During the past two decades, reduction of NOX 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 NOX emissions requirements. Among the available technologies, the installation of some form of low NOX 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 NOX emission requirements, utilities have recently focused on either replacing first or second generation low NOX burners or upgrading existing burners with newer and more advanced low NOX combustion technology. Within this context, the newer burner technology not only decreases
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 NOX 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 NOX 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 NOX 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 NOX 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 NOX 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 NOX combustion.