Nitrogen is a gas that is relatively abundant in the atmosphere. It constitutes 78% of the air we breathe while the oxygen responsible for the maintenance of life constitutes just 21%. At 78%, nitrogen in the air is very impure for industrial applications which led to the invention of nitrogen generators.
Nitrogen generators possess the ability to separate nitrogen molecules from dry compressed air and deliver the pure nitrogen as output. Nitrogen generators can produce purities of up to 99.9999%. This comes in handy as onsite nitrogen generators eliminate the need for purchasing gas cylinders and all other associated costs as well as supply nitrogen on demand and as required.
How Do Nitrogen Generators Work?
As stated earlier, nitrogen is generated by the separation of nitrogen molecules from the other molecules that air is composed of – oxygen is one of the most prominent.
Different uses of compressed nitrogen air require different levels of purity. For applications, such as tire inflation or fire prevention, relatively low purities of 90% to 97% are considered satisfactory. But in industries such as medical, plastic moulding or food/beverage processing, higher levels are required. Often from 97% to 99.9999%.
Two common types of generators can fulfil the need of onsite nitrogen generation, membrane generators and pressure swing adsorption generators.
Membrane Nitrogen Generators
Membrane generators make use of porous hollow fibres of variable length, diameter, material, and efficiency. The generators employ pressure for use in separation the molecules of nitrogen from the stream of compressed air flowing in. This pressure process is termed selective permeation. As the compressed air flows through the inlet and into the fibres, it contacts the membrane, flowing through the fibre bores. Oxygen, other trace gases and water vapour easily permeate the membrane and are discharged while the membranes retain nitrogen. Hence, selective permeability.
Pressure Swing Adsorption Nitrogen Generators
Adsorption, not to be confused with absorption, is the process which atoms or molecules or ions, from a substance (in this case, compressed air) adhere to the surface on an adsorbent.
PSA nitrogen generators make use of a carbon molecular sieve situated into towers (tower A and B) to carry out their separation. Compressed air flows into the PSA generator, nitrogen is isolated, and other gases in the compressed air are adsorbed.
The two pressure towers A and B carry out different processes, the separation and regeneration process, respectively. In the separation process, molecules smaller than nitrogen molecules pass through the carbon sieve while nitrogen molecules flow by, resulting in nitrogen of the desired purity. Most of the nitrogen produced in the separation phase exits the system and is ready for direct use. The remaining nitrogen is used for the second stage.
In the second stage, the nitrogen left from tower A flows into tower B. The flow releases the oxygen that was captured by the carbon sieve. The release of the oxygen molecules is a cleaning process that makes room for new oxygen molecules to be trapped by the sieves in the next adsorption stage.
Pressure swing technology allows for continuous nitrogen flow to processes requiring purity levels of up to 99.999%. They may be more expensive than membrane generators, but they offer the flow volume and purity levels required in some industries.
Benefits of Onsite Nitrogen Generators
Industries, factories or laboratories that make use or required nitrogen can run through cylinders of nitrogen in days often leading to time-sensitive work having to be delayed cylinders are switched or while orders for replacements are carried out. In the medical, laboratory or food/beverage setting, the purity of the nitrogen becomes inconsistent as the level in the tank reduces. Onsite nitrogen generation can put an end to the issues gas cylinders come with because of the following benefits.
Safety of Workers
A factory, construction site, or laboratory’s priority is the safety of its workers. Onsite nitrogen generators remove the hazard accompanied by workers having to move around heavy gas cylinders that if not done properly, can lead to injury and damage of equipment.
Cost Saving
The fluctuation of gas prices throughout the year can lead to an increase in the cost of production for several nitrogen-using industries. Nitrogen generators reduce costs by lessening the costs of purchasing cylinders, shipping and reducing downtime while waiting for shipment to arrive.
Environmental Impact
Production of nitrogen cylinders costs a lot of energy and also releases huge amounts of carbon dioxide into the atmosphere. By employing onsite nitrogen generation, emissions from cylinder manufacturers and trucks delivering the cylinders can be reduced.
Corrosion Prevention
The application of nitrogen in fire sprinkler systems leads to reduced corrosion due to oxygen in the air. Deposit formation is also reduced, which helps mitigate the buildup of obstructive material, ensuring the pipes and the entire system function as required in case of a fire emergency.
