Slug of Condensate

[GasOilEng]

Hi

We have pipeline transporting Gas with MW of 24 to 25g/mol along the 130km, to LPG facility. Every three day, the CPF sending the gas to LPG plant, perform pigging operation. As the result, LPG plant receives a big quantity of cendensates about 130m3/h over 5 to 8hours.Please, I would like to design surge volume of slug-catcher. How to calculate it?.

thank you in advance

 

[LittleInch]

Ah, the slug catcher size issue...

If you're trying to minimise the size then you need to figure out how that 130 m3 arrives and what is your liquid handling flow. Them you have a difference to store in the slug catcher. Then how much safety factor to apply?
Also what happens if your slug catcher overflows? Can the d/s plant handle some level of liquid?
Can you slow the gas flow down as the pig arrives?

So based on your 130 m3, my guess is this could be anywhere from 25 to 150 m3.

Whatever number you choose it will either be too small or too big.

Maybe build a finger type one with room for extra fingers of you need it.

What happens now? Are you getting plant trips?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Here is a rough estimate.

Assume the plant will be running at normal condensate handling rate (at the debutaniser?) - say x m3/hr during the pigging operation.

If the 130m3 slug arrives over a minimum period of 5hours, then surge volume holdup in SC will be (130-5.x)m3.

If you can get plant Operations to temporarily operate the SC condensate level at LAL (on the LIC) during the pigging operation, then this surge volume should be accomodated between LAL and LAH.

Most modern slugcatchers have a high level LIC ( set to operate at anywhere between LAH and LAHH) that will throttle the incoming feed from the pipeline (at an LCV located on the pig receiver bypass line) in case level rises higher than LAH.

In some plants, the debutaniser handling rate x drops as the plant ages due to gradual fouling in the debutaniser reboiler (due to mineral salts in wet condensate caking up on tube surfaces), so use a lower value for x if you think this could happen at your plant too.

 

[GasOilEng]

Hi everybody!

Mr Georgeverghese; If I got you, the 130m3 per hour arrives during 05 hours minimum, Not 130m3 over 05 hours.

Many thanks for you George & LittleInch

 

[LittleInch]

So what are you going to do next?

What size S/C do you need?

A trace of condensate volume over time would be good to see.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GasOilEng]

Hi LittleInch

Firstly,I want to know basing on those flows of liquids, How can I estimate the slug volume.
Secondly, the size of Slugcatcher that I want to have is L<10m, D<3m.

Thanks

 

[dean427]

Don't forget to consider the entire operating envelope of the pipeline e.g. if the fluid is retrograde - at higher export rates & lower landed pressures at the LPG plant more liquids will drop out in the pipeline.

You can use the Cunliffe method to get a simple feel for slugcatcher size.

However, I think normally this type of equipment is sized using a dynamic pipeline simulator with appropriate fluid package and multi-phase flow correlation.

 

[LittleInch]

Like dean427 says, the normal way to do this is either:
Analyse your system using multi phase flow software to generate a flow of liquid over time during pigging
Measure the incoming liquid flow as it enters and leaves your separators

Work out the best way for your site to contain the excess liquid between what is coming in and what the plant can handle as a max flow.

This is either pipe type slug catchers or by the look of your comment a vessel.

Your vessel size is a max 70 m3, but in working volume probably closer to 50.

I have no idea if that is enough storage volume or not. Like I said before there are many inputs into this and whatever size you choose will be too big or too small.

Note that as your gas flow rate, composition or pressure changes over time so will the liquid hold up.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.