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Antifoam Dosing In Mdea Sweetening Unit


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#1 apex

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Posted 29 September 2014 - 08:48 AM

Dear friends,

                      We are using MDEA to remove H2S (less than 4 ppm) & CO2 (maximum slippage). We are encountering flooding problem in regenerator. This flooding subsides after addition of antifoam for 1 min or so. This effect of antifoam lasts for around 10-15 days & then again flooding disturbs the regenerator. The problem is that the antifoam solution which we are using is a mixture of 10% by wt of antifoam & 90% by wt aromatic rich naphtha as a dispersant. If we add more of antifoam then we will contaminate MDEA with hydrocarbons & may lead to foaming subsequently. Can you suggest me an antifoam which can be added to avoid such contamination.



#2 RockDock

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Posted 29 September 2014 - 10:23 AM

An amine unit should not need an anti-foaming agent if proper filtration and conditions are followed. When was the last time your filters were changed? Do you have a coalescer? Are you condensing hydrocarbons in the absorber?



#3 apex

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Posted 29 September 2014 - 10:56 AM

We have precoat filters & precoating is done every 12 days or if the flow through the precoat filters is reduced(below 25 m3/hr). The total MDEA flow rate is 145 m3/hr & precoat filter is a side stream filter. After precoat filter we have charcoal filter through which 2.5 m3/hr of flow is maintained & after charcoal filter there is cartridge filter to contain charcoal fines. We do not have problem of hydrocarbon condensation as inlet gas temp is maintained way above dew point temp.



#4 himant

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Posted 30 September 2014 - 01:05 AM

Normally 20% of total amine flow rate is sent for filtration.

 

I presume that 25 m3/h is maintained through charcoal filter (against your quoted figure of 2.5 m3/h). 

When did you replace your charcoal filters? And what is your oil content in amine? What is color of your amine? Pale yellow?

 

Normally, antifoam is diluted using DM water/Condensate... it may be your licensor specific requirement to dilute with rich naphtha

 

If you want to change your antifoam, contact DOW or other licensor companies.

 

Regards

Himant



#5 P.K.Rao

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Posted 04 October 2014 - 05:14 AM

Please also check HSS. (Heat Stable Salts). They go on accumulating and reduce the efficiency of MDEA. They may also be resposible for foam. If they are high (say more than 10% of MDEA concentration), you will have to remove them



#6 P.K.Rao

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Posted 04 October 2014 - 10:23 PM

For any further assistance, please contact me



#7 fallah

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Posted 05 October 2014 - 01:18 AM

apex,

 

As far as i know the antifoam of "Aqueous Silicon Solution" which is intermittently used for a few minutes in case of severe foaming might remove the problem of amine contamination due to using mentioned antifoam included aromatic rich naphtha...



#8 apex

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Posted 05 October 2014 - 02:15 AM

The MDEA used by us is having HSS in the range of 0.4-0.6%. Otherwise the solution is clear & does not have filtration issue. Can this solution foam? Through the simulation of the unit  I could identify that there is foaming in the regenerator which was limiting the column hydraulically. Initially we were thinking that the tray internals were damaged but after addition of antifoam within 30 min the regenerator got stabilized. The absorber column is not experiencing hydraulic problems due to foaming.  



#9 P.K.Rao

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Posted 05 October 2014 - 09:55 PM

You can do a foam test in he laboratory on a fresh MDEA (prepared in the laboratory) and used MDEA solutions and compare the foaming level of each



#10 Art Montemayor

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Posted 07 October 2014 - 01:01 PM

I agree with RockDock's comment.  The moment you decide to add ANY ingredient to an amine solution other than the designed chemical, you are "dancing with the devil".  In my experience it is only a matter of time before you are forced to pay the price.   I have found through the years I dealt with amine systems that any indication of solution foaming was due to:

  • a bad unit process and/or mechanical design;
  • contaminants in the feed gas;
  • additives in the solution;
  • lack of reclaimer and/or correct activated carbon filtration.

I never experienced a foaming problem when operating with pure aqueous-amine solutions and using carbon filters 100% of the time.

 

Once you employ additives over and beyond the design of the system, you are at the point where you are committed to operating a non-designed absorption system and bad things inevitably start to happen with only one alternative: dump the entire solution and start again.



#11 himant

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Posted 07 October 2014 - 10:11 PM

I just want to share my experience here...

 

I have worked in Gas Sweetening unit operations for three years and we have continuous dosing of antifoam in amine system, though the antifoam solution is made in DM Water/Condensate. It was also observed that moment we stopped antifoam dosing, foaming starts in a minute or two. (in absorber)

 

I am not sure if there was any bad process or mechanical design regarding foaming but we never had contaminants in feed gas. Even if there is any contaminants (liquid HC), feed gas was sent to absorber via knock out drum and then after coalescer.

 

Filtration system was working very good. Oil content in amine was never above 60 ppm and HSS was hardly 0.2 wt%.

 

However,we used AMDEA by adding additives in MDEA solution. This could be one of the reason but that additive was supplied by Licensor only (DOW chemicals)

 

I are still not sure about the possible reasoning for foaming. 

 

Regards

Himant 



#12 P.K.Rao

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Posted 07 October 2014 - 10:24 PM

I suggest you read "Amine Best Practices" in refiningonline portal (www.refiningonline.com). A full chapter deals with foaming.. 



#13 Art Montemayor

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Posted 08 October 2014 - 11:35 AM

P.K.Rao:

 

Thank you very much for the reference to the website www.refiningonline.com.  This website contains some very informative amine processing information valuable to operators.  I am attaching a copy of the download, “Amine Basic Practices Guidelines” offered by them and, I believe, referred by you.  Unfortunately, the full chapter on foaming that you mention is merely 20 lines long.  But this is to be expected, in my experience.  All the volumes written on amine foaming phenomena through the last 50 years amounts to relatively the same amount and quality of comments:  not much is still known about foaming in amine units, what causes it, and how to cure it.

 

I would hope that all members reading this thread note the paradoxical statements made in the attached document:

  • Technically, only surfactant hydrocarbon components cause foaming;
  • Anti-foam compounds are, in themselves, surfactants.

Consequently, it is stated that excessive (?) antifoam usage can actually promote foaming.  How much is “excessive” is not defined.

 

Perhaps this confirms my experiences: I never had foaming in amine solutions, never used any additives, and always operated as pure and clean a solution system as I could – ensuring that anything entering the system –especially the feed gas – had no contributing contaminants.  Strict adherence to plant and operating cleanliness always paid off for me when I operated and managed plant operations.  That was one of the first principles taught to me by my great mentor, Alf Newton.  He always emphasized keeping a process simple and clean and he taught me that as plant manager my first duty was to be the first person in my plant complex early in the morning and walk through all the plant bath rooms.  The cleanliness and upkeep of the bath rooms reflected the cleanliness and upkeep of the plant itself.  He was absolutely right!  I followed this guideline through my career in operations and it paid off in dividends.  I always made it a point to inspect the units and their bath rooms first when I visited or operated plants.  A dirty or filthy bath room always related to a dirty or badly operating plant or unit.  It just makes for common sense.  By demanding cleanliness in my equipment, facilities, and in the process operation itself, we avoided contaminants and recurring process upsets and operating problems.  If you maintain your amine solutions clean and devoid of additives that were not considered in the original design, you have a greater chance of avoiding any side reactions or process problems.

 

I would relish the opportunity to meet with an engineering contractor and have him/her explain in clear, rational terms why an amine system designed by him/her requires an additive in order to avoid foaming.  And if so, then what are the consequences of that addition to the life, efficiency, and stability of the operation.  And this conversation should take place with the supplier of the amine present.  I could be wrong in this, but I don't believe any engineering contractor, amine supplier, or antifoaming agent supplier will ensure, guarantee, or warrant the results of adding antifoam to an amine solution.  If we do it, we do it at our risk.

 

Attached File  Amine Basic Practices Guidelines.pdf   298.59KB   158 downloads



#14 apex

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Posted 08 October 2014 - 12:46 PM

I completely agree with Art with respect to cleanliness. But I would like to mention that MDEA in my Gas Sweetening Units is clear & there is no foaming in the absorber while regenerator foams so badly that it seems there is something wrong with the column. After addition of anti foam the unit gets stabilised in an hour or so & the product gas is <4ppm of h2s. This phenomenon happened in 4 units & the treatment given to all four was same with similar results. This betterment lasts for around 20 days & again addition of anti foam corrects the problem.

#15 Philip le Grange

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Posted 06 January 2016 - 10:50 AM

Hi Apex,

 

You are not alone, foaming is by far the most common problem in Amine systems. Normally this is due to a chemical getting into the system that has surfactant properties. Often this can be eliminated and the foaming removed however some gas plants have surfactants in their feed gas that cannot be readily removed and the only answer is continual anti-foam injection.  Do you have BTEX (Benzene, Toluene, Ethyl-Benzene & Xylene) components in your feed?  These are soluble in amine and will affect its surface tension.

 

Kind Regards,

Philip le Grange

(www.AmineExperts.com)






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