02 Sep, 2026
I. Gas Separation Methods
1. Cryogenic Air Separation
Cryogenic air separation is an air-separation method based on gas liquefaction and fractional distillation. Air is first compressed and precooled, then fractionated at extremely low temperatures to separate different gas components. Cryogenic technology can produce high-purity oxygen, nitrogen and rare gases and is suitable for large-scale industrial applications. Its main advantage is the continuous supply of large quantities of high-purity gas. Its main limitations are high construction and operating costs, the need for complex equipment, and relatively high energy consumption, which may be important where energy cost is sensitive.
2. Pressure Swing Adsorption (PSA)
Pressure Swing Adsorption separates specific gases from air by physical adsorption. Molecular sieves or other adsorbents alternately adsorb and desorb gases under different pressures. PSA is particularly effective for producing relatively high-purity nitrogen and oxygen and is well suited to small- and medium-scale applications. Its advantages include lower operating cost, smaller equipment footprint and flexible operating conditions. However, PSA is less efficient for very large gas flows, and purity normally does not reach the level obtainable with cryogenic air separation. Adsorbent life and performance are also important constraints on PSA technology.
3. Membrane Separation Technology
Membrane separation uses semipermeable membranes to separate different gas molecules. The membrane allows selected gas molecules to pass while blocking others. Its advantages include simple equipment, low energy consumption and easy maintenance, making it suitable for small-scale and remote applications. The main challenges are membrane selectivity and durability. High-performance membrane materials are critical to achieving high separation efficiency and purity, but these materials are often expensive and may degrade over time. Therefore, membrane technology may be less economical or efficient than other methods in some applications.
Cryogenic air separation, PSA and membrane separation each have advantages and disadvantages. Selection depends on the required gas purity, production capacity, cost and energy efficiency for the specific application.
II. Selection of Fittings for Oxygen Pipelines
Main fittings used on oxygen pipelines include elbows, branch fittings, reducers, flange gaskets and filters.
1. Elbows, Branch Fittings and Reducers
Selection of elbows, branch fittings and reducers for oxygen pipelines shall meet the following requirements:
① Wrinkled elbows are strictly prohibited on oxygen pipelines. For carbon-steel elbows made by cold or hot bending, the bending radius shall be no less than 5 times the outside diameter of the pipe. For seamless or pressed-welded carbon-steel elbows, the bending radius shall be no less than 1.5 times the pipe outside diameter. For seamless or pressed stainless-steel or copper-alloy elbows, the bending radius shall be no less than the pipe outside diameter. For rolled welded steel pipe with operating pressure below 0.1 MPa, welded elbows with a bending radius no less than 1.5 times the pipe outside diameter may be used. The inner wall of the elbow shall be smooth and free from sharp edges, burrs and weld beads.
② Branch fittings for oxygen pipelines should preferably be seamless or pressed-welded components. If such fittings are unavailable, they should be prefabricated in a factory or on site and finished without sharp corners, protrusions or weld beads. On-site hole cutting and socket insertion are not recommended.
③ Reducers for oxygen pipelines should preferably be seamless or pressed-welded components. When fabricated by welding, the length of the reducing section should be no less than three times the difference between the outside diameters at the two ends. The inner wall shall be smooth and free from sharp edges, burrs and weld beads.
2. Flange Gaskets
Flanges on oxygen pipelines shall be selected according to applicable current standards. Pipeline flange gaskets must provide good sealing while maintaining adequate strength. Combustible materials should be avoided; requirements become stricter as oxygen pressure increases.
III. Oxygen-Generation Equipment
Industrial oxygen-generation equipment uses air-separation technology. Air is first compressed to high density, and differences in the condensation points of air components are then used to achieve gas-liquid separation at a certain temperature, followed by further rectification. Industrial oxygen is generally obtained by this physical method. Oxygen generators are also called air-separation equipment. According to output, equipment can be divided into small units below 800 m³/h, medium units from 1000 to 6000 m³/h, and large units above 10000 m³/h. Values such as 800 m³/h and 1000–6000 m³/h refer to the hourly oxygen output from the air-separation column.
In China, oxygen-generation equipment generally consists of an air compressor, precooling unit, purification unit, air-separation column, etc.
Operating principle of household oxygen generators: molecular-sieve physical adsorption and desorption technology is used. The oxygen generator contains molecular sieve material. Under pressure, nitrogen in the air is adsorbed, while the remaining unadsorbed oxygen is collected and purified to become high-purity oxygen. When pressure is reduced, the molecular sieve releases the adsorbed nitrogen back into the ambient air. During the next pressurization cycle it adsorbs nitrogen again and produces oxygen. The process is a periodic dynamic cycle, and the molecular sieve itself is not consumed.
The original document states that medical oxygen-generation equipment uses advanced PSA air-separation technology. Separation of oxygen and nitrogen is based on the difference in adsorption capacity of the adsorbent (zeolite molecular sieve) for oxygen and nitrogen. When air enters an adsorbent bed, nitrogen is adsorbed more strongly while oxygen is not, allowing high-concentration oxygen to be obtained at the outlet of the adsorption bed. Because adsorbent capacity changes with pressure, changing the pressure enables alternating adsorption and desorption cycles.
Regardless of application, the oxygen-generation equipment described here uses physical oxygen-generation methods, separating oxygen from air.
