76490639-Partially-Premixed-Combustion-Tutorial.pdf

1
UGM 2002 Confidential
Partially Premixed
Partially Premixed
Combustion in a Co-axial
Combustion in a Co-axial
Combustor
Combustor
Graham Goldin
2002 Fluent Users’ Group Meeting

2
Problem
u A swirler at the center of the combustor
introduces the lean methane/air mixture.
u equivalence ratio=0.8
u axial velocity = 30 m/s
u radial velocity = 30 m/s
u axial velocity of air at outer tube = 10 m/s
u major species involved in the combustion process
are CH4, O2, CO2, CO, H2O, and N2

3
Setup and Solution
u Generate PDF look-up table using prePDF
u Read Grid
u Define Model
u Define Material
u Operating and Boundary Conditions
u 1st and 2nd Order Solutions
u Postprocessing

4
Generate PDF look-up Table (1)
u Start prePDF and define
the model type.
Setup:Case…
u Enable Partially Premixed
Model
u Retain the default settings
for other parameters

5
u Define the chemical species in the system.
u Setup:Species:Define…
u Under Database Species, select the name
u Set the Species number
u Define the species: CH4, O2, CO2, CO, H2O,
and N2

6
u Define fuel composition.
Setup:Species:Composition…
u Set Species Fraction:
l CH4 = 0.0453
l O2 = 0.2264
l CO2 = 0.7283

7
u Define oxidizer composition.
l O2 = 0. 233, N2 = 0.767

8
• Define the system operating conditions.
Setup:Operating Conditions…
u Set the Inlet Temperature for Oxidiser to 650
and retain the default values.
u Retain the default PDF solution parameters
u Save the input file ch4-partialpremixed.inp
u
Calculate the PDF table, and save the pdf file, ch4-partial-
premixed.pdf
Calculate:PDF Table

9
u Examine temperature/mixture fraction, and
species/mixture fraction relationship
Display:Property Curves…:Plot Variable

10
u prePDF automatically fits 3rd-order polynomial
functions (of f ) for unburnt density, temperature,
specific heat and thermal diffusivity.
u prePDF automatically fits a piecewise-linear function for
the laminar flame speed for certain fuels and conditions
u H2, CH4, C2H2, C2H4, C2H6, C3H8
u 1atm < pressure < 40atm
u 300K < Tunburnt < 800K
u For other conditions, you must input the function

11
Read Grid
u Start the 2D version of FLUENT
u Read the grid file, par-premixed.msh
u Scale the grid to inches
u Display the grid

12
Define Model
uDefine:Models:Solver uDefine:Models:Viscous

13
Define Model
u Define:Models:Species
You will be prompted to read the ch4-partial-premixed.pdf file. When
the file is read, the available material properties/methods will
change to accomodate the partially premixed model.

14
Material
u Define:Materials
Fluent will automatically select the material and other parameters.

15
Operating Conditions
u Retain default values.

16
Boundary Conditions (1)
Set boundary conditions for
air inlet.
air-fuel inlet.

17
u Set boundary conditions for outlet.

18
First Order Solutions (1)
u Solve for Flow and Turbulence equation.

19
u Enable the plotting of residuals.

20
u Initialize flow field and compute from all zones.
u Save the case file par-premixed.cas.gz.

21
u Start the calculation (250 iterations).
u Define a region Adapt:Region…
u Patch a region close to fuel-air
inlet.

22
u Solve for all equations

23
Second Order Solutions (1)
u Change the discretization for the parameters:
u Pressure: Second Order
u Momentum: Second Order Upwind
u Turbulence Kinetic Energy: Second Order Upwind
u Turbulence Dissipation Rate: Second Order Upwind
u Progress Variable: Second Order Upwind
u Mean Mixture Fraction: Second Order Upwind
u Mixture Fraction Variance: Second Order Upwind

24
Second Order Solutions (2)
u Start the calculation (250 iterations).
u Save the data file par-premixed.dat.gz.

25
Postprocessing (1)
uVelocity Vectors.
Set Scale Factor to 10 and
Skip Value to 3
uContours of Steam
Function.

26
Postprocessing (2)
uFilled contours of mean
Progress Variable.
uFilled contours of Static
Temperature

27
Postprocessing (3)
uMass fractions of CH4
uMass fractions of H2O

28
Postprocessing (4)
uMass fractions of CO2 uMass fractions of CO

29
Results
u The partially premixed model in FLUENT can
be used to simulate problems with:
u A premixed stream and a non-premixed (or inert
stream such as air)
u Equivalence ratio fluctuations in the premixed inlet
stream
u Can be used in the limit of…
l Perfectly premixed (automatic calculation of props)
l Non-premixed (can study mixed and unburnt flows)

30
3D Simulation of the IFRF
3D Simulation of the IFRF
Industrial Pulverized-Coal
Industrial Pulverized-Coal
Furnace
Furnace
Graham Goldin
2002 Fluent Users’ Group Meeting

31
Overview
u The International Flame Research Foundation
(IFRF) experimental facility is used to validate
industrial coal combustion models.
u This tutorial is an extension of the 2-
dimensional simulation of this furnace by
Peters and Weber.
u The mixture fraction/PDF model with the k-e
turbulence model and P-1 radiation model has
been used.

32
Problem
u To simulate a realistic industrial pulverised-
coal furnace and compare with the measured
data.
u 3D analysis of 2.4 MW Swirling,
Pulverized Coal Flame
Furnace
u One quarter periodic
model of furnace
(shown in fig)

33
Setup and Solution
u Select a Combustion Model
u Generate PDF look-up table using prePDF
u Read Grid
u Define Model
u Define Materials
u Define Operating Conditions
u Compile UDF
u Define Boundary Conditions
u Define Injections
u Solve for non reacting and reacting flows
u Postprocessing

34
Select a Combustion Model
u Assumptions
u Chemical equilibrium
u Modeling the devolatization and char off-gases as a
single mixture
u Combustion Model selected
u Mixture Fraction Model
u Coal Specifications
u Name: Saar Gottelborn hvBb
u High Temperature yield (mole, dry) volatiles 55%, char
36.7%, and ash 8.3%
u Ultimate analysis (mole, dry-ash-free (daf)) C 53%, H
40%, O 6%, and N 1%

35
u Start prePDF and define
a case.
Setup:Case…
u Enable Non-Adiabatic
Heat transfer options
u Enable Fuel stream for
Empirically Defined
Streams
u Retain the default settings
for other parameters

36
u Define the chemical species in the system.
Setup:Species:Define…
u Under Database Species, select the name
u Set the Species number
u Define the species: C, H, O, N, C(S), O2 , CO2,
CO, H2O, N2 , OH, and H2

37
u Define fuel composition.
Setup:Species:Composition…
l C = 0.53
l H = 0.40
l O = 0.06
l N = 0.01
u Lower Caloric Value = 3.232e+07
u Specific Heat = 1100

38
u Define oxidizer composition.
l O2 = 0. 21
l N2 = 0.79

39
u Define the system operating
conditions.
Setup:Operating Conditions…
u Min. Temperature = 370
u Max. Temperature = 2600
u Set the Inlet Temperature
l Fuel = 373
l Oxidiser = 573

40
u Define the solution
parameters.
u Non-Adiabatic Model:
Enthalpy Points = 20
u Fuel Mixture Fraction
Points = 32
u Mixture Fraction Variance
Points = 16
u Disable Automatic
Distribution
u Distribution Center
Point = 0.2
u Calculate the pdf table
and view it with the
graphics routines.
u Save the pdf file
(ifrf.pdf).

41
Grid
u Start the 3D version of FLUENT
u Read the grid
file, ifrf.msh
u Check and
display the grid

42
Define Models (1)
u Define:Models:Solver u Define:Models:Viscous

43
Define Models (2)
u Define:Models:Species
When prompted read the ifrf.pdf
file. When the file is read, the
available material properties
/methods will change to
accomodate the model.
u Define:Models:Radiation
To choose an appropriate
radiation model, calculate optical
thickness = mean beam length
(about 2m) x absorption co-
efficient (around 1 /m for
hydrocarbon combustion)
Since this optical thickness is
greater than unity, the P1 model is
appropriate.

44
Define Models (3)
u Define:Models:Discrete
Phase Model
u Set the Max. Number Of
Steps to 25000
u Deactivate Specify
Length Scale
u Set Step Length Factor
to 20

45
Materials
u Define:Materials
u Set Absorption
Coefficient = wsggm-
cell-based
u Set Scattering
Coefficient = 0.15

46
Operating Conditions
u Retain default values.

47
Compile Interpreted UDFs
u Create a working directory and save the C
functions.
u Start Fluent from the working directory and read
the case file.
u Compile the UDF using the Interpreted UDFs
panel
u Enter name of the C function (ifrf.c)
under Source File Name
u Specify the C preprocessor under CPP
Command Name field
u Retain the default Stack Size
u Click Compile
u Close the panel when compilation is over

48
v-1 zone.
v-2 zone.

49
p-1 zone.
periodic zone.

50
Set boundary conditions for wall zones w-1, w-2, w-3, w-4,
w-5, w-6, w-7, w-8, and w-9 as per the table
0.5
1073
w-9
0.5
1323
w-8
1
udf-wall7temp
w-7
1
udf-wall6temp
w-5
1
udf-wall5temp
w-5
0.6
1273
w-4
0.6
873
w-3
0.6
573
w-2
0.6
343
w-1
Internal
Emissivity
Temperature
Zone
Name

51
Define Injections (1)
u Create Injections
Define:Injections…
u Click Create in the Injections panel
u Set Injection properties
u Injection Type: Surface
u Release From Surfaces: v1
u Particle Type: Combusting
u Diameter Distribution: rosin-rammler
u Turbulent Dispersion: Stochastic Model
u Number Of Tries: 3

52
6
Number Of Diameters
1.36
Spread Parameter
4.5e-05
Mean Diameter
0.003
Max. Diameter
1e-06
Min. Diameter
0.01826
Total Flow Rate
343
Temperature
23.11
Z-Velocity
Value
Parameter
u Under Point Properties, set the
following values:

53
u Modify the properties for the combusting
particle.
u Name: gottelborn-hy
u Set Properties as per table
Value
Parameter
kinetics/diffusion-
limited
Combustion Model
36.7
Combustible Fraction
3e-05
Binary Diffusivity
55.02
Volatile Component Fraction
300
Vaporization Temperature
0
Latent Heat
1100
Cp
1000
Density
Kinetics Limited Rate Pre-exponential
Factor = 6.7
Kinetics Limited Rate Activation Energy =
1.1382e+08`

54
Solution (1)
u Solve for Non reacting flow
u Disable Energy, P1 and
Pdf for equations
u Set pressure discretization
to PRESTO!
u Initialize the solution
u Compute from all-zones
u Set the initial value for
temperature to 2000
u Plot residuals during calculations
u Request 99 iterations
u Save the data file (ifrf1.dat.gz)

55
Solution (2)
u Solve for Reacting flow
u Enable Interaction with Continuous
Phase
l Set Number of Continuous Phase
Iterations per DPM Iteration to 20
u Enable Energy, P1 and Pdf equations
u Set the under-relaxation factors
u Request another 20 iterations
Value
Parameter
0.25
Discrete Phase Sources
0.975
P1
0.5
Momentum
0.5
Pressure

56
Solution (3)
u Modify the properties of the combusting particle
u Request for an additional 200
iterations
Value
Parameter
Activation Energy
= 7.4e+07
Pre-exponential
Factor = 2e+05 W
single-rate
Devolatilization Model
773
Vaporization Temperature

57
Solution (4)
u Set the discretization to Second Order Upwind for:
u Momentum
u Turbulence Kinetic Energy
u Turbulence Dissipation Rate
u Mean Mixture Fraction
u Mixture Fraction Variance
u Energy
u Request for an additional 500
iterations

58
Solution (5)
u Define the NOx Model
Define:Models:Pollutants:NOx...
u Enable the models Thermal NO
and Fuel NO
u Under Turbulence Interaction:
l PDFMode = Mixture Fraction
l Beta PDF Points to 25
u Under Fuel NO Parameters:
l Fuel Type = Solid
l Volatile N Mass Fraction = 0.01015
l Char N Mass Fraction = 0.00435
l BET Surface Area = 25000

59
Solution (6)
u For discrete phase model, set
Number of Continuous Phase
Iterations per DPM Iteration = 0
u Set Solution parameters:
u Disable all the equations except NO
and HCN
u Under-relaxation factors for NO and
HCN to 1
u Discretization scheme as Second
Order Upwind
u Convergence Criterion for NO and
HCN = 1e-06
u Request for 20 iterations

60
Postprocessing (1)
u Check the net in and out fluxes balance.
u Compute gas phase mass fluxes
through all boundaries
l Boundaries : Select all zones
l Click Compute
u Calculate the net mass transfer to the
gas phase from the discrete phase coal
particles.
l Options: Sum
l Cell Zones: fluid
l Field Variable : Discrete Phase Model...
and DPM Mass Source
l Click Compute

61
Postprocessing (2)
u Compute the gas phase energy fluxes through
all the boundaries
l Options : Total Heat Transfer Rate
l Boundaries : Select all zones
l Click Compute
u Calculate the net mass transfer to the
gas phase from the discrete phase coal
particles.
l Options: Sum
l Cell Zones: fluid
l Field Variable : Discrete Phase
Model... and DPM Enthalpy Source
l Click Compute

62
Postprocessing (3)
u Static Temperature u Turbulent Viscosity
Display contours of flow variables of interest

63
Postprocessing (4)
u Mass fractions of CO2 u Particle Tracks

64
Results
u The radial profiles and axial plots of time
averaged flow field values at 0.25m and 0.85m
from the quarl end of the combustor were
collected and can be downloaded from the files
listed in the table.
u Comparison of the experimental data and the
CFD simulation data show an agreement
which can be considered typical.

65
Center-line (z axis) parts-per-million (dry)
radial-NO.xy
Center-line (z axis) carbon-dioxide volume percentage (dry)
radial-CO2.xy
Center-line (z axis) parts-per-million (dry)
radial-CO.xy
Center-line (z axis) temperature (K)
radial-T.xy
Center-line (z axis) oxygen volume percentage (dry)
radial-O2.xy
Tangential velocity (m/s) at z=0.25m
radial-V-1.xy
Tangential velocity (m/s) at z=0.85m
radial-V-2.xy
Axial velocity (m/s) at z=0.25m
radial-U-1.xy
Axial velocity (m/s) at z=0.85m
radial-U-2.xy
NO parts-per-million (dry) at z=0.25m
radial-NO-1.xy
NO parts-per-million (dry) at z=0.85m
radial-NO-2.xy
Carbon-monoxide parts-per-million (dry) at z=0.25m
radial-CO-1.xy
Carbon-monoxide parts-per-million (dry) at z=0.85m
radial-CO-2.xy
Carbon-dioxide volume percentage (dry) at z=0.25m
radial-CO2-1.xy
Carbon-dioxide volume percentage (dry) at z=0.25m
radial-CO2-2.xy
Oxygen volume percentage (dry) at z=0.85m
radial-O2-2.xy
Oxygen volume percentage (dry) at z=0.25m
radial-O2-1.xy
Temperature (K) at z=0.85m
radial-T-2.xy
Temperature (K) at z=0.25m
radial-T-1.xy
Description
File
Experimental
Data :
Files of radial
profiles and
axial plots of
time averaged
flow field
values.
Reference :
Peters, A.F. and Weber,
R. (1997), Mathematical
Modeling of a 2.4 MW
Swirling, Pulverized
Coal Flame, Combustion
Science and
Technology, 122, 131.

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