Featuring a ceramic ion transport membrane, the solid-state device aims to generate high purity oxygen at high pressure. Built with no moving parts, the initial prototype currently operates at a small scale (30-40 slpm – standard litre per minute, 5-10 bar) and was developed primarily to recharge oxygen tanks for astronaut’s spacesuits.
In a world-exclusive reveal, Dr John C. Graf, Technology Development Lead for Life Support at NASA’s Johnson Space Center in Houston, Texas, discussed the agency’s latest innovations in oxygen generation technology during gasworld’s Medical Gases Virtual Event 2022 held today, April 7th.
The Medical-Ceramic Oxygen Generator or M-COG, NASA’s new type of oxygen generation system, is based on a tried and tested method that has been used in engineering labs for years.
Graf stated that the new technology may be applicating to supplying medical gas in parts of the world where it’s presently difficult to get that gas and, although NASA develops flight hardware, given the opportunity to collaborate with partners, the agency intends to deploy the technology for medical systems.
At the heart of the M-COG is thin rock of a hot, solid material.
“We use cerium oxide, but if you get the right kind of solid material and you put it in a high temperature environment, you put it in a hot oven and you put a simple DC potential across, hook it up like a battery circuit in an elementary school science fair project,” he explained.
The electrical potential drives oxygen ions found in the air on one side of the ceramic rock and pumps oxygen ions to the other side where they’re collected. Given the correct engineering procedures are followed, a device that Graf calls an oxygen engine is formed.
“And so you can have a large and effective medical oxygen generator which has one moving part. It’s a processor blower,” he said.
“The blower reminds me of the blower that’s in the ceiling fan that draws humidity out of my bathroom.”
The blower then draws hot process air through the oxygen engine, the oxygen is stored in a tank and delivered in NASA’s design.
Capable of delivering oxygen at a nominal rate of 34 standard litres per minute at a pressure of 4-8 bar, the device is relatively energy efficient, using just 2400 watts continuously.
What is new about this approach?
The new M-COG technology uses wafers. About the size and shape of a cell phone and half as thick, these wafers are organised in a way that allows a series of them be stacked.
NASA’s wafer technology
Graf explained, “We have lots of surface area in a small area and we gap the distance between each of the wafers so that it’s very easy to blow air across all of those surfaces without fans working very hard.”
Small ceramic washers are place around little holes in the wafer, before oxygen is delivered into a small porous layer in the inside of the wafer and then migrates to that central port.
If the wafers are lined up and then lined with a ring, the pipe that comes out at the top acts like a chimney.
“These cell stacks deliver oxygen out of that pipe again with no moving parts, which we think will be sustainable and reliable and long lasting.”
NASA is building and designing around a cell stack consisting of 30 wafers with dimensions of six inches by six inches by three inches in size.
If the user wants four litres of oxygen, one of the cells provides the sufficient amount of surface area to provide that amount.
“If you want 400 litres per minute, you will use more of these cell stacks and embed them into a common design,” said Graf.
Process heat is a key component to the energy efficient nature of the design. The hotter the wafers are, the hotter the cell stacks are, the more chemically efficient they are, resulting in less voltage being required to pump the oxygen.
A catch-22 means that, the hotter the wafers are, the more energy is spend heating incoming process air, reducing the amount of energy saved.
“This method lets the cells act in a series,” revealed Graf. “So one amount of air is used to sweep air and provide oxygen to multiple cell stacks. It heats the air, so when you take the depleted air that is coming out of the last stack, it’s hotter than you started with.”
When put into a heat exchanger, the incoming air is preheated to the point where heaters could be eliminated entirely, with only the intrinsic power needed for pumping oxygen.
The overall size of the prototype is roughly 2m long and 1.6m tall, with the majority of the space taken up by the heat exchanger. The design also possesses an exterior feature that receives all of the oxygen ports and manages gas pressure regulation, gas sampling and routing.
In addition to build the prototype system that delivers 34 litres a minute at 100 psi, Graf revealed that NASA is also designing and prototyping a two-stage device that can produce oxygen capable of filling high pressure cylinders.
By integrating a new ceramic oxygen generator – or a second stage, which is built inside a pressure vessel in a ‘ship in a bottle style’, it’s possible to receive low pressure oxygen and pump it to high pressure oxygen, creating what is, in essence, a solid state oxygen compressor.
It works by the gas pressure being fed into the first stage storage tank, which can deliver up to 150 psi. When it’s up to hospital delivery pressure – around 100 psi – a valve can be opened, enroot oxygen through a tube up to the top before enrooting a second valve, which allows oxygen to be fed into the inside of a second stage wafer.
“Here the oxygen pumping is reversed, the oxygen gets electro-chemically pumped from the inside to the outside of the wafer,” said Graf.
“When you do that, high pressure oxygen can be regulated and compressed to pressures up to 3000 psi.”
The first stage configuration draws air on the outside of the wafer and pumps low pressure oxygen to the wafer before the second stage receives low pressure oxygen on the inside of the water, pumps it to the outside, and – if it’s inside a pressure vessel – that oxygen can accumulate and compress and reach high pressures.
What stage is NASA at?
Graf revealed that the agency is currently building the chassis of the prototype system. As soon as the chassis is built, the team will conduct preliminary engineering testing, the results of which will be published ‘as soon as practically possible.’
Although the primary intention is to use the technology to recharge oxygen tanks in astronaut spacesuits, NASA recognises the possibility for it to benefit hospitals that lack reliable access to oxygen.
To advance the potential for its medical application, Graf invites those interested in a potential partnership to see the chassis and its technological components virtually or physically.
“We plan on showing notional designs of larger and smaller scale systems to help teach the technology and help partners who are interested in different sized systems learn how they might be able to take these ceramic cell stacks and use them for the benefit of other applications,” he added.
Concluding, Graf said, “In summary, we’re building a ceramic oxygen generator and we’re searching for partners and collaborators.”
“We recognise that NASA can do some parts of this job, we can develop technology but we don’t have a chance to build systems for hospitals. If there are people who are involved in that area, stand out and look for a request for information.”
“As soon as the NASA internal legal processes work out, we’ll be releasing that.”