Buying a PSA nitrogen generator without a proper sizing exercise is like buying a compressor without knowing your flow requirement. An undersized generator delivers insufficient flow or inadequate purity, causing production problems from day one. An oversized generator wastes capital and runs inefficiently. This guide gives you a systematic checklist to size your generator correctly before you request a quotation.
Step 1: Define Your Required Purity
Purity is the most critical specification because it directly determines the generator's air-to-nitrogen ratio (the volume of compressed air required to produce each unit of nitrogen). Higher purity requires more compressed air per unit of nitrogen, which means a larger compressor and higher electricity cost for the same nitrogen output.
| Application | Typical N₂ Purity Required | Air:N₂ Ratio (approx.) |
|---|---|---|
| Tyre inflation (automotive / industrial) | 95–97% | 3.5:1 |
| Fire suppression inerting | 97–99% | 4:1 |
| Food packaging (MAP) | 99–99.5% | 4.5:1 |
| Chemical blanketing / tank inerting | 99–99.5% | 4.5:1 |
| Laser cutting (mild steel) | 99.5% | 4.8:1 |
| Heat treatment / annealing | 99.9–99.99% | 5.5:1 |
| Laser cutting (stainless / aluminium) | 99.99–99.999% | 6:1 |
| Electronics / SMT / semiconductor | 99.999% | 6.5–7:1 |
| Pharma blanketing (API storage) | 99.999% | 6.5–7:1 |
Recommendation: Always specify only the purity you genuinely need. Moving from 99.5% to 99.999% typically increases the compressed air requirement by 30–40% for the same nitrogen flow — a significant impact on compressor size and energy cost.
Step 2: Calculate Your Peak Flow Rate
Measure or estimate the maximum simultaneous nitrogen consumption of all users. Do not use average consumption — the generator must meet peak demand. Add each process:
- Laser cutting machines: typically 15–50 Nm³/h each depending on power and material
- Packaging lines (MAP): typically 5–30 Nm³/h per line
- Blanketing headers (chemical / pharma): continuous low-flow demand, 2–15 Nm³/h per vessel
- Heat treatment furnaces: 20–150 Nm³/h per furnace depending on size
After totalling the simultaneous peak demand, add a 15–20% safety factor to account for measurement uncertainties and future production increases. If you plan to expand production within 3 years, size the generator for the expanded demand now — the marginal cost of a larger generator is much less than adding a second unit later.
Step 3: Determine the Required Delivery Pressure
PSA nitrogen generators typically produce nitrogen at 5–10 bar pressure. If your application requires higher pressure — as is the case with laser cutting (12–25 bar) or high-pressure cylinder filling (150–200 bar) — a nitrogen booster compressor is required between the generator and the end user. Always confirm:
- What pressure does each end user require at their inlet?
- What pressure drop will occur in the distribution pipe network?
- Is a booster included in the quotation or is it a separate item?
Step 4: Size the Compressed Air Supply
The compressed air supply is the hidden constraint that is most commonly underestimated. Using the air-to-nitrogen ratio from Step 1 and the nitrogen flow from Step 2:
Required compressed air = Nitrogen flow rate x Air:N₂ ratio
Example: 50 Nm³/h of nitrogen at 99.99% purity, air:N₂ ratio 6:1 = 300 Nm³/h of compressed air required.
The compressed air must be at 6–8 bar, dried to at least −40°C pressure dew point (desiccant dryer — not refrigerated), and filtered to remove oil aerosols to 0.01 mg/m³ or better. Oil contamination will permanently damage the molecular sieve beds, reducing purity and requiring costly replacement.
Step 5: Size the Nitrogen Buffer Tank
A buffer tank is not optional — it is essential. The PSA process cycles between two sieve beds, producing nitrogen in pulses. Without a buffer tank, the supply pressure to end users fluctuates with each cycle. The buffer tank also provides surge capacity during peak demand spikes and a short supply bridge during system transients.
Minimum buffer volume = 10–15 minutes of peak nitrogen consumption. For a 50 Nm³/h system at 7 bar working pressure, minimum buffer = approximately 100–150 litres vessel capacity. For laser cutting applications, where a pressure drop during a cutting sequence causes an immediate quality problem, err toward 20–30 minutes of buffer.
Step 6: Check Compressed Air Quality — The Critical Pre-Treatment Train
A PSA nitrogen generator's molecular sieve is sensitive to oil vapour and moisture. The correct pre-treatment train for the compressed air supply is non-negotiable:
- Stage 1: 1 μm coalescing pre-filter (Grade M) — removes liquid oil and water droplets
- Stage 2: Desiccant dryer to −40°C PDP — refrigerated dryers are not sufficient
- Stage 3: 0.01 μm coalescing filter (Grade S) — removes oil aerosols to trace levels
- Stage 4: Activated carbon filter (Grade ACS) — removes residual oil vapour
- ✓ Required purity confirmed for each application
- ✓ Peak simultaneous nitrogen flow calculated + 20% margin
- ✓ Required delivery pressure confirmed per end user
- ✓ Compressed air supply capacity checked
- ✓ Buffer tank sized for 15–20 minutes of peak demand
- ✓ Pre-treatment train specified: desiccant dryer + oil-free filtration
- ✓ Future expansion requirement noted
Share your application, purity requirement and approximate flow rate with our team. We will size the right Omega Air PSA nitrogen generator and pre-treatment package and provide a full system quotation.