Cryogenic tankers have been transporting medical oxygen from one state to another, carrying hopes of survival and life. But, have you ever wondered why only these white tanks are being used for carrying oxygen?
The term ‘cryogenic’ is widely being used during the second wave of coronavirus.
Let’s decode everything that you should know today about cryogenic tanks and why it is important for the transportation of liquid oxygen.
Oxygen is used in its liquid form in hospitals for medical treatment and oxygen therapy. Oxygen therapy is the use of oxygen for the medical treatment of human beings.
But, What is liquid oxygen?
In simple words, oxygen in its liquid form is known as liquid oxygen. It is cooled and has a temperature of -185°C. This is why liquid oxygen is used as a fuel in aircrafts that fly at high altitude.
Liquid oxygen is pale blue in colour. Its cryogenic nature can cause the material it touches to become extremely brittle.
Oxygen is usually stored in liquid form, even when it is primarily used in gases state, due to ease in storage and handling.
Cryogenic liquids are liquified gases kept in their liquid state at a very low temperature. The word cryogenic means producing, or related to, low temperatures. All cryogenic liquids are extremely cold. Cryogenic containers carry substance less than -150°c to absolute zero temperature.
At normal temperature and pressure, all cryogenic liquids turn to their gases form. Oxygen is used in its liquid form for medical purposes and is kept at -185°C to maintain its form.
It is important to understand that liquid oxygen too is cryogenic liquid.
Okay, but what is a cryogenic tank?
Cryogenic containers are storage materials used for storing and transporting liquid oxygen. Liquid oxygen can be stored either in a cryogenic liquid cylinder or a cryogenic storage tank.
A cryogenic liquid cylinder is an insulated, vacuum-jacketed pressure vessel which has pressure relief valves and rupture disks. This protects the cylinders from pressure buildup.
On the other hand, a cryogenic tank is usually spherical or cylindrical in shape, have a tank, vaporiser and pressure control system. It is mainly used for bulk storage and transport purposes.
Why is a cryogenic tank used for transporting liquid oxygen?
Cryogenic liquids produce large volumes of gas when they vaporize. For example, liquid nitrogen will expand 696 times as it vaporizes.
Similarly, liquid oxygen expands at a ratio of oxygen 862:1. If these liquids vaporize in a sealed container, they can produce enormous pressure that may lead to a crack or break the vessel. This is why pressurized cryogenic containers are usually protected with multiple pressure relief devices. It has the property to bear the temperature and pressure that is needed to hold oxygen safely.
Oxygen is highly reactive in nature and reacts with almost all organic materials and metals, usually forming an oxide. Any material that burns in air, burns more strongly in the presence of oxygen. This is why it is important that the containers used for storing oxygen are made out of such material that do not react with oxygen.
The cryogenic tank is constructed, in principle, like a vacuum bottle. The tank has two layers, inner vessel and outer vessel. In between both the vessels, air is removed and it acts as an insulating medium. This space also keeps heat away from the liquid oxygen kept inside the vessel.
Can any other tank be used for transporting liquid oxygen?
As mentioned before, oxygen reacts with nearly all materials. If it is stored and transported in a vessel in which it can easily react, even a small spark or mechanical shock, can lead to fire and result in great loss. This is why oxygen is not stored in a normal container but a cryogenic container.
In simple words, cryogenic tanks are made up in such a way that it stops oxygen from getting ignited. Therefore, it is used for its storage and transportation purpose.