Performance Analysis of Industrial Selective Catalytic Reduction (SCR) Systems

Abstract

Selective catalytic reduction (SCR) is an established technology for post-combustion nitrogen oxide (NOx) emissions control from different power/chemical plants. This approach requires a reducing agent such as ammonia to reduce NOx selectively in the presence of excess oxygen and a suitable catalyst. The ammonia is injected into the exhaust gas stream and is mixed with NOx. This mixture of ammonia and NOx passes through the catalyst bed, where a high percentage of NOx reacts on the catalyst surface, with adsorbed ammonia decomposing into diatomic nitrogen and water molecules, thereby reducing the NOx level in the exhaust gas. In this study, a 3-dimensional computational fluid dynamics (CFD) model of a single monolith honeycomb structure of the SCR system is developed to investigate the effect of various important parameters including the NO2/NOx ratio, space velocity, shapes and NH3/NOx ratio for stationary SCR applications. The steady state model was developed by considering the conservation of mass, momentum and energy of reacting gases. The results showed that as the NO2/NOx ratio is increased, the nitrogen dioxide (NO2) reaction with ammonia becomes more pronounced and results in an overall improvement of the NOx reduction in the SCR system.