Oxygen concentrator

Team Lead: Praveen C Ramamurthy
Email: praveen@iisc.ac.in

Summary

There are challenges due to the availability of oxygen supplies in remote places and overwhelming situations arise in hospitals due to the COVID-19 pandemic. Generation and availability of oxygen source at the point of care, where cylinders and other centrally distributed systems are unavailable is very important.  Even if oxygen supplies are available at the hospitals, overcrowding due to the pandemic will create stress on the system. In addition, not all patients require complete ventilator systems; some require just monitoring of health and vitals and supply of oxygen at various percentages. Reliable oxygen supply is necessary for the care of these kinds of patients to improve their chances of survival. A low-cost oxygen concentrator fabricated from locally available components would be the most appropriate option for these situations.

Oxygen concentrators provide a sustainable and cost-effective source of medical oxygen to health facilities. An oxygen concentrator has double cartridges containing apparatus to separate oxygen from air. Basically, atmospheric air is pumped into these cartridges under pressure where it passes through zeolite beds to increase oxygen concentration to therapeutic levels for delivery to the patient. Guidelines for the safe administration of oxygen differ across applications. The flow rate and concentration of oxygen required depends on the requirement and can be modified easily.

The advantages of oxygen concentrators are high reliability and low cost compared with oxygen cylinders and piped oxygen supply systems. Challenges with oxygen concentrators include the need for regular, although minimal, maintenance and a reliable power supply.

Working principles of oxygen concentrators:  Atmospheric air is drawn through a compressor and the pressurized air passes through sieve beds that contain zeolite powder and pellets of a particular size. Zeolite is a mineral material that preferentially adsorbs nitrogen gas (N2). Once the cycle of adsorption is complete, the second zeolite enclosure is used for separation. At the same time, the first enclosure is depressurized by applying a slight vacuum in the opposite direction, which helps in removing adsorbed nitrogen. The flow and pressure can be controlled for measured and continuous release of oxygen.

Design, fabrication and results: We are developing low-cost oxygen concentrators that could be coupled with ventilators. Zeolite of a specific size is being used to separate oxygen from the air. A mechanism is being created to control the flow and direction for optimum oxygen generation.  The operation of this process is automated. This concentrated oxygen can be directly used with ventilators.

The first part of the work was to design and fabricate a working prototype to check the suitability of the model for concentrating oxygen in ambient air from 20% to 95%.  First, the model was built using a stainless steel cartridge, in addition to fabricating the control system to operate the valves, vacuum line, and compressor line using Raspberry Pi as shown below.

Prototype 1, design and control unit

The second part was to miniaturize and use less expensive components optimizing the control unit.  Here we used commercially available domestic water filter cartridge as the canister in the concentrator.

The domestic water filter cartridge and new modified control panel

Using this prototype, we found that the percentage of oxygen from the exit port was in the range of >70%. Once the systematic calibration of the sensor is carried out, accurate percentage level will be determined. Targeted specifications for this unit are oxygen concentration of 20-95%, flow rate of 0.5-20 liters / minute, and pressure of 1 bar. Initially the oxygen concentration was measured using a sensor fabricated at Prof. Navakanta Bhat’s laboratory in CeNSE, IISc.

Status update (April 20, 2020)

The next version of the system and the controlling software have been implemented. These changes have been made keeping in view the hardware capabilities, electronic response clocks and software capabilities.  Various optimizations were carried out by conducting multi-parameter designs of the experiments. These experiments have resulted in obtaining oxygen percentage above 94%.

Calibration of the new catalytic oxygen sensor was carried out at 0%, 21% and 100% oxygen concentration.

Oxygen sensor calibration

Control panel was optimized further to tune the timing of the relays and valves to synchronize with the other electronics.

Modified control panel

Performance of the oxygen generation at 1 lpm

This optimization and generation have been carried out at a flow rate of 1 liter/minute. 

Status update (April 28, 2020)

Performance of the oxygen concentrator at various flow rates has been obtained using optimized electronics. New oxygen sensor calibration was again carried out to match these changes.

It is observed that room atmosphere to >90% oxygen concentration is achieved in 180 seconds. Optimizing the oxygen output flow is the next challenge.

Team

  • Praveen C Ramamurthy (praveen@iisc.ac.in)
  • Bhaskar Krishnaswamy
  • Industrial partner: Reveron Pvt Ltd headed by Dr. Arun D Rao
  • Jay Kumar


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