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Cryogenic Air Separation
Air contains 21% Oxygen, 78% Nitrogen, 0.9% Argon and 0.1% other trace gases. At present, medical oxygen mainly uses cryogenic air separation method to producing oxygen. The main components in the air are oxygen and nitrogen. Based on the different boiling points of oxygen and nitrogen, the preparation of oxygen from air is called air separation. Firstly, the air is pre-cooled and purified (remove a small amount of water, carbon dioxide, acetylene, hydrocarbons and other gases and impurities such as dust), and then compressed and cooled to make it into liquid air. Since the boiling points of oxygen and nitrogen are different, the liquid air is evaporated and condensed many times in the distillation tower to obtain pure oxygen (up to 99.6% purity) and pure nitrogen (up to 99.9% purity). The oxygen produced by the air separation device is compressed by the compressor and finally put the compressed oxygen into a high-pressure cylinder for storage.
VPSA and PSA Oxygen Generation
VPSA (Vacuum Pressure Swing Adsorption) and PSA (Pressure Swing Adsorption) oxygen generation use zeolite molecular sieve as the adsorbent and the principle of pressure adsorption and decompression desorption to adsorb and release oxygen from the air, thereby separating oxygen.
Zeolite molecular sieve is a kind of spherical granular adsorbent with micropores on the surface and inside. Its pore type characteristics enable it to realize the kinetic separation of Oxygen and Nitrogen. The separation effect of zeolite molecular sieve on Oxygen and Nitrogen is based on the small difference in the dynamic diameter of the two gases. Nitrogen molecules have a faster diffusion rate in the micropores of zeolite molecular sieve, and Oxygen molecules have a slower diffusion rate. When compressed air passes through an adsorption bed equipped with zeolite molecular sieve, nitrogen is adsorbed by the molecular sieve. Because oxygen is less adsorbed, oxygen is enriched in the gas phase and flows out of the adsorption bed to separate oxygen and nitrogen to obtain oxygen. When the molecular sieve adsorbs nitrogen to saturation, air flow is stopped and the pressure of the adsorption bed is reduced. The nitrogen adsorbed by the molecular sieve can be desorbed, and the molecular sieve is regenerated and can be reused. Two or more adsorption beds can be switched in turn to continuously producing oxygen. Molecular sieve adsorbs oxygen and argon at almost the same rate, so it is difficult to separate. Pressure swing adsorption can only obtain oxygen with a concentration of 90-95%, and the maximum concentration of oxygen is 95.6%.
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