Train cars could capture carbon directly from the air

Researchers from the US based train start-up CO₂Rail, in partnership with the University of Toronto, have published a paper in the Joule journal, demonstrating how modified train cars could be fitted with direct air capture (DAC) technology machines. These can remove CO₂ from the air and compress it for utilization or permanent geological sequestration, promising to reduce overall CO₂ concentrations in the atmosphere and help mitigate global climate change.

1. How does it work?

Currently, the process of carbon removal straight from the air can be energy and land intensive, as well as expensive. “CO₂Rail set their sights on designing DAC technology that uses less energy, less land and at a cost that the world could afford”, reads a press release from the company.

It’s a huge problem because almost everybody wants to fix the climate crisis, but few are happy to have it done in their proverbial ‘backyard’. CO₂Rail does not require special zoning, surveys, or building permits and would be transient and generally unseen by the public.

Geoffrey Ozin, chemist and Albert Einstein World Award of Science medal recipient at The University of Toronto

These DAC rail cars work by using large intakes that extend up into the slipstream of the moving train to move ambient air into the large cylindrical CO₂ collection chamber, thus eliminating 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 crew change or fuelling stops into normal CO₂ rail tank cars for direct transportation into the circular carbon economy as value-added feedstock or to nearby geological sequestration sites.

The authors also argue that rail-based DAC becomes an even more attractive climate solution because much of the required infrastructure is already in place and the energy is there, just waiting to be utilized. The potential impact of this technology was also recently energized when European transport organizations announced earlier this month that they are committed to tripling high-speed rail use by 2050 to curb CO₂-heavy air travel. “We could get a positive feedback loop where the increased utilization of rail not only reduces transportation emissions but also increases CO₂ capture potential which then encourages even more utilization of rail,” said Bachman.

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. I think this technology will sway many shippers towards rail.

E. Bachman, author Rail-based direct air carbon capture

The team says that each DAC car can harvest about 6,000 metric tons of CO₂ from the air per year and more as the technology develops. Since trains are capable of hosting multiple CO₂Rail cars, each train will harvest a corresponding multiple of CO₂ tonnage.

2. Regenerative braking system

Each of these modified cars is 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 entire train’s forward momentum into electrical energy in much the same way as an electric vehicle.

This energy is currently dissipated on trains in the form of heat, but author E. Bachman says it should be captured, stored and used for productive purposes. “For many decades, this enormous amount of sustainable energy has been completely wasted.”

“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”, Bachman added.

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.

Geoffrey Ozin, chemist and Albert Einstein World Award of Science medal recipient at The University of Toronto

With its sustainable power requirements exclusively supplied by train-generated sources that are without incremental cost, savings of 30 – 40% per tonne of harvested CO₂ can be realized 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”, Bachman said. “These kinds of numbers are unheard of in direct air capture,” added Ozin.