Could modified train cars capture carbon from the air? This team has a plan to make it happen
IMAGE: TRAIN CAR FOR DIRECT AIR CAPTURE view more
CREDIT: JOULE/BACHMAN ET AL.
Direct air capture technology removes carbon dioxide from the air and compresses it for sequestration or utilization and promises to help us meet net-zero emissions goals. However, the process of direct air capture can be energy and land intensive and expensive. To design a direct air capture process that uses less energy and less land, a multi-disciplinary team outlines a plan to retrofit train cars to remove carbon from the air at a much lower than average cost per tonne in an article published in a peer-reviewed article in the journal Joule on July 20.
Stationary direct air capture facilities require large areas of land to house their equipment and construct the renewable energy sources required to support them. Obtaining the proper permits to operate can be difficult, and many residents are opposed to the construction of these large facilities in their towns and cities. “It’s a huge problem because most everybody wants to fix the climate crisis, but nobody wants to do it in their backyard,” says co-author Geoffrey Ozin, a carbon dioxide utilization chemist and chemical engineer and director of the solar fuels group at the University of Toronto. “Rail-based direct air capture cars would not require zoning or building permits and would be transient and generally unseen by the public.”
These purpose-built train cars use large vents to intake air, which would eliminate the need for the energy-intensive fan systems that stationary direct air capture systems use. After a sufficient amount of carbon dioxide has been captured, the chamber is closed, and the harvested carbon dioxide is collected, concentrated, and stored in a liquid reservoir until it can be emptied from the train at crew-change or fueling stops for direct transportation into the circular carbon economy or to nearby geological sequestration sites. The carbon-dioxide-free air then travels out the back or underside of the car and returns into the atmosphere.
When a train pumps the brakes, its energy braking system converts forward momentum into electrical energy. As the braking system is applied, the energy is dissipated in the form of heat and discharged out of the top of the train. “That is wasted energy,” says lead author E. Bachman, founder of CO2Rail. “Every complete braking maneuver generates enough energy to power 20 average homes for a day, so we're not talking about a trivial amount of energy.” This energy, the authors suggest, should be used to help mitigate climate change.
The authors argue that direct air capture becomes an even more viable climate solution because the rail system is already in place. “The infrastructure exists,” says Ozin. “That's the bottom line. All you need to do is take advantage of what is already available.”
The researchers say that an average freight train with these direct air capture cars could remove up to 6,000 tonnes of carbon dioxide per year. Because its sustainable-energy needs are being supplied by on-board sources, the price per tonne is significantly lower than that of other direct air capture systems. “The projected cost at scale is less than $50 per tonne, which makes the technology not only commercially feasible but commercially attractive,” Bachman says.
The authors hope this technology could have a positive impact beyond the carbon it removes from the atmosphere. “We could get a positive-feedback loop where the encouragement of rail to broadly deploy these direct air capture rail cars could even further decrease carbon emissions because rail is about five or six times more efficient than trucks,” says Bachman. “By increasing rail utilization, you increase the efficiency of the entire transportation system.”
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Joule, Bachman et al. “Rail-Based Direct Air Carbon Capture” https://www.cell.com/joule/fulltext/S2542-4351(22)00299-9
Joule (@Joule_CP), published monthly by Cell Press, is a new home for outstanding and insightful research, analysis, and ideas addressing the need for more sustainable energy. A sister journal to Cell, Joule spans all scales of energy research, from fundamental laboratory research into energy conversion and storage to impactful analysis at the global level. Visit http://www.cell.com/joule. To receive Cell Press media alerts, contact press@cell.com.
JOURNAL
Joule
METHOD OF RESEARCH
Commentary/editorial
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Rail-Based Direct Air Carbon Capture
ARTICLE PUBLICATION DATE
20-Jul-2022
Modified rail cars clean air of CO2 and help mitigate climate change
Researchers from the University of Sheffield are working with US-based CO2Rail Company to design Direct Air Capture equipment which can be used within special rail cars placed with already running trains
Peer-Reviewed PublicationModified rail cars clean air of CO2 and help mitigate climate change
- New research shows rail systems around the world could be harnessed to help mitigate climate change and clean our air of CO2
- Researchers from the University of Sheffield are working with US-based CO2Rail Company to design Direct Air Capture equipment which can be used within special rail cars placed with already running trains
- On average, each complete train braking manoeuvre generates enough energy to power 20 homes for an entire day - until now this enormous amount of sustainable energy has been wasted
- If the energy of every stop or deceleration for every train in the world could be captured it would harness 105 times more energy than the Hoover Dam produces in the same time period
Rail systems around the world could help mitigate climate change and clean the air of CO2 by capturing the sustainable energy generated when trains break and decelerate.
US-based startup, CO2Rail Company have been working with a world-renowned team of researchers, including engineers from the University of Sheffield, to design Direct Air Capture (DAC) technology that removes carbon dioxide from the air, which can be used within special rail cars placed with already running trains in regular service.
The DAC rail cars work by using large intakes of air that extend up into the slipstream of the moving train to move ambient air into the large cylindrical CO2 collection chamber and eliminate the need for energy-intensive fan systems that are necessary with stationary DAC operations.
The air then moves through a chemical process that separates the CO2 from the air and the carbon dioxide free air then travels out of the back or underside of the car and returns to the atmosphere.
After a sufficient amount has been captured, the chamber is closed and the harvested CO2 is collected, concentrated, and stored in a liquid reservoir until it can be emptied from the train at a crew change or fuelling stop into normal CO2 rail tank cars. It is then transported into the circular carbon economy as value-added feedstock for CO2 utilisation, or to nearby geological landfill sites.
Each of these processes are powered exclusively by on-board generated, sustainable energy sources that require no external energy input or off-duty charging cycles.
When a train pumps the brakes, its energy braking system converts the train’s forward momentum into electrical energy in much the same way as a regenerative electric vehicle. Currently, this energy is dissipated on trains in the form of heat and discharged out of the top of the locomotive during every braking manoeuvre.
Professor Peter Styring, Director of the UK Centre for Carbon Dioxide Utilization at the University of Sheffield and co-author of the research, said: “The direct capture of carbon dioxide from the environment is increasingly becoming an urgent necessity to mitigate the worst effects of climate change.
“Currently the enormous amount of sustainable energy created when a train brakes or decelerates is simply lost. This innovative technology will not only use the sustainable energy created by the braking manoeuvre to harvest significant quantities of CO2, but it will also take advantage of many synergies that integration within the global rail network would provide.
“The technology will harvest meaningful quantities of CO2 at far lower costs and has the potential to reach annual productivity of 0.45 gigatons by 2030, 2.9 gigatons by 2050, and 7.8 gigatons by 2075 with each car having an annual capacity of 3,000 tonnes of CO2 in the near term.”
Unlike stationary DAC operations, which require large areas of land to build equipment and to construct renewable sources of energy to power them, CO2Rail would be transient and would generally be unseen by the public. The potential impact of this technology was recently energised when European transport organisations announced earlier this month that they are committed to tripling high-speed rail use by 2050 to curb CO2-heavy air travel.
Eric Bachman of CO2Rail Company, said: “On average, each complete braking manoeuvre generates enough energy to power 20 average homes for an entire day so it is not a trivial amount of energy.
“Multiply this by every stop or deceleration for nearly every train in the world and you have about 105 times more energy than the Hoover Dam produces within that same period, and that was a hydro-electric construction project that took six years and cost $760 million in today’s dollars.”
He added: “Imagine stepping onto a train each morning, seeing the CO2Rail cars attached, and knowing that your commute to work each day is actually helping to mitigate climate change.
“It will work the same with freight, if there is a choice between rail and another mode of transportation, I think this technology will sway many shippers.”
The team, which includes researchers from the University of Sheffield, University of Toronto, MIT, Princeton, business, and industry, found each direct air capture car can harvest about 6,000 metric tons of carbon dioxide from the air per year and more as the technology develops. Moreover, since trains are capable of hosting multiple CO2Rail cars, each train will harvest a corresponding multiple of CO2 tonnage.
With its sustainable power requirements exclusively supplied by train-generated sources that are without incremental cost, savings of 30 – 40 per cent per tonne of harvested CO2 can be realised from energy inputs alone.
This, along with other significant savings such as land, brings projected cost at scale down to less than $50 per tonne and makes the technology not only commercially viable but commercially attractive.
Professor Geoffrey Ozin from the University of Toronto and co-author of the study, said: “At these price points and with its tremendous capabilities, CO2Rail is likely to soon become the first megaton-scale, first gigaton-scale, and overall largest provider of direct air capture deployments in the world.
“Carbon-neutral in regular transportation and then significantly carbon-negative with ambient air DAC operations. A win-win in every respect and a ‘save humanity’ technology.”
The team is also working on a similar system that can remove the CO2 emissions from the exhaust of diesel-powered locomotives as are universally common in North America and other parts of the world. With the growth of sustainably-sourced rail electrification systems, this point-source capability on diesel lines would make rail the world’s first carbon-neutral mode of large-scale transportation.
The research entitled: “Rail-Based Direct Air Carbon Capture” is published in the Future Energy section of the journal Joule.
Media contact: Amy Huxtable, Media and PR Officer, University of Sheffield, mediateam@sheffield.ac.uk, 07725 213702
JOURNAL
Joule
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Rail-Based Direct Air Carbon Capture
ARTICLE PUBLICATION DATE
20-Jul-2022
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