Condensation gaseous pollutant removal

NOXIOUS GAS REMOVAL. Gaseous pollutants can be removed from air streams either by absorption, adsorption, condensation, or incineration. A list of typical gaseous pollutants that can be treated with these four methods is given in Table 9. Generally, condensation is not utilized as a method for removing a solvent vapor from air or other carrier gas unless the concentration of the solvent in the gas is high and the solvent is worth recovery. Since condensation cannot remove all of the solvent, it can only be used to reduce the solvent concentration in the carrier gas. 

The use of dry adsorbents like activated carbon and molecular sieves has received considerable attention in removing final traces of objectional gaseous pollutants. Adsorption is generally carried out in large, horizontal fixed beds often equipped with blowers, condensers, separators, and controls. A typical installation usually consists of two beds one is onstream while the other is being regenerated. 

Experiments on simultaneous coagulation and growth were made by Husar and Whitby (1973). A 90-m polyethylene bag was filled with laboratory air from which paniculate matter had been removed by filtration. Solar radiation penetrating the bag induced photochemical reactions among gaseous pollutants, probably SO2 and organics, but the chemical composition was not determined. The reactions led to the formation of condensable species and photochemical aerosols. Size distributions were measured in 20-min intervals using an electrical mobility analyzer. The results of one set of experiments for three different time,s are shown in Fig. 11.3. 

The removal of gaseous pollutants from dryer exhaust may be accomplished by several possible processes. Among these are absorption, adsorption, condensation, and incineration [11-16]. The choice of a given process is usually determined by physical and chemical characteristics of the dried product and by economic and environmental considerations. Table 53.3 summarizes some of the basic characteristics of the gaseous emission control equipment. 

The critical temperature of NO is 180 K and NO is a supercritical gas at ambient conditions. Almost all microporous adsorbents cannot sufficiently adsorb supercritical NO, although NO of the representative atmospheric pollutant is desired to be removed with the good adsorbent. A NO molecule has an unpaired electron and gaseous NO shows paramagnetism. It is well- known that NO molecules are dimerized and show diamagnetism at the condensed phase[51]. 

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