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Calculating Gas Composition In Natural Gas Line


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#1 mosa

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Posted 23 July 2020 - 02:28 PM

Dear

 

I have natural 36" Natural Gas(NG)  pipeline of 5 kms. Post maintenance works followed by  commissioning with  Nitrogen at 0.2 kg/cm2g. If we commission the 36"pipeline with NG ( C1 - 96.1mol%, c2-2mol%,c3 - 0.1 mol%, co2 -0.345mol% and N2 -1.5mol%), what is the final composition of the NG+N2 mix when pipeline is pressurized upto 40 kg/cm2g. Assume flowrate to consumer is zero. 



#2 demank

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Posted 31 July 2020 - 01:37 AM

Your query seems not clear for me.

Do you mean pressurize Pipeline with Natural Gas?

and the sum of the composition of your NG is not 100%.

Btw, you can calculate by yourself with common equation P1V1/T1 = P2V2/T2. mass original + mass additional = final mass.



#3 mosa

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Posted 27 September 2020 - 11:06 AM

Dear Demank

 

To clarify , say 36" size line of 5kms parked with Nitrogen at 0.2 kg/cm2g at static condition. Now if i introduce NG having above mentioned composition is pressurized from 0.2 kg/cm2g to 40 kg/cm2. What is the resultant composition ?



#4 MrShorty

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Posted 28 September 2020 - 10:50 AM

Not sure exactly what you need help with. Some depends on what accuracy you require, but here's a general view of how I would expect to do this:

 

1) Compute the amount of N2 in the pipeline. You give pressure and pipeline dimension data, so I assume the intent is to use the PVT properties of N2 (whether from a table or from an equation of state) to take the PVT data and compute the number of moles of N2 in the pipeline.

2) Compute the amount of total gas in the pipeline after adding the NG. Again, it looks like you are starting with PVT data, so you need to use the PVT data and compute moles of total gas.

3) The difference between 1 and 2 is the amount of NG added. Use that to compute the moles of the individual components added.

4) Add the N2 from step 1 to the N2 from step 3 and compute the composition of the gas in the pipeline.

5) Step 2 may have required you to "guess" at the gas composition in order to find the total moles of gas. If so, evaluate your guess with the result from step 4. If you feel so inclined, repeat step 2 with your new, better guess at the composition of the gas and repeat steps 2 through 4 until you are satisfied with the result.






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