Fuel Staging

NO Emission Control It is preferable to minimize NO formation through control of the mixing, combustion, and heat-transfer processes rather than through postcombustion techniques such as selective catalytic reduction. Four techniques for doing so, illustrated in Fig. 27-15, are air staging, fuel staging, flue-gas recirculation, and lean premixing. 

Fuel-Staged Burners Use of fuel-staged burners is the preferred combustion approach for NO control because gaseous fuels typically contain little or no fixed nitrogen. Figure 27-36 illustrates a fuel-staged natural draft refineiy process heater burner. The fuel is spht into primaiy (30 to 40 percent) and secondary (60 to 70 percent) streams. Furnace gas may be internally recirciJated by the primaiy... 

FIG. 27-36 Low-NOj fuel-staged burner for a natural draft refinery process beater. (Callidus Technologies, Inc. )... 

P.G. Kristensen, P. Glarborg, and K. Dam-Johansen. Nitrogen Chemistry during Burnout in Fuel-Staged Combustion. Combust. Flame, 107 211-222,1996. 

When the outlet is non-reflecting, the flame is stable. The mean axial velocity and fuel mass fraction fields are displayed in Fig. 9.15 and 9.16 [320] the central recirculation zone (marked by a white line in Fig. 9.15) is filled by burnt gases which provide flame stabilization. Fuel staging is also apparent in Fig. 9.16. 

The conversion of fuel nitrogen to NO, presents a problem when biomass or waste with a high nitrogen content is used as a fuel. This is a common problem for both conventional boiler plants and IGCC plants, In boilers, NO, reduction can be achieved by primary measures, eg, fuel staging or by selective non catalytic NO, reduction (SNCR) with ammonia injection in the boiler, or selective catalytic NO, reduction (SCR) with ammonia injected in the flue gas duct after the boiler. 

Nussbaumer, Th., Salzinann, R. (1996) Primary measures for NOx reduction in wood combustion by air staging and fuel staging. 1" European Conference on Small Burner Technology and Heating Equipment, Zuerich (CH), September 25-26 1996, pp. 165-174. 

Fuel staging for NOx reduction in automatic wood furnaces... 

Further improvement of the rebuming in power plants lead to the advanced reburning technologies were fuel staging is combined with other NO, reduction technologies". 

Besides the ash removal, the operation of the research facility is completely automatised and controlled by a PLC. The first fuel stage is equipped with an oxygen control to keep the oxygen content within a narrow range (SR = 1.1 to 1.3), For fuel staging, it is essential that the stoichiometric ratio of the first stage is well controlled to enable understoichiometric conditions in the reduction zone with little reburn fuel... 

A summary of the experimental results for fuel staging with different fuel combinations is presented in Fig. 9 The measured NO, emissions are plotted as a function of the temperature in the reburn zone for different reburn fuel rates. The CO emissions of the evaluated measurements were always below 500 mg/Nm at 11 % O2, usually below 250 mg/Nm ... 

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