Step Two
- 2. Step Two (SCR)
- To further increase NOx reduction, selective catalytic reduction technology must be employed. Supplemental ammonia is injected into the flue gas upstream of a catalyst. On the catalyst, NOx and NH3 react when temperatures are 550o to 750oF (300 to 450oC) to form nitrogen and water vapor. Removal efficiencies exceeding 90% can be achieved in retrofit applications where there is sufficient space to expand the duct, SCR systems are commonly used as a post-combustion NOx reduction technology.
- Their advantages include the lack of chemical by-products, and no need to inject solid adsorbents. Conventional stand-alone SCR systems, however, are large-sized, relatively expensive to install, and usually require extensive ductwork to a separate vessel outside of the boiler structure.
- The Wahlco SNRS employs an in-duct catalyst for SCR. This catalyst uses much less space than traditional installation methods; no large separate housing is needed.
- The Wahlco SNRS employs an in-duct catalyst for SCR. This catalyst uses much less space than traditional installation methods; no large separate housing is needed.
