numerical simulation of lignite combustion in o2/co2 ... 5_c/6_1st_inter_oxyfuel... · - cpd...
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Numerical Simulation of Lignite Combustion in O2/CO2 Environment by Eddy-Dissipation Model
Tanin Kangwanpongpan, Hans Joachim KrautzChair of Power Plant TechnologyChair of Power Plant Technology
Brandenburg University of Technology Cottbus, Germany
1st International Oxyfuel Combustion Conference 2009Radisson SAS HotelCottbus, Germany
7th 11th September 20097th – 11th September 2009
Contents
1 Objective
2 Mathematical modelling2 Mathematical modelling
3 Results
4 Conclusions
5 Future Research
1st International Oxyfuel Combustion Conference Cottbus, Germany, 7th – 11th September 20092
Introduction
Objective
To validate the numerical model for an oxyfuel combustion
1st International Oxyfuel Combustion Conference Cottbus, Germany, 7th – 11th September 20093
Contents
1 Objective
2 Mathematical modelling2 Mathematical modelling
3 Results
4 Conclusions
5 Future Research
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Mathematical modelling
• Mathematical models
Turbulent flowRadiation
Combustio
Char combustion
Devolatilizationn model
Volatile Combustion
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Combustion
P ibiliti f th d t il d b d l
Mathematical modelling
1. Radiation
• Possibilities of the detailed sub-models- P1- Discrete Transfer Method (DTM)- Discrete Ordinate Method (DOM)
2. Devolatilization
Discrete Ordinate Method (DOM)
- Single kinetic rate- Two competing kinetic rate- CPD (Chemical Percolation Devol.)
3. Volatile Combustion
Volatile Reaction Mechanism- Global 1-step, 2-step,3-step,4-step- Detailed mechanism
Turbulent Gaseous CombustionTurbulent Gaseous Combustion- Probability Density Function (PDF)- Eddy Dissipation (EDM)- Finite Rate/Eddy Dissipation (FR-ED)- Eddy Dissipation Concept (EDC)
4. Char Combustion- Single kinetic rate- Kinetic Diffusion/ Limited Rate- Intrinsic
1st International Oxyfuel Combustion Conference Cottbus, Germany, 7th – 11th September 20096
5. Turbulent Flow - Standard k- - Realized k-- RNG k- - k- SST
Mathematical modelling
• Formulation of numerical models (Steady state problem)
R di ti P1 (CPU ti i ) WSGG (S ith TF 1982)– Radiation
– Devolatilization CPD (Chemical Percolation Devolatization)
P1 (CPU time saving), WSGG (Smith TF. 1982)
– Volatile reaction mechanism Global 3-step mechanism
– Turbulent gaseous combustion
– Char combustion
Finite rate/Eddy dissipation (FR-ED)
Char + O2 Single kinetic rate (Macro kinetic)Ch + CO & H O Ki ti /Diff i li it d t
– Turbulent flow RNG k-
Char + CO2 & H2O Kinetic/Diffusion limited rate
1st International Oxyfuel Combustion Conference Cottbus, Germany, 7th – 11th September 20097
Mathematical modelling
– Weight Sum of Gray Gases (WSGG) model gas absorption coefficients (a)
• Radiation : P1 model
– Assume Coefficients for 3 gray gases (Smith TF. et. al. 1982) : Air-firing
= wi(T) [ 1 – e-ai s ] ; ai = i p
– Gray formulation (Domain based approach)
s = 3.6 V / A• The mean beam length (s) : based on domain size
y ( pp )
ai = a = - ln (1 - ) / s (The whole spectrum)
• Global absorption coefficient
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i
Mathematical modelling
• Devolatilization
Proximate & Ultimate Analysis CPD model (FLUENT)
- Kinetic parameter estimated by CPD model
Proximate & Ultimate Analysis Carbon (C) Hydrogen (H)Nitrogen (N)O (O)
CPD model (FLUENT)- initial fraction of bridges in the coal lattice, p0
- initial fraction of char bridges, c0
- lattice coordination number,+ 1l t l l i ht MOxygen (O)
Volatile Matter (VM)- Assump. of dry-ash-free basis (DAF)
- cluster molecular weight, Mw,1
- side chain molecular weight, Mw,
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Mathematical modelling
• Volatile reaction mechanism
– Global simplified 3-step mechanism (Hautman. 1981)
CmHnOxNySz + ( m/2 + z – x/2 ) O2 m CO + (n/2) H2 + (y/2) N2 + z SO2
Hydrocarbon
CO + ½ O2 CO2
H + ½ O H OH2 + ½ O2 H2O
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Mathematical modelling
• Turbulent Gaseous Combustion– Finite Rate/ Eddy Dissipation (FR-ED)Finite Rate/ Eddy Dissipation (FR ED)
The net rate of reaction
R min (R R R R P )Ri = min (Ri, RiR, Ri
P )
1. The chemical production or depletion term (kinetic rate)
R ( ’’ ’) M A T [ E/ (RT)]
2. The rate of dissipation of reactant eddies
R R ’ M ( /k) A i [Y / ( ’ M )]
Ri = (i’’ - i’) Mw,i A T exp [ - E/ (RT)]
RiR = i’ Mw,i (/k) AR min [YR/ (R’ Mw,R)]
3. The rate of dissipation of product eddies
R P ’ M ( /k) A Y / ( N ’’ M )
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RiP = i’ Mw,i (/k) AP mP ; mP = PYP/ ( N
J j’’ Mw,j)
Mathematical modelling
• Char combustion
– Char particles (C) react heterogeneously with O2, CO2, H2O
C ½ O CO
C + CO2 2CO
C + ½ O2 COCO + ½ O2 CO2
2
C + H2O CO + H2 H2+ ½ O2 H2O
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Mathematical modelling
• Char combustion (Formulation of equations)
- Char oxidation : Single kinetic rate model
Rox = A e(-E/RT) A, ETGA
- Char react to CO and H O: Baum & Street model (Field 1969)
R = A P / (1/R + 1/R ) i = 1 for CO2
- Char react to CO2 and H2O: Baum & Street model (Field. 1969)
Over all rate
Ri = Ap Pbulk,i / (1/Rd,i + 1/Rk,i) = 2 for H2O
R = (C /d ) [(T +T )/2](0.75)1 Diffusion rate of bulk gas
Ai , EiMayers 1934Rk,i = Ai e(-Ei / RT)2. Kinetic rate of reaction
Rd,i = (Ci /dp) [(Tp+Tg)/2](0.75)1. Diffusion rate of bulk gas
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k,i i
Mathematical modelling
• Kinetic parameters of char oxidation:
Ass mption Kinetic parameters Kinetic parameters(Lusatian lignite)(Rhenish lignite)
Proximate Analysis ( %wt. as received) Ultimate Analysis (%wt. DAF)
Assumption : Kinetic parameters Kinetic parameters
Rhenish lignite (RWTH Aachen)
Lusatian lignite(BTU Cottbus)
Volatiles 46 60 45 64
Rhenish lignite (RWTH Aachen)
Lusatian lignite(BTU Cottbus)
Carbon 77.03 67.05Volatiles 46.60 45.64
Fixed C 40.90 33.24Hydrogen 4.85 6.95
Oxygen 16.80 24.50Moisture 8.40 15.62
Ash 4 1 5 5
yg 6 80 50
Nitrogen 0.98 0.70
Sulfur 0 34 0 80
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Ash 4.1 5.5 Sulfur 0.34 0.80
Mathematical modelling
• Char combustion (Diffusion coefficient, Ci)
Diff i ffi i t St f l l ti– Diffusion coefficients : Step of calculation
1. Following the method of Hirschfelder. 1954 Dref
D D (P /P)(T /T )(3/2)
2. Applying Power law at operating temperature (T). D
D = Dref (Pref/P)(Tm/Tref)(3/2)
3. Determine diffusion coefficient Ci and insert into CFD model
C
Rd,i = 24 D/(dp R Tm) = (Ci /dp) [(Tp+Tg)/2](0.75).
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Ci
Mathematical modelling
• Kinetic parameters of char reaction :– Implemented via UDF-Function in FLUENT
Char + O2 , CO2, H2O
Computational model& Operating conditions
Char+O2(Single kinetic rate)
Macro kinetic parameters
(TGA)
Ch +CO H OCalculation of
UDF-Function
Char+CO2 ,H2O(Kinetic/Diffusion rate)
Calculation of Diffusion coefficients
(Ci)
N i l lt
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Numerical results
Mathematical modelling
• Turbulent Flow
RNG k model Advantange– RNG k- model- Improve accuracy for high swirling flow
Transport equation of kinetic energy ‘k’- Transport equation of kinetic energy k(k)/t+ (kui)/xi = [keff k/xj]/xj+Gk+Gb--Yk+Sk
- Transport equation of dissipation rate ‘’Transport equation of dissipation rate ()/t+ (ui)/xi = [eff /xj]/xj+C1(/k)(Gk+C3Gb)-C2(2/k)-R+S
Coefficients of Std. k-C = 0.09C1 = 1.44C2 = 1.92 = 1 0
Coefficients of RNG k-C = 0.0845C1 = 1.42C2 = 1.68 = 1 393
RNG Theory
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k = 1.0 = 1.3
k = 1.393 = 1.393
Mathematical modelling
• Selected publication for numerical studies
100 kW vertical pilot scaled furnace (Toporov 2008)1– 100 kWth vertical pilot-scaled furnace (Toporov. 2008)1
Data available from publication:
• Geometry of single swirling burner
• Operating conditions p g
• Coal properties and particle distribution
[1] Toporov D., Bocian P., Heil P., Kellermann A., Stadler H., Tschunko S., Förster M., Kneer R.,
• Measurements for numerical validation
1st International Oxyfuel Combustion Conference Cottbus, Germany, 7th – 11th September 200918
[1] Toporov D., Bocian P., Heil P., Kellermann A., Stadler H., Tschunko S., Förster M., Kneer R., Detailed investigation of a pulverized fuel swirl flame in CO2/O2 atmosphere, Combustion and Flame, Vol. 155, Issue 4, pages 605-618, 2008
Mathematical modelling
• Computational cells– 100,000 grid cells– 1/6 model with periodic boundary conditions– FLUENT commercial software
3rd flow
1st flow
(Coal feed)
2nd flow
Staging flow
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g g
Contents
1 Objective
2 Mathematical modelling2 Mathematical modelling
3 Results
4 Conclusions
5 Future Research
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Results
• Temperature profile (C, At symmetric plane)
Peak temperature zone Tmax 1480 C ( Higher than experiment )
• O2 Concentration (% dry by volume, At symmetric plane)
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O2 (exit) 2-3 %(Acceptable accuracy)
Border of flame shape
Results
• Numerical plot : Axial & Tangential velocity (m/s)
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Results
• Numerical plot : Temperature & O2 concentration(% dry Vol.)
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Contents
1 Objective
2 Mathematical modelling2 Mathematical modelling
3 Results
4 Conclusions
5 Future Research
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Conclusions
• Numerical model predict results of lignite combustion• Numerical model predict results of lignite combustion
in an oxyfuel environment
• Necessary determine spectral radiative properties of gases in an oxyfuel conditions
Th ki ti t f TGA O f l b ti
g y
• The kinetic parameters from TGA Oxyfuel combustion
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Contents
1 Objective
2 Mathematical modelling2 Mathematical modelling
3 Results
4 Conclusions
5 Future Research
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Future Research
Char combustionKinetic/diffustion Intrinsic model
Volatile reaction mechanism
3-step 4-step Detailed mechanism
mechanism
Turbulent gaseous Finite rate/Eddy dissipation Eddy Dissipation Concept
gcombustion
WSGG (oxy firing)WSGG (Air firing)
Level of difficulty
Radiation( y g)( g)
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y
Acknowledgement
• Chair of Power Plant Technology• International Graduate School at Brandenburg University of Technology Cottbus.g y gy
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