What is membrane nitrogen generation?

Many industries use nitrogen gas. This includes food and beverage packaging, electronics production, fire prevention, and hardening plastics as part of a more extensive manufacturing process, to name a few. The gas is also used to purge enclosed spaces too, because of its useful, non-reactive properties.

While the atmosphere is composed of 78 per cent nitrogen (N2) and 21% oxygen, sophisticated processes are required to achieve a 95% mix (or better) of pure nitrogen for commercial purposes.

To create sufficient N2, either membrane nitrogen generators or pressure swing adsorption PSA generators are used.

What is Membrane Nitrogen Technology?

Membrane nitrogen generators rely on clean compressed air, which passes through a membrane containing numerous hollow fibres. These permeable fibres permit water vapour, oxygen, and miscellaneous fast gasses to escape. Meanwhile, the membrane fills up with slow gasses, primarily nitrogen.

The control methods for nitrogen generation are the pressure level and flow rate of compressed air moving through the membrane. Nitrogen purity levels vary but sit between a 95-99% range, which is sufficient for scientific labs, and various industrial and commercial settings where N2 is used.

Nitrogen membrane generators do not generate waste gas. Operating them only when additional N2 is required is possible because of their minimal start-up time. Also, the lack of mechanical moving parts helps to avoid breakdowns, too.  

How Does Membrane Technology Work?

With a nitrogen membrane generator, small membrane modules store polymer fibres inside. These are numerous and hollow, to allow both air flow and permeation to occur.

Permeation: What is it?

Permeation is a process whereby compressed air enters, first inside the membrane modules, and later the polymer fibres themselves. As previously cleaned, high-pressure compressed air moves through the fibres, it helps to separate distinct elements.

Gas separation, oxygen molecules, H2O, carbon dioxide, water vapour, air impurities, and oil in a vapourised form permeate the membrane fibres. This permeation process occurs at a different rate, depending on what the element is. 

H2O is removed very quickly, whereas oxygen lags a little. Argon – which is present at a roughly 1% rate in Earth’s atmosphere – will partially permeate when given time to do so. However, some Argon will still be present with the remaining nitrogen.

It’s All About the Membranes

The membranes have a concentration gradient surface on either side. This allows for distinct elements to permeate the sides while nitrogen flows through the hollow fibres unimpeded.

When it comes to N2 purity, the size of the individual pores within the membranes is a significant factor. Therefore, the membranes are specific to the purpose and the purity levels required.

The Need for Venting

No waste gas is expelled during the N2 membrane-based production process. Venting so-called “fast exhaust gasses” is necessary, though, including Argon, H2O, and oxygen. Without doing so, the polymer fibres eventually become clogged, and permeation efficiency suffers. Then purity levels decline sharply too.

Membrane-based generators include a permeate vent to address this issue.

Membrane Nitrogen Technology: Factors to Be Aware

For nitrogen generation, cleaner environments are better than ones containing dirtier air. The latter may restrict nitrogen purity levels or cause machines to get overworked if source air cannot be sufficiently filtered before it reaches the membrane. Carbon molecular sieve membranes perform best when paired with cleaner air systems.

New limits or other restrictions on N2 production apply to scientific labs at a notable elevation above sea level. Discuss this before site implementation.

Air feed requirements vary depending on the technology used. For example, the latest Atlas Copco NGM 7-70 membrane nitrogen generators require 20 per cent less air intake than some competitors or older models.

More energy-efficient systems do not require separate feed heaters. As a result, they operate with a considerably smaller energy footprint.

The start-up speed is mere seconds with better membrane nitrogen systems. This is vastly superior to the primary alternative, pressure swing adsorption PSA. Depending on the reconfiguration, they may require minutes or perhaps over an hour to adjust and start-up. Repeated reconfigurations in a single day severely impact consistent N2 generation on PSA systems.  

Both pressure levels and flow rate are sustainable at consistent levels using membrane tech. Reduced system complexity lowers the instances of potential downtime and ongoing maintenance needs.

Also, note that membranes function best and survive longer when the source intake does not contain liquid water or oil. Depending on the machine, upstream solutions to remove oil or water from intake sources protect the membrane.

How Membrane Technologies Compare to Pressure Swing Adsorption PSA

Nitrogen generators for most applications are superior to pressure swing adsorption methodologies.

The generators themselves are compact, but also lighter too. For busy labs or other locations, membrane nitrogen systems are far quieter. This avoids the need to wear protective earplugs, which in some settings is inconvenient or makes real-time communication problematic.

N2 purity is a critical factor too. Membrane-based generators achieve a 99.9% efficiency rating under perfect conditions. The PSA systems potentially achieve as high as 99.999%, yet rarely is this required in real-world environments.

When nitrogen supply flow rates and pressure levels must remain consistent, then PSA isn’t ideal. Rates and levels may fluctuate and be harder to control with these systems. Nitrogen membrane systems include digital controllers offering precise control. With Atlas Copco’s NGM membrane-based system, external cylinders aren’t required to achieve consistent flow and pressure levels. This results in reliable, efficient production levels rather than uncertain, inefficient ones.

Lastly, membrane technologies do not result in waste gas generation. Unfortunately, PSA produces waste gas during a blow-off phase that must be safely managed. Environmental regulations and the risk of sizable fines remind businesses of the need to do so.

Let Anglian Compressors Help Guide You

Choosing the right nitrogen generation technologies for your business isn’t easy. While there are key benefits to adopting a membrane generator over a PSA system, we can advise correctly for your specific needs.

This way, you’ll receive a best-in-class nitrogen generation system with excellent energy efficiency, using the smallest possible footprint.