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Energy and the Environment
Published in Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will, Commonly Asked Questions in Thermodynamics, 2022
Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will
Direct air capture (DAC) is the process of removing CO2 from the air and generating a concentrated stream of CO2 that may then be stored (as in Question 6.3) or utilized (as in Question 7.3). Whereas CCS is prevention of CO2 entering the atmosphere, DAC is a cure – extracting it back, once it has been released. If the CO2 captured in this way is then stored, it can be deemed to be permanently removed from the atmosphere, a condition termed “negative emissions.” In this regard, it has a similar end point to processes that involve bioremoval of CO2 from the air via photosynthesis, such as bioenergy with CCS (BECCS) (Daggash et al. 2020) or reforestation (Nolan et al. 2021). A typical hardwood tree absorbs up to 22 kg per year from the atmosphere, removing a tonne over a 45-year period. Indeed, DAC devices have been referred to as “artificial trees.” Removing CO2 from air at ~400 ppm and concentrating it to >90% purity requires both more energy and much larger treated gas volumes than for CO2 capture from concentrated point sources as described in Question 6.3. Here, we examine the energy requirements of such DAC processes.
How can carbon be stored in the built environment? A review of potential options
Published in Architectural Science Review, 2023
Matti Kuittinen, Caya Zernicke, Simon Slabik, Annette Hafner
Direct air capture (DAC) is a technology for capturing CO2 directly from the atmosphere (Williamson 2016). For the built environment, Dittmeyer et al. (2019) portray the concept of integrating a DAC system into an air conditioning unit, powered by renewable electricity. This solution can collect CO2 from buildings and convert it into hydrocarbon fuels. The CO2 captured by DAC needs to be processed and compressed for transport before it is used or stored. For building-integrated DAC to qualify as NET, the emissions from processing, transport, and use or storage must not exceed the amount of captured carbon (Lackner 2009). As the options for permanent CO2 storage are still limited, the continued use of CO2 represents an alternative solution. DAC can be used to achieve a closed carbon cycle by using the CO2 to produce short-life synthetic fuels (Fasihi, Efimova, and Breyer 2019), but it could also be used for chemical construction products, as described in Section 3.2.5.
Carbon-dioxide capture, storage and conversion techniques in different sectors – a case study
Published in International Journal of Coal Preparation and Utilization, 2023
Direct air capture (DAC) aims to remove low-concentration CO2 from the atmosphere in addition to point source carbon capture. Because of this, the cost of capturing CO2 from DAC sources is significantly higher than the cost of capturing CO2 from high CO2 emission sources. DAC costs currently range from 94–232 on a pilot scale, depending on the technology used. Costs are expected to fall to 60 by 2040, accelerating the commercial viability of this technology(Ozkan et al. 2022).