6 replies to this topic

[ravi.s]

Dear All,

We are using MDEA solvent for Acid Gas removal from Natural Gas. Since 2 weeks we are facing the Amine Stripper column pressure & column levels fluctuations heavily, which causes straving of Lean amine feed pump. There is no change in the feed gas quality & all other operating parameters are as usual. Can u please help us to find out the root cause/ remedial action?

[Satyajit]

Dear Ravi,
There could be many reasons for foaming. It's nice that you have got the symtoms of foaming. Normally AMDEA system is a really very good and energy efficient and friendly system for acid gas removal system.
You have to start a brain storming session with your staff to find out more informations and then start a Root cause analysis.
I am sure ,you will get the answer.

The propable reasons are:
1. High CO2 loading.
2. improper regeneration of amine solution.
3. inefficiency of trays ( to check the trays for leak,gasket,elevation etc).
4, presence of HC, oil and grease in the system.
5. TSS in the system.
6. Decomposition of antifoam agents you have added before.
I think people working in the plants are the best doctors provided they have sufficient skills to understand and realise the issues.
you can contact BASF rep for this, they will be more than happy to help you.
My last word is :to comment on your problems, one must have the drawing of the columns,trays,PFD with current data, lab analysis etc.
Hope you got some ideas.
Cheers!
Satyajit

[ravi.s]

Dear Satyajit,

Thanks for the helpfull tips. I would like to share the some information

1) The CO2 loading is < 0.44 M/M also lean loading is well within limit.
2) The unit was under shutdown and cleaned one month before the foaming symptoms
3) Total Amine inventory is replaced during S/U & lean amine solution is free of HCs, Oil & Grease.
4) However, column internals are not checked during shutdown, now it may be a major culprit.

We have increased the stripper bottom temperature to 122 deg C from 120 deg C which resulted in increase in reflux flow (however lean loading @ 120 degC is < 0.02 M/M). Since then the frequency of DP fluctuation is minimized.
Cheers!
Ravi

[Satyajit]

Ravi,
What is your operating temperature of the stripper. If it is atmospheric, the temperature of 120C is at higher side, You will have huge reflux and which will cause more disturbance on the stripper top washing trays.
I can foresee that there will be carry over of AMDEA along with the CO2 if the temperature is too high.
One more question: the CO2 loading expressed in M/M. what is t is that?
Please provide more data for better and meaningful discussion.
How much is your Lean temperature at the inlet of Absorber and Gas inlet temperature?
Do you have carbon filter?
What is the frequency of antifoam injection?
I understand your CO2 slip incraesed and also the circulation of Lean solution flowrate.
This is a common plant problem. Earlier it is handled,safer is the plant and its reliability.
Best of luck.
Satyajit

How

[ravi.s]

Hi again,
The stripper operating pressure is at around 25 psia, for this condition I feel the temperature of amine at stripper btm should be between 119 to 122 degC with out carryover of amine along with the saturated acid gas vapour at the top of the stripper. if there any carryover, it will be condensed in Acid Gas condenser & recycled back to the system alongwith reflux water. we have analyzed the reflux water for amine & found only 0.2 to 0.5wt% of amine.

The CO2 loading expressed as Moles of acid gases per moles of Amine (M/M)

The present conditions for the feed gas temp: 35 degC, & Lean amine : 50 degC.

15% slipstream flow of lean amine is passing thro' Activated Carbon bed. And since the foaming problem persisting, the antifoam dosing started to maintain around 10 ppm antifoam concentration. At heavy foaming occurance, sometimes antifoam dosing increased.

There is no significant change in the sweet gas CO2 content as well as lean amine circulation rate.... the major foaming symptoms occured at stripper only.

[Satyajit]

Ravi,
I think at this stage you would like to continue your plant operation keeping eyes on all operating conditions, solution strength, carry over of amine solution, DP across stripper etc.
Looking into your data and operation philosophy, I can say that operation of carbon bed should not be continuous basis.
It should be a batch process. I hope, you have a mechanical fiter upstream of your carbon bed,
You should stop your mechanical filter when you are dosing antifoam.

2nd thing, you should think of keeping Carbon filter operation. If you are keeping continuously on line, you create more problem . It will create more foaming if it is in continuous operation. You should keep in line for few hours daily depending upon the situation.

How much is TSS and Fe in your solution. Please check it before and after your carbon filter.
Are you facing increase in CO2 slip as well. you also need to check your AMDEA sampling and analysis part as well. The CO2 loading in solution differs at hot and cold conditions.

Regards,
Satyajit

[Todd.D]

Dear Ravi,
We seem to be having a very similar problem at our plant. just wondering what you found to be cause/ solution.
thanks,
Todd