When nitrogen use changes through the day, the cheapest plant is rarely the one sized for the peak. A smaller PSA nitrogen generator sized near average demand, plus a storage tank that covers the peaks, usually costs far less to buy and run. In the case below, a food packager needed 120 Nm³/hr, not 160 Nm³/hr, and 99.9% purity, not 99.999%. That cut the plant price from ₹1.2 crore to ₹40 lakh and saved about ₹51 lakh a year in power.
This is Part I of a two-part series. It covers demand that changes with shifts and working hours. Part II covers sudden spikes, such as purging after each batch.
Case study: food packaging with changing shift demand
The plant ran 50 packaging machines, each using 3.5 Nm³/hr of nitrogen. The number of machines running changed through the day:
| Time | Hours | Machines running | Nitrogen use (Nm³/hr) |
|---|---|---|---|
| 08:00–19:00 | 11 | 30 | 105 |
| 19:00–21:00 | 2 | 45 | 157.5 |
| 21:00–06:00 | 8 | 20 | 70 |
| 06:00–08:00 | 2 | 45 | 157.5 |
Sized on the peak, the client had chosen a 160 Nm³/hr plant at 99.999% purity, delivering at 6 barg.
Two changes that made the difference
- The right purity. Food packaging does not need 99.999% nitrogen. 99.9% meets the food-packaging norms the client works to (see food-grade nitrogen and EIGA Doc 941). Every extra “9” of purity needs much more compressed air per Nm³, so this alone shrinks the plant.
- Size for the average and store for the peak. Absstem recommended a 120 Nm³/hr plant at 99.9%, delivering at 2.5 barg (the pressure the machines actually need), with a 20 KL nitrogen storage tank.
| Parameter | Client’s selection | Absstem recommendation |
|---|---|---|
| Nitrogen flow | 160 Nm³/hr | 120 Nm³/hr |
| Purity | 99.999% | 99.9% |
| Plant cost | ₹1.2 crore | ₹40 lakh |
| Compressed air needed | 760 CFM | 230 CFM |
| Compressor power | 110 kW | 37 kW |
| Daily power cost at ₹8/unit | ₹21,000 | ₹7,104 |
| Maintenance cost | High | Low |
Result: about ₹14,000 saved every day, about ₹51 lakh a year, and a plant one-third of the price.
How the storage tank covers the peaks
The gas a tank can deliver depends on the pressure range it works between:
Usable gas = tank volume × (maximum pressure − minimum pressure needed)
For a 20 KL (20 m³) tank charged to 6.5 barg, with the machines needing 2.5 barg:
20 × (6.5 − 2.5) = 80 Nm³ usable nitrogen
Through the day:
- 19:00–21:00 (peak): demand is 157.5 Nm³/hr against 120 produced. The shortfall of 75 Nm³ over two hours comes from the tank, which falls to about 2.75 barg.
- 21:00–06:00: demand drops to 70 Nm³/hr. The plant’s surplus of 50 Nm³/hr refills the tank to 6.5 barg.
- 06:00–08:00 (peak): the tank again covers the 75 Nm³ shortfall.
- 08:00–19:00: demand is 105 Nm³/hr. The 15 Nm³/hr surplus refills the tank before the evening peak.
The cycle repeats every day, so a 120 Nm³/hr plant reliably supplies a demand that peaks at 157.5 Nm³/hr.
How PSA nitrogen generators handle changing conditions
Demand is only one variable. A well-designed plant also adapts to site conditions:
- Low demand: economy or idle mode cuts power when the receiver is full, instead of venting nitrogen. See economy and idle mode in PSA generators.
- Temperature: the PLC adjusts cycle times so purity holds in hot and cold weather.
- Inlet pressure changes: pressure sensors and control valves keep tower pressure steady.
- Moisture and contaminants: dryers and filters protect the carbon molecular sieve.
- Remote monitoring: IIoT lets engineers see purity, pressure and flow in real time and react before a problem stops production.
How to size your own plant
- Log demand hour by hour for a full day, or for each shift pattern you run.
- Set the purity and pressure each process really needs.
- Calculate the average flow and the volume short during each peak.
- Size the tank so its usable gas covers the largest peak shortfall, with some margin.
- Check recovery: the surplus between peaks must refill the tank in time.
For more on tank sizing, read the importance of storage tank volume in PSA systems and sizing a PSA nitrogen generator for your facility.
Get your plant sized
Share your hourly nitrogen use and we will size the plant and tank for you. See nGEN industrial nitrogen generators or email info@absstem.com, call 1800 547 0506.