OCR Text |
Show with the colder combustion products entrained in the flame from the external recirculation zone. This process lowers the peak flame temperature, thus affecting the formation of thermal NOx. The rate of entrainment with combustion products from the recirculation zone in the flame increases with the burner momentum, explaining the N O emission decreases in the water-cooled furnace for the high-momentum burner. NUMERICAL SIMULATIONS Calculations have been performed for three of the cases.presented above (B-R, B-C and C-R), using Fluent CFD package to simulate the different flames. The results obtained using the AL model for N O emission have been compared to the measurements, as well as to two alternate computational results, namely the P W models and the Fluent!2! N O x post-processor. The Fluent model has been used using the Zeldovich mechanism with a partial equilibrium assumption (O2 = 20), with PDFs for temperature and oxygen, as defined by Eq. (11). The Zeldovich mechanism with the equilibrium chemistry assumption is also employed and compared to the alternate models. RESULTS and DISCUSSION The first set of results presents the refractory-lined furnace and the medium-momentum burner B. Figure 3 presents the axial velocity (U), axial turbulent velocity (u'j and the temperature profiles along the burner axis, as resulted from the measurements and from the numerical simulation. It is noted that the temperature profile resulted from the numerical simulation is in relatively good agreement with the measured profile, in both magnitude and trends, with the simulation slightly over-predicting the peak temperatures. 12 |