Oxygen Generation Plant And Its Various Components
Oxygen Production Process
Pressure Swing Adsorption or PSA is the technique used to produce oxygen from the atmosphere. We use special grade Zeolite Molecular Sieves (ZMS) which is specifically imported for the adsorption process.
The air compressor compresses the atmospheric air and this air is cooled to ambient temperature by passing it through the air dryer which is of the refrigerated type. This compressed air is also passed through stages of numerous filters for the removal of oil particles, moisture, and dust from it. The filtered compressed air is then stored in the air receiver tank to remove condensate from it. An electronic timer based automatic moisture drain valve system is used in the process of condensation removal. The air receiver tank is also capable of taking care of pressure pulsations that arise due to fluctuations in the air demand of the PSA system.
The compressed air from the air receiver tank is sent to the Twin Tower PSA module. This module has a packing of a special grade of carbon molecular sieves along with activated alumina. There is a 1+1 minute time cycle between the individual towers of the Twin Tower PSA. While one tower is undertaking the adsorption process the other is undergoing the degenerating process of depressurization to the atmospheric level and the impurities within are vented out to the atmosphere.
There are no harmful impurities in the discharge other than air rich in oxygen, so it causes no harm to anyone. The operation of the Twin Towers is entirely automated and is controlled by a sequence programmer with the use of quick change over valves. Nitrogen of a certain desired purity is made to flow to a surge vessel to help balance out the fluctuations that are noticed in pressure and concentration.
Eventually, oxygen of 93% purity is obtained which is at a pressure of a designed value in kg/cm2g. This is stored in a storage tank having the required capacity.
This system is fully automated and does not need the intervention of any personnel for its operation. Once the system is switched on, it continues to generate oxygen at a constant flow rate and at a constant pressure.
A Note On The Oxygen Generation Plant’s Components
This is of a lubricated screw type, which is air-cooled, and is driven by an electric motor.
Refrigerated Type Air Dryer
The compressed air from the compressor is passed through this unit to dry it. The importance of the air dryer is to make dry and clean air available to all the components downstream of the system.
The compressed hot air output of an air compressor is cooled down to an ambient temperature by its passage through a 2-pass shell which is water-cooled, and which is composed of a heat exchanger made of tubes.
The air receiver stores the compressed and cooled air; the air receiver will act as a temporary storage for the air and it will be utilized for cyclic consumption in the system.
The impingement baffle of the pre-filter takes care of the first stage separation. The second stage is made of some numbers of polypropylene candles, having a pore size in the range of 10 microns.
Oil Filter – Stage 1
Beyond the Pre Filter is the Oil Filter – Stage 1. This is a coalescing type of filter which has a replaceable cartridge. The purpose of the filter is to effectively remove particles including coalesced liquid, oil, and water, to the size extent of 0.1 micron.
Oil Filter – Stage 2
This stage filters coalesced water and oil aerosols to the extent of 0.01 micron in size thus reducing the oil aerosol content in the filtrate to the extent of 0.003 mg/m3.
Activated Carbon Filter
To further remove any remnant traces of oil, an activated carbon bed is used. The carbon bed of this filter filters out oil aerosol traces in the air to the extent of 0.003 mg/m3.
Instrument Air Pot
The dry instrument air finds a temporary storage in the air pot. It is from here that the air passes to all the solenoid valves and the rest of the valve actuators to ensure its automatic operation as per the time cycle.
The filtered air coming off the filters of the previous stages is sent to the twin tower PSA unit. Activated alumina and Zeolite Molecular Sieves, or ZMS, make up the contents of the twin towers. While alumina adsorbs moisture, ZMS adsorbs nitrogen and CO2 present in the air.
Oxygen Surge Vessel
Oxygen from the PSA towers enters this vessel, and due to the high turbulence present within the vessel, the mixing that happens inside the vessel is almost perfect. Further, the oxygen is available for delivery at a constant pressure, and a constant average level of purity is maintained.
Oxygen Flow Meter
The surge vessel’s outlet has a metal tube Rotameter. This gives a reading of the flow of oxygen gas from the surge vessel to the storage tank.
Oxygen Gas Analyzer
In order to monitor the quality of the final oxygen gas, there’s a provision for an online trace with the use of an oxygen gas analyzer.
The exhaust line of the PSA tower has an installation of the silencer. When the process of depressurizing the tower is in progress, the gas desorbing into the atmosphere creates noise, and the silencer is used to minimize the level of this ensuing noise.
Oxygen Storage Tank
Provision is made to store a designed quantity of oxygen at 2.5 Kg/cm2g pressure. The oxygen storage tank is equipped with an inlet and outlet isolation valves, pressure gauge, high pressure switch and safety valves. Based on requirements, lines may be drawn from the storage tank for various applications including packing, emergency use, etc.
Back Pressure Controller
The back pressure controller is also known as the pressure holding valve, and it is installed at the outlet of the drying unit. The operation of the valve is such that when the inlet pressure signal increases and exceeds the spring setting, the outlet port of the valve will open, and the reverse will happen when the pressure goes down.
3-Way Vent Valve
This is a pneumatically operable 3-way valve. In the few minutes after starting the oxygen generator, the gas low in oxygen or low in purity is expelled to the atmosphere through this outlet. The valve will eventually get energized once the purity of the gas starts to improve; at this stage the vent close switch will be positioned in the valve close position. Also, in the eventuality of any abnormality arising in the plant, the valve will tend to open automatically thereby expelling the impure gas into the atmosphere.
The control panel is packaged along with the oxygen generation plant. The control panel is wired to all the important electric and electronic components of the oxygen generator plant. The wiring is handled with care and ferrules are used to identify the wiring in a very easy fashion.
Corrosion resistant paint is used to paint the outer body of all the equipment that’s part of the oxygen generation plant. The control panel is powder coated to give it an elegant feel. The paint job ensures longevity of the components of the plant.