Nitrous Oxide Tank Install

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wrobotronic said:
Wow. Education was my goal in asking the question. Not sure you are the one understanding the purpose of the forum.

Here is a reference to N2O being a cryogenic liquid... https://www.ncbi.nlm.nih.gov/m/pubmed/10215117/

Then NFPA 59A speaks directly to this... and refers to the NEC to Bulk Storage.

lastly in the 2014 NEC handbook pg. 665 specifically refers to storage of cryogenic liquids.

I was just hoping for some help not a lecture about how great you are and how shitty I am. I'm sure you would rather see some one else do the install and have the thing blow up? Which can happen... I'm just trying to educate myself...

Thanks for the help...

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That reference is not correct. The definition of a cryogenic liquid is a liquid with a boiling point of less than -150°C. Nitrous Oxide has a boiling point of -88.5°C.
 
don_resqcapt19 said:
That reference is not correct. The definition of a cryogenic liquid is a liquid with a boiling point of less than -150°C. Nitrous Oxide has a boiling point of -88.5°C.
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Awesome info thank you. But that said, may I ask for your reference? Here's the definition that I found (reference link at the bottom) which is quite different from yours:

A*cryogenic liquid*is*defined*as a liquid*with a normal boiling point below –130°F (–90°C). The most commonly used industrial gases that are transported, handled, and stored in the*liquid*state at*cryogenic temperatures are argon, helium, hydrogen, nitrogen, and oxygen.

I will concede that N2O does not fall into this definition either. No problem. And you are correct about the boiling point.

So then the question becomes why do the articles I have read refer to it as a cryogenic liquid? (and in my case it is being stored in a tank with a coil and refrigerant in a liquid state to answer a previous post) Clearly, there is some kind of disconnect.
http://www.airproducts.com/~/media/...lBrkQFggnMAE&usg=AOvVaw2YYz2wNMZIull1oXxWky9f

I have no issue being incorrect. In fact, my ignorance is why I visit this forum. Unfortunately for you all... :)



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wrobotronic said:
Awesome info thank you. But that said, may I ask for your reference? Here's the definition that I found (reference link at the bottom) which is quite different from yours:

A*cryogenic liquid*is*defined*as a liquid*with a normal boiling point below –130°F (–90°C). The most commonly used industrial gases that are transported, handled, and stored in the*liquid*state at*cryogenic temperatures are argon, helium, hydrogen, nitrogen, and oxygen.

I will concede that N2O does not fall into this definition either. No problem. And you are correct about the boiling point.

So then the question becomes why do the articles I have read refer to it as a cryogenic liquid? (and in my case it is being stored in a tank with a coil and refrigerant in a liquid state to answer a previous post) Clearly, there is some kind of disconnect.
http://www.airproducts.com/~/media/...lBrkQFggnMAE&usg=AOvVaw2YYz2wNMZIull1oXxWky9f

I have no issue being incorrect. In fact, my ignorance is why I visit this forum. Unfortunately for you all... :)



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I see that there is more than one definition in use. https://www.chemicool.com/definition/cryogenic_liquid.html
https://books.google.com/books?id=i...onepage&q=cryogenic liquid definition&f=false
From my hazmat responder training. it is my understanding that if you can keep the product liquid by the use of pressure only, it is not a cryogenic liquid. I don't believe that the typical nirtrous oxide tank is not a vented tank, and keeps the product liquid only by the use of pressure. If you see a transport truck carrying a true cryogenic liquid, you will see puffs of vapor every so often. Those trucks boil off some of the liquid to keep it cool and vent the vapor.
 
don_resqcapt19 said:
I see that there is more than one definition in use. https://www.chemicool.com/definition/cryogenic_liquid.html
https://books.google.com/books?id=i...onepage&q=cryogenic liquid definition&f=false
From my hazmat responder training. it is my understanding that if you can keep the product liquid by the use of pressure only, it is not a cryogenic liquid. I don't believe that the typical nirtrous oxide tank is not a vented tank, and keeps the product liquid only by the use of pressure. If you see a transport truck carrying a true cryogenic liquid, you will see puffs of vapor every so often. Those trucks boil off some of the liquid to keep it cool and vent the vapor.
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I suppose I am splitting hairs at this point don_reqcapt19. The drawings indicate the use of a refrigerant pump and a another thingy ma bob (I don't have the drawings, I'm sorry if I used the non professional indicators hehehe). I can verify in the morning, but I do believe it's a refrigerated tank (again wrong words, please bear with me).

From what I have gathered here is that my use of C1D1 along side this liquid is not the correct way to state my objective. But I think that I can conclude, regardless of its cryogenic definition, is that nothing special is required for the electrical part of the install. Unless, of course, people above my pay grade deem it necessary.

However, the customer could be going at this incorrectly maybe? In that they do, in fact, need the tank to be a pressurized system as opposed to the refrigerated one?

Does anyone have an extra shovel? The one I was using for this hole I'm in has broken... perhaps an excavator?

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wrobotronic said:
I suppose I am splitting hairs at this point don_reqcapt19. The drawings indicate the use of a refrigerant pump and a another thingy ma bob (I don't have the drawings, I'm sorry if I used the non professional indicators hehehe). I can verify in the morning, but I do believe it's a refrigerated tank (again wrong words, please bear with me).

From what I have gathered here is that my use of C1D1 along side this liquid is not the correct way to state my objective. But I think that I can conclude, regardless of its cryogenic definition, is that nothing special is required for the electrical part of the install. Unless, of course, people above my pay grade deem it necessary.

However, the customer could be going at this incorrectly maybe? In that they do, in fact, need the tank to be a pressurized system as opposed to the refrigerated one?

Does anyone have an extra shovel? The one I was using for this hole I'm in has broken... perhaps an excavator?

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Not sure why they would use refrigeration. Nitrous Oxide can be kept in the liquid state with less than 700 psi. You could keep it liquefied at a lower pressure by the use of refrigeration equipment, but that would be an unnecessary cost, as simple pressure does the job.

I guess none of this really matters as the product is a non-flammable product and does not trigger any requirement for the application of the rules in Article 501. As far as I know there is nothing special required for this product by the rules in the NEC.
 
don_resqcapt19 said:
Not sure why they would use refrigeration. Nitrous Oxide can be kept in the liquid state with less than 700 psi. You could keep it liquefied at a lower pressure by the use of refrigeration equipment, but that would be an unnecessary cost, as simple pressure does the job.

I guess none of this really matters as the product is a non-flammable product and does not trigger any requirement for the application of the rules in Article 501. As far as I know there is nothing special required for this product by the rules in the NEC.
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Now that is a valid point. Why indeed would they not pressurize It? These are the things I don't know.

This next statement may be way off base, so please bear with my ignorance... but, the tank is outside. Would the heat from the sun have any dictation on the pressure with in the tank? Could that be a reason for the use of a refrigerant? I will also ask the site super and the engineers, but you certainly seem to have a grasp on this. So just for my own education I ask this...

Thank you again for the info.


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Bluntly, (and I don't really believe this to be the case) if the designers were worried about heat from the sun causing a problem - they weren't designing the system properly in the first place.
 
wrobotronic said:
Now that is a valid point. Why indeed would they not pressurize It? These are the things I don't know.

This next statement may be way off base, so please bear with my ignorance... but, the tank is outside. Would the heat from the sun have any dictation on the pressure with in the tank? Could that be a reason for the use of a refrigerant? I will also ask the site super and the engineers, but you certainly seem to have a grasp on this. So just for my own education I ask this...

Thank you again for the info.


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A bit more research says that the critical temperature for N2O is 97.6°F, so refrigeration would be necessary outside in the sun. The critical temperature of a gas is the temperature above which the gas cannot be liquefied by pressure alone. If the product temperature would exceed 97.6°F the container would BLEVE. (Boiling Liquid Expanding Vapor Explosion) The expansion factor for nitrous oxide when is changes from liquid to gas is about 440, that is the volume of the gas is 440 times larger than the volume of the same mass as liquid.

One of my HazMat instructors defined BLEVE as "Blast Leveling Everything Very Effectively" The force in this explosion is from the instant expansion of the product from liquid to gas when the critical temperature is reached. The same thing can also occur at lower temperatures where the pressure is lost.

Still does not make it an Article 501 application, but there may be special requirements for the power supply to the refrigeration equipment. There would also likely be some type of automatic venting system that would vent the product to prevent the tank from failing as the temperature approaches the critical temperature.
 
Don, Thanks very much for your insight. I've done a fair amount of work with high pressure flammable systems (refineries mostly), but never with pressurized N2O systems.
 
don_resqcapt19 said:
A bit more research says that the critical temperature for N2O is 97.6°F, so refrigeration would be necessary outside in the sun.
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I don't understand why that follows. The critical pressure is 72.45 bar, so if the tank can handle pressures near or above that, and the mass charge of nitrous oxide isn't too large, the tank could contain the supercritical fluid you get at temperatures above the critical temperature. So is the issue economics (cheaper to cool so you can use a smaller tank for the same amount of nitrous oxide), or reducing the safety hazard from overfilling the tank at a lower temperature and then allowing the temperature to rise (the density of the liquid phase goes down rapidly as you approach the critical temperature), or something else?

Cheers, Wayne
 
As I understand it, the critical pressure is the pressure required to keep the product liquid at the critical temperature. When the temperature goes above that, no amount of pressure will keep the product liquid and the volume will expand 440 times, causing catastrophic failure of the container.
 
don_resqcapt19 said:
As I understand it, the critical pressure is the pressure required to keep the product liquid at the critical temperature. When the temperature goes above that, no amount of pressure will keep the product liquid and the volume will expand 440 times, causing catastrophic failure of the container.
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I agree on the possibility of catastrophic container failure, but it is not an instantaneous effect at the critical temperature from a factor of 440 expansion. As mentioned in an earlier thread the density of the liquid itself starts to drop very fast as you approach the critical temperature. Arbitrarily close to the critical temperature itself there should be almost no difference in volume between the liquid and gas phase. Thermodynamics tells us that, I think. :)

For more details see wwhitney's post below....
 
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don_resqcapt19 said:
As I understand it, the critical pressure is the pressure required to keep the product liquid at the critical temperature. When the temperature goes above that, no amount of pressure will keep the product liquid and the volume will expand 440 times, causing catastrophic failure of the container.
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That's not how I understand the physics. As the temperature approaches the critical temperature, the gas phase density goes up (since the vapor pressure goes up and the gas phase density is proportional to that) and the liquid phase density goes down (the liquid expands with the rising temperature). At the critical temperature, those two density curves meet, at a density called the critical density. So at or above the critical temperature, there is no difference between gas phase and liquid phase, just one supercritical phase.

I found staring at this pressure-density isotherm diagram to be helpful: https://www.researchgate.net/figure...es-of-our-infrared-experimental_fig3_49668464
It's for ammonia, but I assume the behavior is typical.

Cheers, Wayne
 
wwhitney said:
That's not how I understand the physics. As the temperature approaches the critical temperature, the gas phase density goes up (since the vapor pressure goes up and the gas phase density is proportional to that) and the liquid phase density goes down (the liquid expands with the rising temperature). At the critical temperature, those two density curves meet, at a density called the critical density. So at or above the critical temperature, there is no difference between gas phase and liquid phase, just one supercritical phase.

I found staring at this pressure-density isotherm diagram to be helpful: https://www.researchgate.net/figure...es-of-our-infrared-experimental_fig3_49668464
It's for ammonia, but I assume the behavior is typical.

Cheers, Wayne
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Thanks, that is a bit different from what I remember from HazMat class but that was some time ago. What happens to the volume of the product when you exceed the critical temperature?
 
I guess what I don't understand is the difference in density between the liquid and the critical density. It is 48.21 pounds per cubic foot in the liquid state and 28.22 pounds per cubic foot at the critical point. To me that indicates a change in volume. How is this new volume contained in the original container?
 
don_resqcapt19 said:
I guess what I don't understand is the difference in density between the liquid and the critical density. It is 48.21 pounds per cubic foot in the liquid state and 28.22 pounds per cubic foot at the critical point. To me that indicates a change in volume. How is this new volume contained in the original container?
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OK, so the 48.21 pcf density you quoted appears to be the density of the liquid phase at room temperature (70F?) and at the vapor pressure (so a liquid in a sealed tank with some volume for vapor phase over it). Liquids at temperatures near the critical temperature are compressible, unlike the usual case. As the temperature goes up, the liquid phase density at the (rising) vapor pressure goes down, approaching the critical density. So one of two things will happen:

1) If the average density of the material in the tank (total mass/tank volume) is less than the critical density, the pressure in the tank will stay at the vapor pressure (which depends on temperature), the liquid will expand but never "run out of room", and the two phase will converge at the critical temperature (I think).

2) If the average density of the material in the tank is greater than the critical density, then before you reach the critical temperature, the vapor will all condense, and the pressure in the tank will shoot up, probably above the critical pressure, causing the liquid to be compressed to a density greater than the density it would have if it were in equilibrium with the vapor phase.

At least, that is my interpretation of the density-pressure-temperature graphs I have been looking at. My physics education has all been by osmosis, so hopefully an actual physicist can verify the above. :)

Cheers, Wayne
 
A correction to the previous post: If the charge in the tank is such that the average density of the material is less than the critical density, then as the temperature increases towards the critical temperature, there will be a point at which the density of the vapor phase matches the average density in the tank. At that point, all of the liquid will have turned to vapor. As the temperature continues to rise to the critical temperature, the tank pressure will also rise, but at the critical temperature the tank pressure will be less than the critical temperature, as the density is less than the critical density.

Cheers, Wayne
 
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