FTEK 2007 
FTEK featured
FTEK on cover 
AIR POLLUTION CONTROL NOxOUT CASCADE® (brochure)
The NOxOUT CASCADE® process is a multistage system, employing both urea-based Selective Non-Catalytic Reduction (SNCR) and a compact Selective Catalytic Reduction (SCR) component.
Fuel Tech’s patented NOxOUT CASCADE systems, which are also referred to as SNCR/SCR Hybrid systems, provide the following:
- NOx reduction capability of up to 80% at a fraction of the cost of conventional SCR systems
- Flexibility for staged implementation to achieve current and future compliance, thereby delaying capital costs until required
- Reduced volume of SCR catalyst, resulting in less conversion of sulfur dioxide (SO2) to sulfur trioxide (SO3)
- An SCR catalyst that promotes (at a rate determined by specific site process conditions) the oxidation of elemental mercury to oxidized mercury, which can then be removed by scrubber systems
The NOxOUT CASCADE process integrates a special urea-based, in-furnace SNCR process with a compact back-end catalyst (SCR) module that is much smaller and less capital intensive than full SCR designs. NOx reduction can reach up to 80%, and efficiency of the chemical reagent usage is much improved over conventional SNCR processes.
Central to NOxOUT CASCADE technology is the NOxOUT® SNCR process, which uses targeted in-furnace injection of stabilized urea reagent to react with NOx from the combustion process. At the back-end of the boiler, ammonia produced by an engineered excess of reagent reacts in a compact catalyst module with the remaining NOx for deeper reduction.
A NOxOUT CASCADE system can be installed complete or in stages to let the user keep pace with tightening regulations in the most cost effective way while both minimizing and avoiding capital investment until required.
It is well established that NOx reduction using the NOxOUT process occurs over a temperature range of ~ 1600°F - 2200°F. In a conventional application of the process, the system would be designed to reduce NOx to the target levels and limit the production of ammonia (NH3) to a relatively low range of 2-10 ppmv. On a stand-alone basis, the NOxOUT process is designed to operate on the "Right Side of the Curve," which minimizes NH3 slip. This is especially important for electric utility units where the NH3 can combine with SO3 emissions to form ammonium bisulfate (ABS), which can affect a boiler’s air pre-heater.
If the NOxOUT process is designed with urea injection to take place in the plateau zone (1650°F -1900°F), NOx reduction may be dramatically improved, but NH3 slip will also increase. Fuel Tech can take advantage of this condition by installing a compact SCR catalyst bed in the back-end section that can use this excess NH3 for further NOx reduction. Since the SCR catalyst need only remove a portion of the NOx, it is significantly smaller and less capital intensive than a full SCR system.
The first stages of several NOxOUT CASCADE systems are currently being installed on six 600 MW units in the People’s Republic of China, and a complete NOxOUT CASCADE system is being installed on a 110 MW unit in the northeastern U.S.
The combination of SNCR and SCR technologies can provide a remarkable combination of flexibility and cost-effective design to address the changing needs of industry. Additional technical information on SNCR/SCR Hybrid systems can be found in the Publication Library in the article: Hybridization of Urea-SNCR with SCR - A Fit for the Future and in the Media Center in the article: Hybrid Solutions for NOx Control.