How to calculate linepack

[SuperG]

Does anyone know how to compute linepack in a natural gas pipeline? I can't seem to match by hand what is being reported in several simulation programs...thanks for the help!

 

[MortenA]

I dont think you can do a "hand" check of a linepack. I have used "pipeline studio" for calculating linepack for natural gas.

Does the simulation programs produce radically different results?

Best regards

Morten

 

[TD2K]

I suppose if I was trying to check a simulation's results I would first look at the pressure/temperature profile in the pipeline. Break the pipeline up into small enough lengths to assume the pressure is constant over each segment (or the average of the inlet and outlet pressure is representative). Use these pressures, temperatures to calculate the density in each segment and with the line lengths, the pipeline inventory.

Repeat for the final conditions. The difference between the two is your line pack.

As Morten says though, how much difference are you seeing?

 

[SuperG]

You are right about a quick check on linepack...it should be iterative.

The answers between the 2 programs are similar, but about 40% off from my calculation, which is more of a volume calculation.

Well, how about this...how much gas would you calculate to fill and start a pipeline? Would you use the lowest operating pressure or the highest operating pressure?

 

[MortenA]

Thats not what i understand as "linepack". My definition is related to an operating pipeline where a downstream valve is closed (or throtled) while upstream compressors continue to send gas into the pipeline.

However: I think that if you procedure would be to add gas to a pipeline initially at atmospheric pressure - with a closed downstream valve until the entire pipeline has a certain pressure - then a simple mass balance should tell you how much gas is needed. You can use a SS process simulator such as HYSYS for this or even a hand calculation.

Best regards

Morten

 

[SuperG]

Well, linepack is a value that is ever changing due to the transients in a pipeline. It is also a number that gas controllers watch, since they like to keep a pipeline as full as possible.

Anyway, I think you are right about filling the pipeline...thanks!

 

[fmaldon]

I assume that the line pack you are calculating is in MMSCF and that you are applying a Supercompressibilty factor to your calculations and are combining Charles' and Boyle's laws.

You may want to refer to the AGA's "Gas Measurement Manual" Catalog No. XQ1081 for these calculations.

Hope this helps