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Cold flow modeling of SCR systems (Project List »)

SCR process calculation

Full-Scale AIG Tuning and Guarentee Testing
(Project List »)

Designed and operate SCR pilot facilities (Project List »)

Laboratory studies of advanced SCR and hybrid technologies and testing of catalyst activity
(Project List »)



Selective Catalytic Reduction (SCR) systems are used for NOx control in stationary combustion systems utilized for power and process steam generation including gas turbine engine systems.  Over the years, FERCo has performed numerous projects optimizing SCR systems and diagnosing performance issues.  These have covered a range of applications from small (3 MW) natural gas-fired turbines to large (1300 MW) coal-fired utility boilers.

FERCo has developed tools for optimization and diagnostic purposes, including instrumentation and methodologies for 1) tuning the ammonia injection grid (AIG), 2) measuring the NH3/NOx and velocity distribution at the catalyst face, 3) identifying flue gas bypass, and 4) monitoring catalyst activity in situ.  These tools are applicable to SCR systems ranging from gas turbines to coal fired power plants.


One of the most important SCR operating parameters is the NH3/NOx distribution across the catalyst surface.  The impact of NH3/NOx ratio maldistributions on SCR performance is illustrated in Figure 1.  The figure was derived using FERCo’s process model for SCR performance prediction based on a typical SCR system.

Figure 1 shows the importance of the NH3/NOx distribution on performance. For overall NOx reductions of 90% or more, the NH3/NOx distribution becomes extremely important.  The maldistribution is characterized the RMS. If lower NOx reductions are required, a much larger NH3/NOx maldistribution (RMS) can be tolerated. 

The emphasis on achieving uniform NH3/NOx ratios across the catalyst points to the importance of the ammonia injection grid (AIG) as part of the SCR system.  AIGs should be designed with the flexibility to bias ammonia flow in multiple zones across both dimensions of the duct even when static mixers are utilized.  Although ductwork design is optimized to achieve a uniform velocity distribution at the AIG inlet, the actual NOx distribution may not be uniform due to the unit’s boiler and combustion system design and overall operating characteristics. 

FERCo has been actively involved in tuning SCR systems and has developed an approach using instrumentation and techniques that allow the NH3/NOx distribution to be measured by making only NOx measurements at the catalyst exit. 

Please contact us for additional information.

NOx vs NH3 slip
Figure 1. Effect of NH3/NOx Maldistributions on SCR Performance

AIG lances

AIG tuning is one of the key startup activities of an SCR installation

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