Flow calculation
Flow calculation
(OP)
Hello,
I have a 30,000 Gallon LPG tank about half full, that will be emptied into an empty second tank, through a piping arrangement. The first tank is pressurized using a compressor. The differential pressure created between the two tanks is 100 PSID
I am trying to figure out an expected flow rate (GPM)at the discharge of the piping going into the tank to be filled
I've attached a sketch, which has layout and sizing information.
also to note, there are excess flow valves at the piping intakes in each tanks, that will shut the flow off at a certain threshold. Unfortunately, the specs on the valves is not known, but I assume they must still be accounted for for friction loss in the head loss calcs.
I am not sure about how to account for the head loss in the entire system. I am using a bernoulli equation but am running into problems in solving it.
As can be seen by the diagram, the 2 inch piping dumps into a 3" header, then back into a 2 line to the second tank, with valves and elbows along the way. All valves, fittings, and piping seams are welded. An approximation is really all that is needed and in fact, all i need to prove is that the flow rate will be at least 250 GPM or more
Any help with this is greatly appreciated,
Thanks,
Dan
I have a 30,000 Gallon LPG tank about half full, that will be emptied into an empty second tank, through a piping arrangement. The first tank is pressurized using a compressor. The differential pressure created between the two tanks is 100 PSID
I am trying to figure out an expected flow rate (GPM)at the discharge of the piping going into the tank to be filled
I've attached a sketch, which has layout and sizing information.
also to note, there are excess flow valves at the piping intakes in each tanks, that will shut the flow off at a certain threshold. Unfortunately, the specs on the valves is not known, but I assume they must still be accounted for for friction loss in the head loss calcs.
I am not sure about how to account for the head loss in the entire system. I am using a bernoulli equation but am running into problems in solving it.
As can be seen by the diagram, the 2 inch piping dumps into a 3" header, then back into a 2 line to the second tank, with valves and elbows along the way. All valves, fittings, and piping seams are welded. An approximation is really all that is needed and in fact, all i need to prove is that the flow rate will be at least 250 GPM or more
Any help with this is greatly appreciated,
Thanks,
Dan





RE: Flow calculation
You didn't say if you expected the flow to be gas, liquid, or two-phase. Unless you're assuming 2-phase flow, you can use D'Arcy-Weisbach for liquid or the Isothermal gas equation for gas. If you expect flashing in the piping then no equation is going to give you a very good representation of flow.
David
RE: Flow calculation
the flow is assumed to be fully liquid, again all I really need is an approximation at best and to know that the flow is at least 250 GPM or more.
So it sounds like I need to use the D'Arcy Weisbach equation in this case, and i assume I would have to calculate the system losses and plug that in?
RE: Flow calculation
Good luck,
Latexman
RE: Flow calculation
The 3" header length is 142"
the two excess flow valve are on the end of 2" piping inside each tank. They are size 2".
RE: Flow calculation
RE: Flow calculation
David
RE: Flow calculation
use standard globe valve bodies to construct our EFVs.
Good luck,
Latexman
RE: Flow calculation
http://www.malema.com/pdf/M_XF.pdf
Good luck,
Latexman
RE: Flow calculation
Regards,
SNORGY.
RE: Flow calculation
Take a look at suppliers filling bulk storage tanks from their tankers, you will see two lines between a tanker and a bulk storage tanks during the transfer of product for the reason stated above and to control fugitive emissions.
RE: Flow calculation
I was hoping there was a quick and dirty way to get a rough approximation but it looks like I'll have to dig up the old fluid mechanics books and look at it closer
Chicopee,
yes you are right, I omitted the vapor return arrangement in the sketch for simplicity's sake. the differential pressure (100psid in this case) from a compressor forces the liquid from the first tank into the second tank. it's not a typical standard procedure to transfer product from tank to tank at this site and the reason they are doing it is to drain the first tank to take it out of service and scrap it.
RE: Flow calculation
Good luck,
Latexman
RE: Flow calculation
RE: Flow calculation
To be conservative, simply assume that all the piping is 2". The 3" section is short and is almost irrelevant, but taking it as 2" will not be far wrong.
The resistances of angle pattern globe valves vary considerably, but as a start take them as having an equivalent length of 150 pipe diameters. As a first guess assume the excess flow valves are the same.
In terms of the physical properties, it is fairly important to get the density close, but the viscosity is of little importance. It only affects the friction factor very slightly in the turbulent regime.
Plugging all this data into an online calculator will tell you that at 250 USgpm your pressure drop will be about 45 psi. BUT if you put 250 USgpm through a 2" Sched 80 pipe your velocity will be about 27 ft/s and this should raise red flags around the excess flow valves. I would guess they will be your limiting factor - not the rest of the piping.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Flow calculation
RE: Flow calculation
Good luck,
Latexman
RE: Flow calculation
RE: Flow calculation
Good luck,
Latexman
RE: Flow calculation
RE: Flow calculation
I would otherwise use anything up to about 250 diameters for the 90-degree globe, fully open.
Regards,
SNORGY.
RE: Flow calculation
RSR2, yes Bernouilli's equation should work fine. Assuming 100 gpm transfer rate, f=.01875 or higher; K=42' for 3" internal valve(assumed as no value is available from mnfctrs.) and strainer;18' for 90d elbows;8' for 45d elbows. Whatever value is obtained for pump HP, tak on a 20% increase.