Nitrogen generators and stations are stationary or mobile air-to-nitrogen production complexes.
Chemical tankers, gas carriers and reefer ships need clean, dry nitrogen for inerting, purging and cargo padding. Onboard nitrogen generators are the most efficient way to provide this. There are two main types of nitrogen generators. One type uses hollow fiber membrane technology and other one is based on the Pressure Swing Absorption (PSA) process. Inert gas generators can produce nitrogen too. Molecular sieves remove the CO2 present in the inert gas.
Adsorption concept of Nitrogen Generators
The adsorption gas separation process in nitrogen generators is based on the phenomenon of fixing various gas mixture components by a solid substance called an adsorbent. This phenomenon is brought about by the gas and adsorbent molecules interaction.
PSA-type nitrogen generator – A typical nitrogen generation plant based on the Pressure Swing Absorption (PSA) process consists of two absorption towers filled with the carbon molecular sieve. Compressed, purified air passes through the towers and oxygen is absorbed on the carbon molecular sieve, whilst nitrogen-enriched gas leaves the tower. While absorption is taking place in one tower, the second tower is regenerated by returning to ambient pressure, with the oxygen enriched gas vented from the system.
Advantages of PSA Technology
- High nitrogen purity: PSA nitrogen generator plants allow production of high-purity nitrogen from air, which membrane systems are unable to provide – up to 99.9995% nitrogen. But in most cases they do not produce more than 98.8% nitrogen with the remainder being argon that is not separated from the nitrogen by the usual PSA process. The argon is not normally a problem, as argon is more inert than nitrogen. This nitrogen purity may also be ensured by cryogenic systems, but they are considerably more complex and justified only by large consumption volumes. The nitrogen generators use CMS (carbon molecular sieve) technology to produce a continuous supply of ultra high purity nitrogen and are available with internal compressors or without.
- Less operating costs: By substitution of out-of-date air separation plants nitrogen production savings largely exceed 50%. The net cost of nitrogen produced by nitrogen generators are significantly less than the cost of bottled or liquefied nitrogen.
- Environmental impact: Generating nitrogen gas is a sustainable, environmentally friendly and energy efficient approach to providing pure, clean, dry nitrogen gas. Compared to the energy needed for a cryogenic air separation plant and the energy needed to transport the liquid nitrogen from the plant to the facility, generated nitrogen consumes less energy and creates far fewer greenhouse gases.
The operation of membrane systems is based on the principle of differential velocity with which various gas mixture components permeate membrane substance. The driving force in the gas separation process is the difference in partial pressures on different membrane sides.
Gas Separation Concept in Membrane technology – The air we breathe contains approximately 78% nitrogen, 21% oxygen and 1% other gases such as argon and water vapour. Membrane systems use this unlimited supply of raw material to produce specific purities of nitrogen.
Selective permeation is the general principle behind a membrane system. Each gas has a characteristic permeation rate that is a function of its ability to dissolve and diffuse through a membrane. The “fast” gases, O2, H2O, CO2 permeate through the membrane wall much faster than the “slow” gases, thus separating the original mixture into two streams. The driving force of the separation process is the differential partial pressure, which is created between the compressed feed airside and the low-pressure side of the membranes.
The membrane separator consists of a bundle of hollow fibres in a cylindrical shell, arranged much like a shell and tube heat exchanger. The compressed air is fed to the inlet end of the separator, and flows inside the hollow fibres towards the opposite end. On the way the air molecules start to permeate through the walls of the fibres according to their permeability. Oxygen, carbon dioxide and water vapour permeate faster than nitrogen, and the result is a super-dry nitrogen stream at the outlet end. The secondary oxygen-rich stream is vented to atmosphere.
Applications of nitrogen generators
- Food and beverage industries: The moment food or beverages are produced, or fruits and vegetables harvested, an aging process kicks in until the complete decay of the products. This is caused by bacteria and other organisms. Generators are used to flood the products with N2 that takes out the oxygen and prolongs the product lifetime significantly because these organisms cannot develop. Furthermore, chemical degradation of food caused by oxidation can be eliminated or stopped.
- Analytical chemistry: Nitrogen generators are required for various forms of Analytical chemistry such as Liquid chromatography–mass spectrometry and Gas Chromatography where a stable and continuous supply of Nitrogen is necessary.
- Aircraft & motor vehicle tires: Although air is 78% Nitrogen, most aircraft tires are filled with nitrogen, and there are many tire and automotive shops with nitrogen generators to fill tires, the advantage being that nitrogen in a tank is dry. Nitrogen allows for maintenance of precise and proper tire pressure for longer than regular air, enhancing performance of motor vehicles. Often a compressed air tank will have water in it that comes from atmospheric water vapor condensing in the tank after leaving the air compressor. Nitrogen maintains a more stable pressure when heated and cooled as a result of being dry and doesn’t permeate the tyre as easily due to being a slightly larger molecule (155 pm) than O2 (152 pm).
- Chemical and petrochemical industries: The primary and very important application of nitrogen in chemical and petrochemical industries is the provision of inert environment aimed at ensuring general industrial safety during cleaning and protection of process vessels. Besides, nitrogen is used for pipelines pressure testing, chemical agents transportation, and regeneration of used catalysts in technological processes.
- Electronics: In electronics, nitrogen serves as an antioxidant in the manufacture of semi-conductors and electric circuits, heat treatment of finished products, as well as in blowing and cleaning.
- Fire Protection: The fire protection industry uses nitrogen gas for two different applications – fire suppression and corrosion prevention. Nitrogen generators are used in hypoxic air fire prevention systems to produce air with a low oxygen content which will suppress a fire. To prevent corrosion nitrogen generators are used in place of or in conjunction with a compressed air system to provide supervisory nitrogen gas in place of air for dry pipe and pre-action fire sprinkler systems.
In addition to Nitrogen Generators, we also offer many type of generators including Diesel Generators. Please contact us for more details.