Screw Compressor tripped due to low Suction Pressure

[u062268]

Hello everyone;



In our Plant we are using a Screw Compressor to compress Hydrogen (Recycle & make-up) to get the desired discharge pressure for Hydrotreating Reactors. At 09:11:07 am, the compressor got alarm for Low Suction Pressure from three pressure indicators (Part of ESD system) as shown in the attached picture. After 4 seconds only ( at 09:11:11) the compressor tripped due to low pressure of suction (16.04 barg). The normal suction pressure of compressor has to be ( 17.6 barg).


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Actually the compressor tripped in just seconds after alarm was showing and suction pressure dropped by around 2 bargs in four seconds only. Nothing was reported abnormal before tripping except the alarm from suction Drum pressure followed by alarm from ESD indicators of suction pressure, other indicators were reading normally. No upset reported before tripping from other parameters in the Area.

We expected that the Pressure Relief valve opened for instant causing Low pressure in Suction Drum and re-set itself automatically because it is (Modulating Relief Valve). But How it comes that Flow indicator (46272.1 Nm3/hr ) didn’t capture any reduction in flow while the pressure indicators in its upstream and downstream were reading low pressure four a few seconds??!!!
Does the RV capable to reduce the pressure by 2 barg in just 4 seconds?

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Any suggestion???

I feel the RVs are not the reason .

[RANGER1]

Man from Oman, Relief valves could reduce pressure of course, but if system operating in stable conditions prior to low pressure cannot see why they would relieve momentarily as you say. Can you check trends to see all flows from control valves entering suction drum were stable? Was compressor fully loaded, could it have overshot set point for whatever reason mechanical hiccup or other. Hydrogen is very sensitive to temperature change, did ambient conditions change, rain, storm etc.

[u062268]

Man from Oman, Relief valves could reduce pressure of course, but if system operating in stable conditions prior to low pressure cannot see why they would relieve momentarily as you say. Can you check trends to see all flows from control valves entering suction drum were stable? Was compressor fully loaded, could it have overshot set point for whatever reason mechanical hiccup or other. Hydrogen is very sensitive to temperature change, did ambient conditions change, rain, storm etc.



Dear RANGER;

Everything is stable before tripping and that is very ware !!!

Any other causes may cause sudden reduction in pressure?

[Iceman717]

Dear RANGER;

Everything is stable before tripping and that is very ware !!!

Any other causes may cause sudden reduction in pressure?


Somebody shut the wrong valve, realized what happened when they heard the compressor trip, opened it back up quick and walked away?

[hookster]

Hi is it a screw compressor as you say or centrifugal compressor? I would expect centrif for this application? My thought was did you have a surge in compressor and compressor speed reduced causing LP or did process change? Some graphic trends on parameters over period of alarm would be interesting.

[u062268]

Somebody shut the wrong valve, realized what happened when they heard the compressor trip, opened it back up quick and walked away?

How this well help my case? Because I am searching for the reason behind sudden drop in Suction Drum and Suction Compressor !!!! So I am looking for the secanrio before trippig, not after !

Today there was another trip similar to the first one. :(

[u062268]

Hi is it a screw compressor as you say or centrifugal compressor? I would expect centrif for this application? My thought was did you have a surge in compressor and compressor speed reduced causing LP or did process change? Some graphic trends on parameters over period of alarm would be interesting.

No change reported for Compressor motor nor speed or Ampere before tripping.

[hookster]

Hi I don't think it would be flare release as your levels seem stable. It would be worth trending PDI across compressor and PI before and after compressor. Is it usual to have 60% feed from nitrogen header tank?

[u062268]

Hi I don't think it would be flare release as your levels seem stable. It would be worth trending PDI across compressor and PI before and after compressor. Is it usual to have 60% feed from nitrogen header tank?

Yes you are right if the RV pop-up there will be many fluctuating in parameters after trip.

But We dont use N2 !!!

We are taking Hydrogan (MAke-up & Recycle )

[u062268]

You can check streams from this pic:


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