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Partially Premixed
Partially Premixed
Combustion in a Co-axial
Combustion in a Co-axial
Combustor
Combustor
Graham GoldinProblem
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
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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
1
stand 2
ndOrder Solutions
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
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Generate PDF look-up Table (2)
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,
Generate PDF look-up Table (3)
u
Define fuel composition.
Setup:Species:Composition…
u Set Species Fraction:
l CH4 = 0.0453 l O2 = 0.2264 l CO2 = 0.7283
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Generate PDF look-up Table (4)
u
Define oxidizer composition.
u Set Species Fraction:
Generate PDF look-up Table (5)
• 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
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Generate PDF look-up Table (6)
u
Examine temperature/mixture fraction, and
species/mixture fraction relationship
Generate PDF look-up Table (7)
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
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Read Grid
u
Start the 2D version of FLUENT
u
Read the grid file,
par-premixed.msh
u
Scale the grid to inches
uDisplay the grid
Define Model
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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
Material
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Operating Conditions
Boundary Conditions (1)
Set boundary conditions for air inlet.
Set boundary conditions for air-fuel inlet.
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Boundary Conditions (2)
First Order Solutions (1)
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First Order Solutions (2)
First Order Solutions (3)
u Initialize flow field and compute from all zones.
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First Order Solutions (4)
u Start the calculation (250 iterations).
u Define a region Adapt:Region…
u Patch a region close to fuel-air
First Order Solutions (5)
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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
Second Order Solutions (2)
u
Start the calculation (250 iterations).
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Postprocessing (1)
uVelocity Vectors.
Set Scale Factor to 10 and Skip Value to 3
uContours of Steam
Postprocessing (2)
uFilled contours of mean
Progress Variable.
uFilled contours of Static
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Postprocessing (3)
Postprocessing (4)
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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)
3D Simulation of the IFRF
3D Simulation of the IFRF
Industrial Pulverized-Coal
Industrial Pulverized-Coal
Furnace
Furnace
Graham Goldin
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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.
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)
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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
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%
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Generate PDF look-up Table (1)
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
Generate PDF look-up Table (2)
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,
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Generate PDF look-up Table (3)
u
Define fuel composition.
Setup:Species:Composition…
u Set Species Fraction:
l C = 0.53 l H = 0.40 l O = 0.06 l N = 0.01
u Lower Caloric Value = 3.232e+07
Generate PDF look-up Table (4)
u
Define oxidizer composition.
u Set Species Fraction:
l O2 = 0. 21 l N2 = 0.79
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Generate PDF look-up Table (5)
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
Generate PDF look-up Table (6)
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
u
Calculate the pdf table
and view it with the
graphics routines.
u
Save the pdf file
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Grid
u
Start the 3D version of FLUENT
u
Read the grid
file, ifrf
.msh
u
Check and
Define Models (1)
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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.
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
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Materials
u Define:Materials u Set Absorption Coefficient = wsggm-cell-based u Set Scattering Coefficient = 0.15Operating Conditions
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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
Boundary Conditions (1)
Set boundary conditions for v-1 zone.
Set boundary conditions for v-2 zone.
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Boundary Conditions (2)
Set boundary conditions for p-1 zone.
Set boundary conditions for periodic zone.
Boundary Conditions (3)
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
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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
Define Injections (2)
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 Rate343 Temperature 23.11 Z-Velocity Value Parameter
u Under Point Properties, set the
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u
Modify the properties for the combusting
particle.
u Name: gottelborn-hy
u Set Properties as per table
Define Injections (3)
Value Parameter kinetics/diffusion-limited Combustion Model 36.7 Combustible Fraction 3e-05 Binary Diffusivity 55.02 Volatile Component Fraction300 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`
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
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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
u Save the data file (ifrf2.dat.gz)
Value Parameter
0.25 Discrete Phase Sources
0.975 P1 0.5 Momentum 0.5 Pressure
Solution (3)
u Modify the properties of the combusting particle
u Request for an additional 200
iterations
u Save the data file (ifrf3.dat.gz)
Value Parameter Activation Energy = 7.4e+07 Pre-exponential Factor = 2e+05 W single-rate Devolatilization Model 773 Vaporization Temperature
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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
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
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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
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...
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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
Postprocessing (3)
u Static Temperature u Turbulent Viscosity
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Postprocessing (4)
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.
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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