The adiabatic desorption of single gaseous components from a fixed bed of solids by a constant pressure gas purge is analyzed in detail using equilibrium theory. The analysis is carried out within the framework of industrial practice using the system C02-Nn-SA molecular sieves as an example. The parameters investigated include the use of adsorber feed and pure product gas as regenerant, and the effect of purge gas temperature and heat capacity, total system pressure, and adsorber feed concentration on the regeneration process. It is shown that the amount of purge gas and adsorber feed treated per unit weight of bed are equal to the relevant slopes of the "characteristics" or "shock chords" on a solid concentration-gas concentration characteristic diagram (hodograph). A simple analysis of the desorption process is thus made possible which is used to arrive at some important conclusions regarding the effect of the parameters on desorption time, regenerant consumption, and the economics of the process. Conditions under which residual solute may be removed from a hot bed advantageously with either cold clean gas or cold adsorber feed are outlined.
The results are reported of an experimental study of the desorption by gas purge of single gases from a 5'/z ft long, 31/2 in. diameter fixed-bed adsorber. Breakthrough curves were measured for the systems c02-N~-5A molecular sieves, COZ-He-carbon and C2HG-He-carbon over a wide range of regenerant temperatures (80-450°F). Nonuniform initial bed loadings caused by adsorption transfer zones and plateaus, as well as uniformly saturated beds were used. The data are in all qualitative respects in agreement with the predictions of equilibrium theory detailed in Part I . In particular, it was confirmed that the desorption time i s independent of pure regenerant temperature when the initial bed loading is located in the region ( I ) of the q-Y diagram. Quantitative predictions of desorption time and gas consumption are satisfactory to excellent for uniformly saturated columns yielding two-zone desorption profiles. The predictions are also good for the important case of columns loaded with low concentration feed to breakthrough only (partial saturation). In the severest test of the theory involving a low-temperature purge yielding a single unstable solute zone, the predicted desorption time was approximately 50% of the measured value over a 3.6 ft length of column.
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