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Show result of the chemical kinetics of the process. At temperatures lower than this window, the reaction requires longer reaction time than is typically available in most commercial combustion systems. Thus, reductions are negligible and ammonia slip is high. At the left side of the curve, NOx reduction increases with increasing temperature; ammonia slips are still significant. Performance at this side of the curve can be generally enhanced by coinjecting urea with oxygenated hydrocarbons such as NOxOUT-35 [10]. At the plateau, reaction rates are optimum for NOx reduction; ammonia slips are decreasing. A temperature variation in this zone has only a small effect on NOx . A further increase in temperature beyond the plateau zone to the right side decreases NOx reduction and also decreases ammonia slips to negligible amounts. The oxidation reactions of urea to NOx become a significant path and compete with NOx reduction reactions for the reagent. At temperatures beyond the right side, NOx increases above the baseline value. Although the reduction is less than the maximum, operation at the right side is practiced and recommended to minimize by-product emissions [11]. The NO), removal efficiency is related to a variable known as Normal~zed stoichiometric Ratio (NSR). The NSR is used as a measure of the rate at which urea is added to the flue gas relative to the amount of baseline NOx ' and is defined as the mole ratio of actual urea to baseline NOx divided by the stoichiometric ratio. For urea the theoretical ratio is 0.5 arising from the chemical " reaction shown previously. The optimization of the NOxOUT Process requires understanding of the physics and chemistry of the process. The chemical reaction between urea and NOx can be described through a mechanism that involves over 90 elementary reactions. The major pathway of the urea breakdown and its reaction with NOx is shown in Figure 3. To understand this network of reactions, a chemical kinetic model that incorporates these reactions is routinely applied to identify the key parameters and process limitations. For these reactions to occur, however, urea must be delivered and mixed with the NOx containing flue gas within the temperature window. This physical process is easily understood and optimized in a laboratory or pilot facility. But, for large utility boilers with swirling flows and overfire air ports, this process is complicated and often limits chemical reaction effectiveness. To overcome this limitation, computational fluid dynamics models are applied on specific units to understand the flow and temperature patterns. The understanding of process chemistry and physics of an application can be accomplished through chemical kinetic and computational fluid dynamics models and is prerequisite for an effective process. NOxOUT Chemical Kinetic Model Process performance is analyzed using a chemical kinetic computer model (CKM). This model describes the reaction between NOx and urea in a post combustion environment and has been verified with |