Underground diesel delivery system 2

[sree2613]

Hello All,

I am designing fuel delivery system for underground mine. I have found similar thread in this forum but I couldn't find the answer I was looking for. Expalining my problem, We have batch tank on surface and we have to send the diesel to an underground tank located 4000 ft below from the batch tank. We have to empty the vertical pipe after each fuelling . So when you start fuelling, the vertical pipe will be empty and diesel will be free falling through the pipe. I have read a standard that the velocity in the pipe should not be more tha 14 ft/sec in order to avoid forming static electricity. So as soon as the fuel enters the vertical section of the pipe, the gravity comes into play and 14ft/sec will be reached with in a second. I used some basic equation to come up with above statement, V=u+gt. Could someone help me how we can limit the velocity in the vertical pipe to 14ft/sec.?

Thanks

 

[bimr]

If you desire to limit the terminal velocity, then you need to limit the flow of fluid into the pipe since the terminal velocity is related to fluid flow.

In a report done by Dawson and Kalinske - "Report of Hydraulics and Pneumatics of Plumbing Drainage Systems' they developed the formulae. The terminal velocity is related to fluid flow and diameter according to the equation:

Vt = 3.0 (q/d)^(2/5) and
Lt = 0.05(Vt)^2

Where Vt is terminal water velocity (fps), and Lt is the developed length to develop terminal velocity (ft). From these formulae it was determined for various standard pipe sizes terminal velocity is about 10-15 fps, and that this velocity is achieved within 10-15 feet of fall.

What this means is that the velocity of falling fluid is about the same regardless if it is falling 2-3 stories, or 100 stories.

http://xnet.rrc.mb.ca/rcharney/interior.htm

"CanuckMiner (Mechanical) 19 Dec 03 13:37
A few clarifications are in order here methinks.

In an underground mine, it is common practise, indeed a requirement, to use a "dry line" (i.e. you are not allowed to fill the pipe with fuel and then open a valve at the bottom for delivery). You must keep the transfer pipe empty except during the immediate transfer. This is for safety and environmental (risk of spill) reasons.

In essence what we have is a batch tank (Tank A) on surface (say 2000 litres). There is an outlet on the bottom of the tank, with a valve. Below this is a 1.5" dia. pipe that drains to the underground tank (Tank B) located far below the surface of the earth. We open the valve at the bottom of Tank A and the fuel starts to flow down the 1.5" dia. pipe. It is not pumped, it is gravity flow.

The underground tank that jreng1 is referring to is not an UST (Underground Storage Tank). It is an AST (Aboveground Storage Tank) installed several thousand feet below surface, located in an open cavern in hard rock (read granite or dolomite...not soil). The tank will be vented to the local ambient atmosphere. Yes the local ambient atmospheric pressure at depth will be higher than on surface (say 18 psi versus 15 psi), but it shouldn't be significant. A vent pipe back to surface is out of the question, and indeed is not installed on other similar installations. The diesel fuel storage area underground will be ventilated, with the fumes being directed to a nearby Return Air Raise (i.e. ultimately exhausted via a big "rock chimney" some 18-feet in diameter to surface).

Standards and codes have been consulted (what little there is that is applicable - NFPA 30, NFPA 122, CSA standards - in Canada, etc.), but there is nothing that describes the "science" part of these things, only the health and safety aspects which are obviously important, but do not answer the questions.

Putting to one side the diesel fuel and the regulations, codes, and standards, there remains the basic physics of the system: a liquid free flowing down a pipe. You do flow calculations based on Bernoulli's equation and you come up with some anticipated flow rate (in fact the fluid reaches a "terminal velocity" based on the falling fluid being impeded by friction in the pipe). However, the equation ASSUMES a full pipe (i.e. filled with the liquid). The question remains: is this a valid assumption? Does the air get pushed down the pipe into the tank and out the vent? Or does the air bubble back up through the liquid, and out through the vent in the upper tank?

The has come up because of what some other mines with similar systems report, namely that when the valve is opened, the line "bubbles and gurgles" and drains slowly, then after a period of several minutes the flow picks up and it drains much more rapidly. We are trying to establish the science/physics of what is going on.

This seems like an elementary problem at first glance, but oddly enough, calculations, discussions, research, consulting of fluids texts, etc. have not produced answers.

We have contacted Chemical Engineering magazine to locate the article katmar describes (Thanks!) and we're trying to "get back" our copy of the Chemical Engineer's Handbook (having had it pilfered from our library).

Hope I didn't bore you all with these details, just trying to outline the background for the simple question asked by my colleague.

Cheers,
CanuckMiner"

http://www.eng-tips.com/viewthread.cfm?qid=81608

 

[dicksewerrat]

You may want to talk to people that design stormwater tunnels. These have venting issues that may compare to your situation. Ever wonder why manhole covers can fly?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BigInch]

Static electricity inside a steel pipe will not be the problem. Voltage differentials inside should be minimum. It becomes a potential problem during the transfer from pipe to the inside of the tank, where you may have a electricl isolation between them and a resulting voltage differential, a potential spray and the possiblity of developing an explosive fuel-air mixture inside the tank. You should limit the velocity at the discharge from pipe into the tank where the diesel may initially spray through any air contained within the tank as filling starts. Fill the tank from a connection towards the bottom, below the lowest liquid level, to prevent sparay and high diesel velocity contact with air above the liquid level in the tank. I presume you could do that with a plug valve (and perhaps including a check valve) at the pipeline connection to the tank, where the hand valve can be opened slowly to control velocity until the diesel level is above the connection level. Additionally, make an electrical bond between the pipe and tank to minimize any possible voltage differentials.



If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[bimr]

Black iron or steel are generally used for diesel piping. Should the piping have surfaces that are oxide-coated or laminated, the piping may not be conductive and may have the potential to generate static.

http://www.shimadzu.com/an/hplc/support/lib/lctalk/14/14lab.html

 

[BigInch]

Now I'll never get another full night's sleep.

If it ain't broke, don't fix it. If it's not safe ... make it that way.