Pollution often earns a bad reputation: It darkens the skies, is acidifying the oceans and is warming the atmosphere. It is one of the inescapable tragedies of the industrial revolution that will only be compounded by the United States leaving the Paris Agreement. Yet the night is always darkest before the dawn. Today four startup companies are pioneering the extraction of industrial CO2 pollution from the atmosphere. Their goal is to turn carbon into gold by distilling it down into a useful product.
1. Carbon Engineering
One of the companies is Carbon Engineering, a Canadian company practising a century old process of capturing carbon in solution. The process begins with the induction of ambient air into an air contactor. Its job is to quickly mix the CO2 with potassium hydroxide. The hydroxide reacts with the CO2 to become potassium carbonate, which is a useful industrial chemical in itself.
The chemical is then pumped into a pellet reactor, where it reacts with calcium hydroxide to produce calcium carbonate and new potassium hydroxide. The CO2 can then be extracted by heating the calcium carbonate. This is done inside a fluid bed calciner, which heats the carbonate to 900 degrees centigrade. The carbonate decomposes in the heat back into calcium oxide and CO2. The calcium oxide is then mixed with water and transformed back into calcium hydroxide for the next cycle. The extracted CO2 is pure commercial quality ready for sale.
2. CO2 Solutions
CO2 Solutions is choosing a different approach, using a thin film of solvent flowing down a smokestack to absorb CO2. They claim that up to 90% of carbon dioxide can be captured using this method. The hot flue gas is first cooled by a blower, which also removes unwanted moisture. The cooled gas is then routed to the absorption tower where a lean solvent of aqueous carbonate, bicarbonate, and a catalyst mix with the gas before emission. The CO2 rich solvent is then washed with hot water at about 85 degrees centigrade. The hot water also evaporates the CO2 rich solvent, raising it to the top of the stripper column. The gaseous water CO2 mixture is then separated and condensed, with the water returned to a receiver tank for reuse. The CO2 is captured in a vacuum blower and the recovery is complete.
An unnamed source within CO2 Solutions said that the up to 90% of carbon dioxide can be recovered from the flue gas using this process, at a cost of $28 per tonne of CO2. The final product is of 99.95% purity and can be recycled in a number of ways depending on the needs of the customer. Carbon dioxide is widely used in chemical manufacturing, oil extraction, and other industries. The source also said that their system is 80% more efficient than amine filter systems, without using any toxic chemicals. The company is presently designing its first commercial plant with the capacity to capture 30 tonnes of carbon per day. They plan to capture much more when the technology matures.
Climeworks is embracing an all around innovative method of capturing CO2 directly from the atmosphere, no smokestack required. Their technology is ripper in that it is solvent-free and does not run in a continuous cycle. The technology is also substantially simpler than the previously mentioned systems. It works by drawing ambient air through a porous granulated filter doped with amines. Amines are nitrogen compounds related to ammonia, but with a lone unbounded pair. The unbounded pair bonds with the captured CO2. Once the filter is saturated, the device is closed and heated to 100 degrees centigrade. The heat breaks the amine bond, releasing the CO2 for reuse.
4. Global Thermostat
Global Thermostat is also pursuing a similar approach of trapping CO2 in amines. In their system, amine sorbents are coated onto filters. The filters can soak up the CO2 directly from the atmosphere, but smokestacks are fine. Once the filter is soaked, it is heated up and the carbon dioxide is extracted.
But is large-scale CO2 capture and storage actually viable?
Climeworks, Global Thermostat, and Carbon Engineering did not respond to requests for comment. However, insights into their performance and engineering can be obtained from research at the Centre for Innovation In Carbon Capture and Storage at the Heriot-Watt University in the UK.
Recovering carbon dioxide from smokestacks is a very energy intensive process, potentially raising electricity costs by 70%. This is a consequence of the flue gas chemistry, the carbon dioxide levels in the gases are low. No more than 14% of coal smoke is carbon dioxide. It is even less at 4% for gas fired plants. Carbon recovery operations must reach concentrations of 95.5% for the product to be effectively transported and stored. Despite this, production rates as high as 800 tonnes of carbon dioxide per day have been achieved. Carbon Engineering’s decision to extract CO2 directly from the atmosphere should be very energy intensive, as air is only 0.04% carbon dioxide.
It should be expected that Climeworks and Global Thermostat’s technique of using amine filters comes with its own set of problems. Amines are very efficient at absorbing carbon dioxide, with rates exceeding 90%. Their performance is very dependent on CO2 concentrations, and significantly high temperatures are needed to extract the carbon dioxide. The environmental pollution caused by the degradation of amines is not known, but they have a reputation for being toxic and corrosive.
Another problem inherent to all carbon capture technologies is the disposal of the end product. Any profitable system would need to transport CO2 over long distances for industrial use, and pipelines are the most efficient option. They are also very expensive and sensitive to impurities in the CO2. Even small amounts of water contamination will produce corrosive carbonic acid.
A clear need. An unclear future.
Carbon dioxide is an important industrial chemical. It’s used in a number of processes, from food to ammonia production. Paradoxically, the deep well injection of carbon dioxide is very effective in oil drilling. Unfortunately, many barriers impede large-scale capitalisation of CO2 capture technology. The International Energy Agency has said that there is no sufficiently large market incentive or penalty for producers to adopt carbon capture technology. Another concern is the unresolved legal liabilities of transporting and permanently storing carbon dioxide geologically. Most financially viable carbon capture projects are related to oil recovery, which have limited storage capacity.
In the end, any meaningful reduction in CO2 pollution will be a composite endeavour of higher efficiency, cleaner fuels, renewable energy, and carbon capture technology. Much of architecture still needs to be developed and is dependent on the fuel source. Scrubbing smokestack flue gas is energy intensive. Amine filters are very efficient, but the environmental consequences of large-scale amine use are unknown. The transport and long term storage of CO2 still needs to be solved.