OCR Text |
Show 1 0 % on #6 oil. O n the boiler equipped with the 134 M M B T U / h burner firing natural gas in the -420 °F preheated air, N O x and C O emissions are under 150 p p m and 100 ppm, respectively. In order to achieve further reduction of NOx and CO emissions, especially with natural gas firing, and to provide other improvement of the Vanflame-2 burner performance data, on one hand, and to reduce its manufacturing cost, on the other hand, it is required to perform an additional theoretical and experimental R & D work that would help us to understand better specific features of the combustion processes taking place in the flame formed by this burner. At the 1st stage of this work, a schematic analysis and approximate calculations of the combustion processes, taking place in the natural gas flame formed by the Variflame-2 burner, were performed. Below some results of that work are presented. For schematic analysis of the gas stage combustion processes in the flame formed by the Variflame-2 burner, we can conditionally take into consideration that, at the 1st approximation, the burner consists of two independent working systems and each of them has formed its o w n gas flame (see Fig.l): (1) the first is a comparatively small center flame where a quasi pre-mixed flow of the center gas gun (CFG) jets and the primary swirled air flow, containing a small amount of internal F G R (EFGR), fires as a regular turbulent gas flame; (2) the second one is a heavily stage diffusion flame formed by outside gas injector jets coming into the straight secondary and tertiary air flows, and ignited from the hot combustion products outside of the first flame; it is located at a comparatively long distance from the center flame and divided from it by a mixture of combustion products a n d air. A current level of the combustion processes knowledge does not allow us to perform precise calculations. Performance of approximate calculations and evaluations is available. For such calculations is very important (and sometimes it is critical) to have and to accept all required conditions which would be close to realistic ones. Below there is a list of the conditions, accepted by us for calculations performed for not only both individual flames, but also for the c o m m o n gas flame: (1) there is a stoichiometric fuel/air ratio in the 1st flame; (2) ratios between the swirled primary, straight secondary and straight tertiary air flow rates chosen for these calculations are 15:71:14%; (3) average velocities of the straight secondary and tertiary air flows are equal, their vectors have one and the same direction, and their average temperature at the burner exit is same; (4) both flames are formed and exist independently each other, so no radiation or convective thermal impact on the neighbor flame; 2 |