LP separator level indicator

[Superfridge]

Hi all,

LP separator level indicators design and operation are varied and at times problematic. Some accumulate oil, some indicate a wrong level, and some show a fluctuating level that can't be a true reflection of the liquid level in the LP separator.

The attached photo is of one such separator sitting above a thermosyphon PHE supplying 2.5degC chilled water on a FRICK package with stable pressure control. The difference between the ammonia level being below the bottom sight glass and above the 3rd sight glass is about 60kg of ammonia which can't be true.

I'm not a fan of this level indicator leg design and connection into the main liquid leg, the drawing shows it is having a fall, yet it is level. I envisage velocity pressure and gravity fall having a bearing on what is seen in the level glasses. With a high side float valve on the outlet of the condenser PHE the entire charge would easily fit into this vessel therefore is a high-level switch really needed.

What do you folks think?


LP.jpg

[seanf]

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[cricri]

connection into the main liquid leg allow a liquid level control during stand still.
During operation the liquid velocity will decrease the level indication.
it's lived experience...

[Superfridge]

connection into the main liquid leg allow a liquid level control during stand still.
During operation the liquid velocity will decrease the level indication.
it's lived experience...

Agreed, I have witnessed another system with a low side float with sight glass positioned 400mm below a LP vessel with sight glass that maintains a normal LP level.

But what I’m seeing here is the opposite. When off there is no level in any of the sight glass’s yet when running the level can be above the 3rd sight glass. I think the system is so short that liquid is pouring down the liquid leg and pushing liquid up the indicator leg.

[RANGER1]

Superfridge,
Looks like a suff up.
Cannot see oil drain off bottom of vessel either.
Try restricting top control column stop valve in case dry suction velocity is pulling up column when running.

[Superfridge]

Thanks RANGER1
I hadn’t considered that the vapour velocity could have a bearing, and yes the level leg vapour connection is very close to the dry suction outlet. And the main liquid leg has an up stand which will hold oil and is probably the reason why it took so long to pump out and was still very smelly afterwards.