Contacting modes staging

Adsorption-Control Equipment If a gas stream must be treated for a short period, nsnally only one adsorption unit is necessary, provided, of course, that a sufficient time interval is available between adsorption cycles to permit regeneration. However, this is usually not the case. Since an nninternipted flow of treated gas is often required, it is necessary to employ one or more units capable of operating in this fashion. The units are designed to handle gas flows without interruption and are charac terized by their mode of contact, either staged or continuous. By far the most common type of adsorption system used to remove an objectionable pollutant from a gas stream consists of a number of fixed-bed units operating in such a sequence that the gas flow remains nninternipted. A two- or three-bed system is nsn ly... 

Table I gives the values of the extraction factor (a) required for americium removals ranging from 80 to 99%. These required values of a are given for the three modes of extraction (single-contact, two stage crosscurrent, and two stage countercurrent).

In onr example, die lowest valoe of that can be attained with erase current contacting with the inlet liquid stream split equally among N stages is 0.013. Theoretically. ya can be reduced to zero with countercurrent contacting in onr example. These results are plotted in Fig. 4.1-5. Thus, this simple ezemple illustrstes the relative effectiveness of the thme classic contacting modes, which are listed in Table 4,1-1. 

To maximize driving forces throughout a particular system, countercurrent contacting is tiequently used. In this contacting mode, the inlet stream for one phase is mixed with the outlet stream of the other phase. For the two-stage countercurrent contacting system. 

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