1
**UGM 2002** Confidential

**Partially Premixed**

**Partially Premixed**

**Combustion in a Co-axial**

**Combustion in a Co-axial**

**Combustor**

**Combustor**

**Graham Goldin**

**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

3

**UGM 2002** Confidential

**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

st### and 2

nd### Order 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

5

**UGM 2002** Confidential

**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: CH_{4}, O_{2}, CO_{2}, CO, H_{2}O,

**Generate PDF look-up Table (3)**

u

### Define fuel composition.

Setup:Species:Composition…

u Set Species Fraction:

l CH_{4 }=_{ }0.0453
l O_{2 }= 0.2264
l CO_{2 }= 0.7283

7

**UGM 2002** Confidential

**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

9

**UGM 2002** Confidential

**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 H_{2}, CH_{4}, C_{2}H_{2}, C_{2}H_{4}, C_{2}H_{6}, C_{3}H_{8}
u *1atm < pressure < 40atm*

u *300K < T*_{unburnt}* < 800K*

11

**UGM 2002** Confidential

**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

**Define Model**

13

**UGM 2002** Confidential

**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**

15

**UGM 2002** Confidential

**Operating Conditions**

**Boundary Conditions (1)**

Set boundary conditions for air inlet.

Set boundary conditions for air-fuel inlet.

17

**UGM 2002** Confidential

**Boundary Conditions (2)**

**First Order Solutions (1)**

19

**UGM 2002** Confidential

**First Order Solutions (2)**

**First Order Solutions (3)**

u Initialize flow field and compute from all zones.

21

**UGM 2002** Confidential

**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)**

23

**UGM 2002** Confidential

**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).

25

**UGM 2002** Confidential

**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

27

**UGM 2002** Confidential

**Postprocessing (3)**

**Postprocessing (4)**

29

**UGM 2002** Confidential

**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**

31

**UGM 2002** Confidential

**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)

33

**UGM 2002** Confidential

**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%

35

**UGM 2002** Confidential

**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), O_{2 }, CO_{2},

37

**UGM 2002** Confidential

**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 O_{2 }= 0. 21
l N_{2 }= 0.79

39

**UGM 2002** Confidential

**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

41

**UGM 2002** Confidential

**Grid**

u

### Start the 3D version of FLUENT

u

### Read the grid

### file, ifrf

### .msh

u

### Check and

**Define Models (1)**

43

**UGM 2002** Confidential

**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

45
**UGM 2002** Confidential

**Materials**

u Define:Materials
u Set Absorption
Coefficient =
wsggm-cell-based
u Set Scattering
Coefficient = 0.15
**Operating Conditions**

47

**UGM 2002** Confidential

**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.

49

**UGM 2002** Confidential

**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**

51

**UGM 2002** Confidential

**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 Rate
343
Temperature
23.11
Z-Velocity
**Value**
**Parameter**

u Under Point Properties, set the

53

**UGM 2002** Confidential

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 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`

**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

55

**UGM 2002** Confidential

**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

57

**UGM 2002** Confidential

**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

59

**UGM 2002** Confidential

**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...

61

**UGM 2002** Confidential

**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

63

**UGM 2002** Confidential

**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.

65

**UGM 2002** Confidential

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