Principle of nitrogen production by carbon molecular sieve air separation

The carbon molecular sieve produced by our company is the adsorbent on the PSA nitrogen production device, which uses the principle of pressure swing adsorption (PSA) to separate nitrogen from the air. The separation effect of carbon molecular sieve on oxygen and nitrogen in air is mainly based on the different diffusion rates of these two gases on the surface of carbon molecular sieve. The gas molecules with smaller diameter (O2) have a faster diffusion rate, and more enter the micropores of carbon molecular sieve. The gas molecules with larger diameter (N2) have a slow diffusion rate and less entry into the micropores of carbon molecular sieve, so nitrogen can be enriched in the gas phase. Therefore, taking advantage of the difference in the adsorption capacity of carbon molecular sieve for oxygen and nitrogen at a certain time, the full-automatic control system applies the cyclic process of pressurized adsorption and atmospheric pressure analysis according to specific programmable procedures to complete the separation of nitrogen and oxygen and obtain the required high-purity nitrogen.

Conditions for controlling nitrogen production from carbon molecular sieves

1. Air compression purification process

It is very necessary for pure raw air to enter the carbon molecular sieve adsorption tower, because particles and organic gas entering the adsorption tower will block the micropores of the carbon molecular sieve and gradually reduce the separation performance of the carbon molecular sieve. The methods of purifying raw air are as follows: 1. Keep the air inlet of the air compressor away from places with oil mist and organic gas; 2. Through the cold dryer and adsorbent purification system, the treated raw air enters the carbon molecular sieve adsorption tower.

2. Concentration and gas production of product nitrogen

When carbon molecular sieve is used to produce nitrogen, its N2 concentration and gas production can be adjusted arbitrarily according to the needs of users. When the gas production time and operating pressure are determined, reduce the gas production, and the N2 concentration will increase. On the contrary, the N2 concentration will decrease. Users can adjust according to actual needs.

3. Equalizing time

In the nitrogen production process of carbon molecular sieve, when the adsorption of one adsorption tower is completed, the pressurized gas in the adsorption tower can be injected into the other regenerated adsorption tower from the upper and lower directions, and the gas pressure of the two towers is the same. This process is called the pressure equalization of the adsorption tower. Selecting an appropriate pressure equalization time can recover energy, but also slow down the impact of the molecular sieve in the adsorption tower, so as to prolong the service life of carbon molecular sieve. The switching speed of the reference valve is generally 1-3 seconds.

4. Gas production time

According to the different absorption and diffusion rates of carbon molecular sieve for oxygen and nitrogen, its adsorbed O2 will reach equilibrium in a short time. At this time, the adsorption amount of N2 is very small, and the shorter gas production time can effectively improve the gas production rate of carbon molecular sieve, but it also increases the action frequency of the valve, so the performance of the valve is also very important. Generally, the adsorption time is 30-120 seconds. Short gas production time is recommended for small-scale high-purity nitrogen generator, and long gas production time is recommended for large-scale low concentration nitrogen generator.

5. Operating pressure

Carbon molecular sieve has both dynamic effect and equilibrium adsorption effect. The partial pressure of adsorbate is high, and the adsorption capacity is also high. Therefore, the adsorption of pressurizer is beneficial, but the adsorption pressure is too high, and the modeling requirements of air compressor are also increased. In addition, the adsorption pressure requirements of atmospheric regeneration and vacuum regeneration are also different. Considering various factors, it is suggested that the adsorption pressure of atmospheric regeneration process should be 5-8kg/cm2; The adsorption pressure of vacuum regeneration process should be 3-5kg/cm2.

6. Service temperature

As an adsorbent, choosing a lower adsorption temperature is conducive to the performance of carbon molecular sieve. If conditions permit, it is beneficial to reduce the adsorption temperature.