Could this technology be the real thing?

Extracting carbon dioxide from the air is possible. But at what cost? The power of negative thinking
Jun 7th 2018

IN MAY some 250 scientists and policy types from around the world convened in Gothenburg, Sweden, to discuss a dirty secret of the three-year-old Paris climate agreement. Virtually all simulations which chart paths toward meeting that compact’s goal—to keep temperature rise “well below” 2°C relative to pre-industrial levels—assume not just a sharp reduction in actual emissions but also the removal of carbon dioxide from the atmosphere on a massive scale. One reason such “negative emissions” have been absent from climate discussions—the Swedish shindig being the first of its kind—is that no one has a good idea of how exactly to bring them about. The obvious solution is to plant lots of trees, to convert CO2 into wood. But this would mean foresting an area with a size somewhere between that of India and Canada. Alternative, engineered fixes have been dogged by potentially stratospheric costs, uncertain efficacy or both. No longer, reckons David Keith. Besides his day job as a climate expert at Harvard university, Dr Keith is a co-founder of Carbon Engineering, a nine-year-old firm that counts Bill Gates among its backers. Dr Keith and his colleagues argue in a paper they have just published in Joule that the CO2 removal technique they have been perfecting is no pipe dream—even if it does contain pipes aplenty.
Their process has four steps. First, air is channelled by fans onto a honeycombed plastic slab called a contactor, where CO2, which is acidic, reacts with aqueous potassium hydroxide, which is alkaline. The resulting solution of potassium carbonate is filtered and exposed to a slurry of calcium hydroxide. This produces potassium hydroxide, which is recycled back to the contactor, and pellets of calcium carbonate. These are whisked to the third receptacle, called a calciner. There the calcium carbonate is heated to 900°C to release pure carbon-dioxide gas ready for capture, and calcium oxide. Finally, the calcium oxide is piped to a “slaker”, where it is dissolved in water to form calcium hydroxide, which is reused in the second step. If that all sounds complicated, chemically speaking it is not. Nor is the idea new. A researcher called Klaus Lackner came up with the principles 20 years ago and Dr Keith patented his version in 2015. A pilot plant with a contactor three by five metres across and three metres deep has been running for three years. It extracts a tonne of carbon dioxide from the air per day. What sets Dr Keith’s latest paper apart from his earlier publications—and, indeed, those of other putative carbon-hoovers—is that it offers a hard-nosed estimate of the system’s cost and scalability. The results look encouraging. That is principally because each step in Dr Keith’s scheme is adapted from known industrial processes. The contactor was pinched from factory cooling towers. The pellet reactor came from water-treatment plants. The calciner was developed from metal-ore purification apparatus. And the slaker was adapted from pulp mills. The required tweaks were small enough to permit Carbon Engineering to procure the paraphernalia for the prototype plant from existing suppliers. Crucially, this also enabled the suppliers—and an independent engineering consultancy hired by Carbon Engineering—to estimate how much it would cost to build a fully fledged facility (envisaged in the picture above) capable of extracting between 100,000 and 1m tonnes of carbon dioxide a year. Factoring in operating costs and the cost of capital, the study concludes that Carbon Engineering’s system could capture a tonne of the greenhouse gas for between $94 and $232. That is well below the $600 per tonne suggested by authors of an influential American Physical Society report from 2011 that reviewed proposed carbon-dioxide-removal schemes. Admittedly, it is still much pricier than the $10 or so that a tonne of the gas is worth in emissions-trading schemes such as theEuropean Union’s. But it is of the order of the $100 or so that most climate economists think would eventually be needed to prompt the transition to the low-carbon economy implicit in the Paris agreement. And Dr Keith thinks the cost can be brought down further with a bit of tinkering. Carbon Engineering and its investors believe they can make money even before this happens. To start with, revenue would be generated by turning captured CO2 back into fuel (technology to do this already exists). Though that sounds thermodynamically bonkers, such fuel would, from a legal point of view, count as “zero carbon” because making and then using it involves no net release of CO2 into the atmosphere. Demand for zero-carbon liquid fuels looks poised to rise as climate-friendly places adopt low-carbon fuel standards. California did this in 2007 and the European Union followed in 2009. Such standards force distributors to keep the average carbon intensity of petrol below a certain threshold, and therefore to offset dirty fuels with clean ones—and none is cleaner than Carbon Engineering’s. California’s requirement, which is in effect a cap-and-trade scheme, translates to a price of $165 per tonne of carbon dioxide, making the company’s product competitive. Steve Oldham, the firm’s boss, therefore hopes to license know-how to fuel producers doing business in such jurisdictions. Mr Oldham says that ground should be broken on the first industrial-scale plant, which is to be built at an undisclosed location in America, before the end of the year. As both Dr Keith and Mr Oldham concede, recycling CO2 in this way means that Carbon Engineering’s current business model offers zero, rather than truly negative, emissions. But it gives the company breathing space to fine-tune its system and demonstrate its feasibility to investors. More Gothenburg-like gatherings may yet prompt governments to take negative emissions seriously. California is already considering subsidies for carbon-dioxide removal. As things stand, the cost of using Carbon Engineering’s kit to scrub 8bn-10bn tonnes of CO2 per year, as the climate models presuppose, would run to trillions of dollars. Then again, no one said guaranteeing civilisation’s survival was going to come cheap.

peanutz wrote: ↑ Whether trees do it or not is sort of a secondary concern...it's the affordable fuel part of the discovery that is supposed to be revolutionary.

nabiul wrote: ↑ It's not affordable and never will be; you cannot violate the second law of thermodynamics. Entropy will always increase and to make two barrels worth of fuel will always require more than two fuel barrels worth of energy to be put into the system.

Plants do it for free and burning wood is carbon neutral if you believe in that nonsense, if not believe in corn subsidies and biofuels.

JoeBlack23 wrote: ↑ Correct, but those "two fuel barrels worth of energy" don't have to come from burning fuels, they could come from renewables. This could close the gap where "the sun doesn't always shine" and "the wind doesn't always blow". You make the fuel while the sun is shining or the wind is blowing, and then use the fuel when they aren't.

We don't have land available the size of India (or bigger) to plant trees - unless you want to use a large chunk of agricultural land. Plus they grow slowly, and in the meantime we are still pumping out CO2 from oil we are digging out of the earth. At least with a solution like this we won't be adding new CO2, instead it becomes a closed system.

I don't think this could become "the solution", as I don't think there is "one" solution that can solve this. I see rather many strategies applied at the same time, this technology might be one of the bigger contributors. And yes, planting as many trees as we can could be one of the contributors.

nabiul wrote: ↑ It's not affordable and never will be; you cannot violate the second law of thermodynamics. Entropy will always increase and to make two barrels worth of fuel will always require more than two fuel barrels worth of energy to be put into the system.

Plants do it for free and burning wood is carbon neutral if you believe in that nonsense, if not believe in corn subsidies and biofuels.

smacd wrote: ↑ Only someone with their head in the sand doesn't believe that CO2 is costing us a fortune and will cost us far more in the future if we don't do something about it now.

nabiul wrote: ↑ It's not affordable and never will be; you cannot violate the second law of thermodynamics. Entropy will always increase and to make two barrels worth of fuel will always require more than two fuel barrels worth of energy to be put into the system.

Plants do it for free and burning wood is carbon neutral if you believe in that nonsense, if not believe in corn subsidies and biofuels.

cgall104 wrote: ↑ A bunch of university students were working on a machine to harvest CO2 from the atmosphere. They wanted it to be autonomous, cost efficient, and run on renewable energy.

Turns out that machine already exists, and nature has a patent: a tree.

cgall104 wrote: ↑ A bunch of university students were working on a machine to harvest CO2 from the atmosphere. They wanted it to be autonomous, cost efficient, and run on renewable energy.

Turns out that machine already exists, and nature has a patent: a tree.