Vapor reuse system

Vapor Reuse, A modification of the multieffect system, shown in Fig. 7-24, has been termed the vapor reuse system (Ref. 12). In it, the feed is introduced into a stripping tower, and the vapor from it is used as the source of heat and the feed of the lower pressure column. The two columns may not be in balance f.e., the minimum heat required for the stripping section may be more or less than that... 

Once VOC emissions have been eliminated or reduced at source, then recovery of the VOC for reuse should be considered. Figure 25.6 shows a vapor recovery system associated with an atmospheric storage tank. The storage tank is fitted with a vacuum-pressure relief valve, which... 

Single-stage evaporators tend only to be used when the capacity needed is small. It is more usual to employ multistage systems which recover and reuse the latent heat of the vaporized material. Three... 

The vacuum extraction process involves using vapor extraction wells alone or in combination with air injection wells. Vacuum blowers are used to create the movement of air through the soil. The air flow strips the VOCs from the soil and carries them to the surface. Figure 18.14 shows the flow diagram for such a process. During extraction, water may also be extracted along with vapor. The mixture should be sent to a liquid-vapor separator. The separation process results in both liquid and vapor residuals that require further treatment. Carbon adsorption is used to treat the vapor and water streams, leaving clean water and air for release, and spent GAC for reuse or disposal. Air emissions from the system are typically controlled by adsorption of the volatiles onto activated carbon, by thermal destruction, or by condensation. 

The CleanSoil process is an ex situ treatment technology that uses steam to remove hydrocarbons and chlorinated solvents from contaminated soils. The steam vaporizes the contaminants from the soil and carries them to a condenser for recovery. The water is converted back into steam and reused in the system. The remaining vapors pass through an activated carbon filter and are released into the atmosphere. The technology has been applied full-scale at multiple sites and is commercially available. 

Evaporation has been successfully used in a number of ways to recover plating bath chemicals. In one technique, water is evaporated from rinsewater to reduce its volume sufficiently to allow the concentrate to be returned directly to the process bath. In another technique, it is water from the process bath that is evaporated, making room in the bath for spent rinsewater to be added as makeup. The water vapor can be condensed in some systems and reused in the rinse system. 

In a mercury diffusion pump, the mercury is heated to the point of vaporization. This vapor travels up into the condenser area where it is ejected at supersonic speeds from little holes. The vapor knocks any wandering gas molecules down toward the mechanical pump outlet which can then expel them from the system. The vapor later condenses and collects in the heating pot for reuse. 

Different designed solvent recovery systems are used. As an example there is the solvent system that consists of fixed bed adsorbers containing activated carbon and a distillation system. The carbon adsorbs the solvent vapors. Then the beds are steamed in sequence to remove the solvent. The solvent and steam are condensed into a large tank. The distillation system is then used to distill the solvent from the water to a purity of 99.99% so that it can be reused. Because of the high cost of solvent, complex monitoring equipment is used to insure a high rate of recover. 

SULF-X [SULFur extraction] A regenerate flue-gas desulfurization process in which the sulfur dioxide is absorbed by aqueous sodium sulfide in a bed packed with pyrite. Ferrous sulfate is produced this is removed by centrifugation and calcined with coke and fresh pyrite. Sulfur vapor is evolved and condensed, and the residue is reused in the scrubber. Developed by Pittsburgh Environmental and Energy Systems. Piloted in the mid-1980s but not commercialized. Not to be confused with Sulfex or Sulph-X. 

This study was undertaken to obtain the necessary vapor-liquid equilibrium data and to determine the distillation requirements for recovering solvent for reuse from the solvent-water mixture obtained from adsorber regeneration. Previous binary vapor-liquid equilibrium data (2, 3) indicated two binary azeotropes (water-THF and water-MEK) and a two phase region (water-MEK). The ternary system was thus expected to be highly nonideal. 

Modem solvent extraction plants recover over 99.9% of the solvent pumped to the extractor. The solvent recovery system includes solvent and water vapor condensation, solvent-water separation, stripping solvent from water and air effluent streams, as well as heating the solvent prior to reuse in the extractor. 

For each mole of acetaldehyde formed, one mole of palladium chloride was reduced to metallic palladium. To make this process industrially attractive, it must be conducted so that palladium chloride acts as a catalyst rather than as an oxidant—i.e., so that the metallic palladium formed is reoxidized to palladium chloride and can be reused for the principal reaction. This was the second fundamental recognition, which helped make this process commercial. The search for proper oxidants for metallic palladium was facilitated by the observation of Smidt et al. (34) that if cupric or ferric chloride were added to palladium chloride in the vapor-phase oxidation of ethylene to acetaldehyde, the acetaldehyde yield was increased. Therefore, these compounds were also used in the liquid-phase oxidation. In such a system, the following reactions will occur in the presence of oxygen and hydrochloric acid, the latter being formed by the reaction above (34). 

Adsorption is a mass transfer process in which gas molecules are removed from an airstream because they adhere to the surface of a solid. In an adsorption system, the contaminated airstream is passed through a layer of solid particles referred to as the adsorbent bed. As the contaminated airstream passes through the adsorbent bed, the pollutant molecules adsorb or stick to the surface of the solid adsorbent particles. Eventually the adsorbent bed becomes filled or saturated with the pollutant. The adsorbent bed must then be disposed of and replaced, or the pollutant gases/vapors must be desorbed before the adsorbent bed can be reused. 

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