Non Cryogenic techniques were developed during the 1970s. For many small scale users of oxygen or nitrogen, non-cryogenic processes renders an efficient, convenient and economical alternative to purchasing gas in high pressure cylinders or for buying bulk liquid products to be vaporized to meet the demand. Pressure swing adsorption (PSA), and membrane diffusion systems, deserve special mention, as they are becoming increasingly significant for smaller or less demanding on-site applications.
Non cryogenic air separation process exploits the physical properties of the gases other than the temperature to discrete and refine elements of air at close-to-atmospheric temperature and produce commercially valuable gaseous products. This kind of air separation processes is widely acceptable as a suitable and cost effective option when high purity product is not required or when the desired production rate is actually small.
Non Cryogenic Systems consists of the following process categories:
PSA (Pressure Swing Adsorption)
The PSA system was the first non-cryogenic process used commercially in nitrogen or oxygen production. Based on absorption by modified carbon and zeolite molecular sieves, the PSA units produce nitrogen or oxygen by passing air through a vessel containing one or more adsorbent (matter that have the capacity or tendency to adsorb) materials.
This adsorbent permits the required product to pass through while carefully eliminating the undesired components.
VSA (Vacuum Swing Adsorption)
The VSA system is commonly used in oxygen generators for producing low purity oxygen, typically at 90 to 95% purity. The process system of VSA is almost similar to that used in PSA's, however, the filtrate materials operate over a different pressure range. According to experts statement, VSA's are more cost effective than PSA's when the production rate exceeds 20 to 30 tons per day.
VPSA (Vacuum Pressure Swing Adsorption) System
The VPSA process is the latest invention and can be best described as a modification of the PSA system. In the present market situation, it can be considered as the fastest developing non-cryogenic process for oxygen production.
Nitrogen Membrane Systems
If looking for a system that ensures low energy consumption, reliability and simple attendance of the plant, Membrane separation of nitrogen is the best available option. Popularly used at higher production rates, Membrane nitrogen generators employs tube bundles which are constructed of special polymers assembled in a way that us similar to a shell and tube heat exchanger.
There are several factors that are considered while selecting a suitable separation technology, like, required volume, purity required, supply continuity, low temperature, location of the customer etc. Though, PSA, VSA and VPSA systems undertake variations when it comes to adsorption of gases on specially-fabricated materials to make the required separations and different adsorbents are used for oxygen and nitrogen generation, but, the physical systems are similar.