Adsorption operating cycles

Adsorbent drying systems are typicaHy operated in a regenerative mode with an adsorption half-cycle to remove water from the process stream and a desorption half-cycle to remove water from the adsorbent and to prepare it for another adsorption half-cycle (8,30,31). UsuaHy, two beds are employed to aHow for continuous processing. In most cases, some residual water remains on the adsorbent after the desorption half-cycle because complete removal is not economically practical. The difference between the amount of water removed during the adsorption and desorption half-cycle is termed the differential loading, which is the working capacity available for dehydration. 

Figure 2.56 Micro channel with alternating segments for reaction and adsorption (above) and operating cycle with pulsed substrate inlet concentration (below).

Physical, thermal, and chemical stability in order to reduce operating costs, solid sorbents must demonstrate stability under flue gas conditions, adsorption operation conditions, and during the multi-cycle adsorption-regeneration process. In particular, stability in the presence of water vapor is essential for the sustainable performance of the solid sorbent. In addition to thermal properties of the solid sorbent, heat capacity and thermal conductivity are also important in heat transfer operations. 

Since properties of both phosphate and arsenate are very similar each other, the adsorption of phosphate was examined prior to the adsorption of arsenic species. Here, the feeding solution in the adsorption operation was 1 mM phosphate solution of pH3. Table 1 summarizes detailed experimental conditions and column performances during repeated adsorption-elution-regeneration cycles. Since supplied volumes of the feed are not constant (101 - 193 BV), it is not easy to judge the efficiency of the adsorption from total uptake of phosphate. Thus, removal of phosphate until 100 BV is listed at the last column of Table 1 as an index of the column performances. 

Operating cycles for liquid contacting processes such as ion exchange are somewhat more complex than those for gas adsorption. They consist of these steps ... 

MTZ (mass transfer zone). 500. 501 multicomponent data, 503 operating cycles, 502 operating parameters, 502 operating practices, 504 packed beds, 500-504 regeneration, 502, 504 regeneration steam, 502 Adsorption equilibria, 495,497... 

Adsorption is usually done in a batch mode in fixed, agitated, or expanded bed adsorption units. The process usually consists of cyclic operations of adsorption and desorption in two steps. Desorption or recovery of the adsorbed solutes from the adsorbents can be done by either changing the temperature or pH, or using a solvent, which also regenerates the adsorbents for use in the next operation cycle. 

Adsorption equipment and operating cycles usually can be designed reliably on the basis of measured adsorption isotherm data and a reasonable number of relatively small-scale experiments 10 determine the mass transfer characteristics of the stream to be treated in the chosan adsorbant bed. If the stream treated contains severe adsorbed components it is generally necessaiy to run experiments on the actual mixture to be treated, since multicomponent isotherm behavior cannot be predicted in general from the individnal isotherms. 

The recovery plants include a desiccant to dry the gas and prevent the formation of hydrate in the transmission lines. The desiccant is used in the same adsorber with the carbon on the inlet side or two adsorbers are used in series, one containing the desiccant and the other, activated carbon. The desiccant also adsorbs the higher-boiling-point hydrocarbons so that the total adsorption is a combined effect of the two. Operating cycles are fairly fast, the adsorption period varying from 20 to 45 minutes. 

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