There is an acute shortage of Oxygen to meet the medical needs of COVID-19 patients in India. But it appears that the problem statement needs to be clearer to solve it.
Medical Oxygen: According to the Indian pharmacopoeia the Oxygen required for medical purposes (hereafter referred to as Medical Oxygen) needs to be 99% pure. The standards are different in different places, and the accepted Medical Oxygen purity is 93%±3% according the USA pharmacopoeia. It is blended with air in different proportions depending on the patient’s oxygen supplement requirements.
Where does it come from? A typical hospital meets its Medical Oxygen needs in 3 ways.
- Liquid oxygen tankers — ideal for large hospitals
- Oxygen cylinders — a solution for midscale hospitals
- Oxygen concentrators — small hospitals or personal use at home. It is onsite production and does not depend on a 3rd party, once it is set up.
Redirecting the Industrial Oxygen: Seeing the emergency situation for the lack of Medical Oxygen, Government has also directed Industrial Oxygen, which is ultra pure for Medical use. This attempts to fill the gaps in categories 1, 2 noted above. Despite this the challenge in hospitals continues.
Logistics Problem: It appears, after talking to several industrial oxygen makers, the challenge is not in the production of oxygen. Rather it is about bringing oxygen in a consumable form to the hospitals.
There are only a finite number of oxygen tankers and cylinders around. So the logistics of refiling them and bringing them to the destination is a severe bottle-neck.
Several teams of Engineers, Scientists, MSMEs are rising upto the occasion and building Oxygen concentrators for home use or for use in smaller hospitals. Several of them are even making the designs publicly available with a good intent. The idea is to bypass the logistics bottlenecks in sources 1 and 2 noted above, and skip to 3 (oxygen concentrators) which may not be the most economical in long run due to high operational costs.
Clarifying the Oxygen concentrator mechanism. In fact, as it turns out the logistics problems continue. The different drawings of DIY designs we find on YouTube or novel designs by scientists/engineers are all many variants of the classic Skarstron cycle, which is decades old. As complicated as the cycles may be the logic is simple-
- Compressor pumps the air, first through the desiccant and then through the zeolite
- Desiccant (such as silica gel) absorbs the humidity from the air
- Zeolite absorbs Nitrogen. For now, let us imagine this as sponge soaking up water.
- Oxygen is ready!! Since the air has 21% Oxygen, 1% Argon, and the rest of it is mostly Nitrogen, the air after passing through Zeolite should be only Oxygen and Argon and hence 93% pure.
- Electronics and valves continuously run the system
Specific Zeolites absorb Nitrogen like it sponge absorbs water. Once the sponge is soaked with water, give it a nice squeeze and begin the cycle again. This is the responsibility of the electronics which will run the Oxygen concentrator Cycle.
Logistics Problems, yet again. Doing a prototype or making a design does not address the problem at hand. The design must be based on the resources available. The logistics problem kick-in, even in this Oxygen Concentrator part.
Zeolite sourcing problems
Ideally if one can work with LithiumX (LiX) material, the material adsorbs Nitrogen at ambient pressure and releases under vacuum. The operations are simpler, the system build will be simple, elegant. However LithiumX can not be easily sourced in India. So, the deceptively cute pictures of the commercial home-use oxygen concentrators are models we aim for, but can not be built practically with no reliable and scalable source of LithiumX. This also means that the technology has to be based on more readily available 13X Molecular Sieve Zeolite.
An additional challenge the substitution of LiX with 13X brings is that the operations change from a vacuum based to a pressure based one (VPSA to PSA technology).
Practically, it requires more quantities of Zeolite, and larger compressors.
Compressor sourcing problems
The compressors used for medical applications should be oil-free. That makes them another hard thing to source. Even considering the designs of personal home-use oxygen concentrator designs, finding a source of oil-free compressors with a lead time of 4 weeks or less is extremely difficult. Needless to say these are also very expensive.
Dehumidification, silica regeneration problems
At present India is in peak summer. The relative humidity levels in many places can be as high as 90%. Which means that no matter how hard silica gel bed tries to absorb humidity, it will be saturated with water very soon. A regeneration by heating the silica gel at 150C or changing the cartridge is another problem.
Our own designs had to be modified several times in the past week, as we frantically looked for sourcing the different components -from compressors to zeolites — and hit roadblocks. Making us realize that the design should be in the context of available resources.
Riding on the Existing Infrastructure
Conceptual solutions or a prototype built with repurposing resources available in the lab do not unfortunately offer a scalable solution if the components can not sourced in the next few weeks.
Interestingly most hospitals have a plant for ultra pure air at the hospital site. This ultra pure air plant design is meant to separate out humidity, dust, oil and it runs with an oil-free compressor (hereafter referred to as Medical Air). The Medical Air is needed in hospital for several reasons, for administering anaesthesia to keep the surgery rooms clean. There is usually also a central line that carries this Medical Air to each bed. Typically Medical Air is made available at 4–7bar pressure.
The availability of the Medical Air at the hospital site at a 4 to 7 bar pressure removes several of the sourcing problems — oil free compressor, removal of humidity which otherwise contaminates the Zeolite.
In the next 2 months in India, converting Medical Air to Medical Oxygen (93% purity) with the readily available 13X seems to be a very practical solution to meet the extreme emergency.
Also, elective surgeries (such as ortho surgeries which may be scheduled later) for which Medical Air will be needed are minimal in this period, as most hospitals are fully committed to meeting COVID-19 needs. Thus, the COVID-19 situation frees up the Medical Air to some degree.
Smaller hospitals: But what if the smaller hospitals do not have Medical Air on site? Hopefully the larger hospitals using this conversion will free-up resources like oxygen cylinders for smaller hospitals.
Arithmetic of Medical Oxygen Production: A reasonable “recovery” one can aim for is 50%, which means that 50% of the Oxygen that is in the air will be absorbed. And the Oxygen percentage in the air, whether it is the ambient or the Medical Air, is about 21%. Thus, the overall production rate of Medical Oxygen one may expect is 10% of the Medical Air that is used.
For every 1000 litres of Medical Air that can be dedicated for this purpose, it will result in nearly 100 liters of Oxygen at the hospital site.
Partial solution: The design, cost, sourcing complexity is reduced by 60 to 70%. Since the design is modular, if needed an additional compressor may be added later to make it a stand-alone unit. It is clear that converting Medical Air to Medical Oxygen is not a replacement for cylinders or other alternative sources of oxygen. Rather, it may be a rapidly deployable ad hoc solution. And all avenues to solve the crisis must be pursued.
An Oil-free compressor for medical applications turns out to be the hardest component also the most expensive one in the entire solution. It can easily cost more than 50% of the total price of the oxygen concentrator. The resources built may well remain an infrastructure in large or even 2-tier or 3-tier towns which currently lack such infrastructure. The design considerations and economics must also note whether this is a project intended to remain as an infrastructure post-COVID-19 emergency or not, justifying the costs, sourcing and timelines.
Regulatory challenges: According to the Indian pharmacopoeia Medical Air is 99% purity. However, 93% is an acceptable standard across the world. The regulatory process of allowing such Medical Air to Medical Oxygen conversion should follow the engineering hack.
The article originally appeared on medium.com
Meher K Prakash, Santosh Ansumali , S. V. Diwakar, Jawaharlal Nehru Centre for Advanced Scientific Research. Arvind Rajendran, University of Alberta. Views are personal.
Acknowledgements. We thank the numerous Doctors, Hospital Technicians and Operations staff who were kind enough to dedicate time to explain how their oxygen and airlines are setup and used.
This work is part of the JNCASR’s response to COVID-19 situation, where we are trying to develop Oxygen Concentrators on an urgent basis.