LPG line Pressure Drop Calculation
LPG line Pressure Drop Calculation
(OP)
Happy New Year to my colleagues!
I was given an assignment to calculate the pressure drop on a 10"ND pipeline where 600MT/hr of refrigerated Propane (-42deg. C) would be discharge from an LPG cargo vessel (via 2,000 KM of submarine pipeline) at the Jetty then, goes 45deg upwards diagonally then horizontally onshore for 500m long up to several "bullet type" storage tanks. I assumed the storage tank temperature would finally be in equilibrium with an ambient temperature of 25deg. C. Discharge static elevation is 25m.
I don't know what condition to use (to based on -42deg. C or 25deg. C) for my pressure drop calculation since I am aware that, with the lenght of the pipeline, Propane will pick-up heat and therefore, cannot assume an isothermal condition. I am thinking of a weighted averaging calculation where an isothermal condition can be assumed for every kilometer or every 100m of pipe lenght then, add the individual pressure drops to get the total. This is of course a tedious calculation but is this a right approach?
Please share if you have any sample calculation or spreadsheet. Actually, my boss prefers a manual calculation because he was used to it during his 1970's schooling and then, I have to countercheck it with an online spreadsheet. I actually had done some manual calculation using Crane's Technical Paper 410 but my counterchecked with an online spreadsheet yielded with an answer 10 times greater than the manual calculation! Hence, obviously as per my engineering "feel", the manual calculation is wrong and can't find the error even with further reviews and checks of the input data and calculations.
My online spreadsheet calculation yielded an acceptable pressure drop but failed on velocity. The criteria I used for a 10"ND line and above is: Allowable velocity = 3.0 - 4.6m/s whilst Allowable max. delta P = 0.45 bar/100m. Are these criteria correct which was just given to me by a colleague.
I had done so many pressure drop calculations in the past but it looks like calculations involving LPG mix, propane & butane is a bit complicated as its density varies along the lenght of a long pipeline.
Indeed, many thanks for the help/assistance.
I was given an assignment to calculate the pressure drop on a 10"ND pipeline where 600MT/hr of refrigerated Propane (-42deg. C) would be discharge from an LPG cargo vessel (via 2,000 KM of submarine pipeline) at the Jetty then, goes 45deg upwards diagonally then horizontally onshore for 500m long up to several "bullet type" storage tanks. I assumed the storage tank temperature would finally be in equilibrium with an ambient temperature of 25deg. C. Discharge static elevation is 25m.
I don't know what condition to use (to based on -42deg. C or 25deg. C) for my pressure drop calculation since I am aware that, with the lenght of the pipeline, Propane will pick-up heat and therefore, cannot assume an isothermal condition. I am thinking of a weighted averaging calculation where an isothermal condition can be assumed for every kilometer or every 100m of pipe lenght then, add the individual pressure drops to get the total. This is of course a tedious calculation but is this a right approach?
Please share if you have any sample calculation or spreadsheet. Actually, my boss prefers a manual calculation because he was used to it during his 1970's schooling and then, I have to countercheck it with an online spreadsheet. I actually had done some manual calculation using Crane's Technical Paper 410 but my counterchecked with an online spreadsheet yielded with an answer 10 times greater than the manual calculation! Hence, obviously as per my engineering "feel", the manual calculation is wrong and can't find the error even with further reviews and checks of the input data and calculations.
My online spreadsheet calculation yielded an acceptable pressure drop but failed on velocity. The criteria I used for a 10"ND line and above is: Allowable velocity = 3.0 - 4.6m/s whilst Allowable max. delta P = 0.45 bar/100m. Are these criteria correct which was just given to me by a colleague.
I had done so many pressure drop calculations in the past but it looks like calculations involving LPG mix, propane & butane is a bit complicated as its density varies along the lenght of a long pipeline.
Indeed, many thanks for the help/assistance.





RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
Did you really mean "2,000 KM of submarine pipeline? Wow, that jetty is WAY off shore. I could believe 2 km.
I think you should do some heat transfer calculations too. Do enough all along the pipeline (beginning to end) so that you understand what is going to happen to the state (gas/liquid/two phase) of the propane (or is it really LPG). This knowledge would have also helped me understand your system better too, because I have no experience in your application.
The criteria from your colleague seems reasonable to me.
You did not mention how the propane is transferred. Is it pushed with pressure or pumped? What pressure is the propane at near the tanker and in the bullet tanks? These details can help others envision your system. Of course the best option is to attach a detailed. well labelled sketch.
Finally, you may consider, after correcting any errors and adding more detail, if needed, to repost this on the "Pipelines, Piping and Fluid Mechanics engineering" forum. I think you will get more responses there. If you do this, please Red Flag this post and ask Site Admin to delete it. Cross posts are not allowed.
Good luck,
Latexman
RE: LPG line Pressure Drop Calculation
An option was proposed to install 2 booster pumps onshore that will run in parallel and a Reheater at the discharge side. It gets complicated but I'll try to draw the sketch with the data/info in it.
What I understand is that Propane and Butane exist as saturated liquid under slightly above atmospheric pressure??
RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
For two-phase flow the following link , chapter 13, may be of some help:
RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
Higher temperatures will require yet greater pressures to keep a liquid phase.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
Good luck,
Latexman
RE: LPG line Pressure Drop Calculation
As per instruction to me, I can initially assume that the Propane was heated by seawater to 10deg.C (for purpose of having a ballpark figure on delta P)and operate isothermally along the lenght of the pipeline with lots of insulation. When it reached the storage tank, its temp. inside the tank will rise to a point where it will be in equilibrium with the ambient temp. I considered a worst case scenario where the temp. will rise up to an average 25deg.C during summer.
1. What is IMO?
2. Had you seen the LPG loading system profile (with some data/info) I attached to my post above on last 13 Jan.,9:59?
3. Do you have any sample calculation on this particular LPG system which I can use as template? Thanks!
Best regards,
Roberto
RE: LPG line Pressure Drop Calculation
RE: LPG line Pressure Drop Calculation
3 - Sorry, no.
Can you estimate/deduce the line pressure right before the bullet tanks? Why don't you share your pressure drop calculations you have done so far? And, tell us about the input data to the online spreadsheet and it's results. That may trigger some helpful discussion.
Good luck,
Latexman
RE: LPG line Pressure Drop Calculation
Pls find attached my calculations. The schematic diagram had been attached in my earlier post as shown above. Hopefully, some comments would shed light if my calculations was done on the right path.
Many thanks
Roberto
RE: LPG line Pressure Drop Calculation
Good luck,
Latexman