Ever Wonder Where Liquid Nitrogen Comes From?
March 2, 2016
Have you ever wondered where liquid nitrogen (LN2) comes from? Just look around you and take a deep breath…
We often just hook our cyro freezers up to a metal cylinder, which a truck dropped off or filled, and magically our freezers stay unbelievable cold. But where does all that super cold fuel come from..?
LN2 boils from a liquid to gas at -195.8°C @ 1ATM (sea level). When in a freezer, the LN2 absorbs the surrounding heat, boils, and thus cools the environment. You can think of the LN2 in your freezer as a fuel source, a sacrificial refrigerant that absorbs heat and in doing so, changes back nitrogen gas (N2).
Converting back to a gas is key here. Nitrogen is not naturally in liquid form (on earth at least, Pluto is another story). So the liquid form of nitrogen we use has to be manufactured.
On earth, nitrogen exists all around us and approximately 78% of the air we breathe is nitrogen. This is the nitrogen source used to create liquid nitrogen.
Liquid nitrogen is created (or changed) from nitrogen gas in a process called Air Separation or Fractional Distillation. It is a complicated process, but essentially takes regular air, purifies, compresses and cools it to clean it up and remove the water and then the fractionation begins. In this process the purified air is significantly cooled, compressed and decompressed using heat exchangers and pressurized tanks. During this process the elements in the air turn to liquid and are then captured and separated.
LN2 isn’t the only liquid separated from the air. More valuable are the other elements in the air, such as oxygen and argon. Some even consider liquid nitrogen a by-product of air separation where more valuable gases are needed (worth more money) and LN2 happens to be created in the same process.
Once liquid nitrogen has been separated, it is kept under very high pressure to keep it in a liquid phase and is transferred to storage tanks, trucks and cylinders. This allows it to be easily transported to where it is needed.
The next time your LN2 freezer tops up you can take a deep breath and ponder that the air all around you is just a phase change away from being the cryo fuel source in your freezer.