Researchers say there is climate-friendly potential in the movement of air during travel and the energy released when trains brake. They present a concept for capturing carbon dioxide from the atmosphere using special wagons during regular train operations. The greenhouse gas is transferred to a liquid medium and can then be used or disposed of. In contrast to previous concepts of active CO2 binding, the wagon system could work much more cost-effectively, energy-efficiently and space-savingly, say the scientists.
Lower carbon dioxide emissions are the major goal in the fight against climate change. But there are also approaches to actively removing the greenhouse gas from the atmosphere: the technical term is Direct Air Capture (DAC). Using technical and chemical processes, CO2 is captured from the air, compressed and then stored or used as a raw material. But the previous concepts have a catch: DAC systems are expensive and require quite a lot of electrical energy. Because, among other things, large fans have to be operated in order to blow the air into the corresponding units for effective CO2 binding.
In addition, the systems require a relatively large amount of space, which is known to be scarce, especially in densely populated regions. “A lot of people want to help solve the climate crisis, but nobody wants to do it in their backyard,” says Geoffrey Ozin of the University of Toronto. Creative implementation strategies are therefore required to lower the hurdles for the commercial applicability of DAC systems, say Ozin and his colleagues. This gave rise to the idea of using the global railway network for an innovative process to capture carbon dioxide from the atmosphere. To implement this concept, the start-up company “CO2Rail Company” was founded in the USA, which is working together with international scientists on the development of the system.
Clever use of rail transport
As the team explains, the highlight of their concept is that effects are used that occur in rail traffic anyway. Only special DAC wagons have to be added to the trains, the construction and function of which the researchers describe in their publication. The constructions are equipped with large openings that catch the wind of the train. The air is thus conveyed into large cylindrical CO2 collection chambers. This aspect of the system means that no energy-intensive intake systems are required, as are required in stationary DAC systems, the scientists explain.
In the collection chamber, the air then runs through chemical processes in certain absorber materials, which lead to the binding of carbon dioxide. With a significantly reduced CO2 content, the air then flows out of the rear of the DAC wagon back into the atmosphere. The captured CO2 is collected in the system, concentrated and stored in a liquid tank, the researchers explain. If the train stops for a long time, the collected carbon dioxide can then be emptied. It can then be used as a raw material or transported to nearby landfills.
Apart from saving the ventilation system, all other functions of the system can be operated exclusively without an external power supply, say the researchers. In addition to solar panels, the DAC wagons could be supplied with the energy that is released when trains brake frequently. With certain technical upgrades, this source can be tapped to generate electricity. “Usually that energy is wasted,” says Eric Bachman, of the CO2Rail Company. “However, each full braking maneuver generates enough energy to power 20 average homes for a day, so we’re not talking about a trivial amount of energy.”
Potential for climate protection
This energy could be used to help mitigate climate change, say the scientists: “Capturing carbon dioxide from the environment is becoming an urgent need to mitigate the worst effects of climate change,” says Peter Styring of the University of Sheffield. “This innovative technology can now use synergies that result from integration into the global rail network,” the researcher sums up.
Even taking into account the increased load that locomotives have to pull through the integrated DAC cars, there is a major advantage over stationary DAC systems, say the researchers. According to their calculations, each DAC car could remove around 6,000 tons of carbon dioxide from the air per year. Since trains can transport several of these units in passenger or freight transport, the contribution to climate protection can be increased accordingly. The bottom line is that the concept has considerable potential, the team is convinced.
“Probable costs at scale are less than $50 per tonne of CO2, making the technology not only feasible but also economically attractive,” says Bachman. Certainly many people would also welcome the effort: “Imagine getting on a train, seeing the CO2Rail carriages and knowing that your journey is actually helping to mitigate climate change,” says Bachman. So it will be interesting to see how the concept will develop.
Source: Cell Press, University of Sheffield, Article: Joule, doi: 10.1016/j.joule.2022.06.025