numerical simulation of lignite combustion in o2/co2 ... 5_c/6_1st_inter_oxyfuel... · - cpd...

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


Contents

1 Objective


3 Results

4 Conclusions

5 Future Research


Mathematical modelling

• Mathematical models

Turbulent flowRadiation

Combustio

Char combustion

Devolatilizationn model

Volatile Combustion


Combustion

P ibiliti f th d t il d b d l


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


5. Turbulent Flow - Standard k- - Realized k-- RNG k- - k- SST


• 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



– 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


i


• 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,



• 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



• 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 )


RiP = i’ Mw,i (/k) AP mP ; mP = PYP/ ( N

J j’’ Mw,j)


• 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



• 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


k,i i


• 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


Ash 4.1 5.5 Sulfur 0.34 0.80


• 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).


Ci


• 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


Numerical results


• 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


k = 1.0 = 1.3

k = 1.393 = 1.393


• 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


[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


• 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


g g

Contents

1 Objective


3 Results

4 Conclusions

5 Future Research


Results

• Temperature profile (C, At symmetric plane)

Peak temperature zone Tmax 1480 C ( Higher than experiment )

• O2 Concentration (% dry by volume, At symmetric plane)


O2 (exit) 2-3 %(Acceptable accuracy)

Border of flame shape

Results

• Numerical plot : Axial & Tangential velocity (m/s)


Results

• Numerical plot : Temperature & O2 concentration(% dry Vol.)


Contents

1 Objective


3 Results

4 Conclusions

5 Future Research


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


Contents

1 Objective


3 Results

4 Conclusions

5 Future Research


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)


y

Acknowledgement

• Chair of Power Plant Technology• International Graduate School at Brandenburg University of Technology Cottbus.g y gy


numerical simulation of lignite combustion in o2/co2 ... 5_c/6_1st_inter_oxyfuel... · - cpd...

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