Nitrogen gas is essential across a wide range of industries, from food processing and pharmaceuticals to manufacturing and electronics. Two primary methods for producing nitrogen gas are Air Separation Units (ASUs) and nitrogen gas generators. Each approach has its own set of advantages and disadvantages, making them suitable for different applications and scales of production.
Air Separation Units (ASUs)
ASUs are large-scale facilities that separate atmospheric air into its primary components: nitrogen, oxygen, and argon. The process involves air intake and compression, purification to remove impurities, liquefaction by cooling the air to extremely low temperatures, and distillation, where the liquefied air is separated into its components based on their different boiling points. Nitrogen, with the lowest boiling point, is separated from oxygen and argon. ASUs can produce very high volumes of high-purity nitrogen. The major industrial gas companies such as Linde or Praxair use ASUs to make immense amounts of high-purity liquid nitrogen which is then either trucked to different customer sites to fill their liquid bulk tanks or filled into liquid nitrogen cylinders called “dewars” or compressed into high-pressure nitrogen gas cylinders. Which storage method is used depends on the quantity of nitrogen the customer needs.
Nitrogen gas generators, on the other hand, produce nitrogen on-site using two main technologies: Pressure Swing Adsorption (PSA) and membrane separation. PSA systems use carbon molecular sieves to selectively adsorb oxygen from compressed air, which is then vented, leaving behind nitrogen. PSA systems are known for their reliability and cost-effectiveness for medium to high-flow applications. Membrane systems use semi-permeable membranes to separate nitrogen and oxygen from compressed air. Oxygen permeates through the membrane at a faster rate than nitrogen, resulting in a nitrogen-rich stream. Membrane systems are generally simpler and more compact than PSA systems, making them suitable for smaller-scale nitrogen generation. For off-shore applications, large membrane systems are deployed in ISO containers, because membranes are less sensitive to water.
ASU vs. Nitrogen Gas Generators: Key Considerations
Here's a comparison of the two methods, considering factors relevant to various applications: Scale of production is a key differentiator. ASU can make massive amounts of liquid nitrogen, which can be stored at the customer’s site in large liquid nitrogen bulk tanks, while generators are ideal for smaller applications, as the cost of nitrogen is just the cost of compressed air and there are no supply contracts involved. Purity requirements also vary: ASU can produce extremely high-purity nitrogen (up to 99.9999%), suitable for applications like electronics manufacturing, laser cutting, and pharmaceutical processes, whereas generators offer nitrogen with purities ranging from 95% to 99.999%, sufficient for many industrial applications. Cost is another important factor. ASU makes liquid nitrogen that then must be down packaged and delivered to the customer, unless the customer’s site is close enough and at a very large scale to connect a pipeline directly from the ASU plant. Having to package and deliver to the customer incurs a lot of costs to the supplier, and thus makes the price of nitrogen per cubic foot much higher than generators which only needs compressed air. However, for applications that need a purity of more than 99.999% or for customers who need a huge amount of nitrogen, having it delivered from the gas company makes more sense.
The "better" choice depends heavily on your specific needs. For very large-scale, high-purity nitrogen demands greater than 99.999%, such as semiconductor applications, gas supply from ASU plants often make more sense. For small to medium-scale nitrogen requirements, on-site nitrogen generators offer a cost-effective, reliable, and flexible alternative. Also, if it is a large application that requires high-pressure nitrogen, liquid nitrogen can be better as it is more costly to compress gas nitrogen to achieve high-pressure versus vaporizing liquid nitrogen.
Introducing Stock # 600 Nitrogen Plant (Best of Both Worlds):
We are offering a system nitrogen plant consisting of (2) unused TGN-3700 Nitrogen Generators, with each train producing 3,332 Nm³/h of gaseous nitrogen at 115 PSIG at 0°C. This system produces about 6,600 Nm³/h (~251,000 SCFH) of nitrogen in total with up to 99.999% purity. When the system is idling, it makes liquid nitrogen that is fed into a 15,000L back-up liquid nitrogen tank for complete supply stability.
Liquid nitrogen expands about 700 times its volume into gas, so you can store about 700 times more volume in a cubic foot of liquid nitrogen vs a cubic foot of gas nitrogen. This means this unit can store much more nitrogen as a back-up than other nitrogen generators.