flue gas usually contains 2-6% oxygen and a few hundred ppm of NOx, which consists of 90-95% NO and 5-10% NO2. The only viable postcombustion process for NOx emission control is chemical conversion to N2 by a reducing agent. Several gases can be used for this purpose including methane, hydrogen, carbon monoxide, and ammonia. However, because the flue gas contains much more than O2 than NOx, the reducing agent must selectively react with NOx rather than O2 to minimize its consumption (Environment Canada: Task Force Report 1989; Nakatsuji 1991). To date, many commercial installations based on the selective reduction of NOx by NH3 can remove about
80% of NOx in the flue gas. The governing equations for the ammonia-based technology are as follows:
The first two reactions dominate when the flue gas is heated to about 1000°C. Above 1100°C, Equation 5.20(35) becomes significant leading to the unwanted formation of NO. If the temperature is below 800°C, the reaction rate is too low for practical use. Thus, the process
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