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PAS air separation oxygen

The main components in the air are nitrogen and oxygen. By selecting adsorbents with different adsorption selectivity for nitrogen and oxygen, an appropriate process is designed to separate oxygen from oxygen.
    Both nitrogen and oxygen have quadrupole moments, but the quadrupole moment of nitrogen (0.31) is much larger than that of oxygen (0.10), so the adsorption capacity of nitrogen on zeolite molecular sieves is stronger than that of oxygen (nitrogen has strong interaction with surface ions of molecular sieves. ). Therefore, when air passes through an adsorption bed equipped with a zeolite molecular sieve adsorbent under pressurized conditions, nitrogen is adsorbed on the molecular sieve. Oxygen is adsorbed less and is enriched in the gas phase and flows out of the adsorption bed, separating oxygen and nitrogen to obtain oxygen. . When the molecular sieve adsorbs nitrogen to near saturation, the air is stopped and the pressure in the adsorbent bed is reduced. Nitrogen adsorbed by the molecular sieve can be desorbed, and the molecular sieve is regenerated and reused. Two or more adsorbent beds alternately operate to produce oxygen continuously.
    The boiling points of argon and oxygen are close to each other, and it is difficult for them to separate. Together, they are enriched in the gas phase. Therefore, a pressure swing adsorption oxygen plant can only obtain oxygen at a concentration of 90% to 95% (limit concentration of oxygen is 95.6%, and the remainder is argon), which is comparable to that of a cryogenic air separation plant with a concentration of 99.5% or more. , also known as oxygen enrichment.
    Process description of pressure swing adsorption air separation oxygen plant
    It can be known from the above principles that the adsorption bed of the pressure swing adsorption air separation plant must contain at least two operating steps: adsorption and desorption. Therefore, when there is only one adsorbent bed, the product oxygen production is intermittent. In order to continuously obtain the product gas, generally two or more adsorption beds are provided in the oxygen production device, and some necessary auxiliary steps are additionally provided from the perspectives of energy saving and consumption reduction and stable operation.
    Each adsorption bed generally undergoes steps of adsorption, forward pressure release, evacuation or decompression regeneration, flushing replacement, and pressure equalization step-up, and the operation is repeated periodically. At the same time, each adsorbent bed is in different operation steps, and is switched under the control of the computer, so that several adsorbent beds work together, and they are staggered at the time step, so that the pressure swing adsorption apparatus can run smoothly and continuously. Product gas.
    According to different desorption methods, pressure swing adsorption oxygen is divided into two processes:
    1, PSA process: pressure adsorption (0.2 ~ 0.6MPa), atmospheric desorption. Small investment, simple equipment, but high energy consumption, suitable for small-scale oxygen production.
    2, VPSA process: Atmospheric or slightly above normal pressure (0 ~ 50KPa) adsorption, vacuum desorption. The equipment is relatively complex, but it has high efficiency and low energy consumption and is suitable for occasions with large scale of oxygen production.
    For the actual separation process, other trace components in the air must also be considered. The adsorption capacity of carbon dioxide and water on the usual adsorbent is generally much greater than that of nitrogen and oxygen. It can be adsorbed and removed by adding an appropriate adsorbent (or using the oxygen adsorbent itself) in the adsorbent bed. The number of adsorption towers required for the oxygen plant depends on the scale of oxygen production, adsorbent performance, and process design ideas. The operation stability of multiple towers is relatively better, but the equipment investment is higher. The current trend is to use high-efficiency oxygen absorbers, minimize the number of adsorption towers, and use short cycle times to increase the efficiency of the plant and save investment as much as possible.