A couple of weeks ago, the Globe and Mail reported on the B.C. company Carbon Engineering’s announcement that it had secured an additional CAD$68 million to commercialize its CO2 removal technology. This is a remarkable achievement for the Squamish, B.C. based firm.
The Globe article referenced a unit cost of less than $100 per tonne of captured carbon dioxide. I spend a lot of my time calculating the cost of GHG reductions from various projects and policies. The article got me very curious about the comparative cost and potential role of this type of technology in addressing the climate crisis. Last year, Carbon Engineering published a paper detailing their carbon capture technology. The technology is known as Direct Air Capture (DAC) and it can be used to extract CO2 directly from the atmosphere. DAC can be thought of as a cousin to the better-known class of technologies commonly known as Carbon Capture and Storage (CCS), which capture CO2 from a large point source of emissions such as a gas processing plant or a thermal power plant. Carbon Engineering has been working on DAC for nine years, and they have built and operated a pilot project in Squamish, B.C. that can extract one tonne of CO2 from the atmosphere per day. Other firms are also developing DAC, but Carbon Engineering has provided more detail on their process than any of their competitors.
Some thoughts on their paper and the technology:
- The process requires energy inputs. Capturing one metric tonne of atmospheric CO2 requires inputs of either 8.81 GJ of natural gas, or 5.25 GJ of natural gas and 366 kWh of electricity. Assuming the second approach, and 100% carbon-free electricity, the process extracts one tonne of atmospheric CO2 but results in an output of 1.3 tonnes of CO2 due to the additional emissions from natural gas combustion. These emissions are captured as part of the process.
- Their reported cost range is US$94 – 232 (CAD$125 – 309) per tonne of captured atmospheric CO2. However, this cost is only for the process to produce a stream of separated CO2. Reducing atmospheric CO2 levels requires pairing DAC with sequestration, which has additional costs. DAC can also be paired with other uses of CO2. Enhanced oil recovery is one of the more commonly discussed uses, but Carbon Engineering is exploring fuel production. Regardless, there are additional costs associated with finding a final home or use for the CO2.
- The lowest end of the cost range above assumes integration with a synthetic fuel production system. This has not yet been proven out. Without the integration of a synthetic fuel production system the lower-end cost estimate would be US$113 (CAD$150) per tonne CO2.
- While the paper provides a thorough cost estimate, it’s not clear if the cost range includes ancillary items such as land and property taxes. Their one tonne per day pilot facility sits on 0.5 hectares of land. It’s important for analysts and policy makers to understand the scope of items included in the cost per tonne in order to allow fair comparisons across technologies and projects. For example, we include space costs and property taxes in most of our evaluations of low-carbon energy systems.
- Carbon capture at major emitters, e.g., fossil fuel-fired generators, will be inherently simpler and more efficient because the density of CO2 in the flue gas stream is much higher than in the ambient air. However, one of the challenges of CCS is how to cost-effectively move CO2 from the emissions location to a storage reservoir (which basically requires replicating something like the natural gas grid, except the mass of CO2 is greater than the mass of fossil fuel that was originally burned). DAC may be a less efficient technology for carbon capture, but one of its advantages is that it can be deployed anywhere, so it can be sited directly on top of an appropriate storage reservoir.
Carbon Engineering is looking to develop an additional pilot facility for a synthetic fuel production process, which would (when paired with DAC) allow for the production of carbon-neutral liquid fuels. This would reduce the accumulation rate of carbon in the atmosphere. Alternatively, if paired with sequestration instead of fuel production, DAC achieves negative emissions and could help to decrease atmosphere levels of CO2 when emissions have stabilized.
I suspect there will be a role for this technology in tackling the climate crisis. Even if we eventually get emissions under control (still a big if), atmospheric levels of CO2 are still likely to overshoot safe levels. Reforestation will help, but given how much fossil carbon has been emitted, we will likely need technologies like this at some point to reduce greenhouse gases in the atmosphere back to safe levels.
But in the near-term, the most pressing issue is to stabilize and reduce current emissions. The production of carbon-neutral fuels will help, and I look forward to seeing the technical and economic results of Carbon Engineering’s pilot synthetic fuel facility. But based on my experience and reviews of other studies there are still a wide range of available measures to reduce GHG emissions that we have not yet implemented, which come at much lower total cost per tonne than DAC.
That said, in the long-run, there may well be a need for these capture technologies. If we get to the point where nearly all large point sources of emissions have been eliminated, and we are pursuing direct air capture to further reduce atmospheric CO2 levels (and perhaps deal with illegal or fugitive emissions), a major question remains: who will pay for sequestration?