Pressure Swing Adsorption (PSA) vs. Membrane Nitrogen Generator Technologies
Nitrogen gas is an important industrial gas that is used in a wide range of applications. In this article we will compare the two common onsite nitrogen generation technologies; PSA and membrane nitrogen generators. We will outline the key differences and similarities between these two technologies, and then provide a brief overview of Advanced Gas Technologies’ onsite nitrogen generation systems.
An Overview of PSA and Membrane Nitrogen Generation Technologies
PSA Nitrogen Generators
PSA technology relies on the principle of adsorption to separate nitrogen from other gases, primarily oxygen, in atmospheric air. A PSA system typically consists of two adsorption beds, each filled with carbon molecular sieve (CMS). The CMS is a material that selectively adsorbs oxygen and other impurities such as H2O, while allowing nitrogen to pass through.
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.
Membrane Nitrogen Generators
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.
Important Differences between PSA and Membrane Nitrogen Generators
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.
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%.
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
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 or 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
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.
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.
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!