Total fixed nitrogen emissions

The reduction of fuel-N to molecular nitrogen in air staging is favored in the fuel rich primary combustion zone ( Fig. 3 ). Investigations on fixed bed wood furnaces have shown that a minimum of the Total Fixed Nitrogen (TFN = HCN+NH3+NO+ NO2+2N2O emission from the primary combustion zone is reached for a stoichiometric ratio of 0.7 to 0.8 and a temperature of 1100 C to 1200 °C and providing a mean residence time of 0.5 s. After the reduction zone the combustion is completed in the burnout zone by injection of the excess air. 

Prompt NO Hydrocarbon fragments (such as C, CH, CH2) may react with atmospheric nitrogen under fuel-rich conditions to yield fixed nitrogen species such as NH, HCN, HjCN, and CN. These, in turn, can be oxidized to NO in the lean zone of the flame. In most flames, especially those from nitrogen-containing fuels, the prompt mechanism is responsible for only a small fraction of the total NO,. Its control is important only when attempting to reach the lowest possible emissions. 

Human production of fixed nitrogen (NH3) is now estimated to be 140 TG N per year, an amount that is similar to non-anthropogenic sources (NSF 1999 Socolow 1999). The total annual commercial production of ammonia was estimated to result in atmospheric emission of ammonia representing approximately 1-5% of nature s global ammonia emission budget (ApSimon et al. 1987 Buijsman et al. 1987 Crutzen 1983 Galbally 1985 Rosswall 1981). 

Fig. 8. Transient NO emissions at synthetic wastes nitrogen contents of (D), 1% ( ), 3% and (0)> 10%, where the % of O2 is 2ero. Aniline is used as a nitrogen source and toluene is used to keep the total hydrocarbon weight fixed at 35 g (29).

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