4 replies to this topic

[IonCube]

We have a N2 tank with a capacity to hold ~3000kg of liq.N2. We have a pressure regulator @4bar downstream ..the pipelines are such designed that via 1st channel we can direct gaseous (internal line is above liq.N2 level) N2 downstream.

 

If needed (in winters internal pressure is quiet low) 2nd channel directs liq.N2 through a bunch of external coils (mini-evaporator, for instance), this internal circulation of N2 back & fro from tank<>coils rises its internal pressure & we can thus revert to using 1st channel. I don't have a pic for now

 

Problem is that even in winters nowadays (~5-8celsius) when previously we have to raise internal pressures via 2nd channel; now the tank is suffering abnormally high pressures of +8bar, this pressure in summer (40-45celsius) is plausible but not in winters! The aftermath is that we have to intentionally bleed liq.N2 downstream to reduce such pressures which thereby increases our N2 consumption.

 

I am aware that tank is double-walled vacuum pulled, like a thermo-flask, however, I was also told recently that company intentionally introduces some kind of filler b/w the walls so as to maintain desired internal pressure (adequate heat transfer=adequate phase change) which should be higher than than the regulator setting of 4bar or otherwise it will act as check valve. So my first question ...does anybody know about such fillers, what are they, any material I can read?

 

Provided that I have replaced valve (in 2nd channel) in b/w tank & external coils which I guessed might be passing & unknowingly increased internal pressures ..but its checked & OK. My 2nd query what may be the problem with the tank internally? Is there any physical symptom I should check?

 

[breizh]

Ion cube ,

You should consider to contact the supplier of N2 who probably owns the tank or provides maintenance service of this equipment .

 

Take a look at the vapor pressure chart attached to confirm your findings .

 

http://encyclopedia....or_Pressure.GIF

 

Good luck.

Breizh

Edited by breizh, 20 January 2016 - 11:13 PM.

[Bobby Strain]

First you should check your nitrogen usage. I presume you have the tank filled occasionally. You should have records around to check against. Could be you are simply using less nitrogen, hence the pressure build.

 

Bobby

[Bodhisatya]

The filler you are talking about is expanded perlite that is used in between the vacuum region of the inner and the outer wall of a VITTs(Vaccum Insulated Transfer Tanks),it is in line with standard practice.

 

The reason for high internal pressure may be a loss of vacuum in between the walls, which has resulted in higher heat in leak and being saturated LIN evaporates.

 

Also, at places I have found the PBC (Pressure Building coil) to pass, resulting in higher pressure,but u have ruled out the issue.

 

If the vacuum level has deteriorated (get it measured by a Pirani gauge),u might find dark wet patches/sweating around the outer wall of the Tank.Check with the Tank vendor what was the initial level of Vaccum when the tank was commissioned.

 

Try to supplement a sketch of the tank u r having, for further analysis.

 

Bodhisatya

Edited by Bodhisatya, 21 January 2016 - 08:13 AM.

[ychong]

1. in cold weather, tank should not increase in pressure. From your past records, i believe this supports the case too.

2. instrument fault could be the problem. regulator and pressure indicator should be checked.

3. passing into the tank could be another problem.