One of the most popular application of Pressure Swing Adsorption or P S A Technology is in the operation of Nitrogen Generators. This Process is based on the selective adsorption phenomena of gas molecules. In this case it is carbon based Molecular Sieve (C. M. S.) The process works like this, in Pressure Swing Adsorption system as soon as compressed air is entered through an adsorption tower filled with Carbon molecular sieve the molecules of gases like oxygen, moisture & other undesired gases are adsorbed on surface of the adsorbent. While Nitrogen that is not adsorbed passes out of adsorption tower.
  It is then collected in a surge vessel. For continuous flow of nitrogen two Adsorption towers are installed. They are interconnected with Auto change over valves. These Auto change over valves are controlled by PLC in the control panel. As the saturation of one tower with oxygen gets completed, in built mechanism makes the process automatically switch to another tower and thus the nitrogen production remains continuous. Nitrogen has a wide range of industrial application primarily to reduce or eliminate altogether oxidation in raw material and food processing. Additional usages can include medical, tyre-filling, swimming pool, sanitation, photo development, etc. In effect it means where oxidation is a problem then a Nitrogen system is the solution.

Key features of PSA Nitrogen Generator:

There are an enormous number of variety available depending on the user's requirements of purity, space constraints, economics etc. A brief of the features that a PSA Nitrogen Gas Generator incorporates is given below:

Purity: 99.5% purity nitrogen can be produced at rates as low as 200 Standard Cubic Feet per hour (5 Nm3/h) or as high as around 1000 Nm3/hr (38,000 Standard cubic feet per hour). Also Nitrogen at purity of 99.999% can be effectively produced by a two-step process. That involves a 99.5% purity PSA combined with a "de-oxo" unit that reduces residual oxygen to the required level.

Delivery pressures: Typically delivery pressures can come in the range of 6 to 7 Bar(g) (87 to 102 pounds per square inch of pressure. More higher pressures are also obtained with the aid of booster compressors like pressures upto to 240 barg (3500 psig).

Bed type: Mono-Bed nitrogen gas generator the flowrate ranges from 200 SCFH - 1000 SCFH @ 99.5% nitrogen purity, while the Dual bed comes with flowrates of 1200 SCFH to 6000 SCFH @ 99.5% nitrogen purity.

Wide range of dew points: Can range from: - 45^oC to 600^oC

Nitrogen generators are available with a multitude of different features and qualities. Some nitrogen generators available on the market, for example, require little or no maintenance after installation. Others include safety shut-off buttons and alarms. To eliminate the possibility of damage, the filter in nitrogen generators should be regularly changed. For proper maintenance, these air filters should be changed every year, and the oxygen sensor should be changed every two years.

The latest technology in nitrogen generators is the use of cryogenic air distillation, which is used to PSA generate nitrogen. With this method, the air is compressed and then purified within the nitrogen generator. Later, it is cooled with a special cooling unit.

Since the air runs through nitrogen generators, it runs through several filters. This process causes the air to become purified and to cool down even more. The oxygen and nitrogen are then separated within the oxygen liquid. The oxygen stays at the bottom, while the nitrogen remains on top.

The entire process allows nitrogen generators to replenish themselves automatically with no manual input. This is achieved by way of the low temperature within the nitrogen generators, which mixes a small amount of liquid nitrogen into the nitrogen that is already produced.

Nitrogen generators are easily installed and calibrated. Before purchasing a nitrogen generator, one must first check the air compressor to see if it provides the required volume of clean compressed air in order for the generator to work successfully.

A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecules small enough to pass through the pores are adsorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level. For instance, a water molecule may not be small enough to pass through while the smaller molecules in the gas pass through. Because of this, they often function as a desiccant. A molecular sieve can adsorb water up to 22% of its own weight.

Often they consist of aluminosilicate minerals, clays, porous glasses, microporous charcoals, zeolites, active carbons, or synthetic compounds that have open structures through which small molecules, such as nitrogen and water can diffuse.

Carbon Molecular Sieve are often utilized in the petroleum industry, especially for the purification of gas streams and in the chemistry laboratory for separating compounds and drying reaction starting materials. The mercury content of natural gas is extremely harmful to the aluminium piping and other parts of the liquefaction apparatus - silica gel is used in this case.

Methods for regeneration of molecular sieves include pressure change (as in oxygen concentrators), heating and purging with a carrier gas (as when used in ethanol dehydration), or heating under high vacuum.