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Backpressure regulator

Backpressure regulator

(OP)
Hi All:
I'm operating a thermic oil system in my plant with an operating temperature of 380 Deg C with Therminol 72. I'm changing the expansion tank vent line forward pressure regulator with a backpressure regulator to hold constant static pressure inside the tank and also to minimize the N2 consumption and thermic fluid wastage
I'm wondering if someone can provide some insight as how to size this backpressure regulator. The tank has a 1/4" port for the vent line
My idea is to size the backpressure regulator based on the flow, when the forward pressure regulator ( on inlet N2 line) fails open
Thanks for all your in advance
Araza

Asif Raza

RE: Backpressure regulator

If you size it for the forward pressure regulator failing open, you'd essentially be using it as a relief device at that point. Not sure if that's the main intent of the regulator, you could end up with something huge (maybe too big for a 1/4" port).

You probably have a heater somewhere in the system. You could take the duty of that heater, calculate the change in density of the system at max duty, and convert that liquid volume into an equivalent nitrogen volume that needs to be vented. That would give you something more reasonable. That's what I usually do for outbreathing requirements...

RE: Backpressure regulator

If we had a P&ID to look at, we could stop guessing.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Backpressure regulator

This makes no sense.

if you're replacing the "forward pressure" regulator for a back pressure regulator, how are you going to keep the pressure constant if the gas volume keeps changing??

How does the gas escape from the tank now??

To maintain a "constant" static gas pressure you need a regulator supplying gas to a certain pressure, say 5psi. your back pressure regulator then is set at say 6 psi so your pressure fluctuates between 5 to 6 psi.

So in this instance, yes, you could size you BP regulator to that or install some pressure relief valves to prevent the pressure going over your vessel design pressure if the incoming supply can over pressure the vessel. This is standard pressure vessel / pressurised vessel design.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Backpressure regulator

Imagination can do anything.

Dejan IVANOVIC
Process Engineer, MSChE

RE: Backpressure regulator

You will need to purge "lights" that are created by the degradation of the oil. Don't for get that.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Backpressure regulator

(OP)
All:

Met11, excellent post..
yes I have a forward pressure regulator set 75 psig to maintain a static pressure to prevent thermic fluid from boiling. 75 psig is 5 psig more than the vapor pressure of the thermic fluid at its highest temperature
I would set the backpressure regulator to 80 psig; in the event the pressure increases inside the expansion tank the BPCV would open and release the pressure
Thanks all for your help
Araza

Asif Raza

RE: Backpressure regulator

So what flow rate are you going to use? I thought that was your key question?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Backpressure regulator

(OP)
I'm going to use Met11's design basis
Thank all is advance
Araza

Asif Raza

RE: Backpressure regulator

In the real world, shell and tube heat exchangers leak. And if the pressure differential between HO and the process medium in the HX is in favor of process fluid leaking into HO, then vaporisation of this process fluid will need to be released continously at the expansion drum BPCV - make a rough estimate of which units could leak thus, the size of a pinhole leak, and that will give you some idea of what this continous vapor release rate would be at the expansion drum.

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