OCR Text |
Show For a gaseous hydrocarbon fuel containing no fuel nitrogen, the Zeldovich mechanism along with its modifying assumptions is the primary source of N O formation. Reactions of the extended Zeldovich mechanism H + N O = N + O H and N + N O = 0 + N 2 are the major N O removal reactions at high temperature. However, fuels which contain appreciable inherent nitrogen demonstrate greatly increased N O formation. In the past, the only demand on Natural Gas (NG) combustion was to reach a high carbon conversion efficiency. However, environmental considerations require combustion modifications for pollutant emission abatement. Martin et al (1971) [1] noted that the introduction of nitrogen-containing additives in hydrocarbon/air flames increased NO emissions through approximately 5 0 % conversion of the nitrogen in the additive to NO. Pershing and Wendt ( 1977 ) [2] completed an experimental study of thermal and fuel N O formation in self-sustaining pulverized coal flames and found that at typical temperatures of pulverized coal firing , fuel nitrogen oxidation was the primary source of N O emissions. Fuel nitrogen oxidation was found to be relatively insensitive to temperature expected at very high flame temperatures. Pershing, Martin and Berkau (1972) [3] suggested that in oil containing significant amounts of fuel nitrogen, fuel nitrogen oxidation may be of primary importance.Chen and coworkers [4,5] completed a series of tests in a 70,000 Btu/hr tunnel furnace for a variety of coals and showed that over 8 0 % of the total emission is the result of oxidation of fuel-bound nitrogen. And, both combustion parameters and coal type can influence the formation of fuel NO; however, under no condition did these investigators find fuel N O to contribute less than 5 0 % of the total emission. Takagi et at (1979) [6] suggested that NOx formation from fuel nitrogen (NH3) in staged combustion is investigated paying attention to NO, HCN, and N H 3 formation in the fuel-rich first-stage combustion and the conversion of residual H CN and N H 3 into N O in the second stage combustion. Heberling and Boyd (1981) [7] observed the yield of N O from fuel-N in overventilated laminar diffusion flames in air decrease sharply when the pressure increase at constant mass flow and inlet temperature. Hao et al (1987) [8] noted that most of the N O x and N 2 0 arose from oxidation of fuel nitrogen with highest concentration observed in coal flames and levels in the natural gas flame. Martin and Brown (1990) [9] presented a modling study of N2O chemistry in lean, premixed .atmospheric-pressure combustion. Hampartsoumian et al (1991) [10] found that staging the combustion air by up to 4 0 % achieved a 4 5 % reduction in N O emission from air oil spray flame using a pressure-jet burner. Goyal et al (1992) [11] show that the flame speed is extremely sensible to the rate constant if the reaction H + N O = N + O H in the premixed H2-NO flames. 2 111-17 |