OCR Text |
Show However, the trends obtained with the two combustors are similar. Minimum NO emissions increase strongly with fuel nitrogen content up to fuel nitrogen levels of approximately 0.5 and then increase only slightly as the nitrogen content is increased to greater than 2 percent, indicating that under staged combustion conditions, minimum NO levels are not solely dependent upon fuel nitrogen content. It has been suggested that the relatively volatility of the fuel nitrogen compounds in liquid fuels will have an impact upon the efficiency of staged combustion as a NO control technique. Those fuels with highly volatile nitrogen compounds will provide longer residence times for the XN specie to follow Path B and maximize N2 production in the rich primary zone. Experiments involving a residual fuel and a distillate oil doped with pyridine and thiophene to give the same nitrogen and sulfur contents showed minimum emissions levels under staged combustion conditions that were 30 percent lower for the doped distillate than for the residual fuel. The results presented in Figure 10 show that for high nitrogen alternate fuels the minimum NO level is much less dependent upon total fuel nitrogen content than for petroleum fuels with lower total nitrogen levels. Highest emissions were obtained for a very high boiling point fraction of refined shale oil. These results have implications for fuel, production schemes, since if denitrification were to remove the majority of the highly volatile nitrogen components leaving a fuel of lower but more refractory total nitrogen content, it might well be that under staged combustion conditions, emissions from both these fuels would be similar. 7-20 |