OCR Text |
Show concentration is XCH4 = 0.075 and X02 = 0.194 corresponding to an equivalence fuel-air ratio (tP) of 0.77. Computation in mode C (stoichiometric) resulted in the same shaped contours but with· increased concentration of methane. Figure 6 shows the temperature contours given by the model in modes A and C. Both Figs. 5 and 6 have been taken at a front cross-section across a hole situated in the first row. Had a cross-section been chosen between the two holes of the two first rows, only the methane and temperature contours in the burner head end region would have changed, showing very low values until the mixing and the reaction effects appear further down. Computed temperature contours for mode B show the same pattern as the other modes but with a maximum temperature of 1757 K. Figure 7 gives the temperature, CH4 , O2 , CO and CO2 profiles in the y direction at the exit of the divergent section and at the middle depth of the domain for the burner in modes A, Band C respectively. The predictions for the prompt-NO concentration for mode A are shown in Fig. 8. The values for thermal-NO in mode A were so small that they are not given here. The maximum concentration of NO per % of CO2 was found to be 0.05 x 10-6 in the turbulent case. Figs. 9 and 10 show the prompt-NO and thermal-NO predictions for modes Band C respectively. Figures 11 and 12 give data for the NO concentrations at the exit of the divergent section of the burner operating in modes A, Band C, promptNO is given in Fig. 11 and the thermal-NO together with the total-NO in Fig. 12. 3.4 NOx Measurements and Predictions 10 Little experimental data are available to validate the model predictions, nevertheless the limited measurements made by the designers of the burner, British Gas and ourselves, agree with results displayed in , Figs. 7 to 12. Two series of measurements have been carried out on a 6 ft long ultra-low NOx burner used to dry malt. Those measurements having been done during a 12 hours long run in normal working conditions, only the very lean mode (mode A) in which the burner is always set was available for experimentation. Two different flow rates of natural gas corresponding to the maximum and the minimum heat inputs in mode A were studied. An |