FIGURE 2. Fuel staging with fluegas inducers involves injecting a portion of the main fuel into the furnace prior to ignition, which serves to dilute the fuel with gases, effectively lowering the flame temperature and inhibiting NOx production FIGURE 3. A typical firetube boiler with fluegas recirculation (FGR) is shown, where the hot recirculated gas stream is diverted before reaching the economizer and combustion systems that can be implemented today, and each one has its own characteristics to reduce NOx and increase efficiency. These methods include the following: * Fuel staging * Fuel staging with fluegas inducers * Fuel- and burner-induced fluegas recirculation (FGR) * High excess air * Two-step combustion (fuel and air injection) * Selective catalytic reduction (SCR) can be added on these technologies to reduce a plant's emissions and NOx Fuel staging Fuel staging injects a portion of the main fuel to mix with combustion gases in the furnace prior to ignition (Figure 2). Thus, it dilutes the fuel with gases, primarily N2 and H2O. Staging the fuel in this manner causes it to ignite off the main flame, and the volume decreases the amount of radiant-heat transfer of the furnace. This radiant-heat transfer helps to cool the flame. Combustion of these two effects reduces the flame temperature, thus lowering the NOx formation. Behind the process, some of the gas injectors on the outer side of the combustion head (or perforated CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM For details visit adlinks.chemengonline.com/82585-12http://adlinks.chemengonline.com/82585-12 http://WWW.CHEMENGONLINE.COM