Machines that suck CO₂ out of the air may be cheaper than we thought | Techilink

If you spill a drink, don’t say, “Oh well, all we can do is spill fewer drinks in the future.” You grab a towel. So there is also a natural appeal to the idea that we need to develop a towel that contains CO . can delete₂ from the atmosphere. That’s not as easy as getting one from a Home Goods store, though, and cost estimates haven’t led to optimism for most methods of doing so.

Reforestation is obvious, but the potential impact is probably smaller than you think. Other biological schemes may include growing biofuels to burn in power plants that capture emissions and store them underground. We’ve also recently seen some working pilot projects that look like a reverse power plant: they suck in air and harvest concentrated CO₂ready for storage.

One of those plants, an hour north of Vancouver, British Columbia, is the brainchild of a company called Carbon Engineering. One of the founders of Carbon Engineering is David Keith of Harvard, a researcher studying these and other conceivable methods of “geoengineering” our planet’s climate. This week the Carbon Engineering team published a full design review, creating the first cost analysis of a working carbon capture plant.

Carbon Engineering’s pilot plant and another pilot plant built by Climeworks in Switzerland disagree on the substance used to capture CO₂ of the air. Climeworks chose solid grains of amine, while Carbon Engineering uses a water-based solution of potassium hydroxide.

Bicycle parts

In their paper, the researchers explain their design choices. Although their final task is clearly different, they were able to adapt the existing machines for each step in the process. By being a little creative and optimizing components, they were able to cut costs significantly from previous estimates. All this has been worked out down to the last detail.

The process begins with what is essentially a cooling tower, where a fan draws air in through a sort of filter through which a continuous stream of water drips. But instead of cooling the water, the goal here is to bring air into contact with the potassium dissolved in the water, which leaves its hydroxide partner to grab CO2 molecules.₂. The team designed a different geometry for the parts through which the water drips to maximize the chemical reaction, but otherwise this machine is essentially standard.

The formed potassium carbonate ends up in a so-called “pellet reactor”, which is more often used for special water treatment systems. The solution flows upward through small spheres of calcium carbonate, leaving them in suspension. Add a little calcium hydroxide and the unfaithful potassium trading partners again. The calcium carbonate that forms causes the grains to grow until they are large enough to sink to the bottom despite the current. Potassium hydroxide flows out the other side, ready to be sent back to the first stage and another CO. to grab₂ dance partner.

The enlarged calcium carbonate pellets are now sent to the third and final stage: heating which separates them into pure CO₂ gas and calcium hydroxide that can go back to phase two. The heat comes from a natural gas furnace that produces steam. The steam travels through loops that efficiently dump heat into the calcium carbonate before reaching a generator turbine that powers the plant.

I know what you’re thinking: they burn fossil fuels to produce CO . to catch₂? While it is possible to redesign this to run fully electrically, in this configuration the CO₂ emissions from burning natural gas are also captured, so from a climate point of view this is not self-destructing.

Carbon neutral fuels

At this point, the pure CO₂ could be compressed into a pipeline and sent to a facility that pumps it underground for storage, reducing its amount in the atmosphere. But Carbon Engineering also has other ideas. If you combine this with hydrogen gas split from water, you can synthesize conventional fuels.

Fossil fuels are made from carbon taken from the atmosphere by plants millions of years ago and slowly boiled deep underground — carbon that we return to the atmosphere when fuels are burned. If you take your carbon out of the atmosphere today and put it back in tomorrow, you have no effect on the concentration of greenhouse gas. It is the industrial equivalent of growing biodiesel. For transport that resists electrification, especially air travel, that could be one way to eliminate greenhouse gas emissions.

Unless you want to build your own hobbyist carbon capture plant, the most important thing here is probably cost estimation. While this pilot plant currently only contains about 200 tons of CO. can catch₂ per year, Carbon Engineering’s estimate is based on a larger “commercial” plant design that could handle about 1 million tons per year – equivalent to the emissions of about 200,000 American cars. Scaling up is easy for the modular components (just stack them), but a few pieces would be more cost effective if they were bigger.

The end result is a cost of $94 to $232 per ton of CO₂ caught by a plant of that size. Previous estimates for catch plants have been everywhere, but are generally much higher than that. For example, a large 2011 report estimated that a plant like this would cost at least $550 per ton.

By comparison, British Columbia’s emissions tax is currently USD 35 per tonne of CO₂, rising to CAN$50 in 2021. That is generally the range of existing carbon prices, although there have certainly been arguments for higher numbers. If a carbon capture plant could get below $100 a ton — and the folks at Carbon Engineering certainly don’t think they’re done cutting costs — it could be debating other plausibly economically viable countervailing technologies. emissions.

Of course, not spilling a drink is still cheaper than buying a towel to clean it up.

Open access on Joules2018. DOI: 10.116/j.joule.2018.05.006 (About DOIs).