Slug volume in OLGA software

[kald]

thread798-156994

in OLGA software , in the TRENDDATA, PROFILEDATA output variables I can found many slug flow characteristics like slug length (LSLEXP) ,bubble length (LSBEXP), slug frequency but i can found slug volume , So how I can calculate the max liquid slug volume and average liquid slug volume

 

[LittleInch]

The best way is simply to get a graph of liquid arrival flow vs time. Over a decent time frame, 15 minutes or an hour or a day you can then calculate average flow and see whether the predicted liquid flow varies from that average. That will give you the excess volume you need to deal with.

The term "slug" is very misleading IMO as liquid outflow rate isn't some simple surge or calculation, but looks more like a mountain range....

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[1503-44]

Take the steepest mountain.
Double it.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

That's why OLGA is better than other software as it gives you the raw data and not some simplified data such as "slug" volume.

Any pipeline which is in slugging mode very rarely gets to 100% liquid fraction, but what you do get is more liquid arriving in a set period of time (say 1 minute) than you would on average.

You need to see the data in that form to get any idea of what sort of slug catcher size or separator you need. But this is always a work or art, not a scientific calculation and I've sized quite a few in my time as has Mr 44...

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

 

[kald]

you are totally right when we need to size the slug catcher or determine the required surge size , we will calculate surge volume as the difference between the accumulated flow rate and drain rate .

but my question if i activated the slug tracking model in OLGA , many variables can be found related to slug flow characteristics like slug length (LSLEXP) ,bubble length (LSBEXP), slug frequency . can i use this to calculate the maximum liquid slug volume out from the pipeline , for example, the max. slug length (LSLEXP) with max. holdup will be the large liquid slug volume . so can I draw the liquid slug volume with time at the pipeline outlet

 

[LittleInch]

The issue is that "slugs" are not some nice simple length times volume. They are complex things which change every second.

Calculating length is much more art than science and its not clear how the program works this it. My guess is that if the liquid hold up is higher than the average it counts a slug. That could though be 1% more or 100% more. Taking length x max holdup will give you a very conservative number.

Ultimately the only issue is how it affects the equipment at the end of the pipeline. Everything else is just information for information sake IMHO.

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

 

[1503-44]

Its not entirely limited to catcher design. Some configurations and flow conditions may have severe implications to the pipeline design itself, especially in regard to positive incline of the profile and the pressure increases due to induced elevation head by length of the slug where either or both extra pressure or a change to a different phase flow mode may be necessary.

There is usually no single answer to slug problems.

I would attempt to define and classify the most likely 2-phase flow modes, either by program, and/or do some "hand calculation" work until you fully understand what range of operating conditions you can expect to have and where you want to set the design point and excursion capability to best accommodate that range. There is often a very wide range of different flow conditions you can get between start up, operation and shut down scenarios. A good understanding of how each variable affects your operating condition in each potential mode of flow is essential.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Agreed, but the program works that out for you. This was about calculating slug volume from the simplistic slug length data that the program generates.

IME you need to look at a graph of liquid hold up or liquid flow at a node over time to get a good handle on "slug" volume.

Slug volumes are a range and not a simple calculation.


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

 

[kald]

Certainly, most of the time, understanding the slug volume and its distribution over time is often just informative. The crucial aspect for designing the slug catcher or separator is the surge volume. However, there are instances when this information is needed for control system design or academic purposes.