Homemade Liquid Nitrogen Generator

Intro: Homemade Liquid Nitrogen Generator

Did you ever think you could make liquid nitrogen in your own garage? This is an industrial process so how can an individual do this? Still doubt me? Intrigued? Read on.

As a lover of science I tried to think of a challenging project that was out of the ordinary. After going through the internet web and Youtube I realized that no one had made liquid nitrogen in his home. Yes, I did see some videos where some would use a Stirling Cooler from a cryorefrigerator and use this to condense nitrogen on the exterior of the cold-head. While one is making liquified gas, this is done using a prefabricated machine. I wanted to make the machine that liquefies the gas. Furthermore, a cryocooler has a very low production rate. You will only get about 500 - 1000ml per day. On the following pages I will walk you through the basics of how to build your own liquid nitrogen generator. Using easily obtained materials you can liquefy nitrogen or air. The unit cools to -320F in under 50 minutes. The production rate is about 350 cc/hr.

A full tutorial and plans are at http://homemadeliquidnitrogen.com This page goes over theory, thermodynamics and more detail on where to get components and how to build this. This Instructable serves as a general introduction to how this baby is put together.

I have just added a new web tutorial on how to make your own N2 gas from the air. I will add this as a new Instructable in the next few days. You can get a link for it at the end of this one.

I have also built a high-precision cryogenic digital LCD thermometer for this project, which you can buy for yourself. You can see how it compares with an Omega digital thermometer here.

Ok. The video above gives you a quick 3 minute overview of the project. At the end of this tutorial I briefly mention the PSA I made for making the pure N2 from the air for the generator. If you're ready for 320 degrees below zero we can begin...

STEP 1: Overview

The liquefication generator has a few basic components. Starting in order:

1. Scrubber - This removes CO2 and H20 from the gas stream. Without this the water and CO2 would freeze and clog the tubing and valves

2. Filter - We need to remove any micro-particles that can clog our compressor valves

3. Compressor - This compresses the gas to high pressure. Two important factors are the pressure and flow rate. This project uses an oil-free scuba compressor delivers a pressure of 3500 psi at a flow rate of 3 SCFM (I jacked it up to 4 SCFM). It is possible to use a regular refrigerator compressor, but the production rate will be significantly reduced

4. Pre-cooler - This cools the hot, compressed gas before entering the cooling tower.

5. Regenerative cooling tower - Hot compressed gas flows through a counter-current system to cool the gas to cryogenic temperatures. Expanded, non-liquid gas returns to get recompressed.

6. Throttle - This is a needle-valve that enables a controlled expansion of the gas without losing the pressure behind it.

7. Baffle - This reduces the velocity of the expanded gas so it does not dissipate the cooled liquid into the gas-stream. It also provides a larger surface area for condensation.

7. Reservoir- This is the collection system that collects the gas. Heat exchange with the environment is minimal.

Above is a picture of an early version of the generator using a recycle can. Later you will see an improved version.

STEP 2: Compressor Filter

You need to protect the compressor's valves and cylinders from debris and water. You can purchase an inexpensive vacuum filter from a distributer. I bought a Vaccon 10 um filter. The part number is VF500F.

STEP 3: Compressor

This is the most expensive component. I used a RIX oil-free SA-3E. This delivers 3 SCFM @ 3500psi (230 ATM). I modified the motor and pulleys to deliver 4 SCFM. A higher flow gives you a faster cool-down and production rate. The high pressure allows you to have a larger temperature drop when you throttle the gas to a lower pressure. You can use a regular refrigerator compressor, but you will be waiting a long time to drop 400 degrees Fahrenheit from the ambient temperature to -320F if you only have 40 ATM of pressure.

My compressor allows me to get to -320F in 45 minutes. I am guessing that a standard compressor at 40 ATM will take 6 times longer, or 4 1/2 hours. Of course, if the flow rate is less then you have to add more time.

STEP 4: The Scrubber

You can make this components out of PVC pipe. I used 4" PCV. You need to get the correct fittings to get to a pipe size that you can then attach to your compressor. The scrubber uses a material called zeolite, or molecular sieve. I specifically used 13x molecular sieve and added some 4A sieve material that had a color indicator added so I know when it has reached saturation. You determine the size of the scrubber based on your flow rate. If you want 3-4 SCFM then you need about 10-15lbs of the material and size the scrubber based on this.

Zeolite is a naturally occurring, finely porous material. By fine I mean the holes are only angstroms in size. Molecular sieve is man-made, but the structure is the same. CO2 and water enter and bind within the pores, letting the other gases, like O2 and N2, to pass through. The color-indicator will change from light blue to gray when the material can not adsorb any more water. One regenerates the material by heating to 350F, driving off the CO2 and water.

Now, back to the device. I cut a disc of 200 micron screening. This holds the 10 lbs of material in place so it does not get sucked into the compressor, but still allows for air-flow. I glued this material between the 4-to-2 inch reducer and the coupler fitting. We need to filter smaller material, so I took 11 MERV air-conditional filter material and cut it into a large circular disc. This should filter 1-3um particles. If you can get a 12 MERV this is better. I fashioned a circular ring of stainless steel that I got at a hardware store and fixed the filter material on top of the 200um screening. Then, poured in 10 lbs of 13x and 4A sieve. I then made another filter disc out of the air-conditioning material and fixed it on the top with a stainless steel ring. This keeps the material clean. You don't want particles clogging the sieve's pores.

The top of the scrubber needs three inputs. One is to allow for fresh gas input. The other connects to the regenerated gas. This is gas from the cooling tower that did not liquefy. The gas is already cool, free of CO2 and water, and in my case is 98.5% nitrogen. I don't want to waste this gas to the atmosphere so I reuse it, reducing the amount of fresh N2 that I need to make. This is why it is called regenerated gas because it comes from the original gas I fed into the tower. The third input allows any excess gas to vent out.

The only other connection is at the bottom where you connect the scrubber to the compressor. I placed a 10um vacuum water trap between the scrubber and the compressor. This will remove particles that can fowl up the compressor, and also serve as a check that no water gets into the cylinders. I also used this spot as a place to insert a gas-analysis meter that I made to monitor the purity of the N2.

You will need to buy a pipe/tube bender to make the coils and rings. I've shown a picture of one above. Mine is meant to bend 1/4" tubing/rod.

STEP 5: Pre-cooler

The compressed gas leaving the compressor is hot. You want to remove this heat using an ice bath. The pre-cooler is sized to fit into a large bucket.

Basically, the precooler is a long coil of tubing. I used 20 feet of 1/4" 304 seamless stainless steel with a 0.035" wall thickness. Again, one could go to 0.027" wall, but this got too thin for me. I did not want a wall rupture at 3500 PSI. I go through the engineering calculations for verifying the integrity of the tubing at the tutorial site.

I added 0.016" thick aluminum fins which increased dT/dt even further by allowing better heat transfer. I carefully drilled a hole 1/64" smaller than the tubing. I then cut the square and snapped the fin in place. I can then submerse the cooler in an ice bath or expose it to sub-freezing outdoor temperatures when available.

STEP 6: Regenerative Cooling Tower

This is the part that will take the most work. My final tower uses a large concrete cardboard form container that is 50 inches high and 24 inches in diameter. However, I had good success with an earlier version that used a 36 gallon plastic recycle can. The compressed gas goes into the tower through a long helical coil and re-expands through a needle valve at the end into the reservoir. The cold gas that did not liquefy returns through Teflon tubing around this coil. This cold gas cools the steel tubing further. This process repeats until the steel tubing is cold enough to liquefy the gas.

I used 305 stainless steel 1/4" tubing with a 0.035" wall thickness. There are many places that sell this near you. If you are going to do this with a standard refrigerator compressor than you can use copper tubing. Just make sure it is rated for the pressure from the compressor. Now the PTFE (Teflon) tubing is critical. It is one of the few materials that is flexible and can withstand cryogenic temperatures. I used plastic tubing in the beginning, but it would eventually crack.

My tower uses 80 feet of tubing. You can do this with 40-60 feet, but this increases the cool-down time. Again, everything is about tradeoffs. You need to insert the steel coil into the Teflon tubing. You want the Teflon tubing diameter to be a little bigger than the coil. Mine was 1" corrugated tubing which allows it to be flexible. This wraps over the 1/4" stainless tubing.

The ends of the tubing need high-pressure, stainless steel fittings and adapters. I got mine from Swagelok, but there are other companies that sell similar parts.

You then insert the coil into the garbage can or container. Industrial manufacturers fill the container with perlite and create a vacuum to prevent heat from entering from the environment. I filled my container with alumina silica high-temperature wool. This is normally used to insulate furnaces to contain the heat. Well, guess what? It also contains the heat of the outside from getting to our coils. You need to loosely fill the container with the material so it stays fluffy. Air is also an excellent insulator.

The pictures above show me using the 36 gallon recycle container. At the end of this tutorial you will see the concrete form container which houses a bigger run of coil. The stainless steel tubing is surrounded by the Teflon tubing. This, in turn, is wrapped with polypropylene foam to further decrease heat penetration.

STEP 7: Throttle

The gas expands using a needle valve as mentioned earlier. One controls the pressure by finely tuning the orifice opening with a large lever/knob. I made a large lever because the standard knob handle is too small for fine control. Furthermore, as the temperature drops one finds difficulty turning the knob because it gets frozen in position. A large lever makes this fact mute.

I extended the stem so it would reach the outside. I insulated the connection to the stem with Teflon to reduce any heat transfer through the stem from the outside.

STEP 8: Baffle

The expanded gas distal to the needle valve moves at a high velocity. This can agitate the liquefied gas in the reservoir and blow it back out into the gas stream. You need to slow the gas down to allow the droplets to collect and drop into the container. Until I figured out this simple step I was never collecting a lot of liquid.

Making this is very easy. I used a fitting and attached it to 1/4" copper refrigerator tubing. I drilled a few holes with a 1/8" drill bit on the other end and fixed some copper abrasive scrubbing sponge that I got at a food store. Make sure the copper wool (abrasive scrubber) does not come off. The other pictures show how this part relates to the needle valve and reservoir.

STEP 9: Reservoir

The reservoir holds the collected liquefied gas, whether that is N2 or air. A simple stainless steel vacuum bottle, or a thermos as many of you would know it, serves this purpose very nicely. Such a simple solution that eluded me for some time. The trick is to fashion an adapter that allows you to contain the expanding gas and direct it to the regeneration Teflon tubing that surrounds the high pressure stainless steel tubing. The details, along with all the other methods I tried, can be found at my extensive tutorial at http://homemadeliquidnitrogen.com

Basically, the baffle connects to the output of the needle valve. The inflow to the valve connects to a tube fitting on the end of the high pressure tubing. A Teflon cylinder surrounds this and just fits over the orifice of the thermos. Small screws keep this fixed so the pressure of the expanding gas does not push it off. A small tube of Teflon goes from the bottom of the thermos to the outside through an insulated jacket to allow the liquefied gas to escape. A small plug keeps the liquid contained until you are ready to drain the system.

In addition to these connections, there is a small opening for a RTD probe for monitoring the temperature. I am currently using a unit I bought, which is seen in the video at the beginning of this Instructable. I have developed a low-cost LCD cryogenic thermometer that is accurate to 0.1F. I plan on posting this as a new Instructable in the near future.

STEP 10: Summary

This project allows an individual to do what only commercial industry has done in the past. You can generate your own liquid air or nitrogen with a high production rate. The cool-down period depends on your compressor, length of regeneration tubing and how well you can insulate your system. In the past, making liquid nitrogen in your garage seemed impossible. Not any more.

Good luck and stay cool.

STEP 11: Making Pure N2 for Liquefication

I have gotten a lot of comments suggesting that I am making liquid air, which contains O2, and not liquid N2. I made a pressure swing adsorper that removes the O2 from the air, leaving 98.5% pure N2. If I used a second stage I could get 99.999% pure N2. I feed this N2 into the liquid nitrogen generator. I am putting out about 30 L/min of 98.5% N2.

I have just finished writing a web tutorial on this subject which you can find here. This can also be used for having a pure source of N2 in your garage. I use it for filling my tires. I will write this as its own Instructable in the next few days.

You can click on the this link to see a video I made, showing my PSA device.

Comments

[Jorge EliecerP1]

How could i upgrade it to make work on a hot climate

[OutsiderX]

If I may ask, were you able to deal with the argon content in the mixture? The 98.5% and 99.999% values could be 1-5% argon by mass and so far I have been unable to locate any form of N2 generation that can avoid that, or any san-industrial method for separating the Ar from the N2.

[emailrobertmiller]

Why is the microscopic filtering so important? I would assume the valve at the cryo end is the smallest aperture in the system? Are the valves in the compressor truly sensitive to such small particles? If so, how are they made? Is this filtering really necessary?
Robert

[KarmanyaG]

How much did it all cost?

[imsmooth]

Compressor $1000
Other stuff $500

[jpsadowitz]

I am a chemist and want to continue to learn, What tutorials can you suggest so that I may educate my self on the principles of refrigeration. And also will these learnings help me in the building of a natural gas liquified? Thanks

[en2oh]

can you give any pointers on where you sourced you CMS?

Btw, I just got my Stirling Cooler up and running. Cooling down as I type.

[imsmooth]

I'm still trying to set up my source to get the CMS for everyone. I have not forgotten your inquiry.

Also, I've developed a high precision cryogenic thermometer. You can read about it on my site at http://homemadeliquidnitrogen.com

[JohnC1133]

I realize that this is old, but any leads on the CMS vender? All I see is Alibaba in China

[en2oh]

I found some on eBay. Good price. Haven't used it yet since I have a membrane separator now. That being said, did you do any calculation on how long a regeneration path you needed for 300bar? I see you are using used coaxial Bain Circuits as part of your regeneration pathway. Is the nitrogen going back into the compressor really significantly colder than ambient? Doesn't the act of compression heat it up significantly? I'm looking to use a cheap 300bar compressor with limited output but wondered if I could get away with a well insulted 25' pathway. Thanks
Doug

[imsmooth]

No calculation. Just made it as long as possible. Longer path means more time for cooling. Also, the work the gas does against the resistance helps drop the temperature. I'm sure you can get away with a shorter length, but your cooling time will be longer. I'd like to see someone do this with a regular refrigerator compressor.

I've measured the temperature going back in and it is lower, and any temperature gradient is worth utilizing. My nitrogen generator is not able to keep up with the amount of nitrogen removed from the system once it liquefies, so scavenging the exhaust nitrogen keeps the percent composition of the intake gas over 95-97% for me.

[en2oh]

thanks for the reply. Am I correct, those are old coaxial anesthetic sets you are using to scavenge the atmospheric nitrogen gas? I'm not sure that the "ordinary" phase change refrigerator will be possible but a dual compressor using Ethylene in the 2nd stage can get to -100C fairly easily. That would be a heck of a precooler. That being said, I was thinking of taking stainless steel corrugated tubing and making a vacuum insulated line to house the stainless steel high pressure compressor outlet... I think that will make the regenerative cooling much more efficient.
Thanks again,
Doug

[imsmooth]

Good eye. Those are coaxial anesthesia circuit sets. They were free and I use them on the last 10-15 feet of my final version. On the final version, seen in the video, I use teflon tubing on the cold section because it can withstand the cryogenic temperatures. My first version, using the blue recycle can, I only used the anesthesia circuit to see if I could get to cryogenic temperatures. I did, but the tubing after a few runs cracked because the plastic could not withstand the temperatures. Of course, the last leg of the regenerative circuit gets close to ambient temperature so it retains its integrity.

[Helen-Hanks]

Hi there,

I work as an engineer for one of the companies that makes Liquid nitrogen. I just want to point out there are some very serious risks with this type of equipment which even the professional companies sometimes fall foul of. My professional advice would be "don't try this without proper chemical engineering training", but since I know you already are, here are some safety tips to consider:

* Never store liquid nitrogen or operate this equipment in an enclosed area, always ensure sufficient ventilation. Nitrogen is an asphyxiate with no smell. The only way to protect yourself is to operate outdoors AND wear a gas composition monitor to warn you if oxygen levels in the air fall below 19.5%

* Make sure the equipment is thermally isolated well as it reaches extremely cold temperatures and you may burn yourself if you touch it. Frostbite may also occur if you spill any cold product on yourself. Always wear full length clothes and insulated gloves.

* If there is any possibility of liquid nitrogen being trapped in a part of the equipment (due to closed valves or ice blockage), fit pressure relief devices. When the liquid warms and expands, it can cause an explosion if there is no escape path.

* Distillation columns take in a lot of hydrocarbons and nitrous oxide with the air. These components build up in the distillation still, and can cause an explosion when they react with the liquid oxygen in the still. Ensure you purge the liquid often enough to remove these contaminants.

*If you are running this in your garage (I know I told you not to), don't enter before you take an atmosphere reading. Make sure oxygen is between 19.5 and 22%.

* Make sure all the pipework and vessel is constructed from clean, oxygen-safe metal. During startup, the unit will produce liquid oxygen before it starts to produce liquid nitrogen. High concentration oxygen reacts with any organic contamination, and even metal can become a fuel source for a fire. Carbon steel is not an appropriate material, stainless steel, aluminium or monel is better. Definitely do not use rubber pipes, seals or oil based lubricants!

* There is a chance the atmosphere around the equipment will be oxygen rich, so take care to eliminate all sources of ignition, such as electrical switches, flames, static on your clothes, sparking tools and anything that gets very hot.

[Andrew_F]

This is a link to get the gas monitor.

https://www.pksafety.com/bw-clip-2-year-single-gas...

Whenever you feel woozy, stop. Using a candle is NOT an indicator of air quality. Too MUCH oxygen can be lethal as well. The majority of suffocation deaths happen when the worker is unaccompanied. Use the buddy system to prevent a Fatality.

[en2oh]

your points, in general are well taking BUT, we are not liquefying Air. We are liquefying 98+% nitrogen. Less efficient, (as compared to air) but the risk of producing significant liquid oxygen is negligible. The other thing to consider is that the IMSmooth clearly has the garage door open. You are more likely to come to harm transporting a Dewar filled with liquid nitrogen in a closed vehicle.

As far as "oxygen toxicity", no - not at atmospheric pressure. Oxygen becomes toxic when it is breathed under pressure ie in diving. The biggest risk here is the nitrogen is contaminated with argon, because this system won't separate this. Argon is not going to be a problem for most of us,

[AlyssonR2]

Excellent points!

Having seen the results of a LOX leak on tarmac - it is NOT a good thing to have hanging around!

[acoleman3]

wow, glad to see someone who's actually "in the know" providing safety tips and not some armchair "expert" like i've seen in the comment section of a lot of 'ibles that had any hazards to them.

[gith]

Helzcurrah

You know us so well, Thanks for the safety tips they may safe someone from great difficulty. You know like death.. all joking aside thanks for pointing out some of the dangers that can be encounterd with this.

[studleylee]

Great instructable!!!

@ helzcurrah Looking forward to seeing you do some instructables on related topics. I think adding a timed fresh air inlet fan to the "garage" to cycle out the undesirable product might be good. I Might be making one of these systems soon.