New Scientist (pgs. 36-39)  [Printer-friendly version]
March 29, 2008


If we could capture carbon dioxide and store it underground we would
slow global warming, so why is progress so slow?

By Fred Pearce

Coal is our cheapest and most abundant source of fossil-fuel energy.
We probably have enough to keep the world powered for hundreds of
years. Trouble is, the carbon emissions from burning it all would make
the planet uninhabitable long before then. Is there a way to get the
energy without the emissions?

There certainly is, say coal technologists. Capture the carbon dioxide
produced when coal burns and bury it underground, back where the coal
came from. Most of the technology to do this is proven, and there are
enough places underground to store the CO2 and keep it secure for
thousands of years. That at least is the pitch for carbon capture and
storage (CCS). If it lives up to the claims, the vast coal reserves in
the US, China, India and elsewhere could fuel the post-industrial era
just as European coal fuelled the industrial revolution two centuries
ago. Forget renewables, coal can be a zero-carbon energy source too.
So what are we waiting for?

CCS has no shortage of fans. Last October, the British government's
senior minister for business, John Hutton, predicted that by 2030 wide
use of CCS "could see up to a third of British electricity generated
in this way".
In Germany, only CCS can make sense of an energy policy
that combines a large number of new coal-fired power stations with
plans for a 40 per cent cut in CO2 emissions by 2020.

Unfortunately, few in the energy industry believe these deadlines are
remotely achievable. A study by the Massachusetts Institute of
Technology called The Future of Coal, published last year, suggests
that the first commercial CCS plants won't be on stream until 2030 at
the earliest. Thomas Kuhn of the Edison Electric Institute, which
represents most US power generators, half of whose fuel is coal, takes
a similar line. In September, he told a House Select Committee that
commercial deployment of CCS for emissions from large coal-burning
power stations will require 25 years of R&D and cost about $20

The energy company Shell, though enthusiastic about the technology,
doesn't foresee CCS being in widespread use until 2050. Yet some
governments appear oblivious to this. When Germany recently approved
its new coal power stations, it stipulated that the plants must be
compatible with any future carbon capture technology. The UK is likely
to take the same approach if ministers, as expected, approve a new
coal-fired station at Kingsnorth in Kent. However, these installations
are likely to have reached the end of their useful lives before the
technology arrives.

From this you might suspect that policy-makers are seizing on CCS as a
painless way out of the difficult political choices posed by climate
change. Yet it is no such thing. The belief that CCS will save them
from acting against coal could prove as false as the belief half a
century ago that nuclear power would be so cheap it wouldn't be worth
metering. This time, though, the consequences of being deluded will be
far more damaging.

Beneath the seabed

The idea of CCS goes back to 1979, when Cesare Marchetti of the
International Institute for Applied Systems Analysis, an east-west
think-tank based in Austria, proposed a CO2 burial system as a way of
countering climate-changing carbon emissions. Yet it took until 1996
for the first such project to be launched, when Statoil, Norway's
state oil company, began stripping CO2 out of natural gas from the
Sleipner West gas field in the North Sea and pumping it back down into
a sandstone aquifer beneath the seabed. The project is still burying a
million tonnes of CO2 every year. Similar schemes now operate at
Weyburn in Saskatchewan, Canada, and at In Salah in Algeria. Both pump
CO2 into existing oil wells to help flush more oil out.

Though welcome, these projects cannot handle the volume of CO2 from a
large coal-fired power station, nor dent the total emissions of CO2
from human activity -- about 24 billion tonnes per year. To cut that by
just 4 per cent would require 1000 Sleipners.

Apart from these schemes, all we have is a flurry of R&D projects,
many of which have yet to make it off the drawing board. This lack of
urgency was underlined earlier this year by the fate of a proposed CCS
plant at Mattoon in Illinois. In December 2007, a US government and
industry consortium called FutureGen had announced that Mattoon would
be the site for a new power station that would test carbon capture
technologies. The plan was to begin burying CO2 in rock beneath the
power station by 2013. "Our strong coal tradition will be revitalised
as we become the home of the cleanest fossil-fuel-fired power plant in
the world," said Illinois governor Rod Blagojevich. Six weeks later,
the project was scrapped, after the government baulked at its $1.3
billion share of the bill.

Back in Europe, the EU says it hopes to have a dozen demonstration
plants working by 2015. In November 2007, for instance, the UK
government announced a competition to build a 300-megawatt power
station that would store CO2 in exhausted oilfields beneath the North
Sea. Unfortunately, support for such schemes remains half-hearted at
best. In a statement on energy policy in January, the EU once again
declared its enthusiasm for CCS, but warned there was "no possibility
of significant funding from the EU budget".

One of the brighter spots today is Australia, a country heavily
dependent on coal, which has state-backed plans for a power plant at
Fairview in Queensland that will burn methane from unmineable coal
seams and bury the resulting CO2. Another is China, where a high-tech
coal power station being built outside Tianjin will include a carbon
capture plant.

If all goes to plan, these projects could become the basis for a huge
global industry. Around a third of human-made CO2 emissions come from
large, fixed sources that could be captured. The world has 5000 power
stations and 3000 industrial plants that emit more than 100,000 tonnes
of CO2 a year .

Capturing the CO2 at such plants can be done before, during or after
the fuel reaches the combustion chamber. The pre-combustion option is
the most complex: the coal is initially converted into a mixture of
gases from which hydrogen is extracted to be fed to a gas-turbine
power generator, while the CO2 goes for burial. This is the technology
that will be used in Tianjin, and would have been adopted at Mattoon.
It is widely regarded as the next big thing in coal power generation,
regardless of its potential for CCS.

CO2 can also be extracted directly from the combustion chamber if the
coal is burned in pure oxygen rather than air. But oxygen is expensive
and the technology is still at an early stage. The simplest and most
developed method is to wait till the coal has been burned and pass the
flue gases through a scrubber containing organic chemicals called
amines, which react with the CO2. The CO2 can then be collected and
buried, while the amines are recycled. The British government wants to
use this technology in its pilot project, partly because it is the
only one that can be retrofitted to existing power stations.

Burial sites

Whichever of these strategies is adopted, the scale of any worthwhile
CCS project will have to be huge. Coal produces around three times its
own weight of CO2. This will all have to be pressurised, liquefied and
moved to a site where it can be interred at depths of a kilometre or
more, where the pressure will ensure that it stays liquid.

Where will these sites be? On the face of it, the best candidates
would be the voids left in worked-out oilfields, such as those beneath
the North Sea. The rocks held oil or gas for millions of years, so
they should be able to hold CO2 too, the thinking goes. Recent studies
show that natural CO2 has been held within the North Sea's Miller
oilfield for the past 120 million years. Oil and gas fields could hold
up to a trillion tonnes of CO2 -- or 50 years' worth of emissions at
the rate at which it is likely to be produced in 2030. Another
possible dump is unmineable coal seams, where CO2 would be adsorbed in
a layer on the surface of the coal.

Then there are deep, porous rocks such as sandstone formations that
are capped by an impermeable layer of shale or other rock that would
trap the CO2. These are widespread beneath both the continents and the
oceans . According to some estimates they could provide storage space
for as much as 10 trillion tonnes of CO2, or 500 years' worth.

How secure would these burial grounds be? Opponents of CCS schemes
recall the disaster in 1986, when a million tonnes of CO2 belched from
the bottom of Lake Nyos in Cameroon. Being denser than air, the gas
formed a blanket that asphyxiated some 1700 people. Though the event
was entirely natural, it has left a potent image of what could go
wrong. As Bert Metz, co-author of a 2005 report on CCS by the
Intergovernmental Panel on Climate Change, says: "Public acceptance is
a possible show-stopper if things are not done properly."

Geologists don't dismiss the possibility of a catastrophic release,
after an earthquake perhaps. But they see slow seepage as at least as
important a concern. To prevent climate change, CO2 has to be stored
safely for millennia. Even a leakage rate of 0.01 per cent a year -- a
suggested industry standard -- would see almost two-thirds of the gas
gone within 10,000 years. The legal question of who has long-term
responsibility for stored carbon is also unresolved, and it could
prove as convoluted a debate as that over nuclear waste. No surprise
then, that next to designing a capture plant, assessing the leakage
threat is the major research focus for CCS.

In 2006, engineers from Australia completed a trial project to store
CO2 in deep coal seams in Silesia in southern Poland. This year, in a
project sponsored by the Australian government, 100,000 tonnes of CO2
will be injected into a saline aquifer off the coast of Victoria and
closely monitored. The EU is sponsoring a similar project in Germany.

The furthest-advanced project is a test site at which engineers have
injected 1600 tonnes of CO2 into a sandstone formation known as the
Upper Frio on the Gulf coast of Texas. The rock, which once contained
oil, is now flooded with salt water. An early report on the Frio
project, published in the journal Geology by Yousif Kharaka of the US
Geological Survey, points to a possible danger of storing CO2 in
formations like these. The CO2 has acidified the brine, allowing it to
dissolve metal-oxide minerals in the rock, and this, Kharaka says,
might eventually create tunnels in the cap rock through which CO2
might escape.

Not everyone involved shares these fears. Nick Riley of the British
Geological Survey, who collaborated on the Frio project, believes that
the danger of a leak occurring this way is slight. He accepts that
there was some acidification, and that a small amount of CO2 did
escape into the overlying layer of rock, but insists that it poses no
problem. Susan Hovorka of the University of Texas, Austin, the
project's principal investigator, agrees. "The CO2 has smeared...
until it cannot move much further." In fact, far from being a problem,
the chemical reactions might gradually convert the CO2 into carbonate
rock that would keep the carbon locked underground indefinitely.

So far, tests have been small-scale, short-term and largely at sites
that geologists judge will perform best. In the real world, Hovorka
points out, geologists will be under pressure to find burial sites
close to power plants, where the rock formations may be less than
perfect. "We know how to recognise an excellent site," she says. "But
we need confidence about when to screen out sites that are too risky."
She also admits there is no method yet for deciding how much CO2 a
particular rock formation can absorb before leaking, and how to spot
if things are going wrong. A study in the journal Advances in Water
Research warns that algorithms modelling the seepage of gas through
rock are untested, so the results could prove inaccurate.

Even moving the gas from power station to burial ground won't be
simple, as the volumes involved will be vast. A study by the
International Energy Agency suggests that the EU would need 150,000
kilometres of pipeline to trunk its CO2 emissions to the North Sea.
Operations will have to be continuous, and a vast new industry will be

The necessary capital investment will be huge, as will the cost of
operating any CCS system. The US government reckons CCS will increase
the cost of coal-fired power generation by 75 per cent. For this to be
commercially viable, it has been calculated that a price tag of more
than [euro]30 per tonne will need to be imposed on CO2 emissions,
either via a carbon tax or through a continuation of the emissions
trading system introduced under the Kyoto protocol.

So exactly what would this hugely costly undertaking achieve? One EU
document on CCS says beguilingly: "The possibility exists for a CO2-
free energy system based on fossil fuels." Yet even the best CCS
systems will not capture all the CO2, and existing methods typically
capture only about 85 per cent. In reality the figures are even more
unfavourable, as the CCS process itself consumes anything from 10 to
40 per cent of the energy produced by a fossil-fuel power station.

Another factor to be taken into account is the energy used by diggers,
trucks and trains to extract coal and transport it to the power
station. In all, this may take up to a quarter of the energy the coal
produces at the power plant, and none of these emissions disappears
when CCS kit is bolted on.

Add all this together, and what do we get? The most detailed published
assessment, by Peter Viebahn of the German Aerospace Center in
Stuttgart, estimates that at best CCS will reduce greenhouse gas
emissions from coal-fired power stations by little more than two-
thirds. That compares with life-cycle emissions for most renewable
energy technologies that are 1 to 4 per cent of those from burning

We are unlikely to give up burning coal any time soon, and CCS could
eventually have an important part to play by allowing coal to be used
without doing unacceptable damage to the global climate. But that
isn't going to happen tomorrow. And as to the dream of coal becoming a
zero-emissions source of power -- forget it.