Config

 

Inputs for configuring the In-Furnace NOx Control technology are entered on the Config parameter screen. The following parameters are provided:

•In-Furnace Controls: This pull-down menu chooses what type of in-furnace NOx controls are used. These technologies reduce NOx between the primary fuel injection into the furnace and the economizer. These can be used in addition to the SCR:

•LNB: (This is the default.) Low NOx burners are a combustion NOx control. These burners replace the upper coal nozzle of the standard two-nozzle cell burner with a secondary air port. The lower burner coal nozzle is enlarged to the same fuel input capacity as the two standard coal nozzles. The LNB operates on the principle of staged combustion to reduce NOx emissions. Approximately 70% of the total air (primary, secondary, and excess air) is supplied through or around the coal-feed nozzle. The remainder of the air is directed to the upper port of each cell to complete the combustion process. The fuel-bound nitrogen compounds are converted to nitrogen gas, and the reduced flame temperature minimizes the formation of thermal NOx. The net effect of this technology is greater than 50% reduction in NOx formation with no boiler pressure part changes and no impact on boiler operation or performance.

•LNB & OFA: Low NOx burners (see above) with overfire air is another combustion NOx reduction method. Overfire air is an enhancement to LNB to reduce NOx formation by further separating the air injection locations. An addition of approximately 10% NOx is reduced by the addition of OFA. A portion of the secondary air used by LNB is diverted to injection ports located above the primary combustion zone, reducing available oxygen in the primary combustion zone. Overfire air in the IECM refers to separated OFA for both wall and tangential-fired boilers.

•Gas Reburn: Gas reburn is a post-combustion NOx reduction method. Gas reburn substitutes up to one-fourth of the heat input of coal with natural gas, reducing the NOx up to 60% as a function of the amount of reburn. The natural gas is injected above the primary combustion zone to create a reducing zone. Reburn has been shown to be effective for wall and tangential-fired boilers and more recently for cyclone boilers.

•SNCR: Selective non-catalytic reduction is a post-combustion NOx reduction method. This process removes NOx from flue gas by injecting one of two nitrogen-based reagents, ammonia or urea, in the presence of oxygen to form nitrogen and water vapor. Optimum removal is achieved in a temperature window of 1600-2000 F. Although the technology is very simple, the narrow temperature window provides the primary challenge. Ammonia slip and ash contamination are additional concerns that must be considered with SNCR.

•LNB & SNCR: Low NOx burners can be used in conjunction with SNCR to achieve very high NOx removals. Both technologies are described in detail above.

•SNCR Reagent Type: This parameter is only displayed when SNCR or LNB & SNCR have been selected in the In-Furnace Controls pull-down menu. Nitrogen-based reagent injection is used in an SNCR to reduce NOx in the presence of oxygen to form nitrogen and water vapor. The reagent choices are:

•Urea: (This is the default.) Urea (CO(NH2)2) is typically diluted to a 15-20% concentration with water. Urea has the advantage of safety and ease of storage and handling.

•Ammonia: Ammonia can be supplied in two forms: anhydrous (NH3) and aqueous (NH4OH). The IECM considers only anhydrous ammonia. Ammonia may be an advantage when using an SNCR in conjunction with an SCR system.

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