There are differences in the proces

There are differences in the process chemistry between SNCR chemicals. The chemistry involved in SNCR processes is becoming moderately well understood and can be generalized by two overall paths dictated by whether the SNCR chemical decomposes to NH2 or HNCO, as shown in Figure 2. For ammonia (NH3), the primary decomposition product is NH2. NOx reduction then occurs by a reaction between NO and NH2, forming N2 and H2O. Cyanuric acid (HNCO)3 initially decomposes to isocyanic or cyanic acid (HNCO), in which case NCO is a major intermediate. The NCO can then react with NO to form N2O and CO. Depending on the temperature, the N2O will decompose to N2 or be emitted as a byproduct. Urea (NH2CO/OH2) is thought to be a hybrid between ammonia and cyanuric acid [5] with decomposition yielding NH3 and HNCO. With NH3 less than 5% of the NOx reduced appears as N2O, with urea on the order of 15% of the NOx reduced is emitted as N2O. With cyanuric acid, N2O emissions can approach 40% of the NOx reduced. This is of potential concern as N2O is both a greenhouse gas and participates in stratospheric ozone chemistry. However, Muzio et al. [6] estimated that if all of the fossil fuel burned in the United States electric utility industry used SNCR, the N2O emissions would be less than 2% of the estimated annual atmospheric production of N2O.