Roof Fired Boilers

In 1994, CFD modeling was employed by Steag Energy Services (formerly ESA) for Duquesne Light Company's Elrama power station to design an overfire air system for three roof fired boilers. These three units faced state requirements to retrofit separated overfire air, but were offered no vendor supplied retrofits other than an expensive change to tangential firing. Steag Energy Services (formerly ESA) employed CFD modeling to develop a low NOx burner (LNB) and a parallel separated overfire air (P/SOFA)system that met all the state requirements and was a fraction of the cost of the alternatives. CFD modeling was used to examine downstream mixing up the parallel overfire air into the main combustion stream. The modeling was used to compare predicted NOx reduction to CO production as a function of overfire air amount and injection angle. The parallel overfire air system resulted in a joint Steag Energy Services (formerly ESA) and Duquesne Light patent, US Patent No 5,546,874, and has been applied at other plants.

In 1996, the CFD modeling lead to consideration of Elrama 2 as a good candidate for FLGR. The original CFD modeling accomplished as part of the LNB and P/SOFA installations revealed that the system resulted in a region of low O2 but moderately high NOx in the front of the furnace. This situation was promising for application of FLGR. Natural gas injection was modeled from three different injection elevations, to determine how the gas might reduce the NOx. Subsequent testing of the installed system resulted in an NOx reduction greater than 25% using only 3 % natural gas by heat input.

In 2001, Steag Energy Services (formerly ESA) revisited the CFD modeling to design an ammonia based SNCR system for use on the Elrama roof fired boilers. Aqueous ammonia injector locations, as well as spray patterns, were evaluated to determine the components of an optimized system.