An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream.
Home medical oxygen concentrators were invented in the early 1970s, with the manufacturing output of these devices increasing in the late 1970s. Union Carbide Corporation and Bendix Corporation were both early manufacturers. Prior to that era, home medical oxygen therapy required the use of heavy high pressure oxygen cylinders or small cryogenic liquid oxygen systems. Both of these delivery systems required frequent home visits by suppliers to replenish oxygen supplies. In the United States, Medicare switched from fee-for-service payment to a flat monthly rate for home oxygen therapy in the mid-1980s, causing the durable medical equipment (DME) industry to rapidly embrace concentrators as a way to control costs. This reimbursement change dramatically decreased the number of primary high pressure and liquid oxygen delivery systems in use in homes in the United States at that time. Oxygen concentrators became the preferred and most common means of delivering home oxygen. The number of manufacturers entering the oxygen concentrator market increased exponentially as a result of this change. Union Carbide Corporation invented the molecular sieve in the 1950s which made these devices possible. It also invented the first cryogenic liquid home medical oxygen systems in the 1960s.
An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream.
Home medical oxygen concentrators were invented in the early 1970s, with the manufacturing output of these devices increasing in the late 1970s. Union Carbide Corporation and Bendix Corporation were both early manufacturers. Prior to that era, home medical oxygen therapy required the use of heavy high pressure oxygen cylinders or small cryogenic liquid oxygen systems. Both of these delivery systems required frequent home visits by suppliers to replenish oxygen supplies. In the United States, Medicare switched from fee-for-service payment to a flat monthly rate for home oxygen therapy in the mid-1980s, causing the durable medical equipment (DME) industry to rapidly embrace concentrators as a way to control costs. This reimbursement change dramatically decreased the number of primary high pressure and liquid oxygen delivery systems in use in homes in the United States at that time. Oxygen concentrators became the preferred and most common means of delivering home oxygen. The number of manufacturers entering the oxygen concentrator market increased exponentially as a result of this change. Union Carbide Corporation invented the molecular sieve in the 1950s which made these devices possible. It also invented the first cryogenic liquid home medical oxygen systems in the 1960s.
Oxygen concentrators using pressure swing adsorption (PSA) technology are used widely for oxygen provision in healthcare applications, especially where liquid or pressurized oxygen is too dangerous or inconvenient, such as in homes or in portable clinics. For other purposes there are also concentrators based on nitrogen separation membrane technology.
An oxygen concentrator takes in air and removes nitrogen from it, leaving an oxygen enriched gas for use by people requiring medical oxygen due to low oxygen levels in their blood.[1] Oxygen concentrators provide an economical source of oxygen in industrial processes where they are also known as oxygen gas generators or oxygen generation plants.
Pressure swing adsorption
Modern Fritz Stephan GmbH FS360 lpm multi molecular sieve multi platform oxygen concentrator
These oxygen concentrators utilize a molecular sieve to adsorb gases and operate on the principle of rapid pressure swing adsorption of atmospheric nitrogen onto zeolite minerals and then venting the nitrogen. This type of adsorption system is therefore functionally a nitrogen scrubber leaving the other atmospheric gases to pass through, leaving oxygen as the primary gas remaining. PSA technology is a reliable and economical technique for small to mid-scale oxygen generation. Cryogenic separation is more suitable at higher volumes and external delivery generally more suitable for small volumes.
At high pressure, the porous zeolite adsorbs large quantities of nitrogen, due to its large surface area and chemical characteristics. After the oxygen and other free components are collected the pressure drops which allows nitrogen to desorb, after which it may be vented.
Animation of pressure swing adsorption, (1) and (2) showing alternating adsorption and desorption
I compressed air input A adsorption
O oxygen output D desorption
E exhaust
An oxygen concentrator has an air compressor, two cylinders filled with zeolite pellets, a pressure equalizing reservoir, and some valves and tubes. In the first half-cycle the first cylinder receives air from the compressor, which lasts about 3 seconds. During that time the pressure in the first cylinder rises from atmospheric to about 2.5 times normal atmospheric pressure (typically 20 psi/138 kPa gauge, or 2.36 atmospheres absolute) and the zeolite becomes saturated with nitrogen. As the first cylinder reaches near pure oxygen (there are small amounts of argon, CO2, water vapour, radon and other minor atmospheric components) in the first half-cycle, a valve opens and the oxygen-enriched gas flows to the pressure equalizing reservoir, which connects to the patient’s oxygen hose. At the end of the first half of the cycle, there is another valve position change so that the air from the compressor is directed to the second cylinder. The pressure in the first cylinder drops as the enriched oxygen moves into the reservoir, allowing the nitrogen to be desorbed back into gas. Partway through the second half of the cycle, there is another valve position change to vent the gas in the first cylinder back into the ambient atmosphere, keeping the concentration of oxygen in the pressure equalizing reservoir from falling below about 90%. The pressure in the hose delivering oxygen from the equalizing reservoir is kept steady by a pressure reducing valve.
Older units cycled with a period of about 20 seconds, and supplied up to 5 litres per minute of 90+% oxygen. Since about 1999, units capable of supplying up to 10 lpm have been available.
There are classic two bed molecular sieve oxygen concentrators existing, as well as newer multi bed molecular sieve oxygen concentrators. The advantage of the multi bed molecular sieve technology is the increased availability and redundancy, as the 10 lpm molecular sieves are staggered and multiplied on several platforms. With this, lpm values up to 960 lpm and more can be realized. The ramp up time (time the concentrator needs to start producing oxygen >90% after being switched on) of multi molecular sieve oxygen concentrators is often less than 2 minutes and much shorter, compared to simple two bed molecular sieve oxygen concentrators. This advantage is often required in mobile emergency applications. The option, to fill standard oxygen cylinders (e.g. 50 l at 200 bar = 10.000l each) with high pressure boosters, to ensure automatic fail over to previously filled reserve cylinders and to ensure the oxygen supply chain e.g. in case of power failure, is given with those systems.
