Liquid stripping zone

A continuous circulation of groundwater is generated in the area surrounding the remediation well, as aquifer waters replace the annulus water. The circulation thus delivers new contaminants to the stripping zone. Volatile contaminants dissolved in the groundwater are transferred from the liquid to the gas phase and are extracted from the groundwater surface via a double-cased screen. Soil air from the unsaturated zone is also extracted and transported to the off-gas treatment system. 

The transport of the substances from the feed solution to the strip side can be divided into the foUowing steps diffusion of substance S across the boundary aqueous layer in the feed (donor) phase, extraction (sorption) of substance on the donor/membrane phase interface, diffusion across the boundary layer on the feed (donor) side, convection transport in the liquid membrane zone, diffusion across the boundary layer on the strip (acceptor) phase of LM, re-extraction (desorption) on the membrane/strip phase... 

The ethanol column (C-1) has practically only stripping zone. Fig. 9.31-left shows composition profile both for liquid and vapour phase. The examination of the composition profiles highlights the role of the entrainer. In the zone close to the top the benzene extracts the ethanol in the liquid phase, and as a result increases the volatility of water, so that on lower stages the water is completely removed. In the lower part practically only the binary ethanol/benzene remains. The distillation trajectory starts from the ternary azeotrope, goes along the ethanol/ benzene saddle and terminates in the ethanol vertex. Because the boiling point of the azeotrope ethanol-water is close to the pure ethanol, the profile could easily jump to the ethanol/water azeotrope. Consequently, the design and operation of the column (C-1) is very sensitive. 

Determine the feed condition q. This signifies the moles of liquid going to the stripping zone from one mole of feed, and can be found as follows ... 

This analysis assumes essentially no stripping of the feed flash liquid in the base section of the tower, although, in a later step, a temperature drop across the bottoms stripping zone will be set. Nelsons correlations show very little stripout at the steam rates usually employed, but experience shows that temperature drops as higli as 30 degrees F between flash zone and bottoms do occur. This is of little real importance, however, since the heat input to the system can be calculated independently of the absolute thermal condition of the feed. 

The catalyst travels to the top of the riser carrying heavy components and coke deposits from preceding reactions. The catalyst enters a stripping zone where some steam is added to further crack and remove the heavy hydrocarbons from the catalyst surface. The catalyst then enters the reactor section where a cyclone separates the catalyst from the product vapor. The separated product vapor is sent to the main fractionation column (Figure 4.2) that separates the product into gaseous and liquid products. The separated catalyst is piped into the regenerator where the coke on the catalyst is burned ofF. 

The heated oil is flashed into the VPS flash zone where vapor and liquid separate. Split between distillate and bottoms depends on flash zone temperature and pressure. Separation of vapor and liquid in the flash zone is incomplete, since some lower boiliug sidestream components are present in the liquid while bottoms components are entrained in the vapor. The liquid from the flash zone is steam stripped in the bottom section of the VPS to remove the lower boiling components. 

The vendor states that tetrachloroethane (PCE), trichloroethene (TCE), and other volatile compounds are difficult to remove from saturated soils because they are relatively insoluble. The vendor states that the technology is especially applicable to sites contaminated with dense non-aqueous-phase liquids (DNAPLs). Using the ISSZT technology creates an unsaturated zone from which these contaminants can be readily air stripped. Other contaminants such as polychlorinated biphenyls (PCBs) or metals can be isolated from groundwater and contained within barriers preventing the spread of contamination. 

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