OCR Text |
Show lower temperatures and less oxygen. It is also an effective technique for dealing with fuel bound nitrogen. Even at 85% of theoretical air, the equilibrium concentration is at a relatively low level, although adiabatic flame temperature has fallen little. Many of the fuel nitrogen compounds are destroyed by thermal dissociation and cannot find enough oxygen to form or reform NO under reducing conditions. FACTORS AFFECTING NOx FORMATION Fundamentally, there are only two basic factors: First, fuel analysis, particularly the quantity of nitrogen compounds combined in the fuel • Second, flame envelope conditions, specifically temperature, whether reducing, oxydizing or inert, completeness and rate of fuel/air mixing. Regarding fuel analysis, the more nitrogenous compounds present in the fuel, the more N available to oxydize to NO during pyrolysis in the flame. The percentage of conversion is more dependent upon oxygen availability than on high temperature. The authors have been unable to ascertain whether the presence of other common fuel impurities and their compounds will influence NO formation in flames. This would seem an interesting line of further investigation. Regarding flame envelope conditions, nitrogen fixation is strongly dependent upon temperature and is only significant above 2800°F. On the other hand, NO formed from fuel nitrogen is reduced under oxygen deficient conditions. Mixing is important because it affects temperature, residence times and the composition of combustion products at points within the overall flame envelope. 13/4 |