Normally the two-bed process of large-scale pressure adsorption and vacuum desorption are adopted in VPSA oxygen generation. After removing mechanical impurities through a filter, the raw air is cooled to -30 ~ -40℃ in the air cooler after being pressurized by roots blower, and enters the lower part of the absorber. To reduce noise, roots blower inlet and outlet are equipped with silencers.
There are two kinds of adsorbents inside the adsorption towers: (1) 13X molecular sieve at the periphery, used to absorb moisture, carbon dioxide, hydrocarbons and other impurities in the air; (2) LiX molecular sieve is installed inside for the separation of oxygen and nitrogen in the air.
When air enters the adsorber tower, after 13X molecular sieve bed, moisture in the air, carbon dioxide and other impurities are adsorbed by the molecular sieve. When clean air enters the LiX molecular sieve bed, nitrogen in the air is absorbed. A large amount of unadsorbed oxygen and a small amount of nitrogen flow from the outlet end of the adsorber with the airflow, that is, product gas.
When the oxygen purity of the product gas begins to decline, it indicates that the nitrogen adsorption capacity of the LiX molecular sieve reaches saturation. At this point, stop supplying air to the adsorbent. Then the adsorber depressurizes, and the airflow flows out from the lower part of the adsorber. As the bed pressure decreases, nitrogen adsorbed by LiX molecular sieve is desorbed, and the desorption is extracted by roots vacuum pump and discharged into the atmosphere. When the adsorber reaches a certain vacuum degree, molecular sieve recovery adsorption capacity.
In order to obtain oxygen products continuously, there must be at least one additional adsorber; adsorption and desorption are carried out respectively and alternately. The switching of modes of adsorbers is realized by pneumatic switching valve, controlled by PLC according to the set time program.
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