Design, Optimization and Economic Analysis of SNCR/SCR Hybrid on a Utility Boiler in the Ozone Transport Region

A full-scale SNCR/SCR Hybrid system, NOxOUT CASCADE, has been designed and installed at the GPU GENCO Seward Station, Unit #15 boiler. The Seward Station hybrid system is a combination of a redesigned existing SNCR with a new downstream SCR. Significant improvements in chemical utilization and overall NOx reduction have been seen in preliminary testing of the SNCR when ammonia slip was permitted to increase above normal operational limits. The integrated system was designed using advanced computational fluid dynamics and cold flow modeling techniques. The units two air pre-heater ducts were retrofit with different types of catalyst, honeycomb in one and plate in the other. Reactor and duct internals were designed to compensate for an existing ash loading imbalance, temperature and velocity variation, and a difference in the SCR pressure drop between the two ducts.