PSA Nitrogen Generation System Composition, Working Principle and Control Process

1. System Composition

The PSA nitrogen generation system mainly consists of an air compressor, air purification system, air storage tank, switching valves, adsorption towers, and nitrogen buffer tank.

The raw air is compressed by the air compressor and then passes through the purification system for dust removal, oil removal, and drying treatment. After purification, the compressed air enters the air storage tank and then flows into the left adsorption tower through the left inlet valve.

At this time, the pressure inside the adsorption tower increases. The nitrogen molecules in the compressed air pass through the carbon molecular sieve (CMS) adsorption bed, while oxygen molecules are preferentially adsorbed by the molecular sieve. The unadsorbed nitrogen gas passes through the adsorption bed and enters the nitrogen buffer tank through the outlet valve. This process is called adsorption, and it usually lasts for several tens of seconds.

After the adsorption process is completed, the left and right adsorption towers are connected through the equalization valve, allowing the pressure between the two towers to reach equilibrium. This process is called pressure equalization, which generally lasts about 3–5 seconds.

After pressure equalization, compressed air enters the right adsorption tower through the right inlet valve and repeats the above adsorption process.

At the same time, the oxygen molecules adsorbed by the carbon molecular sieve in the left adsorption tower are released into the atmosphere through the left exhaust valve during pressure reduction. This process is called desorption. Through desorption, the saturated molecular sieve is regenerated and prepared for the next adsorption cycle.

Similarly, when the right tower is performing adsorption, the left tower performs regeneration. After the right tower completes adsorption, the system enters another pressure equalization process and then switches back to left tower adsorption.

Through this alternating adsorption and regeneration process, the PSA nitrogen generator continuously produces nitrogen gas.

The entire process is automatically controlled by a PLC control system and automatic switching valves.

2. Working Principle of PSA Nitrogen Generator

The PSA nitrogen generator works based on the principle of Pressure Swing Adsorption (PSA).

It uses high-quality carbon molecular sieve (CMS) as the adsorbent to separate nitrogen from compressed air under a certain pressure.

After purification and drying, compressed air enters the adsorption towers, where it undergoes pressurized adsorption and pressure-reduction desorption.

Due to the different diffusion rates of oxygen and nitrogen molecules in the micropores of carbon molecular sieve, oxygen molecules diffuse much faster than nitrogen molecules. Therefore, oxygen is preferentially adsorbed by the carbon molecular sieve, while nitrogen molecules remain in the gas phase and become enriched, forming high-purity nitrogen gas.

After the adsorption process, the adsorption tower pressure is reduced to atmospheric pressure. The adsorbed oxygen and other impurities are released from the molecular sieve, completing the regeneration process.

Normally, the system is equipped with two adsorption towers, Tower A and Tower B.

• One tower performs nitrogen production through adsorption.
• The other tower performs desorption and regeneration.

Through the automatic control of pneumatic valves, the two adsorption towers operate alternately, ensuring continuous production of high-quality nitrogen gas.

3. PSA Nitrogen Generator Control Process

The process flow of the PSA nitrogen generation system mainly includes an air compressor, air purification equipment, adsorption towers, PLC control system, automatic valves, and nitrogen storage tank.

The air compressor provides sufficient air flow and maintains a stable inlet pressure, generally around 0.75–0.8 MPa.

After passing through the refrigeration dryer and purification system, moisture, oil, and solid particles are removed from the compressed air.

To ensure continuous and stable nitrogen output, the system uses two adsorption towers (Tower A and Tower B) working alternately.

The purified compressed air enters Tower A through electrically controlled pneumatic valves Y1 and Y2 from the bottom of the adsorption tower.

As the air passes through the carbon molecular sieve bed, oxygen molecules in the air are adsorbed by the CMS micropores, while nitrogen molecules are concentrated in the gas phase.

The nitrogen product gas flows out from the top of the adsorption tower and enters the nitrogen storage tank through valves Y6 and Y8.

This process is the nitrogen production process of Tower A.

At the same time, oxygen molecules adsorbed in Tower B are released through valve Y5, reducing the pressure of Tower B to atmospheric pressure. This process is called desorption regeneration.

When the adsorption capacity of the carbon molecular sieve in Tower A reaches saturation, Tower A stops adsorption.

At this moment:

• Y1, Y4, Y5, and Y8 valves are closed.
• Y2, Y3, Y6, and Y7 valves are opened.

The two towers perform pressure equalization.

After pressure equalization, the system switches to:

• Tower B adsorption
• Tower A regeneration

Compressed air enters the bottom of Tower B through valves Y1 and Y3.

The carbon molecular sieve inside Tower B adsorbs oxygen molecules, while nitrogen gas flows through valves Y7 and Y8 into the nitrogen storage tank.

This completes the nitrogen production process of Tower B.

By continuously switching between adsorption and regeneration of Tower A and Tower B, the system continuously supplies nitrogen gas.

4. PLC Automatic Control Process

The opening and closing sequence of valves Y1–Y8, switching times, and operating cycles are fully controlled by the PLC system.

Under normal operation, the automatic cycle process is as follows:

1. Press the start button.
2. Refrigeration dryer starts.
3. After a preset delay time, the air compressor starts.
4. After another delay time, the system enters Tower A adsorption.
5. After the adsorption period, pressure equalization between Tower A and Tower B begins.
6. The system switches to Tower B adsorption.
7. Tower B completes adsorption and pressure equalization is performed.
8. The system switches back to Tower A adsorption.

This cycle repeats automatically to continuously produce nitrogen.

When the stop button is pressed, the entire system stops operation.

5. Valve Control Status

During different working stages of the PSA nitrogen generator, the operating status of valves Y1–Y8 is controlled according to the following processes:

Tower A Adsorption

The corresponding valves open to allow compressed air to enter Tower A and nitrogen product gas to flow into the nitrogen storage tank.

Pressure Equalization A → B

The pressure between Tower A and Tower B is balanced through the equalization valves.

Tower B Adsorption

Tower B produces nitrogen while Tower A performs regeneration.

Pressure Equalization B → A

The pressure between the two towers is balanced before switching back to Tower A adsorption.

Note:

• "+" indicates that the valve is open.
• During pressure equalization, related valves open after a preset delay time.
• Delay times can be adjusted within the range of 0–999 seconds according to operating requirements.

6. Control Requirements

The PSA nitrogen generator control system provides two operation modes:

Manual Operation Mode

In manual mode, operators can:

• Check the operating status of valves Y1–Y8.
• Independently start and stop the air compressor and refrigeration dryer.
• Display the opening status of valves during:
  • Tower A adsorption
  • Pressure equalization A=B
  • Tower B adsorption
  • Pressure equalization B=A
• Display all operating conditions through indicator lights.

Automatic Operation Mode

In automatic mode, the system operates according to the preset PSA process sequence.

The simulated process flow diagram displays the current operating status in real time.

All delay times during automatic operation can be adjusted according to production requirements, and the system can display and query the current delay settings in real time.

PSA nitrogen generator technology uses automatic PLC control, dual-tower adsorption regeneration cycles, and carbon molecular sieve separation technology to achieve continuous production of high-purity nitrogen with stable performance and reliable operation.