Direct Air Capture
In direct air capture (DAC), CO 2 is captured from
the ambient air. It is absorbed or adsorbed onto a
solid or liquid sorbent which is regenerated yielding clean sorption substrate and CO 2 for use,
storage, or sequestration. The air-to-CO 2 ratio is
currently 2500:1, so to collect enough CO 2 to be
meaningful, large amounts of ambient air must be
processed. This requirement limits the efficiency
of the process and places requirements on the
materials that can be used. The energy and size
requirements mean that the method is currently
more expensive than other approaches [119].
Reaching the Paris targets, whose goal is to
keep global warming below 2
C by the year
2100, is not possible given current trends. Achieving them would require drastic reductions in CO 2
emissions combined with direct air capture.
The feasibility of a given technology is determined by its cost and to some extent by its
scalability. Estimates of the cost range of DAC
range from $30 to $1000 per ton of CO 2 (/t CO 2 ).
In contrast, the price of CO 2 as a chemical commodity varies from $100 to $300/t CO 2 , depending
on the transport method; this price is a result of
current market conditions, and the price would be
expected to fall if new CO 2 sources went into
production. It is estimated that at a price of $50/t
CO 2 , it would be economically feasible to make
fuel from algae. This process requires CO 2 but is
only in play if the price of CO 2 were to be significantly lower.
Another challenge for CCS is transporting CO 2
from the capture facility to the storage site. This
transportation, whether by road or pipeline,
requires energy and infrastructure. With DAC,
capture and storage can take place at the same site.
Authors have noted that the possibility of DAC
could work against efforts to reduce CO 2 emissions because people may think we can just
Gasification/reforming
H 2 /CO 2 Separation
CO 2
H 2
Air/O 2
Fossil fuels
Compression
& Transport
Heat & Power
Other products
Pre-combustion:
Combustion
CO 2 Separation
CO 2
Air
Fossil fuels
Heat & Power
Post-combustion:
Compression
& Transport
Compression
& Transport
Air separation
Combustion
CO 2
Air
Fossil fuels
Heat & Power
Oxy-fuel combustion:
O 2
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications, Fig. 10 Carbon
capture categories: pre-combustion, post-combustion, and oxyfuel combustion
304
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications
In direct air capture (DAC), CO 2 is captured from
the ambient air. It is absorbed or adsorbed onto a
solid or liquid sorbent which is regenerated yielding clean sorption substrate and CO 2 for use,
storage, or sequestration. The air-to-CO 2 ratio is
currently 2500:1, so to collect enough CO 2 to be
meaningful, large amounts of ambient air must be
processed. This requirement limits the efficiency
of the process and places requirements on the
materials that can be used. The energy and size
requirements mean that the method is currently
more expensive than other approaches [119].
Reaching the Paris targets, whose goal is to
keep global warming below 2
C by the year
2100, is not possible given current trends. Achieving them would require drastic reductions in CO 2
emissions combined with direct air capture.
The feasibility of a given technology is determined by its cost and to some extent by its
scalability. Estimates of the cost range of DAC
range from $30 to $1000 per ton of CO 2 (/t CO 2 ).
In contrast, the price of CO 2 as a chemical commodity varies from $100 to $300/t CO 2 , depending
on the transport method; this price is a result of
current market conditions, and the price would be
expected to fall if new CO 2 sources went into
production. It is estimated that at a price of $50/t
CO 2 , it would be economically feasible to make
fuel from algae. This process requires CO 2 but is
only in play if the price of CO 2 were to be significantly lower.
Another challenge for CCS is transporting CO 2
from the capture facility to the storage site. This
transportation, whether by road or pipeline,
requires energy and infrastructure. With DAC,
capture and storage can take place at the same site.
Authors have noted that the possibility of DAC
could work against efforts to reduce CO 2 emissions because people may think we can just
Gasification/reforming
H 2 /CO 2 Separation
CO 2
H 2
Air/O 2
Fossil fuels
Compression
& Transport
Heat & Power
Other products
Pre-combustion:
Combustion
CO 2 Separation
CO 2
Air
Fossil fuels
Heat & Power
Post-combustion:
Compression
& Transport
Compression
& Transport
Air separation
Combustion
CO 2
Air
Fossil fuels
Heat & Power
Oxy-fuel combustion:
O 2
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications, Fig. 10 Carbon
capture categories: pre-combustion, post-combustion, and oxyfuel combustion
304
Air Pollution and Climate Change: Sustainability, Restoration, and Ethical Implications