Three Ways to Generate or Supply Nitrogen in the Field
When you call a nitrogen service contractor, you are essentially asking them to deliver inert gas to your work location at a specific purity, flow rate, and pressure. The equipment they bring determines what specifications they can actually meet — and not all nitrogen sources are equal. Understanding the three main nitrogen supply technologies helps you specify the right service for your application and ask better questions of your vendor.
Method 1: Membrane Nitrogen Generation
How It Works
Membrane nitrogen generators use hollow-fiber polymer membranes to separate nitrogen from compressed air. Air is compressed by onboard air compressors, dried, filtered, and passed through bundles of thousands of thin membrane fibers. Oxygen, water vapor, and carbon dioxide permeate through the membrane fiber walls faster than nitrogen because their molecules are smaller and more polar. Nitrogen, which has lower permeability, remains concentrated inside the fiber and exits the membrane bundle at the product end at elevated purity.
The key operating principle is the flow-purity tradeoff: the longer the compressed air spends in contact with the membrane (slower flow), the more oxygen permeates out and the higher the purity. Faster flow produces more nitrogen but at lower purity. This tradeoff means membrane generators are optimized for a specific purity-flow combination, and deviating significantly from design conditions affects performance.
Typical Specifications
- Purity range: 95% – 99.5% nitrogen
- Outlet dew point: -40°F to -60°F (well below most pipeline commissioning specs)
- Flow rate range: 200 – 3,000+ SCFM per trailer (purpose-built with multiple units)
- Maximum delivery pressure: 150 – 2,500 psi depending on system design
- Feed requirement: Clean, dry compressed air at 120–150 psi typically
Best Applications
- Pipeline purging — air to nitrogen or hydrocarbon to nitrogen
- Post-hydrotest nitrogen drying
- Nitrogen pressure testing (Class 1 and 2 pipeline segments)
- Gathering system commissioning
- Storage tank blanketing (continuous supply)
- Industrial nitrogen for general plant applications
Limitations
Membrane generators cannot reach purity above approximately 99.5% without significant flow reduction. For applications requiring 99.9%+ purity (LNG, catalyst protection), membrane generators are not sufficient. Membrane performance also degrades in extreme heat (above 100°F ambient) and extreme cold (below -10°F), requiring equipment management in those conditions.
Method 2: PSA Nitrogen Generation (Pressure Swing Adsorption)
How It Works
PSA nitrogen generators use a material called carbon molecular sieve (CMS) to selectively adsorb oxygen from compressed air under pressure. The CMS consists of carefully manufactured carbon granules with pore sizes precisely tuned to admit oxygen molecules while excluding nitrogen molecules. When compressed air flows through the CMS bed, oxygen is adsorbed onto the carbon surface and nitrogen passes through to the product stream.
PSA systems use two vessels alternating between adsorption (producing nitrogen) and regeneration (releasing adsorbed oxygen). While one vessel is producing nitrogen, the other is depressurizing and venting the adsorbed oxygen. This cycling continues automatically, providing a continuous nitrogen output. The two-vessel cycling is what distinguishes PSA from membrane, which is a continuous-flow single-pass process.
Typical Specifications
- Purity range: 99.0% – 99.999% nitrogen
- Outlet dew point: -40°F to -100°F+ (with downstream molecular sieve drying)
- Flow rate range: 100 – 2,000+ SCFM depending on system size
- Maximum delivery pressure: Up to 2,000 psi
- Feed requirement: Clean, dry compressed air at 100–120 psi
Best Applications
- Applications requiring 99.9%+ purity nitrogen
- LNG facility pre-commissioning and drying (with downstream molecular sieve dryer)
- Catalyst bed inerting and protection
- Analytical and instrument nitrogen supply
- Specialty chemical applications with stringent oxygen limits
Limitations
PSA units are more complex and more expensive than membrane generators of equivalent flow rate. The cycling nature of PSA means pressure fluctuations in the output stream that may require a surge vessel to smooth. PSA requires very clean, well-dried compressed air feed — moisture or oil contamination degrades CMS performance rapidly.
Method 3: Liquid Nitrogen (LN2) Vaporization
How It Works
Liquid nitrogen is produced at large industrial gas plants by cryogenic air distillation — the same process used to produce liquid oxygen, argon, and other industrial gases. Air is compressed, cooled, liquefied, and then distilled into its components by their different boiling points. Liquid nitrogen (boiling point -320°F / -196°C) is the result.
LN2 is transported to field locations in insulated cryogenic trailers or Dewar vessels. At the work location, it is vaporized through an ambient vaporizer or a heated vaporizer to produce gaseous nitrogen at whatever pressure and flow rate the job requires. Vaporization is a passive process — no mechanical generation equipment is needed beyond the vaporizer and a pressure regulator.
Typical Specifications
- Purity: 99.999%+ nitrogen (essentially pure, no oxygen)
- Outlet dew point: Extremely low (-150°F or below), limited only by the vaporizer design
- Flow rate: Limited by trailer capacity and vaporizer sizing, typically 100–1,000 SCFM from a single trailer
- Maximum delivery pressure: Up to 3,000+ psi with appropriate high-pressure vaporization equipment
- Supply limitation: Once the trailer is empty, production stops — no continuous generation
Best Applications
- LNG facility ultra-drying (dew points below -100°F)
- Catalyst loading and unloading under ultra-high purity conditions
- Small volumes requiring ultra-high purity
- Backup nitrogen supply during generator maintenance
- Remote locations where onsite air compression is unavailable
Limitations
LN2 supply is limited by trailer capacity. A typical LN2 trailer carries 5,000–7,500 gallons of liquid nitrogen, which vaporizes to approximately 1.0–1.5 million SCF of gas. For large-volume pipeline purging or extended drying operations, logistics planning is important — which adds complexity compared to continuous onsite generation. LN2 is also the highest cost per SCF of the three supply methods when evaluated over large volumes.
Choosing the Right Method
| If you need… | Best choice |
|---|---|
| High volume pipeline purge (50,000+ SCF), 97–99% purity | Membrane generator |
| Pipeline drying to -40°F dew point | Membrane generator |
| High purity (99.9%+) at moderate flow | PSA generator |
| LNG pre-commissioning drying (<1 ppm moisture) | PSA + molecular sieve, or LN2 |
| Small volume, highest purity, immediate availability | LN2 vaporizer |
| Continuous tank blanketing at a fixed facility | Membrane or PSA (onsite) |
NitroTech operates membrane nitrogen trailers for the full range of pipeline commissioning and industrial nitrogen applications. Learn more about trailer rentals or request a quote and tell us your purity and flow requirements.