16 replies to this topic

[rizwangoheer]

I' am working as Process engineer working in Natural Gas Treatment facility.

 

Recently, on of the Amine Absorption columns in our plant is behaving strangely as temperature on tray 5 & 6 is fluctuating while other trays are stable.

 

This column is a low pressure (160psig) column, using floating valve trays. As we have 21 Trays from top to bottom of the column and we managed to monitor temperature fluctuation across the column. It is very strange that temperature is fluctuating only on tray 5 & 6 and remaining trays are stable.

 

A few points to highlight which we already worked on but still problem is there.

 

1. Fluctuation in feed gas H2S and CO2 concentration: Feed gas composition in terms of H2S and CO2 remained  constant and as such will not cause any fluctuation during the absorption process.

2. Fluctuation in the lean DGA flow control valve output: Both lean DGA flow control valve and tray 6 temperature indicator control tuning were checked by control engineer and retuning done for the temperature control.

3.Faulty flow and tray temperature  transmitters: All related flow and temperature transmitters re-calibrated and now functioning properly.

4. Fluctuation as a results of foaming: The antifoaming system is working properly, and the foaming tendency analysis indicates no faming. Liquids hydrocarbons levels also drained from the inlet separators to ensure that no hydrocarbons carry over occurs.

5.Contactor differential Pressure: The contactor differential pressure is well with in the recommended limits.

 

If anyone have opinion the cause of this strange phenomenon for temperature fluctuation only on  tray 5 & 6., please share with me.

 

thank you so much.

 

 

[Bobby Strain]

Sounds like you are not experiencing any problems related to acid gas removal. If not, don't worry about temperature fluctuations. Go solve real problems. And, you should not post as a student unless you are.

 

Bobby

Edited by Bobby Strain, 22 June 2017 - 01:07 PM.

[Mahdi1980]

Hi,

It is not easy to recommend a solution just based on your description because there are a lot of parameters involving the process which shall be checked one by one.

If the process conditions have not been changed and the instrumentation and control system are fine as you said, a mechanical problem might be happen on trays 5 and 6. You should check them in the first shut down.

 

Anyway, Please let us have some trends of the temperature, flow of the sour gas and Amine solution as well as the pressure of the column before the problem time ( Normal conditions ) and after that (now).

Also a simple sketch of your column and its temperature control system ( like a P&ID ) can be helpful.

Has this problem make any negative impact on the quality of the outlet product?

[Art Montemayor]

rizwangoheer:

 

Please respond to Bobby Strain's comment - are you a student?

 

If you are not a student, why are you posting in the Student Forum?

 

Await your response to rectify this discrepancy.

[rizwangoheer]

Hi Bobby Strain,

 

First I would like to say sorry as I did not realize that I am posting on student forum. Definitely I am not student but I want to discuss this real issue at our facility. So please guide where I can post this so that I can have some good discussion with the experts in Gas sweetening like yourself and Art Montemayor.

 

Please response if you guys can share your experience on this subject.

 

thanks

[Bobby Strain]

You have not indicated whether the acid gas removal is satisfactory. If it is, don't be concerned about fluctuating temperature.

 

Bobby

[Art Montemayor]

Since you are not a student, I am moving this thread to the Industrial Professionals Forum.

 

Thank you for clearing this up.

[rizwangoheer]

Dear Bobby Strain,

 

Yes, we are meeting the sweet gas specifications and all other operating conditions in Amine contactor are normal. I understand your point for not worrying about temperature fluctuations if product spec is ok. But temperature fluctuation is some time goes up 40~50F which may be an indication for any major upset in the system in coming days.

 

Any thoughts please.

 

thanks

[Mahdi1980]

 

You did not reply my post with regard to preparing more data of system!!! and without them we cannot help you.

[Art Montemayor]

Rizwangoheer:

 

There are no international standards on tray numbering within distillation or absorption columns.  Therefore, it is not possible for our members to know where your trays #5 &6 are located in your 21-tray column.  Are they in the upper - or lower - 25% of your column?

 

There may be a discrepancy or misunderstanding in your statement:

 

“But temperature fluctuation is some time goes up 40~50F which may be an indication for any major upset in the system in coming days.”

 

In English this would mean that if your absorber is normally operating at 100-120 ^oF, the temperature at your indicated trays is showing approximately 170 ^oF.  Is this a correct interpretation of what you state?  What are the specific temperatures at the top, bottom, and at the indicated trays in your DGA absorber?

 

You state:

• Your impure gas feed rate is kept constant as well as its composition;
• Your product gas meets specifications and hasn’t varied;
• Only two trays - #5 & 6 - are “fluctuating” in temperature (whatever that means); the rest of the trays are all stable in temperature;
• You don’t state if this is a recent problem or a recurring one.  Has the absorber always behaved this way?

From what you describe, I agree with Bobby Strain’s comment.  “If it ain’t broke, don’t try to fix it.”  If your product gas is meeting design criteria, why worry about measured factors that don’t correlate with the operation?  If the absorber were truly undergoing a large, abnormal temperature “bulge”, this would indeed affect the efficiency of the acid gas removal and the negative results would immediately reveal themselves in the product gas purity analysis.  However, your absorber is producing purified gas at or above the specified conditions - and that is primarily what is expected of it.  Therefore, any measurements that show that it should be producing in a negative manner are either erroneous, mis-interpreted, or not being taken correctly.

 

I agree with your concern regarding the quality of the readouts on the tray temperatures and I certainly am not suggesting that you not give them importance.  However, as long as your unit is producing up to specifications, your concern should be more about the reliability of such readings.  I suspect that you are operating the Fluor Econamine process for acid gas removal and if such is the case, you should have a detailed and specific explanation of the expected absorber temperature profile in your plant manual for the specified process gas flow rate and composition.  I worked for El Paso Natural Gas and also worked on Huntsman Projects.  The process is a well-defined one and has been around for +50 years.  Your unit designer and engineering company should have furnished a well-defined operating and maintenance manual for the unit.

 

I am attaching a detailed copy of information on the subject that can be found in the classical “Gas Purification” book.  The subject is well explained and this material should address a lot of your concerns and comments.  This 5^th edition covers the subject material in a more detailed and experienced manner than the older editions with Kohl & Riesenfeld.  This document should help guide you to attacking the probable source(s) of the problem you describe.

 

As Mahdi1980 states, more process basic data is required to probe deeper into the problem.

 

 Amine Absorbers Temperature Profile.docx   334.44KB   42 downloads

[rizwangoheer]

 

Dear Mahdi,

 

Many thanks for your comments and I am really very sorry as I was away from my work location. But we are still facing the same problem. I have attached herewith Unit PFD and operating data trends for your comments. even with this fluctuation in tray temperature we are meeting the treated gas specifications.

I agree with your comment that this fluctuation may be due to some mechanical problem but I just want to check if there is any process condition which can make this upset.

 

Please have a look on attached data and provide your feedback.

 

Many thanks.

Attached Files

•  Plant data.xlsx   502.96KB   26 downloads

[rizwangoheer]

 

Dear Art Montemayor,

 

 

Many thanks for your very detail response and I am really sorry I was away from my work location. Still we are facing the same problem as have tray temperature fluctuation on some tray 5,6 but we are meeting the treated gas specification. As I already motioned we assess all process operating conditions but all a normal and no thing is wrong. Now I will try to give the information as your requested in your post.

 

1. Column trays numbering is from bottom to top and this fluctuation is mainly in the bottom 25% of the column.

2. Column normal operating temperature are Top/ Bottom (140/ 185F) and upset tray max temp is 235F and please also see attached plant in my response to Mehdi post.

3. Agreed with your comment that if the product is on spec then why we worried. As per readings Bulge temp is with in maximum limits as given in design data and we do not see any fluctuation in treated gas specification. We are suspecting if there is any foaming is column which is making this upset but all plant data is not support this. Also our instrument already did the recalibration of all instruments to fix this issue but this did not help.

4. Thanks for your help to mention about the "Gas Purification" book which I have with me. This is really a great book and  I tried to find any reference to our problem but still we are struggling to fix it.

 

It will really great if you can have a look on the data attached in my previous post to Mehdi comments.

 

Thanks and appreciated for all your valuable comments.

 

regards,

rizwnagoheer

[MTumack]

I would guess that perhaps you have inconsistent feed conditions and thus mass transfer efficacy in the first couples trays before the tray valving starts to make your flow regime more consistent through the rest of the tower. This would cause the bulk of the chemical reaction and also your temperature bulge to wander.

 

If this is the case, could be several things;

1) Poor inlet distribution to the tower (maybe a fouled/fouling feed openings, or no feed pipe etc)

2) Inconsistent tray flow regimes (usually from older style trays, fabricated bubble caps etc)

3) Inconsistent feed conditions; perhaps temperature of inlet gas fluctuates with ambient temperature? Most things I deal with here involve winterization and thus pipe-racks have insulation and heat tracing to keep temperatures locked in, but if you operated in a warmer coastal region and had temperature fluxing from say 10 to 30 degC on the inlet gas and only a pressure controller monitoring the raw gas' you could see a significant change in raw gas input. Given that your posted lean amine flowrate seems to follow and lag slightly your fluctuation in tray 4 temperature, i'd say this is feasible.

 

 

Regardless, as long as you have operating head room (which at 25 trays is feasible) and are seeing good outlet conditions you are likely ok. Do you have data on your outlet gas flow rate?

 

Anyway, I would suggest you likely have other things plant-wide that could be worked on or improved that would provide more value. That said, I would continue to monitor and ensure your outlet specs don't see any variations in case you have a growing problem.

[Bobby Strain]

Your data shows everything to be normal. The behavior you see is typical of an absorber with feed gas containing high levels of acid gas. So, you should move your attention to more pressing matters.

 

Bobby

[rizwangoheer]

Dear Bobby Strain,

 

Many thanks for your value able comments. Actually we are worried about the behavior of this amine column because this different than the other amine column which is also processing the same feed gas. Please see attached the temp trends in my other which shows this different.

 

Why GT#1 amine contactor have more temperature fluctuation than the other GT#2 amine contactor if both are processing the same feed gas with same conditions and same compositions.  Both units are the same copy to each other but showing different behavior that,why are looking to find the reason behind.

 

It will be great if you can good suggestion and other than this we are also looking for other pressing issue at our facility which can make value for us.

[rizwangoheer]

 

 

Dear MTumak,

 

Many thanks for your value able comments regarding the problem which we are facing at our gas treating facility.

 

As I understand form your comment that tray 5& 6 temperature fluctuation is due to inconsistent feed gas conditions. But if this is the case then why other Gas Treat unit GT#2 is not showing the same behavior as we are feed the same gas partially to GT#2.

 

Also the tray 3 & 4 are below tray 5 & 6 but both are showing more stable temperature which indicate that the feed conditions are not do much to make tray 5 & 6 temperature fluctuation. I agree that the given reasons in your post may have some impact on tray temperatures but this is not upset in our case.

 

Also again I want to mention that treated gas is on spec and flow rate is following the same pattern as feed gas.

 

thanks & regards

Attached Files

•  GT #1 & GT#2.xlsx   353.86KB   21 downloads

[MTumack]

What all is different between the two trains? Do they have identical flow? Inlet compositions? Designs? Do your columns both see a similar level of total heat of reaction?

 

I would suggest consulting with the internals OEM (IE Koch-Glitsch, Sulzer, Raschig, AMACS, HAT International etc) that supplied the trays, see if they have any experience with these kind of fluctuations.

 

It might be that your GT#1 is within expected results and you are seeing tighter numbers for your GT#2. Also could be a minor install error on GT#1; I have seen trays installed backwards, man-ways left open, entire toolkits left on trays, etc.

 

I must concur with Bobby though, if you are seeing the outlet results you want, and outlet spec is comparable to GT#2 then I would continue monitoring the data, but continue on to other potential operating issues until you have either spec not being made or a pre-scheduled shutdown (in which I would schedule an inspection of the internals.).