Gas purification techniques

Regenerative adsorption

 There is only a then a very small flow non condensable components that possibly sent back to the adsorption circle. At desorption with hot air or is hot inert gas an accumulation of the concentration can be obtained of 10 - 15 time. The desorption gasses to be in this case is less suitable for solvent recuperation but well for afterburning. At the design of the installation the work capacity must be known. The required bed size can be namely twice the size of the calculated fresh adsorbents. This way the work capacity has a large impact on the size of the installation and on the investment - and functioning costs.

There three different implementation forms of adsorption- desorption installations exist:

1. Thermal regeneration

2. Vacuum regeneration

3. Rotor concentrator

At thermal regeneration the installation exists from 2 or more adsorbentbeds. One bed is regenerated, the other bed remains active for adsorption. The possible third bed is dried , cooled and stand-by stand after regeneration. Regeneration is carried out by blowing steam through the bed so that the bed warms up and the VOC desorbs. This happens at temperatures between 80 and 200 °C. After the desorbing cooling air us blown through the bed so that it cools down and dries. This is done till the desired temperature and humidity of the bed has been reached. Thermal regeneration is most suitable for volatile VOC.
To prevent contamination of the VOC with for example steam and to improve the
solvent recovery vacuum regeneration can be applied. One speaks then of pressure swing adsorption. By using a vacuum pump the pressure of the bed it is reduced so that the VOC is already starting to boil at the temperature in the bed. During the boiling of the VOC the temperature of the bed will decrease slowly.        In a rotor concentrator the adsorbing is brought into a turning wheel. The largest surface of the wheel is used to remove the pollutants from the degasses. A small part of the rotor is used to desorb. Sometimes after the desorbing part another a section is placed with a cooling medium to cool down the rotor so that  the adsorption can act with sufficient efficiency. A rotor concentrator is thermal adsorption- desoption unit where the aim generally is destroy the VOC and not to recuperate them. 
The advantages of regenerative adsorption are:

• Robust

• Regeneration of the adsorbents

• Large saving on investment and fuel usage for in series set post-combustion (low solvent concentrations)

• More efficient recuperation of solvents from more concentrated mist

• Specific advantages of adsorbentia

The disadvantages are:

• No end treatment

• High substance qualities can cause constipations.

• Specific disadvantages of adsorbentia

At spray cabins of enamel, glue regenerative adsorption are especially used to reduce the flow
and raise the concentration and thereby reduce the investments
functioning costs of for example afterburing. If the solvent have a high value and cant his be re-used this can also be recuperated. In the process industry regenerative adsorption with steam or warmth
regeneration are applied to win solvents from the degasses. 

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