Oxygen concentrator machine provide supplementary oxygen for patients with chronic obstructive pulmonary disease (COPD).
It provides oxygen in higher concentrations, for severe chronic hypoxemia and pulmonary edema.
This medical device may be used as an adjunct treatment for severe sleep apnea in conjunction with a continuous positive airway pressure unit.
Oxygen concentrators are typically used as stationary sources to provide long-term oxygen therapy
(LTOT) to patients at home.
Situation like Covid-19 where lungs require concentrated oxygen at high flow rate continuously for long time the machine is very useful.
Portable versions can be use as domestic device with little maintenance and can run on domestic power/ battery.
Table of Contents
Oxygen concentrators Principles of operation
Oxygen concentrators are devices increasing oxygen in the air to a purity rate of 90% to 97%. The air which we breathe consists of approximately 78% nitrogen, 21% oxygen and 1% other gases.
The easiest way to separate the oxygen from the air mixture is to use the pressure swing absorption technology developed by NASA.
The process of obtaining oxygen using the pressure swing absorption technology is based on the air being filtered through the aluminosilicate minerals which are known as zeolite.
For this purpose, the minerals are placed into a container known as molecular or zeolite bed. When the ambient air is applied to this structure with a specific pressure.
The oxygen passes through it into the output with the applied pressure while the nitrogen molecules in the air are absorbed with the minerals in the bed.
Pressure Swing Absorption Technology
The concentrator device consists of an air filter, compressor, four-way solenoid valve, molecular sieve, product tank, pressure-regulator, water container and an exhaust component.
In this system, the air taken from the atmosphere is passed through the air filter, and then sent to the first molecular sieve with the pressure provided by compressor.
While the pressurized nitrogen which enters into the molecular sieve is being held in the zeolite bed, the oxygen is allowed to pass through unrestricted into the product tank.
When the pressure in the product tank reaches 23 PSI, the zeolite in the first molecular sieve is completely saturated with nitrogen.
Thus, the compressed air is given to the second sieve by changing the valve position so that oxygen production can continue.
Meanwhile, the first molecular sieve is depressurized and regenerated by the removal of the absorbed nitrogen, carbon dioxide and water vapor.
When the zeolite in the second sieve is saturated with the nitrogen, the pressurized air is given to the first sieve again and the nitrogen in the second sieve starts to be thrown out by the egzost system.
The pressurization and depressurization cycle proceeds alternately during the system operation. The oxygen which is brought into a suitable pressure and a purity of 90 to 95%.
In the product tank is passed through into the pressure regulator and the flow meter respectively. Then, it is given to the patient with a nasal canola or an oxygen mask.
Molecular sieves
The molecular sieves which contain a chemical called “5A molecular sieve” are one of the most important components that affects the device performance.
Two molecular sieves are used to supply the oxygen continuity in the designed system, because this chemical is quickly saturated with nitrogen.
The design of each molecular sieve depends on basic parameters such as the bed length, the bed diameter, the package type of the bed and the air pressure fed to the bed.
Two types of packaging are used in the production of molecular sieves:
Conventional Packaging
The conventional one is a uniform packaging type made by using only one kind of molecular sieve.
In other words, one kind of molecular sieve with the same diameter is uniformly distributed in the adsorption column.
One of the most significant problems faced with this type packaging is that the flow velocity in
the central core of the column is much higher than the velocity in the outside of the central core.
As a result, while the molecular sieve in central core is firstly saturated by adsorbing enough nitrogen, the outside of the central core is still not saturated.
Thus, the molecular sieves in the whole column are not sufficiently used in this type packaging. The drawbacks of the conventional packaging can be eliminated by reducing the flow velocity in the central core.
This function can be achieved by using a multi-layer arrangement called multi-layered packaging instead of using a single type molecular sieve in the whole column.
Multi layered packaging
The small diameter of molecular sieves is packed in the central core while the larger diameter of sieve lies in the outside of the central core.
25 Two-layered packaging containing central core and outer core are used in this study. The dimensions of molecular sieves in the central and outer ones are 1.6mm and 2.1 mm, respectively.
The diameter of each cylinder is 82 mm, with heights of 650mm each.
Compressor
The compressor used to provide the necessary pressure to the molecular sieves is a dry-air compressor.
which comprises a single electric motor and two reciprocating piston mechanisms driven from opposite ends of the motor shaft.
Each mechanism contains a piston which is reciprocated in a cylinder by the motor.
The two cylinders are connected together to provide the required air flow and pressure used to produce oxygen at a desired purity.
The experimental studies show that an electric motor of 330 W/1.5 A can obtain the pressure of 3 bar,
which provides oxygen at a purity of about 95-82% from the oxygen concentrator output at a flow velocity of 1-5 L/min.
Volume of the product tank
Another factor that affects the oxygen purity in the system output is the volume of the product tank used for storing the oxygen from molecular sieves.
The use of a large volume tank in the oxygen concentrator causes the decrease of the oxygen purity in the output of device while a small volume tank increases the fluctuations in oxygen flow.
Therefore, the tank volume in the design of oxygen concentrator is determined in accordance with the dimension of molecular sieves and the compressor power.
An air filter, which filters all particles including harmful substances such as dust, humidity and pollen caused by the environmental conditions until a minimum of 0.3 microns, is used in concentrator input.
A pressure regulator that decreases the pressure of approximately 23 PSI in product tank to 5-10 PSI is connected to the tank output to minimize the flow imbalances in flow meter input.
Then, the oxygen is given to the patient over the water container with a 9 PSI-valve security by setting
the °ow meter to the flow velocity desired.
Oxygen concentrators description as product
The concentrator draws in room air and passes it through a series of filters that remove dust, bacteria, and other particulates.
In the first step of the concentration process, a compressor forces air into one of the two cylinders containing sieve material.
Where nitrogen is adsorbed, leaving concentrated oxygen and a small percentage of other gases found in room air.
Simultaneously, in the other cylinder, nitrogen is desorbed and exhausted into the atmosphere.
In the second step, the function of the cylinders is reversed in a timed cycle, providing a continuous flow of oxygen to the patient.
Operating steps
The concentrator is properly set up by an expert.
• Unit is plugged in to a power source, turned on, and the oxygen flow is adjusted as prescribed by a doctor.
• A nasal cannula or mask is applied to the patient.
• The concentrator is used for the prescribed amount of time, typically continuously for days or weeks at a time.
Reported problems
Oxygen concentrators may fail to produce therapeutic levels of oxygen because of common problems involving the air-intake system, malfunctioning sieve-control valves, and contaminated sieve materials.
Water vapor in room air can compromise the adsorption of nitrogen in the sieve beds by entering through small leaks in the internal tubing.
If sufficient water vapor contaminates the sieve beds once again, the gas delivered will be room air. Patients may suffer irritation from nasal cannulas.
Because excess oxygen enhances and accelerates combustion, extreme care must be taken to avoid using the concentrator near combustible materials and sources of ignition.
A reserve compressed-oxygen tank and regulator should always be available in case of a power failure.
Also wish to know about oxygen level monitoring devices, click on Pulse Oximeter. For critical care device read Ventilator.
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