cryogenic level measurement

[hamo]

hello,

I need to install level measurements (transmitters) in some tanks which are between 7 to 10meters heigh.
The tanks contain cryogenic fluids (oxygen, nitrogen, argon) and go down to temperatures of -196°C.
Tankpressure: max. 50mbarg.
Important note: the tanks cannot be emptied for installing the measurements.
Has anybody experience in this subject or could suggest a type of measurement or supplier?

thanks in advance.

 

[CADShark]

There is a company called Cryomagnetics that uses transistors to sense the level of liquid in a container.
But these sensors need to be in the liquid, not the outside.

"Perfection - a result of many mistakes."
BJH

 

[iainuts]

The way this is typically done is to measure head of the liquid. There are gages designed for this. They need not be cryogenic since they have long tubes at ambient temp which keep the liquid away from the gage. All you need is a place to tap into the bottom and top. Say for example, the PB loop or the fill loop. The gages simply measure the difference in pressure between the top and bottom of the tank, and using a chart which is typically supplied by the tank manufacturer, you can read off the contents.

 

[sailoday28]

A number of "sound speed" measuring devices, placed perpendicular to the height will be able to measure speed of sound across the tank diameter. If gas and liquid sound speeds are very different.

 

[asukid99]

I think you are out of luck if you already don't have taps from the bottom and the top of the tank. You need to add these taps and install 1/4" SS tubing horizontally from the bottom tap for several feet so that any entrained liquid will vaporize. Use something like a Rosemount differential transmitter to measure the differential pressure between the taps. Both tubing runs will be at ambient temps. The transmitter will measure psid or inwc, but you can easily convert to height in LIN or LOX using their sg, for example LOX is 1.14 times as heavy as water.

That is the standard way to measure heights of cryo liquids. Of course, NASA uses thermocouples to detect temperature changes and therefore level changes, but that sounds too complicated to me.

OK, so there is another way. We used to have an old flat bottom tank that used some kind of float that was hooked up to a cable than went outside the tank. The cable moved a chart and the operators used a strap table to calculate the level. This also seems way too complicated. We sure are spoiled these days.

I bet I really haven't helped you much. OK how about this. The gas above the liquid level will be much warmer than the liquid. You can strap several RTDs or TC to the side of the tank and monitor temperature changes. Maybe NASA is on to something after all. You think they figured out they needed to monitor their LOX levels AFTER they built the tank? J/K. Good luck.

Oh and BTW, if you use the dp method, don't elevate the zero. We assume the gas phase of the cryogenic fluid in your tubing doesnt have any weight.

 

[boldfish]

Check out:

http://www.ktekcorp.com/dnn20/Default.aspx?tabid=67&productID=3