Breaking Siphon in Flooded Inverted U 2

[mechanicalchad]

Hi There,

I have inherited the engineering on an upstream oil skimming tank site that utilizes four tanks in series, each tank having a pipe that forms an inverted u within the tank such that the suction side of the inverted u pulls from the bottom of the tank at around 2 feet then goes upwards to the crest of the u at a height x (x varying in each tank but around 5.488 m in the first tank to 3.962 m in the last tank) and then back downards to our nozzle at 2 feet elevation (I've attached a digram of the first two tanks for reference). The inverted U and nozzles are NPS 4.

As explained to me, the idea is that it will pull heavy fluid from the bottom of tank so that with each successive tank you have less light ends being passed along. The inverted U was to stop the flow from one tank to the next when the level dropped below the crest of the U similar to a stand pipe.

It seems to me that since the inlet and outlet will remain fully flooded that I would have a siphon effect drawing down my levels until the tanks are equalized. I've been told that as the fluid slows the siphon will break. Does anyone have any experience with this that they could share some thoughts? I understand the Froude number can be used to determine whether it will be self venting, but will this work if it is fully flooded on both inlet and outlet? I'm wondering do I need to install a siphon break at the crest of the inverted U?

Any ideas or thoughts are muchly appreciated.

Thanks in advance,

Chad

 

[zdas04]

Chad,
This looks a lot like you are trying to accomplish the same goals that a Gun Barrel does. I've built a lot of those, and there are a couple of problems with the inverted "U" in this design. First, the process needs a constant level so you want to set it to "overflow" (with a stinger from the bottom is fine) at your target vessel height. Second, there is nothing to prevent the siphon that (rightfully) worried you. I would expect both tanks to drain to the 2 ft level the first time someone opened the valve on the second tank and walked away.

Look at MuleShoe 2-Day Course on page 318 of 361 (Acrobat thinks it is page 319) for a picture of what I'm talking about. In the gun barrel on the right, the heavier fluid (water) comes off the bottom and the overflow is at the hydrostatic level of just water vs. a mixed column of oil and water. Notice that the upstream leg is vented to break the siphon.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[bimr]

Yes, you need a siphon break to avoid tank draining.

 

[mechanicalchad]

Thanks guys! That helps a lot. Now for Round 2 of explaining to my higher ups why I need a siphon break.

 

[racookpe1978]

Should it be an automatic, or manual, siphon break valve?

 

[zdas04]

Should just be an open-ended pipe.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

David. It's time to write a book.

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

 

[zdas04]

BigInch
I hope that wasn't sarcasm. I'm very fragile right now.

It looks like I'm going to have some dead time late this year and I was thinking really hard about starting a companion book for my 5-day course. Kind of "how to be a facilities engineer in low-pressure gas" from basic reservoir through detailed upstream facilities and deliquification through basic plants. I was going to include your flooded-ditch picture and give you picture credit.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[vpl]

I took it as sincere -- you have a lot of knowledge David.

Patricia Lougheed

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[BigInch]

Serious as a heart attack.
I don't give stars scarcastically.
Nice work.



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