4 replies to this topic

[Lethal83]

Can someone give me the correct calculation for estimating the pressure drop along a 300m length of natural gas line.

 

The inlet pressure is 500mbarG.

The capacity needs to be 1100 Nm3/hr.

The proposed pipe size is 6".

 

[Napo]

Dear Lethal83,

 

You can review the textbook, Branan, Rules of Thumb for Chemical Engineers, in Fluid Flow: Compressible Flow.

 

Regards,

 

Napo.

[breizh]

lethal 83,

 

Enjoy the reading.

 

The pressure drop should be less than 100 mbars , my calculation 78 mbars considering CH4 , T=20C ,Z=1 , viscosity ;0.011 cp , CS pipe , absolute rugosity 0.2 mm .

 

http://checalc.com/s...PipeSizing.html

 

Good luck.

Breizh

Edited by breizh, 18 February 2015 - 01:38 AM.

[Ajay S. Satpute]

Lethal83,

 

You might also wish to refer below link.

http://www.cheresour...p-correlations/

 

 

Regards.

 

Ajay S. Satpute

[katmar]

A very useful bit of knowledge to apply for low pressure gas flow calculations is that for situations where the pressure drop is less than approximately 10% of the absolute upstream pressure, you can use the equations for incompressible flow and still get good accuracy. The equations for incompressible flow are simpler than those for compressible gases and if you are doing the calculations by hand this can save a bit of effort. Here is an example calculation comparing the two methods for air, with a bit more discussion, and where you can see some real numbers.

You have to do the calculation under the assumption of incompressible flow to get the pressure drop, and then compare the calculated pressure drop with the upstream absolute pressure to decide if the calculation is valid. Because pipes are available only in discrete sizes you are really selecting between 4", 6" and 8" pipes in this case and the differences between the pressure drops in these pipe sizes are huge compared with the inaccuracy caused by the incompressible assumption if you stay within the 10% rule of thumb.