CCS…. What
is it??
After a very interesting lecture on Monday on communicating
about CCS, I realised that far all I sort of know what it stands for… I know
very little else about it.. so I figured… id research what it is and post it!!!
CCS- Carbon Capture and Storage
CCS is the process of capturing waste carbon dioxide from
sources such as fossil uel power plants and then taking it to a storage site
and depositing it where It will not enter the atmosphere, normally some form of
underground geological formation.
How it works- Capture
Energy from fossil fuels such as coal, oil and natural gas
is released in the combustion (burning) process. The emission of CO2 is a
by-product of this process.
Capture technology can be applied to any large-scale emissions
process, including coal-fired power generation, gas and oil production, and
manufacture of industrial materials such as cement, iron, steel and pulp paper.
In fact, large CO2 emitter industries around the world have applied capture
technology for decades. Captured CO2 is used, for example, in the food and
beverage industry and in making fertiliser.
In systems where the coal is pulverised to a powder, which
makes up the vast majority of coal-based power plants in North America,
Australia, Europe and China, the CO2 must be separated at fairly diluted
concentrations from the balance of the combustion flue gases (gas exiting via a
chimney or ‘flue’). In other systems, such as coal gasification, the CO2 can be
more easily separated.
There are three basic types of CO2 capture: pre-combustion,
post-combustion and oxyfuel with post-combustion.
Pre-combustion capture
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 be compressed for transport.
Pre-combustion capture is used in industrial processes but
has not been demonstrated in much larger power generation projects. The fuel
conversion steps required for pre-combustion are more complex than the processes
involved in post-combustion, so the technology is more difficult to apply to
existing power plants.
Pre-combustion capture increases the CO2 concentration of
the flue stream, requiring smaller equipment and different solvents with lower
regeneration energy requirements.
The process involves:
·
partially reacting the fuel at high pressure
with oxygen or air and, in some cases, steam, to produce carbon monoxide and
hydrogen
·
reacting the carbon monoxide with steam in a
catalytic shift reactor to produce CO2 and additional hydrogen
·
separating the CO2 and, for electricity
generation, using hydrogen as fuel in a combined cycle plant.
Although pre-combustion capture involves a more radical
change to power station design, most elements of the technology are already
well proven in other industrial processes.
Post-combustion capture
Post-combustion processes separate CO2 from combustion
exhaust gases so that the CO2 can be captured using a liquid solvent. The CO2
is absorbed by the solvent and then released when it is heated to form a high
purity CO2 stream.
The process involves scrubbing the flue with a suitable
solvent, such as an amine solution, to form an amine–CO2 complex, which is then
decomposed by heat to release high purity CO2. The regenerated amine is
recycled to be reused in the capture process.
Post-combustion capture is applicable to coal-fired power
stations but additional measures, such as desulphurisation of the gas stream,
are required to prevent the impurities in the flue gas from contaminating the
CO2 capture solvent.
Two significant challenges for post-combustion capture
involve:
·
the large volumes of gas that must be handled,
requiring large-scale equipment and creating high capital costs
·
the amount of additional energy needed to operate
the process.
Post-combustion capture technology is used widely in the
food and beverage industry.
Oxyfuel combustion
Oxyfuel with post-combustion processes uses oxygen rather
than air for combustion of fuel. This produces exhaust gas that is mainly water
vapour and CO2 that can be easily separated to produce a high purity CO2
stream.
The concentration of CO2 in flue gas can be increased by
using pure or enriched oxygen instead of air for combustion, either in a boiler
or gas turbine. The oxygen is produced by cryogenic air separation (already
used on a large scale industrially), and the CO2-rich flue gas recycled to
avoid the excessively high-flame temperature associated with combustion in pure
oxygen.
The advantage of oxyfuel combustion is that, because the
flue gas contains a high concentration of CO2, the CO2 separation stage is
simplified. The main disadvantage is that cryogenic oxygen is expensive.
Oxyfuel combustion for power generation is currently being
demonstrated at a refurbished power station in Biloela, Queensland.
How CCS works - transport
Safely and reliably transporting CO2 from where it is
captured to a storage site is an important stage in the CCS process.
Transport of CO2 is already a reality, occurring daily in
many parts of the world. CO2 is transported by pipeline, ship and road tanker,
primarily for use in the food industry or to recover more oil and gas from oil
and gas fields.
However, the scale of transportation required for widespread
deployment of CCS is much more substantial than the current scale of transport
and will involve moving dense, concentrated CO2.
How is CO2 transported?
Once separated from other elements of the flue gas (gas
exiting via a chimney or ‘flue’), the CO2 is compressed to make it easier to
transport.
Pipelines are—and are likely to continue to be—the most
common method used to transport the very large quantities of CO2 involved in
CCS. There are already millions of kilometres of pipelines around the world that
transport various gases, includingCO2.
Transport of CO2 by truck and rail is possible for small
quantities. Trucks are used at some project sites, moving the CO2 from where it
is captured to a nearby storage location. Given the large quantities of CO2 that
would be captured via CCS in the long-term, it is unlikely that truck and rail
transport will be significant.
Ship transportation can be an alternative option for many
regions of the world. Shipment of CO2 already takes place on a small scale in
Europe, where ships transport food-quality CO2 (around 1,000 tonnes) from large
point sources to coastal distribution terminals.
Larger scale shipment of CO2, with capacities in the range
of 10,000 to 40,000 cubic metres, is likely to have much in common with the
shipment of liquefied petroleum gas (LPG). There is already a great deal of
expertise in transporting LPG, which has developed into a worldwide industry
over a period of 70 years.
How CCS works - storage
Storing CO2
underground is not a new or emerging technology—it is an existing reality on an
industrial scale. In fact, there are geological systems that naturally contain
CO2 and many others throughout the world that experts have
determined can retain centuries’ worth of injected CO2. This will
help abate climate change by removing and keeping this greenhouse gas out of
the atmosphere.
What can be done with captured CO2?
Generally
speaking, the CO2 can be:
- stored in secure deep
underground geological formations
- used as a value-added
commodity. This can result in a portion of the CO2 being
permanently stored—for example, in concrete that has been cured using CO2
or in plastic materials derived from biomass that uses CO2 as
one of the ingredients
- converted into biomass. This
can be achieved, for example, through algae farming using CO2
as a feedstock. The harvested algae can then be processed into biofuels
that take the place of non-biological carbon sources.
How does
geological storage of CO2 work?
Geological
storage involves injecting CO2 captured from industrial processes
into rock formations deep underground. The formations are selected for their
huge capacity to store and retain injected greenhouse gases indefinitely. This
way, the CO2 is effectively removed and isolated from the
atmosphere.
The
following geologic characteristics are associated with effective storage sites:
- storage formations have
enough voids, or pores, in the rock to allow the injection of CO2
- pores in the rock are
connected well enough, a feature called ‘permeability’, so that the CO2
can move and spread out within the formation, providing the capacity
needed to accept the amount of CO2
- formations must have an
extensive cap or barrier at the top to contain the CO2 for
hundreds to thousands of years, and longer.
Fortunately,
there are many locations around the world that have formations with these
characteristics. Most are found in vast geological features called ‘sedimentary
basins’. Almost all oil and gas production is associated with sedimentary
basins. The types of geologic formations that trap oil and gas (and also
naturally occurring CO2) include sandstones, limestones and
dolomites that are similar to those that make good CO2 storage
reservoirs.
It is the
natural geologic characteristics that resulted in oil and gas being trapped for
millions of years before they were discovered that make secure geologic storage
of CO2 such a viable option for greenhouse gas mitigation.
How is CO2
injected underground and why does it stay there?
Once
captured, the CO2 is compressed into a ‘supercritical state’—a fluid
almost as dense as water—and then pumped down through a well into a porous
geological formation, as described above.
The pores in
underground formations are initially filled with a fluid, either oil, gas or,
much more commonly, very salty water. CO2 can be injected into oil
reservoirs to help with oil recovery but most future large–scale projects will
target saline water-bearing formations for storage because they are more common
and can have enormous capacity. In general, depths greater than 800 metres
are desired to keep the CO2 in the compressed, or dense, state.
Because the
CO2 is initially slightly more buoyant than water, a portion will
migrate to the top of the formation, where it will become trapped beneath the
caprock, which acts as a seal. In most natural systems, there are numerous
thick barriers between the deep reservoir and the surface. Some of the CO2
will start to dissolve slowly into the saline water and become trapped
indefinitely, whereas another portion of CO2 may become residually
trapped in tiny pore spaces.
The ultimate
trapping process involves dissolved CO2 reacting with the reservoir
rocks to form a mineral, much like snails or clams use calcium and carbon from
seawater to form their hard shells. Depending on the reservoir minerals
present, this process can be relatively quick or very slow, but it effectively
transforms the CO2 into a solid mineral.
Is
underground storage of CO2 safe?
Three industrial–scale
storage projects that inject up to two million tonnes of CO2 annually
into saline formations have been operating for many years, along with other
smaller projects actively capturing and storing CO2.
These
industrial–level projects are complemented by numerous research–scale CCS
projects, intergovernmental and industry partnerships, research programs, and
stakeholder networks. No adverse safety, health, or environmental effects have
ever been documented from any of these operations.
How do we
know that it works?
There are
decades of operational experience from projects that are very similar to CCS,
including underground CO2 injection for enhanced oil recovery (EOR)
and the use of technologies analogous to CCS, such as acid gas (a combination of
hydrogen sulphide and CO2) injection, and natural gas storage.
The oil and
natural gas industries have more than 40 years’ experience injecting CO2
into geologic reservoirs to increase oil production. This process is a type of
EOR and uses the properties of CO2 to mix with the oil to move it
out of the reservoir more effectively. In most operations, the CO2
is recycled and will remain in the reservoir indefinitely at the end of the
life of the oil field.
These sites
have been injecting many millions of tonnes of CO2 safely into the
subsurface for decades. The success of these projects and the increasing number
of research demonstrations provides considerable confidence in the potential to
store large quantities of CO2 underground safely, securely and for very
long periods.
How much CO2
can be stored underground?
The United
Nations Intergovernmental Panel on Climate Change estimates the world’s
potential capacity at two trillion tonnes, although there could be a “much
larger potential”. Several regions around the world—the United
States, Canada, China, South Africa, Europe and Australia—are doing significant
amounts of work on characterising potential storage sites.
The 2012
North American Carbon Storage Atlas indicates there is more than
1,600 billion tonnes of CO2 storage potential in saline
formations alone in the United States, Canada and Mexico. This means that there
is centuries’ worth of CO2 geological storage for the region.
A European
Union project estimates the CO2 storage capacity in oil and gas
fields, in and around the North Sea alone, at 37 billion tonnes, which
would enable this region to inject CO2 for several decades once the
fields are depleted.
The Sleipner
project, located some 240 kilometres off the coast of Norway in the North
Sea, is storing more than 2,700 tonnes of CO2 per day, injected
nearly 800 metres below the seabed. Over the lifetime of the project, it
is expected that more than 20 million tonnes of CO2 will be
injected into the saline formation.
Monitoring
surveys of the injected CO2 indicate that over the past
15 years, the gas has spread out over nearly 10 square kilometres
underground, without moving upwards or out of the storage reservoir.
Long-term
simulations also suggest that over hundreds to thousands of years, the CO2
will eventually dissolve in the saline water, becoming heavier and less likely
to migrate away from the reservoir.
A month ago the first
coal power plant with CCS opened in Canada-
Project type: Capture
Scale: Large
Status: Operative
Capital cost: $600 million (canadian $)
Year of operation 2014
Industry: Coal Power Plant
MW capacity: 120
Capture method: Post-combustion
Capture technology: Amine
New or retrofit: Retrofit
Transport of CO2 by: Pipeline
Type of storage: EOR
Volume: 1 million tonnes/CO2
The retrofitted
capture plant captures 1 million tonnes per year of CO2 - or 95% - from one of
Boundary Dam’s aging combustion units, which has a generating capacity of
around 130MW. That’s equivalent to taking more than 400,000 cars off Norwegian
roads annually.
The total amount
of CO2 produced, for all generating units at Boundary Dam Power station, is 5.5
to 6 million tonnes annually.
This $1,24
billion (of which 600 million is for CCS and the rest is for modernizing the
plant) integrated carbon capture & storage project has retrofitted
SaskPower's coal-fired Boundary Dam Power Station in Estevan, Saskatchewan with
a carbon capture system. Captured CO2 is used for enhanced oil recovery and
stored in deep saline aquifers.
The provincial
government approved the proposals in April 2011, which cleared the way for
construction to begin immediately. The capture facility is opening in October
2014, after a test period since April.
The majority of
the captured gas is sold to operator Cenovus for enhanced oil recovery (EOR) at
its Weyburn oilfield. Cenovus has set up injection wells and built a 40
mile-long pipeline connecting Weyburn with Boundary Dam. SaskPower and
Petroleum.
Hopefully over
the next few years many more of these projects will be finished and come
online- expecially with the new “backing” from the IPCC….
Anyway… there it
it… CCS!!! Enjoy!
