LN2 (LIN) delivery system and conversion to N2 gas

[Icecoffee]

Hi all,

I would like to get some advise and help on this problem:

Our ultra-high vacuum vessel requires venting/purging (>15 m^3 volume) and I was charged the assignment to deliver dry gas for this process.

I did sized a compressed clean dry air system, dew point to be -100F (max I can go), with (After acfm and purge loss) approx. 430 scfm so the vaccum can be vented approx in 30-40 minutes, with water content about 1-2 ppm, the vaccum group wasn't happy at all and I was told water shall be <100 ppb at the worst...

Since I am also in process in designing a LN2 delivery system to the facility and I am told to find out a way to "boil-off" LN2 and "suck" that gasoues N2 out and deliver to the vacuum system. Sorry for being so vague. I really don't know where and how to start.... I am a bit lost and any pointers and suggestions to start would be grateful!!!

I also have questions on the "dryness" of the N2 gas boiled off from LN2, does anyone know how much water is in it? (ppm or ppb) I just don't think this N2 gas would be any dryer than say 1ppm... please help!! or please let me know if more information is required!

 

[Icecoffee]

Oh by the way, I will be talking to suppliers etc about LN2 system details however I do want to get inputs from all of you before I talk to those people (my experience is that they dragged me in circles..............)

 

[unclesyd]

I believe your best approach is to get a package supply unit from your LN2 supplier. Even though we have a large LN2 plant onsite we still have several gaseous N2 units in service.
We still use a separate system for very dry high purity N2. We use High pressure bottles of high purity dry N2 but still use a molecular sieve in line to insure the lowest possible moisture content.

Here is one supplier whose equipment we use. They have a considerable amount of technical literature available.

http://www.taylor-wharton.com/

 

[dcasto]

The LIN supplier has vaporizers which are extended surface area tubes. They will calculate the requirements and supply you with the equipment. The heaters just use ambient air and will either "warm up" the LIN that is boiling off from from the tank or they will add enough heaters to vaporize a stream. If you need the N2 at a temp warmer than about 20 F from ambient, you'll need a electric or fuel fired heater.

The N2 is normally recovered from air and the air plant uses mole sieves to remove the water. The process happens at -300F, the air will have to be at .25 ppm water to keep from freezing the plant up.

 

[Gator]

This is a no-brainer if you talk to local industrial gas suppliers.

N2 is about as dry as you can get.

Liquid tanks boil-off (of course, since no insulation is perfect) and the pressure is used via the built-in PB coil to push liquid product out.

Depending on demand, you may need an external vapourizer.

Many industrial gas suppliers offer local N2 generators at lower purity if that suits your application.

Me posting five months later probably doesn't help much.

 

[IRstuff]

Most LN2 suppliers can help you with that. LN2 is often used to supply both cooling as well as dry N2 in the semiconductor industry

TTFN

FAQ731-376

 

[dcasto]

Think about the process everyone uses to make LIN. EVEERYONE uses mole sives, so if all those industrial gas suppliers use mole sieves to make LIN, why can't you do the same.If you can use dry air, you will save money over LIN and the cost of storing and handling it.

Ask a mole sieve vendors and not the off the shelf air dries for a design.