OCR Text |
Show thermodynamic model gives the axial temperature profile as well as the fractions of radiative and convective heat transfer. A total firebox efficiency is also calculated. Emissions were modeled by Alzeta using the PRemixed One-dimensional Flame (PROF) code. The code was developed to accurately model the detailed combustion and pollution formation processes occurring in premixed one-dimensional flames, and includes a detailed chemical kinetics solver, axial diffusion of heat and chemical species, and a radiative heat transfer model. The code has been demonstrated in earlier work to accurately model premixed combustion phenomena, including NOx generation (Reference 3). The kinetics set used for the predictions presented included 49 chemical species and over 200 reactions. A more detailed description of the code, including the governing one-dimensional equations can be found in Reference 4. Due to the similarity in performance between runs with varying levels of FGR when the total dilution level is held constant, one run was selected from the Chevron field test data for modeling by B & W . This run was selected because it was a low-NOx point (7 ppm) and was operated at nominally 60 percent total dilution to achieve this low level of emissions. B & W C O M O Modeling Results Results of the B&W COMO model are shown as Figures 5a to 5e. In this particular test, the burner and furnace are both cylindrical, with combustion products entering the burner at the left of each figure (with the burner centerline at the inlet end being the 0,0 coordinate) and flowing toward the right (toward the 35 ft (10.7 m) coordinate in the axial direction). The furnace gas temperature distribution is shown in Figure 5a, with temperatures ranging from nominally 2500 °F (1370 °C) at the burner surface to 1700-1800 °F (925-982 °C) at the tube walls, and dropping by the 20 foot length (6.1 m ) to 1600-1700 °F (870-925 °C). The gas temperature "slice" at the 4 ft (1.2 m ) dimension is shown in greater detail along with velocity vectors in Figure 5b. The high velocity regions at the burner surface coincide with the blue flame regions of the burners. 6 |