Air flow reduction

Process flow reduction should be targeted and must be in such a way that it will not impact upon the operation of the process or plant. The normal first response by a plant engineer is that air flow reduction cannot be done. However, subsequent investigation has resulted in that most of the time flow reduction can be done. This should be a significant area to focus on when conducting a pollution prevention audit. 

Figure 33.1 Effect of air flow reduction, (a) Clean filters.

Reduction in energy consumption as a result of improved usage patterns and reduced air flow rates... 

A feature of this cycle is the reduction in compressor air flow for the same size of main expansion turbine. The figure shows air for the PO turbine taken from the discharge of the main compres.sor, but it may be taken straight from atmosphere. Note also that steam is raised for injection into the PO reactor and Newby et al. suggested that some of the steam raised in the HRSG may also be used to cool the PO turbine. The chemical reactions for the PO reactor of this case were described in Section 8.5.3. 

Fig. 2.1. Reduction of carbohydrate in an aeration tank at various air flow rates.

The pressures on the sides and roof of the structure build up to the incident overpressure as the blast wave traverses the structure. Traveling behind the blast wave front there is a short period of low pressure caused by a vortex formed at the front edge during the diffraction process (Figures A. 8c and A. 9c). After the vortex has passed, the pressure returns essentially to that in the incident blast wave. The air flow causes some reduction in the loading to the sides and roof, because the drag pressure has a negative value for these surfaces. 

We are not entirely finished with the furnace. There is one more piece missing from the whole picture—the air flow rate. We need to ensure sufficient air flow for efficient combustion. The regulation of air flow is particularly important in the reduction of air pollutant emission. 

The ZSM-5 zeolite had a SAR (silica-to-alumina ratio) value of 38 and were supplied by CENPES/PETROBRAS. These samples, as received, were submitted to two ion exchange processes with ammonium chloride solution at 323K for sodium content reduction, followed by calcinations at 773K under dry air flow for transformation to its acid form. 

Velocity seals are more recent developments in air seal design. They use conical baffles to redirect and focus the purge gas flow field just below the flare tip to sweep air from the flare stack. Some velocity seal designs can reduce the purge gas flow rate requirement to about 1/10 of the rate needed without the seal. Also, some velocity seal designs reportedly require only about 25 to 33 percent of the purge gas used in diffusion seals (AICliE-CCPS, 1998). More details about air (purge reduction) seals may be found in API RP 521 (2007). 

Many of the conservation measures require detailed process analysis plus optimization. For example, the efficient firing of fuel (category 1) is extremely important in all applications. For any rate of fuel combustion, a theoretical quantity of air (for complete combustion to carbon dioxide and water vapor) exists under which the most efficient combustion occurs. Reduction of the amount of air available leads to incomplete combustion and a rapid decrease in efficiency. In addition, carbon particles may be formed that can lead to accelerated fouling of heater tube surfaces. To allow for small variations in fuel composition and flow rate and in the air flow rates that inevitably occur in industrial practice, it is usually desirable to aim for operation with a small amount of excess air, say 5 to 10 percent, above the theoretical amount for complete combustion. Too much excess air, however, leads to increased sensible heat losses through the stack gas. 

Other devices which find varying degrees of success in the treatment of thixotropic materials include rotary beaters and pulsating valves to interrupt the air flow in the drying zone. Both of these result in movement of the cake, giving a reduction in moisture content. 

Ducts are used to transport the exhaust air and its contaminants to the collection area. An important feature of duct design is reduction of resistance to air flow from friction within the wall, aggravated by unnecessary curves and bends (particularly right-angled bends), as well as junctions with other ducts at sharp angles, collections of dust, and changes in duct diameter. 

There has been an accelerated interest in polymer electrolyte fuel cells within the last few years, which has led to improvements in both cost and performance. Development has reached the point where motive power applications appear achievable at an acceptable cost for commercial markets. Noticeable accomplishments in the technology, which have been published, have been made at Ballard Power Systems. PEFC operation at ambient pressure has been validated for over 25,000 hours with a six-cell stack without forced air flow, humidification, or active cooling (17). Complete fuel cell systems have been demonstrated for a number of transportation applications including public transit buses and passenger automobiles. Recent development has focused on cost reduction and high volume manufacture for the catalyst, membranes, and bipolar plates. 

One further degradation mode related to catalysis is a consequence of operating at low current densities typical of portable power application. Under these conditions, overoxidation of the Pt cathode catalyst occurs, reducing cathode and overall MEA performance. Zelenay has shown that starving the cathode of air flow lowers the cathode potential to low values, causing reduction of Pt oxides and restoring cathode activity. ... 

The underwater sensor platform is derived from the Fido explosives vapor sensor, originally developed under the Defense Advanced Research Projects Agency (DARPA) Dog s Nose Program. The vapor sensor, whose operation is discussed in Chapters 7 and 9 and in other publications [7-9], was developed for the task of landmine detection. The underwater adaptation of the sensor is very similar to the vapor sensor. In the underwater implementation of the sensor, thin films of polymers are deposited onto glass or sapphire substrates. The emission intensity of these films is monitored as water (rather than air) flows past the substrate. If the concentration of TNT in the water beings to rise, the polymer will exhibit a measurable reduction in fluorescence intensity. The reduction in emission intensity is proportional to the concentration of target analyte in the water. Because the sensor is small, lightweight, and consumes little power, it proved to be ideal for deployment on autonomous platforms. 

To determine the fate of formaldehyde and formic acid in a coal mine, an unused shaft about 120 m long and 6 m2 in cross sectional area was selected for study. With a ventilation air flow of 190 m3/min and an engine exhaust flow of 1.5 m3/min, complete exhaust dispersion and dilution was observed in about 10 m. Samples collected in the mine air downstream of the diesel engine indicate no significant change in formic acid concentration at increasing distances from the engine (Table VIII). This is certainly not consistent with the loss of formaldehyde in the same interval. The mechanism for loss of formaldehyde is apparently not a gas phase oxidation to formic acid. Interaction with surfaces may be a more suitable explanation of the observed reduction in formaldehyde concentrations. 

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