18 replies to this topic

[User]

Dear all,

I need your help on this.

My aMDEA reboiler level currently fluctuating and i couldn't find any root cause of it. Here is the details:

 

Currently the Circulation rate of the aMDEA is about 25000 kg/h the heating media of the reboiler is LP steam currently with pressure of 2.1kgG and the pressure is about 120 Degree Celcius.

we just replaced the tube bundles with new ones due to the old tube have leaked.

 

I'm just wondering why the level inside the shell is keep on fluctuating. Can any of you brief me on this.

 

[thorium90]

Foaming?

[User]

I dont think it foaming if foaming happen we would have detect it in the column as well. and further more we have running our anti-foam units

[Bobby Strain]

You presume that we know which fluid is on the shell side.

 

Bobby

[User]

LP Steam on the tube side and aMDEA on the Shell side of the reboiler.

This reboiler unit very critical nowdays. few weeks back at the condensate line of the the LPS there are hammering sound observed and we reduced the LPS inlet pressure and increase the opening of the condensate line Valve.

and now the level inside the reboiler is fluctuating.

[Bobby Strain]

I'm surprised that you even have a level indicator on the shell side. Maybe you can post a sketch of the system, including the column sump. And the reboiler type. Include the control valves and instruments.

 

Bobby

[User]

This things already being resolved. Its eventually the LG problems. we just isolated it and Line-up back and no fluctuation observed. anyhow, thanks to all of your comments and recommendations really appreciate it and I've learn a lot. Please do assist me in the future. Thanks again.  

[thorium90]

Bobby, I believe the level gauge is on the column, its just that the reboiler is connected to the column.

 

Perhaps OP could share his LG problem and solution to the world?

[narendrasony]

Perhaps it is a Kettle type re-boiler with level measurement downstream of weir. PO to confirm that.

[User]

 

 

 

This is the type of reboiler with the LG at the weir side.

 

The LG Gasket is actually torn therefore its make the flow through the LG not consistent therefore its showing fluctuations we already replace the gasket and not fluctuations is observed. I think during Last Dec SD they didn't properly fit the LG.

[Satyajit]

Dear Msia,

                   I think leak in LG gasket may be a coincidence with LP steam condensation. My understanding based on your description is improper condensation. As you have reduced the steam pressure and temperature , you are getting proper condensation and so improved thermosyphoning. I am eager to know how did you reduce your LP steam header pressure and temperature without affecting whole LP steam steam network which is normally working at 3.5 kg/cm2g and 175C. Did you throttle steam inlet valve and some quenching?

Kind regards,

Satyajit

[Art Montemayor]

Satyajit:

 

You are mistaken.  This is a Kettle type reboiler (BKU) and, as such, there is no thermosyphoning effect taking place (or expected).   All the kettle reboiler does is effect vaporization by maintaining a heating coil (in this case, a steam coil) submerged under the reboiler's liquid level.  The product of such a reboiler is saturated vapor.  The product of a thermosyphon reboiler is entirely something else: a two-phase mixture of liquid droplets and saturated vapor.

 

I also am perplexed by the explanation of the liquid level sightglass causing a reboiler upset.  But without a clear explanation or a detailed sketch of what kind of level gauge and where it is located on the reboiler, we haven't much to go on as to a sure cause.

[Satyajit]

Dear Art,

                Thanks for your kind explanation. You are right.

Kind regards,

Satyajit

[Bobby Strain]

Art,

  I don't normally speculate. It was never mentioned that there was any problem that I recall. Only observation of a fluctuating level in the LG.

Someone probably observed a leak and then fixed it.

 

Bobby

[User]

Dear all,

 

our concern is if the level inside the reboiler is actually fluctuating it may cause the coil not fully submerged into the liquid and besides that our main concern is the nucleate boiling occurs inside the reboiler.

[Art Montemayor]

Msia:

 

Your information is incomplete and misleading.  You are not being specific when you state you have problems with the reboiler liquid level.

 

The basic fact of the matter here is that you have a kettle reboiler - as you have shown in the sketch supplied.  This type of reboiler has a vertical WEIR inside the shell that is 100% seal-welded.  In other words, the amine solution on the tube bundle side of the weir cannot enter the other side of the weir (the part that is being measured by a liquid level gauge) without going over the weir's horizontal cut.  This is what sets and ensures that the tube bundle will be 100% + covered by amine solution being vaporized.

 

The level you are seeing is the liquid level that DOES NOT COVER THE TUBE BUNDLE.  Therefore, you have no reason to be concerned by this level "fluctuating" (which I seriously doubt, if you are operating the reboiler the way you should).  The level over the tubes CANNOT FLUCTUATE.  It is being held constant by the weir.  There is no "nucleate  boiling" taking place; all the reboiler does is creaste a gentle, simmering vaporization of a portion of the solution.  I know, because I have designed and built these type of amine reboilers in the past and I installed sightglasses on some of these in order to disprove the existance of so-called "foaming" - and I did.  The boiling is very gentle, with no wave action or level fluctuation.

 

Besides all of the above facts, you should know that the level seen in the reboiler level gauge should be steady and constant because it is being held there and controlled by the level control valve on the lean amine going to the contactor tower.  This control valve fixes the steady flow rate of amine going to the contactor.

 

Without you furnishing a decent, detailed sketch of your reboiler and where your level gauge is located and what you have "fixed", we are unable to add any further advice, comments, experience, or expertise on this topic.  What you furnished as your reboiler sketch was a downloaded illustration from the Penn State website offering hydrocarbon phase equilibria information.  You should generate your own, specific sketch.

[User]

Sorry for the incomplete and inaccurate information,

 

Currently after flushing of the LG few times we still observed fluctuations. This problem is restarted again.

This is the reboiler system

LG is located at the bundle side. It supposes the bundle when fully submerged the LG should be at 70%.

Now it fluctuates at 50-60%. Our LP steam Pressure is about 2.1kPa. And the condensate valve (FIC) is open at 40%. We observed hammering at condensate line when the pressure of LP Steam is higher and the opening of the FIC is reduced.

 

Please advise.

[Satyajit]

Hi,
I think level in your regenerator bottom is at lower side. Try to increase regenerator level 5-10 percent more in steps; it will help you to increase l level in reboiler. I would prefer to increase reboiler level to 80~90%. it will help to have stable heat transfer and so also steam condensation. Hammering will disappear. The reason for hammering is steam blow through condensate line. Please do check amdea in condensate to remove the suspicion of tube leak in reboiler.as a matter of safety, i would prefer to keep lp steam pressure at 3.5 kg/cm2g and 150 C as designed.
Please reconfirm foaming tendency of the solution by checking foam height and foam collapse time and other process parameters like column levels, stripper top temperature, column dp . Perform detail solution analysis, check for HSS in the solution. Are you adding any amerol now? if yes, what is the frequency and the amount?
Kind regards,
Satyajit

[Bobby Strain]

Still a lack of information for us to be helpful.

 

Bobby