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Regenerating Adsorbents

Regeneration

Molecular Sieve, Activated Alumina, and Silica Gel can all be regenerated, meaning they can be treated to remove what has been adsorbed, so that the product can be used repeatedly. Both heat and/or vacuum can be utilized to bring molecular sieve to a state of being regenerated. Refer to a typical regeneration scenario below:
 
Overall
Heat the system to increase the temperature of the adsorbent material and residing product stream to evaporation conditions, this process will release most adsorbed water, and any other components co-adsorbed, from inlet gas. Adsorption conditions should be brought to evaporation temperature, remember there’s 1,800 btu/lb H2O/°F for water evaporation. Remember that regeneration requires not only the molecular sieve to be heated, but the metal of the bottle and any other piece around will be heated along with sieve and consuming some energy. Dry product gas is often used to transfer thermal energy to the molecular sieve bottle that is being regenerated, and in cases where the dry product will destruct at regeneration temperature, a separate dry, unreactive gas (such as nitrogen) is used for heating and cooling instead.
 
Calculations
1. Calculate the volume of dry gas required for increasing the temperature of the molecular sieve to the required evaporation temperature.
2. Calculate the flow rate through the molecular sieve that would be required as the threshold for turbulent flow.
3. Calculate the time that would be required to transfer thermal energy to the molecular sieve in the bottle, in order to attain evaporation temperature.
4. Calculate the time that would be required to cool the dry molecular sieve to be able to swing the vessel back on line.
5. The total time of this process must be less than the adsorption time of the parallel bed currently adsorbing. 
 
Regeneration Procedure
1) When the bed that is actively performing is ending the adsorption step, switch the wet feed gas to the next molecular sieve bed, one that is already regenerated, while simultaneously switching flow of regeneration gas to the bed that is counter-current to the adsorption flow.
2) The regeneration gas should next be heated to the temperature defined by the specified flowrate.
3) When the required conditions for heating is reached, end the furnace heat and allow the cooling effect to bring the temperature of the molecular sieve to match the feed temperature. The cooling gas should match the flowrate of the heating gas.
4) By the time the specified time of cooling is reached for one bed, the already cool bed of molecular sieve is beginning its next adsorption cycle, and the bed that will next need to be regenerated should be switched to the heating step.
5) Repeat this cycle to create a continuous adsorption/desorption cycle.

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