Advanced CFD modeling techniques for improved predictions of SNCR performance for NO{sub x} control in utility boilers

Conditions for the selective noncatalytic reduction (SNCR) of NO to N{sub 2} by ammonia in the presence of excess oxygen were first identified by Lyon nearly twenty-five years ago. Since that time, researchers have investigated the effectiveness of other reagents, such as urea and cyanuric acid and effects of process parameters such as temperature, residence time, normalized stoichiometric ratio (NSR), equivalence ratio, initial NOx level, and various additives on SNCR performance. In practical combustion systems, NOx reduction efficiencies are primarily dependent on three factors: (1) mixing, (2) temperature, and (3) residence time. Efficiencies increase when all three act in concert so that the reagent is fully mixed with the flue gas at optimum temperatures over a sufficient time. In practical combustion system, severe design constraints are placed on the reagent injection system that must disperse the reagent throughout the entire combustion product stream while the gases are within the appropriate temperature window. Thus, the design of an SNCR injection system requires an analysis capability that takes into account the nonlinear coupling between these physical processes. In particular, it is critical to (1) couple robust finite-rate SNCR chemistry to the flow field computations, and (2) reduce the time associated with themore » analysis so that the CFD-based analysis remains feasible for design purposes. This paper addresses these 2 issues.« less