Pressure Swing Adsorption (PSA) and membrane nitrogen generators are the two most common onsite nitrogen generation technologies, and they differ primarily in purity output, operating cost, and best-fit application. PSA systems use dual carbon molecular sieve (CMS) beds to deliver nitrogen purity as high as 99.999%, while membrane systems use hollow-fiber polymer membranes to deliver purity between 95% and 99.5% at a lower installed cost and with fewer moving parts.
Advanced Gas Technologies supplies, installs, and maintains both PSA and membrane nitrogen generators, and the sections below break down how each technology works, where each one fits best, and how to decide between them for your facility.
What is a PSA Nitrogen Generator?
PSA technology relies on the principle of adsorption to separate nitrogen from other gases, primarily oxygen, in atmospheric air. A PSA nitrogen generating system typically consists of two adsorption beds, each filled with carbon molecular sieve (CMS). The CMS is a porous carbon material with narrow, uniform pore openings that adsorb smaller gas molecules like oxygen and water vapor while allowing larger nitrogen molecules to pass through. It’s the core separation material inside every PSA nitrogen generator.
During operation, air is passed through the first adsorption bed, where oxygen and other impurities are adsorbed into the CMS. The nitrogen-rich gas that passes through is then collected and stored or used in the process that requires nitrogen. Once the first adsorption bed is full of oxygen, it is purged with nitrogen-rich gas from the second adsorption bed. This process is then repeated, with the two adsorption beds alternately adsorbing oxygen and being purged.
Best Applications for PSA Nitrogen Generators
PSA nitrogen generators are best suited to applications where purity above 98% is required, including laser cutting, where high-purity nitrogen prevents oxidation on cut edges; heat treating, where furnace atmospheres require 99%-99.999% purity to prevent discoloration and weakening of treated metal; and electronics soldering, where purity above 99.9% reduces dross formation. Pharmaceutical manufacturing and laboratory applications requiring 99%-99.999% purity also typically call for PSA technology.
What is a Membrane Nitrogen Generator?
Membrane nitrogen generators work on the principle of selective permeation. A membrane is a semi-permeable barrier that allows certain molecules to pass through, while rejecting others.
In a membrane nitrogen generator, air is passed over one side of a hollow-fiber membrane. The smaller oxygen molecules and other impurities in the air are filtered out by the membrane and exit as waste gas called permeate. The nitrogen-rich gas that passes through the membrane is collected and stored or used in the process that requires nitrogen.
Best Applications for Membrane Nitrogen Generators
Membrane nitrogen generators are well suited to applications with moderate purity requirements and continuous demand, including beverage dispensing and storage, tire inflation, and general industrial inerting and blanketing where purity requirements fall in the 95%-98% range. Their compact footprint and quieter operation also make them a common choice for mobile or space-constrained nitrogen supply.
PSA vs. Membrane Nitrogen Generators: Key Differences
Now that we have a basic understanding of how PSA and membrane nitrogen generators work, let’s take a closer look at the key differences between these two technologies.
Size and Weight
PSA systems are typically larger and heavier than membrane systems as they have pressure vessel adsorption beds and a lot more moving parts including valves and actuators Valve operation on PSA nitrogen generators are automatically controlled using a programmable logic controller or PLC.
Membrane systems on the other had have less moving parts and no bulky pressure vessels to hold CMS. They are typically relatively smaller and lighter and commonly used in applications where a mobile nitrogen source is required.
Purity Range
PSA systems can achieve higher nitrogen purities more efficiently than membrane systems. PSA systems can typically achieve nitrogen purities ranging from 95% to 99.999%. Membrane systems offer decent efficiency at nitrogen purities ranging from 95% to 99%.
Flow Rate and Capacity
PSA and membrane systems handle flow differently. Membrane nitrogen generators are modular so additional membrane cartridges can be added or removed to adjust flow rate, which makes them well suited to applications with steady, continuous nitrogen demand. PSA systems operate on a cyclical adsorption/purge process and are typically better suited to applications requiring both high purity and high flow simultaneously, though flow capacity in either technology should be sized to your facility’s specific peak and average demand.
Operating Cost Efficiency
At purity levels above 98%, the PSA nitrogen generators are significantly more cost efficient than membrane systems to operate.
Membrane nitrogen generators are nearly as efficient as PSA nitrogen generators for purity levels up to 98%. At nitrogen purities above 98% membrane efficiency drops off significantly when compared to PSA.
Effect of Water Exposure
PSA systems are more sensitive to the presence of water than membrane systems. The CMS in PSA systems is sensitive to higher concentrations of moisture. Nitrogen flow capacity and purity will decrease as moisture concentration increases and over time may lead to permanent damage of CMS.
The membrane systems, on the other hand, are somewhat more tolerant of moisture contamination within limits. A brief higher concentration of excessive moisture may cause a temporary reduction in membrane nitrogen performance if water does enter the membrane however once the water dries out of the membrane, the membrane performance will usually be restored.
It should be noted that neither PSA nor membrane nitrogen generators can tolerate exposure to water contamination for prolonged periods of time. A compressed air dryer should always be used to dry compressed air before it enters either type of nitrogen generator.
Effect of Oil Contamination
Both PSA and membrane systems are severely affected by any oil leaking into the system. In both cases, oil contamination will cause a permanent and irreversible decline in performance of the nitrogen generator.
Lifespan
The aging of membranes is the main concern in membrane nitrogen generators. Performance capacity of membrane nitrogen generators will typically gradually decline over a period of years. The system can perform reasonably well for over 10 years if proper maintenance is followed, and the compressed air filtration is replaced as instructed by the manufacturer.
PSA nitrogen generating systems usually have a longer life cycle than membrane nitrogen generating systems. This is because the CMS does not lose capacity over time so long as contamination is avoided. This can help the PSA nitrogen generator continue performing at a high level for over 20 years assuming proper maintenance practices are adhered to.
Also Read: The Evolution of Nitrogen Generating Systems: A Leap Forward with Technology
How to Choose Between PSA and Membrane Nitrogen Generators
Selecting the right technology comes down to two questions:
- What purity does your process require?
- What flow rate do you need to sustain it?
If your application requires purity above 98%, a PSA nitrogen generator is generally the better fit despite its larger footprint and higher maintenance requirements. If your application runs at 95%-98% purity with continuous, steady demand, a membrane nitrogen generator typically delivers comparable performance at a lower installed cost. Facilities with limited floor space or that need a mobile nitrogen source should also weigh membrane’s smaller footprint into the decision.
Onsite Nitrogen Generation Systems at Advanced Gas Technologies
Advanced Gas Technologies offers both PSA and membrane nitrogen generators. PSA systems are ideal for applications that require very high purity of nitrogen, while membrane systems are better suited for applications that require high capacity at lower purities. Contact us today to discuss your application and learn about our onsite nitrogen generation systems!