5 replies to this topic

[quangkhoa90]

Hello,

 

I am a junior process engineer. I would like to calculate the volume of a gas to raise pressure in a pipeline by 1 bar. Please help me out.

 

The stream at outlet of compressor 1 is about 30 kSm3/h at 46 bar and 45°C, refer to the attached file for the stream composition. This stream is sent to compressor 2 to compress to 70 bar. The pipeline between these 2 compressors is 50m in length and 10" in diameter.

When the compressor 2 shuts off, pressure will raise up at downstream of compressor 1, this may cause shutdown of equipment due to high outlet pressure.

 

In this case, I would like to figure out how long will it take to raise pressure at downstream of compressor 1 by one bar, or reach the PSHH at 55 bar.

 

Thank you in advance 

Attached Files

•  Composition.png   15.81KB   2 downloads

Edited by quangkhoa90, 23 October 2016 - 03:41 AM.

[Bobby Strain]

To get the best estimate you must perform a dynamic simulation. But why is this important?

 

Bobby

[quangkhoa90]

I would like to install a pipeline at downstream of compressor 1, in order to prevent the pressure from building up at outlet of this compressor.

 

I performed calculation to estimate the time needed to raise pressure from 45 barg to 50 barg as below:

 

I ran the simulation on hysys at 45 barg, and I found that molar volume is a (m3/kgmole)

I ran again the simulation at 45 barg, and molar volume is A (m3/kgmole)

The volume of pipeline between compressor 1 and compressor 2 is constant and equals to V (m3)

 

Then to raise pressure in that pipeline from 45 barg to 50 barg, we need to add [V*(1/A - 1/a)] (kgmole) of gas

 

From Hysys, we have the flow of gas through this process which is Q (kgmole/h)

 

Conclu, the time it take to raise pressure from 45 barg to 50 barg is: [V/Q * (1/A-1/a) ] * 3600 (s)

 

Does it sound good to you?

 

BR,

Edited by quangkhoa90, 24 October 2016 - 01:43 AM.

[Bobby Strain]

If it is done slowly that is approximately correct. But with your given flow the pipeline pressure will not be uniform from beginning to end.

Hence you need a dynamic simulation.

 

edit: But if I was responsible, I would assume the same pressure profile for the pipeline. That is, assume the pressure at the inlet and outlet both increase by 5 bar.

 

Bobby

Edited by Bobby Strain, 24 October 2016 - 09:00 PM.

[quangkhoa90]

Dear Bobby,

 

I agree, I did assume the same P profile for the pipeline. 

By the way, concerning your previous comment: "But with your given flow the pipeline pressure will not be uniform from beginning to end", then if I take into account for this phenomenon, it would take long time than my calculation to pressurize the pipeline, please correct me if I'm wrong.

 

Thank you

 

Khoa

[shan]

Gas may condenses into the liquid phase at higher pressure to reduce it volume.