Nitrogen membrane system is another popular non cryogenic technique of air
separation. Using this system, air is filtered through a membrane, removing
oxygen, carbon dioxide and water, thereby producing inert nitrogen.
How it Works ?
The system separates gases by using the principle of selective permeation
across the nitrogen membranes wall. The rate of permeation of each gas is
measured by its solubility in the nitrogen membrane material for nitrogen
polymeric membranes while the rate of diffusion is dependent on the
molecular free volume in the nitrogen membrane wall. Gases that are small in
molecular size and display high solubility in the nitrogen membranes
permeate faster than larger, less soluble gases. The system consists of tube
bundles made of special polymers configured in a manner similar to a shell
and tube heat exchanger.
Different gases pass through the film depending on the permeation rates.
Products like oxygen (plus water vapor and carbon dioxide) are "fast
gases" that pass more fast through the tube walls compared to "slow
gases" like argon and nitrogen. This allows dry air to be transformed
to a product which is a kind of mix of mostly nitrogen gas and argon, and
impure products are vented out from the shell. Nitrogen product emerges from
membrane units and since there are no moving parts in the separation
process, these units can be easily activated when required and shut down
when they are not.
This system of air separation is considered to be the most cost effective
for relatively low demand applications. However it is also used today at
higher production rates. This has been made possible by manufacturers
increasing the physical size and production capacity of their largest
modules.
Components of Nitrogen Membrane System
- Feed air filter
- Feed air heater
- Feed air compressors
- Piping and valves
- Membrane separators
Nitrogen Membrane System: Process Diagram
Membrane
Separation System
