PSA or membrane: which nitrogen generator suits your plant?
Both technologies take clean, dry compressed air and remove oxygen. A PSA (pressure swing adsorption) generator passes air through carbon molecular sieve (CMS) in two towers, which holds back oxygen while nitrogen passes. A membrane generator passes air through bundles of hollow fibres; oxygen, water vapour and carbon dioxide permeate the fibre walls faster than nitrogen. The right choice depends mainly on purity and flow.
| Factor | PSA generator | Membrane generator |
|---|---|---|
| Purity range (typical) | 95% to 99.999% | 95% to 99.5%; economical up to about 99% |
| Flow range (typical) | A few Nm³/h to over 1,000 Nm³/h | Small to medium flows, roughly 1 to 300 Nm³/h per package |
| Air factor (typical; air in ÷ nitrogen out) | About 2.5–4 at 99.5–99.9%; about 6–8 at 99.999% | About 2–3 at 95%; 4–6 or more at 99–99.5% |
| Feed pressure (typical) | 7–10 bar(g) (101.5–145 psig) | 7–13 bar(g); more pressure gives more output |
| Feed temperature sensitivity | Moderate; hot feed reduces output | High; often heated to a set temperature, output and purity shift with it |
| Start-up to purity | Minutes (tens of minutes for highest purities) | Fast, usually a few minutes |
| Moving parts | Switching valves cycling every minute or so | Almost none |
| Main maintenance | Valves, silencers, filters, CMS over its life, analyser | Filters, heater, analyser; membrane module after many years |
| Footprint and noise | Two towers plus receivers; exhaust noise each cycle | Compact and quiet; suits mobile and skid units |
As a rule of thumb: above about 99.5% purity, or above about 100 Nm³/h, PSA is usually the cheaper nitrogen per Nm³. For 95–99% purity at modest flow, where simplicity matters (tyre inflation, fire-protection systems, some blanketing), membrane is attractive. The feed-air side of both is covered in detail in our guide to nitrogen generator feed air.
What purity does your application need?
Purity is the single biggest cost driver. Every step towards 99.999% raises the air factor, and therefore compressor size and power. Specify the purity your process or quality document requires, not the highest available. Purity is stated as nitrogen plus argon; the remainder is mostly oxygen, so 99.9% purity means about 0.1% (1,000 ppm) oxygen.
| Application | Typical purity | Typical technology | Notes |
|---|---|---|---|
| Food packaging (MAP: snacks, coffee, dairy powder) | 99–99.9% (residual O2 0.1–1%) | PSA; membrane at lower purity | Product’s residual-oxygen target decides; food-grade filtration downstream |
| Pharma blanketing, purging and transfer | 99.5–99.99% | PSA | Purity, dew point and filtration from the site’s quality documents; validation separate from supply |
| Laser cutting assist gas (stainless, aluminium) | 99.9–99.999% | PSA plus booster to about 15–30 bar(g) | Edge colour and cut quality on thick stainless need the higher purity |
| Heat treatment and brazing atmospheres | 99.5–99.999% | PSA | Bright annealing needs the high end; dew point matters as much as oxygen |
| Electronics (reflow and wave soldering) | 99.9–99.999% | PSA | Oxygen often specified in ppm at the oven |
| Tyre inflation | 95–99% | Membrane or small PSA | Lower purity is adequate |
| Fire protection (dry-pipe sprinkler, inerting) | 95–98% | Membrane or small PSA | Reduces corrosion in dry pipe; follow the fire system designer |
| Oil and gas purging, pipeline drying, tank blanketing | 95–99.5% | Membrane or PSA; booster as needed | See our page on oil and gas compressed air and nitrogen |
All purities above are typical ranges for planning. The buyer’s process specification governs.
Sizing the compressor: from nitrogen flow to cfm and kW
A nitrogen generator is sized from nitrogen flow at purity. The compressor is then sized from the generator’s air factor. Two traps cause most undersized systems: using a lower air factor than the chosen purity needs, and mixing reference conditions. Nitrogen is quoted in Nm³/h (0 °C, 1.01325 bar(a)); compressor free air delivery (FAD) is quoted at intake conditions. At a Hyderabad intake of 35 °C and about 0.950 bar(a), 1 Nm³ of air is (1.01325 ÷ 0.950) × (308.15 ÷ 273.15) = 1.203 m³ of free air.
Worked example: compressor size for a PSA generator
(Illustrative.) A food plant near Hyderabad needs 25 Nm³/h of nitrogen at 99.9% for packaging. Typical PSA air factor at 99.9% is 3.5 (confirm on the generator maker’s data at your pressure and temperature).
- Feed air = 25 × 3.5 = 87.5 Nm³/h.
- Convert to FAD at site intake: 87.5 × 1.203 = 105.3 m³/h = 105.3 ÷ 60 = 1.755 m³/min.
- In cfm: 1.755 × 35.315 = 62.0 cfm.
- Add 10% for filter drains, dryer losses and summer derating: 1.755 × 1.10 = 1.93 m³/min (68.2 cfm).
- At a typical 7 kW per m³/min for a screw compressor at about 8 bar(g) (116.0 psig): 1.93 × 7 = 13.5 kW. Select a 15 kW (20 hp) compressor, which also covers the generator’s minimum inlet pressure with filter and dryer losses.
If the same plant asked for 99.999% (typical air factor 7), the feed becomes 25 × 7 = 175 Nm³/h, or 3.51 m³/min (123.9 cfm); with 10% margin 3.86 m³/min (136.3 cfm), about 27 kW of compressor, so a 30 kW machine. Doubling the compressor for one extra “9” is common; ask whether the process truly needs it.
A heatless desiccant dryer in the feed line would also need its purge added to the compressor flow. Most generators need only refrigerated-dryer quality feed; check the maker’s requirement before adding a desiccant dryer.
Cost per Nm³: on-site generation versus bought nitrogen
On-site nitrogen costs mainly electricity. The figures below use the example above and are illustrative; replace them with your own tariff, hours and supplier rates.
Worked example: energy cost of generated nitrogen
(Illustrative.) 25 Nm³/h at 99.9%, 6,000 hours a year, tariff ₹8 per kWh.
- Compressor power at actual load: 1.755 m³/min × 7 kW = 12.28 kW. Refrigerated dryer about 0.7 kW. Total about 12.98 kW.
- Energy per Nm³ of nitrogen: 12.98 ÷ 25 = 0.519 kWh/Nm³.
- Energy cost: 0.519 × ₹8 = about ₹4.15 per Nm³.
- Annual: 12.98 kW × 6,000 h = 77,900 kWh, or about ₹6.23 lakh, for 150,000 Nm³.
- At 99.999% the same flow needs about 25.27 kW: 1.011 kWh/Nm³, about ₹8.09 per Nm³.
To compare, take your delivered price per Nm³ of liquid or cylinder nitrogen, including rental of the tank or cylinders, transport, evaporation or residual-gas losses and handling labour. If, for example, bought nitrogen worked out at ₹25 per Nm³ (illustrative only; use your own invoices), 150,000 Nm³ would cost ₹37.5 lakh a year against about ₹6.2 lakh of electricity. Add generator and compressor service, filter elements and capital cost to the on-site side before deciding.
Bought nitrogen still makes sense for very small or occasional use, for purities beyond 99.999%, and as a backup supply. Many plants keep a cylinder manifold as standby.
Feed-air quality: what the generator needs
Oil, water and heat damage generators. Oil vapour coats CMS and membranes, and the damage is mostly permanent. Typical requirements (always confirm on the maker’s data):
| Parameter | Typical requirement | How it is met |
|---|---|---|
| Oil (aerosol and vapour) | 0.01 mg/m³ or less at the generator inlet | General and high-efficiency coalescing filters, then activated carbon filter; or an oil-free compressor, still with filters |
| Pressure dew point | +3 °C or drier (some PSA designs ask for lower) | Refrigerated dryer sized for summer conditions |
| Particles | 1 µm or finer | Particulate filtration; clean pipework |
| Inlet temperature | Often 5–40 °C, best below about 35 °C | Effective aftercooler, ventilated room, dryer that cools the air |
| Pressure and flow | Steady at the generator’s rated inlet pressure | Correct compressor size, air receiver, short pipe runs |
In a 45 °C Hyderabad summer the feed can exceed these limits even with a correct design on paper. Watch the compressor room ventilation and dryer correction factors; see our guide to refrigerated air dryers for dryer sizing at high ambient, and our page on air dryers in Hyderabad for supply and service of the feed-air dryer. During the monsoon, drains on the receiver, filters and dryer must work every time; a single slug of water can damage a sieve bed.
Oxygen analyser and nitrogen safety
Nitrogen is not toxic, but it displaces oxygen without any smell or warning. Air with too little oxygen can cause collapse within a few breaths. This is the main hazard of an on-site generator, and it is often overlooked in small rooms.
- Purity analyser: every generator should have an oxygen analyser on the product line that alarms and diverts or stops off-spec nitrogen. Calibrate it with zero and span gas at the interval the maker gives; many plants do it every 3–6 months.
- Room oxygen monitor: fit an ambient oxygen-depletion monitor in the generator room and in any enclosed space where nitrogen is used, with an alarm outside the door. A common alarm point is 19.5% oxygen.
- Vent the exhaust outdoors: PSA towers exhaust oxygen-rich air; membrane permeate is oxygen-rich too. Off-spec nitrogen vents must go outside, not into the room.
- Ventilation: give the room enough fresh-air change for leaks and vents.
(Illustrative.) In a closed 4 m × 5 m × 3 m room (60 m³), mixing in about 4.2 m³ of nitrogen lowers oxygen from 20.9% to about 19.5% (60 × ln(20.9 ÷ 19.5) ≈ 4.2). A 25 Nm³/h generator venting its product into the room would do that in under 10 minutes. Treat any indoor vent or leak as serious.
High-pressure nitrogen from a booster also stores energy. Receivers, hoses and relief valves must be rated for it; see our page on nitrogen booster compressors for the booster side.
Service schedule for nitrogen generators
Typical intervals for a clean, well-ventilated installation running most of the day. The maker’s schedule is the minimum; dusty or hot sites need shorter intervals.
| Interval (typical) | PSA generator | Membrane generator | Feed-air system |
|---|---|---|---|
| Daily | Purity, flow, tower pressures normal; listen for cycle changes | Purity, flow, heater temperature | Drains discharging; compressor pressure and temperature |
| Monthly | Filter differential pressures; silencer condition | Filter differential pressures | Dryer dew-point indicator; condenser cleaning in dusty months |
| 3–6 months | Analyser calibration; check valve timing | Analyser calibration | Verify dew point and oil content at the generator inlet |
| Yearly or 8,000 hours | Replace filter elements and silencers; valve service kits as the maker advises | Replace filter elements; check heater and controls | Compressor service; carbon filter element |
| Condition-based | CMS: often 8–10 years with clean feed; replace when output at purity falls despite good valves and feed | Membrane module: often 10 years or more with clean feed | Dryer and drain overhaul as needed |
When output at purity falls, check the feed first: inlet pressure at the generator, dew point, oil, inlet temperature and valve switching. CMS and membranes are usually blamed before they are guilty.
Nitrogen generator price: what drives it
The cost of a nitrogen plant depends on:
- Flow at purity: the same generator gives much less nitrogen at 99.999% than at 99%.
- Technology: membrane is simple and compact for lower purities; PSA is usually better value for high purity and larger flows.
- Feed-air scope: compressor, dryer, filters and receivers often cost as much as the generator. Compare quotes on the same scope.
- Delivery pressure: a booster and high-pressure receivers for laser cutting add significantly.
- Controls and documents: analyser type, data logging, food or pharma documentation.
- Running cost: a lower air factor saves compressor power every hour; ask each supplier for it at your purity.
How Reddy Compressors helps
- Supplies PSA and membrane nitrogen generators from reputed makers; we are suppliers and service providers, not manufacturers.
- Sizes and supplies the feed-air side: compressor (new, used or refurbished), refrigerated or desiccant dryer, filters, receivers and drains.
- Supplies, rents and services nitrogen booster compressors where higher pressure is needed.
- Services nitrogen generators and their compressors, including under AMC, with 20+ service engineers and technicians; operating since 2002.
- Covers all of Telangana, Andhra Pradesh and districts within about 300 km of Hyderabad; supplies across India.
What to send us
- Nitrogen flow needed (Nm³/h, or litres per minute at each user) and the purity or residual oxygen required.
- Delivery pressure at the user, and whether demand is steady or in bursts.
- Application: packaging, pharma, laser, heat treatment, electronics, tyre, fire protection or other.
- Existing compressor, dryer and receiver details, with nameplate photos.
- Current nitrogen source and monthly consumption or bills, if you want a cost comparison.
- For service: generator nameplate photo, purity and flow readings, and the symptom.
Frequently asked questions
Who supplies nitrogen generators in Hyderabad?
Reddy Compressors, Tarnaka, Secunderabad, supplies PSA and membrane nitrogen generators from reputed makers, together with the compressor, dryer, filters, receivers and booster needed to run them. We service generators of all major makes across Telangana and Andhra Pradesh. We do not manufacture generators; we size, supply and maintain the complete system. Call or WhatsApp 99590 60718 with your flow and purity.
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What is the difference between a PSA and a membrane nitrogen generator?
A PSA generator uses carbon molecular sieve in two towers to hold back oxygen and reaches up to 99.999% purity at a wide range of flows. A membrane generator uses hollow fibres that let oxygen pass through their walls; it is compact, quiet and simple, but is economical mainly up to about 99%. For high purity or flows above about 100 Nm³/h, PSA is usually cheaper per Nm³.
What is the price of a nitrogen generator?
It depends mainly on flow at your purity, the technology, the feed-air equipment included and the delivery pressure. A 99.999% plant needs roughly twice the compressor of a 99.9% plant for the same flow. Compare quotes on the same scope and the same air factor. Send us your flow, purity and pressure, and we will propose a complete package with its running cost per Nm³.
Which nitrogen plant is suitable for pharma?
Most pharma blanketing, purging and transfer duties use PSA nitrogen at 99.5–99.99% purity, with oil-free feed air or full coalescing and carbon filtration, a dry dew point, sterile-grade final filters where the process needs them and a calibrated oxygen analyser. The site’s own quality documents set the purity, dew point and filtration. Validation is a separate activity; we supply and service the equipment.
How much compressed air does a nitrogen generator need?
Multiply the nitrogen flow by the generator’s air factor at your purity. For PSA this is typically about 2.5–4 at 99.5–99.9% and 6–8 at 99.999%. For example, 25 Nm³/h at 99.9% with an air factor of 3.5 needs 87.5 Nm³/h of air, which is about 1.76 m³/min (62 cfm) of compressor FAD at Hyderabad conditions, plus a margin.
Do you provide nitrogen generator service?
Yes. We service PSA and membrane generators of all major makes and the compressors, dryers and filters that feed them: valve and silencer work, filter changes, analyser checks and calibration support, feed-air dew point and pressure checks, and CMS or membrane assessment. Generators can be included in an AMC with the compressor. Send the nameplate photo and current purity and flow readings.
Can an oil-lubricated screw compressor feed a nitrogen generator?
Yes, most generators run on oil-lubricated screw compressors with proper treatment: coalescing filters, an activated carbon filter and a refrigerated dryer, with drains that work. The carbon filter element must be changed on time, because oil vapour breaking through damages the sieve or membrane. An oil-free compressor reduces the risk but still needs drying and filtration.
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Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.