AECOM's advanced overfire air NOx reduction technology that utilizes higher-pressure secondary air and strategically placed injection nozzles in the upper furnace to achieve deeper staging and greater NOx reductions.

AECOM's advanced overfire air system is able to achieve greater NOx reductions when compared to similar technologies, while the high-energy mixing of fuel and air in the upper furnace effectively controls CO and LOI levels. Better mixing and burnout of the furnace gas constituents means excess oxygen can be lowered, resulting in lower net unit heat rate.

The system is comprised of multiple air injection ports located on the upper furnace walls between the burner zone and the nose of the furnace. The location of the boxes and the orientation of the nozzles are determined using field data and in-house CFD engineering.

Multiple nozzles per box ensure maximum coverage of the flue gas while ensuring system flexibility to account for changing furnace conditions.  Burner air modifications are implemented when required for optimum burner performance during air-staged boiler operation.

The high-momentum air injection results in thorough mixing of the furnace gas.  This allows the furnace to be staged deeper and the furnace excess O2 to be lowered without increasing the potential for waterwall tube wastage.  The system also produces a more uniform temperature profile at the furnace exit that improves steam temperature management by reducing the need for attemperation sprays.

System Performance

AECOM's advanced overfire air system is capable of reducing NOx by between 45 and 65% with CO levels typically controlled to below 50 ppm. Pre-installation LOI is normally not impacted, and has been shown to decrease in most applications.

Recent installations have demonstrated NOx reductions up to 40% when applied to larger furnaces that are already equipped with conventional overfire air systems such as close-coupled overfire air (CCOFA) and separated overfire air (SOFA).

AECOM's innovative overfire air and SNCR technology offerings may be applied in combination with LoTOx to meet current and future NOx emission regulations at a lower overall cost than an SCR.