Propane transfer re-visited
Propane transfer re-visited
(OP)
Hi,
I need to conduct a product transfer operation but am not sure how to figure out if it will be possible or not. I'm in a bit rusty on my fluid dynamics and looking for some tips on how to approach this.
I have 2 large capacity liquid propane tanks (24,000 gallons) both about 80% full and need to transfer product from one tank to the other. I'll have 100 PSI differential driving the fluid transfer, my question is whether the limit of excess flow valves will be exceeded at that pressure differential.
I've attached a sketch depicting the layout.
what would be the methodology to solve this- I assume solving for velocity at the intake of the discharge tube of tank 1 (given the 100 psid) is the way to go since I can then figure out the flow rate and see if it exceeds the excess flow valve capacity?
Is the D'arcy equation sufficient to solve for the velocity given all the known variables I currently have?
Any help on this would be greatly appreciated,
Thanks in advance,
Dan
I need to conduct a product transfer operation but am not sure how to figure out if it will be possible or not. I'm in a bit rusty on my fluid dynamics and looking for some tips on how to approach this.
I have 2 large capacity liquid propane tanks (24,000 gallons) both about 80% full and need to transfer product from one tank to the other. I'll have 100 PSI differential driving the fluid transfer, my question is whether the limit of excess flow valves will be exceeded at that pressure differential.
I've attached a sketch depicting the layout.
what would be the methodology to solve this- I assume solving for velocity at the intake of the discharge tube of tank 1 (given the 100 psid) is the way to go since I can then figure out the flow rate and see if it exceeds the excess flow valve capacity?
Is the D'arcy equation sufficient to solve for the velocity given all the known variables I currently have?
Any help on this would be greatly appreciated,
Thanks in advance,
Dan





RE: Propane transfer re-visited
I would suggest using the Crane 410 book and using the K values etc to calculate your dP. The only caution is to check for flashing of the propane from the higher pressure to the lower pressure resulting in two phase flow (which envolves more complicated formulas)
Just from an experience perspective, the 100 psi will force more flow than 225 GPM (not confirmed by detailed calculations)
How will you generate the 100 psi differential? If both tanks are at ambient temperature of say 80 deg F, they will both have a pressure of approximately 128 psig.
I also assume the level in the "receiving" tank will be nearly empty to receive the contents of the full tank.
Propane tanks are typically not allowed to be filled greater than 85% liquid volume of the tank volume. The 15% "free" volume allows for the pressure variations due to temperature changes of the tank contents.
Sorry if I have pointed out the obvious.
Good luck.
RE: Propane transfer re-visited
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Propane transfer re-visited
RE: Propane transfer re-visited
I do indeed realize the added complexity due to the 2 phase condition present. Basically, from my understanding, this is the process they will be using , I was just asked to determine as a rough estimate and provide a calc, as to whether a 100 psid will create a flow that will exceed or fall below the rated capacity of the excess flow valve. This may sound over simplified when considering all the complexities that exist in the system, unfortunately this was handed down from management personnel who don't have engineering background.
With that, I'm looking to keep it as simple as possible to show that it will work or not
I can get a total head loss value, and after that solve for a velocity but I'm not sure how to correlate that to the pressure differential.
BTW- I believe a compressor will generate the dp
RE: Propane transfer re-visited
Start with the 225 GPM as your first flow case
Utilize a simplified Darcy equation to estimate pressure drop per 100 ft of pipe
Utilize your fittings and valves to determine an equivalent length of pipe
Thus for any flow you can calculate your pressure drop
I am pretty sure a 100 psi differential will pass more than 225 GPM for your system.
I do not think you want to put 100 psi additional pressure on your storage tanks (128 + 100 = 228), as it will begin to approach your MAWP (probably 250 - 275 psig). Most transfer systems assume a pressure drop of approximately 30 psi to pass the quantity of liquid you have indicated.
See the attached brochure from Corken showing their propane transfer methods.
Good luck!
RE: Propane transfer re-visited
http://www.corken.com/
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Propane transfer re-visited
RE: Propane transfer re-visited
Good luck.
RE: Propane transfer re-visited
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Propane transfer re-visited
RE: Propane transfer re-visited
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Propane transfer re-visited
Another thing to look at is what type of excess flow valves are installed. Many of them also act as check valves and you won't be able to use the "suction" pipe as an alternate "fill" line.
If you can't find a Crane 410, there are plenty of references on the internet to calculate the dP in your piping.
Again, good luck!
RE: Propane transfer re-visited
As far as the EFV, I was told it would not act as a check valve as they've used the draw tube for filling purposes in the past. Unfortunately, there is no data/specs on the valve itself other than the rated capacity..
RE: Propane transfer re-visited
I used 225gpm and calculated losses in the system based on the velocity at this Q value. It looks to be roughly about 18psi loss across the system. sounds a bit low to me?
Liquid Friction Pressure Loss – 3” pipe sections w/ (2) EFV’s, (2) globe angle valves, (2) 2” reducers
Pressure Loss (psi): 10.14 Head Loss (ft): 47.3
Nominal Pipe Size: 3
Pipe Schedule: SCH 80
Flow Rate (gpm): 225
Viscosity (cP): 0.11
Specific Gravity (water=1): 0.495
Temperature (F): -44
Pipe Roughness (ft): 0.00015
Actual Pipe ID (in.): 2.9
Fluid Velocity (ft/sec): 10.93
Reynolds Number: 1104178
Friction Factor: 0.018
Overall K: 25.49
Piping Length (ft): 22
Lift Check : 2
Angle Valve Flow Down : 2
No. of Reducers: 2
Reducer Outlet Size (in) : 2
Liquid Friction Pressure Loss 2” Pipe section w/ (4) 90deg elbows, (2) 2” globe valves
Pressure Loss (psi): 8.05 Head Loss (ft): 37.6
Nominal Pipe Size: 2
Pipe Schedule: SCH 80
Flow Rate (gpm): 225
Actual Pipe ID (in.): 1.939
Fluid Velocity (ft/sec): 24.46
Reynolds Number: 1651427
Friction Factor: 0.019
Overall K: 4.05
Piping Length (ft): 19.3
Short Radius Elbows: 4
Ball : 2
RE: Propane transfer re-visited
You can treat that separately if need be:
dP for straight pipe: Use the dP = f L (RHO) V sq / 2 gc
Then use your K factors for the fittings and apply that formula.
Your K factors look low for the fittings you have.
I agree, with that type of velocity I would think your losses would be higher.
But I did check with a spreadsheet I have and get similar results.
An aside question: How are you keeping the propane in the tanks at - 44 deg F ?
RE: Propane transfer re-visited
as far as dp for the straight pipe, dP = f L (RHO) V sq / 2 gc -- possibly a silly question but what is the 'c' variable stand for?
and with regards to the LPG at -44, this is the value I was given, to be honest I haven't seen them personally as they are out of state and I work in a different department so all I have to go by are figures I was provided. I wish I had seen them for myself because the sketch I got was vague at best. I assume the tanks are possibly vacuum insulated or super-wrap jacketed or perlite blanketed?
RE: Propane transfer re-visited
Take a look at the Corken brochure. The propane would have to be at atmospheric pressure to be -44 deg F.
Most propane tanks are unisulated pressurized tanks (128 psig at 80 deg F ambient).
Think of your BBQ grill propane tank, just on a bigger scale.
Anyway you have your conclusion:
A differential pressure of 18 - 20 psi will result in a flow that exceeds the capacity of the excess flow valve.
And you have the calculations to prove that.
I commend you for your efforts and working through the calculations; well done!
RE: Propane transfer re-visited
I'm personally not very familiar with propane, the only real experience with LPG was as a refrigerant in a LNG liquefaction triple cascade system, and it is sub-cooled in that type of storage tank (lower operating pressure as well)
I've looked at the values I calculated hoping to catch a mistake but no luck, I guess I'll have to accept the result even though my gut feeling would tell me it should be higher than a 18-20 psi drop with a 225 gpm flow through that size piping..
well I do appreciate all your help, it's been a real long day for me and I think that's where I have to call it a night!
RE: Propane transfer re-visited
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek