Vacating Ammonia Pipeline of Nitrogen Gas?
Vacating Ammonia Pipeline of Nitrogen Gas?
(OP)
I have a startup situation which is quite puzzling:
A ~10 mile, 4 inch anhydrous ammonia pipeline supplies ammonia to our plant process. The line is ~4 foot underground throughout except where it crosses under rail crossings and in two locations where it goes under river.
Initially, the line was pigged and had a nitrogen blanket. Supply pressure is about 180 psig via product pumps from supplier. Pressure at our facility is ~90-100 psig. This pressure drop is not expected and dows not meet our requirements. We are confident that because we are taking low flows, <1200 lb/hr, that there is a nitrogen bubble at the river crossings, causing excess pressure drop. At one river the line goes 60 foot under ground.
Does anyone have any ideas how to vacate the nitrogen? We have tried running continously, 24+ hours, at about 300-400 lb/hr. We can not get higher flow because our process downstream can not take lower pressures.
I have donw some research on the Froude number as someone indicated it may determine what velocity or flow I need to "push" the bubble through, but I can not find anything good on this number????
A ~10 mile, 4 inch anhydrous ammonia pipeline supplies ammonia to our plant process. The line is ~4 foot underground throughout except where it crosses under rail crossings and in two locations where it goes under river.
Initially, the line was pigged and had a nitrogen blanket. Supply pressure is about 180 psig via product pumps from supplier. Pressure at our facility is ~90-100 psig. This pressure drop is not expected and dows not meet our requirements. We are confident that because we are taking low flows, <1200 lb/hr, that there is a nitrogen bubble at the river crossings, causing excess pressure drop. At one river the line goes 60 foot under ground.
Does anyone have any ideas how to vacate the nitrogen? We have tried running continously, 24+ hours, at about 300-400 lb/hr. We can not get higher flow because our process downstream can not take lower pressures.
I have donw some research on the Froude number as someone indicated it may determine what velocity or flow I need to "push" the bubble through, but I can not find anything good on this number????





RE: Vacating Ammonia Pipeline of Nitrogen Gas?
What velocity do you have now, with the 400 lbs/hr ? Is this line supposedly sized for 1200 lbs/hr normal ops?
I don't know offhand, what's the density and the vapor pressure?
(Increase the velocity and/or run another couple of pigs.)
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
I'd think you had some pig parts stuck in the line from the N2 fill.
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
90 58
100 63
180 94
Hmmmm. What's the pressure class/rating of the line? Where's this at, climate-wise?
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
Velocity @ 400 lbs/hr = 0.03 ft/s
The pipeline is oversized, the supplier wanted to be able to supply "other customers" in the future. Maximum flow for our process is 5,000 lbs/hr.
Temp. Vapor Pres.
° F (psig)
40° 58.6
50° 74.5
60° 92.9
65° 103.1
70° 114.1
75° 125.8
dcasto - Our line is not at 1000 psig, it is at 100 psig. I do not understand your questions about vapor pressure??? We have done no specific test for N2, we have spoken to various ammonia folks and they all agree. I have asked multiple times if they left a pig in the line, they say no.
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
Where'd this 1000 psig number come from? Reread the OP.
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
I'd stop all flow and get the line up to 180 psi first so it's as full of liquid as possible. Then, start flow, stop flow, start flow, stop flow, etc.
If that fails, can they trap a high boiler between two pigs and send it through?
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
Anhydrous ammonia.
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
I agree with you, summer time will be a drag, and it is around the corner.
What I meant, is what is the end user (process) for you ammonia?
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
There are many end users on the ammonia pipeline we draw from. Knowing their or our particular end use is not going to help solve your immediate problem, but telling this forum your end use may lead to many other useful suggestions to solve your problem.
Good luck,
Latexman
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
That's way too slow.
I say lower the pipeline outlet pressure and (chill it?) boost it, but you'll probably start gasifying.
Perhaps your best solution for now is to truck it in. Ugh!
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Vacating Ammonia Pipeline of Nitrogen Gas?
Other options are to weld TORs on the top of the pipe at the high points and flare off any nitrogen mix in the line, but use of a flare will burn any anhydrous coming out of the connection.
A big key is the delivery pressure. Have you considered adding a back-pressure control valve (some simple nitrogen bladder type exist) to keep the pipeline pressured to above the vapor pressure throughout the line?
RE: Vacating Ammonia Pipeline of Nitrogen Gas?