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Show Introduction The oxi des of nitrogen, commonly referred as NOx ' contribute to smog, ground level ozone formation, and acid rain. The major sources of anthropogenic NOx emissions are stationary and mobile c ombustion of fossil fuel. Titles 1, 3, and 4 of Clean Air Act Amendments of 1990 address the control of NOx emissions from stationary sources to limit ground level ozone and acid rain. Among methods to lower emissions from stationary sources of NOx ' the following techniques are currently viewed as viable and practical: low NOx burners , selective non-catalytic reduction (SNCR) processes, and selective catalytic reduction (SCR) processes. Through air staging and by lowering the peak flame temperature, NOx emission from the combustion zone is less with low NOx burners than conventional burners. SNCR and SCR processes reduce NOx after its formation is completed. SCR process reduces NOx by reaction with NH3 over various metal or ceramic catalyst bed at temperatures between 300 - 500°C [1]. SNCR reduces NOx with NH3 [2,3] or urea [4] without a catalyst at temperatures between 850 - 1100 °C. SNCR processes are also called post combustion NOx reduction processes because the applicable temperature range is located downstream of the burner zone. NOxOUT Process The SNCR of NOx using urea was initially studied and patented by EPRI [5,6]. Currently, Nalco Fuel Tech is the exclusive licensing agent for this technology and markets the technology under the trade name of NOxOUT®. The process includes EPRI' s original patents and improvements made by Nalco Fuel Tech which extend the applicability of the process and allow the process to operate optimally. These improvements include chemicals, injectors, and modelling techniques, and were tested and verified in laboratory and field. The NOxOUT Process treats the products of combustion with an aqueous solution of chemicals. NOxOUT-A, which contains 50% urea, is typically diluted and injected into a unit with air-atomized wall-mounted injectors. A sketch of a NOxOUT system is shown in Figure 1. The overall chemical reaction for reducing NOx with urea is Some trace quantities of ammonia, carbon monoxide, and nitrous oxide can form; controlling the emission of these byproducts is a part of the NOxOUT Technology [7,8,9,10]. A range of temperatures where significant NOx reductions are obtained is called the temperature window as shown in Figure 2. Within this window, the NOx versus temperature curve consists of three zones: left side, right side and plateau. This shape is a |