14 replies to this topic

[Rahimzadeh]

Dear :

 

Please tell me what happen when the gas flow to amine absorption tower was half of design but amine solution was same as design .

 

Best regards

 

M.R.Rahimzadeh

[Erwin APRIANDI]

More CO2 and H2S content are absorbed, but since there is a contact time which is limited by the design of the absorption tower, therefore the twice of the amine flow will not be directly giving you 2 twice of absorption.

[Rahimzadeh]

Thank erwin:

 my main question is that risk of flooding is increase or not ?

 

best

[Human6]

I believe flooding is when the vapour flow is too high, which causes entrainment in the column. 

[shan]

Waste energy for Amine regeneration and Amine pump around.  No flooding.

[Art Montemayor]

What you are describing is nothing more than a normal, conventional "turn-down" in unit capacity.  This happens in all Amine units when the flow of process gas is reduced while the amine solution is maintained at the design flow rate (which is what should normally happen).

 

You obviously are confused about the term "flooding" and I recommend you use the Google search engine on the internet to find the formal description of "flooding" in an absorption column.  It is NOT what you describe.  All you have described is a processing plant capacity reduction - which happens all the time.  The amine system continues to work as it was designed to do for removing the capacity of acid gas contained in the process gas during normal, full capacity.  If the process gas flow rate is reduced, then the amine regeneration system continues to work at design rates, but in a very energy inefficient manner because you are circulating excessive amine solution for the flow rate of process gas actually going through the amine absober (contactor).

[latexman]

Pardon my lack of knowledge in this area, but could he be referring to "weeping"?

[gegio1960]

Some brainstorming points:

1) Latexman is right. You've weeping when the gas flow is too much low with respect to liquid flow.

2) Normally the turndown for the tower internals is specified around 25-30% of the design flow.

3) You can also reduce liquid flow when you have lower gas flow. This can be done w/o troubles within the plant turndown limits. See Art post  #6.

4) Low gas flow will mainly go towards weeping. Low liquid flow will mainly go towards troubles with the min flow of the pumps.

[Rahimzadeh]

Thanks mr. ART

 i believe Latex man and Gegio 1960 are correct .

I our case the bottom of absorber get level but reboiler inversely can not take a level , we force to shut down the plane for preventing over heating the reboiler tubes.

[shan]

Weeping do nothing to liquid level of tower bottom.  There is no reboiler on an absorber tower.  "Shut down the plane" or shoot down the plane"?  747?

[Rahimzadeh]

Pardon me it was mis typing  my mean was shut down the plant

[shan]

You are cool.  Otherwise, too boring. 

[ColinR33]

Late entry into this discussion, but are you referring to the Amine Contactor (Absorber) or the Amine Regenerator (Stripper), or both?  As Art mentioned, low gas rates in the contactor are a normal turndown operating case, and as Latex and Gegio state, weeping could be an issue.  You would have to check the trays for minimum turndown (or channeling if using packing).  The reboiler is on the Regenerator, which is a totally separate piece of equipment. The lack of liquid in the reboiler could be entirely unrelated to a low gas flow in the Contactor.  We would need to see a schematic of the Regenerator, especially the reboiler set up - eg. what type of reboiler, relative elevations, type of draw off (chimney tray, draw tray, off the bottom of the tower, etc).  If you are using your bottom valve tray as a draw to the reboiler and you are at low rates/startup and not generating steam in the reboiler, the lack of vapour traffic in the bottom tray could cause weeping of the amine directly into the sump of the vessel, preventing flow to the reboiler.  A startup bypass from the bottom of the tower to the reboiler inlet line would be required. You could also have plugging in the liquid line to the reboiler or high fouling in the reboiler itself (do you have a level gauge on the reboiler itself?).  In any case, much more information is required to accurately diagnose the problem.

 

Cheers,

Colin Key

[Satis M]

Dear Mr. Rahimzadeh,

 

Appreciate your interest in solving your problem in a logical way, instead of trying out random adjustments in the plant.

 

As the members have suggested, there are no chances of more fluid flow to your Amine regeneration column. You can check the status valves (auto/manual/ cascade mode), may be the heat generation may be low, in the absorption column, as the gas flow is reduced.

 

There must be a heat exchanger before the regenerator column, that duty might have increased, and heat supply valves may be opening full to meet the heat load.

 

Cheers, Satis.

[ZBR]

Agree wit Colin, if you have last tray as take off to reboiler then you need to check that tray

 

- If is a valve tray and properly designed it should work ok by valve closing due to low vapor velocity. If you have any other type of tray like a sieve tray   (which should not be) it will always give you trouble on turn down by weeping and liquid flowing through tray inetead of down comer.

- If its packing your reboiler take off should be from bottom.

 

check the physical conditions of your tray also most valve on tray get corroded, stuck and are even disloged from their slots and this is not a unlikely situation. 

 

 

But all this is a speculation till we get a schematic from you (see attach also)

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