First, basic knowledge

1. Gas knowledge

Nitrogen, as the most abundant gas in the air, is inexhaustible and used inexhaustible. It is colorless, odorless, transparent, subinert gas, and does not support life. High purity nitrogen is often used as a protective gas to block oxygen or air sites. The content of nitrogen (N2) in the air is 78.084% (the volume group of various gases in the air is divided into: N2:78.084%, O2:20.9476%, argon: 0.9364%, CO2: 0.0314%, other H2, CH4, N2O, O3, SO2, NO2, etc., but the content is very small), molecular weight is 28, boiling point: -195.8℃, condensation point: -210℃.

2. Stress knowledge

Pressure swing adsorption (PSA) nitrogen production technology is pressure adsorption, atmospheric pressure desorption, must use compressed air. The best adsorption pressure of carbon molecular sieve is 0.75~0.9MPa, and the gas in the whole nitrogen system is pressurized and has impact energy.


Second, PSA nitrogen production principle:


The pressure swing adsorption nitrogen making machine is an automatic equipment which is based on carbon molecular sieve as adsorbent, using the principle of pressure adsorption and decompression desorption to adsorb and release oxygen from the air, and then separate nitrogen. Carbon molecular sieve is a kind of coal as the main material, after grinding, oxidation, molding, carbonization and special pass treatment technology processing, the external and internal microporous columnar granular adsorbent, black, its pass distribution as shown in the following figure:


The pore dispersion characteristics of carbon molecular sieves enable them to complete the kinetic separation of O2 and N2. Such pore dispersion allows different gases to disperse at different rates into the micropores of the molecular sieve without crowding out any of the gases in the mixture (air). The separation effect of carbon molecular sieve on O2 and N2 is based on the small difference in the kinetic diameter of the two gases. The kinetic diameter of O2 molecule is small, so it has a faster dispersion rate in the micropores of carbon molecular sieve, while the kinetic diameter of N2 molecule is large, so the dispersion rate is slow. The dispersion of water and CO2 in compressed air is not much different from that of oxygen, while argon disperses more slowly. Finally, the mixture of N2 and Ar is enriched from the adsorption tower.


The adsorption characteristics of carbon molecular sieve for O2 and N2 can be directly displayed by equilibrium adsorption curve and dynamic adsorption curve:

It can be seen from the two adsorption curves that the addition of adsorption pressure can increase the adsorption capacity of O2 and N2 together, and the increase fluctuation of the adsorption capacity of O2 is larger. The pressure swing adsorption period is short, and the adsorption amount of O2 and N2 is far from reaching the equilibrium (maximum value), so the difference in the dispersion rate of O2 and N2 makes the adsorption amount of O2 greatly exceed the adsorption amount of N2 in a short time.

Pressure swing adsorption nitrogen production is the use of carbon molecular sieve selection adsorption characteristics, the selection of pressure adsorption, decompression desorption cycle, so that compressed air replacement into the adsorption tower (can also be completed by a single tower) to complete the air separation, and then continuous production of high purity commercial nitrogen.



3. Basic technical process of PSA nitrogen production:


PSA nitrogen machine basic technical flow diagram

After the air is compressed by the air compressor, it enters the air storage tank after dusting, oil removal and drying, and enters the left adsorption tower through the air intake valve and the left suction intake valve. The pressure of the tower rises, the oxygen molecules in the compressed air are adsorbed by carbon molecular sieve, and the unadsorbed nitrogen passes through the adsorption bed and enters the nitrogen storage tank through the left suction gas valve and the nitrogen gas production valve. The duration is tens of seconds. After the completion of the left suction process, the left adsorption tower and the right adsorption tower are connected through the upper and lower pressure balancing valves, so that the pressure of the two towers reaches equilibrium, this process is called pressure balancing, and the duration is 2 to 3 seconds. After the pressure equalization is completed, the compressed air enters the right adsorption tower through the air intake valve and the right suction intake valve, the oxygen molecules in the compressed air are adsorbed by carbon molecular sieve, and the enriched nitrogen enters the nitrogen storage tank through the right suction gas valve and the nitrogen gas production valve, which is called right suction and lasts for tens of seconds. The oxygen adsorbed by the carbon molecular sieve in the left adsorption tower is released back to the atmosphere through the left exhaust valve. This process is called desorption. In contrast, when the left column adsorbs, the right column also desorbs. In order to completely discharge the oxygen released from the decompression in the molecular sieve into the atmosphere, nitrogen is blown through a normally open reverse blow valve to purge the desorption adsorption tower and blow the oxygen in the tower out of the adsorption tower. This process is called blowback, and it goes hand in hand with desorption. After the right suction is completed, enter the pressure balancing process, and then switch to the left suction process, and continue the cycle.

The operation process of the nitrogen machine is controlled by the programmable controller three two-position five-way pilot solenoid valves, and then the solenoid valve separately controls the opening and closing of eight pneumatic pipeline valves. Three two-position five-way pilot solenoid valves separate from the control of left suction, pressure balancing, right suction conditions. The time flow of left suction, pressure balancing and right suction is now stored in the programmable controller. In the case of power failure, the pilot gas of the three two-position five-way pilot solenoid valves is connected to the closing silence of the pneumatic pipeline valve. When the process is in the left suction condition, the solenoid valve controlled by the left suction is powered on, and the pilot gas is connected to the opening port of the left suction intake valve, the left suction production valve and the right exhaust valve, so that the three valves are opened to complete the left suction process and the right adsorption tower desorption. When the process is in the condition of pressure balancing, the solenoid valve that controls the pressure balancing is energized, and other valves are closed; The pilot gas is connected to the opening port of the upper pressure balancing valve and the lower pressure balancing valve, so that the two valves are opened to complete the pressure balancing process. When the process is in the right suction condition, the solenoid valve controlling the right suction is powered on, and the pilot gas is connected to the right suction intake valve, the right suction production valve, and the left exhaust valve opening port, so that the three valves are opened to complete the right suction process and the left adsorption tower desorption. In each process, except for the valve that should be opened, the other valves should be closed.

Second, pressure swing adsorption oxygen production

Pressure swing adsorption oxygen production, with zeolite molecular sieve adsorbent as the center, according to the adsorbent at a higher pressure to select adsorption nitrogen, unadsorbed oxygen collection at the top of the adsorption tower, as a commercial gas output. When the adsorption column in the adsorption is close to the adsorption full, the material air stops the intake, turns to the other adsorption column that has completed the regeneration pressure, and then the pressure relief regeneration. The material air is introduced into the adsorption column by the pressure equalization. The two adsorption towers are thus replaced and repeated to complete the technical process of oxygen production.


Pressure adsorption and normal pressure desorption processes can be selected for industrial oxygen production by pressure swing adsorption. Ultra-large pressure vacuum desorption process; Through atmospheric pressure vacuum desorption process.