OCR Text |
Show hydrocarbon fuels and for air/fuel ratios of 0.6 - 1.6. It is important to remember that oxygen reaction order (a) will depend on experimental conditions. For example, at high flame temperatures, (a) will approach unity. However, at low Harne temperature the oxygen reaction order will approach zero. In order to obtain a realistic prediction of prompt NO, the oxygen reaction order should be calculated from composition data. 2.3 FUEL NO x It is well known that nitrogen-containing organic · compounds present in liquid and solid fossil fuel can contIibute to total NO formed during combustion processes. This fuel nitrogen is a particularly important source of nitrogen-oxide emissions for residual fuel oil and coal which typically contain 0.3 - 2 % nitrogen by weight. Studies have shown that most of the nitrogen in heavy fuel oils IS in the form of heterocycles and it is believed that the nitrogen components of coal are similar (20). The extent of conversion of fuel nitrogen to NO is dependant on the local combustion characteristics and initial concentration of nitrogen-bound compounds. Fuel-bound nitrogen containing compounds are released into the gas phase when the fuel droplets or paliicles are heated during the devolatisation stage. From the thermal decomposition of these compounds, i.e. Aniline, Pyridine, Pyrroles etc. in the reaction zone, radicals such as HeN, N, eN, NO and NH then can be converted to NO. The above free radicals (i.e. x (11) |