OCR Text |
Show 3 Validation of the composite reaction mechanism will be performed by comparing model predictions with measurements of toxic species concentrations in laboratory flames. The flames chosen, laminar premixed and diffusion flames, have simple, known fluid mechanics, permitting an unambiguous assessment of flame chemistry. Validation conditions will be varied over a broad range of fuel-rich and fuel-lean conditions to exercise the kinetics model over the broad spectrum of stoichiometries encountered in practical burner flames. Integration Track. The composite detailed kinetic model developed in Phase II will be integrated with the fluid mechanics necessary to apply it to burner flames in Phase III, the integration track. Initially the chemical kinetic computations will be performed using simple combinations of wellstirred and plug flow reactors pieced together to approximate burner and furnace conditions. A two-stage Lagrangian jet model, tailored to the burners under study in the assessment track, will be developed and incorporated as part of the program. This model will allow for a more realistic treatment of the burner-furnace flow structure while still retaining fully detailed chemistry. Later in the program, multi-dimensional fluid mechanics will be combined with a partially reduced chemical kinetics set to provide fully coupled calculations of the low molecular weight air toxics (e.g., formaldehyde) from the burners studied in the assessment track. The results from integration of the composite kinetics model with burner-furnace fluid mechanics will be used both to interpret the toxic emission trends measured in the assessment track and to suggest process and flame, flow structure improvements that could lead to a reduction of toxic emissions. The integrated models will also be available to the PERF members for answering "What if' questions. An example question might be: "What if I have a process that produces higher-than-average propylene concentrations in my fuel gas. Will this increase my air toxics emissions?" The integrated models would then be run for the specific cases of interest in order to predict the trends in toxic emissions that might result. Determination of whether the question can be addressed within the scope of one of the integrated models would be made by consulting with the principal investigator. Additionally, the software for the integrated models will be provided to the PERF members so that those who are familiar with running FORTRAN code in a workstation environment can answer "What ifs?" themselves with perhaps some minimal guidance from the principal investigator. Decision Points. Depending upon the progress made in each area of the program, several decision points were included in the program plan. The first is a GolNo-Go decision on the project as a whole at the end of month 18. If sufficient progress has been made and the probability of program success is high, the program will be continued. The second is a branching decision on the submechanisms of air toxic formation. If our assumption that air toxics tend to exhibit class behavior is borne out in the first two years, in the third year the sub-mechanism task will focus on class groupings. If this assumption proves to be incorrect, additional species with high health-risk factors will be selected for development in the sub-mechanism task. The last decision point is a branching decision on the assessment track for the last year of the project. If a sufficient base of knowledge about the chemistry and fluid mechanics of air toxic formation has been developed, the latter part of the third year will be used to develop and test prototype advanced burner concepts (ABCs) capable of reduced air toxic emissions. If this is not the case, an intensive program will be undertaken of focused testing on specific areas where PERF member knowledge remains inadequate. |