Exploring the Prospects and Impact of Carbon Capture Tech
As the climate crisis becomes increasingly dire and talk of what can be done picks up throughout politics and industry, the terms “carbon capture” and “carbon sequestration” have begun appearing more and more.
Both refer to a means of greenhouse gas reduction, a potential piece of the puzzle of at least slowing disastrous climate effects and meeting the objectives laid out by the United Nations Framework Convention on Climate Change. Along with improving energy efficiency and increasing the use of non–carbon energy, carbon capture is likely to play a large role in the stabilization of greenhouse gas concentrations within the atmosphere to prevent dangerous interference with Earth’s climate system.
There are two main types of carbon capture. First, capture at a source such as a power plant or industrial process, followed by storage in non–atmospheric reservoirs. Projects like MIT’s Carbon Capture and Sequestration Technologies Program, which ran until 2016, have sought to do exactly that—store CO2 in places like saltwater aquifers deep beneath the sea floor, taking advantage of existing offshore infrastructure in a method found to be generally safe and permanent.
This type of carbon sequestration also seeks out ever more advanced methods of capture, as current relevant technologies require high operating costs and are quite energy intensive, requiring high temperatures and specialized solvents.
More sustainable methods must be in development, such as an electrochemical device recently developed at the University of Illinois Chicago that provides ultrafast continuous capture.
This system could be made large enough to capture CO2 directly from a smokestack exhaust and because it utilizes electrodialysis, it is an efficient and relatively inexpensive technology.
This and other technologies in a new generation of carbon dioxide traps—generally amines that capture the gas, then are reused once the CO2 is stripped and stored—could eventually make carbon capture practical on a variety of scales, from personal to industrial.
Additionally, a company known as Carbfix, with operations in Iceland and throughout eastern Europe, captures carbon from industrial partners and other sources and mineralizes it in stable deposits. Trees, vegetation, and rocks are a natural form of carbon drawdown from the atmosphere, and Carbfix imitates and accelerates the natural process by which carbon dioxide is dissolved in water and interacts with reactive rock formations like basalts to form stable minerals—permanent and safe carbon sinks.
Yet preventing CO2 from escaping into the atmosphere whenever possible is not enough and must work in tandem with the second mode of carbon capture: the removal of carbon in the atmosphere and subsequent sequestration.
Known as direct–air capture (or DAC), these systems do not need to be attached to an emissions source to be functional. One form this can take is that of enormous facilities run by leading DAC companies, such as Climeworks, Carbon Engineering, and Global Thermostat. Together, these companies run 18 plants of varying sizes, sequestering about half of their captured carbon and selling the other half for use in a variety of products.
Climeworks has been developing carbon removal and sequestration technologies for 13 years. Recently, the company announced the opening of a second commercial–sized plant in late June and plans to capture and store millions of tons of carbon dioxide per year by 2030.
Currently, Climeworks’ facilities capture CO2 from the ambient air and store it in basalt rock, partnering with Carbfix to do so. The company’s new plant, when fully functional, will capture and store 36,000 metric tons per year and will join a smaller factory that has the capacity to remove 4,000 tons per year. Yet this is a small fraction of total global yearly emissions, which hit a record high of 36.3 billion metric tons in 2021.
As DAC systems gain momentum, Climeworks and other operators in the industry are ramping up operations.
Global Thermostat, a company that specializes in DAC in the U.S., has been operating since 2010 to develop DAC technologies and power the growing circular carbon economy. Its eventual goal is the development of “the least resource intensive and lowest cost solution to resolve the climate threat.”
The Global Thermostat DAC solution works by processing air through standard industrial fans into a honeycomb contactor panel that selectively traps CO2. It can then be released by steam injected onto the panel and concentrated for collection or use. Panels are reusable and can be swapped with higher capacity panels as those are developed.
Cost, energy usage, and land usage have long been issues for DAC technologies. In general, a large surface area is necessary to absorb CO2 at an appreciable rate, with a few notable exceptions in progress. It is also relatively expensive—where most reforestation costs less than $50/tonne, DAC technologies can cost between $250 and $600.
Then there’s energy cost. Liquid solvent systems require 900 degrees Celsius to release CO2, while solid sorbent systems require 80 to 120 degrees Celsius. To maximize net capture efficiency, energy sources need to be zero- or low-carbon. Scaling up existing systems would certainly require non–trivial energy use.
CO2Rail, a U.S.–based startup specializing in rail–based, self–powered DAC, is developing specialized rail cars that power an onboard collection of carbon dioxide. These cars can be attached to existing trains and use energy from regenerative braking to turn them into rolling carbon capture plants. While carbon capture facilities, such as those built by Climeworks, require large plots of land and lean on renewable power sources to power their filtering systems, CO2Rail wants to have existing trains do the work.
The specialized rail cars use braking to keep onboard batteries charged, and the slipstream of the moving train eliminates the need for fans. Instead, the intake of air collected as the train moves is directed to a CO2 collection chamber, where the carbon dioxide is chemically separated and stored in a liquid reservoir to be emptied later.
The numbers for this project are promising—every train braking maneuver generates enough energy to power 20 homes for a day. Carbon capture estimates start at 3,000 metric tons per car annually, and has the potential to reach annual productivity of 2.9 gigatons by 2050 at far lower costs than other DAC technologies.
While policy and investment trends have been favoring DAC technology more and more, it is dangerous to rely on carbon removal techniques at the expense of emission reductions. Both DAC and carbon capture and sequestering have potentially concerning connections to the fossil fuel industry, sometimes using captured CO2 to produce more oil from depleted wells in a process known as enhanced oil recovery.
And, as a newer type of infrastructure, the impacts of carbon capture on local communities—positive or negative—still require research on a project–by–project basis. While carbon capture has exciting prospects on the horizon, it cannot be heralded as a single solution and must be developed with a critical eye, especially as we understand more and more of its total impact on our environment.
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