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Show 4197299444 CORP, HQ 489 P07 MAR 17 '94 12:09 varied from 1410·C (2570·F) to 2260·C (4100'F) by using preheated air from 38'C (100·~) to 570'C (1500·F). The combustibles (sum of CO and H2) in flue gases vary from very close to zero to as high as 25 percent in the rich combustion region. For the excess air combustion region considered in this study, the flame temperature varies from 2100·C to 1370·C (3800'F to 2500'F)" and oxygen content varies from 0 to 7.5 percent. In Figure 3, equilibrium values of NOx content of the combustion products fall in two distinct regions. One region in which NOx levels are significantly lower represents sub-stoichiometric combustion and the second region represents near stoichiometric or excess air combustion of natural gas. For the same reaction or flame temperature, the NOx values vary by three orders of magnitude as the air-fuel ratio for the combustion reaction changes. These apparently large differences in NOx ,\ concentrations at a given reaction , temperature are due to the presence of reducing gases 'in the reaction zone. For example, at a 1760'C (3200·F) reaction temperature, NOx .concentrations vary from 5 ppm at 5:1 air-fuel ratio to concentrations of higher than 2000 ppm for a 12:1 air-fuel ratio. Combustion products of 5:1 air-fuel ratio reaction contain approximately 25 percent combustibles with no residual oxygen while at a 12:1 air-fuel ratio the combustion products contain 4.5 percent oxygen and no \\ significant amount of combustibles. Even in the rich combustion region, NOx varies significantly as the air-fuel ratio increases and the combustibles in the reaction zone decrease. FIGURE 3. NOx FORMATION AT DIFFERENT AIR-FUEL RATIOS • " ••• • e ........ . • . . . ....... . .. , ••••• • , • • •••••• ••• •••• • •• , .. .... ....... . • I • • , . .. • • • • .' .' •• • II •• '.0 ••••• ',' • • • '. I • I , , • t . t • • : f. . •• ,' I • to' •• .' •• '0 ' • ••• • ~ ••• •••• '0 •• ', ' • • • • • • t ...... . , ... '0' • • • ....... , • • _ • •• , •• .. ••••• " ••• " • , ••••••• , , '.' •• , • •• •• ','. '~ '. '.',~. '.', '~','. ',~. '.', ., ., '.~,',', -: '.' :.: .. , .. :. .. , .. '. '.:'.'. '~". ':.:.,.,' '~'''.'. ,':, .;'.', ',~.'.'. ';'.. ... ., ..' ,\ OJ +-...,.----.----,--t--.. ....--,.--.--.,....-t--.--......-......-... --+--..'- -..'- -..'- ...........- -1' .1 2500 3000 S!ao AdllbaUc Fli. TtBplrltur, 'f 4000 ~soo |