Primary combustion zone

This system is called wet NO control. Water or steam is injected into the primary combustion zone. This method has been used ef fectively in the past. Current installations are using this system when the water or steam is readily available or if they are already part of the process. Maintenance costs are higher when compared with dry control, because this method requires high quality water. If high quality water is not used, the corrosion associated with dissolved minerals in the water may prematurely damage the turbine. 

Reburning is a process involving staged addition of fuel into two combustion zones. Coal is fired under normal conditions in the primary combustion zone and additional fuel, often gas, is added in a reburn zone, resulting in a fuel rich, oxygen deficient condition that converts the NO, produced in the primai y combustion zone to molecular nitrogen and water. In a burnout zone above the reburn zone, OFA is added to complete combustion. 

Primary air flow, supplied at the bottom of the bed, is insufficient for complete combustion of the fuel. The zone below the elevation of secondary-air jets is endothermic, cracking oil to yield carbon and fuel gas species. These burned in the upper, exothermic zone. Alumina product is withdrawn from a standpipe receiving solid from the upper zone, and burn-off of carbon in this zone is sufficient to yield a product that is acceptably white. Fluidizing-gas velocity being lower in the primary combustion zone than in the secondary, density is higher. Provision of the two zones accomplishes two purposes (1) affording a sufficient solid residence time in the primary zone and (2) reducing horsepower needed for air compression. 

The primary thermal conversion chamber comprises 1) a stoker 2) a pre-drying zone to remove fuel water, 3) a primary combustion zone to produce the required energy for the pyrolysis/gasification process, and 4) a pyrolysis and gasification zone to convert solid fuel into gaseous ones. 

The reduction of fuel-N to molecular nitrogen in air staging is favored in the fuel rich primary combustion zone ( Fig. 3 ). Investigations on fixed bed wood furnaces have shown that a minimum of the Total Fixed Nitrogen (TFN = HCN+NH3+NO+ NO2+2N2O emission from the primary combustion zone is reached for a stoichiometric ratio of 0.7 to 0.8 and a temperature of 1100 C to 1200 °C and providing a mean residence time of 0.5 s. After the reduction zone the combustion is completed in the burnout zone by injection of the excess air. 

When a nebulized sample is carried into a flame, desolvation of the droplets occurs in the primary combustion zone, which is located just above the tip of the burner, as shown in Figure 28-12. The resulting finely divided solid particles are carried to a region in the center of the flame called the inner cone. Here, in this hottest part of the flame, the particles are vaporized and converted to gaseous atoms, elementary ions, and molecular species (see Figure 28-6). Excitation of atomic emission spectia also takes place in this region. Finally, the atoms, molecules, and ions... 

In this technology, the burners in the primary combustion zone are worked with low excess air. Up to 30% of the total fuel heat input is given above the main combustion zone to create a fuel-rich zone during combustion. Rebuming of coal takes relatively longer residence time, approximately 50% of NOx reduction can be achieved. 

Temperature Profiles. Figure 9 3 shows a temperature profile of a typical flame for atomic spectroscopy. The maximum temperature is located in the flame about 2.. i cm above the primary combustion zone, it is important — particularly tor emission methods (Section lOC-I)—to focus the same part of the llanie on the entrance slit for all calibrations and analytical measurements. 

As shown in Figure 9-2. important regions of a flame include the primary combustion zone, the interzonal region, and the secondary combustion zone. The appearance and relative size of these regions vary considerably with the fuel-to-oxidant ratio as well as with the type of fuel and oxidant. The primary combustion zone in a hydrocarbon flame is recognizable by its blue luminescence arising from the band emission of C-, CH, and other radicals. Thermal equilibrium is usually not achieved in this region, and it is, therefore, rarely used for flame spectroscopy. 

A large range of stable combustion stoichiometries is obtained with MgB2/PTFE (40-95 wt%). The burn rate peaks at 75wt% and is a little slower than that with Mg2Si (Figure 8.25). Again it does not correlate with the calculated flame temperature of the primary combustion zone [28]. 

Off-stoichiometric conditions are achieved by modifying the primary combustion zone stoichiometry, i.e., the air/fuel ratio. Burners Out of Service (BOOS), which is an operational... 

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