Burner Modifications for NOx Control

Burner design influences the amount of NOX formed during the combustion process and low-NOx burners have been used or tested in a variety of boiler and process heating applications. Figure 17-13 is a high-capacity low-NOX burner for gas and oil firing. The fuel elements are housed in a central flame stabilizer to improve flame stability and turndown while separating the fuel elements from the combustion air. Combustion air is regulated by dual air zones with multistage adjustable swirl vanes. Figure 17-14 illustrates a dual-fuel, staged low-NOx burner designed to achieve low-NOX operation without the use of flue gas recirculation. The burner, which may be applied in single or multiple units, features a rugged design with no moving parts and wide stability limits.

Figure 17-15 shows typical NOx emissions rates for natural gas-fired industrial boilers in lbm/MMBtu. Emissions rates are shown for uncontrolled operation with low-NOx burners and with low-NOx burners plus 10% and 20% FGR.

Staged air burners are two-stage combustion burners

Fig. 17-13 Low-NOx Burner for Gas and Oil Firing in Very Large Capacity Boiler. Source: Babcock and Wilcox

that are fired fuel-rich in the primary zone (first stage). They increase flame length, delay completion of combustion, and limit peak flame temperature. The reduced temperature in the primary combustion zone inhibits NOx formation. Staged air burners generally lengthen the flame and they are thus limited to installations large enough to avoid impingement. The installation of replacement burners may require substantial changes in burner hardware, including air registers, air baffles and vanes, fuel injectors, and throat design. Existing burners can incorporate staged air burner features by modifying fuel injection patterns, installing airflow baffles, or re-shaping the

Fig. 17-14 Dual-Fuel, Staged Low-NOx Burner. Source: Coen Company
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