How a Nitrogen Generator Works
Nitrogen is an important, odorless, and colorless gas in the chemical industry. It is used in the manufacturing of nitric acid, fertilizers, dyes, nylons, and explosives, among other products. Nitrogen is produced using nitrogen generators by compressing pre-treated air, adsorbing oxygen and other gases while allowing nitrogen to pass through. There are two methods of generating nitrogen gas with nitrogen generation systems. These two primary methods are Pressure Swing Adsorption (PSA) and Nitrogen Separation Membranes. Both of these systems generate high-purity nitrogen by compressing pre-treated air, but in two different ways. Here is how they work.
Pressure Swing Adsorption
Nitrogen is comprised of the highest percentage of the air you breathe. To separate it from other gases in the atmosphere, PSA generators use a Carbon Molecular Sieve (CMS) material that separates nitrogen from the other gases. The CMS material is made up of porous carbon whose pore size is finely controlled. In this process, you pass pre-treated, compressed air through the porous material, where oxygen molecules get absorbed into the pores. The larger nitrogen molecules go all the way to the exhaust and are released as nitrogen gas. This process continues until oxygen molecules saturate the CMS and eventually the separation of gases ceases.
To sustain this process, PSA generators usually have two or multiple adsorption columns. While one column separates the gas, the generator passes high-purity nitrogen in the other, pushing out the adsorbed oxygen and expelling it as waste gas. The system is designed in such a manner that the generator switches from one column to the other after about one minute or 60 seconds. The generators have several automated control valves to allow efficient switching between the two adsorption columns. It also features a nitrogen buffer tank to keep the pressure constant during the switching process. Additionally, the generator has an in-line filtration system to filter particulates and carry-over hydrocarbons before they can come into contact with the CMS material. If they come into contact, these substances, and especially liquid water, can adversely damage the CMS material. To prevent this, the generators are fitted with a refrigerated air dryer at the inlet point to ensure that it is as dry as possible before reaching the CMS material.
This method utilizes a generator that features a separation membrane that is made up of thousands of hollow fibers. Compressed air is passed through these permeable fibers, where some gas molecules pass through easily while some take time to go through. Carbon dioxide, oxygen, and water vapor molecules pass faster than nitrogen molecules and are expelled into the air or atmosphere. Nitrogen molecules, being a ‘slower’ gas, are contained for a longer time while passing through the fiber, resulting in the production of high-purity nitrogen. The generator works purely by controlling the flow rate and the pressure of the compressed air moving through the membrane. This generator also contains an in-line filtration system that helps remove liquid water, particulates, and any carry-over hydrocarbons before entering the air through the separation membrane, thus ensuring high-purity nitrogen.
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