4 replies to this topic

[K. Dolecek]

Dears,

 

We have 30%wt. DEA sweetening of the associated gas with subsequent TEG dehydration in our Gas Plant project. The process configuration is Amine absorber followed by Sweet gas air cooler and Sweet gas separator with demister to condensate and separate water and entrained amine before TEG Dehydration contactor. Operating conditions of the Amine contactor are: 20barg, lean amine temperature is 30 - 45°C (depending on season winter/summer), raw gas temperature is always by about 5°C lower, sweet gas temperature to the Glycol contactor 25 - 40°C.

 

Could you explain me, if it is generally necessary to have sweet gas water washing downstream amine contactor before TEG dehydration? In case of positive answer, which problems can be expected in TEG dehydration if the water wash is missing?

 

Thank you,

Karel

[Art Montemayor]

Karel:

 

The topic of water washing (or scrubbing) the natural gas outlet out of an amine absorber prior to its entrance into a TEG dehydration unit has been discussed many times in our Forums:

 

http://www.cheresour...wash#entry61355

 

http://www.cheresour...wash#entry68461

 

http://www.cheresour...wash#entry78835

 

http://www.cheresour...wash#entry79047

 

I would not tolerate any amines exiting the acid gas absorber to infiltrate the TEG unit.  You are asking for a lot of troubles in securing a steady, dehydrated sales gas.  I never have allowed for “sweet gas” to exit an amine absorber at temperatures in excess of 30 ^oC and enter a TEG unit without a cool water scrubbing operation.  I consider a temperature of 40 ^oC (104 ^oF) far too excessive and asking for trouble in downstream TEG units.  My guidelines are simple: the lower the temperature, the lower the amine vapor pressure, and any subsequent carryover as vapor or particles.  An added feature of a cool water wash prior to the TEG unit is that this cools the entering gas; it does not increase the water vapor content in the sweet gas entering the TEG unit.

 

Of course, the above means capital monies and further processing procedures.  Nothing is free and there are tradeoffs as in all engineering projects.  The engineering contractor is trying to keep the amine absorber as small in diameter as possible; this effect only tends to increase superficial velocities – and consequently drift and entrainment tendencies.  One way to avoid future problems is to insist on exit purity warranties of the sweet gas during the first year of operation at rated design flow rates.  Many operators forget about this option during the bidding and contract negotiations for the plant design.

 

[K. Dolecek]

 

 

Art,

 

Thank you very much for your reply.

 

Our process unit configuration is basically the same as given in attached PFD in your the last link.

My only question relates to DEA content (not water content) in outlet gas stream from amine absorber to the TEG contactor and its consequences on TEG dehydration unit operation.

  

Does have someone experience if the sweet gas water washing downstream amine absorber is „nice to have“ or „must“ because DEA content in the sweet gas is quite low acc to Promax simulation?

 

Thank you very much again.

Happy New Year 2014.

 

Karel

[Art Montemayor]

Karel:

 

You are getting mixed up.  A water scrubber placed between the sweet gas outlet and the TEG dehydrator IS NOT A CONVENTIONAL UNIT OPERATION.  It is a necessity when your process and mechanical design for the amine absorber cannot guarantee the minimum and tolerable amine content in that stream.  It is employed when the design of the absorber results in amine entrainment.  Your simulation program (or anybody else's) CANNOT PREDICT ANYTHING about the entrainment that can or cannot take place.  There is no program that can do that.  All you can do is use a conservative design that is field-proven.  If you simply using a simulation program at this stage, you have nothing that are real life facts.  Your simulation results can only be proven valid and accurate with the field installed results - not the computer printouts.

 

There is nothing "nice to have" about needing a water scrubber.  Your field installed process either produces pure, un-entrained sweet gas or it doesn't.  If it doesn't, then you must resort to some method to remove the impurities (amine entrainment).  That is real-world operations and a very good reason why the specifications and negotiations for purchasing a sweetening process should be done by experienced and capable engineers who have done it before.

[K. Dolecek]

Art,

 

thank you for your explanation.  I understood that in case of proper designed and well operated amine sweetening unit, the sweet gas water washing section downstream amine absorber is not necessary.

 

You have mentioned minimum and tolerable amine content in sweet gas stream upstream TEG treatment. Could you (generally) quantify it or advice some source of detail information about this topic?

 

Thank you,

Karel