Stripping volatile species

Air stripping requires packed towers for maximum operational efficiency [13]. Water is pumped to the top of a tower packed with media as shown in Figure 2.6. The water is evenly distributed across the media. As it flows down under gravity it forms a film layer on the packing surfaces. Air is blown upwards from the bottom contacting the large surface areas. The blown air enhances the removal of the volatile species by mass transfer. Degasification is... 

The stripping factor, S, which describes the stripping of a volatile species i into a flowing gas stream from a flowing liquid stream is the inverse of A. The extraction factor for any species is defined in solvent extraction by... 

The removal of a volatile species, gas or a vapor, from a nonvolatile ahsorhent or solvent hy an inert gas or vapor or by simple heating is called stripping. When air is used as the inert gas, the process is called air stripping, in the case of steam, the term steam stripping is used. The word desorption is also employed. 

These are considered to be equations for the operating line of the bottom half of the column, the so-called stripping section, since the bottom product stream gets stripped of the more volatile species in, for example, distillation. 

From a feed that comprises only vapor that is introduced at the bottom of a column, one could expect to achieve a top distillate stream highly purified in the more volatile species if there is a condenser at the top and there is reflux of the condensate at the top. Therefore such a distillation column has only an enriching section (Figure 8.1.26(a)) which can produce a highly purified distillate. However, there will be considerable loss of the more volatile species in the liquid leaving the column bottom where the vapor feed is introduced since there is no stripping section in the column. Correspondingly if a liquid feed is... 

Note For the conditions shown in Figures 8.1.26(a) and (b), the mode of operation is very similar to that of a type (2) separation system (Figure 8.1.2(a)), for example a gas absorber or a stripper. The condenser at the top of Figure 8.1.26(a) provides essentially a downfiowing liquid stream which acts as the absorbent for the less volatile species. The reboiler at the bottom of Figure 8.1.26(b) provides an upflowing vapor stream which strips the downflowing liquid of the more volatile species as in a stripper. 

Determine the relevant vapor-pressure data. Design calculations involving vapor-liquid equilibrium (VLE), such as distillation, absorption, or stripping, are usually based on vapor-liquid equilibrium ratios, or K values. For the tth species, K, is defined as K, = y, /x, where y, is the mole fraction of that species in the vapor phase and x, is its mole fraction in the liquid phase. Sometimes the design calculations are based on relative volatility c/u], which equals K,/Kj, the subscripts i and j referring to two different species. In general, K values depend on temperature and pressure and the compositions of both phases. 

Andreae described a method for the sequential determination of arsenate, arsenite, mono-, di- and trimethyl arsine, MMAA, DMAA and trimethylarsine oxide in natural waters with detection limits of several ng/1. The arsines are volatilized from the sample by gas stripping the other species are then selectively reduced to the corresponding arsines and volatilized. The arsines are collected in a cold trap cooled with liquid nitrogen. They are then separated by slow warming of the trap or by gas chromatography, and measured with atomic absorption, electron capture and/or flame ionization detectors. He found that these four arsenic species all occurred in natural water samples. 

The samples were analysed for total volatile sulphur gases and the results for the surface microlayer are presented in Figs. 8-18 to 8-20. The data are presented as peak areas from the strip-chart recorder of the analytical unit, as calibration of the response of a pulse of gas containing varying proportions of different species is not possible. On traverse A-A it is clear that there is a distinct pattern of three zones of higher sulphur values. There is a discontinuous series of anomalous values at the southwestern end of the traverse, which begin over the suboutcrop of Zone I and extend into the area underlain by the downdip extension of the mineralisation to a point where the depth to mineralisation is of the order of 80-90 m. This is followed by a series of generally low values until the samples are... 

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