5 replies to this topic

[joeblingz]

Hi, this might be a trivial question but I seem not to be sure of the answer to this. I'm treating a stream containing 70%CH4, 23%CO₂ and 7%H₂O vol% using MEA aqueous solution in an absorption column with the intention of removing as much CO₂ as possible. I'm a little worried about my material balance. I'm just a little concerned that the water content of the stream may reduce the concentration of MEA (since MEA is obviously soluble in water) and hence its absorbing capacity to remove CO₂ (if so, by how much realistically) or is it possible the water content leaves with the treated gas (CH₄) while only CO₂ is absorbed  for some reason. Is this logical? (The amine scrubber is operating at 1bar, inlet temp 37C)

Edited by joeblingz, 05 March 2014 - 06:05 AM.

[joeblingz]

any ideas at all please...

[PingPong]

Water % in amine is in actual operation adjusted by either adding water, or removing water from the reflux drum of the amine regenerator.

[joeblingz]

Thanks Pingpong.. So I understand from what you said that it is possible water content in the feed stream may dissolve in MEA, slightly affect the MEA conc, but the balance in MEA concentration is maintained by removing or adding water in the reflux drum of the stripper. 

 

However, the feed stream water content is in the form of a gas, so water vapour, so is it not also logical to think MEA will not dissolve theoretically at a higher vapour pressure of water vapour than ordinary water and as such the water vapour would escape with the treated gas in vapour phase? The treated gas may further be treated with TEG at relevant operating conditions. (Well this only currently describes my PFD for my design at the moment.) 

[PingPong]

Water enters the system with the feed gas, and leaves the system with the treated gas, and with the sour gas from the regenerator reflux drum. If the leaving gases contain more water vapor than enters with the feed gas, then you have to add liquid water to the system to maintain the required MEA concentration. If less water vapor leaves than enters, then you need to bleed liquid water from the regenerator reflux drum.

 

The amount of water vapor that leaves the system in the treated gas and sour gas depends on temperature and pressure of both gases.

A gas can not contain more water vapor than thermodynamics allow.

Your choice of lean MEA temperature and regenerator condensor temperature have a big impact on the water balance of the amine system.

[joeblingz]

Thanks very much PingPong...Quite understood now...