Overfire Air Systems

B&W’s dual zone overfire air (OFA) port provides an online means to stage the introduction of air into the combustion process for more effective NOx control. A sliding sleeve damper allows the regulation of air to each port. Cutting the amount of air supplied to the burners causes a fuel rich/oxygen lean zone to develop; NOx is suppressed and reduced as it passes through the fuel rich zone. The overfire air system completes the combustion process.

Our dual zone ports simultaneously provide air across the furnace to mix with combustibles well away from the walls, while also supplying air to mix with combustibles in the proximity of the ports. The heavy-duty design is well suited for extreme conditions of utility boilers. Online adjustability provides the means to fine tune mixing and minimize NOx emissions.

Overfire air has proven to very effective in corner-fired boilers originally designed by Combustion Engineering (CE)/Alstom, and is the dominant method of NOx control with modern systems. We developed our innovative overfire air system for corner-fired boilers using proprietary computational fluid dynamic (CFD) modeling and experience gained from full-scale commercial applications.

B&W’s staged combustion system for corner-fired boilers offers these benefits:

• Proven NOx reduction
• Proven design approach with unit-by-unit customization
• Maintains boiler thermal performance
• Design simplicity for ease of construction and maintenance
• Minimal modifications to structural members, sootblower arrangement and platforms
• Superior mechanical reliability and operation
• Operational flexibility
• Rugged design and fabrication for reduced maintenance