How a Nitrogen generator works

The air we breathe is about 78% nitrogen, but nitrogen at a higher level of purity has a wide variety of practical applications across many industries. Companies that use nitrogen can benefit from generating what they need in-house. This enhances production flexibility by ensuring that they have the nitrogen they need, at the level of purity they need, when they need it. Generating nitrogen in-house also removes the worry of running out because there is no third-party supplier. This eliminates constant order processing, refills and delivery costs, and frees up space otherwise needed to store nitrogen bottles (both full and empty).

This technology separates air into component gases by passing inexpensive compressed air through semipermeable membranes consisting of bundles of individual hollow fibers. Each fiber is very small, has a perfectly circular cross-section and a uniform bore through its center. At one end of the module, compressed air is introduced into the fibers and contacts the membrane as it flows through the fiber bores. Oxygen, water vapor and other trace gases easily permeate the membrane fiber and are discharged, but nitrogen is contained within the membrane and flows through the outlet port. Because water vapor permeates through the membrane, the nitrogen gas stream is very dry, with dewpoints as low as -50°C (-58°F). Membrane technology is simple and efficient, with compact, all-in-one units that require little maintenance and have zero operational costs. It’s ideal for applications where the required flow of nitrogen is relatively low and purity levels do not exceed 99%. Membrane technology has a lower initial investment than high flow/high purity technologies such as Pressure Swing Adsorption (PSA).

Adsorption is the process in which atoms, ions or molecules from a substance (compressed air in this case) adhere to a surface of an adsorbent. A PSA generator isolates nitrogen, and the other gases in the compressed air stream (oxygen, CO₂ and water vapor) are adsorbed, leaving behind essentially pure nitrogen. PSA traps oxygen from the compressed air stream when molecules bind themselves to a carbon molecular sieve. This happens in two separate pressure vessels (tower A and tower B), each filled with a carbon molecular sieve, that switch between a separation process and a regeneration process. Clean and dry compressed air enters tower A. Since oxygen molecules are smaller than nitrogen molecules, they pass through the pores of the sieve. Nitrogen molecules cannot fit through the pores, so they bypass the sieve resulting in nitrogen of desired purity. This phase is called the adsorption or separation phase. Most of the nitrogen produced in tower A exits the system, ready for direct use or storage. Next, a small portion of the generated nitrogen is flowed into tower B in the opposite direction. This flow pushes out the oxygen that was captured in the previous adsorption phase of tower B. By releasing the pressure in tower B, the carbon molecular sieves lose their ability to hold the oxygen molecules, which detach from the sieves and get carried away by the small nitrogen flow coming from tower A. This ‘cleaning’ process makes room for new oxygen molecules to attach to the sieves in a next adsorption phase. PSA technology enables continuous, high-capacity nitrogen flow in demanding applications at purity levels up to 99.999%. PSA generators have a higher initial investment cost than membrane generators, but they offer the advantages of higher flow and higher purity levels that some industries and applications demand. Ask an air system professional about the best solution for generating nitrogen in-house.