When it becomes operational in September, Carbon Engineering's prototype direct air capture plant will begin scrubbing a tonne of CO2 from the air every year. It is a small start, and a somewhat larger plant in Texas is in the works, but this is the typical scale of a DAC plant today. It's very powerful tool to have. Most carbon capture focuses on cleaning emissions at the source: scrubbers and filters on smokestacks that prevent harmful gases reaching the atmosphere.
But this is impractical for small, numerous point sources like the planet's billion or so automobiles. Nor can it address the CO2 that is already in the air. That's where direct air capture comes in. If the world wants to avoid catastrophic climate change, switching to a carbon neutral society is not enough. Right now, "we're removing virtually none. We're having to scale from zero. Carbon Engineering's plant in Squamish is designed as a testbed for different technologies.
But the firm is drawing up blueprints for a much larger plant in the oil fields of west Texas, which would fix 1 million tonnes of CO2 annually. Yet he admits the scale of the task ahead is dizzying. It's not going to happen overnight. The science of direct air capture is straightforward. There are several ways to do it, but the one that Carbon Engineering's system uses fans to draw air containing 0.
The potash absorbs CO2 from the air, after which the liquid is piped to a second chamber and mixed with calcium hydroxide builder's lime. The lime seizes hold of the dissolved CO2, producing small flakes of limestone. These limestone flakes are sieved off and heated in a third chamber, called a calciner, until they decompose, giving off pure CO2, which is captured and stored. At each stage, the leftover chemical residues are recycled back in the process, forming a closed reaction that repeats endlessly with no waste materials.
With global carbon emissions continuing to rise , the climate target of 1. The IPCC does present some climate-stabilising models that don't rely on direct air capture, but Gambhir says these are "extremely ambitious" in their assumptions about advances in energy efficiency and people's willingness to change their behaviour. DAC is far from the only way carbon can be taken out of the atmosphere.
Carbon can be removed naturally through land use changes such as restoring peatland , or most popularly, planting forests. But this is slow and would require huge tracts of valuable land — foresting an area the size of the United States, by some estimates , and driving up food prices five-fold in the process. And in the case of trees, the carbon removal effect is limited, as they will eventually die and release their stored carbon, unless they can be felled and burned in a closed system.
The scale of the challenge for carbon removal using technologies like DAC, rather than plants, is no less gargantuan. Gambhir's paper calculates that simply keeping pace with global CO2 emissions — currently 36 gigatonnes per year — would mean building in the region of 30, large-scale DAC plants, more than three for every coal-fired power station operating in the world today.
Climeworks' facility near Zurich, Switzerland, sells the CO2 it captures to nearby vegetable growers for their greenhouses Credit: Alamy. Every one of those facilities would need to be stocked with solvent to absorb CO2. Supplying a fleet of DAC plants big enough to capture 10 gigatonnes of CO2 every year will require around four million tonnes of potassium hydroxide, the entire annual global supply of this chemical one and a half times over.
There he studied existing literature on capturing carbon and made a key decision. Scientists developing techniques to capture CO2 have thus far sought to work at high concentrations of the gas.
But Eisenberger and Chichilnisky focused on another term in those equations: temperature. It would use relatively cheap steam for two purposes. The steam would heat the surface, driving the CO2 off the amines to be collected, while also blowing CO2 away from the surface. Even if air capture were to someday prove profitable, whether it should be scaled up is another question. The upshot? With less heat-management infrastructure than what is required with amines in the smokestacks of power plants, the design of a scrubber could be simpler and therefore cheaper.
The startup has partnered with a Carson City, Nevada-based company called Algae Systems to make biofuels using carbon dioxide and algae. Meanwhile the demand is rising for carbon dioxide to inject into depleted oil wells, a technique known as enhanced oil recovery.
One study estimates that the application could require as much as 3 billion tons of carbon dioxide annually by , a nearly tenfold increase over the market. That still represents a drop in the bucket in terms of the amounts needed to reduce or even stabilize the concentration of CO2 in the atmosphere. But Eisenberger says there are really no alternatives to air capture.
About a quarter mile from the entrance, a foot-high tower of fans, steel, and silver tubes comes into view. This is the Global Thermostat demonstration plant. Eisenberger gazes at the quiet scene around the tower, which includes a tall tree.
But then he corrects himself. At Exxon in the s he led work on solar energy, then served as director of Lamont-Doherty, the geosciences lab at Columbia. After a year or so of preparation, he and Chichilnisky reached out to billionaire Edgar Bronfman Jr.
That largesse has allowed the company to build its demonstration despite basically no federal support for air capture research. The rectangular tower uses fans to draw air in over alternating foot-wide surfaces known as contactors. Each is comprised of ceramic cubes embedded with the amine sorbent. The tower raises one contactor as another is lowered. For now that gas is simply vented, but depending on the customer it could be injected into the ground, shipped by pipe, or transferred to a chemical plant for industrial use.
A key challenge facing the company is the ruggedness of the amine sorbent surfaces. They tend to decay rapidly when oxidized, and frequently replacing the sorbents could make the process much less cost-effective than Eisenberger projects. Adding to the skepticism over the feasibility of air capture is that there are other, cheaper ways to create the so-called negative emissions. A more practical way to do it, Schrag says, would involve deriving fuels from biomass—which removes CO2 from the atmosphere as it grows.
Additionally, it is energy intensive as the flue gas must be reheated after coming into contact with water vapour in the wet scrubber for the gas to be buoyant enough to exit through the smokestacks. The use of scrubbers to clean flue gases before they leave the smokestacks has a drastic, beneficial impact on the environment. By collecting particulate matter and acidic gases, the amount of different pollutants that can exit the plant and be introduced into the environment is dramatically reduced.
This increases air quality and lowers the health risks for people who could come into contact with the different pollutants.
Although there are many positive side-effects of using scrubbers, there are still waste products from the scrubbing process whether wet or dry scrubbing is used. These by-products must be disposed of safely since they can rarely be reused because of their chemical content. This is one reason that dry scrubbing has become more common, as the sheer volume of the waste products is less significant than the waste from a wet scrubbing operation. Fossil Fuels. Nuclear Fuels. Acid Rain.
0コメント