PSA Nitrogen Gas Plants

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Typical Non-cryogenic product generators produces gaseous nitrogen at near-ambient temperature. Compared to cryogenic processes they can most economically meet the needs of many smaller-volume users. Pressure swing adsorption Nitrogen plants (PSA) can produce 99% to 99.9999% oxygen-free nitrogen product at rates that can go upto about even 40,000 scfh. Nitrogen plants with onsite gas supply around 70 lacs SCF/mo, 260 Nm3/h, or 190,000 Nm3/mo are very popular.

PSA Nitrogen plants utilizes mostly a carbon molecular sieve that is quite capable of separating nitrogen and oxygen molecules in the air. The difference in the adsorption speed is due to the respective size of the nitrogen (4. 2×3. 0Å) and oxygen (3. 8×2. 8Å) molecules as they are passed through the narrow, very-fine pore diameter of the activated carbon bed. As difference in adsorption speed is more at the beginning of adsorption, separation of nitrogen and oxygen takes place within the time span of 1-2 minutes of that early stage. The separation process works like this, as pressure is added during adsorption process, small oxygen molecules gets absorbed, and this absorbed oxygen molecules are desorbed if pressure is subsequently reduced. Now if these adsorption and desorption processes are continuously performed in two separate chambers equipped with carbon molecular sieves, nitrogen gas can continuously be separated out.

Features of PSA Nitrogen Plants:

• Energy Saving: Air consumption can be reduced in proportion to the flow volume of the product nitrogen gas, thus holding down the electricity consumption by the air compressor to save energy.
• Stabilization of Oxygen density: Sometimes variations in the volume flow of nitrogen leaves traces of residual oxygen. In built mechanism stabilizes the density (concentration) of the residual oxygen within the range of ±30% of settings. It is to be noted that unstable oxygen concentration can be a prime source of defective product in case of printed circuit board packaging industry.
• Designs are Compact and modular.
• Automatic Plants with automatic, unattended operation, that has advanced monitoring and control system.
• Lower maintenance costs.
• Minimal Start up time.
• Lesser requirement of fuel.

PSA Nitrogen Gas Plants - Process :
Of late onsite high pressure nitrogen gas plants are replacing, the standard cryogenic columns. This is particularly productive in operations that require a constant nitrogen with high purity flow. The separation process includes the following steps:
Compression: Atmospheric air is filtered, compressed and cooled to aroud 10°C in a chiller to reduce the moisture content.
Purification Process: Carbon dioxide and residual moisture are removed in activated alumina PSA system, regenerated by the heated excess waste gas that comes out of the cold-box.
Separation Process: This is carried out in a cold-box that is filled with perlite or other thermally insulating material.

After carrying out the above steps. The purified air is allowed to cool to the dew point in a heat exchanger. The heat exchanger is crossed in countercurrent by the streams of nitrogen and waste gas that is generated. Then it is fed afterwards on to the bottom of a separation column that is internally refluxed. The waste gas (oxygen-rich air stream), coming from the bottom is allowed to expand to a low pressure in a lamination valve. This provides (by Joule effect) the much required cooling energy needed for the reflux. Subsequently, the pure nitrogen leaves out from the top of the column at a mean purity of 99. 99%. It can easily reach for the electronic chip production ideally less than 50 ppb (part per billion) of oxygen impurity.