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Show Unt i 1 recent 1 y, the requ ired NOx emi ss ions cou 1 d be reached by controlling thermal NOx formation. However, NOx measurements that Coen has made in industrial boilers indicate that prompt and third body NOx formation mechanisms generally contribute about 15 ppm NOx. As permit levels fall below 40 ppm NOx, prompt and third body NOx become increasingly important. Below 20 ppm, either thermal NOx control must approach 100% effectivity, or prompt and third body nox formation mechanisms must be controlled. Near-100% effect i veness in any des i gn parameter tends to be comp 1 ex and expens i ve, so cu r rent 10w-NOx des i gns need to supp ress all NOx formation mechanisms. Prompt NOx. Prompt NOx was discovered by Fenimore at G.E. labs in 1971. 1 Fenimore believed that prompt NOx was formed by hydrocarbon fragments, specifically by the following reaction: CH + N2 ==~ HCN + N Further experiments indicated that non-hydrocarbon fuels such as CO and H, did not form prompt NOx. The formation of prompt NOx indicated weak temperature dependence and was maximized in rich flames. This was the first explanation of why conventional staged air burners could not achieve maximum theoretical NOx reduction explained by thermal NOx formation theory alone. Other researchers repeated Fenimore's experiment but postulated other theories. The second explanation was the superequilibrium theory proposed by Sarofin and Pohl in 1973. 2 Miller and Bowman3 conducted a rev i ew of NOx format ion k i net i cs and suggested the following formation mechanisms: Extended thermal, including superequilibrium: o + N2 ==~ NO + N N + O2 = = ~ NO + 0 N + OH ==> NO + H Prompt NOx: CH2 + N2 ==~ HCN + NH CH2 + N2 ==~ H2CN + N C + N2 = = ~ CN + N Coen Company cond~cted a literature review of NOx formation mechanism theories. The extensive review concluded: "The Zeldovich mechanism with superequilibrium considerations is sufficient to account for NOx formation at all equivalent ratios for all fuels in areas well downstream of the primary reaction zone. Page 2 |