Sinergia frequently receives the request of PSA N2 generators, capable of very high purity, exceeding 99,9%.
After inviting customers to better investigate the real need for purity for the specific process, happens to discover that this can be significantly reduced.
Widespread literature defines the LEL (lower explosion limit) of most hydrocarbons as between 1,4% and 2% in volume. This means, generally speaking, that a volume, saturated by nitrogen from 98% – UP, is reasonably safe even in case of ignition, therefore the discriminating point is to determine that UP.
If PSA technology is the one chosen for the nitrogen generator, the maximum purity that Sinergia can supply, in a stable way, (a critical aspect at very high purity) is 99,995%.
Psychologically a higher purity could be considered a guarantee of safer operation, thus affecting the requests, but this is not. A reasonable margin of 98% can be considered for prudency, but how much are you available to pay for this apparent benefit in risk reduction?
The selection of purity has a progressive impact on the ratio between compressed air and nitrogen, and consequently on the power supply for the air compression.
As a case study, with explaining the purpose, we considered a PSA nitrogen generator has following characteristics:
| Capacity | 1000 Nm3/h |
| Variable purity | 98 – 99,99% |
| Ambient temperature | 30°C |
| Operating pressure | 10 barg |
The below table identifies the power consumption increment related to nitrogen purity constant increase (0,5 % each step) from 98% (as base reference) up to 99,99%.
The difference in energy consumption is impressive and the relation is exponential.
Reasonably assuming 315 kW for 98% purity production, the 99,99% purity would ask for a 740 kW air compressor.
If the system would operate 7/7, 24/24 as often asked by Sinergia Nitrogen Generators, over 8500 h/y the result is as follows:
| 98% | 2.677.500 kW/y |
| 99,99% | 6.290.000 kW/y |
| Difference | 3.612.500 kW/y |
Just to give a value of such difference (according to the average price of electric power, globally, stated to be: 0,193 USD/kW ), the difference worth 697.212,50 USD per YEAR.
Considering that design of such plants is typically 20 years of lifetime, the selection of N2 purity appears in all its level of criticality.
Moreover, power supply is the main aspect of OPEX evaluation, but is not the only one, in fact, the bigger the air compressor is, the more expensive will be the maintenance (besides that, we are not considering in this analysis the CAPEX increase, at all).
So the main question is:
“Are you available to pay such a price for a disputable safer operating condition of your process?
and if the answer is yes,
Have you ever considered the impact of this choice on the sustainability of your project?”
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Sinergia promotes investigation about the necessary and sufficient concentration of nitrogen, for the specific process, offering extensive cost/convenience analysis for helping customers to determine their acceptable limit.
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Sinergia promotes sustainability in every aspect. Reducing power wasting saves the Planet.
Sinergia is beside its customers, developing better projects for a better world.
