Thermal regeneration

Carbon adsorption Aqueous solutions typical concentration < 1 % SS < 50 ppm Adsorbate on carbon usually regenerated thermally or chemically... 

Here B can be made greater than 1 to better approximate the case where the heat capacity ratio is not larger than about 10. For a heat capacity ratio of 2, equation (55) is still a good approximation with B = 2. The relationship between the ineffectiveness and the regenerator thermal loss is given by... 

Use of powdered charcoal has the advantage that the amount used can be easily adjusted to the impurity level of the water and that the investment costs are low. Powdered charcoal is, however, not easy to regenerate, whereas granular activated charcoal can be regenerated thermally. Since the composition of the impurities varies from water to water, the conditions required for the treatment of water with granular activated charcoal (e.g. number of filters, contact time) have to be established empirically. The release of already adsorbed compounds e.g. chloro-alkanes into the eluant due to displacement by more easily adsorbed compounds (chromatographic effect) has, however, to be avoided. 

Although carbon is especially effective for the sorption of phosgene, periodic replacement of the carbon is necessary, since it has a limited capacity (perhaps due to modification of the carbon surface [867a]). It can be regenerated thermally and then reused, but the regenerated carbon bed has a lower capacity than fresh material, owing to... 

The trapping component was formulated into a washcoat and supported on a ceramic monolith with 400 cells per square inch (cpsi). The trap material was chosen for NOx adsorption, regenerability, thermal stability and rate of adsorption/desorption. Platinum is incorporated within the trap to oxidize the NO and the injected hydrocarbon. The lean NOx catalyst was Pt (60 gft- ) deposited on y-Al203 on a 400 cpsi cordierite monolith. 

R. K. Shah, Counterflow Rotary Regenerator Thermal Design Procedures, Heat Transfer Equipment Design, R. K. Shah, E. C. Subbarao, and R. A. Mashelkar (eds.), pp. 267-296, Hemisphere Publishing Corp., Washington, DC, 1988. 

Both adsorption and regeneration are operated periodically. The following methods can be considered for regeneration Thermal Swing Adsorption (TSA), Pressure Swing Adsorption (PSA), inert gas stripping, and displacement desorption. 

In adsorption processes one or more components of a gas or liquid stream are adsorbed on the surface of a solid adsorbent and a separation is accomplished. In commercial processes, the adsorbent is usually in the form of small particles in a fixed bed. The fluid is passed through the bed and the solid particles adsorb components from the fluid. When the bed is almost saturated, the flow in this bed is stopped and the bed is regenerated thermally or by other methods, so desorption occurs. The adsorbed material (adsorbate) is thus recovered and the solid adsorbent is ready for another cycle of adsorption. 

For the near future, post-combustion CO2 capture will be one of the first options to be implemented. This will be based on retrofitting power-plants with an absorption-based process to separate the produced CO2 from the flue gas. The main cost for CO2 capture, and CCS in general, from large point sources, like power plants, refineries, and various industries (glass, cement) are associated with the thermal regeneration of the solvent. The solvent is used to remove selectively the CO2 from the gas stream, during the absorption step. The loaded solvent is regenerated thermally in the desorber. 

A highly specialized application of adsorbents is the removal of radioactive isotopes from exhaust air or other gas streams. Ruthven (1988) reports that Kr can be effectively adsorbed by silicalite or de-aluminized hydrogen moidenite (molecular sieves) in a chro-matographic-type column. Other unusual molecular sieve zeolites (silver cation type X or silver cation morganite) are effective adsorbents for and can be regenerated thermally. 

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