5 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   7 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.