PSA
nitrogen gas plants are nitrogen generating system by using the PSA
(pressure swing adsorption) approach. PSA nitrogen plants can produce 99% to
99.9999% oxygen-free nitrogen product from atmospheric air at rates that can
go up to about even 40,000 scfh (1000 Nm3/h). Most PSA plants are very
simple to operate and are very economical for producing nitrogen in small
scale and hence such plants are very popular. Infact compared to the
cryogenic process, for sites which use only nitrogen where purities in the
range of 95 to 99.5% are acceptable, the most cost effective process choice
is nitrogen PSA plant.
The PSA Process of Nitrogen Production
The PSA process involves the adsorption technique to produce nitrogen. A
carbon molecular sieve (CMS) is used to separate nitrogen and oxygen
molecules in the air. There is difference in the adsorption speed because of
the difference in sizes of nitrogen and oxygen molecules. The molecules
passes through the molecular sieve and separation of nitrogen and oxygen
takes place within 1-2 minutes. As pressure is added during adsorption
process, small oxygen molecules gets absorbed. If pressure is subsequently
reduced, the absorbed oxygen molecules are desorbed. Now when the adsorption
and desorption processes are performed one after the other in two separate
chambers fitted with carbon molecular sieves, pure nitrogen gas can
continuously be separated out. While oxygen is retained by adsorbent,
nitrogen passes through freely and the PSA technique allows to recover
nitrogen with purity around 99.95%.
Manufacturing
Process: Steps involved
- Step 1: First the ambient or inlet air is filtered. Then the
air is compressed at the required pressure. This compressed air is
cooled and then dried.
- Step 2: Adsorption and desorption: The compressed air is
passed through CMS. Here the oxygen is adsorbed and nitrogen with
adjustable purity and a residual oxygen of 500 ppm remaining in the gas
stream passes out. The adsorbed oxygen is desorbed using simple pressure
release system and the waste gas stream is vented out to the atmosphere.
- Step 3: Nitrogen buffer: The final nitrogen gas is used
during the PSA process as purge gas. During the same time the buffer
equalizes the product flow and purity.
- Step 4: Back up system (optional): Some manufacturers in PSA
nitrogen plants also provide with a back up system to ensure constant
nitrogen supply during maintenance work.
Advantages of PSA Nitrogen Plants
The key advantages delivered by PSA nitrogen plants are as follows:
- Low energy consumption
- Low nitrogen net cost
- High reliability
- Simple in control and operation
- Compact designs
- Minimal start up time
- Lesser requirement of fuel
- Inspite of consuming the same amount of compressed air at 5-7% oxygen
content by PSA plants, it is to be noted that at 0-1% Oxygen, the PSA
nitrogen plants produces 6 times more Nitrogen pr m3 feed air.
Applications of PSA Nitrogen Plants
PSA
nitrogen plants are suited for a broad range of applications, especially in
those cases where fairly high nitrogen purity is required. The primary areas
of application are as follows:
- Petrochemical
- Chemical · Petroleum industries
- Food and pharmaceutical industries
- Metallurgical Industry
- Synthetic & Fiber Industry
- Food Packaging Industry
- Optical Fiber Industry
- Electronics Industry
Buyer's Guide
Specifications to consider for purchasing PSA nitrogen plants are:
- Product capacity
- Flow rate
- N2 purity
- Pressure standard
- Dew point
PSA
Nitrogen Gas Plant
