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Normal ambient air is made up of 78% nitrogen, 21% oxygen and other trace gases like argon and CO2. In order to remove the nitrogen and trace gases, an oxygen generator is used.
The smallest oxygen generators are no larger than a soda can, while industrial oxygen generators can fill a room. However, all oxygen generators have the same purpose: to provide a safe supply of concentrated oxygen gas.
Businesses who need bulk oxygen gas often start by purchasing tanks of the gas from other companies who fill those tanks using an industrial oxygen generator. If their need for pure oxygen is large and ongoing, it may be cost-effective to purchase their own oxygen generator system and produce oxygen on site. While the up-front cost of the machinery is significant, the cost per cubic foot of oxygen generated is 1/3 to 1/2 that of purchasing bulk oxygen, so over time, the oxygen generator can pay for itself.
One example of this is hospitals that pipe oxygen into patient rooms. Instead of using bottled oxygen, most hospitals have one or more Industrial Oxygen Generators in the building. A system of pressurized pipes are used to flow oxygen to each room.
Types of Oxygen Generators
Pressure Swing Adsorption Oxygen Generator
Pressure Swing Adsorption (PSA) is the most common method of producing oxygen at an industrial scale. PSA generators separate nitrogen from ambient air inside a pressurized tank filled with Zeolite. Zeolite is a natural or man-made mineral that acts as a “molecular sieve.” It is this ability to “sort” molecules by size that makes zeolite so useful. The larger nitrogen molecules are adsorbed by the sieve material while the smaller oxygen molecules drift past and are collected. Pressure is then released, the nitrogen molecules are vented to the atmosphere, and the tank is pressurized again.
Using PSA will result in 90-95% oxygenated gas. Further refinement can be achieved by repeating the process until over 99% “pure” oxygen is generated.
As a side note, the PSA process can also be used to generate nitrogen by collecting the nitrogen molecules and venting the oxygen. PSA is also used in the large-scale commercial synthesis of hydrogen used in oil refineries and in the production of ammonia for fertilizer.
One special kind of Medical Oxygen Generator is more commonly known as an oxygen concentrator which is used as an alternative to oxygen bottles for home health care. While the up-front cost of the machine is more expensive than oxygen cylinders, they are safer than bottled oxygen and over time less expensive than having oxygen tanks delivered to the home.
Membrane Oxygen Generator
Membrane oxygen generators use a compressed air stream passed through semi-permeable materials that allow for the passage of specific molecules. Under pressure, smaller oxygen molecules pass through the membrane, filtered out and collected leaving a stream of nitrogen flowing out the opposite end of the membrane. While membrane-type generators are not as common, they are considered to be more reliable because there are no moving parts that can fail.
Chemical Oxygen Generator
A chemical oxygen generator is a device that releases oxygen by a chemical reaction. A container of inorganic salts called “superoxides” or sodium chlorate is ignited. As they heat they give off oxygen until the compound is consumed.
Because of their long shelf-life, stability and small size (about the size of a can of soda) chemical oxygen generators are used in commercial airliners. Mounted over the seats, each generator can produce enough oxygen for 2-3 masks for 10-20 minutes. A similar device is called an oxygen candle. It works using the same principle of releasing oxygen with heat, and is used as a personal safety oxygen supply in mines, submarines and on the space station.