4 replies to this topic

[RGS]

Hi,

          I was assigned to perform Pressure Surge Analysis for a Liquid Ethylene Import Line from Jetty to Ethylene Storage Tank. The distance between Jetty and Storage Tank is around 1.9km. The following operating scenarios were considered in the Pressure Surge Analysis.

 

1. Case-1: Sudden trip of ship pump while steady import operation is going on

2. Case-2: Sudden Closure of ESD provided at storage tank inlet line while steady import operation is going on

 

If the surge pressure exceeds the design pressure of the pipeline, it is required to consider the mitigation measure to reduce the surge pressure. 

 

Can anyone advice or share their experience about the following?

 

A. The most suitable and economical mitigation measure for the above operation

B. If providing a Pressure Relief Device is an economical mitigation measure, kindly advise about the design          requirements to be considered while designing the mitigation measure.

    

    Since Liquid Ethylene is at cryogenic condition and large amount of liquid ethylene has to be relieved in short period of time (to reduce the surge pressure), how to design a suitable mitigation system for this application?

 

[Bobby Strain]

 

Best to enlist the service of a knowledgeable expert.

 

[Technical Bard]

Relief devices are usually not the best option, because the instantaneous relief rate is high and you get cryogenic liquids to the relief system.  

 

If you can't avoid the liquid hammer event with slow closing valves, then a gas-blanketed surge drum (with a diaphragm if you don't want gas mixing with your liquid) can easily be sized to take up any volume from the surge.  The downside of this is some complex controls.

[RGS]

 

 

Best to enlist the service of a knowledgeable expert.

 

Dear Booby Strain, thanks and appreciate your kind advice.

 

Relief devices are usually not the best option, because the instantaneous relief rate is high and you get cryogenic liquids to the relief system.  

 

If you can't avoid the liquid hammer event with slow closing valves, then a gas-blanketed surge drum (with a diaphragm if you don't want gas mixing with your liquid) can easily be sized to take up any volume from the surge.  The downside of this is some complex controls.

Dear Technical Bard,

                                     Thank you very much for your advice. After had a several technical brainstorming sessions among with my superiors, we identified the following.

 

1. If the surge generated near to the Ethylene Liquid Storage Tank, the surge relieving liquid can be routed to the tank. However, this is subjected to BOG Compressor Capacity & Design Pressure of the tank. Hence it is decided not consider this as a top priority design.

2. The second option is design a suitable surge vessel as you have proposed. One of my fellow engineers highlighted that, only horizontal type surge vessel will be considered for Cryogenic Fluids and it's design is bit difficult against Vertical Surge Vessel. But I am not sure about it. Hence can you share your knowledge about the following?

- Is there any specific criteria available to select surge vessel type (i.e Vertical or Horizontal) for cryogenic applications?

- If any Technical information about cryogenic surge relief is currently available with you or come across to you, kindly share it with me.

 

Once again thanking you for spending your precious time on my concern.

[Technical Bard]

I don't know why you would prefer a horizontal vessel for this service.  The vessel will be quite small.