What is an oxygen concentrator?

What is an oxygen concentrator?

An oxygen concentrator is a device that selectively removes nitrogen from a gas supply (typically ambient air) to produce an oxygen-rich product gas stream. They’re used in industry and as oxygen therapy equipment in hospitals.

The two methods in common use are pressure swing adsorption and membrane gas separation. Pressure swing adsorption (PSA) concentrators use multiple molecular sieves containing zeolite minerals that pressurize nitrogen in rapid cycles.

How do oxygen concentrators work?

Oxygen concentrators using pressure swing adsorption (PSA) technology are widely used for oxygen provision in healthcare applications, particularly where liquid or pressurized oxygen is too dangerous or inconvenient, such as in homes or portable clinics. Concentrators based on nitrogen separation membrane technology are also available for various applications.

An oxygen concentrator takes in the air and removes nitrogen from it, leaving an oxygenated gas for use by people in need of medical oxygen because of low oxygen levels in their blood.

Oxygen concentrators, also known as oxygen gas generators or oxygen generating plants, provide a cost-effective source of oxygen in industrial processes.

These oxygen concentrators function based on fast pressure swing adsorption of ambient nitrogen on zeolite minerals at high pressure and use a molecular sieve to adsorb gases. This type of adsorption system is therefore functionally a nitrogen scrubber, allowing other atmospheric gases to pass through while leaving oxygen as the primary gas. PSA technology is a reliable and economical technology for small-to medium-scale oxygen production. Cryogenic separation is more suitable for high volumes, and external delivery is generally more suitable for small volumes.

At high pressure, porous zeolite adsorbs a large amount of nitrogen due to its large surface area and chemical characteristics. The oxygen concentrator compresses the air and passes it over the zeolite, causing the zeolite to absorb nitrogen from the air. It then collects the remaining gas, which is mostly oxygen and leaves the nitrogen zeolite under reduced pressure.

An air compressor, two zeolite pellet-filled cylinders, a pressure-equalizer reservoir, and additional valves and tubes make up an oxygen concentrator.  The first cylinder receives air from the compressor during the first half cycle, which lasts around 3 seconds. During that time, the pressure in the first cylinder rises to about 2.5 times normal atmospheric pressure (typically 20 psi or 138 kPa gauge, or 2.36 atmospheres absolute) above atmospheric, and the zeolite becomes saturated with nitrogen. As the first cylinder approaches pure oxygen (contains argon, CO2, water vapor, radon, and other small atmospheric constituents) in the first half cycle, a valve opens and oxygenated gas flows into the pressure-equalizing reservoir, which connects to the patient’s oxygen tube. At the end of the first half of the cycle, another valve position changes so that air from the compressor is directed towards the second cylinder. The pressure in the first cylinder is reduced as the enriched oxygen moves into the reservoir, allowing nitrogen to be released back into the gas. In the second half of the cycle, another valve position change occurs to return the gas in the first cylinder to the ambient environment, keeping the oxygen concentration in the pressure-equalizer reservoir from falling below approximately 90%. The pressure in the hose carrying oxygen from the same reservoir is kept constant by a pressure-reducing valve.

The older units cycled for about 20 seconds and supplied 90+% oxygen at a rate of 5 liters per minute. Since about 1999, units capable of supplying up to 10 liters per minute have been available.

Classic oxygen concentrators use a two-bed molecular sieve; the new concentrators use a multi-bed molecular sieve. The advantage of multi-bed technology is increased availability and redundancy, as 10 L/min molecular sieves are staggered and multiplied on multiple platforms. More than 960 liters per minute can be produced from this. Unless a multi-bed concentrator is producing oxygen at a concentration of > 90%, the elapsed time is often less than 2 minutes, making it much shorter than a simple two-bed concentrator. It gets faster. This is a huge advantage in mobile emergencies. The option to fill standard oxygen cylinders (e.g., 50 L at 200 bar = 10,000 L each) with high-pressure boosters is given to ensure automatic failover to pre-filled reserve cylinders and to ensure an oxygen supply chain, for example, in case of power failure, is given with those systems.

Medical oxygen concentrators are used to concentrate oxygen for patients in hospitals or at home. PSA generators are a cost-effective source of oxygen. They’re a better option than cryogenic oxygen tanks or pressurized cylinders because they’re safer, less expensive, and handier. They can be used in a variety of industries, including medical and pharmaceutical production, water treatment, and glass manufacturing.

PSA generators are especially useful in remote or inaccessible parts of the world or mobile medical facilities (military hospitals, disaster facilities).

Membrane separation

In membrane gas separation, membranes act as permeable barriers through which different compounds move at different rates or do not cross at all.