Energy-Tech Magazine

During the past two decades, reduction of NO_X emissions in pulverized coal firing systems has become a high priority for environmental authorities after the Clean Air Act of 1990 and the Clean Air Interstate Rule (CAIR) were promulgated. The recent replacement of CAIR by the Cross-State Air Pollution Rule (CSAPR) has further tightened NO_X emissions requirements. Among the available technologies, the installation of some form of low NO_X burner technology with or without an overfire air (OFA) system is a primary means – or first step – toward meeting EPA emission requirements and reducing the operating and maintenance cost of post-combustion solutions, such as selective catalytic reduction (SCR). In order to meet the increasingly stringent NO_X emission requirements, utilities have recently focused on either replacing first or second generation low NO_X burners or upgrading existing burners with newer and more advanced low NO_X combustion technology. Within this context, the newer burner technology not only decreases

References Patel, R., VonHein, R., Penterson, C., and Dube, R., “Reducing NOX Emissions to 0.15 lb/MMBtu with Babcock Borsig Power Inc.’s Latest CCV® Coal Burner Technology,” presented at the 26th International Technical Conference on Coal Utilization and Fuel Systems, Clearwater, FL, March 5-8, 2001 Courtemanche, B., Esclavon, L., and Curow, C., J., “CCVÒ Components and Overfire Air Improve Existing First Generation Low NOX Burner Emissions”, Electric Power 2005, Chicago, IL, April 2005 Penterson, C., Dorman, D., “Low NOX Retrofit Problems and Solutions.” Presented at the International Joint Power Generation Conference, Minneapolis, MN, October 1995 Hules, R., K., and Penterson, C., “Computational Fluid Dynamics for Cost-Effective Solutions for Problems in Complex Burner and Combustion Systems”, Power- Gen International 2005, Las Vegas, NV, December 2005 Penterson, C., and Hules, R., K., “Reducing NOX Emissions to Below 0.15 lb/106 Btu on a 600 MW Utility Boiler with Combustion Control Only”, DOE/EPRI/EPA/A&WMA Combined Power Plant Air Pollutant Control “Mega” Symposium, Washington, DC, March 2003 Courtemanche, B., Dorman, D., Yilmaz, A., and Esclavon, L., “ Reducing NOX Emissions and Commissioning Time on Southern Company Coal Fired Boilers with Low NOX Burners and CFD Analysis”, 28th International Technical Conference on Coal Utilization & Fuel Systems, Clearwater, FL, March 2003

NO_X emissions an additional 10-20 percent or more from controlled levels, but also provides greater operating longevity and decreased maintenance.

Since the early 1980s, Riley Power Inc. (RPI), a subsidiary of Babcock Power Inc., has been developing the Venturi Series Burner technology to lower NOX emissions from pulverized coal firing systems. This advanced controlled combustion technology is capable of achieving significant NOX reductions in various types of applications, including full burner installation or component only retrofit. The component only retrofit is often preferred by utility customers due to its cost effectiveness, because it involves fewer hardware modifications and easier, less time consuming installation. RPI determined that retrofitting existing original equipment manufacturer (OEM) low NO_X burners with RPI’s Venturi Series Burner components would significantly enhance combustion system burner performance. To date, RPI has completed 14 components only retrofit projects totaling nearly 320 burners.

RPI has implemented components type upgrades to 1st and 2nd generation RPI burners, as well as B&W DRB and XCL Burners. In all cases, CFD modeling was performed to refine the final burner design and shorten the commissioning time by identifying the initial startup settings of the equipment.

Field-testing the installed equipment showed that the modeling accurately represented the field results.

In the past two years, RPI has performed CFD modeling of the same component retrofit methodology applied to other OEM’s low NO_X burners where the components haven’t yet been applied in a retrofit situation. The modeling results show that similar improved burner performance can be achieved on other low NOX burner designs, by applying the same basic RPI components. The CFD results of the B&W XCL Burner, FW PF/SF Burner and the FW IFS burner are discussed.

Component-only retrofit methodology overview
Many pulverized coal wall-fired utility boilers are equipped with 1st or 2nd generation low NO_X coal burners. These burners typically comprise a nozzle that fires a mixture of pulverized coal and air surrounded by two concentric, cylindrically shaped barrels known as secondary (inner) and tertiary (outer) air barrels. The secondary and tertiary air barrels are oriented axial to the coal nozzle.

These designs typically have an adjustable damper that controls the airflow into the secondary and tertiary air barrels, as well as axial or radial vanes in the tertiary air (TA) and possibly the secondary air (SA) annuli, in order to create a swirling motion of the air exiting the burner. This common type of low NO_X burner is generally referred to as a dual air zone burner, double register burner, swirl induced burner, or some combination thereof. Dual air zone burners were designed for their low NO_X capabilities, specifically the ability to stage the combustion process by gradually mixing the combustion air with the coal. The gradual mixing of air and coal reduces the peak flame temperature and creates a more oxygen starved environment, as compared to traditional burner designs, two critical mechanisms for low NO_X combustion.