air with the kiln gasses to quickly cool the
harmful volatile compounds. The water
quench chamber is used to cool the gases
quickly to lower temperature for dust
collection

54.  The by-pass systems installation will
eventually lead to higher power and heat
consumption in the kiln system. Also one of
the major losses with this installation is the
dust loss, since the dust-laden gas streams
are thrown out of the system. At 30%
bypass the fuel consumption increases by
about 8-10% and material loss by about 3-
6%.

55.  The chimney
 The draft-fan
 The electrostatic-precipitator
 Dust handling from the electrostatic-
precipitator collecting screw-conveyor to the
collecting-pin and consists of: The bucket-
elevator, the dust pin, and the granulator to
change the dust into dust balls and the belt
conveyor for the dust balls to the truck

56.  Condition-tower for the hot gas from the quench
chamber to decrease temperature of the gas from
450ºC to 150ºC by water spray system.
 The quenching chamber for mixing the hot gas with
ambient air, laden with the volatile matters from the
kiln riser-duct and decrease gas temperature from
1000ºC to 450ºC in a matter of seconds to freeze the
volatile components in its solid state and prevent it
from existing in the melting phase in the by-pass ducts
system. This mixing chamber is always located in the
duct taking the hot gas from the kiln riser duct and
nearly 800mm away from the connecting point to the
riser duct.