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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 ?