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c z ad used in the treatment of very dilute gases or in specialty applications such as medical uses or gas masks. The most common fluids used in regeneration are hot air and steam. During regeneration, the equations for calculating the velocity and height of the desorption zone can be derived from the Freundich isotherm (cR = aRw|sR) similar to Equations 5.20(17), 5.20(18), and 5.20(19) as follows:

where subscript R refers to regeneration.

Theoretical predictions are not reliable and should be treated as estimates only. Laboratory data may not be available for scale-up because simulating the conditions for a large adiabatic bed is difficult using a small column. For the regeneration of carbon, the reverse flow of steam at 105 to 110°C is often used. The regeneration stops soon after the temperature front reaches the exit, and the typical steam consumption is 0.2 to 0.4 kg/kg carbon. Under these conditions, the carbon is not free of adsorbate. However, prolonging the desorption period is not economic because an excessive amount of steam is required to remove the remaining adsorbate due to the unfavorable shape of the tail of the desorption wave.

If the regeneration time is longer than the adsorption time, three or more beds are required to provide continuous operation.

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