Staged air

Another type of staged combustion approach involves introducing the air rather than the fuel in two stages. In the first stage a fuel-rich fuel/air mixture is reacted 

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First-stage Second—stage Air treatment Oxidation... 

FIG. 12-94 Two -stage air-stream and cage miU, pneumatic-conveyor dryer. (ABB Raymond. )... 

Figure 2-1. Two-water cooled intercoolers on a three-stage air compressor. Ck)urtesy of Elliott Company)...

Oxygen-Nitrogen Because of higher solubility, in many polymers, O2 is faster than N2 by a factor of 5. Water is much faster still. Since simple industrial single-stage air compressors provide sufficient pressure to drive an air-separating membrane, moderate purity N2 (95-99.5%) may be produced in low to moderate quantities quite... 

Alternative 2 consists of preliminary treatment followed by dual-media pressure filtration, and two-stage air stripping (Figure 8.4). The preliminary treatment step for iron removal would be exactly the same as specified under Alternative 1. The filters would be recommended to remove suspended matter and particulate iron prior to the air strippers. The required filtration capacity could be provided with either a duplex system of two 60-in.-diameter filters or a triplex system of three 42-in-diameter filters. 

FIGURE 8.4 Preliminary treatment, filtration, and two-stage air stripping (Alternative 2). 

Flue gas recirculation Flue gas recirculation, alone or in combination with other modifications, can significantly reduce thermal NO,. Recirculated flue gas is a diluent that reduces flame temperatures. External and internal recirculation paths have been applied internal recirculation can be accomplished by jet entrainment using either combustion air or fuel jet energy external recirculation requires a fan or a jet pump (driven by the combustion air). When combined with staged-air or staged-fuel methods, NO emissions from gas-fired burners can be reduced by 50 to 90 percent. In some applications, external flue-gas recirculation can decrease thermal efficiency. Condensation in the recirculation loop can cause operating problems and increase maintenance requirements. 

NO-Char reaction system. Therefore an excess in hydrogen is expected to play an important role in NOx reduction if the fluidized bed combustor is operated under staged air firing. 

A typical CFB boiler, shown in Fig. 6, operates with a two-stage air supply. Primary air supplied through a distributor is substoichiometric, and combustion is completed with secondary air in the upper portions of the boiler. Staging of combustion brings several benefits. Combustion is... 

First-stage Second-stage Air treatment Oxidation Off-gas Acetaldehyde Methyl acetate Acetic acid Glacial acetic Ethyl acetate... 

Figure 19 SEM images of purified SWNTs. (A) Laser-grown SWNTs subjected to two stage air oxidative purification (scale bar 1 im) (a) before purification and (b) after purification. (Reprinted with permission from Ref 100. 2001 American Chemical Society.) (B) Raw HiPco SWNTs subjected to three stage wet-air oxidation (scale bar 500 nm) (a) before purification and (b) after purification. (Reprinted with permission from Ref. 109. 2001 American Chemical Society)...

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