Download - Cycles and Bypass
POLYSIUS S.A.
THE BYPASS
A solution for Process
“In the name of Allah, the Beneficent, the Merciful”
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Let’s talk about bypass…
• What happens in the system ?• What are the minor elements ?• What do the minor elements do ?• Why do we need a bypass system ?• What is the bypass system ?• What are the calculations ?
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What happens in the system ?
Raw Materials
Raw Meal
Grinding Heating up
Hot Meal
Clinker
Clinkerization
Volatilization
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What are the minor elements ?
They are chemical components of the raw materials with a “low” concentration towards the other components.
In the cement industry, Cl, SO3, Na2O and K2O are, among others, particularly monitored
Although some have no impact on the chemical process, others might lead to major troubles.
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What are some elements doing ?
Low volatilization temperature
Extraction from material
Flowing with gases
Condensation on cooler particles
Increase of local
concentration
PROBLEMS
Problem with volatile elements
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What are some elements doing ?
Volatilization temperature+
Condensation temperature
2 Cases
InternalCycle
ExternalCycle
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Internal and External CyclesThis image cannot currently be displayed.
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Internal and External Cycles
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Definition of the Volatility
Volatility of a component
Component
Total
dVolatilize
QQVolatility
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Definition of the Volatilization
Hot meal Clinker
Volatilization of a component X in the kiln
Hm
CkX X
XtionVolatiliza 1100
Recirculation part
Note: Calculation done LOI free
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Volatility or Volatilization ?
Volatility
• is a physical property of a component• is depending on the temperature• Is depending on the crystallographic structure
Volatilization
• is depending on the considered area• is depending on the operation
?
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Different behaviors
• Chloride start evaporate around 650°C• Alkalis start evaporate around 900°C• Sulfur start evaporate around 1000°C
Conclusion :
The various content of element is different according to the analyzed area (kiln feed, meal cyclone 2, hot meal, clinker,…).
Nevertheless, most of the highest concentrations are located at the kiln inlet, depending on the salt formation.
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The salt formation
KClClOK 222 NaClClONa 222
22 CaClClCaO
Chlorines
4232 SOKSOOK 4232 SONaSOONa
43 CaSOSOCaO
Sulfates
3222 COKCOOK 3222 CONaCOONa Carbonates
Form
atio
n or
der
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Calculation of the salt concentration
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Calculation of the salt concentration
With a= K2O% b= Na2O% c= Cl% d= SO3% e= LOI
KClClOK 222 94 71 149
eaKCl
100100
94149
Quantity of KCl formed :
Cl used during the reaction :e
aClKCl
100100
9471
Reaction 1
Cl remaining after the reaction :e
acClR
100100
9471
1
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Calculation of the salt concentration
62 71 117
171622 RClONa Quantity of Na2O that can be used with Cl :
NaCl formed during the reaction : 171117
RClNaCl
Reaction 2
Na2O remaining after the reaction : 12 7162
1001002 RR Clb
eONa
NaClClONa 222
With a= K2O% b= Na2O% c= Cl% d= SO3% e= LOI
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Calculation of the salt concentration
62 80 142
2262
14242 RONaSONa Quantity of Na2SO4 formed with Na2O :
SO3 used during the reaction : 22062803 RNaSO
Reaction 3
SO3 remaining after the reaction : 23 26280
1001003 RR ONad
eSO
With a= K2O% b= Na2O% c= Cl% d= SO3% e= LOI
4232 SONaSOONa
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Why do we need such calculations ?
• Better understanding of the cycles with the analysis• Better understanding of the build ups• Criteria of decision for a bypass system
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What is the bypass system ?
Raw Material composition in minor elements
Volatility of some elements
Process
Cycles creations
Salt formation
Troubles
Bypass system
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What is the bypass system ?
CoolingQuenching chamberConditioning tower
SeparationElectro filter
Dust collection
Clean gas emission
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How much bypass ratio ?
The bypass• Decreases the concentration of minors in the
kiln inlet by taking a part of the kiln gas• Taking part of the heat• Taking part of the production
What has to be the bypassed gas quantity ?
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Two different ways …
1 - Assuming thatBypass % ≈ Cl % input (free of LOI) x 100
2- Complete calculation of the salts, taking into account the volatility, the type of system (kiln, preheater). Using the whole chemical theory.
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POLYSIUS process of decision for BP%
SO3, Cl,Na2O, K2O
Bypass Calculation
X%
Cl < 1% hot meal % Salts in hot meal
X% BP
Yes
X% BP
<4%
> 4%
> 6%
% CaSO4 < 60%
X% BP
> 60%
< 6%
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Example of decision This image cannot currently be displayed.
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Calculation of the bypass ratio
From the measurements done on site
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Definition of the Bypass Ratio
lnKi
Bypass
VV
oBypassRati
V Bypass = Volume of gas going to the bypass
V Kiln = Volume of gas going out of the kiln
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Definition of the calculation parameters
WDt1
VBPt1
VAFt1
%O2(BP)Vata
WDto
VBPto
VAFto
VAto
%O2(k), Vk
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Calculation of V Kiln
The volume coming out of the kiln is composed by :
1. The volume of the gas combustion - V Comb2. The volume of the decarbonation - V CO23. The volume of excess air - V Ex
ExCOCombKi VVVV 2ln
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Calculation of V Comb
C + O2 CO2
S + O2 SO2
H2 + ½ O2 H2O
CXHY + (x+Y/4) O2 x CO2 + Y/2 H2O
CXHY with Y = 2x + 2
The main combustion equations are :
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Calculation of V Comb
100
.22
WgCxHyxCOCOV COComb
100
.2
2222
WgCxHyyOHSHHV OHComb
100
22
WgSHV SOComb
1002
10079.0 min
2WgNVV Air
NComb
100
.4
762,42762,42143,72381,2381,2
min
WgCxHyyxOSHHCOVAir
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Calculation of V Comb
CO, CO2, H2, H2S, H2O, O2, N2, CxHy % from natural gas composition analysis
22202 NCombSOCombHCombCOCombComb VVVVV
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Calculation of V CO2
CO3Ca CO2 + CaO100 44 56
CaOCO5644
2
CO3Mg CO2 + MgO 84,3 44 40,3
MgOCO3,40
442
CaO MgO
CKW
)100
- 100( 1001,9771.092MgOCaO0,748 VCO2
Φ being the carbonation degree
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Calculation of V Ex
V Comb+ V CO2
V Ex
V Kiln
O2 Kiln inlet
O2 Air
)V (V x %O - 21
%O V COMBCO2
)(
)(EX
2
2 k
k
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Calculation of V Kiln
The volume coming out of the kiln is composed by :
1. The volume of the gas combustion - V Comb2. The volume of the decarbonation - V CO23. The volume of excess air - V Ex
ExCOCombKi VVVV 2ln
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Calculation of V BP
WDt1
VBPt1
VAFt1
%O2(BP)Vata
WDto
VBPto
VAFto
VAto
%O2(k), Vk
INPUTS
OUTPUTS
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Calculation of V BP
INPUTVBP x CPGAS x (t1 – 20)
+ Va x CPAIR x (ta – 20)+ WD x CPdust x (t1 – 20)+ VFA x CPair x (ta – 20)
OUTPUTVBP x CPGAS x (t0-20)
+ Va x CPAIR x (t0-20)+ WD x CPdust x (t0 – 20)+ VFA x CPair x (t0 – 20)
With False Air being calculated with O2 content in the bypass
)(%21)(%)(%
2
22
BPOKiOBPOK
BPFA VKV
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Calculation of VBP
As far asInputs = Outputs
20)-(t CP - 20)-(t CPK-20)-(t CP - 20)-(t CP20)-(t CP - 20)-(t CP
W
20)-(t CP - 20)-(t CPK-20)-(t CP - 20)-(t CP20)-(t CP - 20)-(t CP V
V
aAIR0AIR0GAS1GAS
0dust1dustD
aAIR0AIR0GAS1GAS
aAIR0AIRa
BP
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Calculation of the bypass ratio
Finally, knowing V Kiln and V BP
lnKi
Bypass
VV
oBypassRati
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Conclusion
• Minor elements are to be considered for operation decisions
• Chemistry is able to help for any investigation concerning the process troubles
• The volatilization and cycles of the elements can be handled through process operation
• A good knowledge of the element circulation is necessary for a good trouble shooting
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Questions and/or comments ?