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CO2 CAPTURE – HOW DOES IT WORK?
Carbon dioxide (CO2) capture is the first step of carbon
capture and storage (CCS), a suite of technologies that
prevent large quantities of CO2 from being released into
the atmosphere. Large CO2 emitter industries around the
world have applied capture technology for decades,
capturing CO2 for use in the food industry (soda water
and beer for instance), fertiliser and other uses. Carbon
capture can be applied to any large-scale emissions
process – coal and natural gas-fired power generation,
gas and oil production, cement, iron, steel, pulp and
paper, and others. Applying CO2 capture as part of CCS
can play an enormous role in reducing the world’s
greenhouse gas emissions.
Pre-combustion processes convert fuel into a
gaseous mixture of hydrogen and CO2. The hydrogen is
separated and can be burnt without producing any CO2.
The CO2 can then be compressed for transport. The fuel
conversion steps required for pre-combustion are more
complex than the processes involved in postcombustion, making the technology more difficult to
apply to existing power plants. Pre-combustion capture
is used in industrial processes but has not been
demonstrated in much larger coal gasification concepts.
How is CO2 captured?
Energy from fossil fuels (coal, oil, and natural gas) is
released in the combustion (burning) process, which also
results in the emission of CO2 as a by-product. In
systems where the coal is pulverised to a powder, which
makes up the vast majority of coal-based power plants
through North America, Europe and China, the CO2 must
be separated at fairly diluted concentrations from the
balance of the combustion flue gases. In other systems,
such as coal gasification, it can be more easily separated.
There are three basic types of CO2 capture: postcombustion, pre-combustion and oxyfuel with postcombustion.
Post-combustion processes separate CO2 from
combustion exhaust gases. CO2 can be captured using a
liquid solvent. Once absorbed by the solvent, the CO2 is
released by heating to form a high purity CO2 stream.
This technology is widely used to capture CO2 for use in
the food and beverage industry.
Oxyfuel with post-combustion processes use oxygen
rather than air for combustion of fuel. This produces
exhaust gas that is mainly water vapor and CO2 which
are easily separated to produce a high purity CO2
stream.
WWW.GLOBALCCSINSTITUTE.COM
Why are CO2 emissions from the power
sector critical?
Coal and gas-fired power plants generate the largest
percentage of CO2 emissions that are currently vented
into the atmosphere and which are blamed for climate
change. Therefore, applying capture technology to that
sector – whether on new or existing plants – has the
potential for the greatest reduction of CO2 emissions of
most sectors.
CO2 capture technologies can be installed into all types
of new coal and gas-based power plants.
However, CCS represents a significant financial
investment; the absence of appropriate climate policies
and regulations that place a price on carbon is a hurdle
to recovering these costs and to furthering CCS
deployment.
The same is true for retrofitting CCS into existing power
plants, which also has the requirement for space to
install the capture technology.
Is CO2 currently being captured from plants
that generate electricity from coal or gas?
CO2 is not currently captured at full scale from plants
that generate electricity from coal or gas, but there are
some CO2 capture applications at coal or gas-fired power
plants at small/medium scale.
Of the 74 large-scale integrated CCS projects under
development today, approximately one third are from the
industrial sector.
Among the most advanced of these are a fermentation
capture project in the United States and a large
liquefied natural gas project off the coast of Western
Australia. The latest survey (2011) reveals there are two
CCS power projects under construction.
Where does carbon capture technology go
from here?
Carbon capture has been clearly demonstrated on a
small scale. The vital next step is the successful
demonstration of fully-integrated, large-scale CCS
systems at commercial scale. The technology already
works, but more research is required to reduce the cost
and energy penalties for the next generations of
technologies to be made commercially available.
There is a global need for significant financial
investments to bring numerous commercial-scale
demonstration projects on-line in the near future. This
alone can significantly contribute to a lowering of costs
for carbon capture.
For more information on CO2 capture:
Visit: www.globalccsinstitute.com
Contact: [email protected]
Post-combustion separation processes (amine
scrubbers) are currently used commercially in industrial
coal-fuelled boilers to supply CO2 to food and beverage
processors and in chemical industries, but these
applications are at a scale much smaller than that
needed for power-producing coal-fired power plants.
CO2 separation processes suitable for Integrated
Gasification Combined Cycle (IGCC) plants are used
commercially in the oil and gas and chemical industries
at a scale close to that ultimately needed, but their
application requires the addition of more processing
equipment to an IGCC plant and the deployment of gas
turbines that can burn highly-shifted hydrogen-rich gas.
Why are CO2 emissions from the industrial
sector critical?
Industrial processes such as cement, steel, paper pulp,
fermentation, chemicals and natural gas processing are
also significant emitters of CO2. Capture application can
be applied in these industries to further make a
significant reduction in global CO2 emissions.
In some cases CO2 emissions are a by-product of these
processes, rather than the result of burning fossil fuels
in the production process.
Is CO2 currently being captured from the
industrial sector?
Some of the earliest capture projects are in the natural
gas processing and chemicals sector. For example, the
Sleipner project in Norway, operating since 1996, has
captured some 1 million tonnes of CO2 a year. This is
then transported and injected into a deep saline
formation under the North Sea, permanently storing it
away from the atmosphere.
WWW.GLOBALCCSINSTITUTE.COM
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