| OCR Text |
Show burner diameters from the burner exit, where ICP burning out degree is increased from 85.7 to 91.4 %. As it was investigated before, a such leap takes place in the turbulent flames, formed at firing natural gas with ambient air, usually under the one dictating condition: incomplete combustion products have to be burned out of 80-85 to 90-92 %. If it would be less than - 80 %, the flame temperature will not provide a corresponding rate of N O generating. If it would be sufficiently more than ~ 92 %, concentrations of the radicals and atoms, mostly formed in the flame beginning, and participating in the well-known chain reactions of N O formation, will be so small that they cannot provide actual N O generation during short-time activities of these reactions. 3. During residence in the above described -2960 °F zone for ~0.05s, N O concentration is growing from -19 to -89 ppm, so the average N O generation rate is of - 1,400 ppm/s. This N O generation rate is comparable to such rates in the utility high temperature furnaces where natural gas is firing in the preheated air but under much less excess O2. A comparison of that rate with the average N O generation rate in the described furnace (93 ppm/0.49 s - 190 ppm/s) has shown that the rate in the high temperature zone is of - 3.9 times more. 4. The stage gas injector no-FGR flame temperature is under 2,700 °F (> 300°F less than the C F G flame Tmax), that is why a calculated current N O concentration, formed in this flame, is only -20 ppm (Fig.4). There is a comparatively equal N O generation rate during residence in the cold flame, the average rate is - 40 ppm/s, or - 4.5 times less than the average N O generation rate in the furnace. 5. The combustion processes, taking place in the cold flame, are began later and proceeded much slowly, that is why actual ICP burning out completion of 9 9 % and 99.9% takes place sufficiently later than in the C F G flame - at a relative distance from the burner exit of -3.4 (against <2.5 in the C F G flame) and -4.7 (against -3.7 in the C F G flame) burner diameters, respectively (Fig.5). However it is acceptable enough, because practically full burning out is achieved at a comparatively low excess O2 (<3%, Fig.5). 6. Accordingly, it is provided a required fuel gas burning out in the furnace having not only the zones filled with flame but some so-called "the dead zones" (usually located in the furnace comers, their relative volume is not exceed 1 0 % of the furnace volume) as well. Fig.6 has shown that 9 9 % and 99.9% burning out is achieved at -5.2 and - 6.7 burner diameters from the burner exit, respectively. 7. Fig.6 has also shown the N O curve for no - IFGR common flame, that has a comparatively smooth character because it is an intermediate curve between the two N O curves shown in the Fig. 2 and 4. Uncorrected N O concentration does not exceed 32 p p m (for comparison, N O > 90 p p m in the F G R flame and - 20 p p m in the injector flame). A sufficient portion of this N O is formed in the high temperature C F G flame (12 of 32 ppm) and it can be sharply reduced by implementation of various combustion methods including EFGR and external F G R which are capable to provide N O reduction up to - 75 to 80%. Unlike it, an opportunity to reduce N O in the cold injector flame is insignificant (as per the known literature data, it is possible to reduce it here of 15 to 25%). 4 |
