a cfd-flamelet model based time scale analysis of multi
TRANSCRIPT
0 0 Sparking concepts!
TU Bergakademie Freiberg I Institut für Energieverfahrenstechnik und Chemieingenieurwesen Reiche Zeche I 09596 Freiberg I Tel. +49(0)3731/39 4511 I Fax +49(0)3731/39 4555
E-Mail [email protected] I Web www.virtuhcon.de
A CFD-FLAMELET model based time scale analysis of multi-feed stream in a high pressure gasifier
Prasad Vegendla, S. Weise, D. Messig and C. Hasse
6th OpenFOAM Workshop, June 13th – 17th Penn State University
Overview
1
- Introduction
- Flamelet modeling
- OpenFOAM-Flamelet coupling
- Real World Application
- Results
- Time scale analysis
- Conclusion
Introduction What is Gasification
- gasifiers are used to produce clean syngas in an efficient process
- syngas can be used as a fuel or for producing higher hydrocarbons (complex fuels)
- partial oxidation (rich fuel conditions) - high pressures and elevated temperatures
- modeling entire industrial reactors, using conventional approaches (detailed chemistry) requires huge computational effort
2
Combustion and Other Reacting Flow 1 Danny Messig: Modeling laminar partially premixed flames with complex diffusion in OpenFOAM
Flamelet Modeling Resolution / length scales
- Structure of the reaction zone is subgrid - Only highly resolved DNS would not need a subgrid model
ln
vn’
Turbulent eddy
Reaction zone
Discretization on numerical grid
Numerical Grid
3
Flamelet Modeling understanding reaction zones
Mixture fraction Chemical source term
Most of chemical reactions take place in the vicinity of stoichiometric mixture
Example: Combusting Shear Layer
Source: R.J.M. Bastiaans, L.M.T. Somers, DNS of non-premixed combustion in a compressible mixing layer, Modern Simulation Strategies for Turbulent Flow, RT Edwards 2001
Stoichiometic mixture
Locate position of stoichiometric mixture by marker species mixture fraction
Air
Fuel
4
Flamelet Modeling understanding reaction zones
- Changes are mainly in orthogonal direction on iso-mixture fraction surfaces
- Changes of temperature and composition are expressed as a function of the orthogonal coordinate
.
5
Flamelet Modeling flamelet transformation
- Coordinate transformation leads to flamelet equations - Mixture fraction Z is now the independant coordinate - One-dimensional, instationary equations - Scalar dissipation rate / pressure are flamelet parameter - Flamelet parameter are extracted from the turbulent field
Species equation
Scalar dissipation rate
3D
1D
6
solver for CFD domain: flameletFoam (OpenFoam 1.5.x) solver for flamelet domain: inhouse code
OpenFOAM-Flamelet coupling general information flow
7
Dimensions: (1,1,1,18,101,10,28)
Look-up table generated containing: - temperature fuel - temperature oxidizer - pressure - scalar dissipation rate - mean mixture fraction - mean mixture fraction variance - species mass fractions
OpenFOAM-Flamelet coupling flamelet database
8
• Rehm et al. (2009)
Real World Application HP POX gasifier
9
Fuel and steam mixture fraction:
Fuel only mixture fraction variance :
Real World Application extending equations for HP POX
10
operating and boundary conditions
fuel steam oxidizer
feed ratios based on steam
6.8 1 9.738
temperature [K] 657 506.8 506.8
steam/fuel mixture fraction variance
0 0 0
gas turbulent intensity 10% 10% 10%
operating pressure: 61 bar
Real World Application operating conditions
11
Lmax - Length of the reactor L - reactor coordinate
Velocity vector plot
0 0,2 0,4 0,6 0,8 1 0
500
1000
1500
2000
2500
3000
3500
4000
L/Lmax
Tem
pera
ture
(K)
Outlet Inlet
Results
12
overestimation of flame temp. (lacks radiation modeling)
0 0,2 0,4 0,6 0,8 1 0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
L/Lmax
Mas
s fra
c.
CH4 O2 H2 CO CO2 H2O Z Zs
Outlet Inlet
Results reaction evolution
13
Results comparison with exp. data
14
Mass frac. experiment χ = 10-‐5 (s-‐1)
χ = 10-‐4 (s-‐1) Sim
CH4 462% 93% 552% 1% CO -‐4% 1% -‐1% 0% CO2 38% 0% 1% 0% H2 -‐2% 2% -‐2% -‐1% H2O -‐5% -‐2% 1% 1% O2
deviation from equilibrium calculation
Flamelet time scale: Lean fuel: O2 derivative Rich fuel: CH4 derivative
Flamelet time scale: inverse of the selected Eigen-value of the Jacobian
• Rao and Rutland, (2003)
0 0,2 0,4 0,6 0,8 1 1,0E-10
1,0E-09
1,0E-08
1,0E-07
1,0E-06
1,0E-05
1,0E-04
1,0E-03
1,0E-02
1,0E-01
1,0E+00
Mixture frac. (Z) Ti
me
scal
e (s
)
Equilibrium χ = 0.0001 χ =0.001 χ =1 χ =100
HP POX outlet mixture fraction 0.388
Time scale analysis determine chemical time scales
15
0 0,2 0,4 0,6 0,8 1 1,0E-8
1,0E-6
1,0E-4
1,0E-2
1,0E+0
L/Lmax
Tim
e (s
) sca
le
Int. Time
Kolm. Time
Flamelet time scale
Max. Time scale in all reactions
Outlet Inlet
time scales: integral Kolmogorov
Time scale analysis different reaction regimes
16
species time scale
flow time scale
species time scale
flow time scale
flame zone post flame zone
Time scale analysis different reaction regimes
17
- CFD-Flamelet model has shown good agreement with the experimental observations in HP POX
- Scalar dissipation rates influence results significantly
- flamelet time scales were smaller than the Kolomogorov time scale, except for H2 species flamelet time scales in reforming zone
- flamelet approach works for the gasification processes in principal but requires modifications to account for slow reacting species
Conclusions
18
Acknowledgement
19
This research has been funded by the the Federal Ministry of Education and Research of Germany in the framework of Virtuhcon (project number 040201030).
This research has been funded by the Federal Ministry of Economics and Technology of Germany in the framework of COORVED(project number 040201035).