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Carbon molecular sieve is the adsorbent on the PSA nitrogen production equipment, which uses the principle of pressure swing adsorption to separate nitrogen from the air. The separation effect of carbon molecular sieve on oxygen and nitrogen in the air is mainly based on the different diffusion rates of these two gases on the surface of carbon molecular sieve. Gas molecules with a smaller diameter diffuse faster, and more enter the micropores of the carbon molecular sieve. Gas molecules with a larger diameter have a slower diffusion rate and fewer enter the micropores of the carbon molecular sieve, so that nitrogen-rich components can be obtained in the gas phase. Therefore, using the characteristic of carbon molecular sieve that there is difference of the amount of oxygen and nitrogen that are absorbed in a certain period of time, the full-automatic control system applies pressure adsorption according to a specific programmable sequence, and after the cyclic process of atmospheric de-absorption, the separation of nitrogen and oxygen can be completed so as to obtain the required high-purity nitrogen.
(1) Air compression and purification process
It is very necessary for the pure feed air to enter the adsorption tower of carbon molecular sieve, because the 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 the raw material air are:
a. Keep the air compressor's air inlet away from places with oil mist and organic gas;
b. Pass through a refrigeration dryer, adsorbent purification system, etc., and finally the processed feed air enters the adsorption tower of carbon molecular sieve.
(2) Concentration of product nitrogen and gas production rate
When the carbon molecular sieve is used to produce nitrogen, the N2 concentration and gas production rate can be adjusted according to the needs of users. When the gas production time and operating pressure are determined, the gas production rate is reduced, and the N2 concentration will increase. On the contrary, the N2 concentration will decrease. Users can adjust according to actual needs.
(3) Pressure equalization time
In the process of using carbon molecular sieve for nitrogen production, when the adsorption of one adsorption tower is completed, the pressurized gas in the adsorption tower can be injected into another regenerated adsorption tower from the upper and lower directions, and the gas pressure of the two towers is the same. The process is called pressure equalization of the adsorption tower. Choosing an appropriate pressure equalization time can recover energy and mitigate the impact on the molecular sieve in the adsorption tower, so as to extend the service life of the carbon molecular sieve. With reference to the switching speed of the valve, the pressure equalization time is generally 1 to 3 seconds.
(4) Gas production time
According to the different diffusion rates of carbon molecular sieve to oxygen and nitrogen, its adsorption of O2 reaches equilibrium in a short time. At this time, the adsorption amount of N2 is small, and the short gas production time can increase the gas production rate of carbon molecular sieve. But at the same time, the frequency of valve action is increased, so the performance of the valve is also very important. Generally, the adsorption time is 30 to 120 seconds. It is recommended to adopt short gas production time for small high-purity nitrogen generators, and long gas production time for large-scale low-concentration nitrogen generators.
(5) Operating pressure
Carbon molecular sieve has a balanced adsorption effect as well as a dynamic effect. The partial pressure of the adsorbate is high and the adsorption capacity is also high. Therefore, the pressurizer adsorption is advantageous, but if the adsorption pressure is too high, there are also higher requirements on the shape of the air compressor. In addition, the adsorption pressure requirements for the two processes of atmospheric regeneration and vacuum regeneration are also different. Based on various factors, it is recommended that the adsorption pressure of the atmospheric regeneration process be 5-8kg/cm2; the adsorption pressure of the vacuum regeneration process should be 3-5Kg/cm2.
(6) Operating temperature
Choosing a lower adsorption temperature is conducive to the performance of carbon molecular sieve because it is an adsorbent. If condition permits, it is advantageous to reduce the adsorption temperature in the nitrogen generator technology.
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