OCR Text |
Show be complete conversion of the fuel nitrogen to NH. species in the first, rich stage, which will, in turn, be converted to N by reacting with some NO in the second, lean stage. The probable reaction sequence (37) is as follows: NH + NO = N + H O (Rl) NH + NO = N + ... (R2) N + NO = N + 0 (R3) * Equal sign denotes reaction reversibility. Presumably, all the volatile fuel nitrogen could react to produce the intermediates in the first stage, which would then be carried over to the lean, second stage, and bring about reactions (R1-R3). The first stage must be oxidant-deficient in order to prevent the oxidation of the species which can lead to NO formation. FORMATION OF NOX The formation of NO during combustion is thought to be primarily via the X three mechanisms (thermal, fuel, and prompt NO ), as mentioned earlier. A complete review of the considerable literature on NO production in flames will not be attempted here. Instead, the relevant reactions proposed by a number of scientists are listed in order to document the variety of probable intermediate species involved. Thermal NO x For premixed systems, a conservative estimate of potential NO levels can be made by considering the equilibrium given by the following reaction: fC -9- |