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Nitrogen (N) is a colourless, odourless, mostly inert gas. It has the atomic number 7 and sits under group 15 of the period table of elements – the “Non-Metals”. It isn’t totally inert, unlike argon, which is a true noble gas, but for almost all applications it can be considered completely unreactive and inert.
At standard temperature and pressure, two atoms of nitrogen bond to form N2. Although it is generally referred to as “nitrogen”, its chemically accurate name in this form is “dinitrogen”!
Discovery
It was first discovered and isolated by Scottish physician, Daniel Rutherford, in 1772. It wasn’t until advances in refrigeration technology, at the beginning of the 20th century, that it became commercially available in liquid form. The German engineer and entrepreneur, Carl von Linde, had developed a process to liquify air and separate oxygen, nitrogen and argon from the atmosphere.
Daniel Rutherford 1749-1819
Carl von Linde 1842-1934
Nitrogen is the most abundant gas in the Earth’s atmosphere at approximately 78.1% by volume, along with oxygen at 20.9% and argon at 0.93%.
|
Gas |
Symbol |
Volume in Air % |
|
Nitrogen |
N2 |
78.084 |
|
Oxygen |
O2 |
20.9476 |
|
Argon |
Ar |
0.934 |
|
Carbon Dioxide |
CO2 |
0.0383 |
|
Neon |
Ne |
0.001818 |
|
Methane |
CH4 |
0.0002 |
|
Helium |
He |
0.000524 |
|
Krypton |
Kr |
0.000114 |
|
Hydrogen |
H2 |
0.00005 |
|
Nitrous Oxide |
N2O |
0.00003 |
|
Carbon Monoxide |
CO |
0.00001 |
|
Xenon |
Xe |
0.0000087 |
|
Ozone |
O3 |
0.000007 |
|
Nitrogen Dioxide |
NO2 |
0.000002 |
|
Iodine |
I |
0.000001 |
|
Ammonia |
NH3 |
Trace |
Preventing the spoilage of food, beverage, and pharmaceuticals by certain species of microbes that need oxygen to survive and propagate.
Preventing the detrimental oxidization of metals, plastics, and chemicals by “blanketing” with nitrogen to prevent contamination with ambient air and thus oxygen.
Preventing fire and or explosion of flammable materials and chemicals by excluding oxygen.
To support combustion or explosion, 3 critical components are required:
a) A fuel (something that burns or explodes in ambient air).
b) An ignition source such as a spark, static discharge, or naked flame for example.
c) Oxygen – Generally most flammable things can burn or explode when the oxygen level is typically above 10%, so ambient air at nearly 21% supports combustion very well.
These 3 components are named the “Fire Triangle”. But like a triangle, if any one of the sides is removed, it collapses. In this case a collapse means a fire or explosion cannot happen. Displacing ambient air with nitrogen gas will remove the oxygen side of the triangle and prevent fire and or explosion.
Preventing oxygen permeation through materials such as rubber and plastics.
On a scale of gaseous permeability, nitrogen is considered a “slow gas” whereas oxygen is a “medium speed gas”. This means that oxygen will permeate through certain materials much quicker than nitrogen.
For example – Civilian and military aircraft tyres are filled with nitrogen to prevent them partially deflating through oxygen permeation, accelerated by the extremes of temperature and pressure they undergo during a flight. Truck and automobile tyres are often inflated with nitrogen too, for similar reasons.
Much of the nitrogen used by industry is produced and supplied by industrial gas companies via a process called “Cryogenic Separation”. This is carried out within an “Air Separation Unit” (ASU).
The ASU uses clean, dry, oil-free, compressed ambient air and through a series of compression, expansion and heat exchange cycles, the temperature of the air is reduced until the 3 main constituent gases – nitrogen, oxygen and argon become liquid at different temperatures. Within a “distillation column” the different elements are separated and stored as a very cold liquid or evaporated to a gas and compressed into cylinders.
A typical industrial gas company air separation unit plant. The cryogenic distillation column is the tall rectangular structure at the front of the image.
The vast majority of industrial nitrogen is produced by cryogenic air separation. This covers all nitrogen applications including gaseous, as well as liquid, used for freezing and cooling.
Approximately 36% of the global industrial gas demand is supplied in gas cylinder format. This can be as individual cylinders that may be sized to contain anywhere between 1-2m3 of gas up to 13m3. Or, manifolded cylinder pallets that contain multiple individual cylinders can be installed within a frame and piped to a common outlet point, these can contain up to 170m3 of gas approximately. Storage pressures are generally from 180 to 300 barg (2610 to 4350 psig) depending on cylinder design and specification.
Cylinders and manifold pallets use a pressure regulator to reduce the nitrogen stored pressure to the required usage pressure, this is typically between 5 and 10 barg (72.5 and 145 psig).
Gaseous nitrogen applications can also be fulfilled by the on-site storage of liquid nitrogen that can then be converted to a gas. This is done using either mini tanks or bulk storage where the liquid nitrogen is converted using evaporators.
