PSA Nitrogen Gas Plant

PSA NITROGEN GAS GENERATOR

• Fully Automatic Operation requiring no special attention
• Generates Nitrogen as and when required
• Easy to install and maintain
• The purity of Nitrogen can be achieved upto 99.9999%
• Generates Nitrogen at an almost 1/10th cost of cylinder nitrogen
• Proven Technology
• More than 1000 Plants based on PSA Technology operating successfully in India.

The compressed air is passed through a Twin Tower PSA module interconnected with automatic changeover valves. At the bottom of PSA towers, Activated Alumina is provided which has a tendency of adsorbing moisture from compressed air. After passing through this bed of Activated Alumina air gets dried. Supply of dry compressed air from this layer of desiccant (activated alumina) will be continuous without any interruption. Dried compressed air will now come in contact with a bed of carbon molecular sieves (CMS). Carbon Molecular Sieves are a special grade of adsorbent which has the property of preferential adsorption of oxygen molecules. At a time one tower remains under nitrogen production cycle, whereas the other tower undergoes regeneration which is achieved through depressurization of the tower to atmospheric pressure. The two towers of PSA modules are inter-connected with automatic changeover valves through pneumatic signal given by solenoid valve which in turn get the electrical signal from the timer provided in the control panel. The changeover time cycle will be 1 + 1 minute. The outgoing nitrogen gas is sent to a surge vessel where the minimum nitrogen pressure will be maintained with the help of Backpressure Regulator. The product nitrogen will now be sent to the consumer point through a pressure reducing valves at the required pressure.

Downstream equipments for High Purity

Oxygen content in product nitrogen can be brought down to 1-3 PPM with the use of DEOXO Unit.

Palladium De-Oxo Unit:

In this unit, the residual oxygen in Nitrogen From PSA Unit is mixed with Hydrogen and the mixture is passed over Palladium Catalyst where Hydrogen reacts with Oxygen and makes water. The reaction is exothermic and the outlet gas is cooled down in After-Cooler where moisture vapour condenses and it is separated and drained out in moisture separator.

This nitrogen still contains moisture in vapour form which is removed in Gas Dryer and the outlet Nitrogen is at (-) 60 Deg C Dew Point (Atm).

The final product Nitrogen composition is

Oxygen                          3 ppm

Hydrogen                       0.2% (Adjustable)

Dew Point                      (-) 60 Deg C

Nitrogen                         Balance

Copper De-Oxo Unit:

Alternately where hydrogen in product nitrogen is not acceptable, Copper De-Oxo units are used. In this system, one tower remains in the Oxygen removal cycle, whereas, the other tower undergoes regeneration of the catalyst. Oxygen removal is obtained by reaction of Oxygen present in Nitrogen with Copper Catalyst as per following equation.

2Cu  +  O2  =   2CuO

This reaction takes place at around 1800C.  For this purpose, a tower is provided with an embedded heater. Raw-nitrogen passes through the heater before it comes in contact with the copper catalyst. The out-going nitrogen will be totally free from oxygen. As indicated above, the spent catalyst i.e. CuO is converted back to copper by injecting Hydrogen – Nitrogen mixture in the tower under regeneration, so that copper catalyst gets regenerated as per the following reaction:

CuO   +   H2    = Cu  +   H2O

This reaction also takes place at a temperature of around 1800C. which is achieved by the heater embedded in the tower. Nitrogen – Hydrogen mixture, which is used for reaction of spent catalyst is vented to atmosphere. Each tower of copper catalyst remains in Oxygen removal cycle for a period of 8 hours and towers then get changed over automatically which the help of sequence timer provided in the control panel. Pure nitrogen gas coming out of Copper Catalyst De-oxo Reactor will be at 2000C. and its temperature will be brought down to ambient level through an after-cooler which is a shell and tube type heat exchanger. The pure and dry nitrogen gas at ambient temperature.

Following will be the product gas composition at the outlet of Copper Catalyst system:

i)  Oxygen                                :  1 ppm (Max.)

ii) Hydrogen                            :  Nil     

iii)   Nitrogen                           :  Balance

iv) Dew Point                          :  (-)600C.

v)  Gas pressure                     :  5.0 Kg/cm 2g

vi) Gas temperature              :   Ambient

Salient Features:

• The PSA type gas generator is fully automatic and the gas of proper specification is made available within short period after start-up.
• This type of gas generator does not require any fuel.
• Since the feedstock for this gas generator is air, there is no problem like soot formation or
• presence of Co2 etc. – the common problem in fuel combustion based gas generator.
• The gas generator is very compact requiring very small floor area.
• Depending on the pressure in the nitrogen storage tank, the gas generator keeps running with
• ON/OFF operation like compressed air installation.  Therefore, the gas generator would work only to the extent of meeting your gas requirement as and when needed.