OCR Text |
Show to the adiabiatic conditions. Figure 18 illustrates increase of the NOx for varying excess air ratios, with the combustion air temperature kept constant. The last two figures, Fig.19 and 20, show effects of oxygen enrichment on the NOx production. As expected there is a significant increse of the NOx , almost twofold, for all the firing rates. The most interesting result comes with Figure 20, which shows the effects of lance air. The levels of the NOx droped for the lowest and full firing rates. There was an increased of the NOx for the 80% fire rate however, it was much less than for the operation without the lance. The described trend in the NOx behaviour is contributed to the introduction of the second oxygen-fuel mixing interface. The higher velocity jet of the lance air propagates within the annular jet of fuel thus streching the flame longitudinally. This assists in more efficient entrainment of combustion products from the outer zone into the flame and initiates the NOx "reburn" chain of reactions. The blue colour of the flames with the lance air on can indicate better mixing conditions in the flame region and shorter residence times which contribute to the observed NOx reduction. CONCLUSIONS. The use of oxygen enriched combustion air presents an attractive option for increasing the process effectivness in the reheating technology. However, the questions of the necessary changes to the combustion air hardware and the performance deterioration arise if the existing system were to be adapted for the oxygen utilization. The results of this investigation showed that an industrial burner can be sucessfully fitted and operated with the oxygen enriched combustion air, without sacrifice in the burner peformance. The tests with the Bloom Low-NOx burner shown the increase in the heat transfer to the load and the furnace walls. At the same time, the increased levels of the NOx were observed. The latter negative effect was offset by the use of the lance air flow, located within the fuel flow. This promising version of the air staging technique is being investigated further at the CAGCT. ACKNOWLEDGEMENTS The financial support of the Natural Sciences and Engineering Research Council, Energy, Mines and Resources Canada and British Gas is gratefully acknowledged. The authors would like to thank members and technical support personnel of the Centre for Advanced Gas Combustion Technology for their continuous support and trust. 5 |