Pressure swing adsorption technology is an advanced gas separation technology.

The main principle of nitrogen extraction is: due to the different diffusion rates of oxygen and nitrogen gas molecules in the air on the surface of the carbon molecular sieve, the smaller diameter of the oxygen molecule diffusion is faster, more into the molecular sieve solid phase (micropores), the larger diameter of the nitrogen molecule diffusion is slower, into the molecular sieve solid phase (micropores) is also small, so that in the gas phase to obtain nitrogen enrichment components; Under the adsorption equilibrium condition, the higher the air pressure is, the greater the adsorption capacity of carbon molecular sieve is. On the contrary, the lower the pressure, the smaller the adsorption capacity.

The PSA air separation nitrogen production unit put into industrial operation is generally composed of two or more adsorbers, which can achieve continuous nitrogen production and improve the recovery rate of nitrogen by optimizing and alternating cycles.

After purification and drying of compressed air, under the action of pressure swing adsorption, the finished nitrogen is formed. Generally, two adsorption towers are set up in the system, one tower is used to adsorb nitrogen and the other tower to desorption and regeneration. The opening and closing of the pneumatic valve are controlled by PLC program to make the two towers cycle alternately to achieve the purpose of continuous production of high quality nitrogen.

1. Basic knowledge



1. Gas knowledge
Nitrogen, as the most abundant gas in the air, is inexhaustible and used inexhaustible. It is colorless, odorless, transparent, a sub-inert gas, and does not support life. High purity nitrogen is often used as a protective gas in places where oxygen or air is isolated. 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:, condensing point:.



2. Pressure knowledge
Pressure swing adsorption (PSA) nitrogen production process 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 production system is pressurized and has impact energy.

Two, PSA nitrogen production principle:

The pressure swing adsorption nitrogen making machine is an automatic equipment which is based on carbon molecular sieve as adsorbent, and uses the principle of pressure adsorption and pressure drop desorption to adsorb and release oxygen from the air, so as to separate nitrogen. Carbon molecular sieve is a kind of coal as the main raw material, after grinding, oxidation, molding, carbonization and special pass processing process, the surface and inside are full of micropores columnar granular adsorbent, black, its pass distribution as shown in the figure below:


The pore size distribution of carbon molecular sieves enables the kinetic separation of O2 and N2. This pore size distribution allows different gases to diffuse into the pores of the molecular sieve at different rates, without repelling any of the gases in the mixture (air). The separation effect of carbon molecular sieve on O2 and N2 is based on the slight difference between the kinetic diameters of the two gases. The kinetic diameter of O2 molecule is small, so it has a faster diffusion rate in the micropores of carbon molecular sieve, while the kinetic diameter of N2 molecule is large, so the diffusion rate is slow. The diffusion of water and CO2 in compressed air is not much different from that of oxygen, while argon diffuses more slowly. Finally, the mixture of N2 and Ar is enriched from the adsorption column.

Three, PSA nitrogen production basic process:

After the air is compressed by the air compressor, after dust removal, oil removal and drying, it enters the air storage tank, 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 valve and the nitrogen gas production valve. This process is called left suction. The duration is tens of seconds. After the end 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 is balanced, this process is called pressure balancing, and the duration is 2 to 3 seconds. After the end of pressure equalization, 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, this process is called right suction, and the duration is tens of seconds. At the same time, the oxygen adsorbed by the carbon molecular sieve in the left adsorption tower is released back to the atmosphere through the pressure reduction of the left exhaust valve, which is called desorption. On the contrary, when the left column adsorbs, the right column also desorbs. In order to completely discharge the oxygen released from the pressure reduction in the molecular sieve to 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 end of the right suction, enter the pressure balancing process, and then switch to the left suction process, and continue the cycle.

The work flow of the nitrogen machine is completed by the programmable controller controlling three two-position five-way pilot solenoid valves, and then the solenoid valves respectively control the opening and closing of eight pneumatic pipeline valves. Three two-position five-way pilot solenoid valves respectively control the state of left suction, pressure balancing and right suction. The time flow of left suction, pressure balancing and right suction has been stored in the programmable controller. In the state of power failure, the pilot gas of three two-position five-way pilot solenoid valves is connected to the closing port of the pneumatic pipeline valve. When the process is in the left suction state, the solenoid valve controlling 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 these three valves are opened to complete the left suction process and the right adsorption tower desorption. When the process is in the state of pressure balancing, the solenoid valve that controls 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 to open the two valves and complete the pressure balancing process. When the process is in the right suction state, the solenoid valve that controls the right suction is powered on, and the pilot gas is connected to the right suction intake valve, right suction production valve and left exhaust valve opening port, so that these three valves are opened to complete the right suction process and the left adsorption tower desorption. In each process, all valves except those that should be opened should be closed.