Computer Simulation of Catalytic Oxidation of Gaseous Ammonia in Bubbling Fluidized Bed

For long, ammonia has been branded as a harmful acid pollutant causing irreversible damage to the environment. Unlike other pollutants like nitrogen oxides (NOx) and sulphur oxides (SOx), ammonia causes acidification to the environment in a more complex and indirect way. The sequence of reactions between ammonia and acidic aerosols followed with microorganisms to form acidic HNO3 has been well documented in the literature.1,2 The sources of ammonia could be traced to various industries, including fertilizer manufacturing industry, coke manufacture, fossil fuel combustion, and biomass gasification. Moreover, ammonia is not only emitted by direct sources (process) but also through indirect means such as control technologies of other pollutants, especially nitrogen oxides (NOx). Selective catalytic reduction (SCR) is one of the main technologies employed for controlling NOx emissions. A significant amount of ammonia is added to the SCR process to convert NOx to nitrogen according to the reaction: NH3 + NO + 1/4 O2 → N2 + 3/2 H2O. However, depending on the extent of the reaction, excess ammonia may exit the process along with the effluent, a condition referred to as “ammonia slip”.3 Subsequently, an ammonia removal or conversion process has to be installed as a downstream operation in addition to the SCR process to curtail ammonia being released as a pollutant.4,5 Selective catalytic oxidation (SCO) of ammonia is a relatively new technology that converts ammonia to nitrogen and water in the presence of catalysts. Besides providing an efficient and stable operation, it can be selectively used to enhance pure nitrogen production from air and ammonia suitable for various applications.6 The following reactions depict the chemistry of SCO of ammonia: