| OCR Text |
Show INTRODUCTION The mean global concentration of N20 is approximately 300 ppb and has been increasing at a rate of 0.2-0.4% per year (Tirpak, 1987, Weiss, 1981). In the troposphere, N20 is a relatively strong absorber of infrared radiation and, therefore has been implicated as a contributor to the "Greenhouse Effect." Being stable in the troposphere, N20 is transported to the stratosphere where it Is the largest source of stratospheric NO. NO in turn is the primary species responsible for establishing the equilibrium stratospheric 0 3 concentration (Kramlich, et 01, 1988). Direct N20 emissions from fossil fuel combustion have previously been reported to be equivalent to 25-40% of the NOx levels (Hao, et al, 1987, Castaldini, 1983). However, recent tests have shown these measurements to be in error, most of the N20 having been formed as an artifact of the sampling procedure. (Muzio and Kramlich, 1988). Full -scale tests using an on-line N20 analyzer have confirmed that direct emissions of N20 from fossil fuel -fired boilers are low (e.g ., less than 15 ppm). Further, the N20 levels do not in general correlate with the NOx emissions (Muzio, et 01, 1990). While the emissions of N20 from conventional combustion equipment are low, a number of advanced combustion and emission control systems could be responsible for significant N20 emission levels. This paper describes experimental and kinetic modeling studies of selective non-catalytic NOx reduction (SNCR) processes and the potential by-product N20 emissions therefrom. Selective non-catalytic NOx reduction processes Involve the reaction of NO with a nitrogen-based chemical in a temperature region of nominally 10000K to 1350oK. Representative processes in this category of NOx reduction technologies include: • Ammonia (NH3) Injection, (Lyon, 1976) • Urea (NH2CONH2) Injection, (Muzio and Arand, 1976; Mansour, et a!, 1987) • Cyanuric Acid «HNCO)3)/Cyanic Acid Injection, (Perry, 1988) Figure 1 shows the possible major chemical paths leading to the reduction of NOx with these species and possible paths leading to the formation and emission of N20 as a by-product. 2 |
