29 replies to this topic

[Art Montemayor]

Narendra:

 

You state that the operating manual of one of your Amine (MDEA) suppliers indicates that 260 ^oF is the maximum temperature that should be applied in the reboiler.  However, this is the maximum design temperature for Monoethanolamine (MEA) – not Methyldiethanolamine (MDEA).  The boiling point for MEA at atmospheric pressure is 171 ^oC (339 ^oF) and that for MDEA is 247 ^oC (477 ^oF).  MEA decomposes at its boiling point; MDEA does not decompose up to its boiling point (at least not according to Kohl & Riesenfeld).

 

The problem with this lengthy thread is that Vista has not answered my detailed questions.  Furthermore, as Bobby Strain infers, she doesn’t state WHAT the specific problem at hand is with this MDEA stripper.  Why bother to “control” (vary) the stripper pressure when 10 to 15 psig are normal, conventional stripper pressures?

 

I simply fail to recognize what the problem is here.  An amine stripper (be it MEA, MDEA, or even DGA) will easily strip out H₂S with ease.  CO₂ is harder to strip out.  Nevertheless, an acid gas stripper is a very simple tower with very few trays required to effect a successful regeneration of the amine solution in question.  I have designed, built, and operated amine strippers with 6 flat, 5/16” thick trays installed 15” apart.  These “trays” had no holes, valves, or even bubble caps – nothing.  They had a 15% cut to allow cascading of the solution.  They worked very well for years with 85 gpm of solution and a steam bundle in the kettle reboiler.  In another application, I used tunnel caps that I fabricated from half-cut pipe.  This time I used 10 tunnel cap trays.  The results were the same as the first, plain flat tray application – no difference in regenerating the 0.35 mol CO₂/mol MEA rich solution to 0.15.  I never employed any so-called “reflux” in the strippers that I designed and operated.  They all worked exactly as designed and for many years.  This all confirms the simplicity of this Unit Operation.  If I could do it with nothing more than a slide rule and a pad of paper, then today with all the computers, databases, exotic materials of construction, years of research and improvements you guys ought to have processing plants that far outdo what we did over 50 years ago.  Unfortunately, this doesn’t seem to be the case.

[narendrasony]

Dear Art,

We are blessed to have some of the stalwarts like you with creative and real Engineering outlook and with first hand insight in almost all the aspects of  Engineering. You will keep on inspiring us.

MDEA thermal degrdation temperature has been reported by one of reputated suppliers. I'm enquiring them again.

I had loved your idea of diverting so called stripper reflux for recovering amine  from sweetened gas. And I never imagined amine stripper with just 6 trays.  But I'm still trying to figure out how the  trays with just single 15% cut would work, how gas and liquid is contacting? Can you please tell the tale if it is convenient for you? It will be really interesting. I hope Forum members wont mind going off the thread. 

 

Warm regards

Narendra

[Art Montemayor]

Narendra and all other interested members:

 

Please excuse my delay in responding to your request. It took some time to put together what I believe is a direct and positive response.

 

If you go to the following pages within our website, you will find a downloadable workbook answering your concerns:

1. Cheresources.com Community

1. Downloads

1. Community Hall of Fame

1. Amine Acid and Sour Gas Plant Experiences

You can also simply click on this hyperlink and go there: 
http://www.cheresour...nt-experiences/

I hope the documented personal experiences and findings are of help and contribute to your engineering skills.

[narendrasony]

Thanks Art for sharing your wonderful experience. It is a real treasure.

I checked with Amine manufacturer again,  as per them thermal degradation for MDEA starts at 127 DegC. Bulk solution temperature should remain below this value. Temperature of heat source should be < 177 DegC.

 

Amine stripper with just 6 simple segmental trays - perhaps we'll never have a chance to see it in our lives.

Liquid -vapor contact appears to take place below the cut portions, It seems to me that tray efficiency will be poor. But perhaps for these applications tray efficiency is not  important. Have you used these trays in other  applications also ?

 

Regards

Narendra

[Art Montemayor]

Narendra:

 

I hate to add on to this thread with an off-topic item but I will say on an ending note that if you are interested in persuing this point please start a new thread.

 

The common applied top temperature applied to MEA (note this is the primary amine, not MDEA) is 260 ^oF (127 ^oC).  What your amine supplier is telling you doesn't make sense.  Please tell me who you are buying your MDEA from and how I can obtain a written brochure or letter stating the degradation temperatures from them.

 

You can supply that in a new thread.

 

Thank you.