This is a deeper look at the possible role of using existing train movements to help reduce air pollution using direct carbon capture science, through an exclusive interview with the involved scientists—with a few independent observations as to the execution challenges ahead.
What if rail systems around the world could be harnessed to help mitigate climate change and clean our air of CO2? It is a question that the founders of a U.S.-based startup, CO2Rail Company, have been pondering for several years. Direct Air Capture (DAC) technology for removing carbon dioxide from the air with special machines and compressing it for utilization or permanent geological sequestration, promises to reduce overall CO2 concentrations in the atmosphere and help mitigate global climate change. The IPCC has reported that deep net-negative CO2 mitigation is almost certainly necessary to stay within 2°C of warming. However, despite its promise, the process of carbon removal straight from the air can be energy- and land-intensive and often extremely expensive.
CO2Rail Company has assembled a multi-disciplinary team of scientists and engineers from MIT, Princeton, The University of Toronto and the University of Sheffield. The disciplines include business and public entities which have set their sights on designing a new carbon cleaning path using selected rail corridors with DAC technology that potentially use less energy and less land in their capture process.
Their plan is to operate DAC equipment within special railcars placed within already running scheduled trains. The capture cars would be used in regular service on either diesel or electrified rail lines. Their proposal was highlighted in a peer-reviewed paper entitled Rail-Based Direct Air Carbon Capture. It was also in the Future Energy section of the journal Joule released July 20, 2022.
Carbon Dioxide is the Culprit
The sponsors contend that society is well past reasonable debate on whether the climate is getting warmer and “if” excessive atmospheric CO2 concentrations play a deleterious role in the warming effects. Their hypothesis is that, as of 2020, multiple scientific research documentation shows that the global average temperature was near 1.2°C above pre-industrial norms. They also contend that elevated levels of atmospheric carbon dioxide as a result of anthropogenic activities have been the primary driver of this increase in temperature. Now, concentrations have risen from a maximum of 300 ppm in the pre-industrial era to nearly 420 ppm in 2021. Multiple parties are looking for remedial solutions.
One approach by The Intergovernmental Panel on Climate Change (IPCC) estimates that upwards of 1,000 gigatons of CO2 will need to be directly removed from the atmosphere (CDR) by the target year 2100 to stay within 2.0°C of warming. Their independent research suggests that their unique design for a railway operation capture plan might be a critical part of the solution. If true, then the U.S. Department of Energy’s recently launched national push to remove gigatons of carbon pollution from the air by 2050—called the “Carbon Negative Earthshot”—might see a logical direct railway mitigation role.
Before describing their proposed R&D approach, let’s pause and discuss the process of using direct air to capture atmospheric carbon.
What is Direct Air Carbon Capture?
First proposed by Lackner et al. in 1999, DAC systems are a form of carbon removal comprised of a plurality of chemical and mechanical devices that capture CO2 directly from the atmosphere. (Lackner, Ziock, & Grimes, 1999) Current technologies to capture CO2 from air employ liquid or solid adsorbents based on amines, oxides, hydroxides, carbons, zeolites, and metal organic frameworks. (Halliday & Hatton, 2021). No matter the material class, however, all require substantial amounts of energy to coax the captured CO2 from sorbent material and then process it for subsequent storage. It is a complex chemical process whereby after capture, additional energy is required to isolate, compress, and liquefy the carbon dioxide for efficient geological sequestration or commercial utilization.
In the case of Direct Air Carbon Capture and Storage (“DACCS), the CO2 would be permanently impounded in subsurface geologic formations where it remains trapped. Or it might set to react with present minerals to become carbonate rock. The visualization of the process is to change the carbon into one form of true carbon-negative mitigation. CO2Rail’s initial team has developed what it believes to be a novel way by integrating DAC with the very broad global network of rail routes.
Competition from Land-Based DAC Technology
At the current state of development, all known DAC deployments are land-based systems that rely on increases in temperature to release the captured CO2 from either a solid or liquid-based sorbent. These include companies such Climeworks (Switzerland), Global Thermostat (U.S.), and Carbon Engineering (Canada). The industry leader, Climeworks, currently makes use of geothermal or waste heat to provide much of the energy for its existing DAC deployments.
But these land-based systems face challenges. Some recent studies have estimated as much as 25% of global electrical generation capacity will need to be dedicated to land-based DAC deployments by 2100. (Evans, 2019) Furthermore, with a reported yearly capture capacity of 50 tons CO2 per typical land-based, solid-media DAC module unit, it will require the manufacture, operation, care and feeding of approximately 20 million of these machines per gigaton of captured CO2 or hundreds of millions to timely meet the IPCC’s recommendations (Climeworks AG, 2021).
Besides energy, there are also land issues that surround widespread DAC deployment. Stationary DAC operations at any meaningful scale will require large areas of land to build their equipment and even more to construct renewable sources of energy to power them.
In summary, the land based options face their own technology challenges and R&D timelines to demonstrate economic feasibility.
A Deeper Look at Proposed Rail DAC Operations
At this design concept stage, these DAC railcars would 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 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. 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 desorbed from the sorbent. Depending on the sorbent used, this desorption process might take many forms. At this concept stage, the proponents are focused upon deploying different sorbent packages of various temperatures, air pressure, and charge polarity. After the gaseous CO2 begins to flow from the sorbent media, it is collected from within the chamber, compressed, cooled by way of the heat exchanger that doubles as the grille within the front air intake, liquified in second-stage compression, then pumped to the rear of the car for short-term storage.
Depending upon the carbon collection route and the car collection efficiency, the initial design is that these DAC cars would be unloaded daily at crew change or fueling stops track wayside CO2 tanks. The adopted rail collection track network would then redirect the harvested CO2 to special locations for either permanent underground geological sequestration, or perhaps delivery to end-users as feedstock for the circular carbon economy. Their initial mechanical and electrical engineering approach is to try and train on-board resistance braking as part of the energy required for the carbon car capture process.
The two images below show the railcars with one top-mounted intake and one top-mounted vent. This is the design form specific of the Locomotive Emissions Mitigation (LEM) cars. The similar DAC car design would have two top-mounted intakes with extensive venting occurring out the bottom of the car through the battery compartment to provide concurrent battery array cooling capabilities. This also serves to reduce carbon-light, previously treated air from reentering the atmosphere when two or more DAC cars are coupled together. At 69 mph (111 km/h), each intake would be capable of supplying more 10,000 cubic meters/minute of air to the collection chamber.
Can Locomotive Dynamic Braking Be Utilized?
Since the 1950s, dynamic braking has been in common use in nearly all road locomotives. As many know, dynamic braking is an energy braking system that converts a diesel-electric locomotive’s forward momentum into electrical energy, turning the traction motors into generators. Currently, this energy is dissipated in the form of heat and discharged out of the top of the locomotive through resistor grids during dynamic braking application. In regenerative braking, dynamic braking energy is either returned to the power grid (AC catenary or DC third rail) on electrified rail systems, or stored in a battery.
This energy, suggests Eric Bachman of CO2Rail, should be captured, stored, and used for the direct air carbon productive purposes.
“For many decades, this enormous amount of sustainable energy has been completely wasted,” says Bachman. “On average, each complete braking maneuver 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 [diesel-electric-powered] 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.”
If this use of dynamic braking can be successfully integrated, the hypothesis is that this energy generated from regenerative braking is stored in a high-capacity 2,400-kWh battery array integrated into the undercarriage of the Rail DAC car as shown in Image 2. According to some in the engineering world, this might be more difficult than the initial design assumptions. This is why further R&D is needed. Another theory is that certain specially configured CO2Rail DAC cars can remove the CO2 emissions from the exhaust of diesel locomotives with only minor exhaust routing modifications required thereof as shown in Image 3.
How Productive Might CO2 Harvesting Become?
At the system scale, the designers see short-term (1-5 years) annual car productivity at 3,000 tons/year. That’s the initial commercial design expectation in 2022. Out to 5 to 10 years, they believe annual car productivity could increase to levels at or near 6,000 tons/year, with 7,500 tons/year being achievable thereafter. Moreover, since trains are capable of hosting multiple CO2Rail cars rather than just one, they believe that future train consists might harvest a corresponding multiple of CO2 tonnage beyond these first-outlook pro forma projections. Their macro scale strategic vision sees a potential to reach annual global productivity of 0.45 gigatons by 2030, 2.9 gigatons by 2050.
The Joule report covers these alternatives in further detail, for readers interested in knowing more about their assumptions.
CO2Rail’s initial business case assumes that, with what it sees as sustainable on-board train power requirements exclusively supplied by train-generated sources, there could be significant cost savings in the range of perhaps 30% to 40% per ton of harvested CO2. That along with other significant savings such as land, in theory might bring the projected cost at scale down to less than $50 per ton. If that can be done, then this train-direct capture technology could indeed be commercially attractive, particularly if new Biden Administration federal government programs offset some of the capture costs with new R&D rollout funding.
On the demand side, there is an ever-growing list of private companies (Microsoft, Berkshire Hathaway, Stripe, etc.) that have taken a net-zero pledge and that put out annual orders for sequestered CO2 may elect to participate in this service, with the advantage of a recognized federally sequestered CO2 provision under the newly passed 2022 U.S. government so-called 45Q Program, which provides more-predictable initial execution funding. While the 2021 credit currently was around only $50 per sequestered ton, now the numbers are more like $8 to perhaps about $130 a ton. It’s time to test this financial feasibility.
Four Rail-Centric DAC Markets?
The North American diesel-electric-operated geography market has three different economic sectors. One is freight. The other two are commuter and intercity passenger rail networks. The fourth is the international, mostly catenary-electrified markets across Europe and Asia, both passenger and freight. Each market might well have a different pro forma commercial financial return and indeed a different societal economic cost/benefit outcome.
The CO2Rail team argues 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 infrastructure and energy already exist,” says CO2Rail’s Geoffrey Ozin. “That’s the bottom line. All you need to do is take advantage of what is already available.”
With rail being three to five times more fuel-efficient than truck, increased rail utilization and greater CO2Rail deployments will have a positive impact beyond the carbon it removes from the atmosphere. “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,” says Bachman. By increasing rail utilization, you increase the efficiency of the entire transportation system. Additionally, you increase CO2Rail’s ability to remove CO2 from the air because there would be more trains to which DAC cars can be added.”
The potential impact of this technology was recently further energized when European transport organizations announced earlier this year that they are committed to tripling high-speed rail use by 2050 to curb CO2-heavy air travel.
The CO2Rail DAC solution is not yet ready for prime time. There are many steps ahead to fully develop this as a commercial approach. The design and building of the railcar represent a challenge and a timeline in itself. The practical next steps of taking the concept plan off of the paper copy and spreadsheets into molded metal are needed. As of now, there is of yet no prototype equipment ready to test in real-world conditions.
However, the CO2Rail team anticipates beginning the first prototype builds in early 2023. Their initial idea is that the first units will be built from retired or surplus existing tank cars. When complete, these prototype cars would require testing under normal operating conditions. The tests would enable an AAR or an FRA design recertification.
One likely approach is testing of a first prototype car at the FRA’s rail test facility in Pueblo, Colo. Next would come redesign and changes in the manufacturing process and components to have a low cost and high service reliability to build to final design. Thereafter, car construction would need to ramp up, with selected service locomotives upgraded to provide the desired electrical connectivity. Separately, there would be negotiations with both the commercial private railroad freight carriers and some of the passenger services as to rates and targeted train operations. As you read this report in the summer of 2022, it might be prudent to assume a three-year introduction timeline of these CO2Rail DAC cars at any meaningful scale. This is not going to happen overnight.
The overall economic assumption is that participating railroad operating companies would be compensated for their costs. There may be a tariff, or a series of contract service terms negotiated at a future date as operational cars are built and tested—and before the first practical operating service begins. Based upon the intelligence behind the initial design concept that the CO2Rail team shared with me over the past half-year, I’m optimistic. These are my strategic closing observations. This type of environmental application is what strategic R&D railroaders ought to be examining.
Here are a few inter-agency friction points ahead for these environmental cleanup entrepreneurs:
- Are the various federal oversight and financing source agencies available for an integrated testing and deployment?
- Is there a legitimate FRA RT&D participation role? Or is FRA only going to cover safety testing of the carbon-capture cars and their locomotive hook-ups?
- Can EPA or other federal agencies readily utilize the FRA-sponsored testing facilities to demonstrate the commercial functionality of this tech design?
- What’s the participatory R&D role for the private car building sector?
- Are the Class I rail carriers simply the hauling agent?
- How soon before we collectively know the terms for federal grant testing?
- Where is that cooperative PPP partnering leadership coming from to piece of this all together?
- The only certainty is that there is an opportunity for a carbon remedial market for the railways. And always some risk. Who is going step up first from our rail industry? Why? And how?
That’s probably the next story.
The Multi-Disciplinary International Team:
- Eric Bachman, CO2Rail
- Alexandra Tavasoli, Department of Chemistry, University of Toronto; Department of Chemical Engineering, Massachusetts Institute of Technology
- T. Alan Hatton, Department of Chemical Engineering, Massachusetts Institute of Technology
- Christos T. Maravelias, Andlinger Center for Energy and the Environment, Princeton University
- Erik Haites, Margaree Consultants Inc.
- Peter Styring, Department of Chemical and Biological Engineering, University of Sheffield
- Alán Aspuru-Guzik, Department of Chemistry, University of Toronto, Vector Institute for Artificial Intelligence
- Jeffrey MacIntosh, Faculty of Law, University of Toronto
- Geoffrey Ozin, Department of Chemistry, University of Toronto
Bachman, E., Tavasoli, A., Hatton, T. A., Maravelias, C., Haites, E., Styring, P., Ozin, G. (2022, July 20). Rail-Based Direct Air Carbon Capture. Joule, Volume: 6 (Issue: 7), Page: 1368-1381. doi: https://doi.org/10.1016/j.joule.2022.06.025
Climeworks AG. (2021). Direct Air Capture to Help Reverse Climate Change. Retrieved 2021, from Climeworks AG: https://climeworks.com/co2-removal
Evans, S. (2019, July 22). Negative Emissions – Direct CO2 Capture Machines Could Use a Quarter of Global Energy in 2100. Carbon Brief. Retrieved 2021, from https://www.carbonbrief.org/direct-co2-capture-machines-could-use-quarter-global-energy-in-2100
Halliday, C., & Hatton, T. (2021). Sorbents for the Capture of CO2 and Other Acid Gases: A Review. IndU.S.trial & Engineering Chemistry Research, 60(26), 9313-9346. doi: DOI:10.1021/acs.iecr.1c00597
Lackner, K., Ziock, H.-J., & Grimes, P. (1999). Carbon Dioxide Extraction from Air: Is It An Option? U.S. Department of Energy – Los Alamos National Lab.
Independent railway economist and Railway Age Contributing Editor Jim Blaze has been in the railroad industry for more than 40 years. Trained in logistics, he served seven years with the Illinois DOT as a Chicago long-range freight planner and almost two years with the USRA technical staff in Washington, D.C. Jim then spent 21 years with Conrail in cross-functional strategic roles from branch line economics to mergers, IT, logistics, and corporate change. He followed this with 20 years of international consulting at rail engineering firm Zeta-Tech Associated. Jim is a Magna Cum Laude Graduate of St Anselm’s College with a master’s degree from the University of Chicago. Married with six children, he lives outside of Philadelphia. “This column reflects my continued passion for the future of railroading as a competitive industry,” says Jim. “Only by occasionally challenging our institutions can we probe for better quality and performance. My opinions are my own, independent of Railway Age. As always, contrary business opinions are welcome.”