A nitrogen generator is a specialized machine designed to extract a high-purity stream of nitrogen gas directly from the surrounding atmosphere. This process allows industries to generate their own on-demand supply of gas without relying on external suppliers or complex cryogenic methods. Nitrogen is widely used because it is an inert gas, meaning it resists chemical reactions with other substances under normal conditions. This characteristic makes it useful for applications like inerting storage tanks, purging pipelines of flammable vapors, or preventing oxidation in food packaging and electronics manufacturing.
The Raw Material Air Composition
The raw material for any nitrogen generator is the air we breathe. Ambient air is a physical mixture, predominantly made up of nitrogen gas, which accounts for approximately 78.084% of the total volume of dry air. The second most abundant component is oxygen, making up about 20.946% of the air. The remaining fraction consists of various trace gases, including Argon, Carbon Dioxide, and water vapor, which must be accounted for during separation. The generator’s primary task is to efficiently isolate the nitrogen component by removing the oxygen and all other trace contaminants. Both major commercial separation methods focus on selectively removing the unwanted molecules, allowing the nitrogen to be collected as the purified product stream.
Separation Method 1 Pressure Swing Adsorption
Pressure Swing Adsorption (PSA) is an effective method for isolating nitrogen that relies on using a solid adsorbent material to preferentially trap unwanted gas molecules under high pressure. The core component of a PSA generator is a vessel packed with a material known as Carbon Molecular Sieve (CMS). The CMS material contains a vast network of extremely fine pores that are engineered to capture specific gas molecules.
When pre-treated, compressed air is fed into the vessel, the pressure forces the gas mixture into contact with the CMS. Oxygen molecules, along with carbon dioxide and water vapor, are smaller and possess a stronger affinity for the CMS surface, causing them to be adsorbed or stuck within the pores. Nitrogen molecules are larger and cannot enter the microscopic pores easily. They flow past the adsorbent material and exit the vessel as the high-purity product. This adsorption phase continues until the CMS bed becomes saturated with trapped oxygen.
To ensure continuous production, a typical PSA generator uses a twin-tower system operating in alternating cycles. While the first tower is in the high-pressure adsorption phase producing nitrogen, the second tower undergoes regeneration. Regeneration is achieved by rapidly venting the pressure in the saturated vessel down to near-atmospheric pressure. The sudden drop causes the CMS material to release the trapped oxygen and other adsorbed gases, which are then exhausted to the atmosphere as a waste stream.
Before the first vessel becomes fully saturated, the system automatically switches the incoming compressed air flow to the regenerated second vessel. This cyclical swing between high-pressure adsorption and low-pressure desorption allows for a constant, uninterrupted flow of purified nitrogen gas.
Separation Method 2 Membrane Technology
The second major method for nitrogen generation utilizes Membrane Technology, which separates gases based on their differing rates of permeation through specialized polymeric materials. The heart of this system is a membrane module containing thousands of hollow polymeric fibers bundled together. These fibers act as a selective barrier, allowing some gases to pass through their walls quickly while others move slowly.
Compressed air is introduced into one end of the module and flows down the center bore of these hollow fibers. The separation is governed by selective permeation, determined by a molecule’s ability to dissolve in and diffuse through the polymer material. Gases like oxygen, water vapor, and carbon dioxide are considered “fast” gases because they diffuse at a much higher rate. These fast-permeating gases quickly exit through the side of the module and are vented away as the waste stream.
Conversely, nitrogen is a “slow” gas with a significantly lower permeation rate through the polymer. Because it permeates slowly, the nitrogen molecules are retained within the hollow fiber and continue to flow toward the far end of the module. The final purity of the nitrogen stream is controllable by adjusting the flow rate and pressure of the incoming compressed air.