Experimental and kinetic studies on the effect of sulfur-nitrogen interactions on no formation in flames

The participation of fuel-sulfur (fuel-S) in the NO formation/destruction processes occurring in fossil fuel flames has been featured sparingly in the literature, although several studies were performed some years ago. This paper is concerned with the effects of fuel-S on NO formation and destruction processes in liquid-fuel, spray flames. Experimental in-flame measurements of NO, ammonia, and cyanide in a 150-kW test furnace are presented and discussed with the benefit of a kinetic study. Fuel-nitrogen (fuel-N) and fuel-S were simulated using quinoline and tetrahydrothiophene, respectively. The exit gas NO emissions were found to be affected by the addition of S to the fuel to an extent that was dependent on the fuel-S to fuel-N ratio and burner operating conditions. When the burner was operated in low-NO x mode by staging the combustion air, the interactions were found to be dependent on the primary-zone fuel/air equivalence ratios, with greater enhancement of fuel-NO formation observed for fuel-rich conditions. Thermal-NO emissions were reduced with S addition for fuel-lean operation of the primary stage but were relatively unaffected when operating fuel-rich. Comparative studies using SO 2 as the S additive produced similar results, but the magnitude of the changes in the NO emission were less than those found using tetrahydrothiophene. In-flame measurements of the concentration of NO x precursors, ammonia and cyanide, showed that where increases in fuel-NO were observed due to the effect of S, corresponding reductions in ammonia and cyanide were measured, particularly under fuel-rich conditions. Data obtained from the experimental furnace have been adapted for use with a detailed chemical mechanism with the CHEMKIN and the KINALC software packages. This has allowed the nature of the interactions between the sulfur chemistry and the hydrocarbon and nitrogen chemistry that influence NO formation to be investigated.

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