1 AQRP Monthly Technical Report Template Revised January 2011
Monthly Technical Report (Due to AQRP Project Manager on the 8th day of the month following the last day of the reporting period.)
PROJECT TITLE Development of Speciated
Industrial Flare Emission
Inventories for Air Quality
Modeling in Texas
PROJECT
NUMBER
10-022
PROJECT
PARTICIPANTS (Enter all institutions
with Task Orders for
this Project)
Lamar University DATE
SUBMITTED
04/23/11
REPORTING
PERIOD
From: 04/01/11.
To: 04/30/11. REPORT
NUMBER
2
Invoice Number that accompanies this Report: CM5086-2
Amount of funds spent during this reporting period: $0.00
Detailed Accomplishments by Task (Include all Task actions conducted during the reporting
month.)
1. Collection of Flare Operation/Design/Performance Data (Task 2, Limited input data
received, waiting for flare performance data & certain geometry data)
Details given in Appendix A
2. New model development protocol received as a guideline for data needs and modeling
cases. Cases selected and model used are described. (Task 2 & 5A)
Details are given in Appendices A & C.
3. Hardware/Software/Data storage (Task 3)
Details given in Appendix B
4. Combustion Mechanism Validation (Task 4A)
Details given in Appendix B
5. Geometry Creation & Boundary Conditions (Task 5A)
Details are given in Appendix C
6. CFD chemistry model selection, and model parameters (Task 5B)
Details are given in Appendix C
Preliminary Analysis (Include graphs and tables as necessary.)
NA
Data Collected (Include raw and refine data.)
2 AQRP Monthly Technical Report Template Revised January 2011
1. Collection of Flare Operation/Design/Performance Data (Task 2, see Appendix A for
details)
Identify Problems or Issues Encountered and Proposed Solutions or Adjustments
See Section of the Progress of the Task Order to Date.
Goals and Anticipated Issues for the Succeeding Reporting Period
Goals for the next reporting period:
1. Combustion Mechanism Generation & Validation (Task 4A & 4B)
2. CFD Modeling (Cases prescribed in the Model Development Protocol, Task 6A)
3. Model calibration with literature (wind tunnel) data (Task 5D)
Detailed Analysis of the Progress of the Task Order to Date (Discuss the Task Order
schedule, progress being made toward goals of the Work Plan, explanation for any delays in
completing tasks and/or project goals. Provide justification for any milestones completed more
than one (1) month later than projected.)
1. Receipt of the flare test data (input & performance) was delayed for roughly 1 month.
2. Task 6A & 6C will be affected by this delay.
3. All other tasks are on schedule.
Submitted to AQRP by:
Principal Investigator: Daniel H. Chen.
(Printed or Typed)
3 AQRP Monthly Technical Report Template Revised January 2011
Appendix A: April Monthly Report for Task 2
CFD Cases
Both the air and steam based cases are broadly divided in 3 sets, based on the 3 different
Lower Heating values (2100, 600 & 350 BTU/SCF) of the fuel used. Each set further has five
cases, with different vent gas velocity, crosswind and other conditions. These CFD cases are
based on the data provided by AQRP to Lamar University.
Table A1 & A2 show different cases to be run for CFD simulations
Table A1: CFD cases for steam-based flares
Test Actual Vent Gas (VG) Flow Rates Vent Gas Actual Steam Flow Rates Wind Vel No. Propylene TNG Nitrogen Total LHV Vel Center Upper Total
lb/hr lb/hr lb/hr lb/hr Btu/scf fps lb/hr lb/hr lb/hr Mph
S1.5 2337.48 0.00 0.00 2337.48 2145.11 1.52 525.87 3794.01 4319.88 8
S1.8 2338.4 0.00 0.00 2338.4 2145.96 1.5 505.87 7044.07 7549.94 8.6
S 1.9 2336.64 0.00 0.00 2336.64 2144.34 1.5 504.91 7939.33 8444.24 8.8
S 2.2 937 0.01 0.00 937.01 2103.14 0.95 541.62 7769.53 8311.14 10.8
S 2.3 937 0.00 0.00 937 2122.5 0.94 539.31 4761.25 5300.56 7.6
S 3.7 191.29 18.95 715.51 925.74 345.54 0.6 0 227.83 227.83 7.1
S 4.1 490.5 44.96 1799.74 2335.2 349.58 2.0 559.94 536.28 1096.22 5.6
S 4.3 485.21 45.05 1801.62 2331.88 346.37 2.0 567.28 1879.5 2446.77 5.2
S 4.3 500.38 46.62 1802.14 2349.14 355.19 2.0 627.77 2447.42 3075.19 6.6
S 7.3 296.76 29.92 1083.58 1410.26 352.77 1.4 515.59 537.91 1053.51 7.9
S 5.2 319.81 33.78 584.67 938.26 595.36 1.0 454.47 1580.38 2034.85 10.2
S 5.3 312.28 31.73 577.98 921.99 589.58 1.0 481.52 782.52 1264.04 9.3
S 5.4 317.61 32.17 579.44 929.22 595.36 1.0 483.73 1220.85 1704.57 10.9
S 5.6 312.17 31.82 577.17 921.16 590.08 1.0 490.6 462.92 953.53 9.6
S 6.1 826.42 79.13 1455.62 2361.16 608.89 1.9 517.78 1002.85 1520.64 8.8
4 AQRP Monthly Technical Report Template Revised January 2011
Table A2: CFD cases for air-assisted flare
Test Actual Vent Gas (VG) Flow Rates Vent
Gas Vel
Air Flow Wind Vel No. Propylene TNG Nitrogen Total LHV rate
lb/hr lb/hr lb/hr lb/hr Btu/scf fps lb/hr mph
A1.1 918.88 0 0 918.88 2107.71 1.4 149173 12.7
A2.1 355.02 0 0 355.02 2125.45 0.5 83818 12.8
A2.3 352.14 0 0 352.14 2108.22 0.5 88791 10.1
A2.4 352.87 0 0 352.87 2112.57 0.5 148799 10
A2.5 354.71 0 0 354.71 2123.55 0.5 119580 13.3
A3.1 181.23 18.77 702.55 902.55 338.67 1.9 19387 10.3
A3.3 181.23 18.37 700.6 900.2 333.86 1.9 60121 11.1
A3.6 181.23 18.76 704.18 904.17 337.55 1.9 47494 11.9
A5.2 72.29 7.69 274.41 354.39 342.86 0.8 75139.77 2.1
A5.3 71.26 7.55 271.37 350.18 341.87 0.8 32876.17 2.5
A4.3 298.74 30.3 591.1 920.14 562.91 1.9 66471.69 10.7
A6.1 117.8 11.86 221.21 350.87 583.73 0.7 11403.53 15.9
A6.4 118.06 12.08 221.25 351.4 584.89 0.7 40583.88 14.1
A6.5 117.85 12.08 221.11 351.04 584.44 0.7 56593.85 15.5
A6.6 118.55 12.44 220.68 351.66 588.07 0.7 146294.6 15
* LHV: Lower heating value; TNG: Tulsa natural gas
Tulsa Natural Gas
The composition of the TNG (Tulsa natural gas) will be taken as:
* The John Zink Combustion Handbook (Pg 163)
Reference
Baukal, C.E & Schwartz, R. E., The John Zink Combustion Handbook, p. 163, CRC Press: Boca
Raton, 2001.
Tulsa Natural Gas (Volumetric Composition)*
CH4 93.40% C2H6 2.70%
C3H8 0.60% C4H10 0.20%
CO2 0.70% N2 2.40%
5 AQRP Monthly Technical Report Template Revised January 2011
Appendix B: April Monthly Report for Tasks 3 & 4A
Hardware/Software/Data Storage
All purchased servers (1 Dell PowerEdge R710 & 2 Dell PowerEdge R410) in the high
performance cluster have been successfully networked. The purchased FLUENT/CHEMKIN
HPC licenses were also successfully installed for parallel computing.
All the input data received and data generated in this report (e.g., mechanism validation) are
properly stored in Servers/computers at Lamar University. The data will be stored in external
hard drives for three years. As mentioned in the QAPP, the data will include various fluent case
runs and excel files containing data analysis.
Existing 50-Species Mechanism Validation
In the research team’s prior work, a reduced chemical kinetic mechanism for the combustion
of C1-C3 hydrocarbons was generated using a novel algorithm developed on the basis of
sensitivity analysis, quasi-steady state, reaction rates and skeletal approach. The reaction
mechanism file was based on a combined mechanism formed using two widely used chemical
kinetic mechanisms i.e. GRI-3.01 and USC
2. A few aspects of natural gas combustion chemistry
are not described by GRI-Mech 3.0; these include soot formation and the chemistry involved in
selective non-catalytic reduction of NO, which may be important in natural gas reburning at
lower temperatures. The USC mechanism (containing 75 species) was optimized for ethylene
combustion reactions, but the absence of NOx producing species in the mechanism was a
shortcoming. To overcome this problem, both reaction mechanisms were combined so as to yield
a mechanism which could satisfy all the above mentioned criteria. The detailed mechanism,
which has 93 species and 600 reactions, was reduced in a step wise manner to 50 species and 337
reactions.
As often seen in the literature, the fidelity of the mechanism was validated against some
laboratory data3. 4
. The key performance indicators used are laminar burner stabilized flames,
laminar flame speeds, adiabatic flame temperatures, ignition delay test. The following initial
results were submitted in the Quality Assurance Project Plan (Pg. 21~23, Figures 5.1a~5.3b).
Laminar Flame Speed vs. Equivalence Ratio for Methane Air Mixture
Laminar Flame Speed vs. Equivalence Ratio for Propylene Air Mixture
Adiabatic Flame Temperature vs. Equivalence Ratio for Methane
Adiabatic Flame Temperature vs. Equivalence Ratio for Ethylene
Ignition Delay vs. Temperature for Methane
Ignition Delay vs. Temperature for Ethylene
Ignition Delay vs. Temperature for Propylene
The inlet experimental conditions for the CHEMKIN simulation are listed in Table B.1.
Results of various key performance indicators (laminar flame speeds, adiabatic flame
temperature, and ignition delay tests) for methane, ethylene and propylene flames show that the
simulation and experimental literature results are in good agreement for light hydrocarbons.
In this month, using the software package CHEMKIN 4.1.1, the fidelity of the mechanism
was further validated against Burner Stabilized flame laboratory data reported in the literatures.
The experimental data is obtained from the work of Bhargava et. al.3. The fuel is a mixture of
6 AQRP Monthly Technical Report Template Revised January 2011
ethylene, oxygen and argon with ethylene and argon at equivalence ratio of one. A low-pressure
laminar premixed flame stabilized on a 6.0 cm diameter burner was used in the experiment4. The
CHEMKIN model was supplemented with the measured temperature profile. The simulated
species mole fractions along the length of the flame were extracted and compared with
experimental results. Figure B.1 shows the comparison between simulation and experimental
data of the mole fraction of major species, such as C2H4, CO2 and O2. The experimental mole
fractions have an uncertainty of ±10% for the stable intermediates, and a factor of 2 for radicals4.
The USC/GRI mechanism has an uncertainty of 10% for CO, 4% for CO2, 10% for C2H4, 0.005
(mole fraction) for CH4, and 0.004 (mole fraction) for O2,5,6
. Therefore, a good agreement among
the major species is observed. Figure B.2 shows that the reduced mechanism is even capable of
predicting the generation of formaldehyde (a radical producing species in atmospheric
chemistry), which may be important from environmental aspect, with sufficient accuracy. This
comparison thus validates the reduced mechanism against an important aspect of validation,
burner stabilized flame, for ethylene.
Table B.1: Inlet experimental conditions for the model
Species Inlet Composition of
Fuel Mixture (vol%)
Equivalence
Ratio Initial Pressure (atm)
Methane CH4/O2/Ar
(9.1/18.2/72.7) 1 1.8
Ethylene C2H4/O2/Ar
(1/3/96) 1 1
Propylene C3H6/O2/Ar
(3.17/7.83/89) 1 7.9
7 AQRP Monthly Technical Report Template Revised January 2011
Figure B.1: Comparison of the Molar Fraction of Major Species in Burner Stabilized
Flame for C2H4/O2/Ar (phi = 1.9)
Figure B.2: Comparison of Formaldehyde Mole Fraction Data for Burner Stabilized Flame
8 AQRP Monthly Technical Report Template Revised January 2011
References
(1) Smith, G. P, Golden, G. M, Frenklach, M, Moriarty, N. W, Eiteneer, B, Goldenberg,M,
Bowman, T, Hanson, R. K, Song, S, Gardiner, W. C, Lissianski,V. V and Qin, Z.
(2000).http://www.me.berkeley.edu/gri_mech/. Accessed 03 October 2010.
(2) Wang, H. and Laskin, A. (1998). A comprehensive kinetic model of ethylene and acetylene
oxidation at high temperatures, Combustion Kinetics Laboratory, Document, Internal report.
(3) Anuj Bhargava abd Phillip R. Westmoreland, Measured Flame Structure and Kinetics in a
Fuel –Rich Ethylene Flame, COMBUSTION AND FLAME 113: 333-347, 1998
(4) Davis, S. G. and Law, C. K. (1998), "Determination of and Fuel Structure Effects on Laminar
Flame Speeds of C1 to C8 Hydrocarbons", Combustion Science and Technology, 140(1), 427-
449.
(5) R.S.Barlow,A.N.Karpetis, J.H.Frank, J.Y. Chen,”Scalar Profiles and NO formation in
laminar opposed flow partially premixed methane/air flames” Combustion and flame, 2001.
(6) Hai Wang, Xiaoqing You, Ameya V. Joshi, Scott G. Davis, Alexander Laskin, Fokion
Egolfopoulos & Chung K. Law, USC Mech Version II. High-Temperature Combustion
Reaction Model of H2/CO/C1-C4 Compounds. http://ignis.usc.edu/USC_Mech_II.htm, May 2007
9 AQRP Monthly Technical Report Template Revised January 2011
Appendix C: April Monthly Report for Tasks 5A & 5B
1. Geometry Creation & Boundary Conditions (Task 5A)
The geometry of the air-assisted flare as well as the computational domain is under
construction. As seen in Fig. C.1, the computational domain has a width of 30m and a height of
30 m. The flare has a stack of 10m and is located at 5m from the upstream of the crosswind. In
this way, a sufficient space can be applied to examine the effect of crosswind on the flare profile.
Great effort has been made to create the geometry of the flare burner. Due to the extreme
complicity of the actual structure, it is impossible to simulate the detailed flow from many small
jet holes. Simplification is made to introduce the waste gas and air flow without sacrificing the
major feature of the burner. Nine Spider legs are created for waste gas outlet. Figure C.2 shows
the tip of the flare burner, and both flow rate and the jet velocity will be matched to the actual
test.
Figure C.1: Computational Domain Figure C.2: Flare Burner
After the computational domain is created, the next step is to generate a mesh. In this
study, Gambit 2.3.16 is used for the meshing. Different size functions are used to create the
mesh. The final meshed geometry contains 0.77 million cells and 0.70 million nodes. The
number of the grids is a result after balancing the computational time and the simulation
uncertainty. Figure C.3 shows the general structure of the grids in different directions.
2. CFD chemistry model selection, and model parameters (Task 5B)
Two types of combustion/chemical reaction models are being considered:
Eddy-dissipation finite-rate model and non-premixed combustion (PDF) model.
Waste Gas
Inlet
Air Inlet
10 AQRP Monthly Technical Report Template Revised January 2011
Figure C.3: Representation of three dimensional meshed domain
. 2.1 Eddy-dissipation finite-rate model
When the user chooses to solve conservation equations for chemical
species, FLUENT predicts the local mass fraction of each species, Yi, through the solution of a
convection-diffusion equation for the ith species. This conservation equation takes the following
general form:
(C.1)
where Ri is the net rate of production of species by chemical reaction (described later in this
section) and Si is the rate of creation by addition from the dispersed phase plus any user-defined
sources.
The reaction rates that appear as source terms in Equation-1 are computed in FLUENT by one of
three models:
Laminar finite-rate model: The effects of turbulent fluctuations are ignored, and reaction
rates are determined by Arrhenius expressions.
Eddy-dissipation model: Reaction rates are assumed to be controlled by the turbulence,
so expensive Arrhenius chemical kinetic calculations can be avoided. The model is
computationally cheap, but, for realistic results, only one or two step heat-release
mechanisms should be used.
11 AQRP Monthly Technical Report Template Revised January 2011
Eddy-dissipation-concept (EDC) model: EDC model is an extension of the Eddy-
dissipation model. Detailed Arrhenius chemical kinetics can be incorporated in turbulent
flames. However, typical reaction mechanisms are invariably stiff and their numerical
integration is computationally costly. Hence, the model should be used only when the
assumption of fast chemistry is invalid, such as modeling the slow CO burnout in rapidly
quenched flames, or the NO conversion in selective non-catalytic reduction (SNCR).
The generalized finite-rate formulation is suitable for a wide range of applications
including laminar or turbulent reaction systems, and combustion systems with premixed, non-
premixed, or partially-premixed flames.
2.2 Non-premixed combustion (PDF) model
Non-premixed modeling involves the solution of transport equations for one or two
conserved scalars (the mixture fractions). Equations for individual species are not solved.
Instead, species concentrations are derived from the predicted mixture fraction fields. The
thermo-chemistry calculations are preprocessed and then tabulated for look-up in FLUENT.
Interaction of turbulence and chemistry is accounted for with an assumed-shape Probability
Density Function (PDF).
The non-premixed modeling approach has been specifically developed for the simulation
of turbulent diffusion flames with fast chemistry. This approach is valid whenever non-
equilibrium effects such as extinction, reignition, lift-off and blow-out are not important, and it
greatly simplifies the chemistry modeling of any combustion system.
For such systems, the method offers benefits over the eddy-dissipation formulation. The
non-premixed model allows intermediate (radical) species prediction, dissociation effects, and
rigorous turbulence-chemistry coupling. The method is computationally efficient in that it does
not require the solution of a large number of species transport equations. This model is
implemented in Fluent such that chemistry calculations are also preprocessed and tabulated.
When the underlying assumptions are valid, the non-premixed approach is preferred over the
eddy-dissipation formulation.
In Non-premixed combustion model, the mixture fraction concept plays a vital role.
Considering certain assumptions, the instantaneous thermo-chemical state of the fluid is related
to a conserved scalar quantity known as mixture fraction f. First, the mass fraction of species can
be defined as
Consider a mixture of pure waste gas, so mass fraction of waste gas propylene C3H6 (w) = 1. The
mass fraction of carbon C (ZC) = 0.86, and the mass fraction of hydrogen H (ZH) = 0.14. The
elemental mass fractions remain constant throughout all the reactions. In non-premixed
combustion model, flame is considered as co-flow of fuel and oxidizer. In such mixture, Mixture
fraction f for element n at a specific point can be given as:
12 AQRP Monthly Technical Report Template Revised January 2011
When two equations need to be solved in non-premixed combustion model: Mean mixture
fraction equation , and Mixture fraction variance equation . The conservation equation for
the mean mixture fraction is given below:
The conservation equation for the mixture fraction variance is given below:
where
- User defined source term
- Source term due solely to transfer of mass into the gas phase from reacting particles
The constants , , and are 0.85, 2.86, and 2.0, respectively
After that, the probability density function (PDF), written as can be considered as
the fraction of time that the fluid spends in the vicinity of the state f.
where is the time scale, and is the amount of time that f spends in the band. The shape
of the function depends on the nature of the turbulent fluctuations in f. In practice, is
unknown and is modeled as a mathematical function that approximates the actual PDF shapes
that have been observed experimentally.
Figure C.4: Graphical description of the probability density function,