10 replies to this topic

[Abdelilah]

Hi Dear Engineers,

 

I'm reaching out for your support in understanding a recurrent issue with cyclic steam pressure pulsations.

We have a reboiler installed at the bottom of the NGL column that use MP steam as a heating medium. The reboiler vapor return temperature is controlled by a steam flow control valve. The condensed steam is routed to a condensate pot where the pressure is controlled by pressure control valve using also the MP steam. The pot is also equipped with a level control valve.

 

The concern:

We are experiencing a cyclic pressure pulsation in the condensate pot causing a mild intermittent hammering even though the column operation is steady and no operating parameters are changing.

 

Any insight or technical guidance to help me understand the root cause would be highly appreciated.

 

Thank you in advance for your support.

 

N.B: I have attached a DSC screenshot and the process PFD for more clarity.

Attached Thumbnails

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[breizh]

Hi,

Is this a new problem?

Did you try to operate the condensate pot in manual mode? Same for the boiler? 

Why do you need to bring steam to the pot?

Breizh

[Abdelilah]

Hi,

Did you try to operate the condensate pot in manual mode? Same for the boiler?

Why do you need to bring steam to the pot?

Breizh

 

1. We tried to operate all controllers in Man since we suspected some kind of valve stickiness or positioners malfunction. But same behaviour observed in Man.

 

2. the bypass steam to the pot is needed to maintain a pressure of 5 barg. The downstream pressure in the condensate return is 1 barg.

[breizh]

Hi,

Thanks for the feedback.

I don't have explanation for the spikes observed, especially if you say same behavior in manual mode.

EDIT:

What is the time base of apparition of the spikes, it seems to be hours between them, same amplitude, same period. So, nothing to do with controllers. You need to check the events in your process or utilities which could match this time.

Do you have way to scroll back the historical data to find when this started? it could be operation/action from the team. Do you have specific actions from operators or PLC/DCS at a given time during the shift. 

Breizh

Attached Files

•  CONTROLLING_STEAM_HEATERS.pdf   170.86KB   13 downloads

[Abdelilah]

Hi,

Thanks for the feedback.

I don't have explanation for the spike observed, especially if you say same behavior in manual mode.

Breizh

Thank you very much for your help. Hope someone else will have the answer.

[latexman]

Hi Abdelilah,

Again, is this a new problem, or has it always been this way?  Did it evolve slowly, or did it start all at once?

My best guess is slightly leaking reboiler tube(s).  The NGL accumulates in the condensate pot over about a 2.67 hour period and then they are purged.  It is acting similar to the build-up of a non-condensable gas/inert.  Second best guess is inert gas in the steam.

[Abdelilah]

 

Hi Abdelilah,

Again, is this a new problem, or has it always been this way?  Did it evolve slowly, or did it start all at once?

My best guess is slightly leaking reboiler tube(s).  The NGL accumulates in the condensate pot over about a 2.67 hour period and then they are purged.  It is acting similar to the build-up of a non-condensable gas/inert.  Second best guess is inert gas in the steam.

 

 

Hi Dear,

 

Thank you for your comment.

 

The problem has been present since the start-up and doesn't evolve. Tube leaking has been ruled out, as the FEED is mainly C3/C4. Any leakage with the associated stem high temperature would increase the pot pressure, driving the steam PCV to close and the flare PCV to open. None of which is occurring in our case.

Additionally, steam is free from inert since no similar issue is observed in other reboilers.

[carlos infante]

There is a constant cycle of the pot level perturbation. From the graph, it seems to be coming from the steam floe or related to it. Usually, when a period on control variables is observed in a distillation column, it comes of a perturbations in the feed or condenser.

 

Track the column variables and match on time with the level pot, searching if they are related.

 

Carlos 

[latexman]

Any inert gas/steam cross connections? One could be leaking.

[Abdelilah]

Any inert gas/steam cross connections? One could be leaking

 

No inert/steam cross connections.

Edited by Abdelilah, Yesterday, 11:34 PM.

[Abdelilah]

 

There is a constant cycle of the pot level perturbation. From the graph, it seems to be coming from the steam floe or related to it. Usually, when a period on control variables is observed in a distillation column, it comes of a perturbations in the feed or condenser.

 

Track the column variables and match on time with the level pot, searching if they are related.

 

Carlos 

 

 

Dear Carlos, Thank you for your feedback.

 

For context, we have 2 identical trains supplied from the same steam header. One train is operating smoothly without any spikes, while the second train is experiencing these intermittent spikes at flow above 4800 kg/h of steam.

 

At this stage, I suspect a potential hydraulic related issues. I wanted to visit site to evaluate this, unfortunately due health condition, I am currently unable to do so.

 

That's why I am reaching out here to leverage the experience of other professional people. Any insight is appreciated.