Absorber Max. Temperature 3

[aviador2006]

Hello, everybody. Can anyone tell me what should be the maximum allowable temperature (or range of temperature) in an absorber from an alkanolamine plant for gas treating, for the various types of amines, i.e., MEA, DEA, DGA, MDEA?. Thanks.

 

[zzznook]

Inlet temperature of lean amine should be around 40C and the feed about 5C below. The rich outcome amine is about 40 - 80 C and the temperature of the gas depends on the L/G ratio

 

[zzznook]

One more thing. There will be a temperature raise in the column due to the heat of reaction. If the gas has high concetration of H2S and CO2 the L/G will be higher and the solution will carry most of the reaction heat. If the gas is more dilute the gasbulk will carry a larger piece of the heat. And also the heat of reaction will be less relative to the mass of gas and solution taking up the heat.

 

[Chemeng1122]

The max temperature in the contactor should generally be less than about 195F (90C). If you excced this temperature, because of the exothermic raction mentioned in the post above, corrosion in the contactor can become a major concern.

Common fixes to high contactor bulge temperature is lowering the lean amine feed temp (maintaining 5C spread bewteen the feed gas temp), lowering inlet gas temp (if control is available), or increasing amine circ rate (if equiment capacity allows for it).

Andrew Lechelt
Technical Support Engineer
Quadra Chemicals

http://www.quadrachemicals.com

 

[zzznook]

alechelt.
Is this a major problem when dealing with MDEA as well? In my experience MDEA is less corrosive than MEA and DEA. or is this due to its lower heat of reaction so that the contactor temperature never reaches those levels?

What is the limiting factor and temperature when dealing with K2CO3 ?

 

[Chemeng1122]

It can still be a problem with MDEA, as it can be with any amine. I would say that it would less common with MDEA because of the bicarbonarte reaction in MDEA is slower, so this reaction is more spread out in the contactor. With primary and secondary amines, the CO2 reacts directly with the amine in the carbamate reaction, which is very quick.

With primary and seconary amines, the temeprature bulge is generally of greater magnitude because both the H2S and CO2 react quicky.

With poor operating conditions you can still reach high bulge temperatures using MDEA. This being said, I dont really run across this issue very much (high bulge temperature). We might see it more if all contactors had instrumentation to measure tray temps, but they dont.

On your point where you mention that MEA and DEA are less cororsive, clarification is required. No amines are corrosive, they are alkaline fluids and are used as corrosion inhibitors in some applications. You may be referring to the fact that primary and secondary amines have corrosive CO2 degradation products, where MDEA does not. This is a whole other issue entirely.

I cant comment on PotCarb systems as I dont have much experience dealing with them. Sorry about that.

Andrew Lechelt
Technical Support Engineer
Quadra Chemicals

http://www.quadrachemicals.com