2 replies to this topic

[safedude]

Hi guys

Im a final year student and i have to design an absorption column,
The absorption column absorbs carbon dioxide from a gas stream using selexol solvent (dimethyl ether of polyethylene glycol)
Basically, I know that the absorption column can either be a packed or tray column but i have no idea which one would be more suitable for the absorption column in such a process..........

Your help and any assistance whatsoever will be very much appreciated.

Many Thanks

Mo

[Art Montemayor]

Mo:

Rarely have I seen, heard of, or operated a trayed absorption column - with the exception of TEG dehydration contactors. And these are now becoming very rare in view of the results obtained with structured packing.

With respect to the Selexol process, I believe most - if not all of the absorbers - would be packed. And with new technology, probably structured packing is now making inroads.

I see few - if any - advantages in favor or using trays in a Selexol CO2 absorber. If you know or hear of some, please share.

[Nikhiln]

Hello Art & Mo,

I can give a couple of examples of trayed absorbers I operated in my earlier company. One was a CO2 absorber (HotPot process) to absorb CO2 from Ehylene oxide reactor effluent. The other was the Ethylene Oxide absorber in the same unit. EO was absorbed using water. This absorber had two sections: a bottom quench section (5 trays) where the incoming gas was cooled and its acidic components neutralised. The upper section of 17 trays was the actual absorption section.

I actually asked a lot of people the reason why we used trayed absorbers (inspite of the pressure drop) but no on really had any answers. The major reason being the plant was set up in the 1960's and it was taken over and restarted in 2004. The new staff (like me) didnt have much idea of the design basis. We lay our hands on whatever documents we could come across, but till this day, I haven't really got a convincing answer. And sadly, the whole complex was razed to the ground 3 years ago.

I would like to believe that the CO2 absorber was trayed because it involved reactive absorption (CO2 with K2CO3), but I dont have any supporting evidence. I have really no idea why the EO absorber was trayed.

The only other possibility I can come up with, is it was an old plant and packings had not reached the level of success we have now and thats why they stuck to the trays.'

Maybe Art and other Jedis can shed some light.