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Show Precision Flame Shaping and the Effect on Emissions ROBERT L. VOGT Peabody Engineering Corporation Stamford, Connecticut 06906-0331 U S A ABSTRACT Accurate flame fit within the chamber enclosing the heat release zone is essential to reduced emissions. This paper presents generalized relationships between N O x and flame fit, C O and flame fit, N O x and flame temperature, C O and excess air and N O x and excess air. These analytical advancements in flame shaping have been developed for dual fuel applications, and are equally valid for single fuel burners. Many new and retrofit installations where this technology has been applied are benefiting from simultaneously low levels of all regulated pollutants. The precision flame fit analytical methods have now been confirmed repeatedly in validation testing and field operations on single and multi-fuel burners. BACKGROUND This paper considers only turbulent flames. Turbulent flames are neither visually precise shapes nor analytically well behaved. Turbulent flame shapes can be characterized as random geometries which, at best, can be quantified by statistical methods applied to unsteady flickering which is superimposed on continuous motion of entering reactants, formation of intermediates, followed by products approaching equilibrium. The particular flames under consideration are those which emanate from axial flow, low excess air, diffusion limited burners. Both swirl stabilized and bluff body stabilized flames, and combinations of the two have been employed and have benefited from this work. Accuracy in designing the size and shape of flames has long been recognized as desirable but has been elusive. However, the applied engineering sciences have been carefully evolved into a successful, repeatable analytical method for precisely fitting flames inside furnaces of widely varying proportions. These furnaces range from long and narrow, to short and wide Copyright 1997 by the author. All rights reserved. Presented September 23, 1997 at the American Flame Research Committee International Symposium, Chicago, Illinois, USA. including some highly irregular shapes. Many of these installations have been completed with fewer burners required than heretofore possible, due to flame shape accuracy. As the analytical methods have now produced a large number of accurately fitting flames in many furnaces, diagnostic tools have been evolved which greatly facilitate the determination of the cause of undesirable levels of the various controlled pollutants leaving the boilers. It has been repeatedly confirmed that accuracy in flame fitting is essential to minimizing all emissions simultaneously. Accurately fitting flames also provide many other steam generation benefits. Precision flame fit has n o w been validated as a repeatable analytical process. Boiler problems previously related to size and shape of flames in furnaces were only narrowly adjustable for a given burner, and those adjustments compromised other parameters. Problems caused by improperly fitting flames include; boiler rumble, high superheater temperatures, high N O x , high C O , high V O C s , high opacity, tube failures, and increased fouling and maintenance. Historically, many sites have experienced flame fit problems. In one especially noteworthy case, burners which were neither designed nor supplied by Peabody Engineering, created conditions so severe that safe boiler operation was not possible without resolution. The analytical methods being discussed in this paper were entirely successful in eradicating the problem throughout the entire load range. Prior to analytical flame design, some of the most persistent past problem installations remained steadfastly resistant to the usual remedies. Flame fit was one of the most pervasive unsolved problems. Fitting the flame was usually accompanied by increased concentrations of pollutants. As a consequence, some boilers have been in operation for years with flame fits routinely requiring added maintenance or with imposed load limits less than the boiler design rating. Industrial, utility and process burner flames were predicted based on fuel flow, which determined the burner throat diameter, and then adjusted for several smaller effects. Substantial changes in flame lengths and diameters in a given type and size burner have, until now, been difficult to achieve. |