The air that we breathe contains approximately 78% nitrogen, 21% oxygen and 1% other gases, such as Argon and Water Vapour. The membrane systems use this unlimited supply of the raw materials 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. This characteristic allows “fast gases”, such as oxygen to be separated from “slow gases” such as nitrogen. The driving force of the separation process is the differential pressure created between the (compressed) feed air side and the low pressure side of the membrane.
The actual generation of nitrogen takes place in the membrane separator. Each separator consists of a bundle of hollow fiber membranes in a cylindrical shell, arranged much like a shell and tube heat exchanger. The compressed air is feed into 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. The results is a super dry nitrogen stream at the outlet end.