10 replies to this topic

[aanita]

At present our MDEA regenarator bottom temperature is 130 ~ 131 DegC and Top pressure is 1.2 Barg. However when Regen pressure fluctuate due to any upset, pressure increase and consequently Regn bottom temperature also increase( exceed 132 C), and still more than 12 years of plant running we are not facing any corrosion or any integrity issue.

I found in the literature, MDEA thermal degradiation temperature is 126.66 C.

I want to know at 1.2 Barg Regn pressure what is the thermal degradiation temperature of MDEA( Conc is 45 ~ 50 wt%).

 

Thanks in advance.

 

Regards.

Edited by aanita, 20 March 2013 - 08:32 AM.

[paulhorth]

aanita,

 

Some years ago I was having a disussion with a client on this exact point, the degradation temperature of MDEA. I sent a query to Dow Chemicals, who confirmed that their mazimum recommended skin temperture (tube wall temperature) for MDEA was 350 deg F (178 C) and the temperature  when degradation starts is advised as 360 deg F (182 C).

The temperature of 127 C is too low as a limit for MDEA. This is a recommended bulk fluid temperature.

 

Art Montemayor is the amine expert here, so he may wish to correct or qualify this information.

 

Paul

[chandan20]

i m nt sure bt isnt thermal degradation temperature independent of pressure?

that is the reason we do vacuum distillation to lower the boiling temperature of the component otherwise it mighr underfo cracking.

Art montemayor may clarify.........

[Erwin APRIANDI]

Hmmm, 178 deg C seems very high

I ussually design it for max 125 deg C at atmospheric pressure 

 

I'm following this topic for more sharing, especially from Mr. Art Montemayor

[Art Montemayor]

While I am certainly not going to assert myself as an expert in amine technology, I spent a considerable amount of years designing, installing and operating acid gas and sour gas amine units.  In the last 30 years I’ve dealt more with oil and gas related amine units removing CO₂ and H₂S.  So, I am very familiar with the design and concepts of the amine processes and how they should operate.

 

There seems to be some misunderstanding or misinterpretation in this thread of the design limits used on amine acid/sour gas removal processes.

 

Paul Horth is correct in stating that the recognized temperature at which “degradation” starts for MDEA is 360 ^oF (182 ^oC).  However, the term “degradation” itself is subject to a lot of definitions.  ALL AMINES are subject to degradation – temperatures cast aside.  This is something that is inherent and unavoidable.  For example, place any amine in an open beaker on a lab top and come back a week later and you will find that it has “degraded”.  Amine solutions are degraded by reaction with CO₂ oxygen, organic sulfur compounds, and other gas impurities to form heat-stable salts and amine degradation products.  These contaminants cause corrosion and lower the treating capacity of the amine solution.  In other words, factors have to be taken into account before solely blaming a high temperature.  Therefore, when acid / sour gas plant engineers talk about the limits posed on their MDEA solutions they are relating to a PRACTICAL, operating limit on the solution.  (Here, note that I have used the term “solution”.  More on this later.)  There is some degradation taking place at temperatures below 360 ^oF – but that is a tolerable operating characteristic of amine solutions.  Heck, there is going to be degradation taking place also at 212 ^oF (100 ^oC).  All amine plant operators know that there is inherent consumption of amine in any amine process due to the instability of the amine itself – something that can’t be avoided, but can be kept low and within manageable limits.  That limit has been defined by practical usage as 360 ^oF.

 

Now let’s put attention on the DESIGN operating temperature limit for an MDEA solution.  That value is the same as for MEA solutions and is designated as 260 ^oF (127 ^oC).  This is not a degradation limit, but rather an operating limit.  It means that you are recommended to keep your operating amine reboiler at no more than 260 ^oF if you want a steady, reliable operating system.  In the early days (1960) I operated Girder CO₂ plants using a 20% MEA solution in a reboiler at 40 psig.  This put the reboiler at approximately 290 ^oF (143 ^oC)!  Of course, this accelerated the rate of amine degradation and we would have to literally “dump” all the amine solution approximately every 2,000 hours of operation.  (The Girdler Corporation patented the Amine process in 1930)

 

Normally, amine plants (especially MEA types) have a means of reclaiming the amine solution contaminated with degraded products.  This is done thermally and batch-wise.  This is the design feature that allows operators to depend on a continuing, steady-state operation using a solution of a compound that is subject to degradation.  This part of the amine plant design is explained in good (albeit, not excellent) detail in the text “Gas Purification” by Arthur L. Kohl and Richard B. Nielsen.  Note that all amine plants rely on the use of a WATER SOLUTION of the amine.  We are not dealing with the pure compound.  Many researchers have experimented and reported on amine decomposition and degradation based on the PURE compound, not water solutions.  Take note and do not generalize when reading or talking about this subject.  You must stress the exact, field conditions under which the compound is being applied before accepting academic or research data and applying it to your industrial application.

 

The net, bottom line result of a good amine process design in my experience is that the amine reboiler operate at AS LOW AN OPERATING PRESSSURE AS POSSIBLE.  This fixes the temperature of the amine solution at a level as low as possible.  Remember, we are dealing with a water solution of the amine, so you are not boiling amine.  You are evaporating a vapor that is mainly saturated water vapor (steam).

 

Aanita reports that his/her reboiler is operating at 1.2 barg & 131 ^oC – and showing no sign of amine degradation.  There is no mention of what solution reclaiming (if any) there is in this process.  The expected saturated temperature for steam at 1.2 barg is 124 ^oC and the reported additional 7 ^oC in the reboiler doesn’t surprise me because this unit is using 50% (wt) MDEA solution and I would expect an increase in the boiling point with such a strong solution.

 

I hope the above experience notes are of some help in clearing up some questions and doubts regarding amine processes - and more importantly, that they make sense.

[aanita]

There is no reclaim option in amine system, however there is a filtration system. A split range of 15% of the total amine circulation take for filtration and return to Amine Tank. 

I am concern more about amrine bulk temperature instead of skin temperature. The temperature range of 360°F(182.22°C ) mention is supposed to be skin temperature.

Attached papers mention thermal degradiation temperature start more than 260°F(126.67°C). Sine we are operating MDEA plant with a bulk temperature in the range of 130 ~ 131°C, I am surprised, are we degradiating our amine ?

 

Regards.

Attached Files

•  Hc%20Processing%20May-June%201994.pdf   114.04KB   217 downloads
•  Amine Thermal Degradation.docx   23.55KB   197 downloads

[Art Montemayor]

Aanita:

 

Thank you very much for the attached literature.  What I read therein is exactly what I have stated in my prior post – the authors almost use my exact wording.

 

You now mention concern with a bulk temperature.  That is exactly the temperature(s) I refer to in my post, so I don’t understand the concern – especially since you have reported that after “more than 12 years of plant running we are not facing any corrosion or any integrity issue”.  That means you are having good results with your unit’s solution regeneration system.

 

I do not refer to a so-called “skin temperature”.  A skin temperature becomes a concern when one is employing a direct-fired reboiler; but you don’t tell us you have a direct-fired amine reboiler.  Do you?  Even then, how do you know what the skin temperature of the reboiler tubes is?  From your current operating record I would say that your reboiler is operating very well if you have not had degradation problems for 12 years.  It is difficult to make any judgment over your operation without having a full, detail description of what your plant is made of, who designed it, and how you are operating it.

 

Without specific basic data, I can only reply in generalities.  I hate to respond like that, but I have no alternative.

[aanita]

While I agree with Chandan20 that degradiation temperature is independent of pressure, my query is simple and specific: at what temperature (bulk temperature) of MDEA will start themally degradiate?

[Art Montemayor]

My specific response has been:

 

"However, the term “degradation” itself is subject to a lot of definitions. ALL AMINES are subject to degradation – temperatures cast aside."

 

The articles you submitted state the same thing.  If you cannot define WHAT degradation is and WHEN and WHERE it is identified, you are not being specific.  You are not alone and it is not a crime to lack a definition.

[chandan20]

Dear all,
Except higher operating temperatures, what other factors accelerate amine solution degradation?

[Art Montemayor]

Chandan20:

 

Read above post:

 

"Amine solutions are degraded by reaction with CO₂, oxygen, organic sulfur compounds, and other gas impurities to form heat-stable salts and amine degradation products. These contaminants cause corrosion and lower the treating capacity of the amine solution."