How a nitrogen generator works - Atlas Copco USA

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Generating nitrogen in-house

Nitrogen is the vehicle that allows oxygen to sustain life on our planet. But, due to a range of characteristics that make it ideal for many industrial applications, it does much more than “merely” keep us alive. The most important of its features is that nitrogen is an inert gas, which means that it is slow to react with other substances. That makes it ideal for any application in which slow oxidation (e.g. the corrosion of circuit boards in the electronics industry) or fast oxidation (e.g. explosions or fires) have to be prevented. In addition, it is odorless and colorless, which means nitrogen is an ideal medium to be used in the food and beverage industries – for example to extend the expiration date of food products. As a result of these properties, it is no surprise that nitrogen is in constant demand in many sectors – from the automotive and chemical industries to aquaculture and injection molding.

Nitrogen: the world’s most abundant gas

Fortunately, nitrogen is available in abundance, making up most of the air we breathe. But that does not mean that it is ready for use in all of the aforementioned industrial applications as well as many others. Nitrogen can be obtained in three ways. Companies can either lease an on-site nitrogen tank, have the gas delivered in high-pressure bottles, or generate their own. Many businesses quickly realize that the first two options, which rely on a third-party supplier, are inconvenient, inefficient and costly. Fortunately, there are ways for them to generate their own nitrogen and control the amount, purity and pressure for any application – and guarantee that they have an endless supply of nitrogen available around the clock.

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Thus, generating nitrogen in-house enhances production flexibility and, since there is no third-party supplier involved, it eliminates constant order processing, refills and delivery costs, and frees up space otherwise needed to store nitrogen bottles.

How does a nitrogen generator work

Essentially, this is how a nitrogen generator works: it separates nitrogen molecules from the oxygen molecules within compressed air, resulting in a purified supply of nitrogen. Generating nitrogen can be done with a membrane nitrogen generator or a PSA (pressure swing adsorption) nitrogen generator connected to a compressor. But which technology to use? Well, it depends on the nitrogen quality you require. If, for example, you just need to inflate tires or use nitrogen to prevent/suppress fires, then a low nitrogen purity level of 90-99% and a membrane nitrogen generator will suffice. However, a PSA nitrogen generator is required when you have to achieve very high purities of 99.999% or 10 PPM (parts per million) and even higher – for example in the food industry or for plastic molding.

In addition to allowing companies to control how much nitrogen they want to produce with how much pressure and which degree of purity, generating the gas themselves has other benefits. They are no longer subject to price fluctuations on the market, save transport costs, and prevent delays. In addition, businesses generating their own nitrogen do not have to face the safety hazard that come with handling high-pressure cylinders, they incur no waste related to boil-off losses or have to return high pressure bottles that can never be fully emptied. Over time, the initial investment for a nitrogen generator pays off because operating costs are kept significantly lower compared to getting nitrogen from a third party.

Watch this video to learn more about nitrogen

Membrane nitrogen generators

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).

Pressure Swing Adsorption (PSA) nitrogen generators

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.

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