Absorption gaseous pollutant removal

Solvent selection for use in an absorption column for gaseous pollutant removal should be based upon the following criteria ... 

The removal of one or more components from a gas mixture by absorption is probably the most important and familiar operation in the control of gaseous pollutant emissions. Though most often used for the control of inorganic gases, absorption can also be used for recovery of organic compounds. Absorption in-... 

One way to control gaseous pollutants like SO2 and SO3 is to remove the gases from fuel exhaust systems by absorption into a liquid solution or by adsorption onto a solid material. Absorption involves dissolving the gas in a liquid while adsorption is a surface phenomenon. In each case, a subsequent chemical reaction can occur to further trap the pollutant. Lime and limestone are two solid materials that effectively attract sulfur dioxide gas to their surfaces. The ensuing chemical reaction converts the gaseous pollutant to a solid nontoxic substance that can be collected and disposed or used in another industry. 

On the other hand, gaseous pollutant control can be carried out by contacting the gaseous stream with a component (either solid, liquid, or gaseous) that is capable of selectively removing one or more pollutants. One of the most common techniques used for the removal of gaseous pollutants is absorption, mainly for removal of... 

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 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. 

Due to its high vapor pressure at the operating temperature of the electrolysis, mercury, whose circulating tonnage represents 700 to 2400 kg/t per day of chlorine production capacity, pollutes the different gaseous streams produced (chlorine, hydrogen). Similarly, it contaminates the different liquids produced by the operation (spent brine, caustic soda, etc.). This results in substantial losses, which must be limited for economic as well as environmental reasons. Whereas small. amounts of mercury in the chlorine (0.1 to 0.2 g/t) are not detrimental to its subsequent uses, the same cannot be said of caustic soda, especially for food applications, in which it is removed by filtration (up to 15 ppb), for hydrogen, from which it is removed (up to 3 to 5 ppb) by absorption in sodium hypochlorite, adsorption on activated charcoal etc, and aqueous wastes, from which it is removed (up to 5 to 10 ppb) by precipitation, adsorption, reduction or extraction. The spent brine, which normally contains 1 to 10 ppm mercury and occasionally 1000 ppm, is usually recycled and therefore does not require treatment... 

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