Monthly Technical Report

Transcription

1 Monthly Technical Report (Due to AQRP Project Manager on the 8 th day of the month following the last day of the reporting period.) PROJECT TITLE PROJECT PARTICIPANTS (Enter all institutions with Task Orders for this Project) REPORTING PERIOD Development of Speciated Industrial Flare Emission Inventories for Air Quality Modeling in Texas Lamar University PROJECT NUMBER DATE SUBMITTED From: 05/01/11. REPORT To: 05/31/11. NUMBER Invoice Number that accompanies this Report: CM Amount of funds spent during this reporting period: $5, /05/11 3 Detailed Accomplishments by Task (Include all Task actions conducted during the reporting month.) 1. Collection of Flare Operation/Design/Performance Data (Task 2, waiting for Comprehensive flare study final report for flare performance data) Details given in Appendix A 2. Hardware/Software/Data storage (Task 3) Details given in Appendix B 3. Combustion Mechanism Generation/Validation (Task 4A & 4B) Details given in Appendix B 4. Geometry Creation & Boundary Conditions (Task 5A) Details are given in Appendix C 5. Base Case Modeling (Task 6A) Details are given in Appendix A Preliminary Analysis (Include graphs and tables as necessary.) NA Data Collected (Include raw and refine data.) 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. 1

2 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 comprehensive flare study and 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. Geometry creation was impacted by lack of flare tip details and CFD mesh limitations. 4. Task 6A & 6C will be affected by this issue. 5. All other tasks are on schedule. Submitted to AQRP by: Principal Investigator: Daniel H. Chen. (Printed or Typed) Appendix A: May Monthly Report for Task 2 2

3 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 and the details were given in the April monthly report. CFD Fluent Simulations: Air based flares Using the geometry provided in Appendix C, CFD Simulations using FLUENT were started. Due to unusual high flow rate of air (as air-assist), Case A2.1 was taken as the first/base case. The conditions for the case A2.1 as provided by AQRP in file Appendix E Tables E-1, Comprehensive Flare Study QAPP were used [1]. Table A.I: Conditions used for Case A2.1 Vent gas velocity m/s Air-assist Velocity m/s Cross wind Velocity 5.74 m/s Table A. II: Composition of vent gas- Case A2.1 Vent Gas Composition Mass Species Fraction Propylene 1.00 TNG 0.00 Nitrogen 0.00 CFD Model Parameters In the CFD simulation package, various types of turbulence and chemistry-turbulence interaction models are available in CFD packages like FLUENT [2-5]. For the flare simulations the following models were chosen: Turbulence: k-epsilon realizable model The standard k-epsilon model is a semi-empirical model based on model transport equations for the turbulence kinetic energy k and its dissipation rate, Epsilon. The model transport equation for is derived from the exact equation, while the model transport equation for was obtained using physical reasoning and bears little resemblance to its mathematically exact counterpart. In the derivation of the - model, the assumption is that the flow is fully turbulent, and the effects of molecular viscosity are negligible. The standard - model is therefore valid only for fully turbulent flows The term "realizable'' means that the model satisfies certain mathematical constraints on the Reynolds stresses, consistent with the physics of turbulent flows. Neither the standard - model nor the RNG - model is realizable. 3

4 This model has been extensively validated for a wide range of flows, including rotating homogeneous shear flows, free flows including jets and mixing layers, channel and boundary layer flows, and separated flows. For all these cases, the performance of the model has been found to be substantially better than that of the standard - model. Especially noteworthy is the fact that the realizable - model resolves the round-jet anomaly; i.e., it predicts the spreading rate for axis symmetric jets as well as that for plan jets. Turbulence-chemistry interaction: Eddy Dissipation Concept Model The eddy-dissipation-concept (EDC) model is an extension of the eddy-dissipation model to include detailed chemical mechanisms in turbulent flows. It assumes that reaction occurs in small turbulent structures, called the fine scales. The length fraction of the fine scales is modeled as where denotes fine-scale quantities and = volume fraction constant = = kinematic viscosity The volume fraction of the fine scales is calculated as fine structures over a time scale. Species are assumed to react in the where is a time scale constant equal to In EDC model, combustion at the fine scales is assumed to occur as a constant pressure reactor, with initial conditions taken as the current species and temperature in the cell. Reactions proceed over the time scale, governed by the Arrhenius rates of Equation, and are integrated numerically using the ISAT algorithm. ISAT can accelerate the chemistry calculations by two to three orders of magnitude, offering substantial reductions in run-times. The source term in the conservation equation for the mean species, Equation is modeled as 4

5 where is the fine-scale species mass fraction after reacting over the time. CFD Solver During the simulations, the Green-Gauss Cell based solver was used. Apart from that, the discretization method for Pressure equations was changed from standard to PRESTO!, which is considered as more robust than the standard model. Under Relaxation Factors The under relaxation factors are used to stabilize the convergence behavior of the various discretized equations like Pressure, Density, Turbulence kinetic energy, Energy etc. Since, the URFs play an important role; these were changed from time to time, depending on the convergence stage of the problem. Case A2.1 Results The preliminary results of the first case including estimated emissions, flare efficiencies, and temperature/co2 mass fraction contours are given as follows: Emissions Fuel(C3H6) in lb/hr C3H6 out 3.05 lb/hr CO2 out lb/hr C in (as C3H6) lb/hr C out (as CO2) lb/hr The two efficiencies were calculated as: CFD Simulations TULSA Tests DRE 99.15% 97.15% CE 93.21% 95.54% Destruction and Removal Efficiency Combustion Efficiency = = C3H6 fed - C3H6 out C3H6 fed Carbon out as CO2 Carbon fed as fuel 5

6 Figure A.1: Contours of Static Temperature (K) Figure A.2: Contours of Static Temperature (K) zoomed near the flare 6

7 Figure A.3: Contours of Mass fraction of CO 2 Figure A.4: Contours of Mass fraction of CO 2 (zoomed in near the flame) 7

8 References 1) Quality Assurance Project Plan, Texas Commission on Environmental Quality Comprehensive flare Study Project, PGA No FY09-04, Tracking No UT/TCEQ/John Zink). 2) ANSYS FLUENT 6.3 User s Guide, Chapter 12- Modeling Turbulence, Fluent Inc (2006) 3) T.-H. Shih, W. W. Liou, A. Shabbir, Z. Yang, and J. Zhu, A New - Eddy-Viscosity Model for High Reynolds Number Turbulent Flows - Model Development and Validation. Computers Fluids, 24(3): , ) ANSYS FLUENT 6.3 User s Guide, Chapter 14: Modeling Species Transport and Finite Rate Chemistry, Fluent Inc (2006). 5) B. F. Magnussen. On the Structure of Turbulence and a Generalized Eddy Dissipation Concept for Chemical Reaction in Turbulent Flow. Nineteenth AIAA Meeting, St. Louis,

9 Appendix B: May Monthly Report for Tasks 3, 4A, & 4B Hardware/Software/Data Storage 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. Generation of 50-Species Reduced Mechanism with NO2 The full mechanism was reduced based on the strategy of removing the species of least interest. The species to be removed were identified depending on their effect of mole fractions on the species of interest. Initially, the mechanism did not have NO 2, but NO 2 happens to be one of the important species to be studied for the emissions analysis. To incorporate NO 2 in the mechanism, we analyzed the mole fractions of Ar and its effect on other species. Since Argon is an inert gas and was in relatively small concentration, it had least effect on the concentrations of species of interest. We replaced argon with NO 2 and corresponding mechanism data was also incorporated. Evaluation of the Reduced mechanism The simulation results of the reaction mechanisms were compared at different conditions as follows: The initial conditions for the mechanism simulation were: Equivalence ratio of fuel to oxidizer 0.5, 1.0, 1.5 Reactor temperature 1700 K There were three mechanisms under study, viz. 1. Full Mechanism (USC I + GRI) having 93 species 2. Reduced mechanism having 50 species without NO 2 3. Reduced mechanism having 50 species with NO 2 9

10 The species in these mechanisms are as follows: Mechanism Number Species list of Species Full Mechanism (USC I + GRI) 93 H2,H,O,O2,OH,H2O,HO2,H2O2,C,CH,CH2,CH2*,CH3,CH4,CO,CO2,HCO,CH2O,CH2OH,CH3O,CH3OH, C2H,C2H2, H2CC,C2H3,C2H4, C2H5,C2H6,HCCO, CH2CO, HCCOH, C2O, CH2CHO, CH3CHO, CH3CO, C3H2, C3H3, pc3h4, ac3h4, cc3h4, ac3h5, CH3CCH2, CH3CHCH, C3H6, C2H3CHO, C3H7, nc3h7, ic3h7, C3H8, C4H, C4H2, H2C4O, n-c4h3, i-c4h3, C4H4, n-c4h5, i-c4h5, C4H6, C4H612, C4H7, C4H81, C6H2, C6H3, l-c6h4, c-c6h4, A1,A1-, C6H5O, C6H5OH, C5H6, C5H5, C5H4O, C5H4OH, C5H5O, N, NH, NH2, NH3, NNH, NO, NO2, N2O, HNO, CN, HCN, H2CN, HCNN, Reduced mechanism without NO 2 Reduced mechanism with NO 2 HCNO, HOCN, HNCO, NCO, AR, N2 50 H2, H, O, O2, OH, H2O, HO2, CH, CH2, CH2*,CH3, CH4, CO, CO2, HCO, CH2O, CH2OH, CH3O, C2H2, H2CC, C2H3, C2H4, C2H5, C2H6, HCCO, CH2CO, CH2CHO, CH3CHO, C3H3, pc3h4, ac3h4, ac3h5, C3H6, C3H8, C4H2, n-c4h3, i-c4h3, C4H4, N, NH, NH2, NO, N2O, HNO, CN, HCN, HNCO, NCO, Ar, N2 50 H2, H, O, O2, OH, H2O, HO2, CH, CH2, CH2*,CH3, CH4, CO, CO2, HCO, CH2O, CH2OH, CH3O, C2H2, H2CC, C2H3, C2H4, C2H5, C2H6, HCCO, CH2CO, CH2CHO, CH3CHO, C3H3, pc3h4, ac3h4, ac3h5, C3H6, C3H8, C4H2, n-c4h3, i-c4h3, C4H4, N, NH, NH2, NO, N2O, HNO, CN, HCN, HNCO, NCO, NO2, N2 This comparison was done at three different equivalence ratio values 0.5, 1.0, 1.5. The results were studied in terms of Actual error and % error. It was found that at equivalence ratio = 1.0 the mole fractions were close enough to be considered as matching. (Except for the main fuel since the fuel was defined as ethylene). Further comparison was carried out at new values of residence times 0.8 and

11 The plots of mole fractions of species, at various equivalence ratio values are as follows: 3.000E E E E E E E-05 Reduced with NO2, ER=0.5 Full mechanism, ER=0.5 Reduced with NO2, ER=1.0 Full mechanism, ER=1.0 Reduced with NO2, ER= E E E E E+00 Mole fraction CH2O Mole fraction C2H4 Full mechanism, ER= E+00 Mole fraction C3H E E E E E E E E E E E E E E E E E E E E E E E E E E+00 Mole fraction NO 0.000E+00 Mole fraction NO E+00 Mole fraction CO Mole fraction CO2 * The simulation was carried out considering C 2 H 4 as fuel * In further simulations, C 3 H 6 will be considered as fuel and the equivalence ratio 0.8 and 1.0 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). Accessed 03 October (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. 11

12 (3) Anuj Bhargava abd Phillip R. Westmoreland, Measured Flame Structure and Kinetics in a Fuel Rich Ethylene Flame, COMBUSTION AND FLAME 113: , 1998 (4) Davis, S. G. and Law, C. K. (1998), "Determination of and Fuel Structure Effects on Laminar Flame Speeds of C 1 to C 8 Hydrocarbons", Combustion Science and Technology, 140(1), (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, (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 H 2 /CO/C 1 -C 4 Compounds. May

13 Appendix C: May Monthly Report for Task 5A Air assisted flare (Geometry & Boundary Conditions, Task 5A) In order to match the waste gas flow rate the geometry of flare tip has been modified. However, no change was taken place in computational domain. The finalized geometry contains the following key features. Domain is made up of 30 m 30 m enclosed box. The Flare stack is placed 5 m away from the left of the domain and its height is 10 m. The big domain has been chosen to consider the entire flame structure. Fig C.1: Computational Domain At the left side of domain, the velocity inlet boundary condition is applied, which considers the effect of cross wind in the computation. At the bottom of the domain, slip wall boundary condition is applied to simulate a smooth flow. The boundary conditions on all other sides are given as pressure outlet. In this simulation the spider shaped burner is considered as given in the comprehensive flare study document. Rectangular slit is created for waste gas flow to match the exact waste gas outlet area. Flare tip is divided in three parts: 1. Fuel/waste gas outlet 13

14 2. Air outlet 3. Spider wall Velocity inlet boundary condition is applied at the flare tip for fuel and air flows and the rest of the portion is defined as spider wall. Fig C.2: Flare Stack and Flare Tip [Ref: Quality assurance project plan Drawing number TCEQ LHTS-24] 14

15 The structure of flare tip is as shown below: Fuel Air Outlet Spider Wall Fig C.3: Computational Domain of the Flare Tip Meshing: In this study, Gambit is used for the meshing. Firstly, the base of the domain is meshed. Different size functions are used to create structure and linked mesh. Then the meshed base is extended up to the tip of the flare. The entire volume is meshed using cooper algorithm. The tip of flare meshed using very refined mesh. Meshing is done in such a way that the aspect ratio will be equal to one at tip of flare. Total nine spiders are created for fuel outlet. The meshed tip of flare is shown as below: 15

16 Fig C.4: Tip of Flare Fig C.5: Fuel Outlet The complete meshed domain contains 0.95 million cells, 2.7 million faces and 0.88 million nodes. Fig C.6: Representation of three dimensional meshed domain 16