11 replies to this topic

[Simon Pervaiz]

we have a liquid nitrogen storage tank at our site. it is at the end of COSTAIN's nitrogen generating plant. it works on the principle of cryogenic distillation of air. The problem we are facing for quite over a month is that our liquid storage tank keeps on venting. 

the setpoint is 7.0 bar. when the pressure of vessel increases it vents some of the nitrogen to bring pressure down.

we have checked the vacuum of the LIN storage tank it is a bit crude. >1 torr

what other factors shall we check to solve the problem.

PS: its my first post. so dun mind if data is in sufficient or question isn't clear enough.

if you need data or further information i will provide u with tht. 

Thanks

waiting for your replies

[thorium90]

There will always be a certain amount of heat ingress into the tank. If left stagnant, over time the pressure will surely increase.

[fallah]

Simon,

 

The problem you mentioned isn't so clear. It might if you upload a simple sketch of the storage tank system would be more helpful...

[S.AHMAD]

1. Lack of information hampered our contribution.

2. In troubleshooting process plant oroblems, we need a  set of planr data (composition, pressure, tempreatur etc) when the system in good operation and another set of data when the system is giving us problem. We try to identify the pproblem by analysing and comparing these data.

3. In your case the various possibilties are possible such is contamination of N2 or some damage of insulation

Edited by S.AHMAD, 19 November 2013 - 08:47 PM.

[curious_cat]

Do you have historic trend data? Has it started venting more than it used to? 

 

Has weather changed? Were any other changes made when the venting started? Has N2 consumption reduced? Have any set points been changed?

Edited by curious_cat, 21 November 2013 - 02:27 AM.

[Simon Pervaiz]

Dear All

thanks for your interest in the matter.

i am attaching the technical information of the tank plus its diagram

i have one other question regarding this problem

in the vacuum we have perlite. so i want to ask is it possible that perlite replacement is required??

some information regarding perlite's life and its replacement regime will be highly appreciated

 

Link for Data

http://www.viewdocso...document/lle98x

[Simon Pervaiz]

@curious_cat

The answers to your questions are below

 

Has weather changed? No

Were any other changes made when the venting started? No

Has N2 consumption reduced? Consumption has not changed.

Have any set points been changed? at first set points were not changed. But during the troubleshooting we changed some setpoints but no improvements were observed

[thorium90]

Perhaps you can check the regulator on the vaporizer coil. (Attached). The regulator controls the tank pressure by vaporizing some liquid into gas. If the settings has drifted, it could be vaporizing more liquid than before and increasing the pressure unnecessarily. You can check if that is the real problem by temporarily closing the manual valve upstream of the regulator and observing if the rate of pressure increase in the tank reduces.

Attached Files

•  Vaporizer coil.jpg   176.65KB   6 downloads

Edited by thorium90, 21 November 2013 - 08:00 PM.

[Simon Pervaiz]

@thorium90

Thanks for your advice

I have observed the vaporizer coil and the regulator's function. The working is normal. One such indicator is that there is no icing observed on the vaporizer coil. if the regulator is malfunction and vaporizer is in service thn icing must appear on it.

[thorium90]

How long is the time between each time the psv opens? You have any nice trends? If it is slow enough, you will not observe icing... It will just be slightly cool. You have already tried closing the valve i presume? Or you did not try that but simply assumed it works fine simply based on your no ice assumption and pure eye power observation.... Troubleshooting can be such that if all the most probable solutions are exhausted, then the solution must be the least probable one. Sometimes, I feel people do troubleshooting like a monte carlo analysis, randomly trying out stuff in the hopes that one of them works. But I like to think that the best way of troubleshooting is like a bayesian search, trying out solutions from the most probable first and then keep going until the least probable.

Edited by thorium90, 23 November 2013 - 11:19 AM.

[curious_cat]

 

we have checked the vacuum of the LIN storage tank it is a bit crude. >1 torr

 

 

That's the jacket vacuum right? 

 

I may be wrong but 1 torr sounds like a bit on the  high side for a cryo tank jacket. I thought 1 torr is about the point were performance may get degraded. From what I recall 0.1 torr or lower was more like a normal reading on a cold tank. 

 

Again, this could be application / design specific. I've no clue. I'm not an expert. What do your specs. / SOP say about acceptable vacuum levels?  Edit: I re-read the spec sheet you posted. It does say 0.1 mbar. So you are  more than 10 times higher than the vacuum in the spec. Ergo rather than replace perlite I think you need a re-evacuation / check for jacket leaks. 

 

Have you kept good vacuum logs? How do they look.  Is tank-jacket re-evacuation a possibility?

Edited by curious_cat, 23 November 2013 - 02:32 AM.

[thorium90]

Actually, in post 6, the OP has in his document stated a jacket pressure of 0.1mbar. But as also mentioned, the measurement is of some (unknown to us) crude method. The cat is right in that in this case, the jacket pressure does seem to be on the high side if it is >1torr (assuming no typo).