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 info@virtuhcon.de 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).