Liquid Nitrogen Generator

[killie99]

[QUOTE=laywill;1789697Having spoke to the technology teachers, they reckon that using mild steel piping would reduce chances of an explosion because rather than shatter in true Hollywood style, it tends to rip and burst meaning no flying shards of pipe heading towards me!
...[/QUOTE]

What are you using the mild steel piping for? Just curious because if you are using it to hold the LN2 I think it'll cause you problems and will eventually crack due to the cold temperature - you really need to use reasonably good quality stainless. Poor quality metal tends to disintegrate eventually when used with LN2 .......
Personally I think you're madder than Mad Jack McMad ......

[Main]

You're going to need to get your hands on thermodynamic charts (aka. psychometric chart, thermodynamic diagram, phase diagram, mollier diagram) for nitrogen, and maybe air, if you don't have them already. They come in several forms:

• p-T Pressure-Temperature
• p-v Pressure-Volume
• p-h Pressure-Enthalpy
• T-S Temperature-Entropy
• h-S Enthalpy-Entropy

All have their uses and some will be more useful in specific applications. For gas compression and liquifaction p-v and T-S(or p-h) are the most useful respectively, although as a disclaimer I'll note that it's bee a long while since I've used either. All of these charts are also pretty daunting the first time you see them and it might take a bit of time before you know your way around them. You're going to need to know how to plot thermodynamic cycles on them (which is essentially what you use them for) as a means of determining the conditions required/produced, and you're also going to need to know what to do when your cycle enters the 2-phase envelope.

Thanks to the wonders of the internets you can look at other people's mathmatical solutions for similar cases. This also has the only chart for nitrogen I've seen online so far (fig.2 is a p-h diagram).

In this instance, LN2 is produced at atmospheric pressure by pressurising air from 1 x atmospheric (~0.1MPa) to 150 x atmospheric (~15MPa) in a 5 compressor cascade, and then cooling it to 160 Kelvin (-113 C) before passing it through the throttle. This converts 7% by mass of the nitrogen passing through the throttle to liquid.

The same result could have been achieved at a lower pressure, but it would have required a lower temperature too - this is something you will have to take into account, as you're going to be limited by what temperatures and pressures you can achieve.

I could go into more detail, but tiredness is sapping brainpower and I might miss out something important (assuming I haven't already...)

[laywill]

pV=nRT is covered in my AS text book
HOWEVER what it lacks is any data sheets other than basic information and trivial spuotings, such as "don't forget that the IDeal Gas equation only works for gasses!"

DUH!!

In all seriousness, I shall look at getting a copy of said book.

[laywill]

You're going to need to get your hands on thermodynamic charts (aka. psychometric chart, thermodynamic diagram, phase diagram, mollier diagram) for nitrogen, and maybe air, if you don't have them already. They come in several forms:

• p-T Pressure-Temperature
• p-v Pressure-Volume
• p-h Pressure-Enthalpy
• T-S Temperature-Entropy
• h-S Enthalpy-Entropy

All have their uses and some will be more useful in specific applications. For gas compression and liquifaction p-v and T-S(or p-h) are the most useful respectively, although as a disclaimer I'll note that it's bee a long while since I've used either. All of these charts are also pretty daunting the first time you see them and it might take a bit of time before you know your way around them. You're going to need to know how to plot thermodynamic cycles on them (which is essentially what you use them for) as a means of determining the conditions required/produced, and you're also going to need to know what to do when your cycle enters the 2-phase envelope.

Thanks to the wonders of the internets you can look at other people's mathmatical solutions for similar cases. This also has the only chart for nitrogen I've seen online so far (fig.2 is a p-h diagram).

In this instance, LN2 is produced at atmospheric pressure by pressurising air from 1 x atmospheric (~0.1MPa) to 150 x atmospheric (~15MPa) in a 5 compressor cascade, and then cooling it to 160 Kelvin (-113 C) before passing it through the throttle. This converts 7% by mass of the nitrogen passing through the throttle to liquid.

The same result could have been achieved at a lower pressure, but it would have required a lower temperature too - this is something you will have to take into account, as you're going to be limited by what temperatures and pressures you can achieve.

That is excellent information!!
I'm sure a teacher or two can help me get to grips with these if I can'tfathom it out myself.
Stacking compressors would certianly be the most efficient method of doing this I think, because finding a single compressor capable would be hard at the best of times.

[laywill]

What are you using the mild steel piping for? Just curious because if you are using it to hold the LN2 I think it'll cause you problems and will eventually crack due to the cold temperature - you really need to use reasonably good quality stainless. Poor quality metal tends to disintegrate eventually when used with LN2 .......
Personally I think you're madder than Mad Jack McMad ......

Thanks for the pointer. Do you have any idea of the tension capacity of stainless compared to mild steel? If it is going to seriously: affect my bank ballance further or be seriously detrimental not to use it, I may have to have a think.

Personally I think you're madder than Mad Jack McMad ......

That's me!

[TAKTAK]

Do you have any idea of the tension capacity of stainless compared to mild steel? If it is going to seriously: affect my bank ballance further

That all depends on which grade you go for... i.e. A2 or A4

Or B7 (alloy steel) if you have the funds available as it is a petrochem spec that is capable of high temperature fluctuations and pressure, or even further, B8 (stainless), but they will set you back a pretty penny.

As a general rule of thumb, A2 is approx 4 times more expensive than mild steel (ish), with A4 being more expensive than that, and then B8 tipping the scales at a very hefty amount, (if you can even get B8 or B7 in tubular form).

[laywill]

Thanks TakTak.
That sounds like I will be going for A2 or A4 if I can find the money (or some going cheap)

Do you know if they are all not going to be affected by the Nitrogen and oxygen which hopefully will be swshing through thier merry rounds at many atmospheres of pressure?

EDIT: any CO2 will be removed in an NaOH (i think) trap, but no idea how to remove oxygen from the gases (what with it being somewhat corrosive )

[Pob255]

Well the simple application of a match will remove any O2

However if I remeber correctly it shouldn't be much of an issue as Nitrogen will liquify before the oxygen.
Seem to remember oxygen is liquified from air by cooling compressed air with liquid nitrogen.
You may get some but it should boil off before the nitrogen does.

O2 boiling point is 90.6K
N2 boiling point is 77K

[JohnBlake3310]

Hi Laywill,

There are so many benefits nitrogen generators. Really interesting saying that you want to make a liquid nitrogen generator. Sounds like you know exactly what you want/require. Just would like to say, as I have in excess of 25 years experience in air compressor services including nitrogen generators. If you want some extra information on nitrogen generators, I am always happy to provide some assistance. Many thanks!

[Zak33]

Hi Laywill,

There are so many benefits nitrogen generators. Really interesting saying that you want to make a liquid nitrogen generator. Sounds like you know exactly what you want/require. Just would like to say, as I have in excess of 25 years experience in air compressor services including nitrogen generators. If you want some extra information on nitrogen generators, I am always happy to provide some assistance. Many thanks!

Hello

this threaad was last posted on in 2009, so Thread Ressurection award right here

[badass]

£10 says you never complete this project

So. 11 years later. Where's my tenner?

[ik9000]

Hi Laywill,

There are so many benefits nitrogen generators. Really interesting saying that you want to make a liquid nitrogen generator. Sounds like you know exactly what you want/require. Just would like to say, as I have in excess of 25 years experience in air compressor services including nitrogen generators. If you want some extra information on nitrogen generators, I am always happy to provide some assistance. Many thanks!

Hello

this threaad was last posted on in 2009, so Thread Ressurection award right here

I'm calling auto-bot. Noone genuine would 1) try and assist the OP in their misguided endeavours and 2) bother to post in the thread after over a decade has elapsed. @mods block the account now and save us all more spam later.

So. 11 years later. Where's my tenner?

and lost interest.

[ik9000]

That all depends on which grade you go for... i.e. A2 or A4

Or B7 (alloy steel) if you have the funds available as it is a petrochem spec that is capable of high temperature fluctuations and pressure, or even further, B8 (stainless), but they will set you back a pretty penny.

As a general rule of thumb, A2 is approx 4 times more expensive than mild steel (ish), with A4 being more expensive than that, and then B8 tipping the scales at a very hefty amount, (if you can even get B8 or B7 in tubular form).

alright if someone is going to thread resurrect i am at least going to interupt here to pick up on this:

A4 etc are to do with BOLT grades for mechanical applications. Sheet and plate are supplied to different standards and I shan't bore you with all the BS EN standards and DIN and AS equivalents. They are further split into use categories like structural vs general mechanical vs architectural etc etc and that's before you look at toughness banding, temperature regimes and all the other detail engineers have to wade through.

Asking whether stainless is stronger than mild is a silly question. It's like asking is a Ford faster than a Vauxhall! Which model, spec etc all come into it. You can get stainless steels with 460MPa and mild steels with just 200MPa, or less, and vice versa. Also a lot of stainless steels have a secant modulus so lose stiffness with increase in applied stress. It's not an apples-for-apples comparison. Particularly when you get down to a grain structure and the metallurgy and material science at a macro and microscopic level.

Rant over. Suffice to say the OP while admirably ambitious, was on a hiding to nothing!

[DDY]

alright if someone is going to thread resurrect i am at least going to interupt here to pick up on this:

A4 etc are to do with BOLT grades for mechanical applications. Sheet and plate are supplied to different standards and I shan't bore you with all the BS EN standards and DIN and AS equivalents. They are further split into use categories like structural vs general mechanical vs architectural etc etc and that's before you look at toughness banding, temperature regimes and all the other detail engineers have to wade through.

Asking whether stainless is stronger than mild is a silly question. It's like asking is a Ford faster than a Vauxhall! Which model, spec etc all come into it. You can get stainless steels with 460MPa and mild steels with just 200MPa, or less, and vice versa. Also a lot of stainless steels have a secant modulus so lose stiffness with increase in applied stress. It's not an apples-for-apples comparison. Particularly when you get down to a grain structure and the metallurgy and material science at a macro and microscopic level.

Rant over. Suffice to say the OP while admirably ambitious, was on a hiding to nothing!

Don't forget our other Austenite friends; the ISO A*-grade washers and nuts

[ik9000]

That is excellent information!!
I'm sure a teacher or two can help me get to grips with these if I can'tfathom it out myself.
Stacking compressors would certianly be the most efficient method of doing this I think, because finding a single compressor capable would be hard at the best of times.

yes, they're called university professors. Given the time elapsed have you now done a degree in science/engineering, and how did it go? Are you now designing chemical plants for a living?

[ik9000]

Don't forget our other Austenite friends; the ISO A*-grade washers and nuts

or indeed the duplex D grades. I wasn't trying to be exhaustive