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Comparison of VPSA Oxygen Plant and PSA Oxygen Generator

2023/02/10

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VPSA and PSA oxygen generation equipment are primarily adopted for industrial oxygen production.


Pressure Swing Absorption (PSA) oxygen generation technology is a new gas separation process that uses molecular sieves as the adsorbent to separate gas mixtures based on the difference in adsorption properties of molecular sieves for various gas molecules. With air as the raw material, it uses a high-performance, highly selective solid adsorbent to separate the N2 and O2 in the air. Zeolite molecular sieves preferentially adsorb N2, so that oxygen can be enriched in the gas phase. After a defined time, the N2 adsorption by the molecular sieve reaches equilibrium loading. Due to the fact that the amount of adsorbed gas varies at different pressures, depressurization is performed to make the adsorbed N2 leave the zeolite molecular sieve, a process called regeneration. The PSA method usually uses 2 towers in parallel, which alternately perform adsorption under pressurization and regeneration under depressurization to continuously generate oxygen.


(Vacuum Pressure Swing Adsorption) VPSA oxygen generation equipment uses the mixed bed formed by VPSA special molecular sieve and desiccant to selectively adsorb impurities such as N2, CO2, or water vapor in the air, so that oxygen is enriched at the outlet of the bed. The equilibrium-loading molecular sieve bed is desorbed under vacuum conditions so as to produce 90-95% oxygen in circulation.


I. VPSA oxygen equipment mainly consists of the blower, vacuum pump, cooler, adsorption system, oxygen buffer tank and control system.


1、Air Blower & Vacuum Pump


The blower provides air for the whole oxygen system. The blower whose exhaust pressure meets the design conditions is selected according to the design conditions of the VPSA oxygen unit, combined with the user's operating conditions. The vacuum pump ensures the normal desorption of the whole oxygen-generating system in the ideal vacuum state so that the oxygen plant can continuously absorb nitrogen while generating oxygen.


2、Cooler


Compressed air at high temperature and high pressure after pressurization in the blower goes through the water cooler to reduce the temperature down to the required operating level, and then is sent to the adsorption tower for adsorption.


3、Adsorption System


The adsorption system consists of 2 adsorption vessels equipped with the zeolite molecular sieve, piping and valves, etc. Compressed air at low temperature and high pressure enters from the bottom of tower A. When flowing through the adsorbent bed, impurities such as CO, water vapor, and N2 in the air are adsorbed, while oxygen is collected through the adsorption bed at the top of the adsorber as the product gas. At the same time, the B tower is in regeneration. When the adsorption of tower A almost reaches equilibrium, low-temperature and high-pressure air goes into the B tower for adsorption by the control system. Tower A and B thus alternately operate to achieve continuous oxygen production.


4、Oxygen Buffer Tank


To store product gas (oxygen) and stabilize the pressure of the whole set of equipment.


5、Control System


The engineer inputs the pre-written valve control program into the PLC controller, which regulates the opening and closing of each pneumatic valve through the solenoid valve to enable the adsorption system to adsorb and regenerate within the appointed time.


II. PSA oxygen generator mainly consists of the compressor, refrigeration air dryer, degreaser, adsorption system, oxygen buffer tank and control system.


1、Compressor


The compressor supplies the raw air for the whole system. The compressor meeting the design conditions is selected to supply air according to the oxygen gas capacity of the PSA oxygen generator.


2、 Refrigeration Air Dryer


After the compressor pressurizes the air, the compressed air at high temperature and high pressure enters the refrigeration dryer for cooling, drying and impurity removal to get the compressed air at low temperature and high pressure.


3、Degreaser


The degreaser removes the grease mist from the compressed air at low temperature and high pressure to prevent it from affecting the service life of the zeolite molecular sieve.


4、Adsorption System


The adsorption system consists of 2 adsorption vessels equipped with the zeolite molecular sieve, piping and valves, etc. Compressed air at low temperature and high pressure enters from the bottom of tower A. When flowing through the adsorbent bed, impurities such as CO, water vapor, and N2 in the air are adsorbed, while oxygen is collected through the adsorption bed at the top of the adsorber as the product gas. At the same time, the B tower is in regeneration. When the adsorption of tower A almost reaches equilibrium, low-temperature and high-pressure air goes into the B tower for adsorption by the control system. Tower A and B thus alternately operate to achieve continuous oxygen production.


5、Oxygen Buffer Tank


To store product gas (oxygen) and stabilize the pressure of the whole set of equipment.


6、Control System


The engineer inputs the pre-written valve control program into the PLC controller, which regulates the opening and closing of each pneumatic valve through the solenoid valve to enable the adsorption system to adsorb and regenerate within the appointed time.


III. Difference between VPSA oxygen unit and PSA oxygen generator


1、VPSA oxygen plants use blowers to receive and pressurize air, while PSA oxygen systems adopt compressors for air supply.


2、PSA-O2 generators use sodium zeolite whose core component is sodium molecular sieve, and VPSA-O2 plants are filled with lithium molecular sieve.


3、The adsorption pressure of PSA-O2 generator is generally 0.6~0.8Mpa, while that of VPSA-O2 unit is 0.05Mpa.


4、The oxygen flow of a single PSA generator reaches 200~300Nm3/h, but a set of VPSA equipment can achieve 7,500~10,000Nm3/h.


5、Compared with the PSA process, the VPSA oxygen plant has lower energy consumption (0.29~0.32kWh/m3), making it more energy efficient and environmentally friendly.