How a PSA Nitrogen Generator Works

About: How Pressure Swing Adsorption (PSA) nitrogen generators work. Background for all South-Tek PSA nitrogen generators.

A PSA (Pressure Swing Adsorption) nitrogen generator separates nitrogen from ordinary compressed air. This article explains the principle, the role of the carbon molecular sieve, and the alternating two-bed cycle that produces a continuous flow of nitrogen.

▲ Attention — General explanation This article describes how PSA generation works in general. South-Tek systems are engineered to order, so the number of beds, the valves and their names, and the options included (boosters, dryers, analyzers, duplex or staging) vary from one system to the next. The diagram and valve labels below are a simplified, generic representation for explanation only and do not represent any actual South-Tek system.

In this guide

• How PSA separates nitrogen
• The carbon molecular sieve
• The two-bed cycle, step by step
• Typical performance
• How this maps to your system

How PSA separates nitrogen

Ordinary air is roughly 78% nitrogen and 21% oxygen, with small amounts of other gases. A PSA generator takes in clean, dry compressed air and pushes it through a vessel (a "bed" or "tower") packed with carbon molecular sieve. Under pressure, the sieve traps oxygen, carbon dioxide, and water vapor while letting nitrogen pass through to the product line. When the sieve becomes saturated with the trapped gases, the bed is depressurized, which releases those gases so they can be vented to atmosphere. Releasing the trapped gas regenerates the sieve so the bed can be used again. By running two beds out of phase, one producing nitrogen while the other regenerates, the generator delivers a continuous supply.

The carbon molecular sieve

The carbon molecular sieve (CMS) is the material that does the separating. It is a carbon-based adsorbent with microscopic pores sized so that oxygen, carbon dioxide, and water molecules are preferentially adsorbed (held) while the slightly larger nitrogen molecules pass through. The CMS is not consumed in normal use; it adsorbs impurities under pressure and releases them when the pressure drops, over and over. Keeping the feed air clean and dry is what protects it, since liquid water and oil permanently damage the sieve.

The two-bed cycle, step by step

In a typical two-bed system, one bed (call it Bed A) produces nitrogen while the other (Bed B) regenerates. The diagram below shows that arrangement.

Figure 1: Generic representation of a two-bed PSA cycle. Click the diagram to open it full size in a new tab for readable detail. This is a simplified illustration for explanation only and does not represent an actual South-Tek system. Valve names, valve counts, the number of beds, and the arrangement vary by model.

While Bed A is producing, Bed B moves through regeneration in these steps:

1. Adsorption (producing bed). Compressed air enters the producing bed under pressure. The sieve adsorbs oxygen, carbon dioxide, and water vapor, and nitrogen passes through to the product line and on to the storage tank.
2. Depressurization / regeneration. The other bed is isolated from the air inlet and the product line, and its pressure is reduced to near atmospheric. Dropping the pressure releases the gases the sieve had trapped, which are vented to atmosphere through the exhaust.
3. Purge. A small amount of product nitrogen is passed back through the regenerating bed to sweep out the remaining released impurities, preparing the sieve for its next adsorption step.
4. Pressurization / equalization. The regenerated bed is brought back up to operating pressure, either directly with inlet air or by equalizing pressure with the producing bed, so it is ready to take over.

The roles then reverse: the bed that was producing regenerates, and the freshly regenerated bed begins producing. This continuous, alternating swing between pressure (adsorption) and low pressure (regeneration) is what the term "pressure swing adsorption" refers to, and it is what gives a steady supply of nitrogen.

ℹ Note — About the valves Each step is carried out by opening and closing a set of valves that direct air, product, exhaust, and purge flow. In the generic diagram the valves are labeled with simple numbers to show the idea; they are not South-Tek valve names. The valve naming, count, and control sequence on a real unit are specific to its design. For the controls and valve functions on an actual South-Tek generator, see the Controls & Touchscreen Navigation article.

Typical performance

PSA nitrogen generators can deliver nitrogen purity from about 95% up to 99.999%, depending on how they are configured. Delivery pressure, flow rate, and achievable dew point depend on the specific model, the application, and the air pretreatment in front of the generator. Because these figures are set by your system's design, refer to your unit's specifications rather than a general figure: see the Overview & Specifications and Site & Utility Requirements articles for your unit's purity, pressure, flow, and air-quality requirements.

How this maps to your system

The two-bed cycle above is the core idea behind every South-Tek PSA generator, but your actual system may differ in several ways. It may use a different number of beds, different valve names and counts, and a different control sequence. It may also include options such as a high-pressure booster, an air dryer, an oxygen analyzer, or duplex or staging for multiple units. Treat the diagram and step list here as the concept, and rely on your unit's documentation and the controls article for the specifics of your equipment.

Related Articles

• N2-GEN TS, CS, and S Series — Overview & Specifications
• N2-GEN TS, CS, and S Series — Controls & Touchscreen Navigation
• N2-GEN TS, CS, and S Series — Purity, Pressure & Standby
• N2-GEN TS, CS, and S Series — Filter Maintenance

Need help? South-Tek Systems Service — Phone: [phone] · Open a support ticket at [e-mail] or through the Help Center.