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Show reagent release and the chemical reaction time. In order to maximize the effectiveness of SNCR it is necessary to quantify the local interaction of reagent injection temperature, product thennal quench rate, mixing rates and the impact of trace species such as CO. In this study we have evaluated these effects experimentally in a small pilot scale facility and developed a coupled mixing/reacting model for the SNCR process. Experimental Facility Figure 1 shows the 29 kW, refractory lined combustion research facility at the University of Utah which was used in this study. It is 16 cm diameter and 7.3 m long and is constructed of composite refractory walls to minimize heat loss. The furnace is divided into three sections. In this study the combustion section was frred by natural gas doped with ammonia to control the amount of NO entering the SNCR section. The selective reducing reagent, ammonia, was added through a water cooled stainless steel injector with a simple circular orifice placed on the chamber axis at the entry of the SNCR section. The ammonia was injected with nitrogen and the nitrogen flow was controlled to allow variation of the reagent stream momentum and subsequent reagent/product mixing characteristics. Injection temperature was varied by positioning convective cooling tubes upstream of the SNCR injector and the thennal quench rate was varied by placing water cooled coils along the walls of the SNCR section as shown in Figure 1. Exhaust samples were withdrawn from the exhaust sampling probe through a water cooled, stainless steel probe, then filtered and dried. The gas sample was analyzed for NO (chemiluminescence), 02 (paramagnetic), CO (NDIR) and N20INH3 (FTIR). SNCR Mixing/Reacting Model The computer modellS utilized for the combustion simulations (JASPER) is a steady-state, axisymrnetrical, computational-fluid-dynamics-based code which fully couples the effects of reacting gases with turbulent mixing and radiative heat transfer. In order to couple turbulence and heat transfer with reaction chemistry the number of chemical kinetic steps must be small. JASPER contains a partial equilibrium scheme whereby the local instantaneous chemistry is computed from a set of reduced kinetic steps for slow reactions and a minimization of Gibbs free energy for all other species. Mean values for species concentrations, temperature and density are obtained from computed probability density functions that are consistent with a K-E turbulence model. Although more rigorous turbulence models are available this approach has coupled and balanced all the controlling mechanisms in the SNCR process. The resulting model _. is directly applicable to industrial equipment. Radiation is modeled using the discrete.ordinates method and is also fully coupled with the turbulent fluid mechanics and reaction chemistry. This model can be distinguished from other CFD based SNCR modelsl6,17 in that it fully couples and incorporates the chemistry into the CFD calculation. Ell)))' Detailed Chemical Kinetjc Model The chemical kinetic rates used to model SNCR chemistry were obtained from the literature. The kinetic database of Miller and Bowman 18, with modifications from recent Page 3 |