Carbon Capture Utilization and Storage
What
is CCUS?
Carbon
capture, utilisation and storage (CCUS) refers to a suite of technologies that
can play an important and diverse role in meeting global energy and climate
goals. CCUS involves the capture of CO2 from large point sources, including
power generation or industrial facilities that use either fossil fuels or
biomass for fuel.
The
CO2 can also be captured directly from the atmosphere. If not being used
on-site, the captured CO2 is compressed and transported by pipeline, ship, rail
or truck to be used in a range of applications, or injected into deep
geological formations (including depleted oil and gas reservoirs or saline
formations) which trap the CO2 for permanent storage.
Why
CCUS?
The
reason CCUS will have to play a key role is simple: Despite rapid recent growth
in renewable sources like wind and solar, the world still relies on fossil
fuels to meet about 80 percent of its energy needs. Shifting the balance in the
world’s energy mix from a reliance on fossil fuels to renewable energy sources will
require considerable time.
Much
of the focus today is on decarbonizing electric power production, but it should
be noted that only about one quarter of global greenhouse gas (GHG) emissions
are from electricity. Coal, the most carbon-intensive fuel, accounts for about
40 percent of power generation globally. Even if coal consumption were to
plateau within the next few years, it will remain the fuel of choice in Asia
for decades to come. Coal is a cheap, reliable, and secure energy source in
China and India, two countries with the fastest growth in electricity demand.
Rapid closure of coal-fired power plants in these countries is economically and
politically infeasible.
There
are comparable obstacles to changing the energy mix in other sectors. Shifting the
world’s car, truck, plane, and shipping fleets from oil-based to low carbon
fuels will require decades, not years. And in industries like refining,
petrochemicals, and cement and steel production, which together generate about
20 percent of global GHG emissions, carbon abatement is even more challenging.
Four Main Parts to a CCUS
System
1. The
CO2 gas is captured before or after fossil fuels are burned and compressed into
a liquid form.
2. The
liquid CO2 is transported via pipeline to a utilization or geologic storage
site.
3. At the
utilization site, CO2 is transformed into usable materials. Sometimes the
utilization site is also the storage site.
4. At the
storage site, the CO2 is injected deep into the subsurface of the Earth where
it is safely stored and monitored.
All parts of the CCUS
system—CO2 capture, transport, utilization, and storage—are currently done on a
small scale. If CCUS can be used on a large scale, there is potential for CCUS
to capture and store up to 90 percent of the CO2 emitted into the atmosphere
from stationary fossil fuel plants.
How can CO2 be used?
CO2 can be used as an input to a range of products
and services. The potential applications for CO2 use include
direct use, where the CO2 is not
chemically altered (non-conversion), and the transformation of CO2 to a useful product through chemical and
biological processes (conversion).
Today around 230 Mt of CO2 are
used globally each year, primarily to produce fertilisers (around 125 Mt/year)
and for enhanced oil recovery (around 70-80 Mt/year). Other commercial uses of
CO2 include food and beverage production, cooling, water
treatment and greenhouses. New CO2 use pathways include: fuels (using
carbon in CO2 to convert hydrogen into a synthetic hydrocarbon
fuel); chemicals (using carbon in CO2 as an
alternative to fossil fuels in the production of some chemicals); and building
materials (using CO2 in the production of building
materials to replace water in concrete or as a raw material in its
constituents.)
How is CO2 stored – and is it
safe?
Studies have shown that CO2
can be safely stored underground, such as in deep, porous rock formations,
for thousands of years, and we've even found natural pockets of CO2 that
have existed for millions.
There are several types of
reservoir suitable for CO2 storage, with deep saline formations
and depleted oil and gas reservoirs having the largest capacity. Deep saline
formations are layers of porous and permeable rocks saturated with salty water
(brine), which are widespread in both onshore and offshore sedimentary basins.
Depleted oil and gas reservoirs are porous rock formations that have trapped
crude oil or gas for millions of years before being extracted and which can similarly
trap injected CO2.
When CO2 is
injected into a reservoir, it flows through it, filling the pore space. The gas
is usually compressed first to increase its density and the reservoir typically
must be at depths greater than 800 metres to retain the CO2 in
a dense liquid-like state. The CO2 is permanently trapped in
the reservoir through several mechanisms: structural trapping by the seal,
solubility trapping where the CO2 dissolves in the brine
water, residual trapping where the CO2 remains trapped in pore
spaces between rocks, and mineral trapping where the CO2 reacts
with the reservoir rocks to form carbonate minerals (mineralisation).
How does CCUS support carbon
removal?
CCUS technologies can provide
a means of removing CO2 from the atmosphere, i.e., “negative
emissions”, to offset emissions from sectors where reaching zero emissions may
not be economically or technically feasible. There are two principal
approaches:
Bioenergy with carbon capture
and storage, or BECCS, involves capturing and permanently storing CO2 from
processes where biomass (which extracts CO2 from the atmosphere
as it grows) is burned to generate energy. A power station fuelled with biomass
and equipped with CCUS is a type of BECCS technology, as are facilities that
process biomass into biofuels, if the resulting CO2 is captured
and stored.
Direct air capture (DAC)
involves the capture of CO2 directly from ambient air (as
opposed to a point source). The CO2 can be used, for example as
a climate-neutral CO2 feedstock in synthetic fuels, or it can
be permanently stored for carbon removal.
These technology-based
approaches for carbon removal can complement and supplement nature-based
solutions, such as afforestation and reforestation.
CCUS retrofits in the Sustainable Development Scenario
There are three options for
cutting locked-in emissions in the power generation and industrial sectors:
- Investing in modifications to existing
industrial and power equipment to either use less carbon-intensive fuels
or improve energy efficiency
- Retiring plants before the end of their
normal operating lifetimes, or making less use of them (e.g. by
repurposing fossil fuel power plants to operate at peak-load rather than
base-load)
- Retrofitting CO2 capture
facilities and storing or using the CO2.
Strategic value of CCUS
CCUS
carries considerable strategic value as a climate mitigation option. It can be
applied in a number of ways and across a range of sectors, offering the
potential to contribute – directly or indirectly – to emissions reductions in
almost all parts of the global energy system. Consequently, progress in
developing and deploying CCUS technologies in one sector could have significant
spill over benefits for other sectors or applications, including for
technological learning, cost reductions and infrastructure development. The
four main ways in which CCUS can contribute to the transition of the global
energy system to net-zero emissions – tackling emissions from existing energy
assets, providing a platform for low-carbon hydrogen production, a solution for
sectors with hard-to-abate emissions, and removing carbon from the atmosphere –
are listed below:
CCUS
can be retrofitted to existing power and industrial plants that could otherwise
emit 600 billion tonnes of CO2 over the next five decades –
almost 17 years’ worth of current annual emissions. In the Sustainable
Development Scenario an initial focus of CCUS is on retrofitting fossil
fuel-based power and industrial plants. By 2030, more than half of the CO2 captured
is from retrofitted existing assets.
2) A
cost-effective pathway for low-carbon hydrogen production
CCUS can support a rapid
scaling up of low-carbon hydrogen production to meet current and future demand
from new applications in transport, industry and buildings. CCUS is one of the
two main ways to produce low-carbon hydrogen.
Global hydrogen use in the
Sustainable Development Scenario increases sevenfold to 520 megatons (Mt) by
2070. The majority of the growth in low-carbon hydrogen production is from
water electrolysis using clean electricity, supported by 3 300 gigawatts (GW)
of electrolysers (from less than 0.2 GW today). The remaining 40% of low-carbon
hydrogen comes from fossil-based production that is equipped with CCUS,
particularly in regions with access to low-cost fossil fuels and CO2 storage.
CCUS is virtually the only
technology solution for deep emissions reductions from cement production. It is
also the most cost-effective approach in many regions to curb emissions in iron
and steel and chemicals manufacturing. Captured CO2 is a
critical part of the supply chain for synthetic fuels from CO2 and
hydrogen – one of a limited number of low-carbon options for long-distance
transport, particularly aviation.
4)
Removing carbon from the atmosphere
For emissions that cannot be
avoided or reduced directly, CCUS underpins an important technological approach
for removing carbon and delivering a net-zero energy system. When net-zero
emissions is reached in the Sustainable Development Scenario, 2.9 gigatons (Gt)
of emissions remain, notably in the transport and industry sectors. These
lingering emissions are offset by capturing CO2 from bioenergy
and the air and storing it.
Sources:
A new era for CCUS – CCUS in Clean Energy Transitions –
Analysis - IEA
CarbonCaptureUtilizationandStorage.pdf (need.org)
Storing CO2 underground can curb carbon emissions, but is it
safe? (phys.org)
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