Gas Pipeline faces Higher velocity in pipeline network.

[MIANCH]

Hi Als,
See attached screen shot of gas pipeline network, total length of pipeline is 335 km, many users are there, case was run for gas flow 650 MMSCFD and Pressure 740 psig. Pipeline ID is 33.25 inches. I cannot understand why gas velocity has increased after 160 km. Can anyone please explain this phenomenon.
Thanks

 

[LittleInch]

Well from that data it looks like the pressure drops from about 550 psi to 350 psi at the two point SLR07 and the Almergh tie in.

You need more data points or an understanding of what is happening at SLR07. Change of diameter or pressure?

 

[MIANCH]

SLR07 is sphere launcher & receiver in same area and located 98 km from starting point for power plant gas supply tie-in point. the only thing which is pipe facing downhill 80 meter and then uphill 180 meter after 170 km from the starting point.

 

[pierreick]

Hi,
Where are the data coming from? Calibrated sensors?
Did you perform a mass balance to confirm/consolidate the values?
Can you sketch your system for us to visualize better?
Do you have operation issue or it's just for clarification?
Pierre

 

[MIANCH]

Pierre,Thanks for asking such type of questions and hereunder are my explanations,
There is no calibrated sensors, only pressure gauges only. Pipeline is 335 km long and consumers tie-in points are shown. Pipeline design pressure is 780 psig for 400 MMSCFD gas. Operators want to operate at 740 psig and flow rate at 650 MMSCFD. I have run simulation on hysys and pipesime. both give me higher velocity and higher pressure drop as stated in previous post.

 

[katmar]

I'm afraid that my comment below is so trivial and obvious that all it will prove is that I have not understood the question. Perhaps once you have seen where I have missed the point you can re-ask the question more clearly.

If you put the gas through a pipe line, then all else being equal you would expect the velocity to be proportional to the flow rate in standard terms. You have not indicated where the 160 km point is so I have just compared the values at Mellitah and Alkhoms. The quantity of gas drops from 650 mmscfd to 451 mmscfd so you would expect the velocity to decrease to (100 x 451) / 650 = 69.4 % of the original velocity.

As the pressure decreases along the line the gas density will decrease and again, all else being equal, you would expect the velocity to be inversely proportional to the density. If we assume the density is a function of the pressure and temperature then the density over the same distance would decrease to (100 x 336.4 / 619.2) x (84.53 + 459.67) / (72.45 + 459.67) = 55.56 % of the original density. The velocity will therefore increase to 100/55.56 = 180.0 % of the original.

Combining these two effects gives an overall increase in velocity to 100 x 0.694 x 1.800 = 124.9 %.

 

[MIANCH]

Dear Katmar,

Many thanks for your clear and thorough mathematical explanations.

Best regards

 

[LittleInch]

So what is the issue? Your trying to stock 55 % more gas through the line at slightly lower pressure. Frictionallosses will increase so to get more flow pressure will need to do, density reduces, so actual velocity increases. 12 m/ sec is not particularly fast.j

 

[MIANCH]

My concern was this particular gas pipeline segment has more velocity whilst other section velocity remain between 7-8.5 m/s.

 

[Snickster]

Further to what Katmar stated, you can just use the ideal gas equation to determine what the velocity should be at any point in the line as follows:

P(144)(V)(A) = m Z R T

Where P = Pressure psia
V = Velocity ft/sec
A = pipe inside area ft^2
m = mass flowrate lbs/sec (lbs weight not mass)
R = universal gas constant = 1545/MW - where MW is the molecular weight of gas
Z = compressibility factor
T = flowing temperature deg Rankine