Regeneration of spent carbons

Reactors widely used for the thermal regeneration of spent carbon are multiple hearth reactors, rotary kilns, moving bed reactors and fluidized bed reactors. Comparisons of these reactors were made in terms of residence time, steam and fuel consumption in Fig. 9.9 (Suzuki, 1976). 

According to Graham and Bayati (1990), regeneration of spent carbon requires a temperature of about 1,200°F and proceeds through the following steps ... 

The main limitation of GAC in removing gasoline compounds is its cost and the disposal of the generated spent carbon. However, the problem of spent carbon s regeneration has been solved, at least in part.29... 

Regeneration of spent catalyst in the steam stripper may produce enough carbon monoxide and fine catalyst particles to constitute an air pollution problem. 

Facilities are available for disposal and regeneration of spent activated carbon, and the vendor can coordinate transportation and on-site exchange requirements. 

The adsoiptive capacity of carbons is obviously finite. Consequently, it is gradually decreased and finally exhausted after the adsorption of the maximum possible amount of a substance. The exhausted carbon is then characterized as spent and has to be regenerated, reactivated, or properly disposed off. The regeneration of spent adsorbents is the most difficult and expensive part of adsorption technology. It accounts for about 75% of total operating and maintenance cost for a fixed-bed GAC operation. 

In the cases above, a two-parameter model well represents the data. A model with more parameters would be more flexible, but by using a partition constant, K, or a desorption rate constant ka and k, , for the mass-transfer coefficients, the data are well described (see Figs. 3.4-15 and 3.4-13). While K would be a value experimentally determined, kp can be estimated from eqn. (3.4-97) with the external mass-transfer coefficient, km, estimated from the correlation of Stiiber et al. [25] or from that of Tan et al. [27], and the effective diffusivity from the Wakao Smith model [36], Typical values of kp obtained by fitting the data of Tan and Liou are shown in Fig. 3.4-16. As expected, they are below the usual mass-transfer correlations, because internal resistance diminishes the global mass transfer coefficient. These data correspond to the regeneration of spent activated carbon loaded with ethyl acetate, using high-pressure carbon dioxide, published by Tan and Liou [45]. 

Adsorptive materials have been used for many years for the purification of chemicals. These materials include carbons, clays, and synthetic aluminosilicates. The disposal or regeneration of spent adsorbent is usually expensive, and generally viewed as a costly inconvenience. 

Another area where microwave heating is nsed to heat carbon is in the regeneration of activated carbons. When spent activated carbon is snbject to a microwave field, the heat generated within the particles prodnces rapid temperatnre rises and the release of other componnds adsorbed on the carbon [19-23], In a similar process, carbon nsed as adsorbent to remove NO and SO from gas streams can be regenerated with microwaves prodncing CO2 and N2 as gases and elemental snlphnr [24],... 

Johola, A. J., "Regeneration of Spent Granular Activated Carbon," NTIS PB-189 955, U.S. Department of Commerce (February 1969). 

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