The Application of Zonal™ Combustion Monitoring and Tuning System to Coal Boilers for Efficiency Improvement and Emissions Reduction

Abstract

Coal-fired boilers equipped with Low NO_x Burner (LNB) and Overfire Air (OFA) are challenged with maintaining good combustion conditions. In many cases, the significant increases in carbon monoxide (CO) and unburned carbon levels can be attributed to local poor combustion conditions as a result of poorly controlled fuel-air distribution within the furnace. The Zonal^TM combustion monitoring and tuning system developed by GE is available to detect and correct the furnace air-fuel distribution imbalance. The system monitors the boiler excess oxygen (O₂) and combustible gases, primarily carbon monoxide (CO), by using spatially distributed multipoint sensors located in the boiler’s high temperature upper convective backpass region. At these locations, the furnace flow is still significantly stratified allowing tracing of poor combustion zones to specific burners and OFA ports. Using a model-based tuning system, operators can rapidly respond to poor combustion conditions by redistributing airflows to select burners and OFA ports.

By improving combustion at every point within the furnace, the boiler can operate at reduced excess O₂ and reduced furnace exit gas temperature (FEGT) while also reducing localized hot spots, corrosive gas conditions, slag formation, and carbon-in-ash. Benefits include improving efficiency, reducing NO_X emissions, increasing output and maximizing availability. This chapter presents the results from implementing the Zonal combustion monitoring and tuning system on a 460 MW tangential-fired coal boiler in the Western United States.