Carbon Capture, Utilization and Storage
Introduction
The need to limit the harmful effects of climate change
is a powerful motive for preventing carbon dioxide emissions from entering the
atmosphere, and for removing CO2 that is already there, but there can be
subsidiary aims associated with carbon capture, and there are many methods of
accomplishing it.
According to a definition published in 2014, “Carbon
Capture, Utilization, and Storage (CCUS) encompasses methods and technologies
to remove CO2 from … flue gas and from the atmosphere, followed by recycling
the CO2 for utilization and determining safe and permanent storage options”
(RCN-CCUS, 2014a). A definition of carbon capture and storage (CCS) used by
Torvanger (2020) “refers to a group of technologies that reduce emissions of
carbon dioxide from coal-fired or gas-fired power stations, or from process
industries."
The term sequestration is also used for the removal of
CO2 from the atmosphere or from combustion gases, and permanent prevention of
its return to the atmosphere. Since captured CO2 may be used in ways that do eventually
return it to the atmosphere, carbon capture is not necessarily the same as
sequestration. Dieter Helm makes a distinction between two types of
sequestration, natural and industrial, and uses the term carbon capture and
storage to refer to the latter, “siphoning off carbon from power stations and
industrial sites and then piping it into storage wells, such as old oil and gas
fields, salt cavities, and possibly even into the deep sea” (Helm, 2020,
p.146). He regards natural carbon sequestration, “the stuff nature does for us
for free all the time” (p.12) as including recarbonisation of soils,
regeneration of peat bogs, the planting of trees that would not otherwise have
been planted, and the creation of new coastal marshes (pp. 93-4). Fawzy et al.
(2020) include these methods in their list of widely discussed negative
emissions techniques, adding “biochar, enhanced weathering, direct air carbon
capture and storage, ocean fertilization, ocean alkalinity enhancement, soil
carbon sequestration, as well as … mineral carbonation and using biomass in
construction.”
CCS may have a long future. Wiseman (2017) attempted to
chart the major developments of the coming decades that could together avert
climate disaster. He included CSS among these, suggesting that the amounts of
carbon removed from the atmosphere would reach 0.5 gigatonnes of CO2 equivalent
each year (GtCO2e pa) during the decade 2020-2030, 2 GtCO2e pa during 2030-2040,
and 5 GtC02e pa during 2040-2050. After 2050, “strengthening our capacity to
efficiently and equitably sequester C02” would still be a crucial global
priority. Sequestration would be needed until we are able to completely abandon
fossil fuels, and perhaps until we reduce atmospheric CO2 to pre-industrial
levels.
Torvanger summarised the three stages of (industrial) CCS
as capture of CO2 from exhaust gas or other industrial emissions; pressurizing
CO2 and transporting it by pipeline or ships to a geological storage site; and
injecting it “deep into a geological structure that can sequester the gas for
eternity”. Langholtz et al. (2020) discuss bioenergy with carbon capture and
storage (BECCS), particularly with regard to the “scale and cost of CO2 sequestration
from BECCS in the US”, which may have “an untapped potential of about 750 to
1050 million tonnes of biomass per year”. Much of this may come from “wastes,
agricultural residues, and forestland resources, which do not displace food
crops”. The carbon in biomass has been fixed from the atmosphere, and the “CO2
emissions from biomass combusted for energy are captured and stored below
ground.” Thus BECCS can be considered as a negative-emissions technology (NET)
along with afforestation, direct air capture, land management, ocean
fertilization, and enhanced weathering (GCCSI, 2018). Langholtz et al. include
in their discussion some of the objections to BECCS, such as the possible losses
of biodiversity and food security referred to by the IPCC in its 2018 Special
Report on Global Warming of 1.5 ◦C; nevertheless they note that three of the
four potential pathways described in the report as leading to achievement of
its targets rely on BECCS.
Carbon capture
The British Geological Survey article “Understanding carbon capture and storage (CCS)” refers to several methods of carbon capture, of which three can be used when fossil fuels are burnt at power plants (BGS, 2020). Post-combustion methods remove CO2 after burning the fossil fuel; pre-combustion techniques trap CO2 before the fuel is burnt; and oxyfuel combustion is the burning of fossil fuel in oxygen instead of air.
Post-combustion capture normally involves chemical
methods to trap CO2, but the process is influenced by the fact that flue gases
typically contain impurities such as nitrogen oxides and sulphur oxides as well
as CO2. This form of capture can be retrofitted to existing power plants. Abu-Zahra
et al. (2016) describe the post-combustion process in detail. Pre-combustion
techniques involve an initial stage in which the fossil fuel is partially
burned to form a synthetic gas from which CO2 can be captured efficiently; the
process is cheaper than post-combustion, but cannot be retrofitted. Oxyfuel
combustion is the burning of fossil fuel in oxygen rather than air, yielding
almost pure carbon dioxide that can be transported and stored. The BGS article
comments that while this may be the “most effective method of the three, the
initial oxygen burning process is energy intensive”.
Issues surrounding natural carbon sequestration are
discussed by Helm (p. 143 ff.). He sees it as having “the potential not only to
make net zero an achievable goal, but to do this in a way that produces
multiple other benefits”. As part of an integrated plan, these benefits can
include reducing pollution, tidal shocks and storm surges, assisting
biodiversity, and improving our mental and physical well-being. An integrated plan
is a task for government rather than for organisations such as companies, and
Helm argues the case for an effective carbon tax to make it possible.
Carbon utilization
Torvanger notes that worldwide “Fourteen billion tons of carbon dioxide is annually produced from coal-fired power stations”, and this far exceeds the amount that could be used by the global chemical industry. However a much bigger market for CO2 potentially exists in the production of synthetic fuels, where “1.3 Gt carbon dioxide could be used every year”, a substantial portion of the IPCC’s target for CCS. The use of CO2 in chemical production and in synthetic fuels is perhaps better described as mitigation of atmospheric carbon than as sequestration, since the carbon in such fuels will again produce CO2 when they are burned, and the carbon used in many chemical products will eventually become CO2 again. Where captured carbon is incorporated in building materials, a much longer captivity can be anticipated, but none of these utilisations of captured carbon amount to sequestration “for eternity”.
Carbon captured and used in synthetic fuel and then
recaptured from exhaust can form part of a carbon cycle which reduces the use
of fossil fuels, and may help to make carbon capture more economical. Christensen
and Petrenko (2017) referred to synthetic fuels “which use captured CO2 and
electricity to produce drop-in diesel or gasoline, methanol, dimethyl ether
(DME), or other fuels that can be used in vehicles, airplanes, or ships” in
their study of “the potential contribution that CO2-based synthetic fuels could
make towards the European Union’s (EU) climate mitigation goals.” A related
study by d'Amore and Bezzo (2020) of carbon capture, transport, utilization,
and the storage supply chain concluded that “CO2 utilization can contribute
only marginally to achieve the European climate target set for 2030 in terms of
emissions reduction.” However, they acknowledge that carbon utilization can “help
to decrease costs related to the overall carbon capture and sequestration
infrastructure”, that the energy sector “may provide a huge market for
CO2-derived fuels” and that the availability of cheap renewable energy could
have a positive effect on the future of carbon utilization.
Some examples follow of research on producing chemicals
from captured CO2, and of proposed and actual manufacture. Research on
electrocatalysts has shown that they can be used to “turn carbon dioxide and
water into carbon building blocks containing one, two, three, or four carbon
atoms with more than 99 percent efficiency.” This could lead to “the conversion
of carbon dioxide into valuable products and raw materials in the chemical and
pharmaceutical industries", such as plastics, fabrics and resins (Rutgers,
2018).
A review of research at the University of California
points to both the potential for carbon capture and utilisation (CCU) in chemical
production, and some of the difficulties (Futurity, 2019). It is estimated that
“chemical production—which encompasses sectors as diverse as lubricants,
paints, and plastics—accounts for over 3.3 billion metric tons of CO2 per year,
or the equivalent in other greenhouse gases.” The post quotes Sangwon Suh, of Santa
Barbara’s Bren School of Environmental Science & Management, as saying that
“If we can use carbon dioxide as a carbon source for these plastics and
chemicals, then we can capture and store a large quantity of CO2 in the
plastics and chemicals that otherwise would have been emitted, all while
creating value.” The article continues by pointing out that the “process would
increase the industry’s total energy demands mainly because it also needs
hydrogen, which can be produced from water through electrolysis” and that this
energy would have to come from renewable sources. It estimates that “126 to 222 percent of the
world’s current 2030 renewable energy targets” would be needed to realise the
potential of CCU to provide the needs of the chemical industry.
Despite the difficulties referred to above, Tata
Chemicals Europe is building the UK’s first industrial scale CCUS plant at
Northwich, Cheshire, to produce sodium bicarbonate using captured CO2 (Tata,
2020). Wind and solar energy provide
power for the UK ‘Sky Diamond’ project which produces diamonds from atmospheric
carbon (IET, 2020). This report claims that the production of a one carat stone
by traditional methods generates “more than 100kg of carbon emissions”, whereas
the capture process is carbon negative.
According to Renee Cho, “Incorporating CO2 into concrete
is the best prospect for widespread use of CO2 in the near term.” The world
uses huge quantities of concrete and the cement used in making it, accounting
for a significant percentage of global GHG emissions. “CO2 gas can be turned
into a solid aggregate for concrete …
with only minimal external energy” and “can also be used to cure concrete” in a
process where “wet concrete is infused with CO2, which reacts with water and
calcium to form solid calcium carbonates” which “results in concrete that is
four percent CO2” (Cho, 2019). An example of the use of captured CO2 in
building materials is provided by the company Blue Planet, whose synthetic
limestone has been used as part of a new terminal at San Francisco Airport (Yale,
2019).
Carbon storage
Technologies that have been suggested for long-term CO2 storage include storing CO2 in the ocean, in geological formations, “and through mineral sequestration, which involves the formation of solid carbonates from CO2 and minerals” (RCN-CCUS, 2014b). Mineral sequestration occurs in nature over long time periods as the weathering of rock, producing stable carbonates.
The British Geological Survey notes that deep “ocean
storage will increase ocean acidification, a problem that also stems from the
excess of carbon dioxide already in the atmosphere and oceans.” (BGS, 2020). It
reports that deep geological storage is considered the most promising option,
and that areas “such as the North Sea and the US Gulf Coast are believed to
contain a large amount of geological storage space.” In this storage technique
“carbon dioxide is converted into a high pressure, liquid-like form” known as
‘supercritical CO2’, and the article quotes the view of the Intergovernmental
Panel on Climate Change that for “well-selected, designed and managed
geological storage sites, CO2 could be trapped for millions of years, retaining
over 99 per cent of the injected CO2” over a period of a thousand years. The
sedimentary rocks into which the CO2 is injected “may be in old oil fields, gas
fields, or in saline formations”.
Pilorgé et al. (2020) studied the opportunities for
low-cost CCS in the USA, including potential sequestration sites, with emphasis
on economics. They found that
sequestration opportunities “in limestone and sandstone formations have
capacities in the range of 740−1,800,000 MtCO2, adding up to 2,740,000 MtCO2.”
According to the International Energy Agency “plans for
more than 30 new integrated CCUS facilities have been announced since 2017. The
vast majority are in the United States and Europe, but projects are also
planned in Australia, China, Korea, the Middle East and New Zealand.” (IEA,
2020). If all these projects were realised, the world total of CO2 capture
would reach 130 Mt per year. It states that 21 capture facilities are in
operation, noting that 16 of them sell or use the CO2 for enhanced oil recovery
(EOR), in which the gas is pumped into an oil field to increase the output of
crude oil. There are also many pilot and demonstration-scale CCUS facilities
and technology test centres operating in different parts of the world. Jiang et
al. (2019) are mainly concerned with China’s policy on CCUS, but point to the
USA, Norway, Australia and Japan as being leaders in CCUS policy and
development. Torvanger refers to Norway’s Sleipner storage site, where one
million tons of carbon dioxide separated from natural gas has been injected
annually into a geological formation since 1996, noting that the “integrity of
stored carbon dioxide has worked well at this storage site.”
Helm (pp.75-6) claims that the North Sea is “probably among
the best global sites for both offshore wind and CCS”, and that of “all the
technologies that the UK could develop of benefit to the world” CCS might be second
only to offshore wind.
Integration of capture, use and storage
“CCUS technologies involve the capture of carbon dioxide (CO2) from fuel combustion or industrial processes, the transport of this CO2 via ship or pipeline, and either its use as a resource to create valuable products or services or its permanent storage deep underground in geological formations” (IEA, 2020). Since transportation of CO2 by pipeline, ship or other means has a cost, the development of CCUS is likely to be most economically appealing when industrial sources of CO2 are close to suitable locations for sequestration, to other industries which require CO2, or to both. In some cases the proximity of renewable energy sources may also be important. The scope of the IEA article extends to “bio-based processes” and to direct capture of CO2 from the air. The development of industrial CCUS hubs with shared CO2 transport and storage infrastructure, rather than large, stand-alone CCUS facilities, is seen as important and perhaps critical to accelerating the deployment of CCUS. The reduced planning and development effort which results, together with economies of scale which produce lower unit costs, can encourage investment, and make possible the participation of smaller industrial facilities. Leadership and co-ordination by government “are vitally important to the early development of CCUS hubs in most regions, notably in supporting or underwriting investment in new CO2 transport and storage infrastructure.”
Projects
The IEA (2020) claims that development of CCUS hubs has begun “in at least 12 locations around the world” and that they have the potential to capture over 50 Mt of CO2 p.a. In 2020 Canada, France, Germany, Japan, Mexico, Portugal, Singapore, the United Kingdom and the United States all referenced a role for CCUS as part of their mid-century climate strategies.
More than sixty projects, some already operational, are
listed by the International Association of Oil and Gas Producers (IOGP, 2020).
Among the sites which became operational in the last few years are: Gorgon
Carbon Dioxide Injection, Western Australia, which captures carbon dioxide from
natural gas processing, and injects it more than 2km below the earth’s surface
at a rate of 3.4-4 Mtpa; Illinois Industrial Carbon Capture and Storage, which
captures CO2 from the fermentation process used to produce ethanol and stores
it in a geological site at 1 Mtpa;
Alberta Carbon Trunk Line with Agrium CO2 Stream, where CO2 is captured at 0.3-0.6 Mtpa within the
gasification hydrogen supply unit as part of a process to produce synthesis
gas; and Jilin Oil Field, China, at which CO2 captured from a natural gas
processing plant is used for enhanced oil recovery at 0.6 Mtpa. The IOGP list
mentions two earlier Norwegian projects, dating from 1996 and 2008, and in September
2020 the Norwegian government announced its proposal to launch a carbon capture
and storage scheme, named ‘Longship’. Carbon will be captured at Norcem’s
cement factory in Brevik, and funding will
be provided for the transport and storage of liquid CO2 from the capture
facilities to a terminal at Øygarden in Vestland County. From there, CO2 will
be pumped through pipelines to a reservoir beneath the sea bottom (Gov.no,
2020).
“The Strategies for Environmental Monitoring of Marine
Carbon Capture and Storage (STEMM-CCS) project was funded under the European
Union’s Horizon 2020 programme to address the current knowledge and capability
gaps in approaches, methodologies and technology required for the effective
environmental monitoring of offshore carbon capture and storage (CCS) sites.” Work
included the first sub-seafloor release of CO2 to be carried
out under real life conditions. It simulated a CO2 reservoir
leak and showed that it could be successfully detected and quantified using the
instruments, tools and techniques developed during the project. (STEMM-CCS,
2020). The safety and efficacy of carbon storage have been noted as among
public concerns regarding CCUS.
Some of the major factors which emerge from the above
projects and from the literature are the policy decisions of governments in
response to climate change; the time scales involved; technological
developments; the involvement of industry, including the fossil fuel companies;
geography, geology and the proximity of carbon sources and sinks; the
availability of renewable energy; and risk, the engagement of investors and the
attitudes of the public.
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